Power converter

Abstract

To provide a power conversion device capable of suppressing short circuit current even if any of a plurality of switching elements fails.SOLUTION: A power conversion device according to the embodiment configures first through fourth arms respectively with a series circuit of a plurality of switching elements. Each of the plurality of switching element includes a gate circuit and a short circuit detection circuit. The gate circuit supplies a gate signal which controls the switching element in conduction state or non-conduction state to the gate of the switching element. The short circuit detection circuit outputs a detection signal if it detects a state that short circuit current is flowing through the switching element. If the short circuit detection circuit outputs the detection signal corresponding switching element, the gate circuit generates a gate signal for turning off the corresponding switching element.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] Embodiments of the present invention relate to a power conversion device, a control device, and a control method.

Background Art

[0002] In high-voltage motor drives and grid-connected inverters, power conversion devices having multilevel converters have been put into practical use for higher voltage. An example of such a power conversion device is an NPC inverter (Neutral-Point Clamp), which is used in converters for railways and power grids. Such a power conversion device converts DC power into AC power or AC power into DC power by operating a plurality of serially-connected switching elements.

[0003] On the other hand, further increases in the voltage and capacity of the converter are required. In the case of an NPC inverter, increasing the number of levels complicates the circuit and has the drawback that a balance circuit for DC capacitors is required. Therefore, a plurality of switching elements are connected in series to achieve a higher voltage.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in a power conversion device composed of these plurality of switching elements, when one of the switching elements is damaged, a DC short circuit may be induced and the main circuit may be damaged. <00​Therefore, the objective of this embodiment is to provide a power conversion device that can suppress short-circuit current even if any of the multiple switching elements fail. [Means for solving the problem]

[0007] The power converter according to this embodiment forms first to fourth arms, each consisting of a series circuit of multiple switching elements. Each of the multiple switching elements has a gate drive circuit and a short-circuit detection circuit. The gate drive circuit supplies a gate signal to the gate of the switching element to control it to a conduction state or a non-conduction state. The short-circuit detection circuit outputs a detection signal when it detects that a short-circuit current is flowing through the switching element. When the short-circuit detection circuit outputs a detection signal for the corresponding switching element, the gate drive circuit generates a gate signal to turn off the corresponding switching element. [Effects of the Invention]

[0008] Even if one of the multiple switching elements fails, the short-circuit current can be suppressed. [Brief explanation of the drawing]

[0009] [Figure 1] A block showing the schematic overall configuration of a power conversion device according to the first embodiment. [Figure 2] A block diagram showing an example configuration of a control device and gate drive circuit. [Figure 3] A diagram showing an example of the operating characteristics of a clamp circuit. [Figure 4] This diagram shows an example circuit for the switch section of a short-circuit interruption signal generation circuit. [Figure 5] This diagram shows an example where the positive arm is in the ON state and the negative arm is in the OFF state. [Figure 6] This diagram shows a fault example where the positive arm is in the ON position and the negative arm is in the OFF position. [Figure 7] This diagram shows the control operation when the switch is in the OFF state and when the switch is in the ON state. [Figure 8]A diagram showing a state where a short-circuit interruption signal generation circuit outputs a short-circuit interruption signal to the gate circuit of the switch section. [Figure 9] A diagram showing an example where a voltage twice the normal value is applied to the switch section when no short-circuit interruption occurs. [Figure 10] A flowchart showing an example of the processing of the control device. [Figure 11] A diagram showing a configuration example of the power conversion device 1a according to the second embodiment. [Figure 12] A diagram showing an example when the switch section has a short-circuit fault.

Mode for Carrying Out the Invention

[0010] Hereinafter, a power conversion device, a control device, and a control method according to an embodiment of the present invention will be described in detail with reference to the drawings. Note that the embodiments shown below are examples of embodiments of the present invention, and the present invention is not construed as being limited to these embodiments. In the drawings referred to in the present embodiment, the same parts or parts having the same or similar functions are denoted by the same reference numerals or similar reference numerals, and the repeated description thereof may be omitted. Also, the dimensional ratios in the drawings may be different from the actual ratios for the convenience of explanation, or a part of the configuration may be omitted from the drawings.

[0011] (First Embodiment) FIG. 1 is a block diagram showing a schematic overall configuration of a power conversion device 1 according to the first embodiment. As shown in FIG. 1, the power conversion device 1 is a system that converts DC power into AC power by a converter 10 and can supply it to a three-phase power system Pg. More specifically, this power conversion device 1 includes a converter 10, a transformer 20, a circuit breaker 30, and a control device 40, and is a device capable of interrupting the short-circuit current of the converter 10. <00​​​It is taken in and converted into a three-phase (U-phase, V-phase, W-phase) AC voltage. The converter 10 is, for example, an NPC inverter (Neutral-Point Clamp). Note that the converter 10 according to this embodiment is described by taking the NPC inverter as an example, but is not limited thereto. For example, when an NPC converter is used as the converter 10 in the power conversion device 1, the short-circuit current of the converter 10 can also be interrupted. Further details of the NPC inverter converter 10 will be described later.

[0013] The transformer 20 converts the three-phase AC voltage of the converter 10 into the grid voltage of the three-phase power grid Pg. Also, the transformer 20 can limit the short-circuit current from the grid due to an accident or the like.

[0014] The circuit breaker 30 can electrically connect or disconnect the three-phase power grid Pg and the transformer 20. This circuit breaker 30 can disconnect the converter 10 from the three-phase power grid Pg when an accident or a failure occurs.

[0015] The control device 40 is a device that controls the gate drive circuits 400 of the switching elements S11, S12, S21, S22, S31, S32, S41, S42 in the converter 10 to convert the DC voltage into an AC voltage. In FIG. 1, for the sake of simplicity of explanation, only one gate drive circuit 400 is shown, but gate drive circuits 400 capable of outputting gate signals are configured for the gates of the switching elements S11, S12, S21, S22, S31, S32, S41, S42. Also, when operating as a converter, the control device 40 can also control the gate drive circuits 400 of the switching elements S11, S12, S, 21, S22, S31, S32, S41, S42 in the converter 10 to convert the AC voltage into a DC voltage. Furthermore, details of the control device 40 will also be described later. Since the switching elements S11, S12, S21, S22, S31, S32, S41, S42 connected in series have the same configuration for the U-phase, V-phase, and W-phase, hereinafter, for example, the U-phase will be described.

[0016] Here, we will describe the details of the converter 10. As shown in Figure 1, the converter 10 consists of a plurality of switching elements S11, S12, S21, S22, S31, S32, S41, and S42 connected in series. The switching elements S11, S12, S21, S22, S31, S32, S41, and S42 consist of, for example, insulated gate bipolar transistors (IGBTs) and diodes. The diodes are connected in antiparallel to the IGBTs.

[0017] Thus, the switching elements S11, S12, S21, S22, S31, S32, S41, and S42 are composed of semiconductor switching elements (IGBTs) and diodes connected in antiparallel. An insulated-gate bipolar transistor is a type of power transistor that operates in bipolar mode, with, for example, a MOS (Metal-Oxide-Semiconductor) input and a bipolar output. In this invention, IGBTs are used as an example, but the invention is not limited to them. For example, the switching elements may consist of a field-effect transistor (FET) switching element and a clamp element that allows current to flow when a voltage above a certain threshold is applied. Insulated-gate field-effect transistors (MOSFETs) and other types can be used as field-effect transistors (FETs).

[0018] Switching elements S11, S12, S21, S22, S31, S32, S41, and S42 are driven and controlled by a gate drive circuit 400. These multiple switching elements S11 to S42 form a series circuit. Switching elements S11 and S12 constitute the first arm, which is the first switching section S1; switching elements S21 and S22 constitute the second arm, which is the second switching section S2; switching elements S31 and S32 constitute the third arm, which is the third switching section S3; and switching elements S41 and S42 constitute the fourth arm, which is the fourth switching section S4. More specifically, one end of the first arm is connected to the positive terminal of the first DC power supply (C10), and the other end is in contact with one end of the second arm, and the other end of the second arm is connected to the AC output terminal U of the AC system Pg. Similarly, one end of the fourth arm is connected to the negative terminal of the second DC power supply (C20), and the other end is in contact with one end of the third arm, and the other end of the third arm is connected to the AC output terminal U of the AC system Pg. Furthermore, the other ends of the second and third arms of the V phase are connected to the AC output terminal V of the AC system Pg, and the other ends of the second and third arms of the W phase are connected to the AC output terminal W of the AC system Pg, except that the multiple switching elements S11 to S42 of the V phase and W phase have the same structure as the multiple switching elements S11 to S42 of the U phase, as described above.

[0019] Switching elements S11 and S12 are controlled by the same gate signal. Therefore, switching elements S11 and S12 are turned on and off simultaneously. Similarly, switching elements S21 and S22 are turned on and off simultaneously, as are switching elements S31 and S32, and switching elements S41 and S42. In this way, the upper four elements S11, S12, S21, and S22 form the positive arm, and the lower four elements S31, S32, S41, and S42 form the negative arm. In this embodiment, the conductive state of a semiconductor switching element (IGBT) may be referred to as the "on" state of the switching element, and the non-conductive state of a semiconductor switching element (IGBT) may be referred to as the "off" state of the switching element.

[0020] A clamp diode Du1 is connected between the intermediate connection point of the first and second arms and the neutral point C. For example, clamp diode Du1 consists of two diodes connected in series. Similarly, clamp diode Du2 is connected between the intermediate connection point of the third and fourth arms and the neutral point C. For example, clamp diode Du2 consists of two diodes connected in series. Thus, the converter 10 according to this embodiment is a so-called diode clamp type, but is not limited thereto. For example, switching elements S11 to S42 may be connected to clamp diodes Du1 and Du2 to make it an active type. Furthermore, the number of elements in series and the withstand voltage can be designed based on the voltage specifications. For example, the total withstand voltage of the switching elements of the second and third arms can be made greater than the DC voltage VD between the positive terminal P and the negative terminal N.

[0021] In this manner, the switching units S1 to S4 are connected in series for each of the U, V, and W phases, and each outputs a pulsed potential of one of three levels—positive P, negative N, or neutral C—of a DC voltage to its respective AC output terminals U, V, and W, supplying a pulse-width modulated AC voltage to the transformer 20.

[0022] When switches S1 and S2 on the positive arm are simultaneously turned on, the potential of the positive terminal P is output. When switches S3 and S4 on the negative arm are simultaneously turned on, the potential of the negative terminal N is output. When both switches S1 and S4 are turned off, and switches S2 and S3 are simultaneously turned on, the potential of the neutral point C is output via either the neutral point clamp diode Du1 or Du2. When a positive AC voltage is output, switch S2 is in the ON state, and switch S1 is turned on and off. When a negative AC voltage is output, switch S3 is in the ON state, and switch S4 is turned on and off. Switches S1 and S3 and S2 and S4 are controlled to turn on and off complementaryly to each other and never turn on simultaneously. This switching control operation is well known, so a detailed explanation is omitted.

[0023] Here, the details of the control device 40 and the gate drive circuit 400 will be described. Figure 2 is a block diagram showing an example configuration of the control device 40 and the gate drive circuit 400. As shown in Figure 2, the gate drive circuit 400 includes a short-circuit detection circuit 402, a clamp circuit 404, and a gate circuit 406. In the following, for example, the control of switching element S11 and switching elements S12, S21, S22, S31, S32, S41, and S42 are equivalent except for the control timing, so the description of switching elements S12, S21, S22, S31, S32, S41, and S42 may be omitted.

[0024] The short-circuit detection circuit 402 outputs a detection signal when it detects that a short-circuit current is flowing through the switching element S11. This short-circuit detection circuit 402 has a detection circuit that detects the collector voltage of, for example, a semiconductor switching element (IGBT) in the switching element S11. This detection circuit can detect the collector voltage by connecting, for example, a voltage divider resistor or a voltage divider capacitor to the collector C of the semiconductor switching element.

[0025] Furthermore, when a DC short circuit occurs and a large current flows, the semiconductor switching element (IGBT) saturates and the collector potential rises. For example, the short-circuit detection circuit 402 outputs a short-circuit detection signal (S1-1) indicating a DC short circuit when the semiconductor switching element is in the ON state and the collector voltage rises above a predetermined threshold. As described above, the switching element S11 is used as an example, but the gate drive circuits 400 for switching elements S12 to S42 have a similar configuration. Note that the short-circuit detection circuit 402 in this embodiment detects voltage, but is not limited to this. For example, the detection circuit may detect the current flowing through the collector C of the conductor switching element.

[0026] The clamping circuit 404 can clamp the collector voltage of the collector C of the semiconductor switching element to a predetermined value. For example, an active clamping circuit using a diode between the collector C and the gate G of the semiconductor switching element (IGBT) can be used for the clamping circuit 404. Also, a voltage clamping circuit that controls the gate signal so as to suppress the rise of the collector voltage of the switching element to a predetermined value based on the collector voltage can be used. More specifically, this voltage clamping circuit injects a predetermined current into the gate G according to the collector voltage and controls it so as to suppress the rise of the collector voltage of the switching element to a predetermined value.

[0027] Figure 3 is a diagram showing an example of the operating characteristics of the clamping circuit 404. Figure 3(a) is a diagram showing the characteristics of the collector voltage. The horizontal axis represents time, and the vertical axis represents twice the collector voltage of the semiconductor switching element (IGBT). Since there are two switching elements S11 and S12, the collector voltage Vce is shown doubled. That is, for each switching element, the voltage characteristic on the vertical axis becomes half the value. The collector voltage Vce is, for example, the voltage between the collector C and the emitter E. The solid line represents the characteristics when the clamping circuit 404 is used, and the dashed line represents the characteristics when the clamping circuit 404 is not used. Figure 3(b) is a diagram showing the characteristics of the collector current. The horizontal axis represents time, and the vertical axis represents the collector current of the semiconductor switching element (IGBT). The solid line represents the characteristics when the clamping circuit 404 is used, and the dashed line represents the characteristics when the clamping circuit 404 is not used.

[0028] In this way, the clamping circuit 404 clamps the voltage between the collector C and the emitter E to the set voltage Vclp below the breakdown voltage in the semiconductor switching element (IGBT). At this time, as shown in Figure 3(b), the collector current is controlled to decrease over time. Also, in order to suppress the overvoltage after short-circuit interruption, assuming the voltage between the positive electrode P and the negative electrode N is Vdc and the number of series-connected elements is N (N = 2 in Figure 1), the set voltage Vclp of the clamping circuit is set to Vclp < Vdc / N. Due to such characteristics, the clamping circuit 404 can handle the overvoltage V when interrupting a large short-circuit current.surge And, overvoltage V due to voltage imbalance between multiple series connections during normal switching operation surge And the overvoltage V after short-circuit interruption. surge And it is possible to suppress that.

[0029] During normal operation, the gate circuit 406 controls each switching element S11 to S42 by supplying gate signals S1a to S4a generated by the control device 40, so that the converter 10 outputs the desired voltage. As described above, since switching elements S11 and S12 are turned on and off simultaneously, the same gate signal S1a is supplied to them.

[0030] Furthermore, when the gate circuit 406 receives short-circuit blocking signals S1b to S4b, it blocks, or turns off, each switching element S11 to S42. In this way, the gate circuit 406 can control the on / off state of semiconductor switching elements by receiving gate signals S1a to S4a and short-circuit blocking signals S1b to S4b, and controlling the voltage applied to the gates of the semiconductor switching elements. For example, when the gate circuit 406 outputs a high-level signal (turn-on), the gate capacitance and Miller capacitance of each switching element S11 to S42 are charged and they turn on. On the other hand, when the gate circuit 406 outputs a low-level signal (turn-off), the gate capacitance and Miller capacitance of each switching element S11 to S42 are discharged and they turn off.

[0031] The control device 40 includes a control circuit 408 and a short-circuit interruption signal generation circuit 410. The control circuit 408 generates gate signals for general driving, for example. That is, as described above, when the control circuit 408 outputs a positive AC voltage, it turns on switch unit S2 and controls switch unit S1 on and off via gate circuit 406. Also, when the control circuit 408 outputs a negative AC voltage, it turns on switch unit S3 and controls switch unit S4 on and off. Furthermore, the control circuit 408 controls switch units S1 and S3 and S2 and S4 to turn on and off complementaryly to each other so that they do not turn on simultaneously. Note that switch unit S1 may be referred to as the first arm, switch unit S2 as the second arm, switch unit S3 as the third arm, and switch unit S4 as the fourth arm.

[0032] Figure 4 shows an example circuit relating to the switch sections S1 to S4 of the short-circuit interruption signal generation circuit 410. When any of the short-circuit detection signals S1-1 to S4-2 are detected, the short-circuit interruption signal generation circuit 410 outputs an interruption signal to the corresponding gate circuit 406 among the multiple switching elements of each of the first to fourth arms, causing the corresponding switching element to be turned off. More specifically, the short-circuit interruption signal generation circuit 410 has an OR interruption circuit 508a for the short-circuit detection signals S1-1 and S1-2 for the switch section S1. When the OR interruption circuit 508a outputs a high-level signal, for example, it causes the gate circuit 406 to interrupt (turn off) the switching elements S11 and S12 of the switch section S1. Similarly, the short-circuit interruption signal generation circuit 410 has OR interruption circuits 508a for short-circuit detection signals S2-1 and S2-2, OR interruption circuits 508a for short-circuit detection signals S3-1 and S3-2, and OR interruption circuits 508a for short-circuit detection signals S4-1 and S4-2.

[0033] As a result, the short-circuit interruption signal generation circuit 410 according to this embodiment outputs short-circuit interruption signals S1b, S2b, S3b, and S4b when it receives, for example, short-circuit detection signals S1-1, S1-2, S2-1, S2-2, S3-1, S4-2, S4-1, and S4-2 with respect to the switch sections S1 to S4. As a result, if interruption is possible, the switch sections S1 to S4 are interrupted. As described above, the clamping characteristics of the clamp circuit 404 suppress overvoltage breakdown of the semiconductor switching elements. On the other hand, if the semiconductor switching elements are not interrupted, there is a risk of generating excessive heat loss, which may exceed the energy capacity of the semiconductor switching elements. In contrast, according to this embodiment, since the semiconductor switching elements are interrupted, the risk of exceeding the energy capacity of the semiconductor switching elements is suppressed.

[0034] Here, using Figures 5 to 9, specific examples of the operation of the control circuit 408 and the short-circuit interruption signal generation circuit 410 will be explained. Figure 5 shows an example where the positive arm is in the ON state and the negative arm is in the OFF state. The switch unit S1 is in a fault-free state.

[0035] Figure 6 shows an example of a fault where the positive arm is ON and the negative arm is OFF. Switch unit S1 is short-circuited in the state shown in Figure 5. In this state, it is the same as the normal state in Figure 6, so the short-circuit interruption signal generation circuit 410 outputs a high-level signal (ON signal) for normal operation to switch unit S1.

[0036] Figure 7 shows the control state when switches S1 and S4 are in the off state and switches S2 and S3 are in the on state. The control circuit 408 controls switches S1 and S4 to the off state and switches S2 and S3 to the on state. However, contrary to the control of the control circuit 408, switch S1 has a short-circuit failure and remains in a conductive state. In this case, the current path shown by the dashed line is formed. Thus, the short-circuit current flows because a conduction path is formed between the switching elements of three arms, including the second arm S2 and the third arm S3, out of the first arm S1, second arm S2, third arm S3, and fourth arm S4, and the capacitor C10, which is the first DC power supply, or the capacitor C20, which is the second DC power supply.

[0037] As a result, the first arm S1, the second arm S2, and the third arm S3 become conductive, generating a short-circuit current in the capacitor C10. The short-circuit detection circuits 402 of the switch sections S1, S2, and S3 output short-circuit detection signals S1-1, S1-2, S2-1, S2-2, S3-1, and S3-2. The short-circuit interruption signal generation circuit 410, upon receiving these signals, outputs short-circuit interruption signals S1b to S3b to the gate circuits 406 of the switch sections S1, S2, and S3. As a result, in Figure 7, the short-circuit current is interrupted, and the damage to the switch sections S2 and S3 is suppressed.

[0038] Similarly, when the first arm S2, the second arm S3, and the fourth arm S4 (short-circuit fault) become conductive, a short-circuit current is generated in the capacitor C20. The short-circuit detection circuits 402 of the switch sections S2, S3, and S4 output short-circuit detection signals S2-1, S2-2, S3-1, S3-2, S4-1, and S4-2. The short-circuit interruption signal generation circuit 410, upon receiving these signals, outputs short-circuit interruption signals S2b to S4b to the gate circuits 406 of the switch sections S2, S3, and S4. This interrupts the short-circuit current and prevents damage to the switch sections S2 and S3.

[0039] Figure 8 shows the state in which the short-circuit interruption signal generation circuit 410 outputs short-circuit interruption signals S1b to S3b to the gate circuits 406 of the switch units S1, S2, and S3. Switch unit S1 is short-circuited and therefore remains in a state where it cannot be turned off. On the other hand, the gate circuits 406 of the switch units S2 and S3 turn off (interrupt) the switch units S1 and S3 in response to the short-circuit interruption signals S2b and S3b. This prevents damage to the switch units S2 and S3.

[0040] Furthermore, as shown in Figure 8, even when power is supplied from the negative arm, current passes through the diode of the switch section S3 and is output. This suppresses the generation of excessive heat loss and prevents exceeding the energy capacity of the semiconductor switching element.

[0041] Figure 9 shows an example where the voltage applied to switch section S2 is twice the normal voltage when a short circuit is not interrupted. The control circuit 408 controls switch sections S1, S3, and S4 to the off state and switch section S2 to the on state. Here, the timing is shown in the control state where power is supplied from the positive arm. However, contrary to the control of the control circuit 408, switch section S1 has a short circuit failure and remains in the on state. In this timing state, current passes through the diodes of switch sections S3 and S4, and no voltage decrease occurs in switch sections S3 and S4. Therefore, normally, the voltage V would be applied to switch section S2. DC Even though only half is applied, the voltage V DC A voltage may be applied, potentially exceeding the withstand voltage. In contrast, in this embodiment, as described above, the switch sections S2 and S3 are interrupted (turned off), so the short-circuit current of the positive arm is interrupted, and this condition does not occur.

[0042] Figure 10 is a flowchart illustrating an example of the control device 40's processing. Here, we will explain an example where a short-circuit failure occurs in any of the switch units S1, S2, S3, and S4. As shown in Figure 10, a failure occurs in any of the switch units S1, S2, S3, and S4 (step S10). Subsequently, a DC short circuit occurs in any of the switch units S1, S2, S3, and S4 (step S20).

[0043] When the control device 40's short-circuit interruption signal generation circuit 410 receives any of the short-circuit detection signals S1-1, S1-2, S2-1, S2-2, S3-1, S4-2, S4-1, or S4-2 (step S30), it outputs one of the short-circuit interruption signals S1b, S2b, S3b, or S4b corresponding to the short-circuit detection signal (step S40). Next, the control circuit 408 of the control device 40 outputs the short-circuit interruption signals S1b, S2b, S3b, or S4b to all the switch units S1, S2, S3, and S4 (step S50). Then, the control circuit 408 of the control device 40 opens the circuit breaker 30 (see Figure 1) (step S60).

[0044] As described above, according to this embodiment, when the control device 40 receives any of the short-circuit detection signals S1-1, S1-2, S2-1, S2-2, S3-1, S4-2, S4-1, or S4-2, the short-circuit interruption signal 410 of the control device 40 outputs one of the corresponding short-circuit interruption signals S1b, S2b, S3b, or S4b, thereby interrupting the corresponding switch units S1, S2, S3, or S4. As a result, even if the control circuit 408 of the control device 40 continues normal control until it stops driving, the flow of short-circuit current to the switch units S1, S2, S3, or S4 is stopped, and the destruction of the switch units S1, S2, S3, or S4 is suppressed.

[0045] (Second Embodiment) The power converter 1a according to the second embodiment differs from the power converter 1 according to the first embodiment by increasing the number of switching elements in the switch sections S2 and S3 compared to the number of switching elements in the switch sections S1 and S4. The differences from the power converter 1 according to the first embodiment will be explained below.

[0046] Figure 11 shows an example configuration of the power converter 1a according to the second embodiment. As shown in Figure 11, the number of switching elements in series of the second arm and the third arm (switch sections S2 and S3) is greater than the number of switching elements in series of the first arm and the fourth arm (switch sections S1 and S4). In other words, this is an example in which the number of switching elements in switch sections S2 and S3 is set to 3.

[0047] As described above, the clamping characteristics of the clamp circuit 404 suppress overvoltage breakdown of the semiconductor switching element. On the other hand, if the semiconductor switching element is not shut off, there is a risk of generating excessive heat loss, which may exceed the energy withstand capability of the semiconductor switching element. Therefore, the withstand voltage of the switch sections S2 and S3 connected to the AC system Pg is selectively increased.

[0048] Figure 12 shows an example where the switch unit S1 has a short-circuit failure. This is the same condition as in Figure 8 described above. As described above, even if a short circuit occurs before reaching the state shown in Figure 12, similar to Figure 7, the breakdown of the switch units S2 and S3 is suppressed because the withstand voltage of the switch units S2 and S3 has been increased.

[0049] As described above, according to this embodiment, the voltage withstand capability of the switch sections S2 and S3 connected to the AC system Pg is selectively increased. As a result, even if the switch sections S1 and S4 experience a short-circuit failure, the damage to the switch sections S2 and S3 is suppressed. [Explanation of Symbols]

[0050] 1, 1a: Power converter, 40: Control device, 400: Gate drive circuit, 402: Short circuit detection circuit, 404: Clamp circuit, 406: Gate circuit, S1: First arm, S2: Second arm, S3: Third arm, S4: Fourth arm, S11, S12, S21, S22, S31, S32, S41, S42: Switching elements.

Claims

1. The first to fourth arms are each formed by a series circuit of multiple switching elements, One end of the first arm is connected to the positive terminal of the first DC power supply, and the other end is in contact with one end of the second arm. The other end of the second arm is connected to an AC power system. One end of the fourth arm is connected to the negative terminal of the second DC power supply, and the other end is in contact with one end of the third arm. The other end of the third arm is connected to an AC power system. The first to fourth arms are configured such that the total withstand voltage of the switching elements of the second arm and the total withstand voltage of the switching elements of the third arm are greater than the DC voltage between the positive and negative electrodes. The system includes a control circuit that generates a gate signal and is capable of controlling the switching elements of the first arm and the second arm, and the switching elements of the third arm and the fourth arm, to a conductive state and the other to a non-conductive state. Each of the aforementioned plurality of switching elements is A gate circuit that supplies the gate signal, which controls the switching element to a conductive or non-conductive state, to the gate of the switching element, The system includes a short-circuit detection circuit that outputs a detection signal when it detects that a short-circuit current is flowing through the switching element. A power converter wherein, when the short-circuit detection circuit outputs a detection signal for the corresponding switching element, the gate circuit generates the gate signal that causes the corresponding switching element to become non-conductive.

2. The power conversion device according to claim 1, wherein the number of switching elements in series of the second arm and the third arm is greater than the number of switching elements in series of the first arm and the fourth arm.

3. The power conversion device according to claim 1, comprising clamp diodes connected between the intermediate connection point and the neutral point of the first and second arms on the positive side, and between the intermediate connection point and the neutral point of the third and fourth arms on the negative side.

4. Each of the first to fourth arms has a plurality of switching elements connected in series, Each of the first to fourth arms is further provided with a gate circuit corresponding to a plurality of switching elements, which is provided with a short-circuit interruption signal generation circuit that outputs an interruption signal to turn off the gate circuit. The power conversion device according to claim 1, wherein the short-circuit interruption signal generation circuit outputs an interruption signal to the gate circuit corresponding to each of the plurality of switching elements, when it receives a detection signal from any of the short-circuit detection circuits corresponding to each of the plurality of switching elements, which are each of the first to fourth arms.

5. The power conversion device according to claim 4, wherein the short-circuit interruption signal generation circuit is capable of detecting a short-circuit failure in either the first arm or the fourth arm.

6. The system further comprises a circuit breaker for disconnecting the connection between the second arm and the third arm and the AC system, The power conversion device according to claim 1, wherein the circuit breaker disconnects the connection when the short-circuit detection circuit outputs a detection signal.

7. The first to fourth arms are each formed by a series circuit of multiple switching elements, One end of the first arm is connected to the positive terminal of the first DC power supply, and the other end is in contact with one end of the second arm. The other end of the second arm is connected to an AC power system. One end of the fourth arm is connected to the negative terminal of the second DC power supply, and the other end is in contact with one end of the third arm. The other end of the third arm is connected to an AC power system. A control device for a power converter comprising first to fourth arms, wherein the total withstand voltage of the switching elements of the second arm and the total withstand voltage of the switching elements of the third arm are each greater than the DC voltage between the positive and negative electrodes, Each of the aforementioned plurality of switching elements is A gate circuit that supplies a gate signal to the gate of a switching element to control the conduction or non-conduction state of the switching element, The system includes a short-circuit detection circuit that outputs a detection signal when it detects that a short-circuit current is flowing through the switching element, A control circuit that generates the gate signal and controls the switching elements of the first arm and the second arm, and the switching elements of the third arm and the fourth arm, to be in a conductive state and the other to be in a non-conductive state, When the short-circuit detection circuit outputs a detection signal for the corresponding switching element, a short-circuit interruption signal generation circuit is provided that causes the gate circuit to generate the gate signal that turns off the corresponding switching element. A control device equipped with the following features.

8. A control method for a power converter in which a first to fourth arm is formed by a series circuit of multiple switching elements, One end of the first arm is connected to the positive terminal of the first DC power supply, and the other end is in contact with one end of the second arm. The other end of the second arm is connected to an AC power system. One end of the fourth arm is connected to the negative terminal of the second DC power supply, and the other end is in contact with one end of the third arm. The other end of the third arm is connected to an AC power system. The total withstand voltage of the switching elements of the second arm and the total withstand voltage of the switching elements of the third arm are made greater than the DC voltage between the positive and negative electrodes. A gate driving step is performed to supply a gate signal to the gate of the switching element to control the switching element to a conductive or non-conductive state, thereby causing one of the switching elements of the first arm and the second arm, and the switching elements of the third arm and the fourth arm, to be in a conductive state and the other to be in a non-conductive state. A short-circuit detection step that outputs a detection signal when it detects that a short-circuit current is flowing through the switching element, A control method that generates a gate signal that causes a switching element corresponding to the detection signal to be in a non-conductive state when the detection signal is output.

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