Power conversion device and deterioration detection system

Abstract

A power conversion device (1) comprises: an applied voltage detection unit (23) that detects the voltage applied between main terminals (22a, 22b) of a power semiconductor module (20); a leakage current detection unit (24) that detects a leakage current flowing between the main terminals (22a, 22b) of the power semiconductor module (20); and a breakdown voltage degradation determination unit (33) that determines that there is breakdown voltage degradation in a small number of chips if the leakage current when a prescribed voltage is applied to the power semiconductor module (20) is greater than a first reference value and the rate of change of the leakage current in response to the change in voltage when the prescribed voltage is applied is greater than a second reference value, and determines that there is breakdown voltage degradation in a large number of chips if the leakage current is greater than the first reference value and the rate of change of the leakage current is less than the second reference value.

Description

[Technical Field]

[0001] The present disclosure relates to a power conversion device and a deterioration detection system that include a power semiconductor module that incorporates a plurality of power semiconductor chips. [Background technology]

[0002] The following Patent Document 1 discloses a technology in which a series circuit of two resistors is connected to both ends of a DC charging section in a power conversion device having six semiconductor elements, a current detector is provided between the neutral point of the two resistors and the AC output terminal, a DC voltage is applied when the six semiconductor elements are in the off state, and deterioration of each semiconductor element is determined from the direction and value of the current flowing at that time. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-317277 Summary of the Invention [Problem to be solved by the invention]

[0004] It is known that the leakage current of a power semiconductor module increases as it deteriorates. Therefore, the quality of a power semiconductor module can be evaluated based on the leakage current. The technology of Patent Document 1 can be said to essentially evaluate the leakage current.

[0005] On the other hand, for example, in a power conversion device for a railroad vehicle, a high voltage stress is applied to the power semiconductor module provided in the power conversion device, which poses a risk of the power semiconductor module's withstand voltage degradation. Furthermore, in a power conversion device for a railroad vehicle, since the output power of the power conversion device is large, multiple power semiconductor chips are built into even a single power semiconductor module. Therefore, the leakage current detected in this type of power semiconductor module is the sum of the leakage currents flowing through the multiple power semiconductor chips. Therefore, in the case of a power semiconductor module with multiple power semiconductor chips built in, the technology of Patent Document 1 makes it difficult to distinguish whether an increase in leakage current is caused by a breakdown voltage degradation of a majority of chips or a minority of chips.

[0006] It is believed that the breakdown voltage degradation of the majority chips is likely to occur during the wear-out failure period, while the breakdown voltage degradation of the minority chips is likely to occur outside the wear-out failure period. Therefore, it is significant to distinguish between the breakdown voltage degradation of the majority chips and the breakdown voltage degradation of the minority chips.

[0007] The present disclosure has been made in view of the above, and has an object to provide a power conversion device that can distinguish between breakdown voltage deterioration of a majority chip and breakdown voltage deterioration of a minority chip. [Means for solving the problem]

[0008] To solve the above-mentioned problems and achieve the object, a power conversion device according to the present disclosure is a power conversion device equipped with a power semiconductor module incorporating a plurality of power semiconductor chips, and includes an applied voltage detection unit, a leakage current detection unit, and a withstand voltage degradation determination unit. The applied voltage detection unit detects the voltage applied between the main terminals of the power semiconductor module, and the leakage current detection unit detects the leakage current flowing between the main terminals of the power semiconductor module. The withstand voltage degradation determination unit determines that the withstand voltage degradation of the minority chip has occurred if the leakage current when a specified voltage is applied to the power semiconductor module is greater than a first reference value and the rate of change in the leakage current relative to a voltage change when the specified voltage is applied is greater than a second reference value. Furthermore, the withstand voltage degradation determination unit determines that the withstand voltage degradation of the majority chip has occurred if the leakage current is greater than the first reference value and the rate of change in the leakage current is smaller than the second reference value. [Effects of the Invention]

[0009] The power conversion device according to the present disclosure has the advantage of being able to distinguish between breakdown voltage deterioration of a majority chip and breakdown voltage deterioration of a minority chip. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram showing a configuration example of a railway vehicle equipped with a power conversion device according to a first embodiment; [Figure 2] FIG. 1 is a diagram showing a configuration example of a control device provided in a power conversion device according to a first embodiment; [Figure 3] FIG. 2 is a diagram illustrating an applied voltage detection unit and a leakage current detection unit provided in the power conversion main circuit of the power conversion device according to the first embodiment. [Figure 4] FIG. 10 is a diagram illustrating leakage current characteristics used in the method for determining breakdown voltage degradation in the first embodiment. [Figure 5] FIG. 5 is a diagram illustrating a method for determining breakdown voltage degradation in the first embodiment, which is performed using the leakage current characteristics shown in FIG. [Figure 6] 1 is a flowchart showing a flow of a process for determining breakdown voltage deterioration in the first embodiment. [Figure 7]FIG. 10 is a diagram showing a configuration example of a power conversion main circuit according to a second embodiment; [Figure 8] FIG. 5 is a diagram illustrating the temperature characteristics of the leakage current characteristics shown in FIG. 4. [Figure 9] FIG. 10 is a diagram showing an example of a reference value temperature table used in the method for determining breakdown voltage deterioration in the second embodiment. [Figure 10] FIG. 5 is a diagram illustrating a method for determining breakdown voltage degradation in the third embodiment, which is performed using the leakage current characteristics shown in FIG. 4. [Figure 11] 10 is a flowchart showing a flow of a process for determining breakdown voltage deterioration in the third embodiment. [Figure 12] FIG. 10 is a diagram showing a configuration example of a deterioration detection system according to a fourth embodiment. [Figure 13] FIG. 13 is a diagram showing an example of the configuration of the processing device shown in FIG. 12; [Figure 14] FIG. 10 is a diagram showing a configuration example of a ground device that cooperates with a deterioration detection system according to a fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] A power conversion device and a degradation detection system according to an embodiment of the present disclosure will be described in detail below with reference to the accompanying drawings. In the following description, multiple devices and components of the same type will be denoted by reference numerals with subscripts, but when describing them without distinguishing between them, the subscripts will be omitted as appropriate.

[0012] Embodiment 1 1 is a diagram showing an example of the configuration of a railway vehicle 100 equipped with a power conversion device 1 according to embodiment 1. In Fig. 1, the railway vehicle 100 includes a current collector 102, wheels 103, a transformer 106, the power conversion device 1, and a traction motor 140. The power conversion device 1 also includes a power conversion main circuit 2 and a control device 3.

[0013] The power conversion main circuit 2 includes a converter 110, a main circuit capacitor 120, and a three-phase inverter 130. The transformer 106 is disposed on the input end side of the power conversion main circuit 2 and connected to the converter 110. The propulsion motor 140 is disposed on the output end side of the power conversion main circuit 2 and connected to the three-phase inverter 130. The three-phase inverter 130 converts DC power into AC power for the propulsion motor 140. An induction motor or a synchronous motor is used as the propulsion motor 140.

[0014] One end of the primary winding of the transformer 106 is electrically connected to the overhead line 101 via the current collector 102, and the other end is electrically connected to the rail 104, which is at ground potential, via the wheels 103. The AC power supplied from the overhead line 101 is input to the converter 110 via the current collector 102 and the transformer 106.

[0015] The converter 110 includes four power semiconductor modules UPC, VPC, UNC, and VNC that are connected in a single-phase bridge. The converter 110 converts the input AC voltage into a desired DC voltage and outputs it by controlling the power semiconductor modules UPC, VPC, UNC, and VNC using PWM (Pulse Width Modulation).

[0016] A main circuit capacitor 120, which serves as a DC power supply, is connected in parallel to the output terminal of the converter 110. The main circuit capacitor 120 stores the DC voltage input from the converter 110. A three-phase inverter 130 is connected to the output side of the main circuit capacitor 120.

[0017] The three-phase inverter 130 includes three-phase bridge-connected power semiconductor modules UPI, VPI, WPI, UNI, VNI, and WNI. The three-phase inverter 130 converts the capacitor voltage stored in the main circuit capacitor 120 into a desired AC voltage and applies it to the traction motor 140 by PWM-controlling the power semiconductor modules UPI, VPI, WPI, UNI, VNI, and WNI.

[0018] 1 shows a case where the switching elements provided in the power semiconductor modules UPC, VPC, UNC, and VNC provided in the converter 110 and the power semiconductor modules UPI, VPI, WPI, UNI, VNI, and WNI provided in the three-phase inverter 130 are IGBTs (Insulated Gate Bipolar Transistors), but is not limited to this. Each of these switching elements may be, for example, a MOSFET (Metal Oxide Semiconductor Field Effect Transistor).

[0019] 1 shows an example in which the power conversion device 1 according to the first embodiment is applied to an AC-input electric vehicle, but the power conversion device 1 according to the first embodiment can also be applied to DC-input electric vehicles that are frequently used in subways, suburban electric vehicles, etc. When applied to a DC-input electric vehicle, the same configuration as that shown in FIG. 1 can be adopted, except that the transformer 106 and the converter 110 are not required.

[0020] Although FIG. 1 illustrates the converter 110 and the three-phase inverter 130 both as having a two-level circuit configuration, the present invention is not limited to this circuit configuration. Either one or both of the converter 110 and the three-phase inverter 130 may have a three-level circuit configuration. That is, the converter 110 may be a two-level converter and the three-phase inverter 130 may be a three-level three-phase inverter, or the converter 110 may be a three-level converter and the three-phase inverter 130 may be a two-level three-phase inverter, or the converter 110 may be a three-level converter and the three-phase inverter 130 may be a three-level three-phase inverter. Although FIG. 1 illustrates the case where the AC power supplied from the overhead line 101 is single-phase, the AC power supplied from the overhead line 101 may be three-phase. When the AC power supplied from the overhead line 101 is three-phase, the converter 110 has a three-phase circuit configuration.

[0021] Fig. 2 is a diagram showing a configuration example of the control device 3 provided in the power conversion device 1 according to embodiment 1. As shown in Fig. 2, the control device 3 includes a storage unit 31, a display unit 32, and a withstand voltage degradation determination unit 33. The functions of these units will be described in detail later.

[0022] The withstand voltage degradation determination unit 33 can be realized by a processing circuit having a processor and a program memory. The program memory stores a program for executing the processing of the withstand voltage degradation determination unit 33. The processor executes the processing of the withstand voltage degradation determination unit 33 by reading and executing the program stored in the program memory. Alternatively, the withstand voltage degradation determination unit 33 may be realized by a dedicated processing circuit instead of the processor and program memory. Examples of the dedicated processing circuit include a field programmable gate array (FPGA), an application specific integrated circuit (ASIC), and a microcomputer. The storage unit 31 can be realized by a non-volatile or volatile semiconductor memory such as a random access memory (RAM), a flash memory, an erasable programmable read only memory (EPROM), or an electrically EEPROM (registered trademark), or a magnetic disk, an optical disk, a digital versatile disc (DVD), or the like. The determination result by the withstand voltage degradation determination unit 33 can be stored in the storage unit 31. The display unit 32 may be configured to be able to display the determination result by the withstand voltage degradation determination unit 33, and may have a simple display function such as a small liquid crystal display screen or an LED (Light Emitting Diode) lamp.

[0023] Fig. 3 is a diagram illustrating an applied voltage detection unit 23 and a leakage current detection unit 24 provided in the power conversion main circuit 2 of the power conversion device 1 according to the first embodiment. Fig. 3 shows a power semiconductor module 20, a main circuit capacitor 120, and a converter 110 provided in the power conversion main circuit 2. The power semiconductor module 20 represents any one of the power semiconductor modules UPC, VPC, UNC, and VNC provided in the converter 110 of Fig. 1, or any one of the power semiconductor modules UPI, VPI, WPI, UNI, VNI, and WNI provided in the three-phase inverter 130. The power semiconductor module 20 includes a plurality of power semiconductor chips 21.

[0024] 3 also shows an applied voltage detection unit 23 and a leakage current detection unit 24 provided in the power conversion main circuit 2. The leakage current detection unit 24 includes a current sensor 24a and a detection value acquisition unit 24b. In the converter 110, it is desirable to provide the applied voltage detection unit 23 and the leakage current detection unit 24 in all of the power semiconductor modules UPC, VPC, UNC, and VNC, but due to storage space constraints or cost reduction, they may be provided in any one of the power semiconductor modules UPC, VPC, UNC, and VNC. The same applies to the three-phase inverter 130. Furthermore, FIG. 3 shows a withstand voltage degradation determination unit 33 provided in the control device 3.

[0025] The applied voltage detection unit 23 detects the voltage applied between the main terminals 22a and 22b of the power semiconductor module 20. The main terminals 22a and 22b are each one of the main terminals provided on the power semiconductor module 20. The main terminal 22a is a terminal electrically connected to, for example, the collector of the power semiconductor chip 21, and the main terminal 22b is a terminal electrically connected to, for example, the emitter of the power semiconductor chip 21. The main circuit capacitor 120 applies a DC voltage to the power semiconductor module 20 when the power semiconductor module 20 is in an off state. The magnitude of the applied voltage applied from the main circuit capacitor 120 to the power semiconductor module 20 can be adjusted by adjusting the magnitude of the voltage stored in the main circuit capacitor 120. The magnitude of the voltage stored in the main circuit capacitor 120 can be adjusted in advance by the control device 3 switching-driving the power semiconductor module 20 of the converter 110.

[0026] When the power semiconductor module 20 is in an off state, i.e., when the power semiconductor module 20 is gate-off driven, a voltage is applied between the main terminals 22a and 22b of the power semiconductor module 20, and a leakage current flows between the main terminals 22a and 22b depending on the deterioration state of the power semiconductor module 20. The current sensor 24a of the leakage current detection unit 24 detects the current at this time. The detection value acquisition unit 24b acquires the detection value of the current sensor 24a and transmits it to the withstand voltage degradation determination unit 33 of the control device 3. The withstand voltage degradation determination unit 33 determines whether or not the withstand voltage degradation has occurred in the power semiconductor module 20 by comparing the leakage current and the rate of change in the leakage current relative to a voltage change with reference values. The measurement of the leakage current and the determination of whether or not the withstand voltage degradation has occurred can be performed before the start of work of the railway vehicle 100, i.e., immediately before the railway vehicle 100 leaves the railroad depot, or after the end of work of the railway vehicle 100, i.e., immediately after the railway vehicle 100 enters the railroad depot.

[0027] While FIG. 3 illustrates an example in which the applied voltage detection unit 23 and the leakage current detection unit 24 are provided in the power conversion main circuit 2, the present invention is not limited to this example. A dedicated measuring device including the applied voltage detection unit 23 and the leakage current detection unit 24 may be prepared, and the presence or absence of withstand voltage degradation in the power semiconductor module 20 may be determined using the measuring device. Measurement of the leakage current and determination of the presence or absence of withstand voltage degradation using the dedicated measuring device may be performed during maintenance of the railway vehicle 100. If the applied voltage detection unit 23 and the leakage current detection unit 24 are provided inside the power conversion main circuit 2, the applied voltage detection unit 23 and the leakage current detection unit 24 are subject to size, weight, and cost constraints of the power conversion main circuit 2. In contrast, if a dedicated measuring device is used, the applied voltage detection unit 23 and the leakage current detection unit 24 are not subject to size, weight, and cost constraints of the power conversion main circuit 2. Therefore, a configuration using a dedicated measuring device can improve the accuracy of determining the presence or absence of withstand voltage degradation compared to a configuration in which the applied voltage detection unit 23 and the leakage current detection unit 24 are provided in the power conversion main circuit 2.

[0028] Here, we will provide additional information regarding breakdown voltage degradation in the power semiconductor module 20. For the power semiconductor module 20, the manufacturer determines a breakdown voltage specification value, which includes a specified voltage that is a specified applied voltage, a maximum value of leakage current when the specified voltage is applied, and the like. Therefore, if the leakage current when the specified voltage is applied exceeds the breakdown voltage specification value, it can be determined that breakdown voltage degradation has occurred, that is, that the power semiconductor module 20 has breakdown voltage degradation. Note that, in order to ensure a certain degree of margin, a value lower than the breakdown voltage specification value may be set as a determination threshold, and the presence or absence of breakdown voltage degradation may be determined based on this determination threshold.

[0029] Fig. 4 is a diagram illustrating leakage current characteristics used in the method for determining breakdown voltage degradation in the first embodiment. The horizontal axis of Fig. 4 represents the applied voltage applied between main terminals 22a and 22b, and the vertical axis represents the leakage current flowing at that time. Fig. 4 shows three leakage current characteristics that change depending on the degradation state of power semiconductor module 20. Specifically, the solid line represents the leakage current characteristic when power semiconductor module 20 is healthy, the dashed line represents the leakage current characteristic when power semiconductor module 20 is mildly degraded, and the dashed line represents the leakage current characteristic when power semiconductor module 20 is severely degraded.

[0030] First, when the power semiconductor module 20 deteriorates, the curve shown by the solid line transitions to either the curve shown by the dashed line or the curve shown by the alternate long and short dash line depending on the state of deterioration. The severe leakage current characteristic shown by the dashed line is due to breakdown voltage degradation of a minority of the multiple power semiconductor chips 21. Here, "minority" means "one" or at most "two." Furthermore, the mild leakage current characteristic shown by the alternate long and short dash line is due to breakdown voltage degradation of a majority of the multiple power semiconductor chips 21. Here, "majority" means "all" or "most." In other words, a determination that breakdown voltage degradation of a majority of the chips is present means that all or most of the power semiconductor chips 21 built into the power semiconductor module 20 are considered to be experiencing breakdown voltage degradation. In this paper, when it is determined that a power semiconductor chip 21 is experiencing breakdown voltage degradation, if the determination result is not breakdown voltage degradation of a minority of the chips, the power semiconductor chip 21 is determined to be breakdown voltage degradation of a majority of the chips.

[0031] 4, as the deterioration state of the power semiconductor module 20 progresses, the leakage current exhibits a characteristic of increasing sharply. The applied voltage at which the leakage current increases sharply varies depending on the deterioration state of the power semiconductor module 20, and the applied voltage at which the leakage current increases sharply is lower when the breakdown voltage of a few chips is decreased than when the breakdown voltage of a majority chip is decreased. As described above, the leakage current detected in one power semiconductor module 20 is the total value of the currents flowing through the multiple power semiconductor chips 21. For this reason, the leakage current is more sensitive to the applied voltage when the breakdown voltage of a few chips is decreased than when the breakdown voltage of a majority chip is decreased, and exhibits a characteristic of increasing sharply at a lower applied voltage.

[0032] FIG. 5 is a diagram illustrating a method for determining breakdown voltage degradation in the first embodiment, which is performed using the leakage current characteristics shown in FIG. 4. FIG. 5 shows the three leakage current characteristics shown in FIG. 4. The vertical axis of FIG. 5 shows a first reference value, which is a determination threshold for determining the magnitude of the leakage current. The horizontal axis of FIG. 5 shows a specified voltage for the first reference value. The specified voltage is a voltage higher than the normal operating voltage applied to the power conversion device 1, and is determined in relation to the first reference value. The first reference value is set to a value higher than the leakage current detected when the power semiconductor module 20 is healthy. The first reference value is stored in the memory unit 31 together with a second reference value, which will be described later.

[0033] The withstand voltage degradation determination unit 33 determines whether the leakage current exceeds a first reference value each time a leakage current is detected. Point A on the leakage current characteristic shown in FIG. 5 indicates the time when the leakage current reaches the first reference value. At this point, it is unclear whether the degradation of the power semiconductor module 20 is due to withstand voltage degradation of the majority chip or the minority chip. Therefore, the withstand voltage degradation determination unit 33 further compares the rate of change in the leakage current with a second reference value. FIG. 5 shows an enlarged view of point A. The second reference value refers to the slope of the solid line in the enlarged view. The second reference value is set to a value smaller than the slope of the tangent line at point A on the leakage current characteristic of the minority chip shown by the dashed line and larger than the slope of the tangent line at point A on the leakage current characteristic of the majority chip shown by the dashed line. Using such a second reference value, it is possible to determine whether the degradation of the power semiconductor module 20 is due to withstand voltage degradation of the majority chip or the minority chip.

[0034] FIG. 6 is a flowchart showing a process for determining breakdown voltage degradation in the first embodiment. First, under the control of the control device 3, the main circuit capacitor 120 applies a specified voltage between the main terminals 22a and 22b (step S11), and the leakage current detection unit 24 detects the leakage current when the specified voltage is applied (step S12). The processes in steps S11 and S12 are described in more detail below. The control device 3 controls the converter 110 to sweep the voltage stored in the main circuit capacitor 120 around the specified voltage so that the voltage includes the specified voltage. Alternatively, the control device 3 controls the converter 110 so that the voltage stored in the main circuit capacitor 120 is slightly higher than the specified voltage. Thereafter, the control device 3 stops the operation of the converter 110. The voltage stored in the main circuit capacitor 120 decreases due to natural discharge and reaches the specified voltage. The applied voltage detection unit 23 notifies the control device 3 of a first time when the voltage between the main terminals 22a and 22b reaches the specified voltage. The control device 3 determines the output value of the leakage current detector 24 detected at the first time as the detected value of the leakage current.

[0035] The withstand voltage degradation determination unit 33 determines whether the leakage current is greater than a first reference value (step S13). If the leakage current is equal to or less than the first reference value (step S13, No), the withstand voltage degradation determination unit 33 determines that all chips are healthy (step S14), and ends the flow of FIG. 6. If the leakage current is greater than the first reference value (step S13, Yes), the withstand voltage degradation determination unit 33 determines whether the rate of change in the leakage current is greater than a second reference value (step S15). If the rate of change in the leakage current is greater than the second reference value (step S15, Yes), the withstand voltage degradation determination unit 33 determines that the withstand voltage degradation of a minority of chips has occurred (step S16), and ends the flow of FIG. 6. If the rate of change in the leakage current is equal to or less than the second reference value (step S15, No), the withstand voltage degradation determination unit 33 determines that the withstand voltage degradation of a majority of chips has occurred (step S17), and ends the flow of FIG. 6. The determination results of steps S14, S16, and S17 can be displayed on the display unit 32.

[0036] As described above, the power conversion device according to the first embodiment includes an applied voltage detection unit, a leakage current detection unit, and a withstand voltage degradation determination unit. The applied voltage detection unit detects the voltage applied between the main terminals of the power semiconductor module, and the leakage current detection unit detects the leakage current flowing between the main terminals of the power semiconductor module. The withstand voltage degradation determination unit determines that the withstand voltage degradation of the minority chip has occurred if the leakage current when a specified voltage is applied to the power semiconductor module is greater than a first reference value and the rate of change in the leakage current relative to a voltage change when the specified voltage is applied is greater than a second reference value. Furthermore, the withstand voltage degradation determination unit determines that the withstand voltage degradation of the majority chip has occurred if the leakage current is greater than the first reference value and the rate of change in the leakage current is smaller than the second reference value. As such, the power conversion device according to the first embodiment includes a withstand voltage degradation determination unit that, when it determines that the withstand voltage degradation has occurred, further compares the rate of change in the leakage current with the second reference value. This makes it possible to distinguish between the withstand voltage degradation of the majority chip and the withstand voltage degradation of the minority chip. Although the applied voltage detection unit is connected between the main terminals of the power semiconductor module in the above description, the applied voltage detection unit may be connected to a capacitor. Any configuration is possible as long as the applied voltage detection unit detects the capacitor voltage, thereby directly or indirectly determining the voltage applied between the main terminals of the power semiconductor module.

[0037] Embodiment 2 In the first embodiment, a method for distinguishing between breakdown voltage degradation of a majority chip and breakdown voltage degradation of a minority chip using two reference values, a first reference value and a second reference value, has been described. However, these values ​​are considered to be affected by the temperature of the power semiconductor module 20 or the ambient temperature. Therefore, in the second embodiment, a control method that takes into account the influence of these temperatures will be described.

[0038] Fig. 7 is a diagram showing a configuration example of the power conversion main circuit 2 according to embodiment 2. Fig. 7 shows the configuration of the power conversion main circuit 2 according to embodiment 1 shown in Fig. 3, in which a temperature detector 25 capable of detecting the temperature of the power semiconductor module 20 or the ambient temperature is provided. The temperature detector 25 may be any device capable of directly or indirectly detecting the temperature of the power semiconductor chip 21, and may be provided inside the power semiconductor module 20 or, as shown in the figure, outside the power semiconductor module 20. Note that the other configurations are the same or equivalent to those in Fig. 3, and the same or equivalent components are designated by the same reference numerals, and duplicated explanations will be omitted.

[0039] Fig. 8 is a diagram illustrating the temperature characteristics of the leakage current characteristics shown in Fig. 4. As shown in Fig. 8, the leakage current of the power semiconductor chip 21 varies depending on the chip temperature, with the leakage current increasing as the temperature increases. Furthermore, the leakage current of the power semiconductor chip 21 has a characteristic that the difference in leakage current increases as the applied voltage increases. Therefore, it is a preferred embodiment to set the first reference value and the second reference value described in the first embodiment in consideration of the temperature characteristics of the leakage current characteristics.

[0040] Therefore, in the second embodiment, the process of determining the withstand voltage deterioration is performed using the table shown in Fig. 9. Fig. 9 is a diagram showing an example of a reference value temperature table used in the method of determining the withstand voltage deterioration in the second embodiment. The reference value temperature table shown in Fig. 9 can be stored in the storage unit 31.

[0041] 9 shows chip temperatures Tc1, Tc2, Tc3, ..., TcN of the power semiconductor chip 21. The reference value temperature table is a table showing the first reference value and the second reference value in correspondence with the chip temperatures Tc1 to TcN of the power semiconductor chip 21.

[0042] The table values ​​of the first reference values ​​(th11, th12, th13, ..., th1N) and the table values ​​of the second reference values ​​(th21, th22, th23, ..., th2N) in the reference value temperature table can be obtained by prior measurement. In addition, the reference value temperature table can be provided for each model of the power semiconductor module 20.

[0043] The intervals between the chip temperatures Tc1, Tc2, Tc3, ..., TcN do not need to be equal, but may be unequal. Also, all of the table values ​​in the reference value temperature table do not need to be determined by prior measurement, but may be determined by calculation using interpolation, extrapolation, or interpolation of several measured values.

[0044] In the second embodiment, the control device 3 estimates the temperature of the power semiconductor chip 21 in the power semiconductor module 20 based on the detection value of the temperature detector 25. The withstand voltage degradation determination unit 33 of the control device 3 refers to the reference value temperature table and reads out a first reference value and a second reference value corresponding to the estimated temperature value of the power semiconductor chip 21. The withstand voltage degradation determination unit 33 performs the withstand voltage degradation determination process described in the first embodiment using the read out first reference value and second reference value. Note that if the detection value of the temperature detector 25 is not in the reference value temperature table, the first reference value and the second reference value can be found by interpolation, extrapolation, or interpolation.

[0045] As described above, the power conversion device according to the second embodiment includes a temperature detector that can directly or indirectly detect the temperature of the power semiconductor chip. The withstand voltage degradation determination unit performs a process of changing the first reference value and the second reference value based on the value detected by the temperature detector. This process enables the power conversion device according to the second embodiment to perform a process of determining withstand voltage degradation that takes into account the temperature characteristics of the leakage current characteristics. This enables the power conversion device according to the second embodiment to improve the accuracy of the process of determining withstand voltage degradation.

[0046] Embodiment 3 In the third embodiment, an example will be described in which the determination results obtained in the first and second embodiments are applied to the control of the power conversion device 1.

[0047] FIG. 10 is a diagram illustrating a method for determining breakdown voltage degradation in the third embodiment, which is performed using the leakage current characteristics shown in FIG. 4. FIG. 10 illustrates the three leakage current characteristics shown in FIG. 4. The vertical axis of FIG. 10 illustrates the first reference value shown in FIG. 4 as well as a third reference value and a fourth reference value, which are determination thresholds for determining the magnitude of leakage current. The third reference value is a determination threshold greater than the first reference value, and the fourth reference value is a determination threshold greater than the first and third reference values. The horizontal axis of FIG. 10 illustrates the specified voltages for the first, third, and fourth reference values, which are the same voltage value. The specified voltages are higher than the normal operating voltage applied to the power conversion device 1. The specified voltages for the third and fourth reference values ​​may be different from the specified voltage for the first reference value. The third and fourth reference values ​​are stored in the storage unit 31 together with the first and second reference values. Furthermore, the storage unit 31 may also have a reference value temperature table showing the correspondence relationship between the third and fourth reference values ​​and the chip temperatures Tc1 to TcN as shown in FIG.

[0048] Next, a description will be given of the process of determining breakdown voltage degradation in the embodiment 3. Fig. 11 is a flowchart showing the flow of the process of determining breakdown voltage degradation in the embodiment 3. The process flow in Fig. 11 is carried out following the process flow in Fig. 6.

[0049] First, if no breakdown voltage degradation is detected in the process flow of FIG. 6 (step S21, No), the process flow of FIG. 11 is terminated. On the other hand, if breakdown voltage degradation is detected in the process flow of FIG. 6 (step S21, Yes), and the detected breakdown voltage degradation is breakdown voltage degradation of a minority of chips (step S22, Yes), the breakdown voltage degradation determination unit 33 determines whether the leakage current is greater than a third reference value (step S23). If the leakage current is equal to or less than the third reference value (step S23, No), the flow of FIG. 11 is terminated. On the other hand, if the leakage current is greater than the third reference value (step S23, Yes), the breakdown voltage degradation determination unit 33 takes action to prohibit the application of voltage to the power semiconductor module 20 in which breakdown voltage degradation has been detected (step S24), and then terminates the flow of FIG. 11. Also, if the detected breakdown voltage degradation is not breakdown voltage degradation of a minority of chips in the process flow of FIG. 6 (step S22, No), the detected breakdown voltage degradation corresponds to breakdown voltage degradation of a majority of chips. In this case, the withstand voltage degradation determination unit 33 determines whether the leakage current is greater than a fourth reference value (step S25). If the leakage current is equal to or less than the fourth reference value (step S25, No), the flow of FIG. 11 ends. On the other hand, if the leakage current is greater than the fourth reference value (step S25, Yes), the withstand voltage degradation determination unit 33 takes measures to prohibit the application of voltage thereafter to the power semiconductor module 20 in which withstand voltage degradation has been detected (step S24), and then ends the flow of FIG. 11. The determination results of steps S23 and S25 can be displayed on the display unit 32.

[0050] A supplementary explanation will be given regarding the processing flow of FIG. 11. First, as described above, breakdown voltage degradation of a small number of chips is severe breakdown voltage degradation, while breakdown voltage degradation of a large number of chips is mild breakdown voltage degradation. For this reason, the third reference value used in the case of breakdown voltage degradation of a small number of chips is set smaller than the fourth reference value used in the case of breakdown voltage degradation of a large number of chips, making it a stricter judgment reference value. Furthermore, since prohibiting application of voltage to the power semiconductor module 20 leads to a deterioration in the functionality of the power conversion device 1, an appropriate response is required, which prohibits application of voltage when necessary and does not prohibit application when unnecessary. For this reason, by using the third and fourth reference values ​​larger than the first reference value, the measure of prohibiting application of voltage to the power semiconductor module 20 is limited to only when truly necessary.

[0051] As described above, in the power conversion device according to the third embodiment, when the withstand voltage degradation determination unit detects withstand voltage degradation of a minority chip, it compares the leakage current of the power semiconductor module in which the withstand voltage degradation of the minority chip is detected with a third reference value, and if the leakage current is greater than the third reference value, it takes action to prohibit application of voltage to the power semiconductor module. Furthermore, when the withstand voltage degradation determination unit detects withstand voltage degradation of a majority chip, it compares the leakage current of the power semiconductor module in which the withstand voltage degradation of the majority chip is detected with a fourth reference value, and if the leakage current is greater than the fourth reference value, it takes action to prohibit application of voltage to the power semiconductor module. The third and fourth reference values ​​are determination thresholds greater than the first reference value, and the fourth reference value is a determination threshold greater than the third reference value. In the power conversion device according to the third embodiment, in the determination process for prohibiting application of voltage to the power semiconductor module, different determination thresholds are used for the withstand voltage degradation of the majority chip and the withstand voltage degradation of the minority chip. This makes it possible to limit the action of prohibiting application of voltage to the power semiconductor module to only cases where it is truly necessary.

[0052] Embodiment 4 FIG. 12 is a diagram illustrating a configuration example of a deterioration detection system 80 according to a fourth embodiment. FIG. 12 illustrates four power electronics devices 1a to 1d mounted on a railway vehicle, a processing device 50, and a ground device 60. The power electronics devices 1a to 1d are equipped with control devices 3a to 3d, respectively. The deterioration detection system 80 is configured with these power electronics devices 1a to 1d, the processing device 50, and the ground device 60. The processing device 50 is connected to a communication network 8 so as to be able to receive information from the power electronics devices 1a to 1d. The processing device 50 is also configured to be able to communicate with the ground device 60. The communication network 8 is one means of data transmission and is not limited to a wired system. Although FIG. 12 illustrates four power electronics devices 1a to 1d as an example, the present invention is not limited to this example. That is, the number of power electronics devices 1 may be two or three, or may be five or more.

[0053] Fig. 13 is a diagram showing an example of the configuration of the processing device 50 shown in Fig. 12. The processing device 50 receives and stores data relating to the determination results of the withstand voltage degradation determination in the power semiconductor module 20 from each power conversion device 1. To realize this function, the processing device 50 includes a storage unit 51 and a communication unit 52, as shown in Fig. 13.

[0054] The storage unit 51 can be realized by a non-volatile or volatile semiconductor memory such as RAM, flash memory, EPROM, or EEPROM (registered trademark), or a magnetic disk, optical disk, DVD, etc. The communication unit 52 is a receiver and transmitter that perform communication processing. Note that the configuration in FIG. 13 is an example, and the configuration of the device is not limited to the example in FIG. 13.

[0055] The functions of the processing device 50 may be implemented in a train information management device that manages train information transmitted inside the vehicle. Existing train information management devices have a communication function with the power conversion device 1 and a communication function with the ground. Therefore, by using an existing train information management device, the cost of building the system can be reduced.

[0056] 14 is a diagram illustrating an example of the configuration of a ground device that cooperates with a deterioration detection system 80 according to embodiment 4. The ground device 60 includes a receiving unit 61, a storage unit 62, an estimation unit 63, and an output unit 64.

[0057] The receiving unit 61 includes a receiver that performs communication processing, and receives data related to the determination result of the withstand voltage degradation determination from the processing device 50 of the degradation detection system 80. The memory unit 62 stores the received data related to the determination result. When storing the data related to the determination result, the memory unit 62 stores the data in association with an identification number for identifying the vehicle and the power conversion device 1.

[0058] The estimation unit 63 performs processing to estimate future breakdown voltage degradation of the power semiconductor chip for each power conversion device 1 and each power semiconductor module 20 based on the information stored in the storage unit 62. The function of the estimation unit 63 can be realized by a processor such as a CPU (Central Processing Unit). The processor executes a program in which the processing is described. The storage unit 62 also stores the program to be executed by the estimation unit 63, necessary data obtained during the processing, and the like. The storage unit 62 is also used as a temporary storage area for the program.

[0059] The output unit 64 includes a display, a liquid crystal display panel, a printer, etc., and displays the estimation result by the estimation unit 63 on a screen or provides it to the user of the computer system on a paper medium. Note that the configuration in Fig. 14 is an example, and the configuration of the device is not limited to the example in Fig. 14.

[0060] As described above, the deterioration detection system according to the fourth embodiment includes any one of the power conversion devices described in the first to third embodiments, a processing device that receives information transmitted from the power conversion device via a communication network within a railway vehicle on which the power conversion device is mounted, and a ground device that cooperates with the processing device. The ground device includes a receiving unit, a memory unit, an estimating unit, and an output unit. The receiving unit receives information related to the leakage current detection results for each power conversion device and the detection results of the applied voltage detecting unit via the processing device. The memory unit stores the received information related to the detection results. The estimating unit estimates future breakdown voltage degradation of the power semiconductor chips for each power conversion device and each power semiconductor module based on the information stored in the memory unit. The output unit outputs or displays the estimation results by the estimating unit. The deterioration detection system according to the fourth embodiment allows the ground device to be configured as a computer system and allows the ground device to centrally manage data related to the breakdown voltage degradation state of the power semiconductor modules of the power conversion devices. This makes it possible to enjoy the effect of making management of the power conversion devices easier than in the first embodiment.

[0061] The configurations shown in the above embodiments are merely examples, and may be combined with other known technologies, or different embodiments may be combined with each other. It is also possible to omit or modify parts of the configurations as long as they do not deviate from the gist of the invention. Various aspects of the present disclosure are summarized below as appendices. [Appendix 1] A power conversion device equipped with a power semiconductor module incorporating a plurality of power semiconductor chips, an applied voltage detection unit that detects a voltage applied between main terminals of the power semiconductor module; a leakage current detection unit that detects a leakage current flowing between main terminals of the power semiconductor module; a breakdown voltage degradation determination unit that determines that breakdown voltage degradation has occurred in a minority chip when a leakage current when a specified voltage is applied to the power semiconductor module is greater than a first reference value and a rate of change in the leakage current with respect to a voltage change when the specified voltage is applied is greater than a second reference value, and that breakdown voltage degradation has occurred in a majority chip when the leakage current is greater than the first reference value and a rate of change in the leakage current with respect to a voltage change when the specified voltage is applied is less than the second reference value; A power conversion device comprising: [Appendix 2] a temperature detector capable of directly or indirectly detecting the temperature of the power semiconductor chip; The withstand voltage deterioration determination unit changes the first reference value and the second reference value based on the detected value of the temperature detector. 2. The power conversion device according to claim 1, [Appendix 3] The withstand voltage degradation determination unit When a breakdown voltage degradation of a minority of chips is detected, in the power semiconductor module in which the breakdown voltage degradation of the minority of chips is detected, the leakage current is compared with a third reference value, and when the leakage current is greater than the third reference value, application of voltage to the power semiconductor module is prohibited; When a breakdown voltage degradation of a large number of chips is detected, in the power semiconductor module in which the breakdown voltage degradation of the large number of chips is detected, the leakage current is compared with a fourth reference value, and when the leakage current is greater than the fourth reference value, application of voltage to the power semiconductor module is prohibited; The third reference value and the fourth reference value are greater than the first reference value, and the fourth reference value is greater than the third reference value. 3. The power conversion device according to claim 1 or 2. [Appendix 4] Each of the power conversion devices includes a display unit configured to be able to display the determination result by the withstand voltage degradation determination unit. 4. The power conversion device according to claim 1, wherein: [Appendix 5] A deterioration detection system including: a power conversion device according to any one of Supplementary Notes 1 to 4; a processing device that receives information transmitted from the power conversion device through a communication network in a railway vehicle on which the power conversion device is mounted; and a ground device that cooperates with the processing device, the ground device includes a receiving unit that receives information about the detection result of the leakage current for each of the power conversion devices and the detection result of the applied voltage detecting unit via the processing device; a storage unit that stores information about the received detection result; an estimation unit that estimates future breakdown voltage degradation of the power semiconductor chip for each of the power conversion devices and each of the power semiconductor modules based on the information stored in the storage unit; an output unit that outputs or displays an estimation result by the estimation unit; A deterioration detection system comprising: [Explanation of symbols]

[0062] 1, 1a to 1d power conversion device, 2 power conversion main circuit, 3, 3a to 3d control device, 8 communication network, 20, UPC, VPC, UNC, VNC, UPI, VPI, WPI, UNI, VNI, WNI power semiconductor module, 21 power semiconductor chip, 22a, 22b main terminal, 23 applied voltage detection unit, 24 leakage current detection unit, 24a current sensor, 24b detection value acquisition unit, 25 temperature detector, 31, 51, 62 memory unit, 32 display unit, 33 withstand voltage deterioration determination unit, 50 processing device, 52 communication unit, 60 ground equipment, 61 receiving unit, 63 estimation unit, 64 output unit, 80 deterioration detection system, 100 railway vehicle, 101 overhead line, 102 current collector, 103 wheel, 104 rail, 106 transformer, 110 converter, 120 main circuit capacitor, 130 three-phase inverter, 140 propulsion motor.

Claims

1. A power conversion device equipped with a power semiconductor module incorporating a plurality of power semiconductor chips, an applied voltage detection unit that detects a voltage applied between main terminals of the power semiconductor module; a leakage current detection unit that detects a leakage current flowing between main terminals of the power semiconductor module; a withstand voltage degradation determination unit that determines that the withstand voltage degradation of the minority chip has occurred when a leakage current when a specified voltage is applied to the power semiconductor module is greater than a first reference value and a rate of change in the leakage current with respect to a voltage change when the specified voltage is applied is greater than a second reference value, and that the withstand voltage degradation of the majority chip has occurred when the leakage current is greater than the first reference value and a rate of change in the leakage current with respect to a voltage change when the specified voltage is applied is less than the second reference value; A power conversion device comprising:

2. a temperature detector capable of directly or indirectly detecting the temperature of the power semiconductor chip; The withstand voltage deterioration determination unit changes the first reference value and the second reference value based on the detected value of the temperature detector.

2. The power conversion device according to claim 1.

3. The withstand voltage degradation determination unit When a breakdown voltage degradation of a minority chip is detected, in the power semiconductor module in which the breakdown voltage degradation of the minority chip is detected, the leakage current is compared with a third reference value, and when the leakage current is greater than the third reference value, application of a voltage to the power semiconductor module is prohibited; When a breakdown voltage degradation of a large number of chips is detected, in the power semiconductor module in which the breakdown voltage degradation of the large number of chips is detected, the leakage current is compared with a fourth reference value, and when the leakage current is greater than the fourth reference value, application of a voltage to the power semiconductor module is prohibited; The third reference value and the fourth reference value are greater than the first reference value, and the fourth reference value is greater than the third reference value.

2. The power conversion device according to claim 1.

4. The withstand voltage deterioration determination unit When a breakdown voltage degradation of a minority chip is detected, in the power semiconductor module in which the breakdown voltage degradation of the minority chip is detected, the leakage current is compared with a third reference value, and when the leakage current is greater than the third reference value, application of a voltage to the power semiconductor module is prohibited; When a breakdown voltage degradation of a large number of chips is detected, in the power semiconductor module in which the breakdown voltage degradation of the large number of chips is detected, the leakage current is compared with a fourth reference value, and when the leakage current is greater than the fourth reference value, application of a voltage to the power semiconductor module is prohibited; The third reference value and the fourth reference value are greater than the first reference value, and the fourth reference value is greater than the third reference value.

3. The power conversion device according to claim 2.

5. Each of the power conversion devices includes a display unit configured to be able to display the determination result by the withstand voltage degradation determination unit.

2. The power conversion device according to claim 1.

6. Each of the power conversion devices includes a display unit configured to be able to display a determination result by the withstand voltage degradation determination unit.

3. The power conversion device according to claim 2.

7. Each of the power conversion devices includes a display unit configured to be able to display a determination result by the withstand voltage degradation determination unit.

4. The power conversion device according to claim 3.

8. Each of the power conversion devices includes a display unit configured to be able to display a determination result by the withstand voltage degradation determination unit.

5. The power conversion device according to claim 4.

9. 9. A deterioration detection system comprising: the power conversion device according to claim 1; a processing device that receives information transmitted from the power conversion device through a communication network in a railway vehicle on which the power conversion device is mounted; and a ground device that cooperates with the processing device, the ground device includes a receiving unit that receives information about the detection result of the leakage current for each of the power conversion devices and the detection result of the applied voltage detecting unit via the processing device; a storage unit that stores information about the received detection result; an estimation unit that estimates future breakdown voltage degradation of the power semiconductor chip for each of the power conversion devices and each of the power semiconductor modules based on the information stored in the storage unit; an output unit that outputs or displays an estimation result by the estimation unit; A deterioration detection system comprising:

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