Power Conversion Equipment

Abstract

The short circuit detection unit (200) includes the main circuit unit (11) that performs power conversion between the DC circuit unit (100) and the load (120), the voltage detection unit (13) that detects a voltage generated in an inductance component between two points set in a wiring that connects the DC circuit unit (100) and the main circuit unit (11), and the first comparator (201) that outputs a detection signal when the voltage detected by the voltage detection unit (13) exceeds a first threshold voltage, and the second comparator (203) that detects the occurrence of a short circuit when the detection signal of the first comparator (201) continues for a predetermined time or longer. This makes it possible to easily design short circuit detection with a sufficient tolerance against erroneous detection.

Description

[Technical field]

[0001] The present disclosure relates to a power conversion device. [Background technology]

[0002] In power conversion devices, power semiconductors that act as switches are indispensable. In order to ensure the quality of power conversion devices, it is known that power conversion devices have a function of detecting an overcurrent caused by a failure or noise malfunction of the power semiconductor, stopping the power conversion, and preventing the destruction or fire of the device. For example, Patent Document 1 describes a method of detecting a short circuit by providing a current-limiting reactor that limits the current between the inverter and the capacitor and acquiring the voltage across the current-limiting reactor.

[0003] In Patent Document 1, a current-limiting reactor is used, so the short-circuit current is limited, and the time from the start of the short circuit to element destruction is longer than when a current-limiting reactor is not used. This allows for a margin of error in the time from short circuit detection to disconnection. Furthermore, the current-limiting reactor keeps the current gradient constant, so the only variability factors in the voltage across the current-limiting reactor are the inductance of the current-limiting reactor itself and the applied voltage. This makes the design easy, and there is no risk of false detection even if the gate resistance and the input capacitance or gate threshold voltage related to the switching characteristics of the power semiconductor change. In addition, to enable high-speed short-circuit detection, the voltage across the current-limiting reactor below a certain value is cut off by a bias circuit such as a Zener diode, and the short circuit is detected by distinguishing between overcurrent during a short circuit and current during normal operation based on whether or not that voltage remains above a specified time. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Utility Model Application Publication No. 58-11993 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the use of a current-limiting reactor increases the size of the device, which leads to problems with increased costs. Therefore, if short-circuit detection is performed using the voltage generated in the parasitic inductance in the wiring without using a current-limiting reactor, the voltage generated in the parasitic inductance varies depending on the applied voltage of the power semiconductor, the variation in element characteristics, and the operating mode of the power conversion device. This variation makes it difficult to design a detection circuit, and there is a risk of false detection due to the lack of tolerance.

[0006] The present disclosure has been made to solve the problems described above, and aims to provide a power conversion device having a short circuit detection circuit that is easy to design and has a tolerance against erroneous detection, even when a short circuit is detected using the voltage generated in a parasitic inductance. [Means for solving the problem]

[0007] The power conversion device of the present disclosure includes a main circuit unit having two or more phases that performs power conversion between a DC circuit unit and a load, a voltage detection unit that detects a voltage generated in an inductance component between two points on a wiring that connects the DC circuit unit and the main circuit unit, a threshold voltage generating unit that uses a common power supply for generating the first threshold voltage and a common power supply for generating the second threshold voltage and generates the first threshold voltage and the second threshold voltage by resistive voltage division of the power supply voltage; a first comparator that outputs a detection signal when the voltage detected by the voltage detection unit exceeds a first threshold voltage, and a detection signal from the first comparator that continues for a predetermined time or longer; The voltage according to the duration exceeds the second threshold voltage. and a second comparator that detects the occurrence of a short circuit. Effect of the Invention

[0008] According to the power conversion device of the present disclosure, even in the case where short circuit detection is performed using the voltage generated in the inductance component in the wiring, short circuit detection can be performed with ease of design and with a tolerance against erroneous detection. [Brief description of the drawings]

[0009] [Figure 1]1 is a block diagram showing a configuration of a power conversion device according to a first embodiment. [Diagram 2] 1 is a circuit configuration diagram showing an example of a specific configuration of a power conversion device according to a first embodiment. [Diagram 3] 2 is a block diagram showing configurations of a voltage detection unit and a short circuit detection unit of the power conversion device according to the first embodiment. FIG. [Figure 4] 2 is a diagram showing an example of a circuit configuration of a voltage detection unit and a short circuit detection unit of the power conversion device according to the first embodiment. FIG. [Diagram 5] 4 is a turn-on current / voltage waveform diagram illustrating noise components during switching of a power semiconductor element. FIG. [Figure 6] 5A to 5C are schematic waveform diagrams of current and voltage waveforms illustrating a surge voltage at the time of turn-off in a power semiconductor element. [Figure 7] 4 is a schematic waveform diagram illustrating the operation principle of a short circuit detection unit in the power conversion device according to the first embodiment. FIG. [Figure 8] 5A to 5C are schematic waveform diagrams of the detection L voltage and the second comparator input voltage when (a) one phase is switching and (b) two phases are switching, illustrating a method for determining a threshold voltage of the power conversion device according to the first embodiment. [Figure 9] 5A and 5B are schematic diagrams for explaining the tolerance in the short-circuit detection circuit of the power conversion device according to the first embodiment, where (a) shows a case where the power supply Vcc is not shared, and (b) shows a case where the power supply Vcc is shared. [Figure 10] 11 is a diagram showing an example of a circuit configuration of a voltage detection unit and a short circuit detection unit of a power conversion device according to a second embodiment. FIG. [Figure 11] 10 is a schematic waveform diagram illustrating the operation principle of a short circuit detection unit in a power conversion device according to the second embodiment. FIG. [Figure 12] 10 is a schematic diagram illustrating a tolerance in a short-circuit detection circuit of a power conversion device according to a second embodiment. FIG. [Figure 13] 13 is a diagram showing an example of a circuit configuration of a voltage detection unit and a short circuit detection unit of a power conversion device according to a third embodiment. FIG. [Figure 14]13 is a schematic diagram showing a tolerance in a short-circuit detection circuit section of a power conversion device according to embodiment 3. FIG. [Figure 15] 13 is a diagram showing an example of a circuit configuration of a voltage detection unit and a short circuit detection unit of a power conversion device according to a third embodiment. FIG. [Figure 16] FIG. 11 is a block diagram showing a configuration of a power conversion device according to a fourth embodiment. [Figure 17] FIG. 11 is a circuit configuration diagram showing an example of a specific configuration of a power conversion device according to a fourth embodiment. [Figure 18] 4 is a diagram illustrating an example of a hardware configuration in a case where a control unit of a power conversion device according to an embodiment is a microcomputer; FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, preferred embodiments of the power conversion device according to the present disclosure will be described with reference to the drawings. Note that the same reference numerals are used for the same contents and corresponding parts, and detailed descriptions thereof will be omitted. In the following embodiments, the same reference numerals are used to designate the same components, and redundant descriptions will be omitted.

[0011] Embodiment 1 Fig. 1 is a block diagram showing the configuration of a power conversion device according to embodiment 1. In Fig. 1, a power conversion device 10 performs power conversion between a DC circuit section 100 and a load 120, and is made up of a main circuit section 11 and a control section 12 that controls the main circuit section 11.

[0012] The control unit 12 includes a voltage detection unit 13 and a short circuit detection unit 200. The voltage detection unit 13 detects a voltage generated in a parasitic inductance (inductance component) 111 between two points N1 and N2 set in a connection wiring unit 110 between the DC circuit unit 100 and the power conversion device 10. The short circuit detection unit 200 determines the presence or absence of a short circuit in the power conversion device based on the output of the voltage detection unit 13.

[0013] 1 shows an example in which two points N1 and N2 on the negative wiring are set as points for detecting the differential voltage of the connection wiring unit 110, but detection may also be performed using two points on the positive wiring. Using two points on the positive side has the advantage of not being affected by common mode noise, but requires insulation processing when transmitting a short circuit detection signal to the short circuit detection unit 200.

[0014] The wiring of the connection wiring section 110 may be not only wiring on the board, but also cables and wiring inside the power semiconductor elements. If a current detection chip resistor for controlling the main circuit section 11 is present between the main circuit section 11 and the DC circuit section 100, the voltage may be detected using the inductance component of the chip resistor. When detecting with a chip resistor, there is also a voltage rise due to the resistance component, so the detection tolerance can be improved by providing a differentiation circuit in the voltage detection section 13 to remove the voltage rise due to the resistance component.

[0015] Fig. 2 is a circuit diagram showing an example of a specific configuration of the power conversion device according to embodiment 1. In Fig. 2, the DC circuit section 100 has an AC power source 100b and a three-phase PWM converter 100a that converts AC voltage to DC voltage, and the main circuit section 11 has a three-phase inverter 11p that drives a three-phase motor 120a that is a three-phase AC load.

[0016] A three-phase inverter 11p that drives a three-phase motor 120a is widely used in home appliances such as air conditioners and refrigerators, electric automobiles, industrial equipment, and the like.

[0017] The three-phase PWM converter 100a is composed of an AC reactor 101a, power semiconductor elements Ma to Mf, and a capacitor 14. The three-phase inverter 11p is composed of power semiconductor elements M1 to M6. In this embodiment, MOSFETs (Metal-Oxide-Semiconductor Field Effect Transistors) are described as an example of the power semiconductor module, but the present invention is not limited to this and any element that functions as a switching element may be used. It is clear that the number of power semiconductor elements, the number of phases of the power conversion device 10, the number of DC circuit units 100 or loads 120, and detailed circuit configurations are not limited to those described below.

[0018] 2, the capacitor 14 is mounted on the DC circuit section 100, but the capacitor 14 may be provided in the main circuit section 11, or may be provided in both the DC circuit section 100 and the main circuit section 11. Therefore, there is no limit to the number and locations of the capacitors 14. Note that the capacitor 14 does not necessarily need to smooth the frequency components resulting from the AC power source 100b, and a film capacitor or a ceramic capacitor may be used other than an electrolytic capacitor.

[0019] 3 is a block diagram of the voltage detection unit 13 and the short circuit detection unit 200 of the power conversion device according to the first embodiment. The voltage detection unit 13 is configured to monitor a voltage VL generated in an inductance component 111 between two points N1 and N2 set at an interval on the connection wiring unit 110. The short circuit detection unit 200 is configured to detect that a current IL flowing through the inductance component 111 is in an overcurrent state. Hereinafter, the voltage VL is referred to as a detection L voltage VL, and the current IL is referred to as a detection L current IL.

[0020] Specifically, the voltage detection unit 13 is equipped with a filter circuit 13a that removes noise components superimposed on the detection L voltage VL due to switching, etc. Also, the short circuit detection unit 200 is composed of a first comparator 201 that outputs a signal when the voltage becomes equal to or higher than a certain voltage, an integrator 202 that integrates the signal of the first comparator 201 and converts the time width of the signal into a voltage, and a second comparator 203 that outputs an overcurrent detection signal Ssc when the output voltage of the integrator 202 becomes equal to or lower than a predetermined certain value or exceeds it.

[0021] If the noise component superimposed on the detection L voltage VL is small compared to the voltage rise due to the slope of the overcurrent, the filter circuit 13a may not be provided. If the detection L voltage VL is small, an amplifier such as an operational amplifier may be added to amplify it.

[0022] 4 is a diagram showing an example of a circuit configuration of the voltage detection unit 13 and the short circuit detection unit 200 of the power conversion device according to the first embodiment. The filter circuit 13a is a low-pass filter composed of a resistor R1 and a capacitor C1, and a set point N1 on the wiring, a ground point GND (white triangle in FIG. 4) of the filter circuit 13a, and one end of the capacitor C1 are connected, and a set point N2 on the wiring and one end of the resistor R1 of the filter circuit 13a are connected. The other end of the capacitor C1 and the other end of the resistor R1 are connected to the first comparator 201.

[0023] Here, when power semiconductor elements performing high-speed switching operations, such as SiC-MOSFET, GaN-HEMT (High Electron Mobility Transistor), and Si-IGBT (Insulated Gate Bipolar Transistor), are used as switching elements of the three-phase inverter 11p, for example, in the case of MOSFET, the drain current Id, which is a switching current, may pulsate at a frequency fsn immediately after turning on, as shown in Fig. 5. This pulsating current is superimposed as a voltage on the wiring of the voltage detection unit 13, resulting in erroneous detection, so when a low-pass filter is provided in the filter circuit 13a, the cutoff frequency should be set to fsn or less.

[0024] Furthermore, when the above-mentioned power semiconductor element (e.g., MOSFET) performing high-speed switching operation is applied to the three-phase inverter 11p, the drain-source voltage (surge voltage) Vds at turn-off at high speed shown by the solid line becomes larger (Vdsmax in FIG. 6) compared to the low speed shown by the dashed line in FIG. 6, exceeding the element withstand voltage Vdsp and destroying the element, so the inductance for short circuit detection must be set so as to satisfy the condition of the following formula (1). Note that in this example, the power semiconductor element has been described as a MOSFET, but this is not limited to the present embodiment.

[0025]

number

[0026] In formula (1), the inductance component 111 for short circuit detection is L[H], the inductance between the capacitor including the inductance component 111 and the power semiconductor element (MOSFET) is Lloop[H], the inductance between the capacitor not including the inductance component 111 and the MOSFET element is La[H], the element breakdown voltage of the MOSFET element is Vdsp[V], the maximum voltage of the DC circuit section 100 is Vdcmax[V], and the maximum current gradient of the MOSFET element is di / dt, where Lloop=La+L.

[0027] 4, the other end of the resistor R1 and the capacitor C1, which are the output of the filter circuit 13a, is connected to a non-inverting input terminal (+) of a first comparator 201, and a first threshold voltage Vref1 generated by a threshold voltage generating unit 204 is input to an inverting input terminal (-) of the first comparator 201. The output of the first comparator 201 is connected to an integrator 202 composed of a resistor R2 and a capacitor C2. The output of the first comparator 201 is connected to one end of the resistor R2, and one end of the capacitor C2 is connected to a ground point GND. Although the integrator 202 is composed of the resistor R2 and the capacitor C2, an integrating circuit using an operational amplifier may be used.

[0028] A non-inverting input terminal (+) of a second comparator 203 is connected to the output of the integrator 202, and a second threshold voltage Vref2 generated by a threshold voltage generating unit 204 is input to an inverting input terminal (-) of the second comparator 203. The output of the second comparator 203 becomes an overcurrent detection signal Ssc.

[0029] In the threshold voltage generating unit 204, both the first threshold voltage Vref1 and the second threshold voltage Vref2 are generated from a common power supply Vcc by resistor dividers R3 to R5. As will be described in detail later, using a common power supply Vcc has the advantage of improving the tolerance of the detection circuit. Although not shown, the power supply for the first comparator 201 and the second comparator 203 may be the power supply Vcc of the threshold voltage generating unit 204 or another power supply.

[0030] Fig. 7 is a schematic waveform diagram showing the operation principle of the short circuit detection unit 200 in the power conversion device according to the first embodiment. From the top, the diagram shows the detection L current IL, the detection L voltage VL, the output voltage of the first comparator 201, the input voltage of the second comparator 203, and the overcurrent detection signal Ssc. The solid line waveform in Fig. 7 shows an example of the waveform during a short circuit, and the dotted line waveform shows an example of the waveform during a turn-on operation, which is a normal switching operation. In the explanation of the operation principle in Fig. 7, for simplification, it is assumed that no noise components are generated during switching, and the existence of the filter circuit 13a is ignored.

[0031] During normal switching operation, a load current ILoad flows through a certain phase due to a power semiconductor element that is turned on. Also, just before the element is turned on, the load current ILoad flows through the diode connected to the power semiconductor element of that phase that is not turned on. During a short circuit, the arm is short-circuited and no load current ILoad flows, and the element on the opposite side of the phase with the power semiconductor element that is turned on is destroyed or an erroneous signal is input and the element is already on.

[0032] At time t0, a positive or negative power semiconductor element in one phase of the three-phase inverter is turned on, causing the detection L current IL to start flowing, and the detection L voltage VL also rises accordingly. Next, at time t1, the detection L voltage VL becomes greater than the first threshold voltage Vref1, causing the output voltage of the first comparator 201 to rise and become a high detection signal.

[0033] When the output voltage of first comparator 201 becomes a high detection signal, the input voltage of second comparator 203 starts to gradually rise by integrator 202. As can be seen from Fig. 7, the high time width of the output voltage of first comparator 201 is converted into the height of the input voltage of second comparator 203 by integrator 202. By converting in this way, the design is simple and there is a margin for erroneous detection. Up to this point, the operation is the same during normal switching operation and when a short circuit occurs.

[0034] During normal switching operation at time t2, the detection L current IL flows only up to the load current ILoad, so the slope of the detection L current IL becomes gentler and the detection L voltage VL becomes lower than the first threshold voltage Vref1. Therefore, the output voltage of the detection signal of the first comparator 201 also switches from high to low, and the input voltage of the second comparator 203 also starts to gradually decrease. After that, when the detection L current IL becomes the load current ILoad, the switching operation is completed.

[0035] During a short circuit at time t2, the detection L current IL is not limited by the load, unlike in normal switching operation, so the detection L current IL continues to rise even at time t2. As a result, the detection L voltage VL also continues to maintain a value greater than the first threshold voltage Vref1, and the input voltage of the second comparator 203 also continues to rise.

[0036] At time t3, when a short circuit occurs, the input voltage of the second comparator 203 continues to rise, and after a predetermined period of time has elapsed, that is, when the input voltage of the second comparator 203 exceeds the second threshold voltage Vref2, the overcurrent detection signal Ssc goes high, and a short circuit is detected. From the above, it can be seen that the detection circuit of the first embodiment can be used to distinguish between a normal switching operation and a short circuit. When a short circuit is detected in the power conversion device as in the first embodiment, the device destruction due to an arm short circuit can be prevented by controlling the power semiconductor elements of the three-phase PWM converter 100a and the three-phase inverter 11p to be in the off state.

[0037] In the explanation of the operating principle of the short circuit detection unit 200, the values ​​of the first threshold voltage Vref1 and the second threshold voltage Vref2 are set so as to distinguish between normal switching in which one power semiconductor element is turned on and an arm short circuit. However, in order to provide a detection circuit that does not make erroneous detections in the power conversion device of the three-phase inverter 11p, the first threshold voltage Vref1 and the second threshold voltage Vref2 must be determined based on the operating conditions of the three-phase inverter 11p.

[0038] 7, the detection method of the first embodiment distinguishes between normal switching and short circuit based on the difference in the duration of the detection signal when the input voltage of the first comparator 201 exceeds the first threshold voltage Vref1. Note that the above explanation is based on the detection L voltage VL ignoring the filter circuit 13a. Therefore, in order to prevent erroneous detection, first, a maximum duration condition for the input voltage of the first comparator 201 to exceed the first threshold voltage Vref1 during normal switching operation is found, and a minimum duration condition for the input voltage of the first comparator 201 to exceed the first threshold voltage Vref1 during short circuit is found.

[0039] After that, the input voltages of the second comparator 203 under the maximum and minimum time width conditions are obtained, and the second threshold voltage Vref2 is set between the peak values ​​of the two. It can also be seen from Fig. 7 that the second threshold voltage Vref2 is set between the input voltage peaks of the second comparator 203 during normal switching operation and during a short circuit.

[0040] During normal switching operation, the current condition that results in the maximum time width is when the main circuit unit 11 and the load 120 are operating at the maximum current. This is because the larger the current value, the longer the current rise time becomes, and therefore the time width of the detection L voltage VL also becomes larger. In the above explanation of the operating principle of the short circuit detection unit 200, a certain power semiconductor element is turned on in the operating mode. However, for example, in the three-phase inverter 11p, when a three-phase AC voltage is output to the motor 120a by PWM control, the power semiconductor elements of two phases may turn on at approximately the same timing.

[0041] FIG. 8 shows the detection L voltage VL when one phase of the three-phase inverter 11p is switched at the maximum load current and when two phases are switched at approximately the same timing. The total value of the current during two-phase switching is the maximum load current. From FIG. 8, it can be seen that depending on the first threshold voltage Vref1 to be set, the time width t2sw when two phases are switched at approximately the same timing, where the gradients di / dt of the currents overlap, that is, the detection L voltage VL overlap, is larger than the time width t1sw when one phase is switched at the maximum current. Therefore, if the second threshold voltage Vref2 is determined based only on one-phase switching, there is a risk of erroneous detection, so the second threshold voltage Vref2 must be determined based on the maximum time width condition when the gradients of the currents of two or more phases overlap.

[0042] In the above explanation of the operating principle of the short circuit detection unit 200, a short circuit occurs when the load current is not flowing, but there is a mode in which a power semiconductor element is broken down and a short circuit occurs when the load current is flowing. This is called an on-state short circuit. An arm short circuit when the load current is not flowing is from 0 [A] to the saturation current, but an on-state short circuit is from the load current ILoad to the saturation current, so the time during which the detection L voltage VL is generated is shorter. Therefore, if an on-state short circuit is also to be detected, the second threshold voltage Vref2 should be set based on the minimum time width condition during an on-state short circuit.

[0043] In the circuit configuration of the short circuit detection unit 200 described above, the power supply Vcc of the threshold voltage generation unit 204 is common to both the first and second threshold voltages. This is to improve the tolerance against erroneous detection even when a current-limiting reactor is not used and a high-speed switching power semiconductor element is used in the power conversion device.

[0044] That is, FIG. 9 shows the tolerance of the detection circuit of the threshold voltage generating unit 204 when the power supply is not shared (FIG. 9(a)) and when the power supply is shared (FIG. 9(b)). The solid line in the figure indicates the minimum voltage line during short circuit, and the dashed line indicates the maximum voltage line during normal switching operation. The vertical axis represents the input voltage to the first comparator 201, which becomes the detection L voltage VL when there is no filter circuit. The horizontal axis represents the input voltage to the second comparator 203, which is synonymous with the time width at each height of the input voltage to the first comparator 201.

[0045] It is possible to distinguish between a short circuit and a normal switching operation by setting the first and second threshold voltages Vref1, Vref2 halfway between the solid line indicating a short circuit and the dashed line indicating a normal switching operation in Fig. 9. For example, the vertical value of point A in Fig. 9 represents the first threshold voltage Vref1, and the horizontal value of point A represents the second threshold voltage Vref2.

[0046] When the power supply Vcc of the threshold voltage generating unit 204 is not shared, the power supply determining the first threshold voltage Vref1 and the power supply determining the second threshold voltage Vref2 may vary within the same positive range or the same negative range, or may vary within different positive and negative ranges, so the variation in the threshold voltage is within the range of the dotted rectangle as shown in Fig. 9(a). Note that if the dotted rectangle touches the solid line representing a short circuit or the dashed line representing normal switching, a false detection occurs.

[0047] In contrast, when the power supply of the threshold voltage generating unit 204 is shared, the first threshold voltage Vref1 and the second threshold voltage Vref2 only vary to the same positive value or the same negative value, so that the variation in the threshold voltage only varies along the dotted arrow from the upper right to the lower right of the graph as shown in Fig. 9(b). Therefore, it can be seen that the tolerance represented by the solid arrow is improved in Fig. 9(b) compared to Fig. 9(a). Therefore, even if the characteristics during short circuit or normal switching change due to the gate resistance, gate threshold voltage, input capacitance, gate voltage, temperature, etc., it is possible to provide a detection circuit that is less prone to false detection.

[0048] It is also possible to cut off detection L voltage VL below a certain voltage value using a Zener diode or the like, and detect a short circuit when that voltage remains at that value for a predetermined period of time or more. In embodiment 1, however, as shown in FIG. 4, short circuit detection unit 200 is used in which a threshold voltage is generated from a common power source for two comparators 201, 203, and a short circuit is detected when the time during which the input voltage of first comparator 201 exceeds first threshold voltage Vref1 remains at a predetermined period of time or more. The reason for this is that if a Zener diode is used in the bias circuit, the Zener voltage will vary, resulting in the same variation as in Figure 9(a). In addition, the parasitic capacitance present in parallel with the Zener diode is highly voltage-dependent, and the Zener voltage, which is the voltage to be cut, is also current-dependent. Therefore, if a low-pass filter is provided in the filter circuit, the cutoff frequency will change significantly depending on the voltage due to the voltage dependency of the Zener diode's parasitic capacitance, which will complicate the design of the filter circuit 13a.

[0049] Even when filter circuit 13a is not used, the voltage waveform after the Zener diode is not the same as the waveform obtained by cutting off the detection L voltage VL below the Zener voltage due to the voltage characteristics of the parasitic capacitance, so the voltage after the Zener diode must be obtained by actual measurement or simulation analysis, and the first and second threshold voltages Vref1, Vref2 must be set based on that. On the other hand, if short circuit detection unit 200 is configured with two comparators 201, 203, the threshold voltage can be determined from the detection L current IL and the detection L voltage VL, making the design easier. Furthermore, in a Zener diode, the Zener voltage has a current dependency, so the threshold fluctuation range on the vertical axis of FIG. 9(a) further expands, further reducing the tolerance of the detection circuit.

[0050] As described above, the power conversion device 10 according to the first embodiment can perform short circuit detection that is easy to design and has a sufficient margin against erroneous detection, by using the voltage detection unit 13 that detects the detection L voltage VL generated in the inductance component 111 between two points N1 and N2 set in the connection wiring unit 110 between the DC circuit unit 100 and the three-phase inverter 11p, and the short circuit detection unit 200 that is composed of the two comparators 201 and 203. As a result, it becomes possible to prevent the short circuit from spreading to an accident such as a breakdown or fire of the converter.

[0051] Embodiment 2 In the first embodiment, the output voltage of the filter circuit 13a is connected to the non-inverting input terminal (+) of the first comparator 201, and the first threshold voltage Vref1 is connected to the inverting input terminal (-) of the first comparator 201. In the second embodiment, the output of the filter circuit 13a is connected to the inverting input terminal (-) of the first comparator 201, and the first threshold voltage Vref1 is connected to the non-inverting input terminal (+) of the first comparator 201. With this configuration, it is possible to improve the portion of FIG. 9(b) in the first embodiment where the tolerance is low.

[0052] 10 is a diagram showing an example of a circuit configuration of a voltage detection unit 13 and a short circuit detection unit 200 of a power conversion device according to embodiment 2. Note that the overall configuration of the power conversion device is the same as that of embodiment 1, so illustration and description will be omitted.

[0053] The filter circuit 13a is a low-pass filter composed of a resistor R1 and a capacitor C1, and a set point N1 on the wiring is connected to the ground point GND of the filter circuit 13a and one end of the capacitor C1, and a set point N2 on the wiring is connected to one end of the resistor R1 of the filter circuit 13a. The other end of the capacitor C1, which is the output of the filter circuit 13a, is connected to the other end of the resistor R1 and is connected to an inverting input terminal (-) of a first comparator 201. A first threshold voltage Vref1 generated by a threshold voltage generating unit 204 is input to a non-inverting input terminal (+) of the first comparator 201. The output of the first comparator 201 is connected to an integrator 202 composed of a resistor R2 and a capacitor C2. The output of the first comparator 201 is connected to one end of the resistor R2, and one end of the capacitor C2 is connected to the ground point GND.

[0054] A non-inverting input terminal (+) of a second comparator 203 is connected to the output of the integrator 202, and a second threshold voltage Vref2 generated by a threshold voltage generating unit 204 is input to an inverting input terminal (-) of the second comparator 203. The output of the second comparator 203 becomes an overcurrent detection signal Ssc. The threshold voltage generating unit 204 generates both the first threshold voltage Vref1 and the second threshold voltage Vref2 by dividing a common power supply Vcc by resistor dividers R3 to R6.

[0055] Fig. 11 is a schematic waveform diagram showing the operating principle of the short circuit detection unit 200 in the power conversion device according to the second embodiment. From the top, the diagram shows the detection L current IL, the detection L voltage VL, the output voltage of the first comparator 201, the input voltage of the second comparator 203, and the overcurrent detection signal Ssc. The solid line waveform in Fig. 11 shows an example of the waveform during a short circuit, and the dotted line waveform shows an example of the waveform during a turn-on operation, which is a normal switching operation. Note that the prerequisites such as the load current are the same as those in the first embodiment.

[0056] At time t0, a positive or negative power semiconductor element in one phase of the three-phase inverter is turned on, causing the detection L current IL to start flowing, and the detection L voltage VL also rises accordingly. Next, at time t1, the detection L voltage VL becomes greater than the first threshold voltage Vref1, and the output voltage of the first comparator 201 changes from high to low. The high state is 5V, and the low state is 0V.

[0057] When the output voltage of the first comparator 201 goes low, the input voltage of the second comparator 203 starts to gradually drop by the integrator 202. As can be seen from Fig. 11, the time width during which the output voltage of the first comparator 201 is low is converted into the height of the input voltage of the second comparator 203 by the integrator 202. Up to this point, the operation is the same during normal switching operation and during a short circuit.

[0058] During normal switching operation at time t2, the detection L current IL flows only up to the load current ILoad, so the slope of the detection L current IL becomes gentler and the detection L voltage VL becomes lower than the first threshold voltage Vref1. Therefore, the output voltage of the first comparator 201 also switches from low to high, and the input voltage of the second comparator 203 also starts to rise gradually. After that, when the detection L current IL becomes the load current ILoad, the switching operation is completed.

[0059] At time t2, when a short circuit occurs, the detection L current IL during a short circuit is not limited by the load, unlike during normal switching operation, so the detection L current IL continues to rise even at time t2. As a result, the detection L voltage VL also continues to maintain a value greater than the first threshold voltage Vref1, and the input voltage of the second comparator 203 also continues to decrease.

[0060] When a short circuit occurs at time t3, the input voltage of the second comparator 203 continues to drop and becomes smaller than the second threshold voltage Vref2, the overcurrent detection signal Ssc goes low, and a short circuit is detected. From the above, it is understood that the detection circuit of the second embodiment can be used to distinguish between a normal switching operation and a short circuit.

[0061] Fig. 12 shows the tolerance of the detection circuit in the second embodiment. The solid line in the figure indicates the minimum voltage line during a short circuit, and the dotted line indicates the maximum voltage line during normal switching operation. The vertical axis represents the input voltage to the first comparator 201, which would be the detection L voltage VL if there was no filter circuit 13a. The horizontal axis represents the input voltage to the second comparator 203, which is synonymous with the time width at each magnitude of the input voltage to the first comparator 201.

[0062] It is possible to distinguish between short circuit and normal switching by setting the first and second threshold voltages at, for example, point B, the midpoint between the short circuit and normal switching lines in Fig. 12. The vertical axis value at point B in Fig. 12 represents the first threshold voltage Vref1, and the horizontal axis value at point B represents the second threshold voltage Vref2.

[0063] In comparison with the first embodiment, the input of the first comparator 201 is inverted and non-inverted, so that the order of magnitude of the values ​​on the horizontal axis is inverted as shown in Fig. 12, and therefore the fluctuation directions of the first and second threshold voltages Vref1, Vref2 and the maximum and minimum voltage lines during normal switching operation and short circuit are nearly parallel to each other. Therefore, the low tolerance at the upper right and lower left of the arrows representing the threshold fluctuations in Fig. 9(b) in the first embodiment can be improved by adopting the configuration of the second embodiment.

[0064] As described above, the power conversion device of embodiment 2 can improve the areas where the tolerance for short circuit detection of the short circuit detection unit 200 of embodiment 1 is low by connecting the output of the filter circuit 13a to the inverting input terminal (-) of the first comparator 201 and connecting the first threshold voltage Vref1 to the non-inverting input terminal (+) of the first comparator.

[0065] Embodiment 3 In the first and second embodiments, the type of the first comparator 201 is not specified, and the circuit outputs low or high. In the third embodiment, the type of the first comparator 201 is set to be an open collector or open drain, and further, the power supply Vcc of the threshold voltage generating unit 204 and the power supply that pulls up the output unit of the first comparator 201 are configured to be common. The third embodiment improves the tolerance of the short circuit detecting unit 200 of the first and second embodiments.

[0066] 13 is a diagram showing an example of a circuit configuration of the voltage detection unit 13 and the short circuit detection unit 200 of the power conversion device according to the embodiment 3. Note that the overall configuration of the power conversion device is the same as that of the embodiment 1, so illustration and description are omitted.

[0067] The filter circuit 13a is a low-pass filter composed of a resistor R1 and a capacitor C1, and a set point N1 on the wiring, a ground point GND of the filter circuit 13a, and one end of the capacitor C1 are connected, and a set point N2 on the wiring and one end of the resistor R1 of the filter circuit 13a are connected. The other end of the capacitor C1, which is the output of the filter circuit 13a, and the other end of the resistor R are connected, and are connected to a non-inverting input terminal (+) of a first comparator 201. A first threshold voltage Vref1 generated by a threshold voltage generating unit 204 is input to an inverting input terminal (-) of the first comparator 201.

[0068] Here, the first comparator 201 is of an open collector or open drain type, and one end of a resistor R2 and a capacitor C2 of an integrator 202 composed of a resistor R2 and a capacitor C2, and one end of a pull-up resistor R7 connected to a power supply Vcc of the threshold voltage generating unit 204 are connected to the output of the first comparator 201. One end of the capacitor C2 of the integrator 202 is connected to the ground point GND, and the non-inverting input terminal (+) of a second comparator 203 is connected to the output of the integrator 202.

[0069] The inverting input terminal (-) of the second comparator 203 receives the second threshold voltage Vref2 generated by the threshold voltage generator 204. The output of the second comparator 203 becomes the overcurrent detection signal Ssc. The threshold voltage generator 204 generates both the first threshold voltage Vref1 and the second threshold voltage Vref2 by dividing a common power supply Vcc using resistor dividers R3 to R6.

[0070] In the third embodiment, like the first embodiment, the first threshold voltage Vref1 is connected to the inverting input terminal (-) of the first comparator 201, and the output of the filter circuit 13a is connected to the non-inverting input terminal (+), but they may be connected in the opposite direction as in the second embodiment. Also, in the third embodiment, it is sufficient that the power supply for the second threshold voltage Vref2 and the power supply for pulling up the output of the first comparator 201 are common, and the power supply for generating the first threshold voltage Vref1 does not have to be common.

[0071] The operating principle of short circuit detection in the power conversion device according to the third embodiment is the same as that of the first embodiment, and therefore illustration and description thereof will be omitted. Fig. 14 shows the tolerance of the short circuit detection unit 200 in the third embodiment. The solid line in the figure indicates the minimum voltage line during a short circuit, and the dotted line indicates the maximum voltage line during normal switching operation. The vertical axis represents the input voltage to the first comparator 201, which becomes the detection L voltage VL when the filter circuit 13a is not present. The horizontal axis represents the input voltage to the second comparator 203, which is synonymous with the time width at each magnitude of the input voltage to the first comparator 201.

[0072] It is possible to distinguish between short circuit and normal switching by setting the first and second thresholds at, for example, point C, the midpoint between the short circuit and normal switching lines in Fig. 14. The vertical axis value at point C in Fig. 14 represents the first threshold voltage Vref1, and the horizontal axis value at point C represents the second threshold voltage Vref2.

[0073] By adopting the configuration of embodiment 3, even if the power supply of the threshold voltage generating unit 204 varies and the second threshold voltage Vref2 changes at a certain ratio, the input voltage of the second comparator 203 also changes at a similar ratio, so that the second threshold voltage Vref2 on the horizontal axis does not fluctuate.

[0074] Here, in the third embodiment, the type of the first comparator 201 is an open collector or open drain, but even if the first comparator 201 has a push-pull configuration and the power supply voltage of the threshold voltage generating unit 204 and the power supply voltage of the first comparator are shared as shown in Fig. 15, the same effect as in the third embodiment can be obtained. This is because, even if the power supply of the threshold voltage generating unit 204 varies and the second threshold voltage Vref2 changes at a certain ratio, the input voltage of the second comparator 203 also changes at a similar ratio.

[0075] By adopting the configuration of FIG. 14, the second threshold voltage Vref2 on the horizontal axis does not fluctuate, but the first threshold voltage Vref1 on the vertical axis does. To further improve this, the first threshold voltage Vref1 may be varied depending on the magnitude of the change in the voltage difference between the positive side and the negative side of the connection wiring unit 110. This is because, when the voltage difference of the DC circuit unit 100 increases, the short circuit minimum voltage width line shown by the solid line in FIG. 14 increases along both the vertical and horizontal axes. When the voltage difference is large, the first threshold voltage increases, but the short circuit minimum voltage width line also increases along both the vertical and horizontal axes accordingly, improving the tolerance for erroneous detection of a short circuit. As a specific circuit example, there is a configuration in which the first threshold voltage Vref1 is generated by resistor division from the positive side of the DC circuit unit 100.

[0076] Until now, only power supply variations, which have a significant effect on the detection tolerance, have been considered in regard to threshold voltage variations. However, there are also other variations, such as those in voltage dividing resistors, which should also be taken into consideration when designing. As described above, in the third embodiment, the type of the first comparator 201 is an open collector or open drain, and further, the power supply Vcc of the threshold voltage generating unit 204 and the power supply that pulls up the output of the first comparator 201 are made common, thereby making it possible to further improve the tolerance of the short circuit detection unit 200 compared to the first and second embodiments.

[0077] Embodiment 4 The fourth embodiment relates to short circuit detection in a case where the main circuit section of the power conversion device exemplified in the first embodiment has a different configuration and the main circuit sections are arranged in multiple parallel. Fig. 16 shows a block diagram of an example of the configuration of a power conversion device according to embodiment 4. In Fig. 16, a power conversion device 10 performs power conversion between a DC circuit unit 100 and electric motors 120a and 120b that are loads, and has a configuration in which main circuit units 11a and 11b and electric motors 120a and 120b are connected in parallel.

[0078] The power converter 10 includes main circuit units 11a and 11b and a control unit 12 that controls the main circuit units 11a and 11b. The control unit 12 includes a voltage detection unit 13 that detects a voltage generated in an inductance component 111 between set points N1 and N2 on a wiring set in a connection wiring unit 110 between the DC circuit unit 100 and the power converter 10, and a short circuit detection unit 200 that determines whether or not a short circuit has occurred in the power converter based on the output of the voltage detection unit 13. Note that, although the power converter 10 includes only one inductance component 111 for voltage detection in Fig. 16, each of the main circuit units 11a and 11b may be provided with an inductance component for voltage detection.

[0079] Fig. 17 is a block diagram showing a specific configuration of a power conversion device according to embodiment 4. Here, as an example, the DC circuit unit 100 includes an AC power supply 100b, a three-phase PWM converter 100a that converts AC voltage to DC voltage, and main circuit units 11a and 11b include three-phase inverters that drive three-phase motors 120a and 120b that are three-phase AC loads.

[0080] The three-phase PWM converter 100a is composed of an AC reactor 101a, power semiconductor elements Ma to Mf, and a capacitor 14a, and the main circuit units 11a and 11b are composed of power semiconductor elements M1 to M12 and a capacitor 14b. As in the first embodiment, the configuration of the DC circuit unit 100 and the main circuit unit 11, the type and number of power semiconductor elements, the number of phases of the power conversion device 10, the number and locations of the capacitors, etc. are not limited.

[0081] The fourth embodiment is a power conversion device with a two-parallel configuration for driving two three-phase motors 120a and 120b, and is used, for example, in the outdoor unit circuit of an air conditioner. One is a three-phase motor for a compressor, and the other is a three-phase motor for a fan. The configuration of the voltage detection unit 13 and the short circuit detection unit 200 may be any of those in the first to third embodiments, and the operating principle of the short circuit detection unit 200 is also the same. However, in the case of a configuration with only one three-phase inverter, the second threshold voltage Vref2 is determined taking into consideration the case where the maximum current gradients di / dt of two phases overlap, but in the case of the main circuit units 11a and 11b arranged in multiple parallel, the number of phases where the maximum current gradients di / dt overlap further increases, so the second threshold voltage Vref2 must be determined based on the time width when the number of phases where di / dt overlap is at its maximum.

[0082] Also in the configuration of the fourth embodiment, the voltage detection unit 13 and the short circuit detection unit 200 provided in the common control unit 12 can detect a short circuit occurring in the inductance component 111 between the set points N1 and N2 on the wiring set in the connection wiring unit 110 which is the common path of the parallel-connected main circuit units 11a and 11b, and can stop the operation of the power converter for protection. When a short circuit is detected in the power conversion device as in the fourth embodiment, the device destruction due to an arm short circuit can be prevented by turning off the three-phase PWM converter 100a and the power semiconductor elements of the parallel-connected main circuit units 11a and 11b.

[0083] So far, the method of implementing short circuit detection according to the present disclosure in the main circuit section has been described, but it is clear that the present method is also applicable to the DC circuit section 100. Furthermore, regarding the short circuit detection circuit, short circuit detection has been performed using an analog circuit, but short circuit detection may also be performed using a digital circuit such as an FPGA (Field-programmable gate array) or a microcontroller.

[0084] FIG. 18 shows an example of hardware when a microcomputer is used. The microcomputer is composed of a processor 1000 and a storage device 2000. Although not shown, the storage device includes a volatile storage device such as a random access memory and a nonvolatile auxiliary storage device such as a flash memory. Also, instead of the flash memory, an auxiliary storage device such as a hard disk may be included. The processor 1000 performs the above-mentioned short circuit detection by executing a program input from the storage device 2000. In this case, the program is input from the auxiliary storage device to the processor 1000 via the volatile storage device. Also, the processor 1000 may output data of the voltage detected by the voltage detection unit, data of the calculation result, etc. to the volatile storage device of the storage device 2000, or may store the data in the auxiliary storage device via the volatile storage device. Furthermore, when a microcomputer is used, it is easy to output a signal for turning off the three-phase PWM converter 100a and the power semiconductor elements of the paralleled main circuit units 11, 11a, and 11b.

[0085] Although the present disclosure describes various exemplary embodiments and examples, the various features, aspects, and functions described in one or more embodiments are not limited to application to a particular embodiment, but may be applied to the embodiments alone or in various combinations. Therefore, countless variations not exemplified are assumed within the scope of the technology disclosed in this specification, including, for example, the case where at least one component is extracted and combined with a component of another embodiment. [Explanation of symbols]

[0086] 10: power conversion device, 11, 11a, 11b: main circuit section, 12: control section, 13: voltage detection section, 13a: filter circuit, 100: DC circuit section, 110: connecting wiring section, 111: inductance component, 120: load, 200: short circuit detection section, 201: first comparator, 202: integrator, 203: second comparator, 204: threshold voltage generation section.

Claims

1. A power conversion device comprising: a main circuit section composed of two or more phases that performs power conversion between a DC circuit section and a load; a voltage detection section that detects a voltage generated in an inductance component between two points on a wiring connecting the DC circuit section and the main circuit section; a first comparator that outputs a detection signal when the voltage detected by the voltage detection section exceeds a first threshold voltage; and a short-circuit detection section having a second comparator that detects that a short circuit has occurred when the detection signal of the first comparator continues for a predetermined time or longer.

2. A power conversion device comprising: a main circuit section that performs power conversion between a DC circuit section and a load; a voltage detection section that detects a voltage generated in an inductance component between two points on a wiring connecting the DC circuit section and the main circuit section; a first comparator that outputs a detection signal when the voltage detected by the voltage detection section exceeds a first threshold voltage; and a short-circuit detection section having a second comparator that detects that a short circuit has occurred when the detection signal of the first comparator continues for a predetermined time or longer. When the detection signal of the first comparator continues for a predetermined time or longer and a voltage corresponding to the continuous time exceeds a second threshold voltage, the second comparator determines that there is a short circuit. When the voltages detected by the voltage detection section overlap in time due to switching of a plurality of phases of the main circuit section configured by an inverter, the second threshold voltage is determined based on the time width of a period during which the voltage values of the plurality of phases detected overlappingly are equal to or higher than the first threshold voltage. A power conversion device characterized by this.

3. The power conversion device according to claim 2, further comprising a threshold voltage generation section that generates the first threshold voltage and the second threshold voltage, wherein a power source for generating the first threshold voltage and a power source for generating the second threshold voltage are common.

4. The power conversion device according to claim 2, wherein the first comparator has an inverting input terminal and a non-inverting input terminal, the first threshold voltage is input to the inverting input terminal, and the voltage output from the voltage detection section is input to the non-inverting input terminal.

5. The power conversion device according to claim 2, wherein the first comparator has an inverting input terminal and a non-inverting input terminal, the first threshold voltage is input to the non-inverting input terminal, and the voltage output from the voltage detection section is input to the inverting input terminal.

6. The first comparator is an open collector or an open drain, and a power supply for generating the second threshold voltage and a power supply for pulling up the output of the first comparator are common. The power conversion device according to claim 2.

7. The first comparator has a push-pull configuration, and a power supply for generating the second threshold voltage and a power supply of the first comparator are common. The power conversion device according to claim 2.

8. The first threshold voltage is changed according to a change in a voltage difference between a positive-side wiring and a negative-side wiring connecting the DC circuit section and the main circuit section. The power conversion device according to claim 6.

9. The voltage detection unit is provided with a low-pass filter for removing current pulsations generated in the main circuit section. The power conversion device according to any one of claims 2 to 7.

10. An integrator for converting the detection signal of the first comparator into a voltage corresponding to a duration when the detection signal of the first comparator continues for a predetermined time or longer is provided between the first comparator and the second comparator. The power conversion device according to any one of claims 2 to 8.

11. A main circuit section that performs power conversion between a DC circuit section and a load, a voltage detection unit that detects a voltage generated in an inductance component between two points on a wiring connecting the DC circuit section and the main circuit section, a first comparator that outputs a detection signal when the voltage detected by the voltage detection unit exceeds a first threshold voltage, and a second comparator that detects that a short circuit has occurred when the detection signal of the first comparator continues for a predetermined time or longer. A short circuit detection unit having the above, When configured by a plurality of the loads and a plurality of the main circuit sections, the voltage detection unit detects a voltage on a wiring to which the plurality of the main circuit sections and the DC circuit section are connected. A power conversion device.

12. When the short circuit detection unit detects a short circuit, all power semiconductor elements in the DC circuit section and the main circuit section are turned off. The power conversion device according to any one of claims 1 to 8.

13. A main circuit unit that performs power conversion between a DC circuit unit and a load, a voltage detection unit that detects a voltage generated in an inductance component between two points on a wiring connecting the DC circuit unit and the main circuit unit, a first comparator that outputs a detection signal when the voltage detected by the voltage detection unit exceeds a first threshold voltage, and a second comparator that detects that a short circuit has occurred when the detection signal of the first comparator continues for a predetermined time or longer. A capacitor is connected between positive and negative wirings connecting the DC circuit unit and the main circuit unit. Let the inductance between the capacitor including the inductance component L and the power semiconductor element in the main circuit unit be Lloop, the inductance between the capacitor not including the inductance component L and the power semiconductor element be La, the element breakdown voltage of the power semiconductor element be Vdsp, the maximum voltage of the DC circuit unit be Vdcmax, the maximum current slope of the power semiconductor element be di / dt, and Lloop = La + L. Then, 【Number 1】 a power conversion device, characterized in that the following relationship holds.

14. A main circuit unit that performs power conversion between a DC circuit unit and a load, a voltage detection unit that detects a voltage generated in an inductance component between two points on a wiring connecting the DC circuit unit and the main circuit unit, a first comparator that outputs a detection signal when the voltage detected by the voltage detection unit exceeds a first threshold voltage, and a second comparator that detects that a short circuit has occurred when the detection signal of the first comparator continues for a predetermined time or longer. An integrator is provided between the first comparator and the second comparator. The integrator converts the duration of the detection signal of the first comparator into a voltage. When the detection signal continues for a predetermined time or longer, the second comparator determines that a short circuit has occurred when the converted voltage exceeds a second threshold voltage. The first comparator is an open collector or an open drain, and the power supply for generating the second threshold voltage and the power supply for pulling up the output of the first comparator are common. A power conversion device characterized by this.

15. A main circuit section that performs power conversion between a DC circuit section and a load, a voltage detection section that detects a voltage generated in an inductance component between two points on a wiring connecting the DC circuit section and the main circuit section, a first comparator that outputs a detection signal when the voltage detected by the voltage detection section exceeds a first threshold voltage, and a second comparator that detects that a short circuit has occurred when the detection signal of the first comparator continues for a predetermined time or longer. An integrator is provided between the first comparator and the second comparator. The integrator converts the duration of the detection signal of the first comparator into a voltage. When the detection signal continues for a predetermined time or longer, the second comparator determines that a short circuit has occurred because the converted voltage exceeds a second threshold voltage. The first comparator has a push-pull configuration, and a power supply for generating the second threshold voltage and a power supply for the first comparator are common. A power conversion device characterized by this.

16. A main circuit section that performs power conversion between a DC circuit section and a load, a voltage detection section that detects a voltage generated in an inductance component between two points on a wiring connecting the DC circuit section and the main circuit section, a first comparator that outputs a detection signal when the voltage detected by the voltage detection section exceeds a first threshold voltage, and a second comparator that detects that a short circuit has occurred when the detection signal of the first comparator continues for a predetermined time or longer. An integrator is provided between the first comparator and the second comparator. The integrator converts the duration of the detection signal of the first comparator into a voltage. When the detection signal continues for a predetermined time or longer, the second comparator determines that a short circuit has occurred because the converted voltage exceeds a second threshold voltage. The first comparator is an open collector or an open drain, and a power supply for generating the second threshold voltage and a power supply for pulling up the output of the first comparator are common. A power conversion device characterized in that the first threshold voltage is changed according to a change in the voltage difference between the positive-side wiring and the negative-side wiring connecting the DC circuit section and the main circuit section.

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