阅读说明：本技术 二次励磁发电电动装置 (Secondary excitation power generation electric device ) 是由 阪东明 川添裕成 菊池辉 于 2019-08-08 设计创作，主要内容包括：在为使励磁电流检测值与励磁电流指令值一致而将第一点弧脉冲指令输入到3电平NPC功率变换器的二次励磁发电电动装置中,具备：按照电流绝对值的大小顺序识别第一相、第二相、第三相的功能；以及脉冲指令器,其在对第一和第二直流电容器进行充电的方向上将第一相P组或者N组的点弧脉冲固定在接通侧,将相反侧固定在断开侧,第二相P组的点弧脉冲固定在与第一相N组相同的一侧,N组的点弧脉冲固定在与第一相P组相同的一侧,将第三相第一组的点弧脉冲固定为接通,将第二组的点弧脉冲固定为断开,作为第二点弧脉冲指令输出。将点弧脉冲指令输出到3电平NPC功率变换器的脉冲切换器,在电流绝对值超过过电流设定电平1时切换为第二点弧脉冲指令,当电流绝对值在3相均成为过电流设定电平2以下时切换为第一点弧脉冲指令。(A secondary excitation power generation electric device for inputting a first ignition pulse command to a 3-level NPC power converter in order to match a field current detection value with a field current command value, comprising: identifying the functions of the first phase, the second phase and the third phase according to the magnitude sequence of the absolute value of the current; and a pulse commander that fixes the first phase P group or N group of arc pulses to the on side and the opposite side to the off side in the direction of charging the first and second dc capacitors, fixes the second phase P group of arc pulses to the same side as the first phase N group, fixes the N group of arc pulses to the same side as the first phase P group, fixes the third phase first group of arc pulses to on, fixes the second group of arc pulses to off, and outputs the second group of arc pulses as a second arc pulse command. A pulse switch for outputting a firing pulse command to a 3-level NPC power converter switches to a second firing pulse command when the absolute value of the current exceeds an overcurrent setting level 1 and switches to a first firing pulse command when the absolute value of the current is equal to or less than an overcurrent setting level 2 in all phases of 3.)

1. A secondary excitation power generation electric device is provided with: a winding type induction motor in which a stator side armature winding is connected to an alternating current system; a 3-level NPC power converter connected with a rotor-side excitation winding of the winding type induction motor; the first direct current capacitor is connected between the positive direct current end of the 3-level NPC power converter and a neutral point; a second DC capacitor connected between the neutral point and the negative DC terminal; a dc voltage source for supplying a dc voltage to the first dc capacitor and the second dc capacitor; an exciting current detector for detecting an exciting winding current of the winding type induction motor; and an excitation current command device for calculating an excitation current command value of a slip frequency equal to a difference between a frequency of the ac system and a rotation frequency of the winding type induction motor and outputting a first ignition pulse command so that an excitation current detection value from the excitation current detector coincides with the excitation current command value, wherein the secondary excitation power generation motor device inputs the first ignition pulse command to a self-extinction type semiconductor element of the 3-level NPC power converter,

the secondary excitation power generation electric device includes:

a pulse commander having a function of identifying a first phase, a second phase, and a third phase in order of magnitude of an absolute value of a current from the excitation current detector, wherein 4 series-connected self-extinguishing type semiconductor elements, which are composed of a self-extinguishing type semiconductor element P1C between the first phase and a positive-side clamping diode, a self-extinguishing type semiconductor element P1 between the self-extinguishing type semiconductor element P1C and a positive electrode, a self-extinguishing type semiconductor element N1C between the first phase and a negative-side clamping diode, and a self-extinguishing type semiconductor element N1C and a self-extinguishing type semiconductor element N1 between the negative electrode, are divided into a first phase P group composed of a self-extinguishing type semiconductor element P1 and a self-extinguishing type semiconductor element P1C, and a first phase N group composed of a self-extinguishing type semiconductor element N1 and a self-extinguishing type semiconductor element N1C, and a polarity of a current detected value of the first phase is determined, fixing the ignition pulse of either the first phase P group or the first phase N group to the on side and the opposite side to the off side in the direction of charging the first dc capacitor and the second dc capacitor, and dividing 4 series-connected self-extinguishing type semiconductor elements, which are composed of the self-extinguishing type semiconductor element P2C between the second phase and the positive side clamp diode, the self-extinguishing type semiconductor element P2 between the self-extinguishing type semiconductor element P2C and the positive side clamp diode, the self-extinguishing type semiconductor element N2C between the second phase and the negative side clamp diode, and the self-extinguishing type semiconductor element N2C and the self-extinguishing type semiconductor element N2 between the negative side clamp diode, into a second phase P group composed of the self-extinguishing type semiconductor element P2 and the self-extinguishing type semiconductor element P2C, and a second phase N group composed of the self-extinguishing type semiconductor element N2 and the self-extinguishing type semiconductor element N2C, the second phase P group of arc pulses is fixed to the same side as the first phase N group of arc pulses, the second phase N group of arc pulses is fixed to the same side as the first phase P group of arc pulses, and the third phase second group of arc pulses, which is composed of the self-extinguishing type semiconductor device P3C between the third phase and the positive-side clamping diode, the self-extinguishing type semiconductor device P3 between the P3C and the positive electrode, the self-extinguishing type semiconductor device N3C between the third phase and the negative-side clamping diode, and the self-extinguishing type semiconductor device N3C and the self-extinguishing type semiconductor device N3 between the negative electrode, are fixed so that the third phase first group of arc pulses composed of the self-extinguishing type semiconductor device P3C and the self-extinguishing type semiconductor device N3C is turned on, and the third phase second group of arc pulses composed of the self-extinguishing type semiconductor device P3 and the self-extinguishing type semiconductor device N3 is turned off, the output is a second arc-striking pulse instruction,

the secondary excitation power generation electric device is provided with a pulse switcher that switches the first and second arc pulse commands bidirectionally and outputs the switched commands to the 3-level NPC power converter, wherein the pulse switcher switches from the first arc pulse command to the second arc pulse command on condition that an absolute value of any one of detected current values from the excitation current detector exceeds an overcurrent setting level 1, and switches from the second arc pulse command to the first arc pulse command on condition that the detected current value from the excitation current detector is equal to or less than an overcurrent setting level 2 in phase 3.

2. The secondary excitation power generation electric device according to claim 1,

the dc voltage source includes an excitation transformer that supplies 2 sets of ac voltages insulated from the ac system, a first 2-level power converter that connects one of the 2 sets of ac voltages to an ac terminal and connects a dc terminal to the first dc capacitor for voltage control, and a second 2-level power converter that connects the other of the 2 sets of ac voltages to an ac terminal and connects a dc terminal to the second dc capacitor for dc voltage control.

3. The secondary excitation power generation electric device according to claim 1 or 2,

a current bypass circuit is provided between the rotor-side field winding of the winding-type induction motor and the field current detector, and when an overcurrent setting level 3 is a value greater than the overcurrent setting level 1 and an absolute value of any one of current detection values from the field current detector exceeds the current setting level 3, the current bypass circuit is closed, and all of the arc-striking commands to the self-extinction-type semiconductor elements of the 3-level NPC power converter are turned off.

4. The secondary excitation power generation electric device according to claim 1 or 2,

a current bypass circuit is provided between the rotor-side field winding of the winding-type induction motor and the field current detector, and when an overcurrent setting level 4 is a value smaller than the overcurrent setting level 1 and an absolute value of a current of the third phase exceeds the current setting level 4, the current bypass circuit is closed, and all of the arc-striking commands to the self-extinguishing semiconductor elements of the 3-level NPC power converter are turned off.

5. The secondary excitation power generation electric device according to any one of claims 1 to 4,

the voltage control circuit comprises a first direct-current capacitor, a first direct-current voltage sensor, a first active direct-current voltage suppression circuit, a second direct-current voltage sensor, a second active direct-current voltage suppression circuit and a second direct-current voltage suppression circuit, wherein the first direct-current capacitor is connected with the first direct-current voltage sensor in parallel, the resistor and the first self-extinction semiconductor element are connected in series, the second direct-current capacitor is connected with the second direct-current voltage sensor in parallel, the resistor and the second self-extinction semiconductor element are connected in series, when the detection value of the first direct-current voltage sensor exceeds a set range, the first self-extinction semiconductor element is controlled to be switched on and off to suppress direct-current voltage, and when the detection value of the second direct-current voltage sensor exceeds the set range, the second self-extinction semiconductor element is controlled to be switched on and off to suppress direct-current voltage.

Technical Field

The present invention relates to a secondary excitation power generation electric device using a secondary excitation power converter.

Background

An ac excitation generator motor using a secondary excitation power converter can control reactive power output in the same manner as a conventional fixed speed synchronous machine, and can realize high-speed torque control or high-speed active power control in a rotation speed range around a synchronous speed. Therefore, compared to a conventional fixed-speed generator motor, there is an advantage that the prime mover such as a pump turbine system or a wind power generation system can be optimally operated under a wider operating condition. In addition, there is an advantage that the flywheel energy of the rotating part is temporarily released and absorbed into the power system to contribute to the frequency stabilization of the power system.

On the other hand, although the secondary excitation power converter can be smaller than the armature capacitance of the generator, the capacitance is larger and the circuit becomes complicated than the excitation power converter of the conventional fixed speed synchronous machine. Therefore, even if the overcurrent tolerance equivalent to that of the excitation power converter of the conventional fixed speed synchronous machine is ensured, it is difficult to economically ensure the excitation peak voltage.

Therefore, the following method is generally employed: when an abnormality occurs on the AC system side, a short-circuit for an overcurrent in the field winding is operated to bypass the field power converter, thereby suppressing the overcurrent capacity. In particular, when the field winding is short-circuited, the torque of the generator motor rapidly changes to a winding type induction motor torque in which the secondary resistance is short-circuited, and the torque greatly changes depending on the rotation speed before the short-circuiting. As a result, even if the operation of the generator-motor apparatus can be continued, a large fluctuation is applied to the power system, and the system is unstable. Further, when the secondary resistor is short-circuited, the voltage of the ac system is further reduced to consume the reactive power, and therefore, there is a disadvantage that the supply of the electric power to the demand side is hindered.

Non-patent document 1 discloses the following method: in order to cope with this drawback, when an excitation overvoltage is detected in a separately excited secondary excitation power converter in which a thyristor converter having no self-extinguishing function is connected in reverse parallel, the power converter of the opposite polarity to the excitation current command is ignited to continue the operation. In addition, there are the following examples of 400MW class secondary excitation power generation electric devices: the loss is calculated based on the current value of the power semiconductor, and the element junction temperature is always calculated based on the cooling water temperature, so that the overcurrent protection has a time limit, thereby realizing continuous operation without interrupting the excitation control even in a system ground short circuit accident of 250 times or more in 25 years.

On the other hand, recent self-extinguishing semiconductor power devices have been remarkably developed in technology, and self-excited power converters to which igbts (insulated Gate Bipolar converters), igcts (integrated Gate combined inverters) and the like are applied have been developed to have a large capacity and a high voltage. The self-excited power converter has an advantage that the self-excited power converter does not have a function of adjusting a converter power factor and the like. On the other hand, in the case of a secondary excitation power generation electric device which requires continuous operation and continuous reactive power supply even in the event of an abnormality on the electric power system side, it is difficult to economically secure short-time overcurrent tolerance in an inverter using a self-extinguishing semiconductor element. This is because the conventional element such as a thyristor can have an overcurrent tolerance of the order of seconds from 100 milliseconds to the upper junction temperature limit by the heat capacity of the element itself, whereas the current element rated value is determined by the instantaneous current interruption tolerance in the case of the self-extinguishing element.

To cope with this drawback, there is a method of focusing on that a diode connected in anti-parallel with a self-extinguishing element has an overcurrent tolerance in the same bipolar element as the thyristor.

As the simplest method, there is a method of performing a diode bridge operation by turning off the gate for all the self-extinguishing elements. According to this method, the degree of freedom of the current of the exciting circuit is reduced from 2 in the normal state to 1, and therefore, it is difficult to stably return to the degree of freedom of the current 2 at a high speed and return to the normal control.

Patent document 1 discloses a secondary excitation power generation electric device having operation continuation performance and stability not inferior to those of a separate excitation type secondary excitation power converter by adopting a control mode in which a short-circuit is not operated and a gate is not turned off even when an overcurrent occurs at the time of a system accident, that is, a control mode capable of switching between a normal PWM control and a normal PWM control while maintaining a current freedom 2 of an excitation circuit.

Documents of the prior art

Patent document

Patent document 1: japanese patent No. 5401213

Patent document 2: japanese patent No. 3222028

Non-patent document

Non-patent document 1: hitachi review (HITACHI REVIEW)1995Vol.44

Disclosure of Invention

Problems to be solved by the invention

Patent document 1 discloses a method for realizing a self-excited secondary excitation power converter using a self-extinguishing arc element.

When the secondary excitation power converter is increased in capacity in proportion to the increase in capacity of the generator motor, the ac output voltage is required to be increased. However, in the case of a 2-level converter, the ac-side output phase voltage is limited to 2 levels (+ Vc/2) and (-Vc/2) with respect to the dc capacitor voltage Vc. Therefore, it is not necessary to increase the dc capacitor voltage Vc in order to increase the voltage of the secondary excitation power converter.

However, when the dc capacitor voltage Vc is increased, the ac side output phase voltage also increases, and as a result, the time rate of change dV/dt of the voltage applied to the rotor side field winding coil also increases. The insulation specification of the coil is generally defined by a rated ac voltage or a peak voltage value, but it is known that if the time rate of change of the voltage exceeds a predetermined value, the deterioration of the dielectric loss with time rapidly progresses. Even if the predetermined values are the same, if the polarity changes without the voltage zero-crossing period as in the case of the 2-level converter output, "deterioration with time tends to progress more easily than the case where the voltage changes via the voltage zero-crossing period". Further, it is pointed out that the voltage time change rate allowable value restricted by the deterioration with time is greatly reduced in the case of the coil assembled on site, as compared with the coil in which varnish is vacuum-injected in a state of being integrally assembled in a factory.

From the above, there is a problem that it is difficult to continuously apply a 2-level converter as a secondary excitation power converter of an offshore wind turbine having a large capacity originally for a variable-speed secondary excitation power converter of a wind power plant.

As a means for solving the above problem, a method of applying a 3-level NPC power converter is conceivable. In the case of a 3-level converter, voltages of 2 dc capacitors connected in series are set to 3 levels of ac output phase voltages (+ Vc), (0) and (-Vc) with respect to Vc. Even if the dc voltage Vc of the capacitor is the same, the ac output voltage has the effect of ensuring 2 times that of the 2-level converter, and therefore, as a result, the time rate dV/dt of change in the voltage applied to the coil is reduced. Further, since the voltage zero crossing period is provided, even if the time rate dV/dt of the voltage applied to the coil is the same as that of the 2-level converter, the deterioration with time due to the dielectric loss can be alleviated.

However, the method of patent document 1 can be applied only to a 2-level system power converter.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a secondary excitation power generation electric device that uses a 3-level NPC power converter to ensure the operation continuity during a system accident and contribute to system stabilization.

Means for solving the problems

The 3-level NPC power converter connected to the rotor-side field winding is a 3-phase 3-wire circuit having a current degree of freedom of 2, as in the 2-level converter of patent document 1. Therefore, as long as the bypass circuit is not operated and the gates of all the elements are not turned off, the magnitude relation and sign of the absolute values of the 3-phase currents IU, IV, and IW can be defined as the 12 mode shown in fig. 9 at the time of overcurrent occurrence in both the normal operation and the system accident.

In fig. 10, the solution in mode 1 of fig. 9 is shown by the operation of the 3-level NPC power converter described above.

When the absolute value of the V-phase current IV is first large and the polarity is negative, the gates of the element VPC and the element VP are fixed to the on side, and the element VN and the element VNC are fixed to the off side. Thus, the positive side dc capacitor CP is charged by the current IV flowing from the V phase of the power converter.

When the absolute value of the U-phase current IU is the second bit and the polarity is positive, the gates of the element UNC and the element UN are fixed to the on side, and the element UP and the element UPC are fixed to the off side. Thus, the negative-side dc capacitor CN is charged with the current IU flowing from the phase U of the power converter.

Since the absolute value of the remaining W-phase current IW is the third bit (minimum), the gates of the element WPC and the element WNC are fixed to the on side and the gates of the element WP and the element WN are fixed to the off side regardless of the current polarity. Thus, a current IW flowing out of the phase W of the power converter is supplied from the positive-side dc capacitor via the neutral point and the positive-side clamp diode.

As a result, in mode 1, since the absolute value of IV for charging the positive-side dc capacitor is larger than the absolute value of IU for charging the negative-side dc capacitor, the positive-side dc capacitor voltage becomes higher than the negative-side dc capacitor, which causes the voltage balance to be broken.

In fig. 11, the solution in mode 2 of fig. 9 is shown by the operation of the 3-level NPC power converter described above.

When the absolute value of the U-phase current IU is the first largest and the polarity is positive, the gates of the element UNC and the element UN are fixed to the on side, and the element UP and the element UPC are fixed to the off side. Thus, the negative-side dc capacitor CN is charged with the current IU flowing from the phase U of the power converter.

When the absolute value of the V-phase current IV is the second bit and the polarity is negative, the gates of the element VPC and the element VP are fixed to the on side, and the element VN and the element VNC are fixed to the off side. Thus, the positive side dc capacitor CP is charged by the current IV flowing from the V phase of the power converter.

Since the absolute value of the remaining W-phase current IW is the third bit (minimum), the gates of the element WPC and the element WNC are fixed to the on side and the gates of the element WP and the element WN are fixed to the off side regardless of the current polarity. Thus, current IW flowing from phase W of power converter charges the negative side dc capacitor via the neutral point and the negative side clamp diode.

As a result, in mode 2, since the absolute value of IU for charging the negative-side dc capacitor is larger than the absolute value of IV for charging the positive-side dc capacitor, the negative-side dc capacitor voltage becomes higher than the positive-side dc capacitor, which causes the voltage balance to be broken.

Assuming that 3-phase balance of the currents IU, IV, and IW is a precondition, it is considered that the positive and negative dc capacitors alternately repeat overcharge/undercharge every time the polarity of the third current changes, and thus there is a low risk of the voltage balance being largely broken. However, in the case of a system fault in which an overcurrent is generated and operation is required to be continued, since the above-mentioned preconditions are significantly apart, a means for maintaining voltage balance is required.

As a means for this purpose, a circuit configuration disclosed in patent document 2 is used. That is, the positive-side dc capacitor and the negative-side dc capacitor are connected to the dc sides of the 2-stage 2-level converters, respectively, and the ac sides are connected to the 2 sets of ac terminals insulated by the field transformer. In this way, the 2-stage 2-level converters are configured to be able to control the respective dc voltages independently of each other, and are controlled so that the dc capacitor values on the positive side and the negative side are balanced.

The desired object can be achieved by the above apparatus configuration and control method.

Effects of the invention

According to the secondary excitation power generation electric device of the present invention, particularly when a voltage drop such as a ground short fault caused by a lightning strike to the power system occurs, the torque variation of the generator motor is suppressed to the minimum, the operation continuation capability is improved, and the reactive power supply capability is quickly restored, thereby making it possible to contribute to the stable operation of the power system.

Drawings

Fig. 1 is a circuit diagram showing an embodiment of the present invention.

Fig. 2 is a circuit diagram showing another embodiment of the present invention.

Fig. 3 is a diagram showing the operation of the PWM modulation circuit 37 of the 3-level NPC power converter.

Fig. 4 is a diagram showing the operation of the pulse generating circuit 45 of the 3-level NPC power converter.

Fig. 5 is a block diagram of a second PWM modulation circuit 40 of the 3-level NPC power converter.

Fig. 6 is a block diagram of the operation mode switching circuit 41 of the 3-level NPC power converter.

Fig. 7 is a diagram illustrating an operation of the present invention.

Fig. 8 is a diagram illustrating an operation of the present invention.

Fig. 9 is a diagram showing current mode differentiation of a 3-level NPC power converter.

Fig. 10 is a diagram showing a state in which a W-phase positive clamp circuit of a 3-level NPC power converter is flowing.

Fig. 11 shows a state where the W-phase negative clamp circuit of the 3-level NPC power converter is flowing.

Detailed Description

Hereinafter, an embodiment of the secondary excitation power generation electric device according to the present invention will be described in detail with reference to the drawings. The present invention is not limited to the embodiment.

Example 1

The device structure of embodiment 1 of the present invention will be described with reference to fig. 1.

The 3-phase ac system 1 and the stator-side armature winding 5 of the winding type induction motor are connected via a main transformer 2, a phase reversal breaker (89GM)3, and a synchronous breaker (52G) 4. The rotor-side field winding 6 is connected to the ac side of a 3-level NPC power converter 7. A positive-side dc Capacitor (CP)8 and a first dc output terminal (VDC1) of the dc voltage source 71 are connected in parallel between the dc-side positive terminal and the neutral point terminal of the 3-level NPC power converter 7.

On the other hand, a negative-side dc Capacitor (CN)12 and a second dc output terminal (VDC2) of the dc voltage source 71 are connected in parallel between the neutral point terminal and the dc-side negative terminal of the 3-level NPC power converter 7.

An ac terminal of the dc voltage source 71 is connected in parallel to a first terminal of the field breaker (52E)16, and a second terminal is connected in parallel to a winding-type generator-motor side end of the main transformer 2.

The dc voltage source 71 is constituted by an ac/dc power converter. For example, the configuration can be realized by connecting the dc-side positive terminal, the negative terminal, and the neutral point terminal of the 3-level NPC power converter 7 to the back side.

Next, the configuration of the control system of the 3-level NPC power converter 7 will be described.

An Automatic Voltage Regulator (AVR)29 for outputting a d-axis current command (I _ Dref) is provided so that a generator voltage VG calculated by a meter transformer 28 at a stator-side armature end of a winding type induction motor becomes a set value, and an automatic voltage regulator (APR)31 for outputting a q-axis current command (I _ Qref) is provided so that an active power calculated by a meter transformer 3 and a main transformer-side meter converter 30 becomes a set value.

A phase detector (32) for detecting a phase (theta s) of a slip frequency equal to the difference between the AC system frequency and the rotational frequency of a winding type induction motor on the basis of a rotational phase detector (PLG)55 and a main transformer side instrument transformer (17) is provided, 2-phase current commands (I _ Dref, I _ Qref) are input to a 2-phase/3-phase coordinate converter (33), and 3-phase current commands (IU _ ref, IV _ ref, IW _ ref) of the slip frequency are output.

An exciting current meter inverter 34 is provided between a terminal of a rotor-side exciting winding 6 of a winding-type induction motor and a 3-level NPC power converter 7, exciting current values (IU, IV, IW) are detected, and 2-phase current values (I _ DfB, I _ QfB) which become direct current values at the time of stabilization are calculated in a 3-phase 2-phase converter 35.

The field current adjuster 36 outputs modulation rate commands (α U, α V, α W) such that the 2-phase current commands (I _ Dref, I _ Qref) coincide with the 2-phase current values (I _ DfB, I _ QfB), and the 3-phase current commands (IU _ ref, IV _ ref, IW _ ref) coincide with the field current values (IU, IV, IW). The modulation rate commands (α U, α V, α W) are input to 3 PWM modulation circuits 37, 38, 39 provided for each phase, and first modulation commands (MU1, MV1, MW1) are output for each phase.

On the other hand, the excitation current values (IU, IV, IW) from the excitation current meter converter 34 are input, and the second PWM modulation circuit 40 outputs the second modulation command (MU2, MV2, MW 2).

Further, the field current values (IU, IV, IW) from the field current instrument converter 34 are input, and the operation mode switching circuit 41 outputs the command value SW for switching the first modulation command (MU1, MV1, MW1) and the second modulation command (MU2, MV2, MW2) together. Further, a GB command is output, which fixes the arcing commands to all the self-extinguishing type elements to the off side.

The output modulation commands (MU, MV, MW) are selected by the 3 switches 42, 43, 44 of each phase such that the first modulation command (MU1, MV1, MW1) is selected when the command value SW is 0 and the second modulation command (MU2, MV2, MW2) is selected when the command value SW is 1.

Modulation commands (MU, MV, MW) are input to the 3 pulse generation circuits 45, 46, 47 of the respective phases, and gate commands to the self-extinguishing elements of the 3-level NPC power converter 7 are controlled to be turned on and off.

The operation of the U-phase PWM modulation circuit 37 will be described with reference to fig. 3.

The PWM adjustment circuit 37 includes a positive carrier wave between the neutral point (0) and the positive pole (+1) and a negative carrier wave between the negative pole (-1) and the neutral point (0), and outputs a modulation command MU1 selected by 3 values (+1, 0, -1) based on the magnitude relationship between these carrier waves and the modulation wave calculated from the modulation rate command α U on the input side.

The V-phase PWM modulation circuit 38 and the W-phase PWM modulation circuit 39 operate in the same manner as the U-phase PWM modulation circuit 37, and description thereof is omitted to avoid redundancy.

Fig. 4 shows the operation of the pulse generating circuit 45 in a table format.

First, an operation when the GB command from the operation mode switching circuit 41 is at level 0 will be described.

When the modulation command MU is (+1), the gate commands G _ UP and G _ UPC for the self-arc-extinguishing elements UP and UPC are turned on, and the others are turned off. When the modulation command MU is (0), the gate commands G _ UPC and G _ UNC for the self-arc-extinguishing elements UPC and UNC are turned on, and the others are turned off. When the modulation command MU is (-1), the gate commands G _ UN and G _ UNC to the self-arc-extinguishing elements UN and UNC are turned on, and the other is turned off. On the other hand, when the GB command is level 1, gate commands G _ UP, G _ UPC, G _ UNC, and G _ UN to self-arc-extinguishing elements UP, UPC, UNC, and UN are turned off regardless of the value of modulation command MU.

Fig. 5 shows the structure of the second PWM modulation circuit 40.

Absolute values | IU |, | IV |, and | IW |, of the excitation current values (IU, IV, IW) from the instrument converter 34 are obtained by absolute value calculators 101, 102, 103, differences in absolute values are output by subtractors 104, 105, 106, and 2 values (0, 1) are selectively output for the sign determination result by comparators 107, 108, 109. The outputs of the comparators 107, 108, and 109 are input to the logic circuit 110, and the logic circuit 110 outputs a signal 111 which is at a level 1 when | IU | is minimum and at a level 0 when | IU | is otherwise. The logic circuit 110 outputs signals 112, 113 similarly for | IV |, | IW |.

On the other hand, the comparators 114, 115, and 116 output 2 values (0, 1) by selecting the polarity of the excitation current values (IU, IV, and IW). The comparator 114 outputs a signal 117 which becomes level 1 when IU is positive and becomes level 0 when IU is other. Similarly for IV, IW, comparators 115, 116 output signals 118, 119 respectively.

The signals 111, 112, 113, 117, 118, 119 are input to the logic circuit 120, and the logic circuit 120 outputs the 3 values (+1, 0, -1) of the respective phases to the 3-value selection output circuits 121, 122, 123.

The 3-value selection output circuit 121 of the U phase outputs '0' as the second modulation output MU2 when the absolute value of IU is the smallest in 3 phases, outputs '+ 1' as the second modulation output MU2 when IU is positive, and outputs '-1' as the second modulation output MU2 when IU is negative. The V-phase 3-value selection output circuit 122 and the W-phase 3-value selection output circuit 123 operate in the same manner as the U-phase 3-value selection output circuit 121, and a description thereof is omitted to avoid redundancy.

Fig. 6 shows a configuration of the operation mode switching circuit 41. Since the same reference numerals as those in fig. 5 denote the same elements, the description thereof will be omitted to avoid redundancy.

The maximum value selection outputter 202 selects and outputs the maximum values of the absolute values | IU |, | IV |, and | IW |, of the excitation current values (IU, IV, IW) from the converter 34 for meters, and the minimum value selection outputter 201 selects and outputs the minimum values of the absolute values | IU |, | IV |, and | IW |. The comparator 203 outputs a level 1 when the maximum value exceeds the set value I1, and outputs a level 0 in other cases. The comparator 204 outputs a level 1 when the minimum value becomes equal to or less than the set value I2, and outputs a level 0 in other cases. The flip-flop 205, which has the output of the comparator 203 as a set signal and the output of the comparator 204 as a reset signal, outputs the instruction value SW.

When the command value SW is at level 0, the first modulation command (MU1, MV1, MW1) is selected in the switches 42, 43, 44, and when the command value SW is at level 1, the second modulation command (MU2, MV2, MW2) is selected.

Here, the set values I1 and I2 are set to (I1 > I2), and I1 is set to a value not exceeding the maximum breaking current with reference to the maximum breaking current of the self-extinguishing type element of the 3-level NPC power converter 7.

Fig. 7 and 8 show the operation of the secondary-excitation power generation electric device of fig. 1 to 6 when a short-circuit fault occurs at time t0 in the 3-phase ac system 1, and the fault phase is removed at time tCB and the normal operation is resumed.

In the periods (t1, t2) and (t3, t4) in fig. 7, the command value SW becomes level 1 in the periods (t5, t6) and (t7, t8) in fig. 8, and the second modulation command (MU2, MV2, MW2) is selected.

According to the configuration of the invention described in this embodiment, since the 3-level NPC power converter 7 is not bypassed for overcurrent protection and gate block (gate block) is not performed, 2 modulation commands can be switched to each other in a very fine manner, and overcurrent protection and stable continuous operation can be performed.

Example 2

The device structure of embodiment 2 of the present invention will be described with reference to fig. 2.

A positive-side dc Capacitor (CP)8 and a dc terminal of the first 2-level power converter 9 are connected in parallel between the dc-side positive terminal and the neutral point terminal of the 3-level NPC power converter 7, and an ac terminal of the first 2-level power converter 9 is connected to the first excitation transformer 11 via the first harmonic suppression filter 10.

On the other hand, a negative dc Capacitor (CN)12 and a dc terminal of the second 2-level power converter 13 are connected in parallel between the neutral point terminal and the dc-side negative terminal of the 3-level NPC power converter 7, and an ac terminal of the second 2-level power converter 13 is connected to the second excitation transformer 15 via the second harmonic suppression filter 14.

The ac system side ends of the first and second excitation transformers 11 and 15 are connected in parallel to a first terminal of an excitation circuit breaker (52E)16, and a second terminal is connected in parallel to the winding type generator motor side end of the main transformer 2.

Next, the configuration and operation of the control system of the first 2-level power converter 9 will be described.

A first power factor adjuster (APFR1)19 for outputting a d-axis dc command (IC1_ Dref) is provided so that the power factor becomes 1 from the reactive power calculated by a main transformer-side instrument transformer 17 provided on the winding generator motor side of the main transformer 2 and a first instrument-side converter 18 provided between the first harmonic filter 10 and the ac terminal, a voltage VDCP of the positive-side dc capacitor 8 is detected in the first instrument-side dc transformer 20, a first dc voltage adjuster (ADCVR1)21 for outputting a q-axis dc command (IC1_ Qref) is provided so that the voltage VDCP is adjusted to a set value, and the gate of a self-extinction type element (RP1, SP1, 1, RN1, SN1, TN1) constituting the first 2-level converter 9 is controlled to be turned on and off by the first 2-level converter current adjuster 22.

Similarly, the configuration of the control system of the second 2-level power converter 13 will be described.

A second power factor adjuster (APFR2)24 that outputs a d-axis dc command (IC2_ Dref) is provided so that the power factor becomes 1 by the reactive power calculated by the main transformer-side instrument transformer 17 and the second instrument-side converter 23 provided between the second harmonic suppression filter 14 and the ac terminal, a second dc voltage adjuster (ADCVR2)26 that outputs a q-axis dc command (IC2_ Qref) is provided so that the voltage VDCN of the negative-side dc capacitor 12 is detected by the second instrument-side dc transformer 25 and adjusted to a set value, and the gates of self-extinction type elements (RP2, SP2, TP2, RN2, SN2, TN2) constituting the second 2-level converter 13 are on/off controlled by the second 2-level converter current adjuster 27.

According to the above configuration of the first and second 2-level power converters, since the 2-level converters (the first 2-level converter 9 and the second 2-level converter 13) connected to the ac power supply, which are insulated from each other by the 2 exciting transformers (the first exciting transformer 11 and the second exciting transformer 15), independently control the positive and negative dc capacitor voltages VDCP and VDCN, the voltages of the 2 dc capacitors can be stably maintained in balance even at the time of transition such as a system accident.

According to the configuration of the invention described in the present embodiment, since the 2-stage 2-level converters can control the respective dc voltages independently of each other, the control can be performed so that the dc capacitor values on the positive side and the negative side are balanced.

Example 3

The device structure of embodiment 3 of the present invention will be described with reference to fig. 2.

The bypass circuit 48 is provided between the field current instrument converter 34 and the rotor-side field winding 6 terminal of the winding type induction motor. The bypass circuit 48 may be formed of a power semiconductor element, but a vacuum circuit breaker having a significant technical progress such as ensuring the number of operations 150k times may be used as in the present embodiment. The bypass circuit is closed in accordance with the 86E command from the operation mode switching circuit 41. In addition, according to the GB command, the pulse generation circuits 45, 46, and 47 block the gates of the self-extinguishing elements of the 3-level NPC power converter 7, and stop the operation.

Fig. 6 shows a circuit for outputting an operation command (86E command) to the bypass circuit 48.

The maximum value selection circuit 206 selects the maximum value of the absolute values | IU |, | IV |, and | IW | of the output excitation current values (IU, IV, IW), and the comparator 207 outputs a level 1 when the maximum value exceeds the set value I3 and outputs a level 0 otherwise. The output of comparator 207 is output as the GB instruction and the 86E instruction via the and logic circuit 208.

Here, the set value I3 is set to a value greater than the set value I1 (I3 > I1). This is because the overcurrent value generated in the ground fault or the like on the 3-phase ac system 1 side is suppressed by the impedance of the main transformer 2, whereas the overcurrent value at the time of the fault on the winding type induction motor side of the main transformer 2 is not suppressed, and therefore the set value I3 is set with reference to the maximum current caused by the ground fault on the 3-phase ac system 1 side. This makes it possible to distinguish between a failure on the equipment side and a failure on the 3-phase ac system side, and in the former case, the operation can be stopped quickly to protect the equipment.

Example 4

The device configuration and circuit of embodiment 4 of the present invention will be described with reference to fig. 6.

The operation of the output switches 209, 210, 211 will be described. Here, the operation of the output switch 209 for the U phase will be described. The V-phase output switch 210 and the W-phase output switch 211 operate in the same manner as the output switch 209, and therefore, the description thereof is omitted to avoid redundancy.

The signal 111 is at level 1 when | IU | is minimum and at level 0 otherwise, but the output switch 209 outputs | IU | which is the absolute value of the current of the third phase when the signal 111 is at level 1, and outputs "0" when the signal 111 is at level 0.

The maximum value selection circuit 212 selects and outputs the maximum value of the current absolute values | IU |, | IV |, and | IW | of the respective phases, and the comparator 213 outputs a level 1 when the selected and output maximum value exceeds the set value I4, and outputs a level 0 when the selected and output maximum value exceeds the set value I4. Reference numeral 214 denotes an on delay (on delay) circuit, which outputs a level 1 when the absolute value of the current of the third phase continues for a set time or longer, and outputs the level 1 as a GB command and a 86E command via the logical sum circuit 208.

Here, the set value I4 is set to a value smaller than the set value I1 (I4 < I1). This is because the current of the third phase passes through any one of the self-arc-extinguishing elements (UPC, UNC, VPC, VNC, WPC, WNC). Normally, the self-extinction element has a larger current loss than the antiparallel diode, and therefore has a small overcurrent tolerance. Therefore, the equipment can be safely protected by the time-limited overcurrent protection of the third phase.

Example 5

The device structure of example 5 of the present invention will be described with reference to fig. 2.

When the positive side dc capacitor voltage VDCP from the first instrument dc transformer 20 exceeds a set value, the first overvoltage suppressor (OVP1)49 controls the on/off of the switching circuit (CHV1)51 based on the self-extinguishing type element connected in series with the limiting resistor 50, and suppresses the increase in the positive side dc capacitor voltage VDCP by consuming power through the limiting resistor 50.

Similarly, when the negative-side dc capacitor voltage VDCN from the second instrument dc transformer 25 exceeds the set value, the second overvoltage suppressor (OPVP2)52 controls the switching circuit (CHV2)54, which is a self-extinguishing element connected in series with the limiting resistor 53, to be turned on and off, and consumes power by the limiting resistor 53, thereby suppressing the increase in the negative-side dc capacitor voltage VDCN.

According to the configuration of the present invention, when the second modulation command (MU2, MV2, MW2) is selected, the positive-side dc Capacitor (CP)8 and the negative-side dc Capacitor (CN)12 both ensure the charging operation, and therefore, measures for reducing the dc voltage are not required, and only the increase suppression means may be provided. Thus, it is possible to continue stable operation even in the event of a system accident by simply adding a simple voltage suppression circuit.

However, in the case of a 3-level NPC power converter, while the second modulation command (MU2, MV2, MW2) is selected, the charging and discharging by the current of the third phase becomes a factor of the imbalance between the positive-side dc Capacitor (CP)8 and the negative-side dc Capacitor (CN) 12. However, since the positive-side and negative-side dc voltages can be independently suppressed by the configuration of the present invention, stable operation can be continued even in the event of a system failure.

Description of the reference numerals

1: a 3-phase AC system;

2: a main transformer;

3: a phase reversal circuit breaker (89 GM);

4: a synchronous breaker (52G);

5: a stator-side armature winding;

6: a rotor-side excitation winding;

7: a 3-level NPC power converter;

8: a positive-side direct-current Capacitor (CP);

9: a first 2-level power converter;

10: a first higher harmonic rejection filter;

11: a first excitation transformer;

12: a negative side DC Capacitor (CN);

13: a second 2-level power converter;

14: a second higher harmonic rejection filter;

15: a second excitation transformer;

16: an AC system side excitation circuit breaker (52E);

17: a transformer for a main transformer end instrument;

18: a first instrument converter;

19: a first power factor adjuster (APFR 1);

20: a DC transformer for the first instrument;

21: a first direct current voltage regulator (ADCVR 1);

22: a first 2-level converter current regulator;

23: a current transformer for the second instrument;

24: a second power factor adjuster (APFR 2);

25: a DC transformer for the second instrument;

26: a second dc voltage regulator (ADCVR 2);

27: a second 2-level converter current regulator;

28: a transformer for an instrument;

29: an Automatic Voltage Regulator (AVR);

30: a current transformer for a main transformer end instrument;

31: an automatic voltage regulator (APR);

32: a phase detector;

33: a 2-phase/3-phase coordinate transformer;

34: a current transformer for an instrument for exciting current;

35: a 3-phase to 2-phase converter;

36: an excitation current regulator;

37. 38, 39: a PWM modulation circuit;

40: a second PWM modulation circuit;

41: an operation mode switching circuit;

42. 43, 44: a switch;

45. 46, 47: a pulse generating circuit;

48: a bypass circuit;

49: a first overvoltage suppressor;

50. 53: a limiting resistor;

51: a switching circuit (CHV 1);

52: a second overvoltage suppressor;

54: a switching circuit (CHV 2);

55: a rotating phase detector (PLG);

71: a DC voltage source;

101. 102, 103: an absolute value calculator;

104. 105, 106: a subtractor;

107. 108, 109, 114, 115, 116: a comparator;

110. 120: a logic circuit;

111. 112, 113, 117, 118, 119: a signal;

121. 122, 123: a 3-value selection output circuit;

201. 206, 212: a maximum value selection output device;

202: a minimum value selection output device;

203. 204: a comparator;

205: a trigger;

208: a logic and circuit;

209. 210, 211: an output switch;

214: the delay circuit is turned on.