Power conversion device

Abstract

A power conversion device is provided with: an inverter circuit in which switching elements of an upper arm and a lower arm are connected in series; an output current detector that outputs an alternating current output from a connection point of the switching elements of the upper arm and the lower arm; a drive circuit that drives each of the switching elements in accordance with a drive signal input via the switched gate resistor; an overcurrent detection circuit that compares the detection value with one of a plurality of predetermined overcurrent threshold values, and outputs an overcurrent detection signal when the detection value is greater than the overcurrent threshold value; and a controller that transmits the drive signal, transmits a gate resistance switching signal for switching the gate resistance to the drive circuit, transmits an overcurrent threshold switching signal for switching the overcurrent threshold, and switches the overcurrent threshold when the gate resistance is switched to the gate resistance having a low resistance value by the gate resistance switching signal. The controller sets the overcurrent threshold value to a smaller value through the overcurrent threshold value switching signal.

Description

Technical Field

[0001] The invention relates to a power conversion device. Background Art

[0002] A power conversion device for converting direct current into alternating current has a plurality of phases of arms in which switching elements of an upper arm and switching elements of a lower arm are connected in series, and the switching elements are driven by a drive signal input via a gate resistor connected to a gate of the switching element.

[0003] Generally speaking, switching losses occur when a switching element is energized, but the switching speed of the switching element can be increased by switching the gate resistor according to the operating conditions of the switching element such as the applied voltage and current, thereby reducing the loss of the switching element. On the other hand, when the switching element is turned off, a surge voltage is generated in proportion to the speed at which the collector current decreases.

[0004] Patent Document 1 describes a power conversion device that makes gate resistance variable under conditions where a surge voltage becomes high. Prior art literature Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2016-059089 Summary of the invention Problem that the invention aims to solve

[0006] In the technology described in Patent Document 1, when the motor current increases suddenly due to some abnormality while the resistance value of the gate resistor is reduced, the switching element may fail due to the surge voltage, thereby reducing the reliability of the power conversion device. Technical means of solving problems

[0007] The power conversion device of the present invention comprises: an inverter circuit having a plurality of phase arms, wherein the plurality of phase arms are formed by connecting a switch element of an upper arm and a switch element of a lower arm in series between a positive terminal and a negative terminal of a direct current; an output current detector, which detects an alternating current output from a connection point between the switch element of the upper arm and the switch element of the lower arm and outputs a detection value; a drive circuit, which has a gate resistance switching circuit for switching a gate resistance connected to a gate of each switch element, and drives each switch element according to a drive signal input through the switched gate resistance; and an overcurrent detection circuit, which detects an alternating current output from a connection point between the switch element of the upper arm and the switch element of the lower arm and outputs a detection value. The detection value detected by the detector is compared with one of a plurality of predetermined overcurrent thresholds, and when the detection value is greater than the overcurrent threshold, an overcurrent detection signal is output; and a controller, which sends the drive signal to the drive circuit, and sends a gate resistance switching signal for switching the gate resistance to the drive circuit, and sends an overcurrent threshold switching signal for switching the overcurrent threshold to the overcurrent detection circuit, and when the gate resistance is switched to the gate resistance with a lower resistance value by the gate resistance switching signal, the controller sets the overcurrent threshold to a smaller value by the overcurrent threshold switching signal. Effects of the Invention

[0008] According to the present invention, even when the resistance value of the gate resistor is reduced, the reliability of the power conversion device can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 It is a diagram showing the overall configuration of the power conversion device according to the first embodiment. Figure 2 This is a detailed configuration diagram of the main parts of the power conversion device according to the first embodiment. Figure 3 (a) Figure 3 (b) is a graph showing the relationship between the collector-emitter voltage of the switching element and the gate resistance, the overcurrent threshold, and the AC current. Figure 4 It is a detailed configuration diagram of the main parts of the power conversion device according to the second embodiment. Figure 5 It is a detailed configuration diagram of the main parts of the power conversion device according to the third embodiment. DETAILED DESCRIPTION

[0010] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. The following description and drawings are examples for illustrating the present invention, and appropriate omissions and simplifications have been made for the sake of clarity. The present invention may also be implemented in various other ways. Unless otherwise specified, each constituent element may be single or multiple.

[0011] [First embodiment] Figure 1 It is a diagram showing the overall configuration of the power conversion device 1000 according to the first embodiment. The power conversion device 1000 converts direct current supplied from a direct current power source 2000 such as a battery into alternating current to drive a motor 3000. The direct current power source 2000 supplies direct current between a positive terminal P and a negative terminal N of the power conversion device 1000 via a contactor 2001. The motor 3000 is, for example, a three-phase induction motor and is used as a driving source for a vehicle.

[0012] The power conversion device 1000 includes a voltage detector 100, a capacitor module 200, and an inverter circuit 300. The voltage detector 100 is connected in parallel between the positive terminal P and the negative terminal N, and detects a DC voltage between the positive terminal P and the negative terminal N. The capacitor module 200 smoothes the DC current. The inverter circuit 300 performs power conversion. In addition, the power conversion device 1000 includes an output current detector 400, an overcurrent detection circuit 500, a controller 600, a cutoff circuit 700, and a drive circuit 800.

[0013] The inverter circuit 300 includes a power module 310, which has an upper and lower arm series circuit composed of a switch element 311 and a diode 312 that act as an upper arm, and a switch element 321 and a diode 322 that act as a lower arm. In addition, the power module 310 is set to three phases (U phase, V phase, W phase) corresponding to each phase winding of the motor 3000. That is, the inverter circuit 300 has a three-phase arm, which is formed by connecting the switch element 311 of the upper arm and the switch element 321 of the lower arm in series between the positive terminal P and the negative terminal N of the direct current. Here, the example of three phases is used for explanation, but for example, it is also possible to have a power module 310 with multiple phases in accordance with the number of phases of the motor 3000.

[0014] The output current detector 400 detects the AC current output from the connection point of the upper arm switching element and the lower arm switching element for each phase, and outputs each detection value Ei to the overcurrent detection circuit 500 and the controller 600. The detection value Ei is a voltage value representing the magnitude of the detected AC current.

[0015] The overcurrent detection circuit 500 is provided for each phase, and when the detected value of the AC current is larger than the overcurrent threshold, it outputs an overcurrent detection signal Em to the controller 600 and the cutoff circuit 700. The details of the overcurrent detection circuit 500 will be described later.

[0016] The controller 600 is connected to the low voltage power supply 4000 from the outside of the power conversion device 1000, and the low voltage is supplied from the low voltage power supply 4000 when the ignition key of the vehicle is turned on. Then, according to the torque command from the upper controller (not shown), the detection voltage Vdc from the voltage detector 100, the detection value Ei from the output current detector 400, and the overcurrent detection signal Em from the overcurrent detection circuit 500, the drive signal Pw is output to the drive circuit 800 via the cut-off circuit 700. In addition, the controller 600 outputs the overcurrent threshold switching signal Ts to the overcurrent detection circuit 500. Furthermore, according to the detection value from the output current detector 400, the gate resistance switching signal Rs for switching the gate resistance is sent to the drive circuit 800. The details of the controller 600 will be described later.

[0017] The cutoff circuit 700 is provided corresponding to the drive circuit 800, and cuts off the drive signal Pw from the controller 600 to the switch elements 311 and 321 in response to the overcurrent detection signal Em outputted from the overcurrent detection circuit 500. The details of the cutoff circuit 700 will be described later. The drive circuit 800 is provided corresponding to each of the switch elements 311 and 321, and includes a gate resistance switching circuit for switching the gate resistance connected to the gate of each of the switch elements 311 and 321, and drives the switch elements 311 and 321 by a drive signal Pw inputted via the switched gate resistance. The details of the drive circuit 800 will be described later.

[0018] Figure 2 This is a detailed configuration diagram of the main parts of the power conversion device 1000 of the first embodiment. In this figure, an overcurrent detection circuit 500 corresponding to the power module 310 of one phase and a cut-off circuit 700 and a drive circuit 800 corresponding to the switching element 321 of the lower arm of the power module 310 of one phase are shown. That is, the cut-off circuit 700 and the drive circuit 800 corresponding to the switching element 311 of the upper arm of the power module 310 of one phase are omitted from the illustration, but have the same configuration as the cut-off circuit 700 and the drive circuit 800 corresponding to the switching element 321 of the lower arm. In addition, the overcurrent detection circuit 500 corresponding to the power module 310 of other phases and the cut-off circuit 700 and the drive circuit 800 corresponding to the switching elements 311 and 321 of the power modules 310 of other phases are also the same. Figure 2 Same composition.

[0019] The detection value Ei from the output current detector 400 is input to the overcurrent detection circuit 500 and the controller 600. The detection voltage Vdc from the voltage detector 100 is input to the controller 600.

[0020] The controller 600 sends a drive signal Pw to the drive circuit 800 via the cut-off circuit 700. In addition, a gate resistance switching signal Rs for switching the gate resistance is sent to the drive circuit 800. The drive signal Pw is a PWM signal. When an overcurrent detection signal Em, which will be described in detail later, is input from the overcurrent detection circuit 500, the cut-off circuit 700 immediately cuts off the drive signal Pw. As a result, the drive circuit 800 stops driving the switch element 321.

[0021] The driving circuit 800 includes a driving circuit 810 and a gate resistance switching circuit 820. The gate resistance switching circuit 820 switches the gate resistances Rf1 and Rf2 connected to the gate of the switching element 321 according to the gate resistance switching signal Rs. The gate resistance Rn0 is a resistance connected when the switching element 321 is turned on. The gate resistances Rf1 and Rf2 are resistances connected when the switching element 321 is turned off, and the resistance value of the gate resistance Rf1 is lower than the resistance value of the gate resistance Rf2. In response to the input of the gate resistance switching signal Rs, the resistance when the switching element 321 is turned off is switched to the gate resistance Rf1.

[0022] Generally, the switching loss generated in the switching element 321 becomes the main reason for reducing the efficiency of the inverter circuit 300 and even the cruising range of the vehicle. Therefore, according to the operating conditions of the switching element 321 such as voltage and current, when the switching element 321 is turned off, the switching speed is increased by switching to the gate resistor Rf1 with a low resistance value, thereby reducing the switching loss of the switching element 321. Specifically, when the DC voltage as the detection voltage Vdc detected by the voltage detector 100 is low and the current flowing through the motor 3000 detected by the output current detector 400 is low, the allowable surge voltage becomes higher. In this case, switching to the gate resistor Rf1 with a low resistance value further increases the switching speed and reduces the switching loss.

[0023] However, in a state where the resistance value of the gate resistor is reduced, when the current flowing through the motor 3000 increases sharply due to some abnormality, the switching element 321 may fail due to a surge voltage. Therefore, when switching to the gate resistor Rf1 with a low resistance value, the controller 600 sends the overcurrent threshold switching signal Ts to the overcurrent detection circuit 500 described later, and sets the overcurrent threshold to a smaller value. That is, when the controller 600 switches to the gate resistor Rf1 through the gate resistor switching signal Rs, it outputs the overcurrent threshold switching signal Ts at approximately the same time, and sets the overcurrent threshold of the overcurrent detection circuit 500 to a smaller value. In this way, the failure of the switching element 321 can be prevented, and the reliability of the power conversion device 1000 can be improved even when the resistance value of the gate resistor is reduced.

[0024] like Figure 2As shown, the overcurrent detection circuit 500 includes a threshold switching unit 510 and a comparison unit 520. The threshold switching unit 510 switches the threshold to the overcurrent threshold VH1, VL1 or the overcurrent threshold VH2, VL2 through the switch SW. Specifically, according to the overcurrent threshold switching signal Ts from the controller 600, the switch SW is actuated to select the overcurrent threshold VH1, VL1. If there is no overcurrent threshold switching signal Ts, the overcurrent threshold VH2, VL2 is selected. The unit of the threshold is voltage, and the relationship is that the overcurrent threshold VH1 < the overcurrent threshold VH2, and the overcurrent threshold VL1 < the overcurrent threshold VL2. The overcurrent thresholds VH1, VL1, VH2, and VL2 are supplied by a plurality of power supplies with different voltage values.

[0025] The comparison unit 520 includes a comparator CH for comparing the detection value Ei from the output current detector 400 with the overcurrent threshold value VH1 or the overcurrent threshold value VH2, and a comparator CL for comparing the detection value Ei with the overcurrent threshold value VL1 or the overcurrent threshold value VL2, and outputs an overcurrent detection signal Em according to the comparison result. In the case where there is no overcurrent threshold switching signal Ts and the overcurrent threshold values ​​VH2 and VL2 are selected, if the detection value Ei is within the range of the overcurrent threshold values ​​VH2 and VL2, the overcurrent detection signal Em is not output. When the detection value Ei exceeds the range of the overcurrent threshold values ​​VH2 and VL2, the overcurrent detection signal Em is output. In the case where the overcurrent threshold values ​​VH1 and VL1 are selected according to the overcurrent threshold switching signal Ts, if the detection value Ei is within the range of the overcurrent threshold values ​​VH1 and VL1, the overcurrent detection signal Em is not output. When the detection value Ei exceeds the range of the overcurrent threshold values ​​VH1 and VL1, the overcurrent detection signal Em is output. The overcurrent detection signal Em is input to the controller 600 and the cutoff circuit 700 .

[0026] When the switching element 321 is driven with the resistance value of the gate resistor Rf2, the overcurrent threshold values ​​VH2 and VL2 are set to values ​​indicating a current value at which the voltage applied to the switching element 321 does not exceed the allowable value of the switching element 321. In addition, when the switching element 321 is driven with the resistance value of the gate resistor Rf1, the overcurrent threshold values ​​VH1 and VL1 are set to values ​​indicating a current value at which the voltage applied to the switching element 321 does not exceed the allowable value of the switching element 321.

[0027] When the overcurrent detection signal Em is input, the controller 600 performs control such as stopping the output of the drive signal Pw to prevent overcurrent in the motor 3000. Since the overcurrent detection signal Em is also input to the cutoff circuit 700, the drive signal Pw can be cut off immediately without waiting for the output of the drive signal Pw of the controller 600 to stop.

[0028] Figure 3(a) is a graph showing the relationship between the voltage Vce applied between the collector and the emitter of the switching element 321 and the current value I detected by the output current detector 400. The horizontal axis represents the current value I, and the vertical axis represents the voltage Vce. Figure 3 (b) is a graph showing the relationship between the overcurrent threshold and the detection value Ei of the AC current, wherein the horizontal axis represents time and the vertical axis represents voltage.

[0029] Generally, when the switch element 321 is turned off, the voltage Vce applied between the collector and emitter of the switch element 321 increases as the current flowing through the switch element 321 increases. In addition, the magnitude of the magnitude increases more when the switching speed is fast. Furthermore, the switching speed when turned off is inversely proportional to the magnitude of the resistance value of the gate resistor, and there is a tendency to become slower when the resistance value is high and faster when the resistance value is low. Therefore, the surge voltage becomes smaller when the resistance value is high, and the surge voltage becomes larger when the resistance value is low.

[0030] On the other hand, when the switching speed is fast, the switching loss of the switching element 321 can be reduced, so the resistance value of the gate resistor can be reduced in the low current region, and the surge voltage can be suppressed to a permissible value or less, thereby reducing the loss.

[0031] exist Figure 3 In (a), the current value when switching to the gate resistor Rf1 with a low resistance value is set to I0, the overcurrent detection level of the gate resistor Rf1 with a low resistance value is set to I1, and the overcurrent detection level of the gate resistor Rf2 with a high resistance value is set to I2. Vm is the allowable withstand voltage of the switching element 321.

[0032] Figure 3 The graph shown in (a) shows an example in which the controller 600 switches to the gate resistor Rf2 when the current value I is greater than the current value I0 and switches to the gate resistor Rf1 when the current value I is less than the current value I0 based on the detection value Ei from the output current detector 400.

[0033] Here, the case where the gate resistance Rf2 is maintained without switching the gate resistance regardless of the current value I is considered. Figure 3 As shown by the dotted line Vf2 in (a), the voltage Vce applied to the switching element 321 gradually increases as the current increases from 0 (A) to I0 (A), I1 (A), and I2 (A).

[0034] However, when the motor 3000 or the like is in an abnormal state and the current increases sharply and exceeds the maximum current, the voltage Vce applied to the switch element 321 may exceed the allowable withstand voltage Vm, and the switch element 321 may fail. In response to this situation, overcurrent thresholds VH2 and VL2 are set. The overcurrent thresholds VH2 and VL2 are equivalent to the overcurrent detection level I2. When the current reaches the overcurrent detection level I2, the controller 600 prevents the increase of the current flowing through the motor 3000 by stopping the transmission of the PWM signal and other controls, so that the voltage Vce applied to the switch element 321 does not exceed the allowable withstand voltage Vm.

[0035] On the other hand, when switching the gate resistors Rf1 and Rf2, the gate resistor Rf1 with a low resistance value is switched in the low current region where the current is less than I0, and the switching speed of the switching element 321 is increased. Here, when the overcurrent state suddenly occurs in the state of the low gate resistor Rf1, the increase in the surge voltage is greater than when the resistance value is high. Therefore, if the overcurrent detection level is maintained at I2, Figure 3 As shown by the dotted line Vf1 in (a), when the current is larger than I1, the voltage Vce exceeds the allowable withstand voltage Vm.

[0036] In this embodiment, when the gate resistance is set to a low value, the overcurrent detection level is set to an overcurrent detection level I1 which is lower than I2. The overcurrent detection level I1 is equivalent to the overcurrent thresholds VH1 and VL1. This is a value at which the voltage applied to the switch element 321 does not exceed the allowable value of the switch element 321 when the switch element 321 is driven by the gate resistance Rf1. Figure 3 As shown by the thick solid line Vf in (a), the overcurrent detection level is set to the overcurrent detection level I1 when the gate resistance Rf1 is switched to the low state, and is set to the overcurrent detection level I2 when the gate resistance Rf2 is switched to the high state.

[0037] like Figure 3 As shown in (b), when the gate resistance Rf1 is switched to a low state, when the detection value Ei from the output current detector 400 exceeds the range of the overcurrent thresholds VH1 and VL1, the overcurrent detection circuit 500 detects it and outputs an overcurrent detection signal Em. Thus, even when the resistance value of the gate resistor is switched to increase the switching speed of the switching element 321 , it is possible to prevent a failure of the switching element 321 , thereby improving the reliability of the power conversion device 1000 .

[0038] In addition, in this example, the gate resistance is switched to two stages, but it can also be switched to three stages or more. In this case, the gate resistance switching circuit 820 switches multiple gate resistances, and the overcurrent detection circuit 500 switches multiple overcurrent thresholds according to the switched gate resistances.

[0039] [Second Embodiment] Figure 4 FIG. 1 is a detailed configuration diagram of the main parts of the power conversion device 1000 according to the second embodiment. Figure 2 Similarly, the figure shows an overcurrent detection circuit 500 corresponding to a power module 310 of one phase, and a cutoff circuit 700 and a drive circuit 800 corresponding to a switching element 321 of a lower arm of the power module 310 of one phase. Figure 2 The same parts are marked with the same symbols and their descriptions are simplified. Figure 1 same. The configuration of the overcurrent detection circuit 500 of the second embodiment is different from that of the first embodiment.

[0040] like Figure 4 As shown in FIG. 5 , the overcurrent detection circuit 500 includes a threshold switching unit 510 and a comparison unit 520. Figure 2 Similarly, the comparison unit 520 has a comparator CH and a comparator CL. The comparator CH compares the detection value Ei from the output current detector 400 with the overcurrent threshold VH1 or the overcurrent threshold VH2, and the comparator CL compares the detection value Ei with the overcurrent threshold VL1 or the overcurrent threshold VL2, and outputs an overcurrent detection signal Em according to the comparison result.

[0041] The threshold switching unit 510 includes resistors R1, R2, and R3 connected in series with a reference power supply, a resistor R4 connected in parallel with the resistor R1 via a FET511, and a resistor R5 connected in parallel with the resistor R3 via a FET512. A plurality of overcurrent thresholds are provided by dividing the voltage from a single power supply. In a low level when the overcurrent threshold switching signal Ts from the controller 600 is not output, the FET511 through the NOT gate 513 and the FET512 not through the NOT gate 513 are disconnected. In this case, the overcurrent threshold VH2 divided by the resistors R1, R2, and R3 is input to the comparator CH, and the overcurrent threshold VL2 is input to the comparator CL. When the overcurrent threshold switching signal Ts from the controller 600 is output at a high level, the FETs 511 and 512 are turned on, so that the resistor R4 is connected in parallel with the resistor R1, and the resistor R5 is connected in parallel with the resistor R3, and the resistance value is reduced. Therefore, the overcurrent threshold value VH1 is input to the comparator CH, and the overcurrent threshold value VL1 is input to the comparator CL.

[0042] When the gate resistor switching signal Rs is switched to a gate resistor with a low resistance value, the controller 600 sets the overcurrent threshold to a smaller value through the overcurrent threshold switching signal Ts. In addition, when the overcurrent detection signal Em is input, the controller 600 performs control such as stopping the output of the drive signal Pw to prevent overcurrent in the motor 3000. According to this embodiment, even when the resistance value of the gate resistor is switched to increase the switching speed of the switching element 321 , failure of the switching element 321 can be prevented, the reliability of the power conversion device 1000 can be improved, and the structure of the overcurrent detection circuit 500 can be simplified.

[0043] [Third Embodiment] Figure 5 1 is a detailed configuration diagram of the main parts of the power conversion device 1000 according to the third embodiment. In this figure, a cutoff circuit 700 and a drive circuit 800 corresponding to the switching element 321 of the lower arm of the power module 310 of one phase are shown. The overcurrent detection circuit 500 is provided in the drive circuit 800. Figure 2 The same parts are marked with the same symbols and their descriptions are simplified. Figure 1 same. In the third embodiment, the configurations of an output current detection circuit 410 and an overcurrent detection circuit 500 are different from those in the first embodiment.

[0044] like Figure 5 As shown, the switch element 321 has a current sensing terminal for diverting the current flowing through the switch element 321. The output current detection circuit 410 converts the diverted current into a voltage value using a sense resistor Rj, and outputs the voltage value to the overcurrent detection circuit 500 as a detection value Ej.

[0045] The overcurrent detection circuit 500 includes a threshold switching unit 510 and a comparison unit 520. In the absence of an overcurrent threshold switching signal Ts from the controller 600, the threshold switching unit 510 selects the overcurrent threshold V2 through the switch SW, and in the presence of the overcurrent threshold switching signal Ts, selects the overcurrent threshold V1. The relationship is that the overcurrent threshold V1 < the overcurrent threshold V2. The comparison unit 520 compares the detection value Ej from the output current detection circuit 410 with the overcurrent threshold V1 or the overcurrent threshold V2, and outputs the overcurrent detection signal Em according to the comparison result.

[0046] When the gate resistor switching signal Rs is switched to a gate resistor with a low resistance value, the controller 600 sets the overcurrent threshold to a smaller value through the overcurrent threshold switching signal Ts. In addition, when the overcurrent detection signal Em is input, the controller 600 performs control such as stopping the output of the drive signal Pw to prevent overcurrent in the motor 3000. According to this embodiment, even when the resistance value of the gate resistor is switched to increase the switching speed of the switching element 321, failure of the switching element 321 can be prevented, the reliability of the power conversion device 1000 can be improved, and the structure of the output current detection circuit 410 and the overcurrent detection circuit 500 can be simplified.

[0047] According to the above-described embodiment, the following effects can be obtained. (1) A power conversion device 1000 comprises: an inverter circuit 300 having a plurality of phase arms, wherein the plurality of phase arms are formed by connecting a switch element 311 of an upper arm and a switch element 321 of a lower arm in series between a positive terminal and a negative terminal of a direct current; an output current detector 400, which detects an alternating current output from a connection point between the switch element 311 of the upper arm and the switch element 321 of the lower arm and outputs a detection value Ei; a drive circuit 800, which comprises a gate resistance switching circuit 820 for switching gate resistances Rf1 and Rf2 connected to gates of the respective switch elements 311 and 321, and drives the respective switch elements 311 and 321 according to a drive signal Pw inputted via the switched gate resistances Rf1 and Rf2; and an overcurrent detection circuit 500, which compares the detection value Ei detected by the output current detector 400 with the detection value Ei. A controller 600 is configured to compare one of the predetermined multiple overcurrent thresholds VH1, VL1, VH2, and VL2, and output an overcurrent detection signal Em when the detection value Ei is greater than the overcurrent thresholds VH1, VL1, VH2, and VL2; and a controller 600 is configured to send a drive signal Pw to the drive circuit 800, and send a gate resistance switching signal Rs to the drive circuit 800 to switch the gate resistances Rf1 and Rf2, and send an overcurrent threshold switching signal Ts to the overcurrent detection circuit 500 to switch the overcurrent thresholds VH1, VL1, VH2, and VL2. When the gate resistance switching signal Rs is switched to the gate resistance Rf1 with a low resistance value, the controller 600 sets the overcurrent thresholds VH1, VL1, VH2, and VL2 to a smaller value through the overcurrent threshold switching signal Ts. Thus, even when the resistance value of the gate resistance is reduced, the reliability of the power conversion device can be improved.

[0048] The present invention is not limited to the above-described embodiments, and other embodiments that can be conceived within the scope of the technical concept of the present invention are also included in the scope of the present invention as long as the features of the present invention are not impaired. In addition, a configuration combining the above-described embodiments is also possible. Explanation of symbols

[0049] 100…voltage detector, 200…capacitor module, 300…inverter circuit, 310…power module, 311, 321…switching element, 312, 322…diode, 400…output current detector, 410…output current detection circuit, 500…overcurrent detection circuit, 510…threshold switching unit, 520…comparison unit, 600…controller, 700…cutoff circuit, 800…drive circuit, 810…drive circuit, 820…gate resistor Switching circuit, 1000…power conversion device, 2000…DC power supply, 2001…contactor, 3000…motor, 4000…low-voltage power supply, Rn0, Rf1, Rf2…gate resistance, Rs…gate resistance switching signal, Pw…drive signal, Vdc…detection voltage, Ei, Ej…detection value, VH1, VL1, VH2, VL2, V1, V2…overcurrent threshold, Ts…overcurrent threshold switching signal, Em…overcurrent detection signal.

Claims

1. A power conversion device, characterized in that: have: An inverter circuit having a plurality of phase arms, wherein the plurality of phase arms are formed by connecting a switching element of an upper arm and a switching element of a lower arm in series between a positive terminal and a negative terminal of a direct current; an output current detector that detects an alternating current output from a connection point of the switching element of the upper arm and the switching element of the lower arm and outputs a detection value; A driving circuit having a gate resistor switching circuit for switching a gate resistor connected to a gate of each of the switching elements, and driving each of the switching elements according to a driving signal input through the switched gate resistor; an overcurrent detection circuit, which compares the detection value detected by the output current detector with one of a plurality of predetermined overcurrent thresholds, and outputs an overcurrent detection signal when the detection value is greater than the overcurrent threshold; as well as a controller that sends the drive signal to the drive circuit, sends a gate resistance switching signal for switching the gate resistance to the drive circuit, and sends an overcurrent threshold switching signal for switching the overcurrent threshold to the overcurrent detection circuit, When the gate resistor is switched to a gate resistor having a low resistance value by the gate resistor switching signal, the controller sets the overcurrent threshold to a smaller value by the overcurrent threshold switching signal.

2. The power conversion device according to claim 1, characterized in that: When the switching element is driven by the gate resistor after the switching, the overcurrent threshold is set to a value indicating a current value at which a voltage applied to the switching element does not exceed an allowable value of the switching element.

3. The power conversion device according to claim 1 or 2, characterized in that: The overcurrent detection circuit includes: a threshold switching unit that switches the plurality of overcurrent thresholds using the overcurrent threshold switching signal; and a comparison unit that compares the detection value with the overcurrent threshold.

4. The power conversion device according to claim 3, characterized in that: The multiple overcurrent thresholds are supplied by multiple power supplies having different voltage values.

5. The power conversion device according to claim 3, characterized in that: The plurality of overcurrent thresholds are provided by dividing a voltage from a single power source.

6. The power conversion device according to claim 1 or 2, characterized in that: A cut-off circuit for cutting off the drive signal sent from the controller to the drive circuit is provided, The cutoff circuit cuts off the drive signal in response to the overcurrent detection signal output from the overcurrent detection circuit.

7. A power conversion device, characterized in that: have: An inverter circuit having a plurality of phase arms, wherein the plurality of phase arms are formed by connecting a switching element of an upper arm and a switching element of a lower arm in series between a positive terminal and a negative terminal of a direct current; an output current detection circuit, which detects the current flowing through each of the switch elements and outputs a detection value; A driving circuit having a gate resistance switching circuit for switching a gate resistance connected to a gate of each of the switching elements, and driving each of the switching elements according to a driving signal using the switched gate resistance; an overcurrent detection circuit, which compares the detection value detected by the output current detection circuit with one of a plurality of predetermined overcurrent thresholds, and outputs an overcurrent detection signal when the detection value is greater than the overcurrent threshold; as well as a controller that sends the drive signal to the drive circuit, sends a gate resistance switching signal for switching the gate resistance to the gate resistance switching circuit, and sends an overcurrent threshold switching signal for switching the overcurrent threshold to the overcurrent detection circuit, When the gate resistor is switched to a gate resistor having a low resistance value by the gate resistor switching signal, the controller sets the overcurrent threshold to a smaller value by the overcurrent threshold switching signal.

8. The power conversion device according to claim 7, characterized in that: The output current detection circuit detects a current from a current sensing terminal that divides a current flowing through the switching element and outputs the detection value.

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