Power Conversion Device

Abstract

A power conversion device that suppresses erroneous detection of a short-circuit state of a semiconductor switching element. [Solution] The device comprises a semiconductor switching element having a first main terminal, a second main terminal, and a gate terminal; a drive circuit that inputs a signal to turn the semiconductor switching element on and off to the gate terminal; a first diode connected to the first main terminal; a capacitance element having a positive terminal connected to the first diode and a negative terminal connected to the second main terminal; a charging circuit unit having a current source that charges the capacitance element, the current source charging the capacitance element; a short-circuit determination unit that determines whether the semiconductor switching element is short-circuited; and a current bypass circuit unit that prevents current that has reverse-conducted the first diode from flowing into the capacitance element, wherein the short-circuit determination unit determines that the semiconductor switching element is short-circuited when the voltage across the capacitance element is higher than a predetermined determination threshold voltage, and if the short-circuit determination unit determines that the semiconductor switching element is short-circuited, the drive circuit inputs a signal to turn the semiconductor switching element off to the gate terminal.

Description

[Technical Field]

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

[0002] In recent years, automobiles equipped with electric powertrains such as hybrid vehicles, plug-in hybrid vehicles, electric vehicles, and fuel cell vehicles (hereinafter referred to as "electric vehicles") have become widespread. These electric vehicles are equipped with a rotating electric machine drive system. The rotating electric machine drive system incorporates a DC power supply, an AC rotating electric machine for propelling the vehicle, and a power conversion device that receives power from the DC power supply and controls the AC rotating electric machine. The power conversion device has a semiconductor switching element and a drive circuit connected to the gate terminal of the semiconductor switching element. The drive circuit controls the semiconductor switching element to turn on and off, thereby allowing the power conversion device to perform power conversion.

[0003] When a semiconductor switching element mounted on a power conversion device is short-circuited, an overcurrent flows through the semiconductor switching element due to the short circuit, which can damage the semiconductor switching element. For this reason, various methods for detecting a short-circuited state of a semiconductor switching element have been proposed (see, for example, Patent Document 1).

[0004] Patent Document 1 discloses a method for detecting short circuits in semiconductor switching elements by detecting whether the collector-emitter or drain-source voltage of the semiconductor switching element is an abnormally high voltage that would not occur in the on-state of normal switching operation, and determining whether a short circuit has occurred. This method is called the DESAT method. Even during normal switching operation, the collector-emitter or drain-source voltage of the semiconductor switching element is in a high-voltage state for a period of several microseconds from when the semiconductor switching element is turned on until it reaches a steady state. Therefore, the DESAT method cannot accurately detect a short circuit during this period. Therefore, to avoid falsely detecting normal switching operation as a short circuit, it is necessary to set this period as a period during which short circuit detection is not performed (hereinafter referred to as a mask period).

[0005] Generally, the mask period is designed to prevent false detection even when the time it takes for the semiconductor switching element to reach a steady state after being turned on is at its longest, taking into account individual variations in the semiconductor switching element and the components mounted on the drive circuit, as well as temperature effects. However, if the mask period is too long, it will take a long time to detect a short circuit when it actually occurs. If the time it takes to detect a short circuit increases, the energy tolerance required to prevent the semiconductor switching element from being destroyed by a short circuit also increases, which creates the problem of increasing the cost of the semiconductor switching element.

[0006] In order to solve this problem, it is desirable to shorten or reduce the mask period during which short circuit detection is not performed, and to quickly detect the short-circuit state of the semiconductor switching element and perform protection operation for the semiconductor switching element. Therefore, a method has been proposed in which the mask period during which short circuit detection is not performed is shortened or reduced to detect the short-circuit state of the semiconductor switching element (see, for example, Patent Document 2). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-208847 [Patent Document 2] Patent No. 5861787 Summary of the Invention [Problem to be solved by the invention]

[0008] Patent Document 2 proposes a method for initiating short-circuit detection immediately after the gate-emitter or gate-source voltage begins to rise in order to perform protection operation early in the event of a short circuit. However, during the period between when a drive circuit outputs a signal to turn on a semiconductor switching element and the signal is input to the semiconductor switching element, but before a collector current or drain current begins to flow through the semiconductor switching element, the collector-emitter or drain-source voltage of the semiconductor switching element may suddenly fluctuate due to some factor external to the power conversion device, such as a load current fluctuation. A new problem has been discovered in short-circuit detection circuits with such a shortened mask period: due to this sudden voltage fluctuation, the semiconductor switching element may erroneously detect a short circuit even when it is not. Such a malfunction of the short-circuit detection function is undesirable because it prevents the power conversion device from operating normally.

[0009] Therefore, an object of the present disclosure is to provide a power conversion device that suppresses erroneous detection of a short-circuit state of a semiconductor switching element. [Means for solving the problem]

[0010] The power conversion device of the present disclosure has a first main terminal, a second main terminal, and a gate terminal, and includes a plurality of semiconductor switching elements that turn on and off a main current flowing between the first main terminal and the second main terminal according to the voltage of the gate terminal relative to the second main terminal; a drive circuit that inputs a signal to the gate terminal that turns on or off the semiconductor switching elements; a first diode having a cathode connected to the first main terminal; a capacitance element having a positive terminal connected to the anode of the first diode and a negative terminal connected to the second main terminal; and a current source that charges the capacitance element; the drive circuit outputs a signal to the gate terminal that turns on the semiconductor switching elements; The driving circuit includes a charging circuit section in which a current source charges the capacitance element when a current source is input to the gate terminal, a short-circuit determination section connected to the capacitance element and determining whether or not the semiconductor switching element is short-circuited, and a current bypass circuit section connected in parallel to the capacitance element and preventing current that has reverse-conducted the first diode from flowing into the capacitance element, wherein the short-circuit determination section determines that the semiconductor switching element is short-circuited when the voltage across the capacitance element is higher than a predetermined determination threshold voltage, and when the short-circuit determination section determines that the semiconductor switching element is short-circuited, the driving circuit inputs a signal to the gate terminal to turn off the semiconductor switching element. [Effects of the Invention]

[0011] According to the power conversion device of the present disclosure, the power conversion device includes a plurality of semiconductor switching elements each having a first main terminal, a second main terminal, and a gate terminal; a drive circuit that inputs a signal to the gate terminal to turn the semiconductor switching elements on and off; a first diode connected to the first main terminal; a capacitance element having a positive terminal connected to the first diode and a negative terminal connected to the second main terminal; a charging circuit unit having a current source that charges the capacitance element, the current source charging the capacitance element; a short-circuit determination unit that determines whether the semiconductor switching elements are short-circuited; and a current bypass circuit unit that prevents current that has reverse-conducted the first diode from flowing into the capacitance element, wherein the short-circuit determination unit determines whether the semiconductor switching elements are short-circuited when the voltage across the capacitance element is higher than a predetermined determination threshold voltage. When the short-circuit determination unit determines that a short circuit has occurred, the drive circuit inputs a signal to the gate terminal to turn off the semiconductor switching element. Therefore, the drive circuit outputs a signal to turn on the semiconductor switching element. Even if the voltage between the first main terminal and the second main terminal of the semiconductor switching element fluctuates sharply during the period from when the signal is input to the gate terminal of the semiconductor switching element until a main current starts to flow through the semiconductor switching element, the displacement current corresponding to this voltage fluctuation flows through the current bypass circuit unit and is prevented from flowing into the capacitive element. Therefore, erroneous detection of a short-circuit state of the semiconductor switching element can be suppressed without impairing the operation of the short-circuit determination unit, which quickly detects a short-circuit state of the semiconductor switching element. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a block diagram showing an outline of the configuration of a rotary electric machine drive system equipped with a power conversion device according to a first embodiment. [Figure 2] 1 is a configuration diagram showing an outline of a main part of a power conversion device according to a first embodiment. [Figure 3] 3 is a diagram illustrating waveforms of voltage and current during operation of the power conversion device according to the first embodiment. FIG. [Figure 4] 3 is a diagram illustrating waveforms of voltage and current when a short circuit occurs in the power conversion device according to the first embodiment. FIG. [Figure 5]FIG. 10 is a configuration diagram showing an outline of a main part of a power conversion device according to a modification of the first embodiment. [Figure 6] FIG. 2 is a configuration diagram illustrating an outline of a main part of a power conversion device of a comparative example. [Figure 7] 10A and 10B are diagrams illustrating waveforms of voltage and current during operation of a power conversion device of a comparative example. [Figure 8] FIG. 10 is a configuration diagram showing an outline of a main part of a power conversion device according to a second embodiment. [Figure 9] 10 is a diagram illustrating waveforms of voltage and current during operation of the power conversion device according to the second embodiment. FIG. [Figure 10] FIG. 10 is a configuration diagram showing an outline of a main part of a power conversion device according to a modification of the second embodiment. [Figure 11] 10 is a schematic circuit diagram illustrating an operation of a drive circuit of a power conversion device according to a second embodiment to turn on a semiconductor switching element. FIG. [Figure 12] 10 is a diagram illustrating a comparison of voltage and current waveforms during normal switching of a semiconductor switching element of a power converter according to a second embodiment and when a short circuit occurs. FIG. [Figure 13] 10 is a current-voltage characteristic diagram for schematically explaining the relationship between the gate-source voltage and the drain current of the semiconductor switching element of the power converter according to the second embodiment. FIG. [Figure 14] FIG. 10 is a configuration diagram showing an outline of a main part of a power conversion device according to a third embodiment. [Figure 15] 10 is a diagram illustrating waveforms of voltage and current during operation of the power conversion device according to the third embodiment. FIG. [Figure 16] FIG. 11 is a configuration diagram showing an outline of a main part of a power conversion device according to a modification of the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, a power conversion device according to an embodiment of the present disclosure will be described with reference to the drawings. Note that the same or equivalent components and parts in each drawing will be described with the same reference numerals. Also, each drawing relates to one embodiment, and the present disclosure is not limited by these drawings.

[0014] Embodiment 1 FIG. 1 is a block diagram showing an outline of the configuration of a rotating electric machine drive system 200 equipped with a power conversion device 2 according to a first embodiment. FIG. 2 is a configuration diagram showing an outline of a main part of the power conversion device 2 and showing details of a drive control unit 10. FIG. 3 is a diagram illustrating voltage and current waveforms during operation of the power conversion device 2. FIG. 4 is a diagram illustrating voltage and current waveforms during a short circuit in the power conversion device 2. FIG. 5 is a configuration diagram showing an outline of a main part of the power conversion device 2 according to a modified example, showing parts equivalent to those shown in FIG. 2. The power conversion device 2 is, for example, a device that converts an input current from DC to AC, AC to DC, or an input voltage to a different voltage. In this embodiment, the power conversion device 2 is described as an inverter equipped in the rotating electric machine drive system 200, but the power conversion device 2 is not limited to an inverter. Furthermore, the power conversion device 2 equipped in the rotating electric machine drive system 200 is not limited to the power conversion device 2 according to the first embodiment, and may be a power conversion device 2 according to other embodiments described later.

[0015] <Rotating Electric Machine Drive System 200> An example of the configuration of a rotating electric machine drive system 200 will be described with reference to Fig. 1. The rotating electric machine drive system 200 mounted on an electric vehicle includes a DC power supply 1, an AC rotating electric machine 5 which is a load device for propelling the vehicle, and a power conversion device 2 which receives power supply from the DC power supply 1 and controls the AC rotating electric machine 5. The power conversion device 2 is the part surrounded by a dashed line. The DC power supply 1 is, for example, a high-voltage battery of 400 to 800 V.

[0016] The power conversion device 2 includes a smoothing capacitor 3 connected in parallel to the DC power supply 1, upper-stage semiconductor switching elements 4a, 4c, and 4e connected to the positive electrode of the DC power supply 1, lower-stage semiconductor switching elements 4b, 4d, and 4f connected to the negative electrode of the DC power supply 1, and a drive control unit 10 connected to the semiconductor switching elements 4a to 4f. The drive control unit 10 includes a controller 11, short-circuit determination units 13 provided corresponding to each of the semiconductor switching elements 4a to 4f, and drive circuits 12 connected to each of the semiconductor switching elements 4a to 4f. The smoothing capacitor 3 has functions such as suppressing ripples in the DC power supply 1 and absorbing surge voltages.

[0017] In a normal operating state, the power conversion device 2 performs power conversion by having the drive circuit 12 control the on / off of each of the corresponding semiconductor switching elements based on a command signal from the controller 11. The power conversion device 2 converts DC power from the DC power source 1 into predetermined AC power by turning on and off the semiconductor switching elements 4a to 4f at a predetermined switching frequency, thereby adjusting the torque and rotation speed of the AC rotating electric machine 5. The short-circuit determination unit 13 determines whether the corresponding semiconductor switching element is in a short-circuit state. If the short-circuit determination unit 13 determines that the semiconductor switching element is short-circuited, the drive circuit 12 outputs a signal to turn off the corresponding semiconductor switching element.

[0018] <Power conversion device 2> Next, the detailed configuration of the power conversion device 2 will be described with reference to FIG. 2. In this embodiment, the semiconductor switching elements 4a to 4f are controlled in basically the same manner, so only the semiconductor switching element 4a and the circuit unit connected to the semiconductor switching element 4a will be described here. The semiconductor switching element 4a has a first main terminal 41, a second main terminal 42, and a gate terminal 43. A main current flowing between the first main terminal 41 and the second main terminal 42 is turned on and off depending on the voltage of the gate terminal 43 relative to the second main terminal 42. The first main terminal 41 may be, for example, a drain terminal or a collector terminal, and the second main terminal 42 may be, for example, a source terminal or an emitter terminal. The main current may be, for example, a drain current or a collector current.

[0019] In this embodiment, a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) is used as the semiconductor switching element 4a. The semiconductor switching element 4a is not limited to a MOSFET and may be a bipolar transistor or the like. The gate terminal 43 serving as a control terminal and the pair of main terminals may be equivalently referred to as, for example, the drain terminal as a collector terminal and the source terminal as an emitter terminal depending on the type of semiconductor switching element, and therefore, hereinafter, the respective terminals will not be described together.

[0020] The drive control unit 10 includes a controller 11, a drive circuit 12, and a short-circuit determination unit 13, as well as a charging circuit unit 14 and a current bypass circuit unit 15. The drive circuit 12 is connected to a gate terminal 43 with a second main terminal 42 as a reference potential. The drive circuit 12 inputs a signal to the gate terminal 43 to turn on or off the semiconductor switching element 4a.

[0021] The charging circuit unit 14 is connected to the first main terminal 41, with the second main terminal 42 serving as a reference potential. The charging circuit unit 14 has a first diode 141 having a cathode connected to the first main terminal 41, a capacitance element 142 having a positive terminal connected to the anode of the first diode 141 and a negative terminal connected to the second main terminal 42, and a current source 143 that charges the capacitance element 142. In the charging circuit unit 14, the drive circuit 12 outputs a signal to the gate terminal 43 to turn on the semiconductor switching element 4a, and when the signal is input to the gate terminal 43, the current source 143 charges the capacitance element 142.

[0022] The current bypass circuit unit 15 is provided inside the charging circuit unit 14. The current bypass circuit unit 15 is connected to the anode of the first diode 141 at a connection point a, with the second main terminal 42 serving as a reference potential. The positive terminal of the capacitance element 142 is connected to the current bypass circuit unit 15 at a connection point b. The current bypass circuit unit 15 is connected in parallel to the capacitance element 142 and prevents a current that has reverse-conducted the first diode 141 from flowing to the capacitance element 142. In this embodiment, the charging circuit unit 14 has a filter resistor 144 between the connection point b and the positive terminal of the capacitance element 142. In this way, the charging circuit unit 14 may have a configuration in which the capacitance element 142 and the filter resistor 144 form a filter circuit.

[0023] The short-circuit determination unit 13 is connected to the capacitance element 142 of the charging circuit unit 14. The short-circuit determination unit 13 determines whether or not the semiconductor switching element 4a is short-circuited. The short-circuit determination unit 13 determines that the semiconductor switching element 4a is short-circuited when the voltage across the capacitance element 142 is higher than a predetermined determination threshold voltage Vscth during the period when the drive circuit 12 is inputting an on-signal to the gate terminal 43 of the semiconductor switching element 4a. If the short-circuit determination unit 13 determines that the semiconductor switching element 4a is short-circuited, the drive circuit 12 inputs a signal to the gate terminal 43 to turn off the semiconductor switching element 4a. The short-circuit determination unit 13 is composed of one or both of a digital circuit such as an IC and an analog circuit such as a comparator.

[0024] The dotted arrows in the figure indicate the route along which the displacement current Idi, which is generated due to the change in the drain-source voltage over time and flows via the parasitic capacitance of the first diode 141, flows to the charging circuit unit 14. Details of the displacement current Idi, which is generated due to the change in the drain-source voltage over time, will be described later.

[0025] With this configuration, even if the voltage between the first main terminal 41 and the second main terminal 42 of the semiconductor switching element 4a fluctuates suddenly during the period from when the drive circuit 12 outputs a signal to turn on the semiconductor switching element 4a and when the signal is input to the gate terminal 43 of the semiconductor switching element 4a until the main current starts to flow through the semiconductor switching element 4a, the displacement current Idi corresponding to this voltage fluctuation flows through the current bypass circuit section 15 and is prevented from flowing into the capacitive element 142. This does not impair the operation of the short-circuit determination section 13, which quickly detects the short-circuit state of the semiconductor switching element 4a, and therefore makes it possible to obtain a power conversion device 2 that suppresses erroneous detection of the short-circuit state of the semiconductor switching element 4a.

[0026] <Comparative Example> Before describing the detailed configuration of the current bypass circuit section 15, which is a main part of the first embodiment, a comparative example will be described, which does not have the current bypass circuit section 15. Fig. 6 is a configuration diagram showing an outline of the main parts of a power conversion device 2a of the comparative example, and is a diagram showing parts equivalent to Fig. 2, and Fig. 7 is a diagram explaining the voltage and current waveforms during operation of the power conversion device 2a of the comparative example. The short-circuit determination section 13 of the comparative example is configured to erroneously detect that the semiconductor switching element 4a is in a short-circuit state even though the semiconductor switching element 4a is not in a short-circuit state.

[0027] The configuration of the drive control unit 10a of the comparative example is different from the configuration of the drive control unit 10 in the present embodiment 1. In the comparative example, as shown in Fig. 6, the charging circuit unit 14a of the drive control unit 10a does not have the current bypass circuit unit 15, and the anode of the first diode 141 is connected to the positive terminal of the capacitance element 142 via the filter resistor 144.

[0028] 3 and 7 show switching waveforms when the semiconductor switching element 4b on the lower side switches from an ON state to an OFF state and the semiconductor switching element 4a on the upper side switches from an OFF state to an ON state. From top to bottom, the figures illustrate the gate-source voltages of the semiconductor switching elements 4a and 4b, the output current flowing from the power converters 2 and 2a to the AC rotating electric machine 5, the drain-source voltages of the semiconductor switching elements 4a and 4b, and the voltage across the capacitance element 142, which the short-circuit determination unit 13 uses to determine whether the semiconductor switching element 4a is in a short-circuit state. The direction of the output current is defined as positive when it flows from the power converters 2 and 2a to the AC rotating electric machine 5, and negative when it flows from the AC rotating electric machine 5 to the power converters 2 and 2a. In the figures, the waveform of the semiconductor switching element 4a is indicated by a solid line, and the waveform of the semiconductor switching element 4b is indicated by a dashed line.

[0029] During the period from when the lower-side semiconductor switching element 4b switches from an ON state to an OFF state until the upper-side semiconductor switching element 4a switches from an OFF state to an ON state, the output current may fluctuate instantaneously due to external influences on the power conversion devices 2, 2a, such as the influence of ripple current from the AC rotating electric machine 5. For example, as shown in FIG. 7, assume that the output current reverses from negative to positive before the upper-side semiconductor switching element 4a switches from an OFF state to an ON state. When the output current reverses from negative to positive, the freewheel diode of the semiconductor switching element 4b turns on, causing a steep rise in the drain-source voltage of the semiconductor switching element 4a. At this time, if the time change in the drain-source voltage of the semiconductor switching element 4a is d(Vds) / dt, when this time change d(Vds) / dt is applied to the first diode 141, a displacement current Idi (=Cj×d(Vds) / dt) is generated via the parasitic capacitance Cj of the first diode 141, and therefore a current that reverse-conducts the first diode 141 flows to the charging circuit section 14.

[0030] 6, in the comparative example, the displacement current Idi flows through the current path indicated by the dotted arrow, and the displacement current Idi charges the capacitance element 142. Therefore, as shown in FIG. 7, the voltage across the capacitance element 142 rises sharply, and becomes higher than the determination threshold voltage Vscth. As a result, the short-circuit determination unit 13 erroneously determines that the semiconductor switching element 4a is short-circuited.

[0031] The above is the principle behind why fluctuations in the drain-source voltage of the semiconductor switching element 4a in the power conversion device 2a of the comparative example cause the short-circuit determination unit 13 to erroneously detect the semiconductor switching element 4a as being in a short-circuit state even though the semiconductor switching element 4a is not in a short-circuit state.

[0032] Furthermore, if the output current reverses from negative to positive during the period when the upper-stage semiconductor switching element 4a switches from the on state to the off state and when the lower-stage semiconductor switching element 4b switches from the off state to the on state, the short-circuit determination unit 13 will similarly erroneously detect that the semiconductor switching element 4b is short-circuited. Furthermore, with regard to the semiconductor switching elements 4c to 4f, the same result can be obtained by replacing the semiconductor switching element 4a with the semiconductor switching element 4c or the semiconductor switching element 4e, and by replacing the semiconductor switching element 4b with the semiconductor switching element 4d or the semiconductor switching element 4f.

[0033] <Current bypass circuit section 15> The configuration of the current bypass circuit unit 15, which is a main part of the first embodiment, will be described in detail with reference to FIG. 2. The current bypass circuit unit 15 has a Zener diode 152 whose cathode is connected to the anode of the first diode 141 and whose anode is connected to the second main terminal 42. The cathode of the Zener diode 152 is connected to the connection point a. The Zener voltage of the Zener diode 152 is higher than the determination threshold voltage. In this embodiment, the current bypass circuit unit 15 further has a diode 151 whose cathode is connected to the connection point a and whose anode is connected to the connection point b. Note that the current bypass circuit unit 15 is not limited to a configuration including the Zener diode 152. Instead of the Zener diode 152, the current bypass circuit unit 15 may be configured to include a switch element that is turned on during a period when the displacement current Idi flows, or may be configured to include a capacitive element.

[0034] This configuration allows the displacement current Idi to bypass the Zener diode 152 by flowing from its cathode toward its anode (the bypass current path indicated by the dotted arrow in FIG. 2). The diode 151 restricts the path through which the displacement current Idi flows, ensuring that the displacement current Idi flows through the bypass current path. Therefore, as shown in FIG. 3, even if the drain-source voltage of the semiconductor switching element 4a fluctuates, the capacitance element 142 is not rapidly charged by the displacement current Idi, and the voltage across the capacitance element 142 does not exceed the determination threshold voltage Vscth. This prevents the short-circuit determination unit 13 from erroneously detecting a short-circuit state of the semiconductor switching element 4a. The same effect can be achieved by configuring the other semiconductor switching elements 4b to 4f in the same way.

[0035] The reason why the Zener voltage Vz of the Zener diode 152 is set higher than the determination threshold voltage will be explained using FIG. 4. FIG. 4 shows waveforms when a short circuit occurs due to erroneous turning-on of the semiconductor switching element 4a while the semiconductor switching element 4b is in the on state. From top to bottom, the figure illustrates the gate-source voltage of the semiconductor switching element 4a, the drain current which is the short-circuit current flowing through the semiconductor switching element 4a, the drain-source voltage of the semiconductor switching element 4a, and the voltage across the capacitive element 142 at which the short-circuit determination unit 13 determines whether the semiconductor switching element 4a is in a short-circuit state. The Zener voltage Vz at which the Zener voltage Vz is lower than the determination threshold voltage Vscth is defined as voltage Vz1, and the Zener voltage Vz at which the Zener voltage Vz is higher than the determination threshold voltage Vscth is defined as voltage Vz2.

[0036] 4, when a short circuit occurs, the drain-source voltage of semiconductor switching element 4a is high, and therefore a voltage is applied to first diode 141 in the direction from cathode to anode, i.e., in the reverse direction of the diode. Because a reverse leakage current of about several microamperes flows through first diode 141, Zener diode 152 turns on, and the voltage at node a is fixed to Zener voltage Vz. At this time, the voltage across capacitive element 142 becomes equal to the voltage at node a and is fixed to Zener voltage Vz.

[0037] 4, when the Zener voltage Vz of the Zener diode 152 is voltage Vz1, the voltage across the capacitance element 142 does not exceed the determination threshold voltage Vscth, and therefore the short-circuit determination unit 13 cannot detect a short circuit even when the semiconductor switching element 4a is in a short-circuited state. On the other hand, when the Zener voltage Vz of the Zener diode 152 is voltage Vz2, the voltage across the capacitance element 142 exceeds the determination threshold voltage Vscth even when the semiconductor switching element 4a is in a short-circuited state, and therefore the short-circuit determination unit 13 can accurately determine that a short circuit has occurred.

[0038] In the power conversion device 2 according to the first embodiment, the current bypass circuit unit 15 has the Zener diode 152, the cathode of which is connected to the anode of the first diode 141 and the anode of which is connected to the second main terminal 42, thereby forming a path for bypassing the displacement current Idi in the direction from the cathode to the anode of the Zener diode 152. By making the Zener voltage Vz of the Zener diode 152 higher than the determination threshold voltage Vscth of the short-circuit determination unit 13, the short-circuit determination unit 13 can accurately determine whether a short circuit has occurred.

[0039] Generally, a gate driver IC with a built-in DESAT function is used in the power conversion device 2 as the drive circuit 12 and the short-circuit determination unit 13. In such gate driver ICs, the determination threshold voltage Vscth can often be set in the range of 6 to 14 V. On the other hand, the withstand voltage of the electronic components mounted in the drive control unit 10 is often 25 to 50 V, and taking into consideration the prevention of breakdowns of these electronic components due to the withstand voltage being exceeded, the Zener voltage Vz of the Zener diode 152 is set in the range of 14 to 25 V.

[0040] <Modification> A modified example of the configuration shown in the first embodiment will be described below with reference to Fig. 5. The modified example shown in Fig. 5 differs from the configuration shown in Fig. 2 in the configuration of the drive control unit 10.

[0041] In order to reduce the time required to detect a short circuit in a semiconductor switching element, the charging circuit unit 14 may be configured to supply a current corresponding to the gate-source voltage of the semiconductor switching element 4a to the capacitance element 142 to charge the capacitance element 142. In a modified example, the current source 143 is a resistance element 145 that is connected between the gate terminal 43 and the positive terminal of the capacitance element 142, and supplies a current corresponding to the voltage of the gate terminal 43 to the capacitance element 142 to charge the capacitance element 142.

[0042] With this configuration, the capacitance element 142 can be charged by the resistance element 145 connected to the gate terminal 43 of the semiconductor switching element 4a. Because the capacitance element 142 is charged by the resistance element 145 connected to the gate terminal 43, the voltage across the capacitance element 142 rises in conjunction with the gate-source voltage of the semiconductor switching element 4a, so that a short-circuit state of the semiconductor switching element 4a can be detected quickly without providing a mask period during which short-circuit detection is not performed. On the other hand, since there is no need to provide a mask period, the problem to be solved by the present disclosure is more likely to occur, and the effects obtained from the first embodiment can be more prominently demonstrated.

[0043] As described above, the power conversion device 2 according to the first embodiment includes a plurality of semiconductor switching elements each having a first main terminal 41, a second main terminal 42, and a gate terminal 43, a drive circuit 12 that inputs a signal to turn on / off the semiconductor switching elements to the gate terminal, a first diode 141 connected to the first main terminal 41, a capacitance element 142 having a positive terminal connected to the first diode 141 and a negative terminal connected to the second main terminal 42, and a current source 143 that charges the capacitance element 142, the current source 143 charging the capacitance element 142, a short-circuit determination unit 13 that determines whether the semiconductor switching elements are short-circuited, and a current bypass circuit unit 15 that prevents a current that has reverse-conducted the first diode 141 from flowing to the capacitance element 142, and the short-circuit determination unit 13 determines whether the voltage across the capacitance element 142 is higher than a predetermined determination threshold voltage. When the short-circuit determination unit 13 determines that the semiconductor switching element is short-circuited, the drive circuit 12 inputs a signal to the gate terminal 43 to turn off the semiconductor switching element, so that the drive circuit 12 outputs a signal to turn on the semiconductor switching element. Even if the voltage between the first main terminal 41 and the second main terminal 42 of the semiconductor switching element fluctuates sharply during the period from when the signal is input to the gate terminal 43 of the semiconductor switching element until a main current starts to flow through the semiconductor switching element, the displacement current Idi corresponding to this voltage fluctuation flows through the current bypass circuit unit 15 and is prevented from flowing into the capacitive element 142. Therefore, erroneous detection of a short-circuit state of the semiconductor switching element can be suppressed without impairing the operation of the short-circuit determination unit 13, which quickly detects a short-circuit state of the semiconductor switching element.

[0044] The current bypass circuit unit 15 has a Zener diode 152 whose cathode is connected to the anode of the first diode 141 and whose anode is connected to the second main terminal 42. When the Zener voltage Vz of the Zener diode 152 is higher than the judgment threshold voltage Vscth, a path can be formed that bypasses the displacement current Idi and flows from the cathode to the anode of the Zener diode 152. By making the Zener voltage Vz of the Zener diode 152 higher than the judgment threshold voltage Vscth of the short-circuit judgment unit 13, the short-circuit judgment unit 13 can accurately judge whether a short circuit has occurred.

[0045] When the current source 143 is a resistive element 145 that is connected between the gate terminal 43 and the positive terminal of the capacitive element 142, supplies a current to the capacitive element 142 according to the voltage of the gate terminal 43, and charges the capacitive element 142, the capacitive element 142 is charged by the resistive element 145 connected to the gate terminal 43, and the voltage across the capacitive element 142 rises in conjunction with the gate-source voltage of the semiconductor switching element 4a. This makes it possible to quickly detect a short-circuit state of the semiconductor switching element 4a without providing a mask period during which short-circuit detection is not performed.

[0046] Embodiment 2 A power converter 2 according to a second embodiment will now be described. FIG. 8 is a schematic diagram illustrating the essential components of the power converter 2 according to the second embodiment, showing details of the drive control unit 10. FIG. 9 is a diagram illustrating voltage and current waveforms during operation of the power converter 2. FIG. 10 is a schematic diagram illustrating the essential components of the power converter 2 according to a modified example, showing the same components as those in FIG. 8. FIG. 11 is a schematic circuit diagram illustrating the operation of the drive circuit 12 of the power converter 2 to turn on the semiconductor switching element 4a. FIG. 12 is a diagram illustrating a comparison of voltage and current waveforms during normal switching of the semiconductor switching element 4a of the power converter 2 and when a short circuit occurs. FIG. 13 is a current-voltage characteristic diagram illustrating the relationship between the gate-source voltage and the drain current of the semiconductor switching element 4a of the power converter 2. The power converter 2 according to the second embodiment includes a voltage clamping unit 16a, and is configured to prevent the displacement current Idi via the parasitic capacitance Cj of the first diode 141 from charging the capacitance element 142.

[0047] <Voltage fixing unit 16a> The voltage clamping unit 16a is connected to the capacitance element 142 and clamps the voltage across the capacitance element 142 to a voltage less than a predetermined determination threshold voltage while a signal to turn off the semiconductor switching element 4a is being input to the gate terminal 43 and for a predetermined period after a signal to turn on the semiconductor switching element 4a is input to the gate terminal 43. After the period has elapsed, the short-circuit determination unit 13 determines that the semiconductor switching element 4a is short-circuited when the voltage across the capacitance element 142 is higher than the predetermined determination threshold voltage. If the short-circuit determination unit 13 determines that the semiconductor switching element 4a is short-circuited, the drive circuit 12 inputs a signal to turn off the semiconductor switching element 4a to the gate terminal 43. The predetermined period is, for example, a mask period.

[0048] With this configuration, a path (a current bypass path indicated by a dotted arrow in FIG. 8) along which the displacement current Idi detours can be formed in the voltage fixing unit 16a. Therefore, as shown in FIG. 9, even if the drain-source voltage of the semiconductor switching element 4a fluctuates, the displacement current Idi does not rapidly charge the capacitance element 142, and the voltage across the capacitance element 142 is fixed to a voltage sufficiently lower than the determination threshold voltage Vscth. This makes it possible to prevent the short-circuit determining unit 13 from erroneously detecting a short-circuit state of the semiconductor switching element 4a. Similar effects can be obtained by configuring the other semiconductor switching elements 4b to 4f in the same way.

[0049] 8 shows a configuration in which the capacitance element 142 is charged by the current source 143, but the configuration for charging the capacitance element 142 is not limited to this. As in the modified example shown in FIG. 10, the current source 143 may be a resistance element 145 that is connected between the gate terminal 43 and the positive terminal of the capacitance element 142, supplies a current corresponding to the voltage of the gate terminal 43 to the capacitance element 142, and charges the capacitance element 142. With this configuration, the capacitance element 142 can be charged by the resistance element 145 connected to the gate terminal 43 of the semiconductor switching element 4a.

[0050] <Details of voltage clamp unit 16a> The configuration of voltage clamping unit 16a, which is a main part of embodiment 2, will be described in detail with reference to Fig. 8. Voltage clamping unit 16a has a switch element 161 connected in parallel to capacitive element 142. Voltage clamping unit 16a keeps switch element 161 on while a signal to turn off semiconductor switching element 4a is being input to gate terminal 43 and for a predetermined period after a signal to turn on semiconductor switching element 4a is input to gate terminal 43, and keeps switch element 161 off after the predetermined period has elapsed. When switch element 161 is in the on state, the voltage across capacitive element 142 is fixed to a voltage less than the determination threshold voltage.

[0051] In this embodiment, the voltage clamping unit 16a has a timer 162 that transmits a signal to turn off the switch element 161 after a predetermined time tblank has elapsed since the drive circuit 12 output a signal to turn on the semiconductor switching element 4a and the signal was input to the semiconductor switching element 4a. The part that transmits the signal to turn off the switch element 161 to the switch element 161 is not limited to the timer 162, and may be a circuit part that controls the switch element 161 in accordance with the operation of the drive circuit 12. The timer 162 is configured from one or both of a digital circuit such as an IC and an analog circuit such as a comparator.

[0052] The setting of the time tblank will now be described. As described above, the displacement current Idi is generated when the freewheel diode of the semiconductor switching element 4b on the upper side switches on when the semiconductor switching element 4a on the upper side switches from the off state to the on state. In other words, the displacement current Idi is not generated if the semiconductor switching element 4a is in a conductive state before the freewheel diode of the semiconductor switching element 4b switches on. Therefore, in order to suppress erroneous detection by the short-circuit determination unit 13, it is sufficient to turn on the switch element 161 during a period in which the gate-source voltage of the semiconductor switching element 4a is lower than Vth, which is the voltage at which a drain current starts to flow from the first main terminal 41 to the second main terminal 42 of the semiconductor switching element 4a.

[0053] Incidentally, the gate-source voltage of the semiconductor switching element 4a from when the drive circuit 12 outputs a signal to turn on the semiconductor switching element 4a and when the signal is input to the semiconductor switching element 4a until the gate-source voltage of the semiconductor switching element 4a reaches Vth is the charging voltage of the input capacitance Ciss of the semiconductor switching element 4a in the RC series circuit shown in FIG. 11.

[0054] Let Vth be the voltage at gate terminal 43 when the main current starts to flow from the first main terminal 41 to the second main terminal 42, Ciss be the input capacitance of semiconductor switching element 4a, VH be the voltage of the signal that drive circuit 12 uses to turn semiconductor switching element 4a on, VL be the voltage of the signal that drive circuit 12 uses to turn semiconductor switching element 4a off, and Rg be the resistance value of the resistor that is connected to gate terminal 43 of semiconductor switching element 4a and limits the input of current of the signal that turns gate terminal 43 on. Then, the time t1 from when the signal that turns semiconductor switching element 4a on is input to gate terminal 43 until the voltage between gate terminal 43 and second main terminal 42 reaches Vth is expressed by Equation 1.

number

[0055] After a signal for turning on the semiconductor switching element 4a is input to the gate terminal 43, the voltage clamping unit 16a

number

[0056] The value of Vth may be a predetermined voltage value, or a Vth diagnostic function for determining the Vth of the semiconductor switching element 4a may be provided in the drive control unit 10, and the voltage value determined by the Vth diagnostic function may be used. By using the voltage value determined by the Vth diagnostic function, the problem to be solved by the present disclosure can be reliably prevented even if there is individual variation in the Vth of the semiconductor switching element 4a.

[0057] On the other hand, if a short circuit actually occurs, the short-circuit determination unit 13 cannot determine the short-circuit state of the semiconductor switching element 4a during the mask period, so if the time tblank is too long, it will take a long time to start short-circuit detection. Generally, the mask period is set longer than the period from when the semiconductor switching element 4a turns on until it reaches a steady low-voltage state, making it impossible to quickly detect the short-circuit state of the semiconductor switching element 4a. In contrast, the power conversion device 2 of this embodiment provides the time tblank to solve the problem to be solved by the present disclosure. However, since the time tblank can be set to a shorter period than the mask period, short-circuit detection can be performed without impairing the operation of quickly detecting the short-circuit state of the semiconductor switching element 4a.

[0058] Next, the maximum time tblank that can be set to quickly detect a short-circuit state of the semiconductor switching element 4a will be explained using Figure 12. Figure 12 illustrates, from top to bottom, the waveforms of the semiconductor switching element 4a during normal switching and when a short circuit occurs: the gate-source voltage, the drain current, and the drain-source voltage. In the figure, the waveform during a short circuit is shown by a solid line, and the waveform during normal switching is shown by a dashed line.

[0059] The voltage at the gate terminal 43 during normal switching during the period in which the voltage between the first main terminal 41 and the second main terminal 42 transitions from the voltage when the semiconductor switching element 4a is in the OFF state to the voltage when the semiconductor switching element 4a is in the ON state is defined as Vmiller. During normal switching, as shown by the dashed line in Fig. 12, at the timing when the gate-source voltage reaches Vmiller, which is a predetermined voltage, the drain current becomes equal to the output current IL of the power conversion device 2, and the drain-source voltage transitions from the OFF state to the ON state.

[0060] On the other hand, when a short circuit occurs, as shown by the solid line in Figure 12, the drain current continues to increase even after the gate-source voltage reaches Vmiller, and the drain-source voltage remains in a high voltage state, which is the off state. Furthermore, during the period until the gate-source voltage reaches Vmiller during normal switching, the voltage and current waveforms are the same during normal switching and during a short circuit. In other words, when the gate-source voltage becomes higher than Vmiller, the voltage and current waveforms differ depending on whether the semiconductor switching element 4a is in a short-circuit state. Therefore, if tblank is set to a time longer than the time it takes for the gate-source voltage to reach Vmiller, the operation of quickly detecting a short-circuit state of the semiconductor switching element 4a will be impaired.

[0061] Therefore, it is desirable to set the time tblank of the power conversion device 2 as follows: The time t2 from when a signal to turn on the semiconductor switching element 4a is input to the gate terminal 43 until the voltage between the gate terminal 43 and the second main terminal 42 reaches Vmiller is expressed by Equation 3.

number

number

[0062] Equation 5 is derived from equations 2 and 4.

number

[0063] <Vmillerについて> In this embodiment, Vmiller is a voltage value at an output current value that is half the peak-to-peak value of the ripple current generated in the output current of the power conversion device 2. The value of Vmiller when setting the time tblank will be described below with reference to FIG.

[0064] It is known that the gate-source voltage of semiconductor switching element 4a during the period in which the drain-source voltage of semiconductor switching element 4a transitions from the voltage when the element is in the OFF state to the voltage when the element is in the ON state varies depending on the drain current flowing through semiconductor switching element 4a, as shown in Fig. 12. That is, Vmiller, which is the gate-source voltage during normal switching, can be determined using the current-voltage characteristics of semiconductor switching element 4a by determining the value of the drain current, which is the output current of power conversion device 2, as shown in Fig. 13.

[0065] As described in the first embodiment, the principle behind the short-circuit determination unit 13 erroneously detecting a short-circuit state of the semiconductor switching element 4a is that if the output current reverses from negative to positive before the upper-stage semiconductor switching element 4a switches from an OFF state to an ON state, the freewheeling diode of the semiconductor switching element 4b turns on, causing the drain-source voltage of the semiconductor switching element 4a to rise sharply, and a displacement current Idi flows to the charging circuit unit 14 via the parasitic capacitance Cj of the first diode 141. The reason for the output current reversing from negative to positive before the upper-stage semiconductor switching element 4a switches from an OFF state to an ON state is thought to be a momentary fluctuation in the output current due to the influence of, for example, a ripple current of the AC rotating electric machine 5. In other words, the time tblank may be set so that the switch element 161 is turned on during the period from the OFF state to the ON state of the drain-source voltage of the semiconductor switching element 4a when the output current of the power conversion device 2 is lower than the ripple current of the AC rotating electric machine 5, which may cause the problem to be solved by the present disclosure.

[0066] In light of the above, by setting Vmiller to the voltage value of the gate-source voltage of the semiconductor switching element 4a according to the current-voltage characteristics of Fig. 13 when the output current of the power conversion device 2 is an output current value half the peak-to-peak value of the ripple current of the AC rotating electric machine 5, it is possible to prevent the time tblank for turning on the switch element 161 from becoming unnecessarily long. Therefore, according to the power conversion device 2 configured as described above, it is possible to obtain a power conversion device 2 that can detect a short-circuit state of the semiconductor switching element 4a at an even faster speed and that can solve the problem to be solved by the present disclosure.

[0067] The ripple current of the AC rotating electric machine 5 is generally determined by the mutual influence of the inductance value L of the AC rotating electric machine 5, the phase voltage which is the voltage applied to the inductance of one phase of the AC rotating electric machine 5, and the power factor and modulation factor of the AC power which is the output of the power conversion device 2.

[0068] As described above, in the power conversion device 2 according to the second embodiment, the voltage fixing unit 16a is connected to the capacitance element 142, and fixes the voltage across the capacitance element 142 to a voltage lower than a predetermined determination threshold voltage while a signal for turning off the semiconductor switching element 4a is being input to the gate terminal 43 and for a predetermined period after a signal for turning on the semiconductor switching element 4a is input to the gate terminal 43. After the period has elapsed, the short-circuit determining unit 13 determines that the semiconductor switching element 4a is short-circuited when the voltage across the capacitance element 142 is higher than the predetermined determination threshold voltage, and If the short-circuit determination unit 13 determines that the switching element 4a is short-circuited, the drive circuit 12 inputs a signal to the gate terminal 43 to turn off the semiconductor switching element 4a, and a path for the displacement current Idi to bypass is formed in the voltage fixing unit 16a. Therefore, even if the drain-source voltage of the semiconductor switching element 4a fluctuates, the displacement current Idi does not rapidly charge the capacitance element 142, and the voltage across the capacitance element 142 is fixed to a voltage that is sufficiently lower than the determination threshold voltage Vscth, thereby preventing the short-circuit determination unit 13 from erroneously detecting a short-circuit state of the semiconductor switching element 4a.

[0069] The voltage fixing unit 16a has a switching element 161 connected in parallel to the capacitive element 142. The voltage fixing unit 16a turns on the switching element 161 while a signal for turning off the semiconductor switching element 4a is input to the gate terminal 43 and for a predetermined period after a signal for turning on the semiconductor switching element 4a is input to the gate terminal 43. After the elapse of the predetermined period, the switching element 161 is turned off. When the switching element 161 is in the on state, the voltage across the capacitive element 142 is fixed to a voltage less than the determination threshold voltage. When the time until the voltage between the gate terminal 43 and the second main terminal 42 reaches Vth is t1, after a time tblank satisfying t1 < tblank elapses from when a signal for turning on the semiconductor switching element 4a is input to the gate terminal 43, the voltage fixing unit 16a turns off the on-state switching element 161 and starts charging the capacitive element 142. When the time tblank is the above-mentioned predetermined period, since the switching element 161 is turned on during a period when the gate-source voltage of the semiconductor switching element 4a is lower than Vth, which is the voltage when the drain current starts to flow from the drain terminal, which is the first main terminal 41 of the semiconductor switching element 4a, to the source terminal, which is the second main terminal 42, false detection by the short-circuit determination unit 13 can be suppressed.

[0070] When the voltage between the first main terminal 41 and the second main terminal 42 transitions from the voltage when the semiconductor switching element 4a is in the off state to the voltage when the semiconductor switching element 4a is in the on state, the voltage of the gate terminal 43 during normal switching is defined as Vmiller. When the time until the voltage between the gate terminal 43 and the second main terminal 42 reaches Vmiller after a signal for turning on the semiconductor switching element 4a is input to the gate terminal 43 is t2, after a time tblank satisfying tblank < t2 elapses from when a signal for turning on the semiconductor switching element 4a is input to the gate terminal 43, the voltage fixing unit 16a turns off the on-state switching element 161 and starts charging the capacitive element 142. When the time tblank is the above-mentioned predetermined period, the short-circuit state of the semiconductor switching element 4a can be detected at high speed.

[0071] When Vmiller is the voltage value at an output current value that is half the peak-to-peak value of the ripple current generated in the output current of the power conversion device 2, it is possible to prevent the time tblank for turning on the switch element 161 from becoming unnecessarily long, and a power conversion device 2 configured in this way can detect the short-circuit state of the semiconductor switching element 4a even more quickly.

[0072] Embodiment 3 A power conversion device 2 according to a third embodiment will now be described. Fig. 14 is a configuration diagram showing an outline of the main parts of the power conversion device 2 according to the third embodiment, and is a diagram showing details of the drive control unit 10, Fig. 15 is a diagram explaining voltage and current waveforms during operation of the power conversion device 2, and Fig. 16 is a configuration diagram showing an outline of the main parts of the power conversion device 2 according to a modified example, and is a diagram showing parts equivalent to Fig. 14. The power conversion device 2 according to the third embodiment includes a voltage clamping unit 16b different from the voltage clamping unit 16a of the second embodiment, and is configured to prevent the displacement current Idi passing through the parasitic capacitance Cj of the first diode 141 from charging the capacitive element 142.

[0073] <Voltage fixing unit 16b> The configuration of voltage clamping unit 16b, which is a main part of embodiment 3, will be described in detail with reference to Fig. 14. Voltage clamping unit 16b has a switch element 161 connected in parallel to capacitive element 142. Voltage clamping unit 16b keeps switch element 161 on while a signal to turn semiconductor switching element 4a off is input to gate terminal 43 and for a predetermined period after a signal to turn semiconductor switching element 4a on is input to gate terminal 43, and keeps switch element 161 off after the predetermined period has elapsed. When switch element 161 is in the on state, the voltage across capacitive element 142 is fixed to a voltage less than the determination threshold voltage.

[0074] The voltage of the gate terminal 43 when the main current starts to flow from the first main terminal 41 to the second main terminal 42 is defined as Vth, and a predetermined voltage of the gate terminal 43 is defined as a reference voltage Vref. The voltage fixing unit 16b determines whether the voltage of the gate terminal 43 becomes equal to or lower than the reference voltage Vref after a signal for turning on the semiconductor switching element 4a is input to the gate terminal 43.

number

[0075] In the present embodiment, voltage clamping unit 16b has a voltage determination unit 163 instead of timer 162 included in voltage clamping unit 16a of embodiment 2. After drive circuit 12 outputs a signal to turn on semiconductor switching element 4a and the signal is input to gate terminal 43 of semiconductor switching element 4a, voltage determination unit 163 transmits a signal to turn off switch element 161 to switch element 161 after the voltage of gate terminal 43 reaches determination voltage Vref that satisfies equation 6. Voltage determination unit 163 is configured from one or both of a digital circuit such as an IC and an analog circuit such as a comparator.

[0076] The following describes how the voltage evaluation unit 163 sets the reference voltage Vref when turning off the switch element 161. Based on the contents of the second embodiment, the switch element 161 can be turned on while the gate-source voltage of the semiconductor switching element 4a is lower than Vth, which is the voltage at which a drain current starts to flow from the drain terminal (first main terminal 41) of the semiconductor switching element 4a to the source terminal (second main terminal 42) of the semiconductor switching element 4a. That is, as shown in FIG. 15 , by setting the reference voltage Vref so that the magnitude relationship between the reference voltage Vref and Vth satisfies Equation 6, a power conversion device that can solve the problem to be solved by the present disclosure can be obtained. The same effect can be achieved by configuring the other semiconductor switching elements 4b to 4f in the same way.

[0077] The Vth value may be a predetermined voltage value. Alternatively, the drive control unit 10 may have a Vth diagnostic function for determining the Vth of the semiconductor switching element 4a, and the voltage value determined by the Vth diagnostic function may be used as the Vth value. By using the voltage value determined by the Vth diagnostic function as the Vth value, the problem to be solved by the present disclosure can be reliably solved even if there is individual variation in the Vth of the semiconductor switching element 4a.

[0078] In recent years, gate driver ICs with built-in slew rate switching functions have been increasingly used as the drive circuit 12. Gate driver ICs with built-in slew rate switching functions can switch the speed at which semiconductor switching elements turn on. In a power conversion device 2 employing such a slew rate switching function, during slow switching, it takes a long time for the gate-source voltage of the semiconductor switching element 4a to reach Vth. Therefore, in light of the content described in the first embodiment, the problem to be solved by the present disclosure is likely to occur. On the other hand, if a short circuit occurs during fast switching, the short-circuit current starts to flow earlier than during slow switching, making it necessary to detect the short-circuit state of the semiconductor switching element 4a more quickly.

[0079] However, as described in the second embodiment, when the switch element 161 is switched on and off according to time, the time tblank must be set taking into consideration the time it takes for the gate-source voltage of the semiconductor switching element 4a to reach Vth during slow switching, and therefore, if a short circuit occurs during fast switching, the short-circuit determination unit 13 cannot determine whether the semiconductor switching element 4a is in a short-circuit state until the time tblank has elapsed. Therefore, the short-circuit state of the semiconductor switching element 4a cannot be detected quickly.

[0080] According to the power conversion device 2 of the third embodiment, the gate-source voltage of the semiconductor switching element 4a is directly determined to switch the switch element 161 on and off, so there is no need to set a mask period according to slow switching, and therefore no delay occurs in short-circuit detection during fast switching. Therefore, according to the power conversion device 2 of the third embodiment, even when a slew rate switching function is applied to the drive circuit 12, it is possible to obtain a power conversion device 2 that can quickly detect the short-circuit state of the semiconductor switching element 4a and can solve the problem to be solved by the present disclosure.

[0081] Next, the maximum settable determination voltage Vref for quickly detecting a short-circuit state of the semiconductor switching element 4a will be described with reference to Fig. 15. If the determination voltage Vref is set unnecessarily high, the timing at which the switch element 161 is switched off will be delayed, making it impossible to quickly detect a short-circuit state of the semiconductor switching element 4a.

[0082] When the voltage at the gate terminal 43 during normal switching is Vmiller during a period in which the voltage between the first main terminal 41 and the second main terminal 42 transitions from the voltage when the semiconductor switching element 4a is in the OFF state to the voltage when the semiconductor switching element 4a is in the ON state, the voltage clamping unit 16b determines whether the voltage at the gate terminal 43 is

number

[0083] As described in the second embodiment, Vmiller is preferably a voltage value at an output current value that is half the peak-to-peak value of the ripple current generated in the output current of the power conversion device 2. This configuration can prevent the period during which the switch element 161 is turned on from becoming unnecessarily long. Therefore, according to the power conversion device 2 configured as described above, it is possible to obtain a power conversion device 2 that can detect a short-circuit state of the semiconductor switching element 4a at an even faster speed and can solve the problem that the present disclosure is intended to solve.

[0084] Equation 6 and Equation 7 lead to Equation 8.

number

[0085] 14 shows a configuration in which the capacitance element 142 is charged by the current source 143, but the configuration for charging the capacitance element 142 is not limited to this. As in the modified example shown in FIG. 16, the current source 143 may be a resistance element 145 that is connected between the gate terminal 43 and the positive terminal of the capacitance element 142 and supplies a current corresponding to the voltage of the gate terminal 43 to the capacitance element 142, thereby charging the capacitance element 142. With this configuration, the capacitance element 142 can be charged by the resistance element 145 connected to the gate terminal 43 of the semiconductor switching element 4a.

[0086] In each embodiment, the semiconductor switching elements 4a to 4f constituting the power conversion device 2 are power control semiconductor switching elements such as MOSFETs or IGBTs (Insulated Gate Bipolar Transistors), or free wheel diodes, etc. However, the semiconductor switching elements 4a to 4f are not limited to these and may be other semiconductor switching elements such as bipolar transistors.

[0087] In addition, in each embodiment, the semiconductor switching elements 4a to 4f have been described using diagrams of MOSFETs in which the parasitic diodes of the MOSFETs are used as freewheeling diodes, but the configuration of the semiconductor switching elements 4a to 4f is not limited to this. When semiconductor switching elements without parasitic diodes, such as IGBTs, are used as the semiconductor switching elements 4a to 4f, a freewheeling diode may be provided in parallel with the IGBT.

[0088] The semiconductor switching elements 4a to 4f are formed on a semiconductor substrate made of a material such as silicon (Si), silicon carbide (SiC), or gallium nitride (GaN). A wide bandgap semiconductor having a bandgap wider than that of silicon can be used for the semiconductor switching elements 4a to 4f.

[0089] The power conversion device 2 according to each embodiment can be used particularly for on-vehicle, railway, and industrial equipment as a power conversion device such as an inverter or a converter in the field of power electronics. The power conversion device 2 is, for example, an inverter circuit that controls an AC rotating electric machine 5 using a high-voltage battery of 400 to 800 [V] as a DC power supply 1. For an inverter corresponding to such a high voltage, a MOSFET formed of silicon carbide, which is a wide-bandgap semiconductor, is used. Since a wide-bandgap semiconductor is generally suitable for high-speed switching and has a characteristic that the drain-source voltage easily changes steeply, the problems to be solved by the present disclosure are more likely to occur显著. Therefore, when a wide-bandgap semiconductor is used for the semiconductor switching elements 4a to 4f of the power conversion device 2 according to each embodiment, the operational effects obtained from each embodiment can be more显著 shown.

[0090] As described above, in the power conversion device 2 according to Embodiment 3, the voltage fixing unit 16b has a switching element 161 connected in parallel with the capacitive element 142. The voltage fixing unit 16b turns on the switching element 161 while a signal for turning off the semiconductor switching element 4a is input to the gate terminal 43 and for a predetermined period after a signal for turning on the semiconductor switching element 4a is input to the gate terminal 43, and turns off the switching element 161 after the elapse of the predetermined period. When the switching element 161 is in the on state, the voltage across the capacitive element 142 is fixed to a voltage less than the determination threshold voltage. Let the voltage of the gate terminal 43 when the main current starts to flow from the first main terminal 41 to the second main terminal 42 be Vth, and the predetermined voltage of the gate terminal 43 be the determination voltage Vref. After a signal for turning on the semiconductor switching element 4a is input to the gate terminal 43 and the voltage of the gate terminal 43 reaches the determination voltage Vref that satisfies Vth < Vref, the voltage fixing unit 16b turns off the on-state switching element 161 and starts charging the capacitive element 142. Since the time until the voltage of the gate terminal 43 reaches the determination voltage Vref is the above-mentioned predetermined period, a power conversion device 2 that suppresses misdetection of the short-circuit state of the semiconductor switching element 4a can be obtained.

[0091] When the voltage between the first main terminal 41 and the second main terminal 42 transitions from the voltage when the semiconductor switching element 4a is in the off state to the voltage when the semiconductor switching element 4a is in the on state, and when the voltage of the gate terminal 43 during normal switching is Vmiller, after the voltage of the gate terminal 43 reaches the determination voltage Vref that satisfies Vref < Vmiller, the voltage fixing unit 16b turns off the on-state switch element 161 and starts charging the capacitor element 142. If the time until the voltage of the gate terminal 43 reaches the determination voltage Vref is the above-mentioned predetermined period, the short-circuit state of the semiconductor switching element 4a can be detected at high speed.

[0092] When the semiconductor switching element is a wide-gap semiconductor, the wide-bandgap semiconductor is generally suitable for high-speed switching and has the characteristic that the drain-source voltage changes steeply. Therefore, a power conversion device 2 that suppresses false detection of the short-circuit state of the semiconductor switching element can be obtained.

[0093] Although various exemplary embodiments and examples are described in the present disclosure, the various features, aspects, and functions described in one or more embodiments are not limited to the application of a specific embodiment, but are applicable to the embodiments alone or in various combinations. Therefore, countless variations not illustrated are envisioned within the scope of the technology disclosed in this specification. For example, it includes cases where at least one component is modified, added, or omitted, and further, cases where at least one component is extracted and combined with components of other embodiments.

[0094] Hereinafter, aspects of the present disclosure will be summarized and described as appendices.

[0095] (Appendix 1) a plurality of semiconductor switching elements each having a first main terminal, a second main terminal, and a gate terminal, and each switching on and off a main current flowing between the first main terminal and the second main terminal in response to a voltage of the gate terminal relative to the second main terminal; a drive circuit that inputs a signal to turn on or off the semiconductor switching element to the gate terminal; a charging circuit section including a first diode having a cathode connected to the first main terminal, a capacitance element having a positive terminal connected to an anode of the first diode and a negative terminal connected to the second main terminal, and a current source that charges the capacitance element, wherein the drive circuit outputs a signal to the gate terminal that turns on the semiconductor switching element, and the current source charges the capacitance element when the signal is input to the gate terminal; a short-circuit determination unit connected to the capacitance element and determining whether the semiconductor switching element is short-circuited; a current bypass circuit unit connected in parallel to the capacitance element to prevent a current that has reverse-conducted the first diode from flowing into the capacitance element, the short-circuit determination unit determines that the semiconductor switching element is short-circuited when the voltage across the capacitance element is higher than a predetermined determination threshold voltage; When the short circuit determination unit determines that the semiconductor switching element is short-circuited, the drive circuit inputs a signal to the gate terminal to turn off the semiconductor switching element. (Appendix 2) the current bypass circuit unit includes a Zener diode having a cathode connected to the anode of the first diode and an anode connected to the second main terminal, 2. The power conversion device according to claim 1, wherein the Zener voltage of the Zener diode is higher than the determination threshold voltage. (Appendix 3) a plurality of semiconductor switching elements each having a first main terminal, a second main terminal, and a gate terminal, and each switching on and off a main current flowing between the first main terminal and the second main terminal in response to a voltage of the gate terminal relative to the second main terminal; a drive circuit that inputs a signal to turn on or off the semiconductor switching element to the gate terminal; a charging circuit section including a first diode having a cathode connected to the first main terminal, a capacitance element having a positive terminal connected to an anode of the first diode and a negative terminal connected to the second main terminal, and a current source that charges the capacitance element, wherein the drive circuit outputs a signal to the gate terminal that turns on the semiconductor switching element, and the current source charges the capacitance element when the signal is input to the gate terminal; a short-circuit determination unit connected to the capacitance element and determining whether the semiconductor switching element is short-circuited; a voltage fixing unit connected to the capacitance element, fixing a voltage across the capacitance element to a voltage less than a predetermined determination threshold voltage while a signal for turning off the semiconductor switching element is being input to the gate terminal and for a predetermined period after a signal for turning on the semiconductor switching element is input to the gate terminal; the short-circuit determination unit determines that the semiconductor switching element is short-circuited when the voltage across the capacitance element is higher than the predetermined determination threshold voltage after the period has elapsed, When the short circuit determination unit determines that the semiconductor switching element is short-circuited, the drive circuit inputs a signal to the gate terminal to turn off the semiconductor switching element. (Appendix 4) the voltage fixing unit has a switch element connected in parallel to the capacitance element, and keeps the switch element on while a signal for turning off the semiconductor switching element is input to the gate terminal and for a predetermined period after a signal for turning on the semiconductor switching element is input to the gate terminal, and keeps the switch element off after the predetermined period has elapsed, and when the switch element is in an on state, a voltage across the capacitance element is fixed to a voltage less than the determination threshold voltage; When the voltage of the gate terminal when the main current starts to flow from the first main terminal to the second main terminal is defined as Vth, the input capacitance of the semiconductor switching element is defined as Ciss, the voltage of the signal that the drive circuit uses to turn on the semiconductor switching element is defined as VH, the voltage of the signal that the drive circuit uses to turn off the semiconductor switching element is defined as VL, and the resistance value of a resistor that is connected to the gate terminal of the semiconductor switching element and limits the input of the current of the signal that turns on the gate terminal is defined as Rg, the time t1 from when the signal that turns on the semiconductor switching element is input to the gate terminal until the voltage between the gate terminal and the second main terminal reaches Vth is expressed as follows:

number

number

number

number

number

number

[0096] REFERENCE SIGNS LIST 1 DC power supply, 2, 2a power conversion device, 3 smoothing capacitor, 4a, 4b, 4c, 4d, 4e, 4f semiconductor switching element, 5 AC rotating electric machine, 10, 10a drive control unit, 11 controller, 12 drive circuit, 13 short circuit determination unit, 14, 14a charging circuit unit, 15 current bypass circuit unit, 16a, 16b voltage fixing unit, 41 first main terminal, 42 second main terminal, 43 gate terminal, 141 first diode, 142 capacitance element, 143 current source, 144 filter resistor, 145 resistance element, 151 diode, 152 Zener diode, 161 switch element, 162 timer, 163 voltage determination unit, 200 rotating electric machine drive system

Claims

1. a plurality of semiconductor switching elements each having a first main terminal, a second main terminal, and a gate terminal, and each switching on and off a main current flowing between the first main terminal and the second main terminal in response to a voltage of the gate terminal relative to the second main terminal; a drive circuit that inputs a signal to turn on or off the semiconductor switching element to the gate terminal; a charging circuit section including a first diode having a cathode connected to the first main terminal, a capacitance element having a positive terminal connected to an anode of the first diode and a negative terminal connected to the second main terminal, and a current source that charges the capacitance element, wherein the drive circuit outputs a signal to the gate terminal that turns on the semiconductor switching element, and the current source charges the capacitance element when the signal is input to the gate terminal; a short-circuit determination unit connected to the capacitance element and determining whether the semiconductor switching element is short-circuited; a current bypass circuit unit connected in parallel to the capacitance element to prevent a current that has reverse-conducted the first diode from flowing into the capacitance element, the short-circuit determination unit determines that the semiconductor switching element is short-circuited when the voltage across the capacitance element is higher than a predetermined determination threshold voltage; When the short circuit determination unit determines that the semiconductor switching element is short-circuited, the drive circuit inputs a signal to the gate terminal to turn off the semiconductor switching element.

2. the current bypass circuit unit includes a Zener diode having a cathode connected to the anode of the first diode and an anode connected to the second main terminal, The power conversion device according to claim 1 , wherein the Zener voltage of the Zener diode is higher than the determination threshold voltage.

3. a plurality of semiconductor switching elements each having a first main terminal, a second main terminal, and a gate terminal, and each switching on and off a main current flowing between the first main terminal and the second main terminal in response to a voltage of the gate terminal relative to the second main terminal; a drive circuit that inputs a signal to turn on or off the semiconductor switching element to the gate terminal; a charging circuit section including a first diode having a cathode connected to the first main terminal, a capacitance element having a positive terminal connected to an anode of the first diode and a negative terminal connected to the second main terminal, and a current source that charges the capacitance element, wherein the drive circuit outputs a signal to the gate terminal that turns on the semiconductor switching element, and the current source charges the capacitance element when the signal is input to the gate terminal; a short-circuit determination unit connected to the capacitance element and determining whether the semiconductor switching element is short-circuited; a voltage fixing unit connected to the capacitance element, fixing a voltage across the capacitance element to a voltage less than a predetermined determination threshold voltage while a signal for turning off the semiconductor switching element is being input to the gate terminal and for a predetermined period after a signal for turning on the semiconductor switching element is input to the gate terminal; the short-circuit determination unit determines that the semiconductor switching element is short-circuited when the voltage across the capacitance element is higher than the predetermined determination threshold voltage after the period has elapsed; When the short circuit determination unit determines that the semiconductor switching element is short-circuited, the drive circuit inputs a signal to the gate terminal to turn off the semiconductor switching element.

4. the voltage fixing unit has a switch element connected in parallel to the capacitance element, and keeps the switch element on while a signal for turning off the semiconductor switching element is input to the gate terminal and for a predetermined period after a signal for turning on the semiconductor switching element is input to the gate terminal, and keeps the switch element off after the predetermined period has elapsed, and when the switch element is in an on state, a voltage across the capacitance element is fixed to a voltage less than the determination threshold voltage; When the voltage of the gate terminal when the main current starts to flow from the first main terminal to the second main terminal is Vth, the input capacitance of the semiconductor switching element is Ciss, the voltage of the signal that the drive circuit uses to turn on the semiconductor switching element is VH, the voltage of the signal that the drive circuit uses to turn off the semiconductor switching element is VL, and the resistance value of a resistor that is connected to the gate terminal of the semiconductor switching element and limits the input of the signal that turns on the gate terminal is Rg, the time t1 from when the signal that turns on the semiconductor switching element is input to the gate terminal until the voltage between the gate terminal and the second main terminal reaches Vth is [Equation 1] After a signal for turning on the semiconductor switching element is input to the gate terminal, the voltage fixing unit [Equation 2] 4. The power conversion device according to claim 3, wherein the switching element in an on state is turned off and charging of the capacitance element is started after a time tblank that satisfies the above condition has elapsed, and the time tblank is the period.

5. When the voltage of the gate terminal during normal switching during a period in which the voltage between the first main terminal and the second main terminal transitions from the voltage when the semiconductor switching element is in the OFF state to the voltage when the semiconductor switching element is in the ON state is Vmiller, the time t2 from when a signal to turn on the semiconductor switching element is input to the gate terminal until the voltage between the gate terminal and the second main terminal reaches Vmiller is expressed as follows: [Equation 3] After a signal for turning on the semiconductor switching element is input to the gate terminal, the voltage fixing unit [Equation 4] 5. The power conversion device according to claim 4, wherein the switching element in an on state is turned off and charging of the capacitance element is started after a time tblank that satisfies the above condition has elapsed, and the time tblank is the period.

6. the voltage fixing unit has a switch element connected in parallel to the capacitance element, and keeps the switch element on while a signal for turning off the semiconductor switching element is input to the gate terminal and for a predetermined period after a signal for turning on the semiconductor switching element is input to the gate terminal, and keeps the switch element off after the predetermined period has elapsed, and when the switch element is in an on state, a voltage across the capacitance element is fixed to a voltage less than the determination threshold voltage; The voltage of the gate terminal when the main current starts to flow from the first main terminal to the second main terminal is defined as Vth, and a predetermined voltage of the gate terminal is defined as a reference voltage Vref. The voltage fixing unit determines whether the voltage of the gate terminal is equal to or lower than Vth after a signal for turning on the semiconductor switching element is input to the gate terminal. [Equation 5] 4. The power conversion device according to claim 3, wherein the period is a time until the voltage of the gate terminal reaches the determination voltage Vref, after which the switch element in an on state is turned off, charging of the capacitance element is started, and the voltage of the gate terminal reaches the determination voltage Vref.

7. When the voltage of the gate terminal during normal switching in a period in which the voltage between the first main terminal and the second main terminal transitions from the voltage when the semiconductor switching element is in an off state to the voltage when the semiconductor switching element is in an on state is Vmiller, the voltage fixing unit determines whether the voltage of the gate terminal is [Equation 6] 7. The power conversion device according to claim 6, wherein the period is a time period during which the voltage of the gate terminal reaches a determination voltage Vref that satisfies the above condition, the switch element in an on state is turned off, charging of the capacitance element is started, and the voltage of the gate terminal reaches the determination voltage Vref.

8. 8. The power conversion device according to claim 5, wherein Vmiller is a voltage value at an output current value that is half the peak-to-peak value of a ripple current generated in the output current of the power conversion device.

9. 4. The power conversion device according to claim 1, wherein the current source is a resistive element connected between the gate terminal and the positive terminal of the capacitance element, and supplies a current corresponding to the voltage of the gate terminal to the capacitance element to charge the capacitance element.

10. 4. The power conversion device according to claim 1, wherein the semiconductor switching elements are wide-gap semiconductors.

Images