JP6302760B2 - Power conversion device having degradation diagnosis function - Google Patents

Description

  The present invention relates to a power conversion device having a deterioration diagnosis function.

  In recent years, in order to reduce switching loss in power conversion devices, IGBTs (Insulated Gate Bipolar Transistors) and MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors), which are voltage-driven switching elements, are applied.

  It has been reported that these switching elements deteriorate over time due to long-term use, and characteristics such as on-resistance and on-voltage are deteriorated. As the deterioration progresses, the power conversion device may be damaged due to a short circuit or an open failure. In order to prevent destruction of a power converter, attention has been paid to a technique for detecting deterioration of a switching element.

  Since the on-resistance and on-voltage of the switching element have temperature dependency, the on-resistance and on-voltage are detected to detect the deterioration, and the junction temperature of the switching element is detected with high accuracy to diagnose the deterioration. There is a need to. However, since the junction temperature changes from moment to moment according to the state of the switching element, and it is difficult to accurately detect the temperature, a technique for diagnosing the deterioration of the switching element without using a temperature sensor is required.

  There exists Unexamined-Japanese-Patent No. 2009-159671 (patent document 1) as background art of this technical field. This publication states that “the failure detection device detects the voltage between the main electrodes of the IGBT as a power element through a diode. In the failure detection device, the anode voltage of the diode is lower than a predetermined reference voltage. The IGBT is determined to be a short-circuit failure, and preferably, when it is determined that the anode voltage of the diode is higher than a predetermined reference voltage, the flywheel diode is in the on state. Can be excluded "(see summary).

  Moreover, there exists Unexamined-Japanese-Patent No. 2010-220470 (patent document 2) as another background art. In this publication, “a fault diagnosing device has a rectifying element whose cathode is connected to the collector of the IGBT, a resistance element whose one end is connected to the anode of the rectifying element, and a positive voltage is applied to the emitter at the other end. A deterioration determining unit for determining deterioration of the battery, wherein the deterioration determining unit detects between the anode of the rectifying element and the emitter of the IGBT, which is detected when the magnitude of the main current matches a predetermined reference current. It is determined whether or not the voltage exceeds the reference voltage, and the reference current is set such that the magnitude of the main current is a boundary between the first region and the second region. The region where the voltage between the emitters has a negative temperature dependency, and the second region is the region where the voltage between the collector and the emitter has a positive temperature dependency ”(see the summary). .

JP2009-159671 JP 2010-220470

  The above two prior art documents are devices for diagnosing a failure or deterioration using a cross point having no temperature characteristic in the main current dependence of the collector-emitter voltage of the IGBT. However, since there is no cross point in the main current dependency of the drain-source voltage of the MOSFET, the technique described in the prior art document cannot diagnose the deterioration of the MOSFET unless the junction temperature of the switching element is accurately detected. There was a problem.

In order to solve the problem, for example, the configuration described in the claims is adopted. The present application includes a plurality of means for solving the above-described problems. To give an example, a switching device including a switching element whose main current changes according to a control signal input to a gate terminal is predetermined. Gate voltage switching means for switching the gate voltage of the switching element to a predetermined diagnosis voltage when a reference current and the main current match, and the main current when the gate voltage switching means is operated is A switching device comprising diagnostic means for inputting a gate stop control signal to the gate terminal of the switching element or outputting an alarm when different from a reference current.

  According to the present invention, it is possible to detect the presence or absence of deterioration of a switching element regardless of the junction temperature of the switching element.

It is a graph which shows the characteristic of MOSFET used by the degradation diagnostic means of this invention, and IGBT. It is a flowchart which shows the process of the degradation diagnostic means by Example 1 of this invention. It is a figure which shows the gate voltage etc. at the time of applying Example 1 of this invention. It is a circuit diagram of the power converter device to which the degradation diagnosis means of the present invention is applied. It is a circuit diagram of the power converter device to which the degradation diagnosis means of the present invention is applied. It is a circuit structure which implement | achieves the deterioration diagnostic means used in Example 1 of this invention. It is a graph which shows the characteristic of IGBT and MOSFET which are used with the degradation diagnostic means of Example 2 of this invention. It is a circuit diagram of the power converter device which implements Example 2 of the present invention.

  Embodiments will be described below with reference to the drawings. In the drawings and examples, MOSFETs are taken up as switching elements, but the present invention is also applicable to voltage-driven switching elements such as IGBTs.

In the first embodiment, a deterioration diagnosis unit that detects that the characteristics of the MOSFET have deteriorated will be described.
(Characteristics of MOSFET used for deterioration diagnosis)
FIG. 1 shows the characteristics of the MOSFET used when diagnosing the deterioration of the MOSFET in the first embodiment. The characteristics of the IGBT are the same as in FIG. The horizontal axis represents the gate voltage input to the gate terminal of the MOSFET, and the vertical axis represents the main current flowing through the drain electrode and the source electrode of the MOSFET. The solid line and the broken line show the characteristics of the saturation current with respect to the gate voltage when the temperature of the switching element is 25 ° C. and 125 ° C., respectively.

  The MOSFET is switched between on and off states by applying a gate voltage to the gate terminal. If this gate voltage is equal to or higher than the threshold voltage Vth of the MOSFET, the transistor is turned on and a saturation current corresponding to the gate voltage flows between the source and drain. On the other hand, if the gate voltage is less than the threshold voltage of the MOSFET, it is turned off. Here, the threshold voltage Vth varies depending on the temperature. Generally, the threshold voltage is lower at 125 ° C. than at 25 ° C. For example, it is 3.2 V at 125 ° C. and 2.5 V at 125 ° C.

  Here, as shown in FIG. 1, there is a temperature-independent cross point 102 in the saturation current dependence of the MOSFET gate voltage for different temperatures. In the region where the gate voltage is lower than the cross point 102, the saturation current increases as the temperature increases even if the gate voltage is constant. That is, in this region, the saturation current has a positive temperature dependency. On the other hand, in the region where the gate voltage is higher than the cross point 102, the saturation current decreases as the temperature increases. That is, the saturation current has a negative temperature dependency.

  The gate voltage and saturation current at the cross point 102, which is the boundary between the two regions, are set as the deterioration diagnosis voltage 103 and the reference current 101, respectively. Since the MOSFET does not change in saturation current due to temperature at the cross point 102, detecting the characteristics of the gate voltage and saturation current at the cross point 102 enables deterioration diagnosis that does not require a temperature sensor.

  In this embodiment, in order to reduce the conduction loss of the MOSFET, a voltage sufficiently higher than the threshold voltage Vth is applied as the gate voltage when the MOSFET is normally turned on. The gate voltage that normally turns on is referred to as an operating gate voltage 105. In general, the deterioration diagnosis voltage 103 is lower than the operation gate voltage 105. For example, the operating gate voltage 105 is 18V, and the deterioration diagnosis voltage 103 is 9V. However, the deterioration diagnosis voltage 103 does not necessarily have to be lower than the operation gate voltage 105.

Although the reference current 101 and the deterioration diagnosis voltage 103 at the cross point 102 differ depending on individual MOSFETs, the reference current 101 is generally about 0.8 times the current rating, and the deterioration diagnosis voltage 103 is within the breakdown voltage of the gate voltage. . That is, deterioration can be diagnosed if the MOSFET is operated within the rated range. When the MOSFET has deteriorated, characteristics such as the threshold voltage Vth and transconductance of the MOSFET change from the initial state. For this reason, when operating with the deterioration diagnosis voltage 103 of the cross point 102 when the element has changed compared to the initial state due to deterioration of the element, the main current has a current value different from that of the reference current 101. For example, a main current (saturation current at the operating point 104) lower than the reference current 101 flows. That is, it is possible to diagnose the deterioration of the switching element regardless of the temperature of the switching element by detecting the main current when operated with the deterioration diagnosis voltage 103 and confirming whether or not it matches the reference current 101. it can.
(Deterioration diagnosis flowchart)
Next, a flowchart of the deterioration diagnosis unit 100 will be described with reference to FIGS. FIG. 2 shows a flowchart of deterioration diagnosis.

  Referring to FIG. 2, in step 1, a gate signal and an operating gate voltage 105 are input to the gate terminal of the MOSFET, and the MOSFET is turned on. When this operation is completed normally, the process proceeds to step 2.

  In step 2, the main current flowing in the MOSFET is detected during the period when the gate signal and the operating gate voltage 105 are input to the MOSFET, and the process proceeds to step 3.

  In step 3, in order to determine whether or not to operate at the cross point 102 shown in FIG. 1, it is determined whether or not the main current of the MOSFET and the reference current 101 match. If the main current and the reference current 101 do not coincide with each other, the process returns to step 1 and a predetermined gate signal and the operating gate voltage 105 are continuously input to the MOSFET. Migrate to

  In step 4, the operation of the gate voltage switching means is started, so that the deterioration diagnosis voltage 103 is applied to the gate terminal of the MOSFET, and the process proceeds to step 5.

  In step 5, the saturation current of the MOSFET during the period in which the gate voltage switching means is operating is detected, and the process proceeds to step 6.

  In step 6, the deterioration of the MOSFET is diagnosed by comparing the saturation current of the MOSFET with the reference current 101. As described above, the saturation current matches the reference current 101 if the MOSFET is not deteriorated. If the saturation current matches the reference current 101, the process returns to step 1.

On the other hand, when the MOSFET is deteriorated, the saturation current at the time of operation at the deterioration diagnosis voltage 103 is different from the reference current, so the main current and the reference current 101 are different, not the cross point 102 in the initial state. Operates at the operating point 104. In such a case, the process proceeds to step 7. If the deteriorated MOSFET continues to be used, the power conversion device is destroyed. Therefore, in step 7, the MOSFET gate signal and gate voltage are quickly stopped. Alternatively, an alarm notifying deterioration may be output instead of stopping the gate signal.
FIG. 3 is a diagram showing temporal changes in the gate voltage, the drain voltage, and the main current when the deterioration diagnosis is performed according to the flowchart described above. First, the period from t1 to t5 in which the processing from step 1 to step 3 is repeated will be described. When the ON signal is input based on the gate signal, the operating gate voltage 105 (for example, 18V) is applied to the gate, and when the OFF signal is input, the low voltage (for example, 0V) is applied to the gate. . During the ON state (t1 to t2, t3 to t4), the drain voltage becomes 0 V, and the main current gradually increases. During the off state (t2 to t3, t4 to t5), the drain voltage becomes the input voltage (for example, 600V), and the main current becomes 0A.

  At time t1, when an ON gate signal is input in step 1, the main current Id is detected in step 2. Since the current has not yet risen at time t1, the main current is zero A here. Therefore, even if the main current (zero A) and the reference current 101 are compared in step 3, they do not match, so the process returns to step 1. This process is repeated until the main current and the reference current match.

  When the main current gradually increases and the main current increases to the value of the reference current at time t6, the process proceeds to step 4 and the operation of the gate voltage switching means starts. That is, at time t6, the gate voltage is decreased from 18V of the operating gate voltage 105 to 9V of the deterioration diagnosis voltage 103. Since the deterioration diagnosis voltage 103 is set to the same value as the gate voltage of the cross point 102, when the switching element is not deteriorated, as shown in FIG. 3, regardless of the temperature of the switching element, the cross point The saturation current (reference current) in 102 flows through the MOSFET as the main current. If the switching element is deteriorated, the operating point is changed to 104 as shown in FIG. 1, so that the saturation current is lower than the reference current 101.

  Therefore, in the example shown in FIG. 3, the main current detected in step 5 matches the reference current in the period from t6 to t7, and it can be confirmed in step 6 that the main current and the reference current match. Return to 1. On the other hand, if the main current detected in step 5 does not match the reference current, it can be determined that the switching element has deteriorated, so the process proceeds to step 7 and the gate signal is stopped.

(Power converter with degradation diagnosis function)
FIG. 4 is a circuit diagram of a motor drive power converter to which the deterioration diagnosis unit of the first embodiment is applied. The power conversion device 3 shows a three-phase inverter, and includes a capacitor 2, MOSFETs Q1 to Q6, gate drive circuits 6a to 6f for applying gate signals and gate voltages for driving the MOSFETs Q1 to Q6, and diodes D1 to D6. The A capacitor 2 is connected to the DC power 1 in parallel for the purpose of stabilizing the DC power 1.

  Of MOSFETs Q1 to Q6, Q1 and Q2 are connected in series to form a U phase, V phase is connected to Q3 and Q4, W phase is connected to Q5 and Q6 in series, and U phase, V phase, W A three-phase inverter is constructed. Here, a three-phase inverter is taken as an example, but other circuit systems may be used as long as it is a power conversion device using a power switching element such as a single-phase inverter or a converter.

  A power line is drawn from a connection point between two MOSFETs connected in series to each phase and is connected to the motor 5. The motor 5 is described as an equivalent circuit using reactors 5a to 5c. Here, although the motor is described by the star connection, other connection methods may be used. Moreover, although the motor 5 is connected to the output of the power converter 3, a system such as a commercial power source may be used.

  The power conversion device 3 converts the DC power 1 into AC power and outputs it by switching the MOSFETs Q1 to Q6 between the on state and the off state. The converted AC power flows in each of the three phases of U phase, V phase, and W phase to drive the motor 5.

  Switching between the on-state and off-state of MOSFETs Q1-Q6 is driven using gate drive circuits 6a-6f, respectively. When the DC power 1 is converted into AC power, for example, pulse width modulation (PWM) is used as a gate signal. By using PWM, the frequency and peak value of the current flowing to the motor 5 can be controlled.

  Diodes D1 to D6 are connected in parallel to MOSFETs Q1 to Q6 constituting the power conversion device 3. The diodes D1 to D6 are connected to circulate the current flowing through the motor 5 when the MOSFETs Q1 to Q6 are turned off. The diodes D1 to D6 may be body diodes or external diodes generated due to the structure of the MOSFET. In the case of external connection, the cathodes of the diodes D1 to D6 are connected to the drain electrodes of the MOSFETs Q1 to Q6, and the anodes of the diodes D1 to D6 are connected to the source electrodes of the MOSFETs Q1 to Q6. Further, when Q1 to Q6 are not MOSFETs but IGBTs, it is necessary to connect diodes D1 to D6.

  In order to diagnose the presence or absence of deterioration in the present invention, it is necessary to detect the main current of the power converter 3. As shown in FIG. 4, the main current can be detected by inserting current sensors 4 a to 4 c into a power line connecting the power converter 3 and the motor 5. Here, it is only necessary that one current sensor is connected to each of the U phase, V phase, and W phase of the motor 5. Alternatively, current sensors 7a to 7f may be inserted into the drain electrodes of MOSFETs Q1 to Q6 as shown in FIG. Further, any means capable of detecting current rather than a current sensor may be used.

(Circuit configuration of deterioration diagnosis means)
FIG. 6 is an example of a circuit configuration for realizing the flowchart of the degradation diagnosis unit 100 of FIG. Hereinafter, as an example, the operation of the deterioration diagnosis means for the MOSFET Q1 in FIG. 4 will be described. The MOSFETs Q2 to Q6 can be diagnosed for deterioration with the same circuit configuration.

  A gate drive circuit 203 is connected to the MOSFET Q1. The gate drive circuit 203 switches the on / off state of the MOSFET Q1 according to the gate signal 202. Here, when the gate signal 202 outputs an ON signal, the transistor 201a operates, and a voltage of the operation gate voltage 105 is applied to the gate terminal as a gate voltage. In order to turn on the MOSFET Q1, it is necessary to apply a gate voltage higher than the threshold voltage of the MOSFET Q1. For example, if the threshold voltage is 3.2V, the operating gate voltage 105 is about 18V.

  On the other hand, when the gate signal 202 outputs an off signal, the transistor 201b operates, and the voltage of the DC power supply 211 is applied to the gate terminal as the gate voltage. In order to turn off the MOSFET Q1, it is necessary to apply a gate voltage lower than the threshold voltage of the MOSFET Q1. These DC power supply 211 and operating gate voltage 105 must be values within the maximum rating of MOSFET Q1. The gate signal for switching the on / off state is, for example, the above PWM.

  Hereinafter, the operation of the gate voltage switching means 213 will be described. The logic circuit 209 always operates by being supplied with power from the DC power supply 217, and determines whether or not the main current 210 flowing through the MOSFET Q1 matches the reference current 101. Here, the main current 210 is measured using the current sensor 4a, and the current sensor 4a is inserted in the power line to the motor, but may be inserted in the drain electrode of the MOSFET Q1 or the source electrode of the MOSFET.

  Semiconductor switches 208 a and 208 b are connected to the output of the logic circuit 209. When the main current 210 and the reference current 101 do not match, the semiconductor switch 208a is turned on by outputting a low level, and when it matches, the semiconductor switch 208b is turned on by outputting a high level.

  The gate voltage applied to the MOSFET Q1 when the logic circuit 209 outputs a low level and the semiconductor switch 208a is on will be described. When the gate signal 202 outputs an ON signal, the transistor 201a is turned ON, so that the operation gate voltage 105 is applied as a gate voltage to the gate terminal. On the other hand, when the gate signal 202 outputs an off signal, the transistor 201b is turned on, so that the DC power supply 211 is applied as a gate voltage to the gate terminal. That is, when the logic circuit 209 outputs a low level, the operation gate voltage 105 is applied because the deterioration diagnosis of the MOSFET Q1 is not performed.

  Next, the gate voltage applied to the MOSFET Q1 when the logic circuit 209 outputs a high level and the semiconductor switch 208b is on will be described. When the gate signal 202 outputs an off signal, the transistor 201b is turned on, and the DC power supply 211 is applied as a gate voltage to the gate terminal of the MOSFET Q1. On the other hand, since the semiconductor switch 208b is in an on state when the gate signal 202 outputs an on signal, the operating gate voltage 105 is applied to the gate terminal of the MOSFET Q1 through the Zener diode 207 as the gate voltage. A voltage that is lower than the operating gate voltage 105 by the Zener voltage is applied to the gate terminal. The deterioration diagnosis voltage 103 is generated by adjusting the Zener voltage of the Zener diode, and the deterioration diagnosis voltage 103 is applied to the gate terminal of the MOSFET Q1.

  For example, if the operating gate voltage 105 is 18V and the deterioration diagnosis voltage is 9V, the Zener voltage of the Zener diode 207 is 9V. Here, the resistor 206 is suppressed so as not to exceed the current rating of the Zener diode 207, and the capacitor 205 is added to eliminate noise of the Zener diode 207 and stabilize the voltage of the resistor 206. Here, although the Zener diode 207, the resistor 206, and the capacitor 205 are used as the switching means for the gate voltage, other means may be used.

  Next, the operation of the deterioration diagnosis unit 219 will be described. When the logic circuit 209 outputs a high level, the semiconductor switch 215 is turned on, and power is supplied from the DC power supply 216 to the logic circuit 217, whereby the operation of the logic circuit 217 is started. That is, the logic circuit 209 operates when the saturation current of the MOSFET Q1 matches the reference current 101, and the degradation diagnosis unit 219 of the MOSFET Q1 starts operating.

  The logic circuit 217 diagnoses the deterioration of the MOSFET Q1 by comparing the saturation current of the MOSFET Q1 with the reference current 101. Specifically, when the saturation current and the reference current 101 match, a low level is output, and it is determined that the MOSFET Q1 has not deteriorated. On the other hand, when the saturation current and the reference current 101 are different, the logic circuit 217 outputs a high level to determine that the characteristic of the MOSFET Q1 has changed from the initial state, that is, has deteriorated.

  If the deteriorated MOSFET is continuously used, the deterioration proceeds, a short circuit or an open failure occurs, and the power conversion device is destroyed. When it is determined that the MOSFET Q1 has deteriorated and the logic circuit 217 outputs a high level, it is necessary to stop the operation of the power conversion device 3 quickly. Therefore, the gate stop signal 218 is output to Stop output. Alternatively, instead of stopping the gate, an alarm notifying that the MOSFET Q1 has deteriorated may be issued. Alternatively, both a gate stop signal and an alarm may be output.

  When the deterioration of any one of the MOSFETs Q1 to Q6 of the power conversion device in FIG. 4 becomes clear, the gate stop signals of all the MOSFETs Q1 to Q6 are output in addition to the corresponding MOSFET. Even if only the gate signal 202 of the MOSFET Q1 is stopped, the AC power continues to be supplied to the motor due to the operation of the MOSFET of the other phase, so that this is prevented.

  FIG. 7 shows the characteristics of the MOSFET realizing the second embodiment of the present invention. As described in the first embodiment, the degradation diagnosis unit of the present invention uses the gate voltage dependence of the current flowing through the drain electrode or the source electrode of the MOSFET. In the present invention, the deterioration diagnosis using the cross point having no temperature dependence is the same as that in the first embodiment, and the description thereof is omitted.

  Even if the same type of product is used for the characteristics of the MOSFET, there are some individual differences in the characteristics due to manufacturing reasons. If an example is given regarding the threshold voltage, the representative value is 3.2V and the maximum value is 4.8V. As a result, as shown in FIG. 7, when the characteristics of MOSFET 1 and MOSFET 2 having different threshold voltages are compared, the cross points having no temperature dependence differ in the gate voltage dependence of the main current. Individual differences in these characteristics can be obtained by measuring the characteristics in advance.

  Since the MOSFET 1 is operated at the cross point 102a for deterioration diagnosis, it is necessary to apply the deterioration diagnosis voltage 103a to the gate terminal when the main current becomes the reference current 101a. When diagnosing deterioration of the MOSFET 2, the cross point 102b In order to operate, it is necessary to apply the deterioration diagnosis voltage 103b to the gate terminal when the main current becomes the reference current 101b. That is, the cross point at which the degradation diagnosis means should operate differs depending on each MOSFET.

  FIG. 8 is a circuit diagram of a power converter configured using six MOSFETs having different characteristics. This power conversion device includes MOSFETs Q1 to Q6, and the on / off states are switched by gate drive circuits 6a to 6f, respectively. The configuration of the gate drive circuit and the deterioration diagnosis means is the same as that of FIG. Here, since only the method in which each MOSFET operates at a different cross point is described, the gate drive circuits 6a to 6f pay attention to the operation of the logic circuits 301a to 301f.

  The deterioration diagnosis is started in the MOSFET Q1 when the main current becomes the reference current 101a. That is, the logic circuit 301a of the MOSFET Q1 compares the main current with the reference current 101a and outputs the deterioration diagnosis voltage 103a. Since the operation of the deterioration diagnosis unit after outputting the deterioration diagnosis voltage 103 is the same as that of the first embodiment, description thereof is omitted. On the other hand, at the time of deterioration diagnosis of MOSFET Q2, logic circuit 310b outputs deterioration diagnosis voltage 103b by comparing main current and reference current 101b.

In such a power conversion device using a plurality of MOSFETs having different characteristics, the deterioration of each MOSFET can be accurately determined by setting the reference current for deterioration diagnosis and the gate voltage for deterioration diagnosis at the cross points of each MOSFET. Can be detected. Therefore, the gate signal can be stopped and the deterioration alarm can be output only when deterioration occurs, and the operating rate of the power converter can be improved.

  Similarly, by measuring cross points in advance for MOSFETs Q3 to Q6 and inputting a reference current and a deterioration diagnosis voltage to the logic circuit, it is possible to detect only deterioration by eliminating the influence of individual differences in MOSFETs Q1 to Q6. It becomes possible.

The switching element using the MOSFET or IGBT in each of the embodiments described above is configured using, for example, silicon or a semiconductor material having a larger band gap than silicon as a base material.

Q1-Q6 Switching element (MOSFET)
D1 to D6 Diode 1 DC power 2 Capacitor 3 Power converters 4a to 4c Current sensor 5 Motors 5a to 5c Reactors 6a to 6f Gate drive circuits 7a to 7f Current sensor 100 Degradation diagnosis means 101 Reference currents 101a to 101f References of MOSFETs Q1 to Q6 Current 102 Crosspoint 102a, 102b Crosspoint 103 of MOSFET1, MOSFET2 Deterioration diagnosis voltage 103a-103b Degradation diagnosis voltage 104 of MOSFETQ1-Q6 Operation point 200 at the time of deterioration 200 Switching device 201a, 201b Transistor 202 Gate signal (PWM)
203 Gate drive circuit 205 Capacitor 206 Resistor 207 Zener diode 208a, 208b Semiconductor switch 209 Logic circuit (first logic circuit)
210 Main current 211 DC power supply (first DC power supply)
213 Gate voltage switching device 215 Semiconductor switch 216 DC power supply (third DC power supply)
217 logic circuit (second logic circuit)
218 Gate stop signal 219 Degradation diagnosis units 301a to 301f Logic circuits of MOSFETs Q1 to Q6

Claims (10)

In a switching device including a switching element in which a main current changes according to a control signal input to a gate terminal,
Gate voltage switching means for switching the gate voltage of the switching element to a predetermined diagnostic voltage when the main current matches a predetermined reference current,
A switching device comprising diagnostic means for stopping a gate of the switching element or outputting an alarm when a main current when the gate voltage switching means is operated is different from the reference current. The switching device according to claim 1,
The gate voltage at the cross point where the saturation current with respect to the gate voltage does not depend on the temperature of the switching element is the diagnostic voltage,
A switching device characterized in that a saturation current at the cross point is used as the reference current. In the switching device according to any one of claims 1 to 2,
The gate voltage switching means includes a first logic circuit that determines whether or not the reference current and the main current coincide with each other, a first Zener diode, and a first resistor. A switching device comprising: a diagnostic voltage generation circuit configured to generate the diagnostic voltage from a first DC power supply when it is determined that the reference current and the main current match. The switching device according to claim 1 ,
The diagnostic means includes a second logic circuit for determining whether or not the reference current and the saturation current matches, when the main current when the gate voltage switching means is operated is different from the reference current, the switching And a device for inputting a gate stop control signal or outputting an alarm to a gate terminal of the element. In the switching device according to any one of claims 1 to 4,
The switching device is characterized in that silicon or a semiconductor material having a larger band gap than silicon is used as a base material. In the switching device according to any one of claims 1 to 5,
The switching device is a MOSFET voltage-driven device.   7. The switching device according to claim 1, wherein when the main current when the gate voltage switching unit operates is different from the reference current, the switching device is input to the gate terminal of the switching element. A switching device that stops the control signal.   A power converter using a plurality of the switching devices according to any one of claims 1 to 7 to convert DC power into AC power and supplying the AC power to a motor, wherein the main current is the The power conversion device is measured by a current sensor inserted in a power line connecting the power conversion device and the motor or a current sensor inserted in a drain electrode of the switching element. The power conversion apparatus using a plurality of switching devices according to any one of claims 1 to 8, when the main current before you cross means any one of the switching elements differs from the reference current, wherein All the control signals inputted to the gate terminals of a plurality of switching elements are stopped. A power converter characterized by things. In the power converter device using a plurality of switching devices according to any one of claims 1 to 9,
The plurality of switching devices, each said different reference current and previous you gate stopped based on the cross-sectional voltage, or power conversion apparatus characterized by determining whether the output of the alarm.