阅读说明：本技术 电力变换装置及发电系统 (Power conversion device and power generation system ) 是由 加藤修治 高桥良和 远藤哲郎 于 2020-03-30 设计创作，主要内容包括：本发明提供了能抑制检测到的电压的纹波以及检测延迟的电力变换装置及发电系统。本发明的电力变换装置通过电抗器17R、17S、17T与电力系统50连接,具备：变换器11,输出规定交流电压；连接点电压检测装置20,检测电力系统50的连接点电压V；以及控制装置30,通过脉冲宽度调制控制来控制变换器11,连接点电压检测装置20通过针对由电压检测器检测到的检测电压,计算用于脉冲宽度控制的载波的一周期部分的期间的移动平均,来检测连接点电压V,控制装置30具有基于通过移动平均计算出的系统电压计算变换器11的电压指令值的功能。(The invention provides a power conversion device and a power generation system capable of suppressing ripple and detection delay of detected voltage. The power conversion device of the present invention is connected to a power system 50 through reactors 17R, 17S, and 17T, and includes: an inverter 11 that outputs a predetermined ac voltage; a connection point voltage detection device 20 for detecting a connection point voltage V of the power system 50; and a control device 30 that controls the converter 11 by pulse width modulation control, the connection point voltage detection device 20 detects the connection point voltage V by calculating a moving average of a period of one cycle part of a carrier wave for pulse width control with respect to the detection voltage detected by the voltage detector, and the control device 30 has a function of calculating a voltage command value of the converter 11 based on the system voltage calculated by the moving average.)

1. A power conversion device connected to a power system via a connection impedance, the power conversion device comprising:

a converter that switches at a predetermined switching cycle, and outputs electric power to the power system via the connection impedance;

a voltage detector that detects a voltage at a connection point between the power conversion device and the power system; and

and a control device for controlling the inverter based on the output voltage of the voltage detector which performs moving average for a predetermined period in correspondence with the switching cycle.

2. The power conversion device according to claim 1,

the control device calculates an instantaneous voltage based on the output voltage, and generates a voltage command value of the converter from the instantaneous voltage.

3. The power conversion device according to claim 1,

the control device takes a real multiple value of the output voltage as an effective current command value.

4. The power conversion device according to claim 1,

the control device calculates an instantaneous voltage based on a current command value obtained by multiplying the real number of the output voltage, and generates a voltage command value for the converter from the instantaneous voltage.

5. A power conversion device is characterized in that,

the power conversion device is connected to a system functioning as an AC voltage source through a connection impedance,

the power conversion device includes:

an inverter having a switch that is switched so as to output pulses of different widths at a substantially constant cycle and that outputs a predetermined alternating voltage;

a voltage detector detecting a system voltage of the system; and

a control device for controlling the inverter,

the voltage detector has: a detection unit that detects a voltage value of a predetermined portion of the system to which the inverter is connected; and a filter unit that performs moving averaging or calculates an approximate value of the moving average for a period of one cycle portion or several cycle portions of a constant cycle on the output voltage of the detection unit.

6. The power conversion device according to claim 5,

the control device includes a voltage command value generation unit that calculates a voltage command value by adding at least one of an active power component voltage command value for outputting active power and an reactive power component voltage command value for outputting reactive power to the system voltage.

7. A power conversion device connected to a power system via a connection impedance, the power conversion device comprising:

a converter for outputting a predetermined AC voltage;

a system voltage detection device that detects a system voltage of the power system; and

a control device for controlling the converter by pulse width modulation control,

the system voltage detection means detects the system voltage by calculating a moving average of a period part or a number of period parts of a carrier wave for the pulse width modulation control with respect to the detected voltage,

the control device has a function of calculating a voltage command value of the converter based on the system voltage calculated by moving average.

8. The power conversion device according to claim 7,

the control device includes a voltage command value generation unit that adds at least one of an active power component voltage command value for outputting active power and an reactive power component voltage command value for outputting reactive power to the system voltage to calculate the voltage command value.

9. The power conversion device according to claim 8,

the control device has a function of calculating an effective power component voltage command value by using the system voltage multiplied by a real number as the ineffective power component voltage command value and using the system voltage as a current command value.

10. The power conversion device according to claim 8 or 9,

the control device has a function of calculating the active power component voltage command value by time-differentiating the system voltage.

11. The power conversion device according to any one of claims 8 to 10,

the active power component voltage command value is deviated 1/4 cycle phases from the system voltage.

12. The power conversion device according to any one of claims 8 to 11,

the control device has a differential operation unit that calculates the active power component voltage command value by time-differentiating a voltage obtained by dividing the system voltage by a connection impedance value.

13. The power conversion device according to claim 7,

the control device is a vector control means for calculating the voltage command value by vector control based on the system voltage.

14. The power conversion device according to any one of claims 7 to 12,

the power conversion device includes a voltage compensation unit that calculates a peak value of the system voltage, and adds a difference between a rated voltage of the power system and the peak value to the system voltage to compensate for a difference between the system voltage and the rated voltage.

15. The power conversion device according to claim 8,

the control device has a function of calculating the reactive power component voltage command value and the active power component voltage command value by time-differentiating the system voltage.

16. The power conversion device according to claim 8 or 15,

the control device includes an effective component calculation unit that calculates the effective power component voltage command value by time-differentiating an effective current command effective value calculated based on the system voltage multiplied by a real number.

17. The power conversion device according to claim 16,

the effective component calculation means includes a differentiation calculation means that differentiates the effective current command effective value, and calculates the effective power component voltage command value by adding a product of the differentiated effective current command effective value and an inductance value of the connection impedance to a product of the effective current command effective value and a resistance value of the connection impedance.

18. The power conversion device according to claim 8 or 15,

the control device includes an ineffective component calculation unit that calculates the ineffective power component voltage command value by time-differentiating an ineffective current command effective value calculated based on the system voltage whose phase has advanced by 90 degrees, which is calculated by performing three-phase two-phase conversion, and then performing two-phase three-phase conversion by rotating the phase by 90 degrees using a rotation matrix.

19. The power conversion device according to claim 18,

the reactive component calculation means includes a differentiation calculation means for differentiating the reactive current command effective value, and calculating the reactive power component voltage command value by adding a product of the differentiated reactive current command effective value and an inductance value of the connection impedance to a product of the reactive current command effective value and a resistance value of the connection impedance.

20. The power conversion device according to claim 16 or 17,

the control device includes a voltage compensation value calculation unit that calculates a voltage compensation value for compensating the effective current command effective value based on the system voltage and a rated phase voltage of the power system.

21. The power conversion device according to claim 18 or 19,

the control device includes a voltage compensation value calculation unit that calculates a voltage compensation value for compensating the reactive current command effective value based on the system voltage and a rated phase voltage of the power system.

22. The power conversion device according to claim 5,

and taking a value which is real multiple of the system voltage as a current instruction value.

23. The power conversion device according to claim 5,

the power conversion device includes a differential operation unit that calculates a product of a differential value or an incomplete differential value of the system voltage multiplied by a real number and an inductance value of the connection impedance.

24. The power conversion device according to claim 5,

the power conversion device includes a differential operation unit that calculates a product of a differential value or an incomplete differential value of the system voltage multiplied by a real number multiple and phase-advanced by 90 degrees or phase-delayed by 90 degrees and an inductance value of the connection impedance.

25. The power conversion device according to claim 7,

and taking a value which is real multiple of the system voltage as a current instruction value.

26. The power conversion device according to claim 7,

the power conversion device includes a differential operation unit that calculates a product of a differential value or an incomplete differential value of the system voltage multiplied by a real number and an inductance value of the connection impedance.

27. The power conversion device according to claim 7,

the power conversion device includes a differential operation unit that calculates a product of a differential value or an incomplete differential value of the system voltage multiplied by a real number multiple and phase-advanced by 90 degrees or phase-delayed by 90 degrees and an inductance value of the connection impedance.

28. A power generation system including the power conversion device according to any one of claims 1 to 27.

Technical Field

The present invention relates to a power conversion device and a power generation system.

Background

As renewable energy sources, wind power, sunlight, and the like are attracting attention. In a power generation device that generates power by wind power or solar energy, a power conversion device called a power conditioner is used to convert direct current power generated by the power generation into alternating current power and output the alternating current power to a power system. For example, a power conversion device for solar power generation includes an inverter, and supplies a dc power generated by power generation to a dc part of the power conversion device, and the dc voltage is shaped into a predetermined ac waveform by the inverter. In this case, the inverter connected to the grid via the impedance can supply the effective power generated by the power generation device to the power grid by controlling the output voltage so that a predetermined difference voltage is generated between the grid voltage and the output voltage of the power conversion device.

In such a power converter, if the phase of the power system is changed due to a system accident or the like, the difference voltage between the system voltage and the output voltage of the power converter becomes large, and an overcurrent flows through the power converter, which may cause a failure. Therefore, in order to operate the power conversion device for a long time without causing a failure, some measures such as quickly separating the power conversion device from the power grid when a grid fault occurs are required.

For example, patent document 1 discloses a power conversion device that detects a voltage of a power system, determines whether or not a system fault is a system fault in which protection should be stopped based on the detected voltage of the power system, and stops operation when it is determined that protection should be stopped.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2001 and 268798

Disclosure of Invention

Problems to be solved by the invention

A typical power conversion device outputs a pulse voltage or a voltage obtained by combining pulse voltages. Therefore, a vibration component (also referred to as a ripple) is superimposed on the output of the power conversion device. As a result, ripple is also superimposed on the power system. When the voltage or the like at the connection point between the power system and the power converter is detected and effectively used for the power converter control, it is preferable to remove the ripple component from the detected value. For example, a first-order lag low-pass filter is provided in the power converter, and the ripple of the output of the voltage detector can be removed by passing the output of the voltage detector that detects the voltage at the connection point through the filter. In this case, if the time constant of the low-pass filter is set small, the detection delay generated by the output of the low-pass filter, that is, the detection voltage is small, but the ripple remains in the detection voltage. On the other hand, if the time constant of the low-pass filter is set large, the ripple of the detection voltage becomes small, but the detection delay becomes large.

Therefore, in the case of using the first-order lag low-pass filter, if the time constant is decreased, the detection delay can be decreased but the ripple cannot be removed, and if the time constant is increased, the ripple can be removed but the detection delay becomes large. The removal of the ripple of the detection voltage is not mentioned in patent document 1. Therefore, even if the time constant is set to be large and the voltage command of the power conversion device is set to zero, there is a possibility that a current flows from the power conversion device and an overcurrent cannot flow following a sudden voltage when the phase of the system voltage is largely changed. In addition, the ripple cannot be removed by setting the time constant to be small, and the ripple may cause erroneous detection of whether or not the power conversion device is stopped. In this way, in the method using the first-order lag low-pass filter, there is a possibility of overcurrent and malfunction depending on the setting of the time constant, and a power converter capable of suppressing the detection delay and ripple of the detected voltage is required.

The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a power conversion device and a power generation system capable of suppressing a ripple and a detection delay of a detected voltage.

Means for solving the problems

A power conversion device according to the present invention is connected to a power system via a connection impedance, and includes: a converter that switches a converter switch at a predetermined switching cycle and outputs electric power to the power system through the connection impedance; a voltage detector that detects a voltage at a connection point between the power conversion device and the power system; and a control device for controlling the inverter based on the output voltage of the voltage detector which is subjected to moving average for a predetermined period in correspondence with the switching cycle.

A power conversion device according to the present invention is a power conversion device connected to a system functioning as an ac voltage source via a connection impedance, the power conversion device including: an inverter having a switch that is switched so as to output pulses of different widths at a substantially constant cycle, and outputting a predetermined alternating voltage; a voltage detector detecting a system voltage of the system; and a control device that controls the converter, the voltage detector having: a detection unit that detects a voltage value of a predetermined portion of the system to which the inverter is connected; and a filter unit that performs moving averaging or calculates an approximate value of the moving average for a period of one cycle portion or several cycle portions of a constant cycle on the output voltage of the detection unit.

A power conversion device according to the present invention is connected to a power system via a connection impedance, and includes: a converter for outputting a predetermined AC voltage; a system voltage detection device that detects a system voltage of the power system; and a control device that controls the converter by pulse width modulation control, the system voltage detection device detecting the system voltage by calculating a moving average of a period of one cycle portion or several cycle portions of a carrier wave used for the pulse width modulation control for the detected voltage, the control device having a function of calculating a voltage command value of the converter based on the system voltage calculated by the moving average.

The power generation system of the present invention includes the power conversion device.

Effects of the invention

According to the present invention, the ripple and the detection delay of the detected voltage can be suppressed. In particular, by detecting the voltage by calculating a moving average of the period of one cycle portion of the carrier wave used for the pulse width modulation control, it is possible to suppress the ripple and the detection delay.

In addition, by detecting the voltage by calculating the moving average of the period of the carrier wave for the pulse width modulation control over the period of the several cycles, the ripple and the detection delay can be further suppressed.

Drawings

Fig. 1 is a schematic diagram showing an example of a power generation system including a power conversion device according to a first embodiment of the present invention.

FIG. 2: fig. 2A is a schematic diagram showing a configuration of a node voltage detection device using analog calculation, and fig. 2B is a schematic diagram showing a configuration of a node voltage detection device using digital calculation.

Fig. 3 is a schematic diagram showing a control device for a power converter according to a first embodiment of the present invention.

Fig. 4 is a schematic diagram showing a control device according to a second embodiment of the present invention.

Fig. 5 is a schematic diagram showing an enlarged view of a part of a control device according to a modification of the second embodiment of the present invention.

Fig. 6 is a schematic diagram showing a voltage compensation value calculation module provided in a control device according to a modification of the second embodiment of the present invention.

Fig. 7 is a schematic diagram showing an example of a power generation system including a power conversion device according to a fourth embodiment of the present invention.

Fig. 8 is a schematic diagram showing a control device of a power converter according to a fourth embodiment of the present invention.

Fig. 9 is a schematic diagram showing an example of a power generation system including a power conversion device according to a fifth embodiment of the present invention.

Fig. 10 is a schematic diagram illustrating a voltage compensation unit of a power conversion device according to a fifth embodiment of the present invention.

FIG. 11: fig. 11A is a diagram showing the junction voltage detected by the junction voltage detection device calculated by simulation in the power conversion device of the first embodiment, and fig. 11B is a diagram showing the output current of the power conversion device in the case of feedforward of only the junction voltage calculated by simulation in the power conversion device of the first embodiment.

Fig. 12 is a diagram showing a simulation result of an operation of the power conversion device according to the modification of the second embodiment with respect to a phase jump of the system voltage.

Detailed Description

(1) First embodiment

(1-1) the entire configuration of a power generation system including the power conversion device according to the first embodiment of the present invention

In the first embodiment, a power converter according to the first embodiment will be described by taking a case of being used in a power generation system as an example. First, the configuration of the power generation system will be explained. As shown in fig. 1, the power generation system 100 is connected to an ac voltage source 55 (an infinite bus line for three-phase ac) via a power system 50. The power system 50 functions as an ac voltage source. The power generation system 100 includes an active power supply 15 and a power conversion device 10, and the active power supply 15 is connected to the power conversion device 10 through a dc wiring. The active power source 15 is a power generation device such as a wind power generation device or a solar power generation device. The power conversion device 10 is connected to each of the terminals LPR, LPS, and LPT (hereinafter also referred to as connection points) of the power system 50 via reactors 17R, 17S, and 17T as connection impedances. The configuration of the power converter 10 will be described later. In the present embodiment, an ac voltage source 55 and an electric power system 50 are provided, the frequency of the ac voltage being 50 Hz.

The operation of the power generation system 100 will be described. In the power generation system 100, the active power source 15 generates dc power and outputs a dc voltage to the power conversion device 10. The power generation system 100 may be a system that generates ac power and converts the generated power into dc power, such as wind power generation, or a battery system that transmits and receives electric power. In the former case, the wind turbine generator is connected to the power conversion device 10 as an active power supply 15 by AC-DC, and in the latter case, a chargeable and dischargeable battery such as a secondary battery is connected to the power conversion device 10 as the active power supply 15. In this way, the active power source 15 supplies active power to the power conversion device 10.

The power conversion device 10 converts a dc voltage supplied from the active power supply 15 into an ac voltage, and outputs the converted ac voltage to the power system 50. Thus, the power conversion device 10 transmits and receives active power and reactive power between the power system 50 and the ac voltage source 55. The power system 50 is actually composed of electric wires and the like, and therefore has an impedance component. Therefore, in fig. 1, impedance components 53R, 53S, and 53T of each phase of the power system 50 are represented as resistive components 51R, 51S, and 51T and reactive components 52R, 52S, and 52T.

(1-2) configuration of Power conversion device according to first embodiment of the present invention

Next, the configuration of the power conversion device 10 will be described. As shown in fig. 1, the power conversion device 10 includes an inverter 11; reactors 17R, 17S, 17T; a junction voltage detection device 20; control device 30 and capacitance voltage detector 43. The configuration of the control device 30 will be described later.

First, the structure of the inverter 11 will be described. The inverter 11 is an inverter configured by a three-phase full bridge circuit. Inverter 11 includes R-phase converting unit 11R, S-phase converting unit 11S, T-phase converting unit 11T, capacitor (dc capacitor) 14, positive input terminal P, and negative input terminal N. Inverter 11 has a configuration in which R-phase converting unit 11R, S-phase converting unit 11S, T-phase converting unit 11T and capacitor 14 are connected in parallel between positive input terminal P and negative input terminal N. The active power supply 15 is connected to the inverter 11 at a positive input terminal P and a negative input terminal N. The capacitor 14 is a dc capacitor, and the rated voltage of the capacitor 14 is appropriately selected based on the magnitude of the active power and the reactive power to be output.

R-phase conversion unit 11R, S phase-change unit 11S and T-phase conversion unit 11T have high-side switch 12H and low-side switch 12L connected in series, high-side switch 12H connected to positive-side input terminal P, and low-side switch 12L connected to negative-side input terminal N. R-phase converting unit 11R has output terminal 13R at a connection point between high-side switch 12H and low-side switch 12L, S-phase converting unit 11S has output terminal 13S at a connection point between high-side switch 12H and low-side switch 12L, and T-phase converting unit 11T has output terminal 13T at a connection point between high-side switch 12H and low-side switch 12L.

The output terminal 13R of the R-phase conversion unit 11R is connected to u of the power system 50 through the reactor 17R and the terminal LPR, the output terminal 13S of the S-phase conversion unit 11S is connected to v of the power system 50 through the reactor 17S and the terminal LPS, and the output terminal 13T of the T-phase conversion unit 11T is connected to w of the power system 50 through the reactor 17T and the terminal LPT, whereby the power conversion device 10 is connected to the power system 50.

The high-side switch 12H and the low-side switch 12L are each composed of, for example, a switching element and a flywheel diode, and the switching element is composed of an IGBT or the like. In the first embodiment, the high-side switch 12H and the low-side switch 12L have the following configurations: the positive side of the switching element (collector of the IGBT) is connected to the negative side of the flywheel diode, the negative side of the switching element (emitter of the IGBT) is connected to the positive side of the flywheel diode, and the switching element and the flywheel diode are connected in antiparallel.

In this way, by connecting the switching element and the free wheel diode in antiparallel with the high-side switch 12H and the low-side switch 12L, when a voltage is applied from the negative side to the positive side of the high-side switch 12H and the low-side switch 12L, a current can be caused to flow through the free wheel diode, and a current can be prevented from flowing from the emitter to the collector of the IGBT as the switching element, thereby protecting the IGBT. The high-side switch 12H and the low-side switch 12L may be formed of switching elements such as SiC (silicon carbide) MOS-FETs (metal oxide semiconductor field effect transistors: MOS-type field effect transistors), GaN (gallium nitride) FETs (field effect transistors), and GaN formed on Si (silicon). These switches are switched in such a manner that pulses of different widths are output at a substantially constant period.

Next, the configuration of the node voltage detection device 20 as a system voltage detection device will be described with reference to fig. 2A. As shown in fig. 2A, the node voltage detection device 20 includes a voltage detector (detection means) 41 and a filter means 21. The connection point voltage detection device 20 detects the voltage of each phase of the power system 50 by the voltage detector 41, performs moving averaging for a predetermined period of time for each detected voltage of each phase by the filter unit 21, and outputs the voltage obtained by the moving averaging to the control device 30 as the system voltage of each phase. Hereinafter, the configuration of each part of the node voltage detection device 20 will be described.

The voltage detector 41 is provided at a predetermined portion of the power system 50 and detects a voltage at the predetermined portion. In the present embodiment, the voltage detector 41 includes an R-phase detector, an S-phase detector, and a T-phase detector (not shown in fig. 2A), which are connected to connection points of the R-phase, the S-phase, and the T-phase of the power conversion device 10 and u-phase, v-phase, and w-phase of the power system 50, respectively, via measurement terminals 41 a. The measurement terminal 41a is constituted by two terminals, one of which is connected to the connection point and the other of which is connected to the reference potential. The measurement terminals 41a are provided one for each phase, but only one measurement terminal 41a is shown in fig. 2A for convenience. The R-phase detector, S-phase detector, and T-phase detector of the voltage detector 41 detect potentials of the terminals LPR, LPS, and LPT (hereinafter also referred to as connection points) with reference to a reference potential, respectively. Thus, the voltage detector 41 detects the voltage at the connection point. The voltage detected by the voltage detector 41 is a voltage having an ac neutral point as a reference potential, and corresponds to a phase voltage of each phase of the power system 50. The voltage detection is not limited to the above-described method, and may detect a line-to-line voltage.

The filter unit 21 removes a ripple component generated by switching of the converter 11, and performs moving average of the output of the voltage detector 41. The moving average may be implemented only by the filter unit 21, or may be executed by combining with the control device 30 of the subsequent stage. The filter unit 21 may calculate an approximate value of the moving average. The approximate value is meant to include a value including an error when a window (period) of the moving average is not an integral multiple of the calculation cycle of the control device and includes a small error (e.g., ± 3%). Even in such a case, the power conversion device can be used although the operation performance is slightly lowered.

When each switch of the inverter 11 is driven by PWM (pulse width modulation) control of a triangular wave comparison method, it is preferable that the output of the voltage detector 41 be integrated by an analog circuit as the simplest concrete means of the filter means 21. For example, as shown in fig. 2A, a moving average can be calculated by integrating with an integrating circuit using an operational amplifier or the like. The filter unit 21 shown in fig. 2A includes a 2-terminal input terminal 21a, a resistor 21b, a capacitor 21c, a 2-terminal output terminal 21d, and an operational amplifier 21 e. One of the input terminals 21a is connected to the negative terminal of the operational amplifier 21e via a resistor 21b, and the other input terminal 21a is connected to the positive terminal of the operational amplifier 21e and one of the output terminals 21 d. The output of the operational amplifier 21e is connected to the other of the output terminals 21d, and is fed back to the negative terminal of the operational amplifier through the capacitor 21 c. In this way, the filter unit 21 is constituted by an integration circuit, and calculates a moving average by integrating the detected voltage. The filter unit 21 has one such integration circuit for each phase, and only one is shown in fig. 2A for convenience. The resistance value of the resistor 21b, the capacitance value of the capacitor 21c, the gain of the operational amplifier 21e, and the like may be appropriately set in consideration of the frequency of the ripple wave.

Next, the capacitance voltage detector 43 will be explained. The capacitance voltage detector 43 is connected to both ends of the capacitor 14, and detects a capacitance voltage of the capacitor 14. Capacitance voltage detector 43 outputs the detection result to control device 30.

(1-3) operation of the Power conversion device according to the first embodiment of the present invention

Next, the operation of the power conversion device 10 will be described. The power conversion device 10 outputs a sum voltage of a voltage component fed forward through the node voltage V, a voltage component output based on the active power component voltage command value, and a voltage component output based on the reactive power component voltage command value. Since the R phase, the S phase, and the T phase are the same, the operation of the power conversion device 10 will be described with the R phase as a representative. First, the operation of the inverter 11 will be described. Inverter 11 shown in fig. 1 inputs gate pulse signals from gate pulse generating unit 37 (see fig. 3) to high-side switch 12H and low-side switch 12L of R-phase converting unit 11R. Specifically, for example, a predetermined voltage is input to the gates of the IGBTs constituting the high-side switch 12H and the low-side switch 12L.

When a gate pulse signal for turning the switch on is input to the high-side switch 12H and a gate pulse signal for turning the switch off is input to the low-side switch 12L, the R-phase conversion unit 11R outputs a positive capacitance voltage to the output terminal 13R of the R-phase conversion unit 11R. On the other hand, if a gate pulse signal for turning the switch off is input to the high-side switch 12H and a gate pulse signal for turning the switch on is input to the low-side switch 12L, the R-phase conversion unit 11R outputs a negative capacitance voltage to the output terminal 13R of the R-phase conversion unit 11R. In this way, inverter 11 switches on and off high-side switch 12H and low-side switch 12L of R-phase conversion unit 11R, thereby converting the dc voltage of capacitor 14 into an ac voltage and outputting the ac voltage to the u-phase of power system 50. The inverter 11 outputs a three-phase ac voltage by controlling each phase so as to output an ac voltage whose phases are shifted by 120 degrees from each other to the power system 50 by the same method.

The converter 11 is not particularly limited as long as it can convert an input dc voltage into a three-phase ac voltage and output the three-phase ac voltage to a power system, and may be a multilevel converter such as an MMC (Modular multilevel converter), a 3-level converter capable of outputting a predetermined voltage of 3 levels, and particularly a so-called NPC3 level converter.

Next, the operation of the node voltage detection device 20 will be described. The connection point voltage detection device (voltage detection device) 20 detects a system voltage of a system functioning as an ac voltage source. Specifically, the node voltage detection device 20 detects a node voltage V, which is a voltage at the node, as a system voltage of the power system 50. The voltage detector 41 detects voltages at the connection points LPR, LPS, LPT of the respective phases, and outputs the detected voltages of the respective phases from the detection terminal 41b to the filter unit 21. The filter unit 21 integrates the detected voltage of each phase inputted from the input terminal 21a for each phase by an integration circuit. The filter unit 21 calculates a moving average by time-integrating the detection voltage. Filter section 21 outputs the moving average result as a connection point voltage V of each phase from output terminal 21d to control device 30. In this way, the voltage V at the connection point of each phase is measured by detecting the voltage at the connection point of each phase and moving-averaging the detected voltage by time integration. The filter unit 21 filters the node voltage V by moving averaging the output voltage of the voltage detector 41 for a predetermined period.

In the first embodiment, the control device 30 then obtains the difference between the current value of the detected junction voltage V (the result of moving average) and the past value of the junction voltage V detected before the period of one cycle of the triangular wave (carrier wave) of the PMW, and appropriately adjusts the magnitude of the difference value (gain adjustment). By obtaining the difference between the current value and the past value of the tie-point voltage V, the period between the time point at which the past value is detected and the current value corresponds to the period of moving average, and the difference value becomes the average value of the tie-point voltage V detected during this period. In this way, in the first embodiment, the moving average during one period part (one period part of the constant period) of the carrier wave, which is a wave that fluctuates at a constant period for pulse width control, is calculated. The node voltage detection device 20 may perform this operation and output the difference value as the node voltage V.

The moving average may be obtained not by the analog calculation but by the digital calculation described below. In this case, the connection point voltage detection device 25 shown in fig. 2B is used. The node voltage detection device 25 includes a voltage detector 41 and a filter unit 26. Since the voltage detector 41 has the same configuration, the description thereof is omitted. The filter unit 26 is composed of a memory 27 and an arithmetic unit 28, and filters the output voltage of the voltage detector 41 by performing a periodic moving average. The memory 27 periodically stores the detection voltage of each phase detected by the voltage detector 41. The memory 27 is a well-known storage device such as a DRAM, an SRAM, a flash memory, and a hard disk drive. The calculation unit 28 calculates an average value of the detection voltages stored in the memory 27 for each phase, and outputs the calculation result to the control device 30 as the connection point voltage V of each phase. The calculation unit 28 may be dedicated hardware for calculating the average value of the detected voltage, may be realized by a general-purpose processor and embedded software, or may be realized by a program using a PC.

The operation of the node voltage detection device 25 will be described. The voltage detector 41 detects voltages at the connection points LPR, LPS, LPT of the respective phases, and outputs the detected voltages to the filter unit 26. In the filter unit 26, the memory 27 sequentially stores the input detection voltages, and holds the voltages for a period of one period of a triangular wave (carrier wave) which is a wave that fluctuates at a constant period and is used for PWM control of a triangular wave comparison method of the control device 30 to be described later. The memory 27 sequentially erases the detection voltages held and stored after the detection voltages have passed through a period of one cycle. That is, the memory 27 updates the stored detection voltage along with the elapse of time, and the memory 27 stores the detection voltage detected during a period from the present time to before the period of one cycle portion of the carrier wave.

The arithmetic unit 28 reads all the detection voltages stored in the memory 27, calculates an average value of the read detection voltages, and outputs the calculated average voltage to the control device 30 as the connection point voltage V. Since the memory 27 stores the detection voltage detected during a period from the present to before the period of one cycle of the carrier and updates the detection voltage with the elapse of time, the arithmetic unit 28 reads all the detection voltages stored in the memory 27 and calculates the average value of the detection voltages, thereby calculating the moving average of the detection voltages during one cycle of the carrier.

The configuration of the node voltage detection devices 20 and 25 is not particularly limited as long as the moving average of the detected voltage can be calculated or a part of the calculation can be performed.

Control device 30 controls the open and closed states of the switches of inverter 11 based on connection point voltage V and the like detected in this manner, and controls the output voltage of inverter 11. In the first embodiment, the connection point voltage V detected by moving averaging is fed forward to the voltage command value to control the output voltage of the inverter 11. The node voltage V detected by moving average may be fed forward as it is, that is, if the node voltage V is used to perform PWM of the triangular wave comparison method, the converter 11 desirably outputs the same voltage as the node voltage V, and therefore robustness against voltage variation can be secured to some extent. In particular, the robustness against voltage variation at current zero is extremely high. However, since a signal delay occurs by the moving average, it is preferable that each switching frequency of the inverter 11 is higher in order to reduce the signal delay. Therefore, a switching element having a high switching frequency is preferably used for each switch of the inverter 11.

(1-4) configuration and operation of control device for power conversion device of first embodiment

Next, the configuration and operation of the control device 30 will be described with reference to fig. 3. First, the configuration of the control device 30 will be explained. As shown in fig. 3, the control device 30 includes an reactive power component voltage command value generation unit 31, a current calculation unit 32, an active power component current command value generation unit 33, an active power component voltage command value generation unit 34, a gain control unit 35, a voltage command value generation unit (voltage command value generation means) 36, and a gate pulse generation unit 37. The reactive power component voltage command value generation unit 31 is configured by a multiplier having a gain q (real number).

The current calculation unit 32 is constituted by a divider that divides the connection impedance value. The active power component current command value generation unit 33 is configured by a multiplier having a gain d (real number). The active power component voltage command value generation unit 34 is configured as a differential operation means for performing a differential operation on the active power component current command value

L·(dI/dt)+RI···(1)

Calculation of such an equation (1). The active power component voltage command value generation unit 34 is configured by combining a calculation circuit capable of calculating the above expression, for example, a differentiator, an adder, and the like.

The voltage command value generation unit 36 is constituted by an adder. The gate pulse generating unit 37 is configured to generate a gate pulse signal for controlling the on/off of each switch of the inverter 11 by well-known PWM control. The gain control unit 35 is configured to control the value of the gain d of the reactive power component current command value generation unit 33 and the value of the gain q of the reactive power component voltage command value generation unit 31.

Next, the operation of control device 30 will be described. Control device 30 adds a voltage whose phase advances by 90 degrees with respect to the connection point voltage for outputting the effective voltage to a voltage whose phase is the same as the connection point voltage for outputting the ineffective voltage, and further feedforward-calculates a connection point voltage vp to calculate a voltage command value Vpp, and controls the output voltage of inverter 11 based on this voltage command value Vpp. The operation will be specifically described below.

In the control device 30, the pad voltage V detected by the pad voltage detection device 20 is input to the reactive power component voltage command value generation unit 31, the current calculation unit 32, the gain control unit 35, and the voltage command value generation unit 36. The reactive power component voltage command value generation unit 31 multiplies the input detection value of the node voltage V by q to generate a reactive power component voltage command value Vqp, and outputs the generated value to the voltage command value generation unit 36. The current calculation unit 32 divides the detected value of the node voltage V by the value of the reactor 17R (ω L, ω is the frequency of the node voltage V, and L is the inductance value of the reactor 17), which is the connection impedance value, converts the detected value of the node voltage V into a current value, and outputs the converted current value to the active power component current command value generation unit 33. In addition, since the resistance component of the reactor 17R is preferably 0, the resistance component of the reactor 17R is not considered in the present embodiment. The active power component current command value generation unit 33 multiplies the input current value by d to generate an active power component current command value. The active power component current command value generation unit 33 outputs the active power component current command value to the active power component voltage command value generation unit 34.

The effective power component voltage command value generation unit 34 calculates the above equation (1) for the effective power component current command value, converts the current command value calculated from the connection point voltage into a voltage command value, calculates an effective power component voltage command value Vdp, and outputs the effective power component voltage command value Vdp to the voltage command value generation unit 36. Since the resistance component of the reactor 17 is preferably 0, the resistance component of the reactor 17 is set to zero in the present embodiment. Here, equation (1) is an equation for calculating a voltage drop in the reactor from a current flowing through the reactor, and the product of the resistance component of the reactor and the current is added to a value obtained by time-differentiating the current and multiplying the current by the inductance value of the reactor (L represents the inductance value of the reactor, R represents the resistance component of the reactor, and I represents the current flowing through the reactor). In addition, regarding the relationship between the voltage and the current in the reactor, the phase of the current is delayed by 90 degrees with respect to the phase of the voltage.

Therefore, the voltage value (effective power component voltage command value Vdp) calculated by equation (1) advances by 90 degrees in phase with respect to the current value (effective power component current command value) used for calculation. As a result, the effective power component voltage command value Vdp advances by 90 degrees with respect to the connection point voltage V having the same phase as the effective power component current command value. In this way, control device 30 has a function of calculating a voltage (an effective power component voltage command value Vdp for outputting effective power) whose phase advances by 90 degrees from connection point voltage V by differentiating connection point voltage V. For example, the differential value of the active power component current command value may be calculated by calculating the time difference from the previous control cycle and the difference of the active power component current command value for each control cycle and dividing the time difference by the difference of the active power component current command value.

Command value generation unit 36 adds the input detected value of node voltage V, reactive power component voltage command value Vqp, and active power component voltage command value Vdp to generate voltage command value Vpp. In this way, control device 30 has a function of calculating voltage command value Vpp of inverter 11 based on the system voltage calculated by the moving average. The voltage command value generation unit 36 outputs the generated voltage command value Vpp to the gate pulse generation unit 37. Gate pulse generator 37 generates a carrier wave (e.g., a triangular wave) for PWM control, and modulates input voltage command value Vpp with the carrier wave. Specifically, the gate pulse generating unit 37 normalizes the voltage command value Vpp, and compares the normalized voltage command value Vpp with the carrier wave to generate a gate pulse signal. The gate pulse generating unit 37 generates a gate pulse signal for controlling the on and off of the high-voltage side switch 12H and the low-voltage side switch 12L of the R-phase converting unit 11R of the inverter 11 by modulating the voltage command value Vpp with the carrier wave. The gate pulse generator 37 outputs the generated gate pulse signal to the switch. By doing so, control device 30 controls the opening and closing of high-side switch 12H and low-side switch 12L of R-phase converting unit 11R.

The gain control unit 35 controls the value of the gain d of the reactive power component current command value generation unit 33 and the value of the gain q of the reactive power component voltage command value generation unit 31. The gain control unit 35 determines the values of the gain q and the gain d based on the node voltage V detected by the node voltage detection device 20, the frequency of the power system 50 (ac voltage source 55) calculated from the node voltage V, and the capacitance voltage of the capacitor 14 of the converter 11 detected by the capacitance voltage detector 43, and controls the reactive power and the active power output by the power conversion device 10.

For example, when the capacitance voltage detected by the capacitance voltage detector 43 is higher than the predetermined range, the capacitance voltage can be reduced by increasing the effective power flowing out from the power conversion device 10 to the power system 50 to be larger than the effective power flowing in from the effective power supply 15 to the power conversion device 10. In this way, the gain control unit 35 increases the value of the gain d to increase the effective power output by the power conversion device 10, thereby balancing the effective power flowing from the effective power supply 15 to the power conversion device 10 with the effective power flowing from the power conversion device 10 to the power system 50. On the other hand, when the capacitance voltage is lower than the predetermined range, the capacitance voltage can be increased by making the effective power flowing out from the power conversion device 10 to the power system 50 smaller than the effective power flowing in from the effective power supply 15 to the power conversion device 10. In this way, the gain control unit 35 reduces the effective power output by the power conversion device 10 by reducing the value of the gain d, and can balance the effective power flowing from the effective power supply 15 to the power conversion device 10 and the effective power flowing from the power conversion device 10 to the power system 50.

For example, when the tie-point voltage V detected by the tie-point voltage detection device 20 is lower than the reference range, the gain control unit 35 increases the value of the gain q to increase the tie-point voltage V, that is, the system voltage. On the other hand, when the connection point voltage V is higher than the reference range, the gain control unit 35 decreases the value of the gain q to lower the system voltage.

If the frequency of the power grid 50 calculated from the connection point voltage V is lower than the reference range, the power grid 50 is required excessively. In this case, the gain control unit 35 increases the value of the gain d to increase the supply amount of the effective power to be supplied to the power system 50. On the other hand, if the frequency of the power grid 50 is higher than the reference range, the power grid 50 is not sufficient. The gain control unit 35 decreases the value of the gain d, decreases the supply amount of the active power to the power system 50, and decreases the frequency. Alternatively, the gain control unit 35 sets the value of the gain d to a negative real number, and causes the active power to flow from the power system 50 to the power conversion device 10.

(1-5) action and Effect

In the above configuration, the power conversion device 10 of the first embodiment includes: a converter 11 connected to the power system 50 via connection impedances (reactors 17R, 17S, 17T) and outputting a predetermined ac voltage; a system voltage detection device (connection point voltage detection device 20) that detects a system voltage (connection point voltage V) of the power system 50; and a control device 30 that controls the inverter 11 by pulse width modulation control, wherein the connection point voltage detection device 20 detects the connection point voltage V by calculating a moving average of a period of a one-cycle part of a carrier wave used for pulse width control with respect to the detected voltage (the detected voltage detected by the voltage detector 41), and the control device 30 calculates a voltage command value of the inverter 11 based on the connection point voltage V calculated by the moving average.

Therefore, since the node voltage detection device 20 detects the node voltage V by calculating the moving average of the period of one period part of the carrier wave for pulse width control for the detected voltage detected by the voltage detector 41, the power conversion device 10 of the first embodiment can suppress the ripple and the detection delay of the detected voltage. Therefore, even when a phase jump occurs in the power system 50, the output voltage of the power conversion device 10 can follow the variation in the voltage of the power system 50, and the flow of an overcurrent through the power conversion device 10 can be suppressed.

Further, the power converter 10 according to the first embodiment is configured to calculate the effective power component voltage command value by time-differentiating the detected junction voltage V, so that the effective power component voltage command value can be calculated quickly, and the flow of an overcurrent through the power converter 10 can be further suppressed.

(2) Second embodiment

In the power converter according to the second embodiment, the tie-point voltage as the grid voltage of the power grid detected by the tie-point voltage detecting means as the grid voltage detecting means is used as the current command value. To explain more accurately, since the phase of the effective current is the same as that of the connection point voltage, the effective current command value is calculated as a real multiple of the connection point voltage, and the effective voltage command value (effective power component voltage command value) is calculated from the effective current command value. In the second embodiment, the effective current command value is determined using the node voltage as the current command value 1 pu.

In this regard, if the description is made in more detail, in the second embodiment, the effective current command value is determined by using the connection point voltage as the current command value 1pu for the sake of easy description. The effective current command value does not necessarily need to be 1pu as long as it is a value proportional to the node voltage.

For example, when the effective current command value (pu value) is 0.2pu, a product of the node voltage and 0.2 is taken as the effective current command value. On the other hand, as for the reactive current command value, a value shifted by 90 degrees from the phase of the connection point voltage is set as a current command value 1 pu. Similarly to the active current command value, the inactive current command value is determined by multiplying a value shifted in phase by 90 degrees from the connection point voltage by a real number (inactive current command value (pu value)) times. In this way, the real multiple value of the node voltage V is set as the current command value. The configuration of the control device of the power converter of the second embodiment is different from the configuration of the control device 30 of the power converter 10 of the first embodiment. The other configurations are the same as those of the power conversion device 10 of the first embodiment, and therefore, the description thereof is omitted.

(2-1) configuration and operation of control device according to second embodiment of the present invention

Fig. 4 is a diagram illustrating a control device 4000 of a power conversion device according to a second embodiment. The control device 4000 includes a phase compensation module 4100, a 90-degree phase advance operation module 4200, an invalid component operation module (invalid component operation unit) 4300, an effective component operation module (effective component operation unit) 4400, a voltage command value generation module 4001 (voltage command value generation unit), and a PWM module 4500. The operation of the control device 4000 will be described below.

The detected junction voltage V is smoothed by the junction voltage detection device 20 and then taken into the control device 4000. A signal of the junction point voltage V of the control device 4000 is input to the phase compensation module 4100. The output of the phase compensation module 4100 is input to the effective component operation module 4400, the 90-degree phase advance operation module 4200, and the voltage command value generation module 4001. In the effective component operation block 4400, the connection point voltage V input from the phase compensation block 4100 is multiplied by the effective current command value (pu value) by the multiplier 4401, and then the product result of the multiplier 4401 is converted into the effective current command effective value Iref _ dr by the current converter 4402. In the effective component calculation module 4400, the effective current command effective value Iref _ dr is input to the voltage estimation unit 4403, a voltage value (effective component voltage estimation value Vi _ d) to be applied to the connection impedance (reactor) in order to flow the current is estimated from the effective current command effective value Iref _ dr, and the estimation result is output to the voltage command value generation module 4001 as an effective voltage command value. Specifically, the voltage estimating unit 4403 as differential operation means performs time differentiation on the effective current command effective value Iref _ dr calculated from the node voltage V, and adds the product of the effective current command effective value Iref _ dr and the inductance value of the connection impedance to the product of the effective current command effective value Iref _ dr and the resistance value of the connection impedance, thereby estimating the effective component voltage estimated value Vi _ d.

In the 90-degree phase advance operation block 4200, the phase of the connecting point voltage V input from the phase compensation block 4100 is rotated by 90 degrees by a phase rotation matrix to advance by 90 degrees and input to the invalid component operation block 4300. In the invalid component operation module 4300, the multiplier 4301 multiplies the output of the 90-degree advance operation module by an invalid power command value (pu value), and the current conversion unit 4302 converts the output of the multiplier 4301 into an invalid current command effective value Iref _ qr. Then, in the ineffective component calculation module 4300, the ineffective current command effective value Iref _ qr is input to the voltage estimation unit 4303, the voltage value (ineffective component voltage estimation value Vi _ q) to be applied to the connection impedance (reactor) in order to flow the current is estimated from the ineffective current command effective value Iref _ qr, and the estimation result is output to the voltage command value generation module 4001 as an ineffective voltage command value (ineffective power component voltage command value). Specifically, the voltage estimation unit 4303, which is differential operation means, differentiates the reactive current command effective value Iref _ qr calculated from the connection point voltage V whose phase has advanced by 90 degrees, and adds the product of the differentiated reactive current command effective value Iref _ qr and the inductance value of the connection impedance to the product of the reactive current command effective value Iref _ qr and the resistance value of the connection impedance to estimate the value. In this way, the voltage estimating units 4303 and 4403 differentiate the ineffective current command effective value Iref _ qr and the effective current command effective value Iref _ dr calculated from the node voltage, which corresponds to differentiating the node voltage V. In this way, the control device has a function of calculating the reactive power component voltage command value and the active power component voltage command value by time-differentiating the connection point voltage V.

The voltage command value generation module (voltage command value generation unit) 4001 adds the phase-compensated junction voltage V input from the phase compensation module 4100, the effective voltage command value input from the effective component calculation module 4400, and the ineffective voltage command value input from the ineffective component calculation module 4300 to generate a voltage command value of the power conversion device. In this way, control device 4000 has a function of calculating a voltage command value of the inverter based on the system voltage calculated by the moving average. The voltage command value is input to the PWM module 4500, and is normalized in the PWM module 4500. In the PWM module 4500, the normalized voltage command value is modulated by PWM control of a triangular wave comparison method, gate pulses of the respective switches of the inverter are generated, and the gate pulses are output to the respective switches to drive the respective switches.

Next, the operation of each module constituting the control device 4000 will be described. First, the operation of the phase compensation module 4100 will be described. The phase compensation module 4100 compensates for the phase of the junction voltage V delayed by the smoothing in the junction voltage detection device 20. Specifically, the phase of the input node voltage V is advanced by a phase portion delayed in the node voltage detection device 20. More specifically, it is preferable that the phase advance is advanced by a time corresponding to a half of the period during which the moving average calculation is performed. As a method of advancing the phase, as shown in a 90-degree phase advancing operation block 4200 described later, after three-phase two-phase conversion, the phase of the phase portion is advanced by the rotation matrix, and two-phase three-phase conversion is performed. It is preferable to include the phase compensation module 4100, but the phase compensation module 4100 may not be provided.

Next, the operation of the 90-degree phase advance operation module 4200 will be described. The 90-degree phase advance calculation module 4200 performs three-phase two-phase conversion on the connection point voltage V of each phase input from the phase compensation module 4100 by the three-phase two-phase conversion unit 4201, and advances the phase of the connection point voltage V after the three-phase two-phase conversion by 90 degrees by the phase rotation unit 4202 using a rotation matrix. The 90-degree phase advance calculation module 4200 performs two-phase and three-phase conversion on the node voltage V whose phase has advanced by 90 degrees by the two-phase and three-phase conversion unit 4203, and outputs the node voltage V of each phase whose phase has advanced by 90 degrees to the invalid component calculation module 4300. In addition, the 90-degree phase advance operation module 4200 may delay the phase by 90 degrees. However, in this case, the sign of the reactive current command value becomes opposite.

Next, the invalid component operation block 4300 and the effective component operation block 4400 will be explained. These two modules will be described together since their actions are basically the same. The current conversion unit 4302 and the current conversion unit 4402 divide the voltage value (output of the multiplier 4301 or multiplier 4401) by the phase voltage rated voltage, convert the voltage value into a current rated value ampere value, and calculate an effective current command effective value Iref _ dr and an ineffective current command effective value Iref _ qr.

The voltage estimation unit 4303 and the voltage estimation unit 4403 calculate an effective component voltage estimation value Vi _ d from the effective current command effective value Iref _ dr, and calculate an ineffective component voltage estimation value Vi _ q from the ineffective current command effective value Iref _ qr. This calculation is performed using the following instantaneous formulas such as formula (2) and formula (3).

Vi_d＝(Ls+R)·Iref_dr····(2)

Vi_q＝(Ls+R)·Iref_qr····(3)

Here, L is an inductance value of each phase, R is a resistance value of a reactor of each phase, and s is a laplace operator. The effective component voltage estimated value Vi _ d (ineffective current command effective value Iref _ qr) is calculated by differentiating the effective current command effective value Iref _ dr and multiplying the result by the inductance value L and adding the product of the effective current command effective value Iref _ dr (ineffective current command effective value Iref _ qr) and the resistance value. The invalid component operation module 4300 outputs the calculated invalid component voltage estimated value Vi _ q as an invalid voltage command value to the voltage command value generation module 4001, and the effective component operation module 4400 outputs the calculated effective component voltage estimated value Vi _ d as an effective voltage command value to the voltage command value generation module 4001.

(2-2) action and Effect

The power converter according to the second embodiment has the same configuration as the power converter according to the first embodiment, and the control device 4000 is configured to calculate the voltage command value of the inverter 11 based on the node voltage V calculated by the moving average.

Therefore, the power conversion device according to the second embodiment includes the node voltage detection device 20 that detects the node voltage V by calculating the moving average of the period of one period of the carrier wave for the pulse width control, as in the first embodiment, and therefore can suppress the ripple and the detection delay of the detected voltage. Therefore, even when a phase jump occurs in the power system, the output voltage of the power conversion device can follow the variation of the voltage of the power system, and the overcurrent can be prevented from flowing through the power conversion device.

The power converter according to the second embodiment is configured such that the controller 4000 sets a current command and calculates a required voltage from an instantaneous equation, thereby providing high robustness against phase jump. (2-3) modified example of the second embodiment

(modification 1 of the second embodiment)

When noise enters the detected tie-point voltage V, Vi _ d and Vi _ q calculated by the voltage estimation unit 4303 and the voltage estimation unit 4403 greatly fluctuate. In this case, the voltage estimation unit 4303 and the voltage estimation unit 4403 may calculate the effective component voltage estimation value Vi _ d and the ineffective component voltage estimation value Vi _ q using an expression obtained by calculating the differential of the expressions (2) and (3) as an incomplete differential, such as the following expressions (4) and (5). T in the formulae (4) and (5) is a time constant and can be set arbitrarily.

Vi_d＝(Ls/(Ts-1)+R)·Iref_dr····(4)

Vi_q＝(Ls/(Ts-1)+R)·Iref_qr····(5)

(modification 2 of the second embodiment)

In consideration of the fact that the influence of noise cannot be avoided even by incomplete differentiation, it is preferable to add a limiter to the outputs of the invalid component operation block 4300 and the effective component operation block 4400. For example, a limiting module is provided at a stage subsequent to the invalid component operation module 4300 and the valid component operation module 4400, and when the outputs of the invalid component operation module 4300 and the valid component operation module 4400 are out of a predetermined range, a limiting value preset in the limiting module is output. The limit value is preferably the same as the voltage (both positive and negative) applied to the connection impedance when the rated current is supplied to the connection impedance, or is set to a value having a slight margin, for example, about 1.5 times the voltage.

(modification 3 of the second embodiment)

In addition, if a harmonic voltage is superimposed on the power system, a harmonic is also superimposed on the connection point voltage V. As shown in the second embodiment, when the detected value of the node voltage V is regarded as the current command value, if the system voltage (node voltage V) fluctuates due to superposition of harmonics, the current command value also fluctuates. Therefore, it is preferable to take measures against these. The fluctuation of the system voltage (the node voltage V) mentioned here means that a difference occurs between a rated value of the system voltage and a value of the node voltage.

First, countermeasures against harmonics are described. Preferably, for the low harmonics, for example, the detected junction voltage V is passed through a notch filter or a filter that attenuates a frequency that is an integral multiple of a predetermined frequency, and for the high harmonics, for example, the detected junction voltage V is passed through a low-pass filter or the like to attenuate harmonics superimposed on the junction voltage V and to attenuate harmonics superimposed on the current command value. The harmonic may also be attenuated by filtering the effective current command value, the ineffective current command value, and the like.

Further, if the low-pass filter is used as a countermeasure against the harmonic wave and the incomplete differential calculation by the above equations (4) and (5), the effective voltage command value and the ineffective voltage command value are delayed in phase. In order to compensate for this phase delay, it is preferable that the phase delay be compensated for by adding the active current and the reactive current by slightly increasing the active current command value when the reactive current flows from the power conversion device. Similarly, when the active current flows from the power conversion device, it is preferable to compensate for the phase delay by slightly increasing the reactive current command value and adding the reactive current to the active current. The active current means a current for the power conversion device to output active power, and the reactive current means a current for the power conversion device to output reactive current, both of which are components of the current output by the power conversion device.

(modification 4 of the second embodiment)

Next, in modification 4, measures against various errors of the node voltage V will be described. First, when the effective current command value Iref _ dr and the ineffective current command value Iref _ qr are converted into voltages applied to the connection impedances, if not differentiation but incomplete differentiation calculation is used, the phase is delayed. A method of compensating for this phase delay will be described. The control device of modification 4 is different from the control device 4000 of the second embodiment shown in fig. 4 in the configurations of the invalid component calculation module 4300 and the effective component calculation module 4400. Fig. 5 is an enlarged view showing a part of the control device of modification 4, and corresponds to a region surrounded by an alternate long and short dash line in the control device 4000 shown in fig. 4. The configuration of the control device outside the region shown in fig. 5 is the same as that of the second embodiment, and therefore, the description thereof is omitted.

As shown in the invalid component operation block 4300a and the valid component operation block 4400a shown in fig. 5, when phase delay compensation is performed, the two blocks cannot be completely separated, and interfere with each other.

First, the operation of the invalid component calculation module 4300a will be described. As in the second embodiment, the ineffective current command effective value Iref _ qr of each phase converted from the ineffective current command value by the current conversion unit 4302 is multiplied by the multiplier 4309 by the voltage compensation value of each phase calculated by the voltage compensation value calculation module described later, between the same phases, thereby compensating for voltage fluctuations. The reactive current instruction effective value Iref _ qr compensated for voltage variation is output to the filter module 4305 to attenuate harmonics. The filter module 4305 is constituted by a low-pass filter, for example.

The invalid current command effective value Iref _ qr after attenuating the harmonic is added to a current for phase delay compensation in the filter block 4305 calculated by multiplying the valid current command effective value Iref _ dr by a real number β by the multiplier 4406 by the multiplier 4307, and is input to the voltage estimating section 4303. Then, the voltage estimating unit 4303 calculates an ineffective component voltage estimated value Vi _ q, which is a voltage of the connection impedance required for flowing a current corresponding to the ineffective current command effective value Iref _ qr to which the current for phase delay compensation is added, by the above equation (5), and outputs the calculated value as an ineffective voltage command value. In addition, formula (3) may be used instead of formula (5).

It is preferable that a limiter be provided for the current invalid voltage command value and the valid voltage command value so that an excessive current does not flow. Therefore, in modification 4, a limiting module 4308 is provided between the voltage estimating unit 4303 of the invalid component calculating module 4300a and the voltage command value generating module 4001, and a limiting module 4408 is provided between the voltage estimating unit 4403 of the valid component calculating module 4400a and the voltage command value generating module 4001. These limiting modules 4308 and 4408 preferably set the limiting values to values that have a necessary margin for the minimum value and the maximum value of the voltage applied to the connection impedance when the rated current flows.

In the limit block 4038, when the invalid voltage command value input from the voltage estimation unit 4303 is within a predetermined range, the invalid voltage command value is output as it is to the voltage command value generation block 4001, and when the invalid voltage command value is out of the predetermined range, a preset limit value is output as the invalid voltage command value that is the output of the invalid component calculation block 4300a to the voltage command value generation block 4001. In the invalid component operation block 4300a, the invalid current command effective value Iref _ qr whose harmonic is attenuated by the filter block 4305 is multiplied by a real number β by the multiplier 4306, and is output to the valid component operation block 4400a as a current for phase delay compensation in the filter block 4405.

Next, the operation of the effective component calculation module 4400a will be described. As in the second embodiment, the effective current command effective value Iref _ dr of each phase converted from the effective current command value by the current converter 4402 is multiplied by the multiplier 4409 with the voltage compensation value of each phase calculated by the voltage compensation value calculation module described later, between the same phases, to compensate for the voltage fluctuation. The effective current command effective value Iref _ dr compensated for the voltage variation is output to the filter module 4405, so as to attenuate the harmonic. The filter module 4405 is formed of, for example, a low-pass filter.

The effective current command effective value Iref _ dr obtained by attenuating the harmonic is added to a current for phase delay compensation in the filter block 4305 calculated by multiplying the effective current command effective value Iref _ qr by a real number β by the multiplier 4306 by the multiplier 4407, and is input to the voltage estimating unit 4403. Then, the voltage estimating unit 4403 calculates an effective component voltage estimated value Vi _ d, which is a voltage of the connection resistance required for flowing a current corresponding to the effective current command effective value Iref _ dr obtained by adding a current for phase delay compensation, by the above equation (4), and outputs the calculated value to the limiting module 4408 as an effective voltage command value. In addition, formula (2) may be used instead of formula (4).

In the limitation module 4408, when the effective voltage command value is within the predetermined range, the effective voltage command value is output to the voltage command value generation module 4001 as it is, and when the effective voltage command value is out of the predetermined range, a preset limitation value is output to the voltage command value generation module 4001 as the effective voltage command value that is the output of the effective component operation module 4400 a. In addition, in the effective component operation block 4400a, the effective current command effective value Iref _ dr obtained by attenuating the harmonic by the filter block 4405 is multiplied by a real number β by the multiplier 4306, and is output to the ineffective component operation block 4300a as a current for phase delay compensation in the filter block 4305.

The voltage command value generation module (voltage command value generation unit) 4001 adds the phase-compensated junction voltage V input from the phase compensation module 4100, the effective voltage command value input from the effective component calculation module 4400, and the ineffective voltage command value input from the ineffective component calculation module 4300 to generate a voltage command value of the power conversion device.

Finally, a voltage compensation value calculation module that calculates a voltage compensation value for compensating for voltage variation will be explained. The voltage compensation value calculation module is provided in the control device, and calculates a voltage compensation value for each phase based on the input connection point voltage V of each phase. Fig. 6 shows a voltage compensation value calculation block (voltage compensation value calculation means) 4700 that calculates a voltage compensation value for compensating a current command value (an ineffective current command effective value, an effective current command effective value) when a voltage change occurs during stabilization. In the voltage compensation value calculation block 4700, voltage compensation values for the respective phases (u-phase, v-phase, and w-phase) are calculated. Since the voltage compensation value calculation operation is the same for each phase, the u-phase will be described as a representative example.

The voltage compensation value calculation block 4700 receives the detected value of the u-phase connection point voltage V smoothed by the connection point voltage detection device 20, and calculates the square value of the connection point voltage by the multiplier 4701. The square value of the connection point voltage is output to 1/4 cycle delay unit 4702 and adder 4703. The 1/4 cycle delay unit 4702 is formed of, for example, a memory. The 1/4 cycle delay unit 4702 holds the square value of the node voltage V in the memory for 1/4 cycles, and outputs the past value of the square value of the node voltage V before 1/4 cycles to the adder 4703 after 1/4 cycles have elapsed. Adder 4703 adds the square value (current value) of node voltage V input from multiplier 4701 and the past value of the square value of node voltage V input from 1/4 cycle delay unit 4702, and outputs the result to square root operation unit 4704.

The square root arithmetic unit 4704 calculates the square root of the output of the adder 4703 and outputs the square root to the divider 4705. The divider 4705 divides the output of the square root operation unit 4704 by √ 2. The division result is a value corresponding to the effective value of the u-phase connection point voltage V. Divider 4705 outputs the division result to u-phase voltage compensation value calculation unit 4706 as an effective value of connection point voltage V. The value of the rated phase voltage of the u-phase is also input to the u-phase voltage compensation value calculation unit 4706. The u-phase voltage compensation value calculation unit 4706 calculates a u-phase voltage compensation value by dividing the rated voltage of the u-phase by the effective value of the connection point voltage V of the u-phase.

In addition, since voltage fluctuation at the time of stabilization is small in a normal Power system, voltage fluctuation is allowed in many cases for PCS (Power Conditioning Subsystem) applications. For example, the voltage variation of the distribution system at the time of domestic stability in japan is only ± 10%.

In addition, if voltage compensation for voltage fluctuation is performed during a system accident, an unnecessary current flows. Therefore, when the connection point voltage value exceeds the stable range, it is preferable that the voltage fluctuation compensation is not performed. In the voltage compensation implementation and non-implementation, it is preferable to set a limiter to each phase voltage compensation value with reference to a voltage allowable value at the time of stabilization or a voltage value having a certain margin. For example, the limiter can be implemented by inserting a limiting block having the same configuration (different limiting value) as the limiting block 4308 described above between the voltage compensation value calculation block 4700 and the multiplier 4309 or between the voltage compensation value calculation block 4700 and the multiplier 4409.

Further, as in modification 4, if the voltage compensation calculation (calculation by the multipliers 4309 and 4409) is put in front of the differential calculation (calculation by the voltage estimating units 4303 and 4403), there is a possibility that a large voltage command value is output in the differential calculation immediately after the switching of the presence or absence of the voltage fluctuation compensation. It is therefore preferred to place the voltage compensation calculation in the later stage of the differentiation calculation. In addition, in the case of inserting the former stage, the following measures are required: a multiplier capable of multiplying by a real number, such as a multiplier, is inserted between the voltage compensation value calculation block 4700 and the multipliers 4309 and 4409, and the gain of the multiplier is reduced little by little so as not to stop the voltage compensation suddenly.

(3) Third embodiment

A power converter according to a third embodiment is a device that controls the output of a power converter by feeding back a current output from the power converter, as compared with the power converter according to the second embodiment. The current feedback control will be described below.

In the feedback control of the current output from the power converter, there are a case where the active power output from the power conversion device is controlled by feeding back the active current and a case where the reactive power output from the power conversion device is controlled by feeding back the reactive current. If the power system is close to the three-phase balance, the instantaneous effective power may be fed back while the effective power is controlled, and the instantaneous ineffective power may be fed back while the ineffective power is controlled. This is because, for three-phase balance, the instantaneous effective power is the three-phase sum of the product of the effective current and the connection point voltage V, and the instantaneous reactive power is the three-phase sum of the product of the ineffective current and the connection point voltage V, so the effective current is proportional to the instantaneous effective power, and the ineffective current is also proportional to the instantaneous reactive power.

Specifically, for example, the control device 4000 is provided with: the instantaneous power operation module is used for calculating instantaneous effective power and instantaneous ineffective power output by the power conversion device; a multiplier capable of adjusting gain; and a subtractor that calculates a difference with the current command value. The instantaneous effective power and the instantaneous ineffective power output from the instantaneous power calculation module are multiplied by a predetermined gain by a multiplier, the magnitude of the resultant is adjusted, the difference between the effective current command value and the instantaneous effective power and the difference between the ineffective current command value and the instantaneous ineffective power are calculated by a subtractor, the instantaneous effective power is fed back to the effective current command value, and the instantaneous ineffective power is fed back to the ineffective current command value. This action corresponds to current feedback control.

The power converter according to the third embodiment has the same configuration as that of the second embodiment, and therefore can achieve the same effects, and can control the current (i.e., active power and reactive power) output by the power converter more accurately by controlling the output of the power converter by feeding back the current (active power and reactive power) as described above.

(4) Fourth embodiment

(4-1) Overall Structure of Power conversion device according to fourth embodiment

A power conversion device according to a fourth embodiment will be described with reference to fig. 7 in which the same components as those in fig. 1 are denoted by the same reference numerals. As shown in fig. 7, the power conversion device 10a of the fourth embodiment is used in a power generation system 100a, as in the first embodiment. The power conversion device 10a is different from the power conversion device 10 of the first embodiment in that it includes a control device 60 that performs vector control, and specifically, the control device 60 is a vector control mechanism that calculates a voltage command value of the inverter 11 by vector control based on the system voltage, unlike the control device 30 (see fig. 3) of the first embodiment. The configuration other than the control device 60 is the same as that of the power conversion device 10 of the first embodiment, and therefore, the description thereof is omitted.

(4-2) configuration and operation of control device for power conversion device of fourth embodiment

Control device 60 generates a voltage command value for inverter 11 based on the connection point voltage, which is the grid voltage of power grid 50, by a known vector control method. In the present specification, as an example, the control device 60 will be described as a control device to which the vector control method disclosed in japanese patent application laid-open No. 4373040 is applied.

First, the configuration of the control device 60 will be described. Since a control device of a self-excited converter is required to perform high-speed control, a three-phase ac is generally converted into two-phase dc components of an active component and an inactive component by dq conversion, and the two-phase dc components are constituted by a decoupled vector control system. As shown in fig. 8, the control device 60 includes an active current command generating unit 61d, an inactive current command generating unit 61q, a phase detecting unit 68, a qd converting unit 69 (only output terminals indicated by circular symbols in the drawing are shown in fig. 8), an inverse qd converting unit 66, a gate pulse generating unit 67, operational amplifier circuits 63d and 63q, adders 62d, 62q, 65d and 65q, and a multiplier 64 d.

The effective current command generating unit 61d generates an effective current command value Idp based on the node voltage V, the frequency of the power system 50 calculated from the node voltage V, the capacitance voltage of the capacitor 14 of the inverter 11, and the like. The reactive current command generating unit 61q generates a reactive current command value Iqp based on the connection point voltage V, the frequency of the power system 50, the capacitance voltage of the capacitor 14 of the inverter 11, and the like. The Phase detecting unit 68 detects the Phase of the node voltage V from the node voltage V by using a known calculation method such as PLL (Phase Locked Loop) or DFT (Discrete Fourier transform). The qd converter 69 converts the three-phase ac into two-phase dc components of an active component and an inactive component by dq conversion using the phase detected by the phase detector 68 as a reference phase. The inverse qd conversion unit 66 performs inverse dq conversion on the effective component voltage command value and the ineffective component voltage command value, and further performs two-phase/three-phase conversion, thereby generating three-phase output voltage command values (VRp, VSp, VTp). Gate pulse generator 67 generates a gate pulse signal for controlling the on/off of each switch of inverter 11 by known PWM control based on the voltage command value.

Next, the operation of the control device 60 will be described. Control device 60 controls inverter 11 using the active power and the reactive power as command values. In the control device 60, the node voltage V detected by the node voltage detection device 20 is input to the active current command generation unit 61d, the reactive current command generation unit 61q, and the phase detection unit 68. The phase detection unit 68 detects the phase of the node voltage V from the node voltage V by means of a PLL, and outputs the detected phase to the qd conversion unit 69 and the inverse qd conversion unit 66 as a reference phase.

The qd conversion unit 69 performs two-phase conversion on the connection point voltage V of each phase and the current of each phase detected by a current detector not shown, and calculates an effective voltage detection value Edf, an effective current detection value Idf, an ineffective voltage detection value Eqf, and an ineffective current detection value Iqf.

Since the control device 60 performs the decoupling control of the calculation of the active power component voltage command value and the calculation of the reactive power component voltage command value, the operations of these calculations will be described in order. First, an operation of calculating the effective power component voltage command value will be described. The effective current command generating unit 61d receives the node voltage V, the capacitance voltage of the capacitor 14 from the capacitance voltage detector 43, calculates the frequency of the power system 50 from the node voltage V, generates an effective current command value Idp for outputting predetermined effective power based on the calculated frequency, and outputs the generated effective current command value Idp to the adder 62 d.

The adder 62d calculates a deviation between the effective current command value Idp and the effective current detection value Idf obtained by the two-phase conversion in the qd conversion unit 69, and outputs the calculated deviation to the operational amplifier circuit 63 d. The operational amplifier circuit 63d performs operational amplification on the deviation. The effective current is feedback-controlled by calculation in the adder 62d and the operational amplifier circuit 63 d. The operational amplifier circuit 63d outputs the amplified difference to the adder 65 d. At this time, the effective current detection value Idf is input to the multiplier 64d having a gain of the impedance Xt, which is a connection impedance (reactor in this embodiment), multiplied by the gain Xt, and output to the adder 65 q.

The adder 65d adds the difference amplified by the operational amplifier circuit 63d, the effective voltage detection value Edf obtained by the two-phase conversion by the qd converter 69, and the ineffective current detection value Iqf multiplied by Xt to generate an effective power component voltage command value. Control device 60 performs decoupling control from calculation of the reactive power component voltage command value by adding a signal obtained by multiplying reactive current detection value Iqf by impedance Xt. The generated active power component voltage command value is output to the inverse qd converter 66.

Next, the operation of calculating the reactive power component voltage command value will be described. The reactive current command generating unit 61q receives the node voltage V and the capacitance voltage of the capacitor 14, calculates the frequency of the power system 50 from the node voltage V, generates a reactive current command value Iqp for outputting predetermined reactive power based on the calculated frequency, and outputs the generated reactive current command value Iqp to the adder 62 q.

The adder 62q calculates a deviation between the reactive current command value Iqp and the reactive current detection value Iqf obtained by the two-phase conversion by the qd conversion unit 69, and outputs the calculated deviation to the operational amplifier circuit 63 q. The operational amplifier circuit 63q operational-amplifies the deviation. The reactive current is feedback-controlled by calculation in the adder 62q and the operational amplifier circuit 63 q. The operational amplifier circuit 63q outputs the amplified difference to the adder 65 q. At this time, the reactive current detection value Iqf is input to a multiplier 64d having a gain of an impedance Xt connecting an impedance (reactor in this embodiment), multiplied by the gain Xt, and output to an adder 65 d.

The adder 65q adds the difference amplified by the operational amplifier circuit 63q, the ineffective voltage detection value Eqf obtained by the two-phase conversion by the qd converter 69, and the effective current detection value Idf multiplied by Xt, to generate an ineffective power component voltage command value. The control device 60 performs decoupling control from the calculation of the active power component voltage command value by adding a signal obtained by multiplying the impedance Xt by the active current detection value Idf. The adder 65d outputs the generated reactive power component voltage command value to the inverse qd converter 66.

The inverse qd converter 66 performs inverse dq conversion on the input active power component voltage command value and reactive power component voltage command value, further performs two-phase/three-phase conversion to generate voltage command values VRp, VSp, VTp of each phase of the converter 11, and outputs the voltage command values to the gate pulse generator 67. Gate pulse generator 67 generates a carrier wave (e.g., a triangular wave) for PWM control, and modulates the input voltage command values VRp, VSp, and VTp of the respective phases with the carrier wave. The gate pulse generating unit 67 generates a gate pulse signal for controlling the opening and closing of the high-voltage side switch 12H and the low-voltage side switch 12L of each of the R phase converting unit 11R, S phase converting unit 11S and the T phase converting unit 11T of the inverter 11 by modulating the voltage command value with a carrier wave. The gate pulse generator 67 outputs the generated gate pulse signal to each switch. By doing so, control device 60 controls the opening and closing of high-side switch 12H and low-side switch 12L of R-phase transformation unit 11R, S phase transformation unit 11S and T-phase transformation unit 11T of inverter 11, respectively.

(4-3) action and Effect

The power converter 10a according to the fourth embodiment has the same configuration as the power converter 10 according to the first embodiment, and therefore can achieve the same effects as those of the power converter according to the first embodiment. The power converter 10a according to the fourth embodiment is configured as a vector control means for calculating a voltage command value by vector control based on the system voltage (connection point voltage V). Therefore, even when the vector control is used, the power conversion device 10a can reduce the ripple by providing the node voltage detection device having the filter means using the moving average, can reduce the detection delay, can detect the node voltage, can perform feed-forward, and can achieve the same effect as the power conversion device according to the first embodiment. There is an advantage that the connection point detection unit can be replaced with only a vector control device that has been widely used so far. I.e. the retrofitting of existing products is easy.

(5) Fifth embodiment

(5-1) Overall Structure of Power conversion device according to fifth embodiment

A power conversion device according to a fifth embodiment will be described with reference to fig. 9 in which the same components as those in fig. 1 are denoted by the same reference numerals. As shown in fig. 9, the power conversion device 10b according to the fifth embodiment is used in a power generation system 100b, as in the first embodiment. The power conversion device 10b is different from the power conversion device 10 of the first embodiment in that it includes a voltage compensation unit 70 that compensates for the detected junction voltage V. The voltage compensation unit 70 compensates for a difference between the rated voltage of the power grid 50 and the grid-connection-point voltage V detected by the grid-connection-point voltage detection device 20 as the grid voltage detection device. More specifically, the peak value Vpeak of the detected connection point voltage V is calculated, and the difference between the rated voltage and the peak value Vpeak is added, and the other configurations are the same as those of the power conversion device 10 according to the first embodiment, and therefore, the description thereof is omitted.

(5-2) configuration and operation of the Voltage Compensation section of the fifth embodiment

First, the structure of the voltage compensation unit 70 will be described. As shown in fig. 10, the voltage compensation unit 70 includes a peak value calculation unit 71, a subtractor 72, and an adder 73. The peak value calculation unit 71 can calculate the peak value Vpeak of the connection point voltage by the following equation (6). Therefore, the peak value calculation unit 71 includes a square calculation unit 75, a temporary data holding unit 76, an adder 77, and a square root calculation unit 78.

Vpeak＝((Vp²+(Vp²)b))^0.5···(6)

Here, Vp is a detection value of the junction voltage V, (Vp)²) b is a square value Vp of a detection value of the junction voltage V before the 1/4 cycle period²Past values of (c).

Squaring operationThe unit 75 is configured to divide the signal line from the node voltage detection device 20 (see fig. 10) into two and connect the two signal lines to the multiplier 75a, and calculates the square value of the node voltage V by the multiplier 75 a. The square operation unit 75 is not particularly limited as long as it can calculate the square value of the node voltage V. The temporary data holding unit 76 includes a known memory such as a DRAM, an SRAM, a flash memory, and a hard disk drive, and squares Vp of detected values²The square value stored in the memory is outputted after the 1/4 period of the node voltage V is held.

Next, the operation of the voltage compensation unit 70 will be described. In the voltage compensation unit 70, the detected value Vp of the node voltage V is input to the peak value calculation unit 71 and the adder 73. Once the detected value Vp is input to the peak value calculation unit 71, the square calculation unit 75 calculates a square value Vp of the detected value Vp²And outputs the squared value to the temporary data holding unit 76 and the adder 77. The temporary data holding section 76 receives the square value Vp of the detection value Vp once²Then the square value Vp of the detection value is used²Storing the square value Vp in a memory, maintaining the 1/4 period of the junction voltage V, and storing the square value Vp in the memory²As past value (Vp)²) b, outputting. That is, the temporary data holding unit 76 does not use the square value Vp of the detection value Vp²But the square value Vp calculated before 1/4 cycles²As past value (Vp)²) b, outputting. The temporary data holding unit 76 holds the square value Vp of the detection value²Sequentially stored in the memory, held at the node voltage V for a period of 1/4 cycles, and then sequentially output the past value (Vp) to the adder 77²)b。

The adder 77 adds the square value Vp of the detection value²And square value Vp²1/4 past before cycle (Vp)²) b are added, and the addition result (Vp) is added²+(Vp²) b) to the square root operation unit 78. Upon receiving the addition result (Vp), the square root operation unit 78²+(Vp²) b), the square root of the addition result is calculated, and the peak value Vpeak of the node voltage V is calculated (Vp)²+(Vp²)b)^0.5. The square root arithmetic unit 78 outputs the calculated peak value Vpeak to the subtractor 72. By doing so, the peak value calculation unit 71 calculates the peak value Vpeak of the connection point voltage V by performing the calculation of equation (6). The peak value Vpeak of the connection point voltage V is a dc value.

The subtractor 72 is inputted with the rated voltage and the peak value Vpeak of the power system 50, and calculates a difference between the rated voltage and the peak value Vpeak as a compensation voltage. The subtractor 72 outputs the compensation voltage to the adder 73. Adder 73 receives compensation voltage and node voltage V, adds the node voltage V to the compensation voltage, and outputs the compensated node voltage V to control device 30. In this way, the voltage compensation unit 70 calculates the difference between the rated voltage and the peak value Vpeak of the node voltage V as a compensation voltage, and adds the calculated compensation voltage to the node voltage V to compensate for the deviation between the node voltage V and the rated voltage.

(5-3) action and Effect

The power conversion device 10b according to the fifth embodiment has the same configuration as the power conversion device 10 according to the first embodiment, and therefore can achieve the same effects as those of the power conversion device according to the first embodiment. The power conversion device 10b according to the fifth embodiment includes a voltage compensation unit 70 that compensates for a difference between the system voltage (the connection point voltage V) and the rated voltage of the power system 50, and the voltage compensation unit 70 calculates a peak value Vpeak of the connection point voltage V and adds the difference between the rated voltage and the peak value Vpeak to the connection point voltage V to compensate for the connection point voltage V. Therefore, the power conversion device 10b according to the fifth embodiment can reduce the difference voltage between the connection point voltage V and the voltage component fed forward by the connection point voltage V, and can further follow the variation of the connection point voltage V. Further, when the active power component voltage command value and the reactive power component voltage command value are zero, the output of current from the power conversion device 10b can be suppressed.

(6) Modification example

(modification 1)

In the power conversion device 10 of the first embodiment, the case where the effective voltage component voltage command value after the phase has advanced from the node voltage V by 1/4 cycles is calculated by time-differentiating the detected node voltage V has been described, but the present invention is not limited to this. In this case, for example, while the detected junction voltage V is held in a memory or the like for 1/4 cycles, a voltage delayed by 1/4 cycles from the junction voltage V is generated, and a voltage advanced by 1/4 cycles from the junction voltage V is generated by multiplying-1 by the voltage delayed by 1/4 cycles. Then, based on the voltage advanced by 1/4 cycles from the node voltage V, an effective voltage component voltage command value advanced by 1/4 cycles in phase from the node voltage V is calculated.

(7) Verification test

(verification test 1)

As a verification test 1, the power conversion apparatus 10 shown in fig. 1 was simulated, the output of the node voltage detection apparatus 20 was calculated, and the ripple state of the detected node voltage V was confirmed. In addition, when the gain q of the reactive power component voltage command value generation unit 31 and the gain d of the active power component current command value generation unit 33 are set to zero and the power conversion device 10 outputs a voltage substantially equal to the junction point voltage V, that is, only feedforward of the junction point voltage V, the current output from the power conversion device 10 is calculated and a state in which the detection of the junction point voltage V is delayed is confirmed.

Here, the reason why the state of the detection delay of the node voltage V can be investigated by performing feedforward of the node voltage V only to the power conversion device 10 and calculating the output current of the power conversion device 10 will be described. When there is no detection delay of the node voltage V, a voltage substantially equal to the node voltage V is output from the power conversion device 10, the difference voltage between the output voltage of the power conversion device 10 and the grid voltage of the power grid 50 becomes substantially zero, and the output current of the power conversion device 10 also becomes substantially zero. On the other hand, when there is a detection delay in the node voltage V, a difference voltage corresponding to only the detection delay of the node voltage V is generated between the output voltage of the power conversion device 10 and the grid voltage of the power grid 50, and a current is output from the power conversion device 10. Therefore, by causing the power conversion device 10 to output a voltage substantially equal to the node voltage V and calculating the output current of the power conversion device 10, the state of the detection delay of the node voltage V can be investigated.

The results of the verification test 1 are explained below. Fig. 11A shows the calculation results of the detection value of the node voltage V detected by the node voltage detection device 20, with time(s) on the horizontal axis and the voltage value (P.U) on the vertical axis. A solid line 711 in fig. 11A shows the detected value of the R-phase junction voltage V, an interrupted line 712 shows the detected value of the S-phase junction voltage V, and a broken line 713 shows the detected value of the T-phase junction voltage V. When fig. 11A is observed, it can be confirmed that there is no ripple in the detected value of the node voltage V of each phase, and the ripple can be suppressed by calculating the moving average of the detected voltage detected during one period of the carrier wave and setting the moving average as the detected value of the node voltage V.

Fig. 11B shows the calculation result of the output current of the power conversion device 10 in the case of feedforward with time(s) on the horizontal axis and the current value (P.U) on the vertical axis and only the node voltage V. A solid line 711 in fig. 11B shows a calculated value of the current of the R-phase, an interrupted line 712 shows a calculated value of the current of the S-phase, and a broken line 713 shows a calculated value of the current of the T-phase. When fig. 11B is observed, it can be confirmed that the output current of each phase is small, the detection value of the node voltage V follows the node voltage V, and the detection delay of the node voltage V can be suppressed. Therefore, it was confirmed that the power conversion device of the present invention can suppress the ripple and the detection delay of the detected voltage.

(verification test 2)

In the verification test 2, as an example, the power converter of modification 4 of the second embodiment having the control device 4000 shown in fig. 5 was simulated, the phase jump was generated in the connection point voltage V in the simulation, and the changes in the output voltage, the output current, the active power, and the reactive current of the power converter were examined, and the robustness of the power converter was examined. Meanwhile, as a comparative example, a power converter which controls an output only by a conventional vector control was simulated, and changes in the output voltage, the output current, the active power, and the reactive power of the power converter with respect to a phase transition of the node voltage were examined in the same manner as in the example, to evaluate robustness. The results are shown in fig. 12.

Fig. 12 (a) shows a time change of the system voltage, a solid line 1201 is a u-phase voltage, an interrupted line 1202 is a v-phase voltage, and a broken line 1203 is a w-phase voltage. Fig. 12 (b) shows a temporal change in phase angle. Fig. 12 (c) shows a control result of the embodiment, that is, a time change of the output current of the power conversion device of the embodiment, a solid line 1211 shows the output current to the u-phase, an intermittent line 1212 shows the output current to the v-phase, and a broken line 1213 shows the output current to the w-phase. Fig. 12 (d) shows a time change in the output current of the power conversion device of the comparative example, a solid line 1204 shows the output current to the u-phase, an interrupted line 1205 shows the output current to the v-phase, and a broken line 1206 shows the output current to the w-phase. Fig. 12 (e) shows the temporal change in the output of the effective power of the power conversion device of the embodiment and the power conversion device of the comparative example, the broken line shows the embodiment, and the solid line shows the comparative example. Fig. 12 (f) shows a temporal change in the output of reactive power of the power conversion device of the embodiment and the power conversion device of the comparative example, the broken line shows the embodiment, and the solid line shows the comparative example.

When (a) was observed, it was found that a phase transition of the system voltage occurred in the vicinity of 0.075 seconds. Accompanying this, the phase angle also changes (see (b)). When (c) is observed, it is determined that, in the power converter of the embodiment, the output current is reduced following the phase jump of the system voltage, and thereafter, is restored without an overcurrent flowing. On the other hand, when (d) is observed, it is found that, in the power converter of the comparative example, even if a phase jump occurs, the output current does not change with the phase jump, and after about 0.01 second, a current larger than the control target flows through each phase, and an overcurrent flows through the power converter.

When (e) and (f) are observed, it is found that the amount of change in the outputs of the active power and the reactive power that change due to the phase jump is small on the embodiment side and the output can be returned to the control target amount more quickly than on the comparative example. As described above, it was found that the power conversion device according to modification 4 of the second embodiment is more robust than the conventional vector control.

In the above-described embodiment, the case where the voltage detector serving as the voltage detection device is provided with the filter means 21 for performing moving averaging or calculating the approximate value of the moving average for a period of one cycle of a constant period of the output voltage of the detection means has been described, but the present invention is not limited to this. For example, the voltage detector serving as the voltage detection device may be provided with a filter unit that performs moving averaging of the output voltage of the detection unit for a period of several cycles of a constant period (i.e., a period exceeding the constant period) or calculates an approximate value of the moving average.

In the above-described embodiment, the case where the node voltage detection device 20 (system voltage detection device) calculates the moving average of the detected voltage in the period of one cycle of the carrier wave used for the pwm control and detects the moving average as the system voltage has been described, but the present invention is not limited to this. For example, the connection point voltage detection means 20 (system voltage detection means) may calculate a moving average of a period of a few period parts of the carrier wave for the pulse width modulation control (i.e., a period part exceeding the carrier wave) with respect to the detected voltage and detect it as the system voltage.

In the above-described embodiment, the converter 11 has been described as a converter that switches at a predetermined switching cycle and outputs power to the power system via the connection impedance, in which the switching of the converter 11 is switched so as to output pulses of different widths at a substantially constant cycle and the converter 11 outputs a predetermined ac voltage, but various cycles can be applied as the switching cycle of the converter (the cycle of the carrier wave used for the pulse width modulation control).

However, the switching period of the inverter is more preferably 13kHz or more above the audible range.

As described above, in the present embodiment, the power conversion devices 10 and 10a include: a converter 11 that switches the switches of the converter 11 at a predetermined switching cycle, and the converter 11 outputs electric power to the power system 50 through connection impedances (reactors 17R, 17S, and 17T); a voltage detector (connection point voltage detection device 20) that detects a voltage at a connection point (terminals LPR, LPS, LPT) between the power conversion device 10 and the power system 50; and control devices 30, 4000, and 60 for controlling inverter 11 based on the output voltage of the voltage detector that is subjected to moving averaging for a predetermined period in accordance with the switching cycle. With such a configuration, it is possible to realize a power converter and a power generation system that can suppress a ripple and a detection delay of a detected voltage.

In the control device 4000 of the power converter, a value that is a real multiple of the output voltage of the voltage detector, which is subjected to moving averaging for a predetermined period in accordance with the switching period, may be used as the effective current command value, and the converter 11 may be controlled by the voltage command value calculated based on the effective current command value.

In the control device 4000 of the power converter, based on the output voltage of the voltage detector that is subjected to moving averaging for a predetermined period in accordance with the switching cycle, instantaneous voltages (the effective component voltage estimated value Vi _ d and the ineffective component voltage estimated value Vi _ q) may be calculated from the instantaneous expressions of the above expressions (2) and (3) and the instantaneous expressions of the above expressions (4) and (5), and the voltage command value of the inverter 11 may be generated based on the instantaneous voltages.

In addition, in such a control device 4000 of the power converter, the above-described configuration may be combined, for example, a value obtained by multiplying a real number of the output voltage of the voltage detector by a moving average for a predetermined period in accordance with the switching cycle is used as a current command value, instantaneous voltages (the effective component voltage estimated value Vi _ d and the ineffective component voltage estimated value Vi _ q) are calculated from the instantaneous expressions of the above-described expressions (2) and (3) and the instantaneous expressions of the above-described expressions (4) and (5) on the basis of the current command value, and the voltage command value of the converter 11 is generated from the instantaneous voltages.

Further, although the measurement is performed by the connection point voltage, the measurement may be performed not at the connection point but at another part of the power system as long as the impedance from the inverter can be estimated.

The voltage at the connection point may be determined by measuring and calculating the voltage at another location, for example, the connection impedance, instead of directly measuring the voltage at the connection point.

Description of the reference numerals

10. 10a, 10b power conversion device

11 converter

15 active power supply

17R, 17S, 17T reactor

20. 25 connecting point voltage detection device

30. 60, 4000 control device

50 electric power system

55 ac voltage source

70 voltage compensation part

100. 100a, 100b power generation system