Power conversion device

Abstract

The present invention relates to a power conversion device. In this power conversion device, the control unit is configured to determine whether an abnormality related to the gate drive unit, the drive power supply unit, and the switching element has occurred based on the detected current between the gate drive unit and the drive power supply unit.

Description

Technical Field

[0001] The present invention relates to a power conversion device, and more particularly to a power conversion device including a drive power supply unit that supplies power for generating a drive current in a gate drive unit. Background Art

[0002] Conventionally, a power conversion device is known which includes a drive power supply unit that supplies power for generating a drive current in a gate drive unit, and the gate drive unit outputs a drive current for controlling a switching element. For example, such a power conversion device is disclosed in Japanese Patent Application Laid-Open No. 2000-152636.

[0003] Japanese Patent Application Laid-Open No. 2000-152636 describes a power conversion device including: a semiconductor element; a gate drive power supply (drive power supply unit) that supplies gate drive power to the semiconductor element; and a gate drive circuit (gate drive unit) that outputs, based on a gate drive signal (control signal) input from a control circuit, the power supplied from the gate drive power supply to the semiconductor element. In the power conversion device described in Japanese Patent Application Laid-Open No. 2000-152636, abnormalities such as a failure of the gate drive power supply or the gate drive circuit, a poor contact or a short circuit between wirings in a wiring path from the gate drive power supply to the semiconductor element are determined based on a gate drive power value output from the gate drive power supply. Further, in the power conversion device described in Japanese Patent Application Laid-Open No. 2000-152636, the gate drive power supply is added with a function of transmitting a signal indicating the gate drive power value.

[0004] However, in a conventional power conversion device as described in Japanese Patent Application Laid-Open No. 2000-152636, a gate drive power supply (drive power supply unit) is added with a function of transmitting a signal indicating the value of gate drive power, in order to determine a failure of the gate drive power supply or the gate drive circuit, a poor contact in the wiring path from the gate drive power supply to the semiconductor element, or an abnormality such as a short circuit between wirings (hereinafter referred to as an abnormality related to the gate drive unit, the gate drive power supply (drive power supply unit), and the switching element). Therefore, in the conventional power conversion device as described in Japanese Patent Application Laid-Open No. 2000-152636, there is a problem that the circuit structure of the gate drive power supply (drive power supply unit) is complicated corresponding to the addition of a function other than the function of supplying power for generating a drive current (original function). Therefore, a power conversion device that can determine an abnormality related to the gate drive unit, the gate drive power supply (drive power supply unit), and the switching element without adding a function other than the original function to the gate drive power supply (drive power supply unit) is desired. In addition, it is preferable that no function other than the original function is added, which is the same for the gate drive unit and the switching element. SUMMARY OF THE INVENTION

[0005] The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a power conversion device that can determine an abnormality related to a gate drive unit, a drive power supply unit, and a switching element without adding a function other than the original function to the gate drive unit, the drive power supply unit, and the switching element.

[0006] In order to achieve the above object, a power conversion device according to an aspect of the present invention includes: a power conversion unit including a switching element, the power conversion unit converting the input power and outputting it to a load; a gate drive unit outputting a drive current for controlling the switching element; a control unit outputting a control signal for generating a drive current to the gate drive unit; and a drive power supply unit supplying power for generating a drive current in the gate drive unit, wherein the control unit is configured to determine whether an abnormality related to the gate drive unit, the drive power supply unit, and the switching element has occurred based on a detection current between the gate drive unit and the drive power supply unit.

[0007] In the power conversion device according to one aspect of the present invention, as described above, the control unit is configured to determine whether an abnormality related to the gate drive unit, the drive power supply unit, and the switching element has occurred based on the detected current between the gate drive unit and the drive power supply unit. Thus, when the detected current is abnormal (for example, in a state where it is too small or too large and continues), the control unit can determine that an abnormality such as an open circuit or a short circuit has occurred in the circuit including the gate drive unit, the drive power supply unit, and the switching element. In addition, the detected current can be easily obtained by measuring the current between the gate drive unit and the drive power supply unit. As a result, it is possible to determine an abnormality related to the gate drive unit, the drive power supply unit, and the switching element without adding functions other than the original functions to the gate drive unit, the drive power supply unit, and the switching element.

[0008] In the power conversion device according to one aspect described above, preferably, the control unit is configured to determine whether at least one of the following four abnormalities has occurred based on the detected current. The four abnormalities are a short circuit inside the gate drive unit, a failure of the drive power supply unit, a short circuit inside the switching element, and a poor connection of the wiring between the switching element and the gate drive unit. With such a configuration, it is possible to determine whether at least one of the inside of the gate drive unit including components with a relatively high failure rate, the drive power supply unit, the inside of the switching element, and the wiring between the switching element and the gate drive unit has an abnormality.

[0009] In this case, preferably, a display unit is further provided, and the control unit is configured to: when it is determined that at least one of the four abnormalities has occurred, control the display unit to display that at least one of the four abnormalities has occurred. With such a configuration, by displaying that at least one of the four abnormalities has occurred on the display unit, it is possible to make an operator or the like who performs maintenance inspection of the power conversion device easily and quickly recognize that at least one of the four abnormalities has occurred. As a result, for example, compared with the case where an operator uses a measuring device to perform inspections related to the four abnormalities, even when not having specific expertise, it is possible to check whether at least one of the four abnormalities has occurred, and it is possible to suppress an increase in the downtime (time when the device cannot be used) of the power conversion device due to the prolongation of the maintenance inspection.

[0010] In the structure in which the control unit determines whether or not at least one of the four types of abnormalities has occurred as described above, preferably, there is also an abnormality detection circuit that detects whether or not at least one of the four types of abnormalities has occurred based on a detection current or a detection voltage obtained by converting the detection current into a voltage. The abnormality detection circuit is configured to output a detection signal indicating that at least one of the four types of abnormalities has been detected to the control unit when at least one of the four types of abnormalities is detected. With this configuration, the control unit can easily determine whether or not at least one of the four types of abnormalities has occurred based on the detection signal indicating that at least one of the four types of abnormalities has been detected and input from the abnormality detection circuit.

[0011] In this case, preferably, the abnormality detection circuit is configured to detect at least one of a failure of the drive power supply unit and a poor connection of the wiring between the switching element and the gate drive unit when the detection current or the detection voltage is smaller than a specified first threshold value, and to detect at least one of a short circuit inside the gate drive unit and a short circuit inside the switching element when the detection current or the detection voltage is larger than a specified second threshold value. The second threshold value is larger than the first threshold value. With this configuration, when the detection current or the detection voltage becomes too small due to a failure of the drive power supply unit or a poor connection of the wiring between the switching element and the gate drive unit, the abnormality detection circuit can appropriately detect whether or not at least one of a failure of the drive power supply unit and a poor connection of the wiring between the switching element and the gate drive unit has occurred based on the first threshold value. In addition, when the detection current or the detection voltage becomes too large due to a short circuit inside the gate drive unit or a short circuit inside the switching element, the abnormality detection circuit can appropriately detect whether or not at least one of a short circuit inside the gate drive unit and a short circuit inside the switching element has occurred based on the second threshold value.

[0012] In a structure for detecting at least one of a short circuit inside a gate drive unit and a short circuit inside a switching element when a detected current or a detected voltage is greater than a second threshold, it is preferable that: a common drive current is output from one gate drive unit to a plurality of switching elements connected in parallel to each other, and the second threshold is set to a value corresponding to a state where internal short circuits occur simultaneously in three or more switching elements. Here, in a structure where a common drive current is output from one gate drive unit to each of a plurality of switching elements connected in parallel to each other, the detected current or the detected voltage is substantially proportional to the number of switching elements in which internal short circuits occur simultaneously. Therefore, by configuring as described above, the second threshold can be set to a relatively high value, and thus it is possible to suppress the abnormal detection circuit from erroneously detecting whether an internal short circuit has occurred in the switching element because the detected current or the detected voltage exceeds the second threshold when no internal short circuit occurs in the switching element. In addition, in the above-described structure for outputting a common drive current, internal short circuits often occur simultaneously in a plurality of switching elements. Therefore, even when configured as described above, it is possible to substantially detect an internal short circuit in the switching element.

[0013] In a structure for outputting a detection signal indicating that at least one of four types of abnormalities has been detected to the control unit when the above-described abnormality detection circuit detects at least one of the four types of abnormalities, it is preferable that the abnormality detection circuit is configured to: while the control unit is continuously outputting a pulsed control signal for turning the switching element on and off to the gate drive unit, continuously output a pulsed detection signal when no abnormality among the four types of abnormalities is detected based on the detected current or the detected voltage, and continuously output a non-pulsed detection signal when at least one of the four types of abnormalities is detected. By configuring in this way, the control unit can more easily determine whether at least one of the four types of abnormalities has occurred based on the pulsed detection signal and the non-pulsed detection signal continuously input from the abnormality detection circuit.

[0014] In this case, preferably, the abnormality detection circuit includes: a pulse generation circuit that outputs a low level (Low) when the detected current or the detected voltage is smaller than a specified first threshold value and outputs a high level (High) when the detected current or the detected voltage is larger than a third threshold value, the third threshold value being larger than the first threshold value; an overcurrent determination circuit that outputs a high level when the detected current or the detected voltage is smaller than a specified second threshold value and outputs a low level when the detected current or the detected voltage is larger than the second threshold value, the second threshold value being larger than the third threshold value; and an AND circuit that is input with the output of the pulse generation circuit and the output of the overcurrent determination circuit. With such a configuration, in a state where the control unit continuously outputs a pulsed control signal to the gate drive unit, when the detected current or the detected voltage does not become too large or too small, a pulsed signal (where a high level and a low level are alternately repeated at a fixed period) and a high level can be continuously output from the pulse generation circuit and the overcurrent determination circuit, respectively. Therefore, a pulsed signal (pulsed detection signal) can be continuously output from the AND circuit. Further, in the above state of continuously outputting the control signal, when the state where the detected current or the detected voltage is too small continues, a low level and a high level can be continuously output from the pulse generation circuit and the overcurrent determination circuit, respectively. Therefore, a low level (non-pulsed detection signal) can be continuously output from the AND circuit. Further, in the above state of continuously outputting the control signal, when the state where the detected current or the detected voltage is too large continues, a high level and a low level can be continuously output from the pulse generation circuit and the overcurrent detection circuit, respectively. Therefore, a low level (non-pulsed detection signal) can be continuously output from the AND circuit. As a result, in a case where none of the four types of abnormalities is detected and in a case where at least one of the four types of abnormalities is detected, a pulsed detection signal and a non-pulsed detection signal can be easily and continuously output from the abnormality detection circuit, respectively.

[0015] In a structure in which a non-pulsed detection signal is continuously output when at least one of the four types of abnormalities is detected by the above-described abnormality detection circuit, preferably, the control unit is configured to determine that at least one of the four types of abnormalities has occurred when the non-pulsed detection signal is continuously output from the abnormality detection circuit throughout a predetermined first period, and the predetermined first period is a period set based on the period of the pulsed control signal. With this configuration, when the non-pulsed detection signal is continuously output from the abnormality detection circuit throughout the first period, it is determined that at least one of the four types of abnormalities has occurred, so that it is possible to suppress misjudgment that at least one of the four types of abnormalities has occurred when the non-pulsed detection signal is temporarily output due to noise or the like. In addition, by setting the first period based on the period of the pulsed control signal, the first period can be appropriately set so that the first period is sufficiently longer than the period of the pulsed detection signal corresponding to the period of the pulsed control signal.

[0016] In this case, preferably, the control unit is configured to determine that none of the four types of abnormalities has occurred when the detection signal indicating that at least one of the four types of abnormalities has been detected is not continuously output from the abnormality detection circuit throughout at least the predetermined second period starting from the start of determination of whether at least one of the four types of abnormalities has occurred, and the predetermined second period is longer than the first period. With this configuration, it is determined whether at least one of the four types of abnormalities has occurred during the first period. Therefore, when the detection signal indicating that at least one of the four types of abnormalities has been detected is not continuously output throughout the second period that is longer than the first period, it can be reliably determined that none of the four types of abnormalities has occurred.

[0017] In the above-described power conversion device according to one aspect, preferably, the load is an induction heating coil of an induction heating furnace for melting metal by induction heating. With this configuration, in the power conversion device for an induction heating furnace, it is possible to determine abnormalities related to the gate drive unit, the drive power supply unit, and the switching element without adding functions other than the original functions to the gate drive unit, the drive power supply unit, and the switching element. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 FIG. is a diagram showing the overall structure of a power conversion device according to an embodiment of the present invention.

[0019] Figure 2 FIG. is a block diagram showing details of an abnormality detection circuit in a power conversion device according to an embodiment of the present invention.

[0020] Figure 3It is a diagram showing a detection current, a detection voltage, and a detection signal in the case where a connection failure of a wiring between a switching element and a gate drive unit in a power conversion device based on an embodiment of the present invention is detected.

[0021] Figure 4 It is a diagram showing a detection current, a detection voltage, and a detection signal in the case where a short circuit inside a gate drive unit in a power conversion device based on an embodiment of the present invention is detected.

[0022] Figure 5 It is a diagram showing a detection voltage and a detection signal in the case where a short circuit inside a switching element in a power conversion device based on an embodiment of the present invention is detected.

[0023] Figure 6 It is a timing chart of fault diagnosis in a power conversion device based on an embodiment of the present invention.

[0024] Figure 7 It is a diagram showing a detection voltage and a detection signal in the case where a short circuit inside a switching element in a power conversion device based on a comparative example is detected. Detailed Embodiments

[0025] Hereinafter, embodiments in which the present invention is embodied will be described based on the drawings.

[0026] Refer to Figures 1 to 6 to describe the structure of a power conversion device 100 based on an embodiment of the present invention.

[0027] As Figure 1 shown, the power conversion device 100 includes a rectifier circuit 11, a smoothing capacitor 12, and an inverter unit 13. The rectifier circuit 11 is configured to convert an AC voltage input from an AC power supply 200 into a DC voltage and then output it. The smoothing capacitor 12 is configured to smooth the DC voltage output from the rectifier circuit 11. The DC voltage smoothed by the smoothing capacitor 12 is input to the inverter unit 13. The inverter unit 13 converts the input DC voltage (power) into an AC voltage by switching a switching element 13a described later and outputs it to a load 300. The load 300 is an induction heating coil of an induction heating furnace for melting metal by induction heating. That is, the power conversion device 100 is a power conversion device for an induction heating furnace. In addition, the inverter unit 13 is an example of the "power conversion unit" in the present invention.

[0028] The inverter unit 13 includes a switching element 13a. The switching element 13a is an IGBT (Insulated Gate Bipolar Transistor). The inverter unit 13 has a full-bridge circuit structure constituted by switching elements Q1, Q2, Q3, and Q4. In addition, although not shown, in each of the switching elements Q1, Q2, Q3, and Q4 of the power conversion device 100, a plurality (six) of the switching elements 13a are connected in parallel with each other.

[0029] The power conversion device 100 includes a gate drive unit (GDU) 14 and a GDU power supply 15. The gate drive unit 14 is configured to output a drive current (a current for applying a voltage between the gate and the emitter) for controlling the switching element 13a to the switching element 13a. In addition, the GDU power supply 15 is configured to supply power for generating the drive current in the gate drive unit 14. In addition, the GDU power supply 15 is an example of the "drive power supply unit" of the present invention.

[0030] One gate drive unit 14 and one GDU power supply 15 are respectively provided for each of the switching elements Q1, Q2, Q3, and Q4. In addition, in Figure 1 only the gate drive unit 14 and the GDU power supply 15 corresponding to the switching element Q2 among the gate drive units 14 and the GDU power supplies 15 respectively corresponding to the switching elements Q1, Q2, Q3, and Q4 are shown.

[0031] In the power conversion device 100, it is configured to output a common drive current from one gate drive unit 14 to a plurality (six) of the switching elements 13a connected in parallel with each other (in the switching elements Q1, Q2, Q3, and Q4 respectively).

[0032] The power conversion device 100 includes a control unit 16 for controlling each part of the power conversion device 100. The control unit 16 includes a control board 16a as a main control part and an auxiliary control board 16b as an auxiliary control part. The control board 16a and the auxiliary control board 16b are provided separately from each other. The control board 16a is electrically connected to the auxiliary control board 16b. The control board 16a and the auxiliary control board 16b are circuit boards including, for example, a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), etc. In addition, the control unit 16 is an example of the "control part" of the present invention.

[0033] The control unit 16 is configured to output a control signal 21 for generating a drive current to the gate drive unit 14. Specifically, the control substrate 16a generates a pulsed control signal 21 for turning on and off the switching element 13a. The control substrate 16a outputs the generated control signal 21 to the gate drive unit 14 via the auxiliary substrate 16b. In addition, the control signal 21 is output from the auxiliary substrate 16b to the gate drive unit 14 for the switching element Q1, the gate drive unit 14 for the switching element Q2, the gate drive unit 14 for the switching element Q3, and the gate drive unit 14 for the switching element Q4, respectively.

[0034] The power conversion device 100 includes a display unit 17 that is controlled by the control substrate 16a to display the states of the various parts of the power conversion device 100 and the like. An operator who performs maintenance inspections and the like on the power conversion device 100 can confirm the states of the various parts of the power conversion device 100 based on the information displayed on the display unit 17.

[0035] Here, in the present embodiment, the control unit 16 is configured to determine whether an abnormality related to the gate drive unit 14, the GDU power supply 15, and the switching element 13a has occurred based on the detection current 31 (see Figure 3 ) between the gate drive unit 14 and the GDU power supply 15. Specifically, the control unit 16 is configured to determine whether at least one of four types of abnormalities has occurred based on the detection current 31, including a short circuit inside the gate drive unit 14, a failure of the GDU power supply 15, a short circuit inside the switching element 13a, and a poor connection of the wiring between the switching element 13a and the gate drive unit 14.

[0036] In addition, in the present application specification, "a short circuit inside the gate drive unit 14" refers to a short circuit of the drive FET (Field Effect Transistor) in the gate drive unit 14. Further, "a short circuit inside the switching element 13a" refers to a short circuit between the gate and the emitter of the IGBT. Additionally, "the wiring between the switching element 13a and the gate drive unit 14" refers to the gate wiring.

[0037] Next, a structure for the control unit 16 to determine whether at least one of the four types of abnormalities has occurred will be described.

[0038] In the present embodiment, the power conversion device 100 includes an abnormality detection circuit 40 that detects whether at least one of the four types of abnormalities has occurred based on a detection voltage 32 (see Figure 3 ) obtained by converting the detection current 31 (see Figure 3 ) between the gate drive unit 14 and the GDU power supply 15 into a voltage. Specifically, as Figure 2As shown, the abnormality detection circuit 40 includes a current detection unit 41, a current-voltage conversion circuit 42, a pulse generation circuit (power-off generation circuit) 43, an overcurrent determination circuit 44, and an AND circuit 45.

[0039] In the power conversion device 100, abnormality detection circuits 40a, 40b, 40c, and 40d corresponding to the switching element Q1, the switching element Q2, the switching element Q3, and the switching element Q4 are provided respectively. In addition, the AND circuit 45b for the switching element Q2 is used in parallel with the abnormality detection circuit 40a for the switching element Q1. Further, the AND circuit 45c of the abnormality detection circuit 40c for the switching element Q3 is used in parallel with the abnormality detection circuit 40d for the switching element Q4.

[0040] The current detection unit 41 detects the current between the gate drive unit 14 and the GDU power supply 15. The current detection unit 41 is a CT (Current Transformer: (instrument use) current transformer). The detected current 31 detected by the current detection unit 41 (refer to Figure 3 ) is input to the current-voltage conversion circuit 42. The current-voltage conversion circuit 42 converts the input detected current 31 into a detected voltage 32 (refer to Figure 3 ). The detected voltage 32 converted by the current-voltage conversion circuit 42 is input to the pulse generation circuit 43 and the overcurrent determination circuit 44 respectively.

[0041] In the state where the control unit 16 (refer to Figure 1 ) continuously outputs a pulsed control signal 21 (refer to Figure 1 ) for turning on and off the switching element 13a (refer to Figure 1 ) to the gate drive unit 14 (refer to Figure 1 ), in the case where no abnormality among the four types of abnormalities occurs, the detected current 31 (refer to Figure 1 ) changes in a substantially pulsed manner corresponding to the pulsed control signal 21. In addition, as shown in Figure 3 , in the control signal output state, in the case where a failure of the GDU power supply 15 (refer to Figure 3 ) and a connection failure of the wiring between the switching element 13a (refer to Figure 1 ) and the gate drive unit 14 occur, the detected current 31 continues to be in a state of being too small. In addition, as shown in Figure 1 and Figure 4 and Figure 5 , in the control signal output state, in the case where a short circuit inside the gate drive unit 14 (refer to Figure 1 ) and the switching element 13a (refer to Figure 1In the case of a short circuit inside , the detected current 31 continues to be in an excessive state. Further, the detected voltage 32 changes in proportion to the detected current 31.

[0042] As Figure 2 shown, the pulse generation circuit 43 is configured to output a low level when the detected voltage 32 (see Figure 3 ) is smaller than a specified first threshold V th1 (see Figure 3 ). Further, the pulse generation circuit 43 is configured to output a high level when the detected voltage 32 is larger than a third threshold (not shown) (larger than the first threshold V th1 ). As Figure 3 shown, the first threshold V th1 is set such that, in the control signal output state, the detected voltage 32 output in the state where the pulsed control signal 21 (see Figure 1 ) is at a low level is sufficiently smaller than the third threshold and larger than the first threshold V th1 . Further, the third threshold is set such that, in the control signal output state, the detected voltage 32 output in the state where the pulsed control signal 21 is at a high level is sufficiently larger than the first threshold V th1 and smaller than the third threshold. Further, Figure 3 shows a state where the detected voltage 32 is lower than the first threshold V th1 continuously, and the detection signal 22 (described later) is continuously at a low level.

[0043] Accordingly, as Figure 2 shown, the pulse generation circuit 43 continuously outputs a pulsed signal (where a high level and a low level are alternately repeated at a fixed period) in the control signal output state when the detected voltage 32 is not too small. Further, the pulse generation circuit 43 continuously outputs a low level in the control signal output state when the state where the detected current 31 is too small continues. That is, in the present embodiment, the abnormality detection circuit 40 is configured to detect at least one of a failure of the GDU power supply 15 (see th1 ) and a poor connection of the gate wiring when the detected voltage 32 is smaller than the first threshold V Figure 1 .

[0044] The overcurrent determination circuit 44 is configured to output a high level when the detected voltage 32 (see Figure 4 ) is smaller than a specified second threshold V th2 (see Figure 4 ) (larger than the third threshold). Further, the overcurrent determination circuit 44 is configured to output a low level when the detected voltage 32 is larger than the second threshold V th2 . As Figure 4 and Figure 5As shown, the second threshold value V th2 is set to be larger than the detection voltage 32 output in the state where the pulsed control signal 21 (refer to Figure 1 ) is at a high level in the control signal output state. Further, in Figure 4 and Figure 5 , it is shown that in the middle of the time axis, the detection voltage 32 exceeds the second threshold value V th2 thereby detecting that the detection signal 22 (described later) changes from a high level to a low level, and the state where the detection voltage 32 exceeds the second threshold value V th2 continues, showing the state where the detection signal 22 continues to be at a low level.

[0045] As Figure 5 shown, in the present embodiment, the second threshold value V th2 is set to a value corresponding to a state where internal short circuits occur simultaneously in three or more switching elements 13a (refer to Figure 1 ). Further, in a structure where a common drive current is output from one gate drive unit 14 to a plurality of switching elements 13a connected in parallel to each other, the detection voltage 32 is substantially proportional to the number of switching elements 13a in which internal short circuits occur simultaneously. Thus, as shown in the comparative example of Figure 7 , when the second threshold value is set to a value corresponding to a state where internal short circuits occur simultaneously in one or more switching elements 13a (second threshold value V th12 ), the second threshold value V th12 becomes a smaller value (about (1 / 3)) compared to the second threshold value V th2 of the present embodiment. In this case, it is difficult to distinguish from the detection voltage 32 output in the state where the pulsed control signal 21 (refer to Figure 1 ) is at a high level in the control signal output state, which becomes a main cause of false detection.

[0046] Accordingly, as shown in Figure 4 and Figure 5 , the overcurrent determination circuit 44 continuously outputs a high level in the control signal output state. Further, the overcurrent determination circuit 44 continuously outputs a low level in the control signal output state when the state where the detection current 31 is excessive continues. That is, in the present embodiment, the abnormality detection circuit 40 is configured to detect at least one of an internal short circuit in the gate drive unit 14 (refer to Figure 1 ) and an internal short circuit in the switching element 13a (refer to Figure 1 ) when the detection voltage 32 is larger than the second threshold value V th12 .

[0047] As Figure 2As shown, the AND circuit 45 is configured to receive the outputs of the input pulse generation circuit 43 and the overcurrent determination circuit 44. The AND circuit 45 outputs a high level when all inputs are high level, and outputs a low level when at least one of the inputs is a low level abnormal input.

[0048] Thus, when the state where the detected current 31 changes in a substantially pulsed manner corresponding to the pulsed control signal 21 continues (when the states of being too small and too large do not continue), a pulsed signal (where high level and low level alternate repeatedly at a fixed period) and a high level are continuously input to the AND circuit 45 from the pulse generation circuit 43 and the overcurrent determination circuit 44 respectively, and the AND circuit 45 continuously outputs a pulsed signal (where high level and low level alternate repeatedly at a fixed period). Additionally, when the state where the detected current 31 is too small continues, a low level and a high level are continuously input to the AND circuit 45 from the pulse generation circuit 43 and the overcurrent determination circuit 44 respectively, and the AND circuit 45 continuously outputs a low level. Moreover, when the state where the detected current 31 is too large continues, a high level and a low level are continuously input to the AND circuit 45 from the pulse generation circuit 43 and the overcurrent determination circuit 44 respectively, and the AND circuit 45 continuously outputs a low level.

[0049] With the above circuit structure from the current detection unit 41 to the AND circuit 45, in the present embodiment, the abnormality detection circuit 40 is configured to continuously output a pulsed detection signal 22a (refer to Figure 3 ) when, in the control signal output state, no abnormality among the four types of abnormalities is detected based on the detection voltage 32 (refer to Figure 6 ). Additionally, the abnormality detection circuit 40 is configured to continuously output a non-pulsed detection signal 22b (refer to Figure 6 ) when, in the control signal output state, at least one of the four types of abnormalities is detected based on the detection voltage 32. Furthermore, in the power conversion device 100, it is not determined whether a certain abnormality among the four types of abnormalities has occurred.

[0050] Moreover, in the present embodiment, the abnormality detection circuit 40 is configured to output a detection signal 22 (non-pulsed detection signal 22b) indicating that at least one of the four types of abnormalities has been detected to the control unit 16 (refer to Figure 1 ) when at least one of the four types of abnormalities is detected (refer to Figure 6)。In addition, as described below, the outputs of the abnormality detection circuits 40a for the switching element Q1, the outputs of the abnormality detection circuits 40b for the switching element Q2, the outputs of the abnormality detection circuits 40c for the switching element Q3, and the outputs of the abnormality detection circuits 40d for the switching element Q4 are combined in a logic circuit and then output to the control unit 16. That is, in the power conversion device 100, it is not determined whether any of the four abnormalities has occurred in the part associated with a certain switching element 13a (Q1, Q2, Q3, Q4).

[0051] Specifically, the output of the pulse generation circuit 43a of the abnormality detection circuit 40a, the output of the overcurrent determination circuit 44a of the abnormality detection circuit 40a, the output of the pulse generation circuit 43b of the abnormality detection circuit 40b, and the output of the overcurrent determination circuit 44b of the abnormality detection circuit 40b are input to the AND circuit 45b. Similarly, the output of the pulse generation circuit 43c of the abnormality detection circuit 40c, the output of the overcurrent determination circuit 44c of the abnormality detection circuit 40c, the output of the pulse generation circuit 43d of the abnormality detection circuit 40d, and the output of the overcurrent determination circuit 44d of the abnormality detection circuit 40d are input to the AND circuit 45c.

[0052] The output of the AND circuit 45b is input to the NOT circuit 46b. In addition, the output of the AND circuit 45c is input to the NOT circuit 46c. The NOT circuits 46 (46b, 46c) invert and output the input (high level or low level). The output of the NOT circuit 46b and the output of the NOT circuit 46c are input to the OR circuit 47. The OR circuit 47 outputs a high level when any of the inputs is a high level, and outputs a low level when both of the inputs are low levels. The output of the OR circuit 47 is input to the NOT circuit 48. The NOT circuit 48 inverts and outputs the input (high level or low level). Moreover, the output of the NOT circuit 48 is input as the detection signal 22 (refer to Figure 6 ) to the auxiliary substrate 16b of the control unit 16 (refer to Figure 1 ).

[0053] Moreover, in the present embodiment, as Figure 6 shown, the control unit 16 (refer to Figure 1 ) is configured to determine that at least one of the four abnormalities has occurred when the non-pulsed detection signal 22b is continuously output from the abnormality detection circuit 40 (refer to 1 ) throughout a specified first period T Figure 1 which is based on the pulsed control signal 21 (refer to 1 ), and the specified first period T Figure 1The period of the period setting of (). In addition, the control unit 16 is configured to start from the start of determining whether at least one of the four types of abnormalities has occurred for at least the entire specified second period T 2 When the detection signal 22 (non-pulsed detection signal 22b) indicating that at least one of the four types of abnormalities has been detected is not continuously output from the abnormality detection circuit 40, it is determined that none of the four types of abnormalities has occurred, and the specified second period T 2 is longer than the first period T 1 .

[0054] Specifically, as shown in (A) of Figure 6 , the control board 16a (refer to Figure 1 ) continuously outputs a signal (fault diagnosis start signal) for starting fault diagnosis based on the operator's operation to the auxiliary board 16b (refer to Figure 1 ). In addition, the control board 16a continuously outputs a pulsed control signal 21 (refer to Figure 1 ) to the gate drive unit 14 via the auxiliary board 16b. That is, it becomes the control signal output state. In addition, in (A) of Figure 6 , the state where the fault diagnosis start signal is high level and the state where it is low level are respectively the state where the fault diagnosis start signal is not input and the state where the fault diagnosis start signal is input, and the high level and the low level can also be reversed.

[0055] As shown in (B) of Figure 6 , in the control signal output state, when the state that changes in a substantially pulsed manner corresponding to the pulsed control signal 21 (refer to Figure 1 ) continues (the state of being too small or too large does not continue), a pulsed detection signal 22a is continuously output to the auxiliary board 16b (refer to Figure 1 ). In addition, in the control signal output state, when the state where the detection current 31 (refer to Figure 3 ) is too small or too large continues, a low level (non-pulsed detection signal 22b) is continuously output to the auxiliary board 16b.

[0056] As shown in (C) of Figure 6 , the auxiliary board 16b (refer to Figure 1 ) detects the rise (from low level to high level) and fall (from high level to low level) of the input detection signal 22. The auxiliary board 16b starts the timer from when the fault diagnosis start signal is input (measurement time). Moreover, the auxiliary board 16b resets the timer when the detection signal 22 rises and falls. Moreover, the auxiliary board 16b repeatedly determines whether the time of the timer has reached the period T 1A . The period T 1Ais the period starting from when the timer is not reset. Period T 1A corresponds to a first period T starting from when the pulsed detection signal 22a changes to the non-pulsed detection signal 22b. That is, the auxiliary substrate 16b is configured to indirectly determine whether the non-pulsed detection signal 22b has been continuously output throughout the first period T 1 based on the rise and fall of the detection signal 22. 1 Moreover, the period T of the pulsed detection signal 22a

[0057] corresponds to the period of the pulsed control signal 21 (see S ). Therefore, the period T Figure 1 (the first period T Figure 1 ) is set based on the period of the pulsed control signal 21 (see 1A (the first period T 1 ) to avoid misjudgment in the case of too short a period. The period T 1A (the first period T 1 ) is, for example, several tens to several hundreds of times the period of the pulsed control signal 21.

[0058] As shown in (D) of Figure 6 , when the time of the timer on the auxiliary substrate 16b (see Figure 1 ) reaches the period T 1A , it is determined that at least one of the four types of abnormalities (faults) has occurred. When the auxiliary substrate 16b determines a fault, it changes the output of the fault determination from the high level (normal) state to the low level (abnormal) state and continuously outputs the low level (abnormal) state.

[0059] As shown in (A) of Figure 6 , when the time elapsed from the start of outputting the fault diagnosis start signal on the control substrate 16a (see Figure 1 ) reaches the second period T 2 , the output of the fault diagnosis start signal and the output of the pulsed control signal 21 are stopped, and the fault diagnosis based on the auxiliary substrate 16b is ended. The second period T 2 is set to a period at least longer than the first period T 1 . The second period T 2 is, for example, several times to several tens of times the first period T 1 . Moreover, when the time of the timer on the auxiliary substrate 16b does not reach the period T 2 throughout the second period T 1A , it is determined that none of the four types of abnormalities (no fault) has occurred.

[0060] Furthermore, as shown in Figure 1As shown, in the present embodiment, the control unit 16 is configured to control the display unit 17 to display that at least one of the four types of abnormalities has occurred when it is determined that at least one of the four types of abnormalities has occurred. Specifically, the auxiliary substrate 16b outputs the determination result of whether a failure has occurred or not to the control substrate 16a. Moreover, the control substrate 16a controls the display unit 17 to display the determination result of whether a failure has occurred or not. In addition, the above-mentioned failure determination is performed in the uncharged state.

[0061] (Effect of the embodiment)

[0062] In the present embodiment, the following effects can be obtained.

[0063] In the present embodiment, as described above, the control unit 16 is configured to determine whether an abnormality related to the gate drive unit 14, the GDU power supply 15, and the switching element 13a has occurred based on the detection current 31 between the gate drive unit 14 and the GDU power supply 15. Thus, when the detection current 31 is abnormal (when the state of being too small or too large continues), the control unit 16 can determine that an abnormality such as an open circuit or a short circuit has occurred in the circuit including the gate drive unit 14, the GDU power supply 15, and the switching element 13a. In addition, the detection current 31 can be easily obtained by measuring the current between the gate drive unit 14 and the GDU power supply 15. As a result, it is possible to determine an abnormality related to the gate drive unit 14, the GDU power supply 15, and the switching element 13a without adding functions other than the original functions to the gate drive unit 14, the GDU power supply 15, and the switching element 13a.

[0064] In addition, in the present embodiment, as described above, the control unit 16 is configured to determine whether at least one of the four types of abnormalities, namely, a short circuit inside the gate drive unit 14, a failure of the GDU power supply 15, a short circuit inside the switching element 13a, and a poor connection of the wiring between the switching element 13a and the gate drive unit 14, has occurred based on the detection current 31. Thus, it is possible to determine whether at least one of an abnormality has occurred inside the gate drive unit 14 including components with a relatively high failure rate, the GDU power supply 15, inside the switching element 13a, and the wiring between the switching element 13a and the gate drive unit 14.

[0065] In addition, in the present embodiment, as described above, the power conversion device 100 includes the display unit 17. Moreover, the control unit 16 is configured to control the display unit 17 to display that at least one of the four types of abnormalities has occurred when it is determined that at least one of the four types of abnormalities has occurred. Thus, by displaying that at least one of the four types of abnormalities has occurred on the display unit 17, an operator or the like performing maintenance inspection of the power conversion device 100 can easily and quickly recognize that at least one of the four types of abnormalities has occurred. As a result, for example, compared with the case where an operator uses a measuring device to perform inspections related to the four types of abnormalities, even when not having specific expertise, it is possible to check whether at least one of the four types of abnormalities has occurred, and it is possible to suppress an increase in the downtime (time when the device cannot be used) of the power conversion device 100 due to prolonged maintenance inspection.

[0066] In addition, in the present embodiment, as described above, the power conversion device 100 includes the abnormality detection circuit 40, and the abnormality detection circuit 40 detects whether at least one of the four types of abnormalities has occurred based on the detection voltage 32 obtained by converting the detection current 31 into a voltage. Moreover, the abnormality detection circuit 40 is configured to output a detection signal 22 (non-pulsed detection signal 22b) indicating that at least one of the four types of abnormalities has been detected to the control unit 16 when at least one of the four types of abnormalities has been detected. Thus, the control unit 16 can easily determine whether at least one of the four types of abnormalities has occurred based on the detection signal 22 indicating that at least one of the four types of abnormalities has been detected and input from the abnormality detection circuit 40.

[0067] In addition, in the present embodiment, as described above, the abnormality detection circuit 40 is configured to detect at least one of a failure of the GDU power supply 15 and a poor connection of the wiring between the switching element 13a and the gate drive unit 14 when the detection voltage 32 is smaller than a specified first threshold V th1 In addition, the abnormality detection circuit 40 is configured to detect at least one of a short circuit inside the gate drive unit 14 and a short circuit inside the switching element 13a when the detection voltage 32 is larger than a specified second threshold V th2 The second threshold V th2 is larger than the first threshold V th1 Thus, when the detection voltage 32 is too small due to a failure of the GDU power supply 15 or a poor connection of the wiring between the switching element 13a and the gate drive unit 14, the abnormality detection circuit 40 can be based on the first threshold V th1To appropriately detect at least one of a failure of the GDU power supply 15 and a poor connection of the wiring between the switching element 13a and the gate drive unit 14. Further, in the case where the detection voltage 32 becomes excessive due to a short circuit inside the gate drive unit 14 or a short circuit inside the switching element 13a, the abnormality detection circuit 40 can be based on the second threshold V th2 To appropriately detect at least one of a short circuit inside the gate drive unit 14 and a short circuit inside the switching element 13a.

[0068] Further, in the present embodiment, as described above, it is configured to output a common drive current from one gate drive unit 14 to a plurality of switching elements 13a connected in parallel to each other. Moreover, the second threshold V th2 Is set to a value corresponding to a state in which internal short circuits have occurred simultaneously in three or more switching elements 13a. Thereby, the second threshold V th2 Can be set to a relatively high value, so that it is possible to suppress the detection voltage 32 from exceeding the second threshold V when there is no internal short circuit in the switching element 13a th2 And causing the abnormality detection circuit 40 to erroneously detect whether an internal short circuit has occurred in the switching element 13a. In addition, in a structure in which a common drive current is output from one gate drive unit 14 to a plurality of switching elements 13a connected in parallel to each other, internal short circuits of the plurality of switching elements 13a often occur simultaneously. Therefore, even in the case of the above-described configuration, it is possible to generally detect an internal short circuit of the switching element 13a.

[0069] Further, in the present embodiment, as described above, the abnormality detection circuit 40 is configured such that, in a state where the control unit 16 continuously outputs a pulsed control signal 21 for turning on and off the switching element 13a to the gate drive unit 14, when no abnormality among the four types of abnormalities is detected based on the detection voltage 32, a pulsed detection signal 22a is continuously output, and when at least one of the four types of abnormalities is detected, a non-pulsed detection signal 22b is continuously output. Thereby, the control unit 16 can more easily determine whether at least one of the four types of abnormalities has occurred based on the pulsed detection signal 22a and the non-pulsed detection signal 22b continuously input from the abnormality detection circuit 40.

[0070] Further, in the present embodiment, as described above, the abnormality detection circuit 40 includes a pulse generation circuit 43, an overcurrent determination circuit 44, and an AND circuit 45. The pulse generation circuit 43 is configured to output a low level when the detection voltage 32 is smaller than a specified first threshold V th1 And output a high level when the detection voltage 32 is larger than a third threshold, and the third threshold is larger than the first threshold Vth1 is large. In addition, the overcurrent determination circuit 44 is configured to output a high level when the detected voltage 32 is smaller than a specified second threshold V th2 and output a low level when the detected voltage 32 is larger than the second threshold V th2 , and the second threshold V th2 is larger than the third threshold. Moreover, the AND circuit 45 is configured to be input with the output of the pulse generation circuit 43 and the output of the overcurrent determination circuit 44. Thus, in a state where the control unit 16 continuously outputs the pulsed control signal 21 to the gate drive unit 14 (control signal output state), when the detected voltage 32 does not become too large or too small, a pulsed signal (where high and low levels alternately repeat at a fixed period) and a high level can be continuously output from the pulse generation circuit 43 and the overcurrent determination circuit 44 respectively. Therefore, a pulsed signal (pulsed detection signal 22a) can be continuously output from the AND circuit 45. In addition, in the control signal output state, when the state where the detected voltage 32 is too small continues, a low level and a high level are continuously output from the pulse generation circuit 43 and the overcurrent determination circuit 44 respectively. Therefore, a low level (non-pulsed detection signal 22b) can be continuously output from the AND circuit 45. In addition, in the control signal output state, when the state where the detected voltage 32 is too large continues, a high level and a low level can be continuously output from the pulse generation circuit 43 and the overcurrent determination circuit 44 respectively. Therefore, a low level (non-pulsed detection signal 22b) can be continuously output from the AND circuit 45. As a result, in the case where none of the four types of abnormalities is detected and in the case where at least one of the four types of abnormalities is detected, a pulsed detection signal 22a and a non-pulsed detection signal 22b can be easily and continuously output from the abnormality detection circuit 40 respectively.

[0071] In addition, in the present embodiment, as described above, the control unit 16 is configured to determine that at least one of the four types of abnormalities has occurred when the non-pulsed detection signal 22b is continuously output from the abnormality detection circuit 40 throughout a specified first period T 1 , and the specified first period T 1 is a period set based on the period of the pulsed control signal 21. Thus, since it is determined that at least one of the four types of abnormalities has occurred when the non-pulsed detection signal 22b is continuously output from the abnormality detection circuit 40 throughout the first period T 1 , it is possible to suppress misjudgment that at least one of the four types of abnormalities has occurred when the non-pulsed detection signal 22b is temporarily output due to noise or the like. In addition, by setting the first period T 1 based on the period of the pulsed control signal 21, the first period T can be appropriately set.1 so that the first period T 1 is sufficiently longer than the period T of the pulsed detection signal 22a corresponding to the period of the pulsed control signal 21 S is.

[0072] In addition, in the present embodiment, as described above, the control unit 16 is configured to determine whether at least one of the four types of abnormalities has occurred during at least the entire specified second period T starting from the start of the determination of whether at least one of the four types of abnormalities has occurred 2 When the detection signal 22 (non-pulsed detection signal 22b) indicating that at least one of the four types of abnormalities has been detected is not continuously output from the abnormality detection circuit 40, it is determined that none of the four types of abnormalities has occurred, and the specified second period T 2 is longer than the first period T 1 . Thus, since it is determined whether at least one of the four types of abnormalities has occurred during the first period T 1 , it is possible to reliably determine that none of the four types of abnormalities has occurred when the detection signal 22 (non-pulsed detection signal 22b) indicating that at least one of the four types of abnormalities has been detected is not continuously output during the second period T 1 which is longer than the first period T 2 .

[0073] In addition, in the present embodiment, as described above, the load 300 is an induction heating coil of an induction heating furnace for melting metal by induction heating. Thus, in the power conversion device 100 for an induction heating furnace, it is possible to determine abnormalities related to the gate drive unit 14, the GDU power supply 15, and the switching element 13a without adding functions other than the original functions to the gate drive unit 14, the GDU power supply 15, and the switching element 13a

[0074] [Modification Example]

[0075] All points of the embodiments disclosed herein should be considered illustrative rather than restrictive. The scope of the present invention is shown not by the description of the above embodiments but by the claims, and the scope of the present invention also includes all modifications (modification examples) within the meaning and scope equivalent to the claims

[0076] For example, in the above-described embodiment, an example is shown in which an AND circuit 45b for the switching element Q2 is used in parallel with the abnormality detection circuit 40a for the switching element Q1, and an AND circuit 45c for the switching element Q3 is used in parallel with the abnormality detection circuit 40d for the switching element Q4. However, the present invention is not limited thereto. In the present invention, the AND circuit 45b for the switching element Q2 may not be used in parallel with the abnormality detection circuit 40a for the switching element Q1, or the AND circuit 45c for the switching element Q3 may not be used in parallel with the abnormality detection circuit 40d for the switching element Q4. Additionally, the AND circuit 45b for the switching element Q2 may be used in parallel with the abnormality detection circuit 40a for the switching element Q1, the abnormality detection circuit 40c for the switching element Q3, and the abnormality detection circuit 40d for the switching element Q4.

[0077] Furthermore, in the above-described embodiment, an example is shown in which a NOT circuit 46, an OR circuit 47, and a NOT circuit 48 are sequentially provided between the AND circuit 45 and the auxiliary substrate 16b. However, the present invention is not limited thereto. In the present invention, only an OR circuit may be provided between the AND circuit and the auxiliary substrate.

[0078] Furthermore, in the above-described embodiment, an example is shown in which the auxiliary substrate 16b is configured to indirectly determine whether a non-pulsed detection signal 22b is continuously output throughout the entire first period T based on the rise and fall of the detection signal 22. 1 However, the present invention is not limited thereto. In the present invention, the auxiliary substrate may be configured to directly determine whether a non-pulsed detection signal is continuously output throughout the entire first period.

[0079] Furthermore, in the above-described embodiment, an example is shown in which the second threshold V th2 is set to a value corresponding to a state in which internal short circuits have occurred simultaneously in three or more switching elements 13a. However, the present invention is not limited thereto. In the present invention, the second threshold may be set to a value corresponding to a state in which internal short circuits have occurred simultaneously in two or more switching elements, or may be set to a value corresponding to a state in which internal short circuits have occurred simultaneously in N (where N is 4) or more switching elements.

[0080] Furthermore, in the above-described embodiment, an example is shown in which the abnormality detection circuit 40 is configured to detect whether at least one of four types of abnormalities has occurred based on a detection voltage 32 obtained by converting a detection current 31 into a voltage. However, the present invention is not limited thereto. In the present invention, the abnormality detection circuit may be configured to detect whether at least one of four types of abnormalities has occurred based on the detection current itself.

[0081] In addition, in the above-described embodiment, an example is shown in which the control unit 16 (control section) is configured to control the display unit 17 to display that at least one of the four types of abnormalities has occurred when it is determined that at least one of the four types of abnormalities has occurred. However, the present invention is not limited thereto. In the present invention, the control unit may also be configured not to control the display unit to display that at least one of the four types of abnormalities has occurred when it is determined that at least one of the four types of abnormalities has occurred. In this case, it may also be configured to cause the control section to notify by sound that at least one of the four types of abnormalities has occurred so that the operator can confirm the result of the failure determination. In addition, the control section may also be configured to notify an external device of the power conversion device that at least one of the four types of abnormalities has occurred.

[0082] In addition, in the above-described embodiment, an example is shown in which the control substrate 16a and the auxiliary substrate 16b are provided separately from each other. However, the present invention is not limited thereto. In the present invention, the control substrate and the auxiliary substrate may also be provided integrally.

[0083] In addition, in the above-described embodiment, an example is shown in which a plurality (six) of the switching elements 13a are connected in parallel to each other in each of the switching elements Q1, Q2, Q3, and Q4. However, the present invention is not limited thereto. In the present invention, the number of switching elements connected in parallel to each other in the switching elements Q1, Q2, Q3, and Q4 may also be several.

[0084] In addition, in the above-described embodiment, an example is shown in which the power conversion device 100 is a power conversion device for an induction heating furnace. However, the present invention is not limited thereto. In the present invention, the "power conversion device" may also be a power conversion device other than for an induction heating furnace.

Claims

1. A power conversion device, comprising: A power conversion unit including a switching element, which converts the input power and outputs it to a load; A gate drive unit that outputs a drive current for controlling the switching element to the switching element; A control unit that outputs a control signal for generating the drive current to the gate drive unit; And A drive power supply unit that supplies power for generating the drive current in the gate drive unit, wherein the control unit is configured to determine whether an abnormality has occurred in at least one of the inside of the gate drive unit, the drive power supply unit, the inside of the switching element, and the wiring between the switching element and the gate drive unit based on a detection current between the gate drive unit and the drive power supply unit.

2. The power conversion device according to claim 1, wherein the control unit is configured to determine whether at least one of the following four abnormalities has occurred based on the detection current. The four abnormalities are a short circuit inside the gate drive unit, a failure of the drive power supply unit, a short circuit inside the switching element, and a poor connection of the wiring between the switching element and the gate drive unit.

3. The power conversion device according to claim 2, wherein it further includes a display unit, and the control unit is configured to control the display unit to display that at least one of the four abnormalities has occurred when it is determined that at least one of the four abnormalities has occurred.

4. The power conversion device according to claim 2, wherein it further includes an abnormality detection circuit, and the abnormality detection circuit detects whether at least one of the four abnormalities has occurred based on the detection current or a detection voltage obtained by converting the detection current into a voltage, and the abnormality detection circuit is configured to output a detection signal indicating that at least one of the four abnormalities has been detected to the control unit when it detects that at least one of the four abnormalities has occurred.

5. The power conversion device according to claim 4, wherein the abnormality detection circuit is configured to detect at least one of a failure of the drive power supply unit and a poor connection of the wiring between the switching element and the gate drive unit when the detection current or the detection voltage is smaller than a specified first threshold, and to detect at least one of a short circuit inside the gate drive unit and a short circuit inside the switching element when the detection current or the detection voltage is larger than a specified second threshold, and the second threshold is larger than the first threshold.

6. The power conversion device according to claim 5, wherein the power conversion device is configured to output a common drive current to a plurality of the switching elements connected in parallel to each other from one gate drive unit, and the second threshold is set to a value corresponding to a state in which internal short circuits have occurred simultaneously in three or more of the switching elements.

7. The power conversion device according to claim 4, wherein The circuit for anomaly detection is configured such that, in a state where the control unit is continuously outputting the pulsed control signal for turning on and off the switching element to the gate drive unit, when none of the four anomalies is detected based on the detected current or the detected voltage, a pulsed detection signal is continuously output, and when at least one of the four anomalies is detected, a non-pulsed detection signal is continuously output.

8. The power conversion device according to claim 7, wherein, the circuit for anomaly detection includes: a pulse generation circuit that outputs a low level when the detected current or the detected voltage is smaller than a prescribed first threshold value, and outputs a high level when the detected current or the detected voltage is larger than a third threshold value, the third threshold value being larger than the first threshold value; an overcurrent determination circuit that outputs a high level when the detected current or the detected voltage is smaller than a prescribed second threshold value, and outputs a low level when the detected current or the detected voltage is larger than the second threshold value, the second threshold value being larger than the third threshold value; and an AND circuit to which the output of the pulse generation circuit and the output of the overcurrent determination circuit are input.

9. The power conversion device according to claim 7, wherein, the control unit is configured such that, when the non-pulsed detection signal is continuously output from the circuit for anomaly detection throughout a prescribed first period, it is determined that at least one of the four anomalies has occurred, the prescribed first period being a period set based on the period of the pulsed control signal.

10. The power conversion device according to claim 9, wherein, the control unit is configured such that, when no detection signal indicating that at least one of the four anomalies has been detected is continuously output from the circuit for anomaly detection for at least the entire prescribed second period starting from the start of determination of whether at least one of the four anomalies has occurred, it is determined that none of the four anomalies has occurred, the prescribed second period being longer than the first period.

11. The power conversion device according to claim 1, wherein, the load is an induction heating coil of an induction heating furnace for melting metal by induction heating.

Images