阅读说明：本技术 电力转换装置 (Power conversion device ) 是由 鹤间义德 于 2017-05-18 设计创作，主要内容包括：本发明的目的在于提供能够提高三相电压型逆变器的转换效率的电力转换装置。本发明的实施方式的电力转换装置(1)具备三相电压型逆变器(5)、二相/三相转换部(11)、三次谐波生成部(12)、加法器(13)、PWM控制部(14)及三次谐波振幅决定部(15a)。三次谐波生成部(12)生成正弦波状的三次谐波信号(Vh),该正弦波状的三次谐波信号与三相的电压指令信号(Vu、Vv、Vw)同步且具有三相的电压指令信号的三倍的频率。而且,三次谐波生成部(12)具备三次谐波振幅决定部,该三次谐波振幅决定部基于与二相的电压指令信号(Vd、Vq)对应的电压振幅指令值及与对电力系统的输出请求对应的输出功率因数指令值,决定三相电压型逆变器(5)的电力损失为最小的三次谐波信号(Vh)的振幅。(The invention aims to provide a power conversion device capable of improving conversion efficiency of a three-phase voltage type inverter. A power conversion device (1) according to an embodiment of the present invention is provided with a three-phase voltage source inverter (5), a two-phase/three-phase conversion unit (11), a third harmonic generation unit (12), an adder (13), a PWM control unit (14), and a third harmonic amplitude determination unit (15 a). A third harmonic generation unit (12) generates a sinusoidal third harmonic signal (Vh) that is synchronized with the three-phase voltage command signals (Vu, Vv, Vw) and has a frequency three times that of the three-phase voltage command signals. The third harmonic generation unit (12) is provided with a third harmonic amplitude determination unit that determines the amplitude of a third harmonic signal (Vh) that minimizes the power loss of the three-phase voltage source inverter (5) on the basis of a voltage amplitude command value corresponding to the two-phase voltage command signals (Vd, Vq) and an output power factor command value corresponding to an output request to the power system.)

1. A power conversion device is characterized by comprising:

a three-phase voltage-type inverter having a circuit in which three branch lines are connected in parallel, two arms in each of which a switching element and a reflux diode are connected in anti-parallel are connected in series, the three-phase voltage-type inverter converting a direct-current voltage from a direct-current power supply into a three-phase alternating-current voltage and outputting the three-phase alternating-current voltage to a power system;

a two-phase/three-phase conversion unit that converts a two-phase voltage command signal into a sinusoidal three-phase voltage command signal;

a third harmonic generation unit that generates a sinusoidal third harmonic signal synchronized with the three-phase voltage command signals and having a frequency three times that of the three-phase voltage command signals;

an adder that outputs a three-phase modulated wave signal in which the third harmonic signal is superimposed on the three-phase voltage command signal; and

a PWM control unit for generating gate signals for driving the switching elements by comparing the three-phase modulated wave signals with triangular-wave carrier signals,

the third harmonic generation unit includes a third harmonic amplitude determination unit configured to determine an amplitude of the third harmonic signal at which a power loss of the three-phase voltage-source inverter is minimized, based on a voltage amplitude command value corresponding to the two-phase voltage command signal and an output power factor command value corresponding to an output request to the power system.

2. The power conversion apparatus according to claim 1,

the two-phase voltage command signal includes a d-axis voltage command signal and a q-axis voltage command signal,

the voltage amplitude command value is a square root of a sum of a square of a value of the d-axis voltage command signal and a square of a value of the q-axis voltage command signal.

3. The power conversion apparatus according to claim 1 or 2,

the third harmonic amplitude determination unit determines the amplitude of the third harmonic signal corresponding to the combination of the voltage amplitude command value and the output power factor command value, based on a table that specifies the relationship among the voltage amplitude command value, the output power factor command value, and the amplitude of the third harmonic signal at which the power loss of the three-phase voltage-source inverter is minimized.

4. The power conversion apparatus according to claim 1 or 2,

the third harmonic amplitude determining unit determines the amplitude of the third harmonic signal based on a function having the voltage amplitude command value and the output power factor command value as arguments.

Technical Field

The present invention relates to a power conversion device.

Background

As a control method of the inverter, pwm (pulse Width modulation) control is known. In the three-phase inverter, a sinusoidal voltage command signal is generated in each phase of U, V, W, and the three-phase PWM control is performed by comparing the voltage command signals with a carrier signal which is a triangular wave.

However, in the PWM control of the sine wave-triangular wave comparison method, in order to normally perform modulation, it is necessary that the voltage command signal of each phase is within the amplitude of the carrier signal, and the amplitude of the fundamental wave of the output voltage of the inverter is limited to √ 3/2 or less of the dc voltage. Therefore, there is a problem that the voltage utilization rate of the dc voltage is low.

In order to improve the voltage utilization efficiency, a method of superimposing a third harmonic in synchronization with three-phase voltage command signals is known (japanese patent application laid-open No. 2009-124799). As shown in fig. 5, by superimposing a third harmonic (51) of a frequency three times that of the fundamental wave on the voltage command signal (50) of each phase to reduce the peak value of the voltage command signal (52), the maximum value of the fundamental wave component of the output voltage can be increased, and the voltage utilization rate of the inverter can be improved. This is to utilize the fact that even if the third harmonic is superimposed, the line-to-line output does not include the harmonic. It is also known that the voltage utilization rate can be improved to the maximum extent by setting the amplitude of the third harmonic signal to about 1/6 with respect to the voltage command signal (fig. 6).

Disclosure of Invention

Problems to be solved by the invention

Therefore, in general, the amplitude of the third harmonic is set to about 1/6 with respect to the voltage command signal in order to improve the voltage utilization rate. However, this setting does not necessarily optimize the conversion efficiency of the inverter. According to the new findings of the present inventors, the amplitude of the third harmonic can be used to improve the conversion efficiency of the inverter. The following description will be specifically made with reference to fig. 7 and 8.

Fig. 7 is a diagram for explaining a path of a current flowing through the voltage-type inverter. The path through which the current flows changes according to the ON/OFF of the switching element during the operation of the inverter. The direction of the current is positive in fig. 7, which indicates that the current flows from the inverter to the load side. Then, paths of the current flowing in the positive direction are a and B, and paths of the current flowing in the negative direction are C and D. B and C are paths through the switching element, and A and D are paths through the diode.

Fig. 8 is a diagram for explaining a loss in the switching element (transistor). It takes some time to switch from OFF to ON, or from ON to OFF. During this switching period, the voltage and current are not completely ON or OFF, and thus power loss occurs. In addition, the switching element is not completely turned ON even during the ON period, and a drop voltage is generated between the collector and the emitter, which causes a power loss. Such power loss occurs in other semiconductor elements (for example, diodes), but the amount of power loss varies. In fig. 8, (1) and (3) show periods of power loss due to switching, and (2) shows periods of power loss due to conduction. In addition to the effect of the power loss on the conversion efficiency, the larger the thermal energy to be released as the thermal energy, the larger the need for a large-scale cooling unit, and therefore the smaller the power loss is preferable.

As described above, when the third harmonic is superimposed ON the three-phase voltage command signal, the waveform of the voltage command signal changes (fig. 5), and the state of the gate pulse, that is, the ON/OFF ratio of the inverter output voltage changes. As a result, the time ratio of the current flowing through the path having the switching element and the path having the diode also changes. Since the power loss varies depending on the current path (fig. 7 and 8), the conversion efficiency of the final inverter may vary. The degree of change in the waveform of the voltage command signal also changes according to the amplitude of the superimposed third harmonic. The present inventors paid attention to this point, and used the amplitude of the third harmonic in order to improve the conversion efficiency of the three-phase voltage source inverter.

The present invention has been made to solve the above-described problems, and an object thereof is to provide a power conversion device capable of improving the conversion efficiency of a three-phase voltage-type inverter.

Means for solving the problems

A power conversion device according to an embodiment of the present invention includes a three-phase voltage-source inverter, a two-phase/three-phase conversion unit, a third harmonic generation unit, an adder, a PWM control unit, and a third harmonic amplitude determination unit. A three-phase voltage-type inverter, which has a circuit in which three branch lines are connected in parallel, for example, and two arms in which a switching element and a reflux diode are connected in anti-parallel are connected in series to each branch line, converts a direct-current voltage from a direct-current power supply into a three-phase alternating-current voltage and outputs the three-phase alternating-current voltage to a power system, is provided. The three-phase voltage type inverter is not limited to this configuration, and may be, for example, a neutral point clamped three-level inverter or a neutral point switching three-level inverter as long as it converts direct current into three-phase alternating current. The two-phase/three-phase conversion unit converts the two-phase voltage command signal into a sinusoidal three-phase voltage command signal. The third harmonic generation unit generates a sinusoidal third harmonic signal having a frequency three times that of the three-phase voltage command signal in synchronization with the three-phase voltage command signal. The adder outputs a three-phase modulated wave signal in which a third harmonic signal is superimposed on the three-phase voltage command signal. The PWM control unit generates gate signals for driving the switching elements by comparing three-phase modulation wave signals with triangular wave carrier signals. The third harmonic generation unit includes a third harmonic amplitude determination unit that determines an amplitude of the third harmonic signal that minimizes a power loss of the three-phase voltage-source inverter, based on a voltage amplitude command value corresponding to the two-phase voltage command signal and an output power factor command value corresponding to an output request to the power system.

As described above, the ON/OFF ratio of the gate signal changes depending ON the amplitude of the third harmonic signal, and thus the time ratio of the current flowing through the switching element and the free wheeling diode also changes. The power loss varies depending on the current path (fig. 7 and 8), and the conversion efficiency of the final inverter also varies. In the present embodiment, the amplitude of the third harmonic signal is determined so as to minimize the power loss of the three-phase voltage source inverter. Therefore, according to the power conversion device 1 of the present embodiment, the conversion efficiency of the three-phase voltage source inverter can be improved.

Preferably, the two-phase voltage command signal includes a d-axis voltage command signal and a q-axis voltage command signal. The voltage amplitude command value is the square root of the sum of the square of the value of the d-axis voltage command signal and the square of the value of the q-axis voltage command signal.

Preferably, the third harmonic amplitude determining unit has a table that specifies a relationship among the voltage amplitude command value, the output power factor command value, and the amplitude of the third harmonic signal at which the power loss of the three-phase voltage-source inverter is minimized. The third harmonic amplitude determining unit determines the amplitude of the third harmonic signal corresponding to the combination of the voltage amplitude command value and the output power factor command value, based on the table.

Preferably, the third harmonic amplitude determining unit determines the amplitude of the third harmonic signal based on a function having the voltage amplitude command value and the output power factor command value as arguments. By using the function, the memory usage amount can be reduced as compared with the case of using the table.

Effects of the invention

According to the power conversion device of the embodiment of the present invention, the conversion efficiency of the three-phase voltage source inverter can be improved.

Drawings

Fig. 1 is a diagram showing a system configuration of a power conversion device according to embodiment 1 of the present invention.

Fig. 2 is a block diagram showing a configuration of a control device according to embodiment 1 of the present invention.

Fig. 3 is a diagram for explaining a method of determining the amplitude of the third harmonic signal Vh in embodiment 1 of the present invention.

Fig. 4 is a diagram for explaining a method of determining the amplitude of the third harmonic signal Vh in embodiment 2 of the present invention.

Fig. 5 is a diagram showing an example in which the third harmonic is superimposed on the voltage command signal.

Fig. 6 is a diagram showing an example in which the amplitude of the third harmonic signal is determined to be 1/6 with respect to the voltage command signal.

Fig. 7 is a diagram for explaining a path of a current flowing through the voltage-type inverter.

Fig. 8 is a diagram for explaining a loss in the switching element (transistor).

Fig. 9 is a conceptual diagram illustrating an example of the hardware configuration of a control device included in the power conversion device.

Detailed Description

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, the same reference numerals are given to the common elements in the drawings, and redundant description is omitted.