JP2020014295A - Power conversion device and current control method in the same - Google Patents

Abstract

To provide a power conversion device and a current control method in the same, capable of preventing a power semiconductor element forming a pair of arms from being damaged, thereby achieving energy saving and high reliability.SOLUTION: A power conversion device 4 includes: power semiconductor elements 41 to 42 forming a pair of arms; a control unit 11 for outputting a control command for gates of the power semiconductor elements 41 to 42; gate driving devices 21 to 22 for driving the power semiconductor elements 41 to 42 by applying a voltage to the gates according to the control command. The control unit 11 outputs to the gate driving devices 21 to 22 a return operation command for conducting a return current in a reverse direction of the power semiconductor elements 41 to 42. The gate driving devices 21 to 22 respond to the return operation command to apply a predetermined voltage to all the power semiconductor elements 41 to 42 of the pair of arms.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a power converter and a current control method in the power converter, and is suitably applied to, for example, a power converter that drives a power semiconductor element having a body diode.

  There is a power converter using a power semiconductor element. For example, in a driving device for a railway vehicle, a configuration in which a driving force is obtained by rotating an electric motor with three-phase AC power obtained by converting power taken from an overhead line into a desired frequency and voltage by a power conversion device such as an inverter has become mainstream. I have.

  In recent years, in such power conversion devices, for example, a SiC-MOSFET (Metal Oxide Semiconductor Field Effect Transistor) has been used instead of an IGBT (Insulated Gate Bipolar Transistor) as a power semiconductor element for further energy saving. SiC has a larger band gap than silicon and a dielectric strength of about 10 times that of silicon. For this reason, the SiC-MOSFET can reduce the thickness of the element to about 1/10 as compared with the IGBT, the resistance during conduction can be suppressed to about 1/10, and the conduction loss can be reduced.

  Further, since the resistance of the SiC-MOSFET during conduction can be reduced, even when the SiC-MOSFET is used as a high-voltage element of a railway vehicle having a rated voltage of, for example, 3.3 kV, a bipolar device such as an IGBT that accumulates charges and lowers the conduction resistance. There is no need for a structure. That is, the SiC-MOSFET can have a unipolar device structure such as a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) or a JFET (Junction FET). A unipolar device has less switching loss than a bipolar device because there is no charge accumulation, and can contribute to further energy saving of a power conversion device.

  Further, unlike the IGBT, the SiC-MOSFET can conduct current in the opposite direction by applying a predetermined voltage to the gate (for example, see Patent Document 1). Therefore, the SiC-MOSFET has a feature that a freewheel diode is not required, and the element can be downsized.

JP 2013-207821 A

  In general, in a power converter, when any abnormality (such as a mismatch between an on / off gate command and an actual on / off state) is detected in a power semiconductor element, it is determined that the power semiconductor element has failed, and the power semiconductor element has failed. Are all turned off to stop the power converter. In this way, in the power converter, it is possible to prevent the failure from spreading to other power semiconductor elements and prevent the element destruction from expanding.

  However, for example, in a railway vehicle, when any abnormality is detected in the SiC-MOSFET and the power converter is stopped by completely turning off the SiC-MOSFET, the current generated by the rotating permanent magnet type synchronous motor that continues to rotate is converted to the power conversion. Flow into the device. This current flows through the body diode, which is a parasitic diode of the SiC-MOSFET, because the SiC-MOSFET cannot flow a current in the reverse direction because the gate is turned off. The body diode has a problem that a large forward voltage drop causes a large loss when energized, and the SiC-MOSFET is thermally damaged.

  As a countermeasure against this problem, if any abnormality is detected in the SiC-MOSFET, the SiC-MOSFET is turned on all the way, and the current flows to the switching element side (between the source and the drain) of the SiC-MOSFET instead of the body diode. There is a method of performing synchronous rectification drive. However, in a power converter that is stopped due to some abnormality, there is a possibility that any of the SiC-MOSFETs has failed. This SiC-MOSFET and the SiC-MOSFET forming the opposite arm are simultaneously turned on to cause a so-called arm short-circuit that short-circuits the positive and negative power supply lines, which may cause a serious failure.

  The present invention has been made in consideration of the above points, and prevents part or most of the return current flowing through a body diode of a power semiconductor element forming an opposite arm from flowing to a switching element side, thereby preventing damage to the power semiconductor element. It is intended to propose a power conversion device and a current control method in the power conversion device that can achieve energy saving and high reliability.

  In order to solve such a problem, in the present invention, the power conversion device includes a plurality of power semiconductor elements forming a pair of arms, a control unit that outputs a control command for a gate of the plurality of power semiconductor elements, and a control unit that responds to the control command. A gate driving device for driving the power semiconductor element by applying a voltage to the gate. The control unit, when an abnormality is detected in the power conversion device, outputs a return operation command to apply a predetermined voltage for conducting a current in the reverse direction of the power semiconductor element to the gate driving device, The gate driving device applies the predetermined voltage to all the power semiconductor elements of the paired arms according to the return operation command.

  Further, in the present invention, a plurality of power semiconductor elements forming a pair of arms, a control unit for outputting a control command for a gate of the plurality of power semiconductor elements, and applying a voltage to the gate in accordance with the control command, A gate drive device for driving a power semiconductor device, wherein the control unit controls the return of the power semiconductor device to apply a predetermined voltage for conducting a current in a reverse direction of the power semiconductor device. An operation command is output to the gate drive device, and the gate drive device applies the predetermined voltage to all the power semiconductor elements of the paired arms in response to the return operation command.

  According to the power conversion device and the current control method in the power conversion device, a part or most of the return current flowing through the body diode of the power semiconductor element forming the paired arm can flow to the switching element side.

  ADVANTAGE OF THE INVENTION According to this invention, the power converter which can prevent damage of a power semiconductor element, and can achieve energy saving and high reliability, and the electric current control method in a power converter can be implement | achieved.

FIG. 1 is a diagram illustrating a configuration of a power conversion device according to a first embodiment. FIG. 2 is a diagram illustrating a configuration of a gate drive device according to the first embodiment. FIG. 3 is a diagram illustrating a configuration of a gate voltage output circuit according to the first embodiment. 5 is a time chart illustrating changes in current flowing through the switching element and the parasitic diode according to the first embodiment. FIG. 6 is a diagram illustrating a configuration of a power conversion device according to a modification of the first embodiment. FIG. 6 is a diagram illustrating a configuration of a power conversion device according to a modification of the first embodiment. FIG. 9 is a diagram illustrating a configuration of a power conversion device according to a modification of the first embodiment. FIG. 9 is a diagram illustrating a configuration of a power conversion device according to a modification of the first embodiment. FIG. 9 is a diagram illustrating a configuration of a gate drive device according to a second embodiment. FIG. 9 is a diagram illustrating a configuration of a gate voltage output circuit according to a second embodiment. FIG. 14 is a diagram illustrating a configuration of a gate voltage output circuit according to a third embodiment. FIG. 14 is a diagram illustrating a configuration of a gate voltage output circuit according to a modification of the third embodiment. It is a figure showing the composition of the power converter of a 4th embodiment.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In the following description of each embodiment and each modification, the same reference numerals are given to the same components, and the description thereof will be omitted. In addition, each of the following embodiments and each of the modifications may be partially or entirely combined within a range not inconsistent.

(1) First Embodiment (1-1) Configuration of Power Conversion Device According to First Embodiment FIG. 1 is a diagram illustrating a configuration of a power conversion device according to a first embodiment. The railway vehicle 100 including the power conversion device 4 according to the first embodiment uses, for example, a two-level inverter as the power conversion device 4 included in the motor driving device.

  As shown in FIG. 1, the railway vehicle 100 includes a current collector (pantograph) 1 that collects power from an overhead line, a filter reactor 2, a filter capacitor 3, a power converter 4, a motor (motor) 5, wheels 6, and It has a circuit breaker 7.

  The power converter 4 is connected to a positive power line and a negative power line. The positive power line is connected to the overhead line via the current collector 1. The negative power line is connected to the rail via wheels 6. The filter reactor 2 and the filter capacitor 3 constitute a filter circuit operating at, for example, several tens of Hz.

  When an overcurrent and an overvoltage occur, the circuit breaker 7 protects the power converter 4 by cutting off the power from the overhead line. The power conversion device 4 converts the power taken from the overhead wire into three-phase AC power of U, V, and W and outputs the converted power. The electric motor 5 is connected to output terminals of the U, V, and W phases of the power converter 4 and is driven by three-phase AC power output from the power converter 4. The electric motor 5 is, for example, a permanent magnet synchronous motor (PMSM).

  The power conversion device 4 includes a control unit 11, gate driving devices 21 to 26, and power semiconductor elements 41 to 46. The control unit 11 and the gate driving devices 21 to 26 are connected via the signal line 12.

  The control unit 11 sends a gate command 111 (ON gate command and OFF gate command, see FIG. 2) for turning on and off each gate of the power semiconductor elements 41 to 46 via the signal line 12 to the gate driving devices 21 to 26. Output to each. Further, the control unit 11 outputs, via the signal line 12, a reflux operation command 117 (see FIG. 2) for causing the power semiconductor elements 41 to 46 to perform a reflux operation to the gate driving devices 21 to 26, respectively. Further, the control unit 11 receives, via the signal line 12, a feedback signal (see FIG. 2) indicating the on / off state of each gate of the power semiconductor elements 41 to 46 from each of the gate driving devices 21 to 26.

  The power semiconductor elements 41 to 46 are SiC-MOSFETs (SiC-Metal Oxide Semiconductor Field Effect Transistors). Each of power semiconductor elements 41 to 42, 43 to 44, and 45 to 46 forms an upper and lower arm of each phase of the two-level inverter.

  The power semiconductor element 41 includes a switching element 41a and a body diode 41b connected in parallel to the switching element 41a. In the present embodiment, a portion between the source and the drain of the power semiconductor element 41 that conducts current when the gate is turned on and shuts off current when the gate is turned off is referred to as a switching element 41a. The body diode 41b is a parasitic diode of the power semiconductor device 41. The gate driver 21 is connected to the gate of the switching element 41a. Similarly, the power semiconductor elements 42 to 46 have switching elements 42a to 46a and body diodes 42b to 46b, respectively, as shown in FIG. Gate drivers 22 to 26 are connected to the gates of the switching elements 42a to 46a, respectively.

(1-2) Configuration of the Gate Driving Device According to the First Embodiment FIG. 2 is a diagram illustrating the configuration of the gate driving device according to the first embodiment. FIG. 2 shows a gate drive device 21 for driving the power semiconductor element 41 constituting the upper arm of the U phase of the three phases U, V, and W among the gate drive devices 21 to 26 of the first embodiment. However, the same applies to the gate drive device 22 for driving the power semiconductor element 42 constituting the lower arm of the U phase, and the other two-phase power semiconductor elements 43 to 46 and the gate drive devices 23 to 26.

  The gate driving device 21 includes an insulation circuit 101, a gate voltage output circuit 102, and an on / off state determination circuit 103.

  The insulating circuit 101 insulates the gate command 111, the return operation command 117, and the feedback signal 116. The insulating circuit 101 converts the gate command 111 received from the control unit 11 into a gate command 112 and outputs the gate command 112 to the gate voltage output circuit 102 and the on / off state determination circuit 103. Further, the insulating circuit 101 converts the reflux operation command 117 received from the control unit 11 into a reflux operation command 118 and outputs the same to the gate voltage output circuit 102. Further, the insulating circuit 101 converts the feedback signal 115 received from the on / off state determination circuit 103 into a feedback signal 116 and outputs the feedback signal 116 to the control unit 11.

  The gate voltage output circuit 102 receives the gate command 112 from the insulating circuit 101 and applies a gate voltage 113 corresponding to the gate command 112 to the gate of the power semiconductor device 41. Further, the gate voltage output circuit 102 receives the reflux operation command 118 from the insulating circuit 101 and applies a gate voltage 113 corresponding to the reflux operation command 118 to the gate of the power semiconductor element 41. Further, the gate voltage output circuit 102 monitors the gate voltage of the power semiconductor element 41, and outputs a gate voltage monitoring signal 114 indicating the gate voltage to the on / off state determination circuit 103 simultaneously with the output of the gate voltage 113.

  The gate voltage 113 is the first voltage (VDD1) equal to or higher than the threshold voltage Vth for turning on the gate of the power semiconductor element 41 and conducting current in the forward direction in the case of the ON gate command 112. Further, in the case of the off gate command 112, the gate voltage 113 is 0 or a predetermined negative second voltage (less than the threshold voltage Vth for turning off the gate of the power semiconductor element 41 and cutting off the current). VSS). In the case of the reflux operation command 118, the gate voltage 113 is lower than the threshold voltage Vth and lower than the second voltage (VSS) for conducting current in the reverse direction (between the source and the drain) of the power semiconductor element 41. This is a large third voltage (VDD2). For example, when the threshold voltage Vth of the power semiconductor element 41 is 4V, the third voltage (VDD2) is controlled to be less than 4V.

  Here, when the third voltage (VDD2) is applied to the power semiconductor elements 41 to 46, the current flows in the reverse direction of the power semiconductor elements 41 to 46 by utilizing the substrate bias effect. The substrate bias effect means that the threshold voltage Vth varies with the voltage of the back gate (substrate). When a current flows in the reverse direction due to the substrate bias effect, that is, when a reverse voltage is applied to the power semiconductor elements 41 to 46, the drain voltage becomes negative, so that the threshold voltage Vth decreases equivalently, and the gate voltage decreases. Even if a voltage lower than the threshold voltage Vth is applied, a channel is formed and a current flows through the power semiconductor elements 41 to 46. On the other hand, when the current flows in the forward direction, that is, when the forward voltage is applied to the power semiconductor elements 41 to 46, the substrate bias effect is reduced or no longer occurs, and the threshold voltage Vth returns to the normal value. When the voltage applied to the gate is lower than the threshold voltage Vth, no current flows through the power semiconductor elements 41 to 46.

  The on / off state determination circuit 103 receives the gate voltage monitoring signal 114 from the gate voltage output circuit 102, and determines the state of the gate of the power semiconductor element 41 based on the gate voltage monitoring signal 114. For example, the on / off state determination circuit 103 compares the gate voltage monitoring signal 114 with the reference voltage. If the gate voltage monitoring signal 114 is equal to or higher than the reference voltage, the gate of the power semiconductor element 41 is in an on state. A feedback signal 115 indicating the state is generated and output to the insulating circuit 101.

  The control unit 11 monitors the state of the power semiconductor element 41 based on the feedback signal 116 converted from the feedback signal 115 by the insulating circuit 101, and determines whether or not the gate command 111 matches the feedback signal 116 (hereinafter, “FB mismatch”). Is detected, it is determined that the power semiconductor element 41 has failed. When detecting the FB mismatch, the control unit 11 outputs an off gate command 111 to the gate driving devices 21 to 26 to turn off all the power semiconductor elements 41 to 46 and stop the power conversion device 4. The control unit 11 monitors, for example, a drop in the overhead line voltage, an overvoltage, and the like, and when any abnormality is detected, outputs an off gate command 111 to the gate driving devices 21 to 26 to output the power semiconductor elements 41 to The power converter 4 may be stopped by completely turning off the power supply 46.

  Here, since the electric motor 5 has a magnet in the rotor, when the control unit 11 detects any abnormality during the rotation of the electric motor 5 and stops the power conversion device 4, the electric motor 5 generates electric power. It operates as a motor, and the current generated by the rotation of the electric motor 5 flows into the power converter 4. This current flows into the filter capacitor 3 through the body diodes 41b to 46b of the power semiconductor elements 41 to 46 stopped by the abnormality detection, and charges the filter capacitor 3.

  Therefore, the control unit 11 determines that a failure has occurred due to some abnormality while the electric motor 5 is operating, turns off all the power semiconductor elements 41 to 46, and then outputs a return operation command 117 to the gate driving devices 21 to 26. I do. Upon receiving the reflux operation command 117, the gate driving devices 21 to 26 apply a third gate voltage to the power semiconductor elements 41 to 46. The power semiconductor elements 41 to 46 allow a part or most of the return current from the electric motor 5 to flow in the reverse direction in response to the application of the third gate voltage, so that the switching elements 41 a to A reflux operation for flowing to the 46a side is performed. Thus, the return current flowing through the body diodes 41b to 46b of the power semiconductor elements 41 to 46 can be suppressed, and the body diodes 41b to 46b can be prevented from being damaged by heat generation.

  When the control unit 11 and the gate driving device 21 are connected by an electric wire, the control unit 11 driven at a low voltage and the power semiconductor element 41 driven at a high voltage, the gate voltage output circuit 102, and the on / off state determination circuit 103 are insulated. Therefore, the insulating circuit 101 is provided with an insulating function. On the other hand, when the control unit 11 and the gate driving device 21 are connected by an optical line, the insulating circuit 101 only converts the gate command 111, the reflux operation command 117, and the feedback signal 116 from an optical signal to an electric signal. Therefore, this insulating function is not required.

(1-3) Configuration of Gate Voltage Output Circuit According to First Embodiment FIG. 3 is a diagram illustrating a configuration of a gate voltage output circuit according to the first embodiment. The gate voltage output circuit 102 according to the first embodiment includes transistors 121, 122, and 123, a switch 125, resistors 131, 132, and 133, level converters 141, 142, and 143, voltage generators 151, 152, And 161. The resistor 131 controls the switching characteristics of the power semiconductor elements 41 to 46. The voltage generators 151 and 152 output the voltage VDD1. The voltage generator 161 outputs the voltage VDD2. The intermediate potential between the level converters 141 and 142 and 143 and the voltage generators 151 and 152 is grounded by the source ground line 110.

  When the gate command 112 is on, the gate voltage output circuit 102 turns on the transistor 121 and outputs the gate voltage 113 of the first voltage (VDD1). When the gate command 112 is off, the gate voltage output circuit 102 turns on the transistor 122 and outputs the gate voltage 113 of the second voltage (VSS). When the return operation command 117 is on, the gate voltage output circuit 102 turns off the transistor 122 by the switch 125 and outputs the gate voltage 113 of the third voltage (VDD2).

  Although FIG. 3 illustrates a case where MOSFETs are used for the transistors 121 to 123, a similar effect can be obtained when a bipolar transistor is used.

(1-4) Change of Current Flowing Through Switching Element and Parasitic Diode of First Embodiment FIG. 4 is a time chart showing change of current flowing through the switching element and the parasitic diode of the first embodiment. FIG. 4 illustrates a case where the control unit 11 detects an abnormality at time t1 in a state where the control unit 11 issues an ON command to the gate driving devices 21 and 24. The power semiconductor elements 41 to 42 of the upper and lower arms will be described as an example, but the same applies to the power semiconductor elements 43 to 44 and 45 to 46 connected in series as the paired arms of the other phases.

  At time t2, the control unit 11 outputs an off gate command 111 to the gate driving devices 21 and 24. The gate voltage 113 of the power semiconductor element 41 starts to decrease in response to the off gate command 111, and at time t3 when the gate voltage 113 falls below the threshold voltage Vth, the current that is the return current from the electric motor 5 flows into the body diode 41b of the power semiconductor element 42. Id2 flows out. At time t4 when the gate voltage 113 of the power semiconductor element 41 is at the voltage VSS, the control unit 11 outputs the reflux operation command 117 to all of the gate driving devices 21 to 26.

  Since the MOSFET does not have a storage carrier like an IGBT, if a predetermined time of, for example, 0.5 μs elapses after the control unit 11 outputs the gate command 111, the switching according to the gate command 111 ends. . Therefore, it is preferable that the control unit 11 outputs the recirculation operation instruction 117 after the time t4 when the first predetermined time of 0.5 μs elapses, for example, after outputting the gate command 111 of all off at the time t2. Thus, the recirculation operation can be performed while eliminating the influence of switching based on the all-off gate command 111.

  When the control unit 11 outputs the return operation command 117, the gate voltage 113 of the power semiconductor element 41 and the gate voltage 113-2 of the power semiconductor element 42 start increasing, and at the same time, the return current from the motor 5 is reduced by the power semiconductor element 42. From the body diode 42b to the switching element 42a (between the source and drain of the power semiconductor element 42), the current Id2 flowing through the body diode 42b decreases, and the current Ids2 flowing through the switching element 42a increases.

  After time t5 when the potential between the power semiconductor elements 41 to 42 exceeds the zero cross, the currents Id2 and Ids2 stop flowing, and the current Id1 of the body diode 41b of the power semiconductor element 42 and the switching element 41a (the source of the power semiconductor element 41) -Drain current) flows between the drains. As described above, by flowing a part or most of the return current to the switching element 41a of the power semiconductor element 41, the current Id1 flowing through the body diode 41b is reduced, the heat generation of the body diode 41b is suppressed, and the power semiconductor element 41 is broken. Can be prevented.

  When turning on the gates of the power semiconductor elements 41 to 46, the control unit 11 applies a third voltage to the power semiconductor elements 41 to 46, and then applies a third predetermined voltage of, for example, 0.5 μs for a second predetermined time. After the time when has elapsed, a gate command 111 for applying the first voltage (VDD1) for turning on the gate to the power semiconductor elements 41 to 46 is output. The first and second predetermined times may be the same or different.

(1-5) Effects of First Embodiment According to the first embodiment, when an abnormality of a power semiconductor element is detected, all the power semiconductor elements are turned off after all the power semiconductor elements are turned off. A third voltage is applied to cause a current to flow in the reverse direction due to the substrate bias effect, and a return operation is performed in which a part or most of the return current flowing through the body diode flows to the switching element side. Therefore, it is possible to prevent the power semiconductor element from being thermally destroyed by the return current flowing through the body diode. Further, when an abnormality occurs in the power semiconductor element forming the paired arm, it is possible to prevent the failure from spreading to other power semiconductor elements forming the paired arm.

(1-6) Modification of First Embodiment In the present embodiment, the power converter 4 that outputs three phases has been exemplified. However, the present invention is not limited to this. The power converter may have a power semiconductor element or may have two pairs of power semiconductor elements forming two-phase upper and lower arms.

  Further, in the present embodiment, the control unit 11 outputs the reflux operation instruction 117 at a time after a predetermined time has elapsed since the output of the gate instruction 111 for turning off all the power semiconductor elements. However, the present invention is not limited to this. The recirculation operation command 117 may be output immediately after the all-off gate command 111 is output.

  In the present embodiment, the power semiconductor elements 41 to 46 have been described by exemplifying SiC-MOSFETs. However, the power semiconductor element is not limited to this. The power semiconductor element can use a body diode as a freewheel diode, and has another band gap semiconductor element having a band gap of a predetermined value or more, that is, power semiconductors such as silicon, gallium nitride, and diamond. It may be an element.

  In the present embodiment, the case where body diodes 41b to 46b of power semiconductor elements 41 to 46 are used as freewheel diodes has been described. However, the present invention is not limited to this, and freewheel diodes 51 to 52 are connected in parallel with the power semiconductor elements 41 to 42, as in a power converter 4A exemplified by the U-phase power semiconductor elements 41 to 42 in FIG. Is also good. Also in this case, the current flowing through the body diodes 41b to 42b can be suppressed to prevent the power semiconductor element from being broken.

  In the present embodiment, it is assumed that one power semiconductor element 41 to 46 is driven by each of gate drive devices 21 to 26. However, the present invention is not limited to this, and two or more power semiconductor elements 41-1 to 41-4 connected in parallel, such as a power conversion device 4B exemplified by the U-phase power semiconductor elements 41-1 to 42-2 in FIG. -2 may be driven by the gate driver 21-1, and the two power semiconductor elements 42-1 to 42-2 connected in parallel may be driven by the gate driver 22-1. In this case, the return current flowing through each body diode 41b connected in parallel with the power semiconductor elements 41-1 to 41-2 and 42-1 to 42-2 is dispersed, and a part of the current flowing through each body diode 41b to 42b Alternatively, by flowing the majority to each switching element 41a, the effect of suppressing heat generation and preventing the power semiconductor element from being broken can be enhanced. In the example shown in FIG. 6, power semiconductor elements 41-1 to 41-2 form an upper arm, power semiconductor elements 42-1 to 42-2 form a lower arm, and these upper arm and lower arm Make a pair arm. FIG. 6 shows an example in which one gate driver 21-1 drives the power semiconductor elements 41-1 to 41-2 and one gate driver 22-1 drives the power semiconductor elements 42-1 to 42-2. Show. However, the power semiconductor device 41-1 is driven by the gate driver 21-1 and the power semiconductor device 41-2 is driven by the gate driver 21-2 as in the power converter 4B-1 shown in FIG. The power semiconductor element 42-1 may be driven by the gate driver 22-1, and the power semiconductor element 42-2 may be driven by the gate driver 22-2.

  In the present embodiment, the power conversion device 4 is a two-level inverter. However, the present invention is not limited to this, and even if it is a multi-level inverter of three or more levels as in the power converter 4C exemplified by the power semiconductor elements 41-3, 41-4, 42-5 and 42-6 in FIG. Good. FIG. 8 illustrates a three-level inverter, in which a power semiconductor element 41-3 driven by a gate driver 21-3 and a power semiconductor element 41-4 driven by a gate driver 21-4 are paired arms. The power semiconductor element 42-5 driven by the gate driving device 22-3 and the power semiconductor element 42-6 driven by the gate driving device 22-4 are paired arms.

  In the present embodiment, the control unit 11 monitors the states of the gates of the individual power semiconductor elements 41 to 46 based on the feedback signal 116 obtained by converting the feedback signal 115 output from the on / off state determination circuit 103, It is determined that a failure has occurred. However, the present invention is not limited to this, and various known methods can be used to monitor the states of the individual power semiconductor elements 41 to 46 and determine a failure based on the monitoring result.

  Further, in the present embodiment, when the failure of the power semiconductor elements 41 to 46 is detected, the control unit 11 turns off all the power semiconductor elements 41 to 46 to stop the power converter 4, and thereafter, Of the power semiconductor elements 41 to 46 perform the reflux operation. However, the present invention is not limited to this. When the power conversion device 4 is stopped, the control unit 11 supplies all the power semiconductor elements 41 to 46 irrespective of whether a failure of the power semiconductor elements 41 to 46 is detected. A reflux operation may be performed.

(2) Second Embodiment FIG. 9 is a diagram illustrating a configuration of a gate drive device according to a second embodiment. FIG. 10 is a diagram illustrating a configuration of a gate voltage output circuit according to the second embodiment. The power converter 4D of the second embodiment differs from the first embodiment in that a temperature sensor 105 such as a thermistor for measuring the temperature of the power semiconductor element is added. FIG. 9 illustrates a gate driving device 21D that drives a power semiconductor element 41 forming the upper arm of the U phase among the three phases U, V, and W. The power semiconductor element forming the lower arm of the U phase is illustrated in FIG. The same applies to the gate driving device 22D that drives the driving device 42, and the other two-phase power semiconductor devices 43 to 46 and the gate driving device.

  The threshold voltage Vth of the SiC-MOSFET has a temperature characteristic of decreasing at a high temperature and increasing at a low temperature. For this reason, the third voltage (VDD2) also needs to be corrected according to the temperature in accordance with the change in the threshold voltage Vth. As shown in FIG. 10, in the present embodiment, the voltage generation section 119 of the gate voltage output circuit 102 </ b> D is smaller than the threshold voltage Vth that changes depending on the temperature indicated by the temperature signal 120 of the power semiconductor element 41, and And generates a third voltage (VDD2) higher than the voltage (VSS).

  The voltage generator 119 may be implemented by a programmable circuit such as a PLD (Programmable Logic Device). In this case, for example, based on the temperature data obtained by AD (Analog to Digital) conversion of the temperature signal 120, the voltage generation unit 119 refers to a prepared table or the like to generate a third voltage corresponding to the temperature data. Acquisition, DA (Digital to Analog) conversion and output. Alternatively, for example, the voltage generation unit 119 switches a plurality of parallel resistors having different resistance values based on temperature data obtained by AD (Analog to Digital) conversion of the temperature signal 120, or changes the voltage dividing resistor by a regulator. By doing so, the third voltage may be output.

  The gate voltage output circuit 102D applies the third voltage generated in this manner to the gate of the power semiconductor element 41 when detecting an abnormality. As described above, by performing the temperature correction on the third voltage, the return current can be supplied to the power semiconductor module by the substrate bias effect without depending on the temperature, so that the power semiconductor element is stable regardless of the heat generation of the power semiconductor element and the surrounding temperature. As a result, heat generation of the body diode can be suppressed, and destruction of the power semiconductor element can be prevented.

(3) Third Embodiment (3-1) Configuration of Gate Voltage Output Circuit of Third Embodiment FIG. 11 is a diagram illustrating a configuration of a gate voltage output circuit of a third embodiment. The gate voltage output circuit 102F included in the power conversion device according to the third embodiment is different from the first embodiment in that the third voltage (VDD2) is generated by resistance division. When receiving the reflux operation command 118, the gate voltage output circuit 102F turns off the transistors 121 to 122, turns on the transistors 123 to 124, and outputs the third voltage (VDD2) by dividing the resistances of the resistors 133 and 134. A gate voltage 113 is generated and output. According to the present embodiment, there is an advantage that the voltage generation unit 161 for generating the third voltage (VDD2) in the first embodiment can be reduced.

(3-2) Modification of Third Embodiment FIG. 12 shows a modification of generating the third voltage (VDD2) by resistance division. FIG. 12 is a diagram illustrating a configuration of a gate voltage output circuit according to a modification of the third embodiment. The condition under which the third voltage (VDD2) can be output with the configuration of the gate voltage output circuit 102G shown in FIG. 12 is such that the resistance value of the resistor 132 is about several tens mΩ, which is the resistance value when the transistors 122 to 123 are turned on. This is the case where it is sufficiently large (for example, 10Ω or more). Under this condition, the loss in the transistors 122 to 123 is small, and the allowable loss due to heat generation of the transistors 122 to 123 does not cause a problem. In this modification, the transistors 122 to 123 can be turned on to generate and output the third voltage (VDD2) by the voltage division of the resistors 132 and 133. According to this modification, the voltage generation unit 161 can be reduced, and the transistor 124 and the resistor 134 can be reduced from the configuration of the gate voltage output circuit 102F in FIG. 11, so that the gate voltage output circuit and the gate driving device can be further reduced in size. It is possible.

(4) Fourth Embodiment FIG. 13 is a diagram illustrating a configuration of a power conversion device according to a fourth embodiment. As shown in FIG. 13, a railway vehicle 100 </ b> H according to the fourth embodiment includes a current collector 1 that collects power from overhead lines, a filter reactor 2, a filter capacitor 3, a power converter 4, a motor 5, wheels 6, It has a circuit breaker 7, a transformer (transformer) 8, and a converter 9. The converter 9 includes a control unit 61, gate driving devices 27 to 30, and power semiconductor elements 91 to 94. The control unit 61 is connected to the gate driving devices 27 to 30 via a signal line 62.

  The AC voltage input from the current collector 1 connected to the overhead wire is rectified by the power semiconductor elements 91 to 94 and converted into a DC voltage smoothed by the filter capacitor 3. The circuit breaker 7 protects the converter 9 by cutting off the power from the overhead line when an overcurrent and an overvoltage occur.

  The control section 61 outputs a gate command (ON gate command and OFF gate command) for turning on / off each gate of the power semiconductor elements 91 to 94 to the gate driving devices 27 to 30 via the signal line 62. Further, the control unit 61 outputs, via the signal line 62, a reflux operation command for causing the power semiconductor elements 91 to 94 to perform a reflux operation to each of the gate driving devices 27 to 30. Further, the control unit 61 receives, via the signal line 12, a feedback signal indicating the on / off state of each gate of the power semiconductor elements 91 to 94 from the gate driving devices 27 to 30.

  The power semiconductor elements 91 to 94 are SiC-MOSFETs. Each of power semiconductor elements 91 to 92 and 93 to 94 constitutes an upper and lower arm of each phase of the converter.

  The power semiconductor element 91 has a switching element 91a and a body diode 91b connected in parallel to the switching element 91a. In the present embodiment, a portion between the source and the drain of the power semiconductor element 91 that conducts current when the gate is turned on and shuts off current when the gate is turned off is referred to as a switching element 91a. The body diode 91b is a parasitic diode of the power semiconductor element 91. The gate driver 27 is connected to the gate of the switching element 91a. Similarly, the power semiconductor elements 92 to 94 have switching elements 92a to 94a and body diodes 92b to 94b, respectively, as shown in FIG. Gate drivers 28 to 30 are connected to the gates of the switching elements 92a to 94a, respectively.

  The control unit 61 monitors the states of the power semiconductor elements 92 to 94 and determines that the power semiconductor element that has detected a mismatch between the gate command and the feedback signal (FB mismatch) is a failure. When detecting the FB mismatch, the control unit 61 outputs an off gate command 111 to the gate driving devices 27 to 30 to turn off all the power semiconductor elements 91 to 94 and stop the converter 9.

  At this time, since an alternating current from the overhead wire flows into the power semiconductor elements 92 to 94, the current flows through the body diodes 91b to 94b of the power semiconductor elements 92 to 94 when the power semiconductor elements 92 to 94 remain in the off state. ~ 94 is destroyed.

  Therefore, similarly to the control unit 11 of the first embodiment, the control unit 61 returns to the gate driving devices 27 to 30 at a point of time, for example, 0.5 μs or more after all the power semiconductor elements 91 to 94 are turned off. Output operation command. As a result, a part or most of the alternating current from the overhead wire flows through the switching elements 91a to 94a of the power semiconductor elements 92 to 94, so that the current flowing through the body diodes 91b to 94b is reduced and the heat generation is suppressed. The destruction of the elements 91 to 94 can be prevented.

  Note that converter 9 is not limited to a two-level converter, and may be a multi-level converter having three or more levels.

(5) Fifth Embodiment In the first to fourth embodiments, when any abnormality occurs in the power semiconductor element of the power converter, all the power semiconductor elements of the power converter are turned off. However, it is not limited to this. In the fifth embodiment, when any abnormality occurs in the power semiconductor element, the control units 11 and 62 determine whether the power semiconductor element detects the FB mismatch and the power semiconductor element connected in series to the power semiconductor element. As in the first to fourth embodiments, a return operation command is output to the paired arm power semiconductor element composed of. This prevents short-circuit destruction caused by turning on a power semiconductor element connected in series to the failed power semiconductor element, and suppresses current flowing through the body diode to prevent destruction of the power semiconductor element.

  On the other hand, the gate command is turned on at the timing when the return current flows to the power semiconductor element of the pair arm that has not failed, and the synchronous rectification operation of supplying the return current to the switching element side of the power semiconductor element is continued. Thereby, loss and heat generation in the power semiconductor element unrelated to the failure can be suppressed.

  The present invention is not limited to the above-described embodiments and modifications, but may be applied to other forms that can be considered within the technical idea of the present invention without departing from the gist of the present invention. Included in the range. The present invention can be implemented in various forms without departing from the spirit of the present invention. For example, each configuration and each process illustrated in each of the above-described embodiments and each of the modifications may be appropriately integrated or separated according to the implementation mode and the processing efficiency.

4, 4A, 4B, 4B-1, 4C, 4D: power conversion device, 5: electric motor, 9: converter, 11, 61: control unit, 21 to 26, 21 to 21 -4, 22-2 to 22-4, 21D, 22D, 27 to 30... Gate drive devices, 41 to 46, 41-1 to 41-2, 42-1 to 42-2, 41-3 to 41 -6, 91 to 94: power semiconductor element, 41a to 46a, 91a to 94a: switching element, 41b to 46b, 91b to 94b: body diode, 105: temperature sensor, 111, 112 .. Gate command, 113 gate output voltage, 114 gate voltage monitoring signal, 115, 116 feedback signal, 117, 118 reflux operation command.

Claims (16)

A plurality of power semiconductor elements forming a pair of arms; a control unit for outputting a control command for a gate of the plurality of power semiconductor elements; and applying a voltage to the gate in response to the control command to drive the power semiconductor element. And a gate drive device,
The control unit outputs a return operation command to the gate drive device for applying a predetermined voltage for conducting a current in the reverse direction of the power semiconductor element,
The power conversion device, wherein the gate drive device applies the predetermined voltage to all the power semiconductor elements of the paired arms in response to the return operation command. The power conversion device according to claim 1, wherein the control unit outputs the return operation command to the gate drive device when an abnormality is detected in the power conversion device. The control unit, when an abnormality is detected in the power conversion device, after outputting a cutoff command for cutting off the current of the power semiconductor element to the gate drive device, the return operation command to the gate drive device. Output,
The gate drive device, after applying a voltage for interrupting a current in response to the shutoff command to all of the power semiconductor elements of the paired arms, applies the predetermined voltage in response to the return operation command. The power converter according to claim 2, wherein The gate driving device outputs a monitoring result of the state of the gate to the control unit,
4. The power converter according to claim 2, wherein the control unit outputs the recirculation operation command to the gate drive device when the monitoring result indicates an abnormality that does not match the control command. 5. The said predetermined voltage is a voltage which is less than the threshold voltage of the said power semiconductor element, and is larger than the voltage which cuts off the electric current of the said power semiconductor element, and produces a substrate bias effect in the said power semiconductor element. Or the power converter according to 4. The power converter according to claim 5, wherein the predetermined voltage is a voltage that causes a return current to flow between a source and a drain together with a parasitic diode in the power semiconductor element. The control unit outputs the recirculation operation command to the gate drive device after a first predetermined time has elapsed after outputting the shutoff command to the gate drive device. The power converter according to claim 1. The control unit, when conducting a current in a forward direction of the power semiconductor element, applies a current in a forward direction of the power semiconductor element after a second predetermined time has elapsed after applying the predetermined voltage to the power semiconductor element. The power converter according to claim 7, wherein a conduction command for causing the gate drive device to be conducted is output to the gate drive device. Including a plurality of said paired arms,
The control unit outputs the return operation command to apply the predetermined voltage to the power semiconductor elements of all the paired arms to the gate driving device,
The power conversion device according to any one of claims 1 to 8, wherein the gate drive device applies the predetermined voltage to all the power semiconductor elements of the paired arms according to the return operation command. apparatus. Including a plurality of said paired arms,
The control unit outputs the return operation command for applying the predetermined voltage to all the power semiconductor elements of the paired arms including the power semiconductor element whose monitoring result indicates an abnormality to the gate driving device. ,
The said gate drive device applies the said predetermined voltage to all the said power semiconductor elements of the said arm including the said power semiconductor element whose monitoring result shows abnormality according to the said freewheeling operation command. Item 9. The power converter according to any one of Items 4 to 8. The power converter according to any one of claims 1 to 10, wherein the predetermined voltage is corrected according to a temperature of the power semiconductor element detected by a temperature detector. The power converter according to any one of claims 1 to 11, wherein the power semiconductor element is a wide gap semiconductor having a band gap equal to or more than a predetermined value. The power converter according to any one of claims 1 to 12, wherein the power semiconductor elements are connected in parallel in each arm of the paired arms. The power converter according to any one of claims 1 to 13, wherein the power converter is an inverter that converts DC power into AC power. The power converter according to any one of claims 1 to 14, wherein the power converter is a converter that converts AC power into DC power. A plurality of power semiconductor elements forming a pair arm,
A control unit that outputs a control command for the gates of the plurality of power semiconductor elements,
A gate drive device that drives the power semiconductor element by applying a voltage to the gate in accordance with the control command; and a current control method executed in a power conversion device having:
The control unit outputs a return operation command to the gate drive device for applying a predetermined voltage for conducting a current in a reverse direction of the power semiconductor element,
The gate control device applies the predetermined voltage to all of the power semiconductor elements of the paired arms in response to the return operation command.

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