Power conversion device and diagnostic method of power conversion device

Abstract

To provide a power conversion device which detects leak current of a semiconductor switching element with a simple configuration.SOLUTION: A power conversion device comprises: an upper arm comprising a first semiconductor switching element 1; a lower arm comprising a second semiconductor switching element 2; a first control unit 13 which controls the upper and lower arms; a first current detector 25 connected in parallel with the first semiconductor switching element; and a second current detector 26 connected in parallel with the second semiconductor switching element. The first current detector comprises: a first current detection element 18; and a third semiconductor switching element 16 connected in series with the first current detection element. The second current detector comprises: a second current detection element 19; and a fourth semiconductor switching element 17 connected in series with the second current detection element. A second control unit 22 controls the third semiconductor switching element and the fourth semiconductor switching element.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a configuration of a power conversion device and a diagnostic method thereof, and particularly relates to a technique effective for diagnosing semiconductor switching elements constituting the power conversion device.

Background Art

[0002] Power conversion devices used for controlling motors for railways and large industrial equipment, and power conversion devices used for high-capacity frequency conversion such as for power systems, perform power control of high voltage and large current using high-capacity power semiconductor elements.

[0003] In such devices, if a failure occurs during operation, system damage or an unplanned system stop may occur, resulting in a large economic loss. For the purpose of preventing such a situation, it is necessary to detect deterioration and abnormal signs of the power conversion device, prevent destruction due to function stop, notify relevant parties of the necessity to update the device, and perform life extension control of the power conversion device.

[0004] As one of the failure factors of the power conversion device, destruction of the semiconductor switching elements constituting the power conversion device is known. As one of the destruction factors of the semiconductor switching elements, breakdown voltage failure due to an increase in leakage current during voltage blocking is known.

[0005] For the purpose of preventing destruction of semiconductor switching elements due to breakdown voltage failure, techniques for detecting breakdown voltage failure of semiconductor switching elements are known. For example, Patent Document 1 discloses a technique for detecting breakdown voltage deterioration from voltage information applied to a semiconductor switching element.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] Incidentally, in order to detect deterioration and abnormalities of semiconductor switching elements in advance, it is effective to detect the main withstand voltage leakage current of the power conversion device, that is, the leakage current of the switching element.

[0008] In the method described in Patent Document 1, the operations of the switching elements provided on the high side and the low side are stopped, and the control circuit determines the withstand voltage deterioration of both switching elements from the voltage values detected by the voltage detector in a state where the temperatures of both switching elements are higher than the ambient temperature.

[0009] However, Patent Document 1 does not mention any method for quantitatively measuring the leakage current of the switching element, and there is room for improvement from the viewpoint of detecting signs of deterioration and abnormalities of the power conversion device.

[0010] Therefore, an object of the present invention is to provide a power conversion device and a diagnosis method thereof that can detect the leakage current of a semiconductor switching element with a relatively simple configuration in a power conversion device having the semiconductor switching element.

Means for Solving the Problems

[0011] To solve the above problems, the present invention provides an upper arm including a first semiconductor switching element, a lower arm including a second semiconductor switching element connected in series to the first semiconductor switching element, a first control unit for controlling the first semiconductor switching element and the second semiconductor switching element, a first current detector connected in parallel to the first semiconductor switching element for detecting a leakage current generated in the lower arm, and a second current detector connected in parallel to the second semiconductor switching element for detecting a leakage current generated in the upper arm. The first current detector includes a first current detection element and a third semiconductor switching element connected in series to the first current detection element. The second current detector includes a second current detection element and a fourth semiconductor switching element connected in series to the second current detection element. The present invention is characterized by further including a second control unit for controlling the third semiconductor switching element and the fourth semiconductor switching element.

[0012] The present invention also provides a method for diagnosing a power conversion device having upper and lower arms, including: (a) a step in which a first control unit turns off a first semiconductor switching element of the upper arm and a second semiconductor switching element of the lower arm; (b) a step in which a second control unit turns off a third semiconductor switching element of a first current detector connected to the upper arm and turns on a fourth semiconductor switching element of a second current detector connected to the lower arm; and (c) a step in which an arithmetic unit calculates a leakage current generated in the upper arm based on a value obtained by subtracting a current value detected by the first current detector from a current value detected by the second current detector.

Advantages of the Invention

[0013] According to the present invention, in a power conversion device having semiconductor switching elements, it is possible to realize a power conversion device and a diagnosis method thereof that can detect the leakage current of semiconductor switching elements with a relatively simple configuration.

[0014] As a result, it becomes possible to detect deterioration and signs of abnormality in the power conversion device, and the reliability of the power conversion device can be improved.

[0015] Problems, configurations, and effects other than those described above will be clarified by the description of the following embodiments.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

Figure 4A

Figure 4B

Figure 4C

Figure 5

Figure 6

Figure 7

Modes for Carrying Out the Invention

[0017] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In each drawing, the same components are denoted by the same reference numerals, and detailed descriptions of overlapping parts are omitted.

Embodiment

[0018] Referring to FIGS. 1, 2, and 6, a power conversion device and a diagnostic method thereof according to Embodiment 1 of the present invention will be described.

[0019] FIG. 1 is a diagram showing a schematic configuration of the power conversion device of this embodiment. FIG. 2 is a timing chart showing an operation example of the power conversion device of FIG. 1 and its current detectors 25 and 26. FIG. 6 is a flowchart showing a diagnostic method of the power conversion device of this embodiment.

[0020] As shown in FIG. 1, in the power conversion device of this embodiment, commands output by the control unit 13 are respectively input to the gates of semiconductor switching elements 1 to 6 in which an IGBT (Insulated Gate Bipolar Transistor) and a diode are connected in antiparallel via gate drive circuits 7 to 12. By switching the semiconductor switching elements 1 to 6, DC power from the DC power supply 14 is converted into AC power and output to control a load 15 such as a motor.

[0021] Each of the gate drive circuits 7 to 12 is connected to the gate terminal and the source terminal of each of the semiconductor switching elements 1 to 6, and a voltage is applied to the gate terminal of each of the semiconductor switching elements 1 to 6 with reference to the source terminal of each of the semiconductor switching elements 1 to 6.

[0022] A current detector 25 is connected in parallel to the semiconductor switching element 1, and a current detector 26 is connected in parallel to the semiconductor switching element 2.

[0023] In this embodiment, the current detector 25 and the current detector 26 are connected to the same-phase arm. However, for example, the current detector 25 may be connected in parallel to the semiconductor switching element 3, and the current detector 26 may be connected in parallel to the semiconductor switching element 6, etc., and they may be connected to different phases.

[0024] The current detectors 25 and 26 each include semiconductor switching elements 16 and 17 formed of MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors), current detection elements (resistors) 18 and 19, and signal output units 23 and 24. A command output from the control unit 22 is input to the gates of the semiconductor switching elements 16 and 17 via the gate drive circuits 20 and 21.

[0025] The gate drive circuit 20 is connected to the gate terminal of the semiconductor switching element 16 and the source terminal of the semiconductor switching element 1, and applies a voltage to the gate terminal of the semiconductor switching element 16 with reference to the source terminal of the semiconductor switching element 1.

[0026] Also, the gate drive circuit 21 is connected to the gate terminal of the semiconductor switching element 17 and the source terminal of the semiconductor switching element 2, and applies a voltage to the gate terminal of the semiconductor switching element 17 with reference to the source terminal of the semiconductor switching element 2.

[0027] In this embodiment, the current detection elements 18 and 19 are each connected to the source side of the semiconductor switching elements 16 and 17, but there is no problem even if they are connected to the drain side.

[0028] In this embodiment, since resistors are connected as the current detection elements 18 and 19 to the source side of the semiconductor switching elements 16 and 17, even if, due to a malfunction, the semiconductor switching elements 16 and 17 simultaneously turn on in an unintended timing, for example, in a short-circuit state, when the current reaches a predetermined value, the gate-source voltage of the semiconductor switching elements 16 and 17 decreases to near the threshold value due to the electromotive force generated in the current detection elements 18 and 19, and the semiconductor switching elements 16 and 17 become in a state close to being self-turned off, and there is an advantage that the current can be limited.

[0029] Next, the operation of measuring the leakage current will be described with reference to FIG. 2.

[0030] The measurement of the leakage current is carried out with all the semiconductor switching elements 1 to 6 in the off state.

[0031] First, in order to measure the leakage current of the lower arm, only the semiconductor switching element 16 is turned on. Then, since the voltage element ability of the current detector 25 is lost, almost all of the voltage from the DC power supply 14 is applied to the semiconductor switching elements 2, 4, 6, 17 on the lower arm side. At this time, a leakage current flowing through the semiconductor switching elements 2, 4, 6, 17 and a parasitic leakage current flowing through the mounting part of the power conversion device are generated.

[0032] On the other hand, at this time, on the upper arm side, since the resistance of the current detector 25 is significantly lower than the resistance of the semiconductor switching elements 1, 3, 5, most of the above-mentioned leakage current generated on the lower arm side flows through the current detector 25.

[0033] Therefore, if the signal output from the current detection element 18 is taken out from the signal output unit 23 through an isolation AD converter (not shown), the leakage current flowing through the semiconductor switching elements 2, 4, 6, 17 and the mounting part of the power conversion device can be calculated.

[0034] Also, at this time, the signal output from the current detection element 19 reflects the leakage current flowing through the semiconductor switching element 17. If the signal is taken out from the signal output unit 24 through an isolation AD converter (not shown), the leakage current flowing through the semiconductor switching element 17 can be calculated.

[0035] Then, by subtracting the leakage current flowing through the semiconductor switching element 17 from the leakage current flowing through the semiconductor switching elements 2, 4, 6, 17 and the mounting part of the power conversion device, the total value of the leakage current flowing through the semiconductor switching elements 2, 4, 6 and the mounting part of the power conversion device can be calculated.

[0036] Note that the calculation of the leakage current flowing through the semiconductor switching elements 2, 4, 6, 17 and the mounting part of the power conversion device, the calculation of the leakage current flowing through the semiconductor switching element 17, and the subtraction of the leakage current flowing through the semiconductor switching element 17 from the leakage current flowing through the semiconductor switching elements 2, 4, 6, 17 and the mounting part of the power conversion device may be performed by incorporating an arithmetic unit in the control units 13 and 22, or an arithmetic unit independent of the power conversion device may be provided.

[0037] The above-described method for measuring the leakage current of the lower arm is shown in the flowchart of FIG. 6.

[0038] First, in step S1, based on a command output by the control unit 13, all of the semiconductor switching elements 1 to 6 are controlled to be off.

[0039] Next, in step S2, based on a command output by the control unit 22, only the semiconductor switching element 16 is controlled to be on.

[0040] Next, in step S3, an arithmetic unit (not shown) extracts a signal output from the current detection element 18 from the signal output unit 23 via an isolation AD converter, and calculates the leakage current flowing through the semiconductor switching elements 2, 4, 6, 17 and the mounting part of the power conversion device.

[0041] Next, in step S4, an arithmetic unit (not shown) extracts a signal output from the current detection element 19 from the signal output unit 24 via an isolation AD converter, and calculates the leakage current flowing through the semiconductor switching element 17.

[0042] Finally, in step S5, an arithmetic unit (not shown) subtracts the leakage current flowing through the semiconductor switching element 17 from the leakage current flowing through the semiconductor switching elements 2, 4, 6, 17 and the mounting part of the power conversion device, calculates the total value of the leakage current flowing through the semiconductor switching elements 2, 4, 6 and the mounting part of the power conversion device (i.e., the leakage current value of the lower arm), and ends the process.

[0043] When measuring the leakage current of the upper arm, if the semiconductor switching element 16 is turned off and the semiconductor switching element 17 is turned on, as described above, from the signal output unit 24, the leakage current flowing through the semiconductor switching elements 1, 3, 5, 16 and the mounting part of the power conversion device is calculated, and from the signal output unit 23, the leakage current flowing through the semiconductor switching element 16 is calculated. Therefore, the leakage current flowing through the semiconductor switching elements 1, 3, 5 and the mounting part of the power conversion device can be calculated by subtraction processing.

[0044] As described above, with the configuration of the power conversion device and its diagnosis method of this embodiment, it becomes possible to measure the leakage current of the upper and lower arms of the power conversion device with high accuracy, and it becomes possible to prevent element breakdown due to breakdown voltage deterioration of the semiconductor switching element.

[0045] In this embodiment, as an example, the case where n-type MOSFETs are used for the semiconductor switching elements 16 and 17 has been described, but p-type MOSFETs may also be used. Further, instead of MOSFETs, switching elements such as HEMT (High Electron Mobility Transistor) and IGBT may be used.

Embodiment

[0046] Referring to FIG. 3, the power conversion device and its diagnosis method according to Embodiment 2 of the present invention will be described. In this embodiment, an example of measuring the leakage current by variably controlling the measurement accuracy will be described.

[0047] FIG. 3 is a diagram showing a schematic configuration of the power conversion device of this embodiment.

[0048] The difference from Embodiment 1 (FIG. 1) is that current detection elements 27 and 28 are provided in parallel with the current detection elements 18 and 19 respectively, and semiconductor switching elements 29 to 32 are provided in series with each of the current detection elements 18, 19, 27, and 28, and gate drive circuits 33 to 36 for driving the semiconductor switching elements 29 to 32 based on commands output from the control unit 22.

[0049] By combining the on / off controls of the semiconductor switching elements 29 and 30, it is possible to control whether the leakage current on the lower arm side flows through the current detection element 18 or the current detection element 27. By changing the resistance values of the current detection element 18 and the current detection element 27, the measurement range and measurement accuracy of the leakage current on the lower arm side can be controlled.

[0050] Also, by combining the on / off controls of the semiconductor switching elements 31 and 32, it is possible to control whether the leakage current on the upper arm side flows through the current detection element 19 or the current detection element 28. By changing the resistance values of the current detection element 19 and the current detection element 28, the measurement range and measurement accuracy of the leakage current on the upper arm side can be controlled.

[0051] Therefore, with the configuration of the power conversion device and its diagnosis method of this embodiment, it is possible to measure the leakage currents of the upper and lower arms of the power conversion device with both a wide measurement range and high resolution.

[0052] In this embodiment, as an example, an example of two in parallel for the current detection element 18 and the current detection element 27, and two in parallel for the current detection element 19 and the current detection element 28 is shown, but they may be configured with three in parallel or more.

Embodiment

[0053] With reference to FIGS. 4A to 4C, a power conversion device and its diagnosis method according to Embodiment 3 of the present invention will be described. In this embodiment, an example of applying the present invention to a high-voltage power conversion device will be described.

[0054] Each of FIGS. 4A to 4C is a diagram showing a configuration example of the semiconductor switching elements of the power conversion device of this embodiment. Note that the configuration other than the semiconductor switching elements is the same as that of Embodiment 1 (FIG. 1).

[0055] In a high-voltage power conversion device, the withstand voltages of semiconductor switching elements 1 to 6 need to be high. At the same time, semiconductor switching elements 16 and 17 included in current detectors 25 and 26 connected in parallel to semiconductor switching elements 1 and 2 also need to have a high withstand voltage.

[0056] Of course, it is also possible to apply high withstand voltage MOSFETs or the like to semiconductor switching elements 16 and 17. However, the cost can be reduced by combining low withstand voltage semiconductor switching elements and treating them as high withstand voltage semiconductor switching elements.

[0057] Figures 4A to 4C show an example of the connection relationship of multi-series semiconductor switching elements that replace semiconductor switching element 16 and semiconductor switching element 17. In this embodiment, the number of series-connected low withstand voltage semiconductor switching elements is set to 3, but the number of series-connected elements can be arbitrarily changed. Also, as an example, an alternative example of an N-type MOSFET is shown, but it is also possible to use a P-type MOSFET for replacement.

[0058] Figure 4A is an example of a multi-stage cascode connection using N-type MOSFETs 37 to 39. At least N-type MOSFETs 38 and 39 are normally-on type semiconductor switching elements.

[0059] The gate of N-type MOSFET 38 is connected to the source of N-type MOSFET 37, the gate of N-type MOSFET 39 is connected to the source of N-type MOSFET 38, and the on and off of N-type MOSFETs 37 to 39 are controlled by the voltage applied to the gate of N-type MOSFET 37.

[0060] When the N-type MOSFET 37 is in the on state, the gate-source voltage of the N-type MOSFET 38 is approximately 0V, so the N-type MOSFET 38 turns on. Similarly, the N-type MOSFET 39 also turns on. When the N-type MOSFET 37 transitions to the off state, the gate-source voltage of the N-type MOSFET 38 becomes negative and the N-type MOSFET 38 turns off. Similarly, the N-type MOSFET 39 also turns off. Therefore, the operation of the N-type MOSFETs 37 to 39 can be controlled by the voltage applied to the gate of the N-type MOSFET 37.

[0061] Figure 4B is an example of a multi-stage cascade connection, and at least the N-type MOSFETs 43 and 46 are normally-off semiconductor switching elements.

[0062] P-type MOSFETs 41 and 42 are connected between the gate of the N-type MOSFET 40 and the gate of the N-type MOSFET 43, and P-type MOSFETs 44 and 45 are connected between the gate of the N-type MOSFET 43 and the gate of the N-type MOSFET 46.

[0063] When a positive voltage is applied to the gate of the N-type MOSFET 40, a positive voltage is also applied to the gates of the N-type MOSFETs 43 and 46, and the N-type MOSFETs 40, 43, and 46 turn on. When the N-type MOSFET 40 transitions to the off state, the gate-source voltage of the P-type MOSFET 42 increases and the P-type MOSFET 42 turns off. When the P-type MOSFET 42 turns off, the gate-source voltage of the P-type MOSFET 41 decreases and the P-type MOSFET 41 turns on, and the gate-source of the N-type MOSFET 43 is short-circuited and the N-type MOSFET 43 turns off. Similarly, the N-type MOSFET 46 also turns off. Therefore, the operation of the N-type MOSFETs 40, 43, and 46 can be controlled by the voltage applied to the gate of the N-type MOSFET 40.

[0064] FIG. 4C is a modification of FIG. 4B. As shown in FIG. 4C, by connecting a P-type MOSFET 47 between the gate of the N-type MOSFET 40 and the P-type MOSFET 42, and connecting a P-type MOSFET 48 between the gate of the N-type MOSFET 43 and the P-type MOSFET 45, the breakdown voltage can be further improved.

[0065] Therefore, with the power conversion device and its diagnosis method of this embodiment, the leakage current of the upper and lower arms of a high-voltage power conversion device can be measured with a low-cost configuration.

Embodiment

[0066] Referring to FIG. 5, a power conversion device and its diagnosis method according to Embodiment 4 of the present invention will be described. In this embodiment, an example of measuring the junction temperature of a semiconductor switching element and an example of measuring the leakage current of a specific semiconductor switching element will be described.

[0067] FIG. 5 is a diagram schematically showing the relationship between the junction temperature and the leakage current of the semiconductor switching element of the power conversion device of this embodiment. The configuration of the power conversion device is the same as that of Embodiment 1 (FIG. 1).

[0068] As shown in FIG. 5, since the leakage current increases as the junction temperature of the semiconductor switching element increases, the junction temperatures of the semiconductor switching elements 1 to 6 can be estimated from the leakage current calculated by the method of Embodiment 1.

[0069] In the method described in Embodiment 1, as the leakage current on the lower arm side, the total value of the leakage currents flowing through the semiconductor switching elements 2, 4, 6 and the mounting portion of the power conversion device can be calculated, and as the leakage current on the upper arm side, the total value of the leakage currents flowing through the semiconductor switching elements 1, 3, 5 and the mounting portion of the power conversion device can be calculated, but the leakage current of each individual semiconductor switching element cannot be separated.

[0070] Therefore, in this embodiment, for example, by measuring the leakage current on the upper arm side before and after energizing only the semiconductor switching element 1 in the upper arm to increase the junction temperature, only the leakage increment due to the increase in the junction temperature of the semiconductor switching element 1 is calculated as the difference. By increasing the junction temperature by energization and measuring the leakage current under a plurality of conditions, the temperature characteristics of the leakage current of the semiconductor switching element 1 can be calculated.

[0071] Therefore, with the power conversion device and its diagnosis method of this embodiment, the junction temperature of the semiconductor switching element can be estimated. Also, the leakage current of each individual switching element can be separately measured.

Embodiment

[0072] With reference to FIG. 7, a power conversion device and its diagnosis method according to Embodiment 5 of the present invention will be described. In this embodiment, an example will be described in which a current detector 25 is provided only on the upper arm of the power conversion device without providing a current detector on the lower arm of the power conversion device.

[0073] FIG. 7 is a diagram showing a schematic configuration of the power conversion device of this embodiment.

[0074] The difference from Embodiment 1 (FIG. 1) is that a current detector 26 is not provided on the lower arm of the power conversion device, and a current detector 25 is provided only on the upper arm of the power conversion device. Other configurations are the same as those in Embodiment 1 (FIG. 1).

[0075] Using the same method as in Embodiment 1 (FIG. 1), the current detector 25 measures the leakage current of the lower arm.

[0076] On the other hand, regarding the leakage current of the upper arm, if the circuit configurations of the upper and lower arms of the power conversion device are the same, the leakage current of the upper arm is substantially the same as the leakage current of the lower arm, so it can be estimated from the leakage current of the lower arm measured by the current detector 25.

[0077] Therefore, with the power conversion device and its diagnosis method of this embodiment, the leakage currents of the upper and lower arms of the power conversion device can be measured with a lower-cost configuration.

[0078] Note that the present invention is not limited to the above-described embodiments, and various modifications are included. For example, the above-described embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described. Also, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Further, for a part of the configuration of each embodiment, addition, deletion, or replacement with other configurations is possible.

Explanation of Reference Numerals

[0079] 1 to 6... Semiconductor switching elements (where IGBTs and diodes are connected in antiparallel) 7 to 12, 20, 21, 33 to 36... Gate drive circuits 13, 22... Control units 14... DC power supply 15... Load 16, 17, 29 to 32... Semiconductor switching elements (MOSFETs) 18, 19, 27, 28... Current detection elements (resistors) 23, 24... Signal output units 25, 26... Current detectors 37 to 40, 43, 46... N-type MOSFETs 41, 42, 44, 45, 47, 48... P-type MOSFETs.

Claims

1. An upper arm including a first semiconductor switching element, A lower arm including a second semiconductor switching element connected in series to the first semiconductor switching element, A first control unit for controlling the first semiconductor switching element and the second semiconductor switching element, A first current detector connected in parallel to the first semiconductor switching element for detecting a leakage current generated in the lower arm, A second current detector connected in parallel to the second semiconductor switching element for detecting a leakage current generated in the upper arm, and comprising: The first current detector has a first current detection element and a third semiconductor switching element connected in series to the first current detection element, The second current detector has a second current detection element and a fourth semiconductor switching element connected in series to the second current detection element, A power conversion device comprising: a second control unit for controlling the third semiconductor switching element and the fourth semiconductor switching element.

2. The power conversion device according to claim 1, When the first control unit turns off the first semiconductor switching element and the second semiconductor switching element, When the second control unit turns off the third semiconductor switching element and turns on the fourth semiconductor switching element, Based on the value obtained by subtracting the current value output by the first current detection element from the current value output by the second current detection element, the leakage current generated in the upper arm is measured. A power conversion device characterized by this.

3. The power conversion device according to claim 1, When the first control unit turns off the first semiconductor switching element and the second semiconductor switching element, When the second control unit turns on the third semiconductor switching element and turns off the fourth semiconductor switching element, Based on the value obtained by subtracting the current value output by the second current detection element from the current value output by the first current detection element, the leakage current generated in the lower arm is measured. A power conversion device characterized by this.

4. The power conversion device according to claim 1, The first semiconductor switching element, the second semiconductor switching element, the third semiconductor switching element, and the fourth semiconductor switching element are any one of MOSFET, IGBT, and HEMT, or a combination thereof. A power conversion device characterized by this.

5. The power conversion device according to claim 1, At least one of the first semiconductor switching element, the second semiconductor switching element, the third semiconductor switching element, and the fourth semiconductor switching element is a circuit configured by connecting a plurality of semiconductor switching elements in series. A power conversion device characterized by this.

6. The power conversion device according to claim 1, The first current detection element is connected between the source terminal of the third semiconductor switching element and the first semiconductor switching element, A power conversion device, characterized in that the second current detection element is connected between the source terminal of the fourth semiconductor switching element and the second semiconductor switching element.

7. The power conversion device according to claim 1, The first current detection element and the second current detection element are composed of resistors. A power conversion device characterized by this.

8. The power conversion device according to claim 1, The first current detector has a fifth semiconductor switching element connected in series to the first current detection element, and a third current detection element and a sixth semiconductor switching element connected in parallel to the first current detection element and the fifth semiconductor switching element, The second current detector has a seventh semiconductor switching element connected in series to the second current detection element, and a fourth current detection element and an eighth semiconductor switching element connected in parallel to the second current detection element and the seventh semiconductor switching element. A power conversion device characterized by this.

9. The power conversion device according to claim 2, A power conversion device, characterized in that the junction temperature of the first semiconductor switching element is calculated from the measured value of the leakage current.

10. The power conversion device according to claim 3, A power conversion device, characterized in that the junction temperature of the second semiconductor switching element is calculated from the measured value of the leakage current.

11. The power conversion device according to claim 2, A power conversion device, characterized by calculating the temperature characteristics of the leakage current of the first semiconductor switching element from the values of the leakage current measured under a plurality of temperature conditions.

12. The power conversion device according to claim 3, A power conversion device, characterized by calculating the temperature characteristics of the leakage current of the second semiconductor switching element from the values of the leakage current measured under a plurality of temperature conditions.

13. A diagnostic method for a power conversion device having upper and lower arms, (a) a step in which a first control unit turns off a first semiconductor switching element of the upper arm and a second semiconductor switching element of the lower arm; (b) a step in which a second control unit turns off a third semiconductor switching element of a first current detector connected to the upper arm and turns on a fourth semiconductor switching element of a second current detector connected to the lower arm; (c) a step in which an arithmetic unit calculates the leakage current generated in the upper arm based on a value obtained by subtracting the current value detected by the first current detector from the current value detected by the second current detector; A diagnostic method for a power conversion device, characterized by comprising the above steps.

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