Power conversion device

Abstract

In this power conversion device (1), diodes (206a, 206b) are respectively provided in bypass circuits of power modules (103a, 103b) connected in parallel, and the diodes (206a, 206b) are disposed between gates of the power modules so as to face each other, whereby the flowing resonance current can be reduced and erroneous turning-on of the power modules (103a, 103b) due to the resonance of the power modules (103a, 103b) can be suppressed.

Description

Power Conversion Device

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

[0002] Power conversion devices used in electric powertrains are configured by connecting multiple power modules in parallel, each using a switching element such as an insulated gate bipolar transistor (IGBT) or a metal oxide semiconductor field effect transistor (MOSFET), and efforts are being made to achieve higher speed switching. By simultaneously switching these power modules, the power capacity of the power conversion device is increased.

[0003] When one of the power modules constituting the upper and lower arms is turned on, a large potential fluctuation (= dv / dt) occurs between the drain and source of the other power module, which is turned off. This potential fluctuation causes a current (= C * dv / dt) to flow into the gate via the parasitic capacitance C of the power module. This causes the gate potential of the other power module to rise, and if the gate-source voltage exceeds the threshold voltage, the other power module will turn on, shorting the upper and lower arms and potentially destroying the power modules.

[0004] Therefore, as shown in Patent Document 1, a switching element (MOSFET) is provided between the gate and source of a power module, and the switching element is forcibly turned on when the power module is off, thereby creating a low impedance between the gate and source of the power module and preventing unintentional turn-on (hereinafter referred to as "false turn-on"). The switching element between the gate and source switches in accordance with the on / off of the power module. In order to accommodate the high-speed switching and high-frequency of the power module, the switching element between the gate and source is made up of a fast-switching MOSFET.

[0005] Japanese Patent Application Laid-Open No. 2006-296119

[0006] The power conversion circuit described in Patent Document 1 can prevent false turn-on by connecting the gates and sources of power modules with low impedance. However, when power modules are used in parallel, using bidirectional elements such as MOSFETs to achieve low impedance between the gates and sources of each power module also results in low impedance between the gates of the power modules. Differences in characteristics between power modules connected in parallel or variations in inductance in the main circuit or control circuit of the power conversion device can cause timing discrepancies in the switching between the power modules, resulting in potential differences in the drain-source voltage. The potential difference between power modules causes a resonance phenomenon due to the inductance between the power module and its parasitic capacitance and the inductance components of the control line (e.g., the gate line or source line of the transistor that constitutes the power module). When a portion of this resonance current flows between the gates of the power modules, the gate voltage rises. In other words, the lower the impedance between the gates of the power modules, the larger the current that flows in and the greater the increase in gate voltage, leading to false turn-on and potential power module failure.

[0007] The present disclosure discloses a technique for solving the above-described problems, and aims to provide a power conversion device that can suppress false turn-on due to resonance of a power module.

[0008] The power conversion device of the present disclosure includes: a control unit that switches between an on voltage and an off voltage and outputs a switching control signal; first and second power modules connected in parallel and performing switching based on the switching control signal; a first control wiring that connects the control unit and the first power module; a second control wiring that connects the control unit and the second power module; a first bypass circuit having a first diode connected between the first control wiring and an off voltage wiring such that the first control wiring is on the anode side and the off voltage wiring is on the cathode side; a second bypass circuit having a second diode connected between the second control wiring and the off voltage wiring such that the second control wiring is on the anode side and the off voltage wiring is on the cathode side; and switches that turn the first bypass circuit and the second bypass circuit on and off.

[0009] According to the power conversion device of the present disclosure, by providing a diode in each of the first and second bypass circuits connected in parallel and arranging the diodes facing each other between the gates of the power module, it is possible to reduce the resonant current flow and suppress false turn-on due to resonance of the power module.

[0010] 1 is a schematic circuit diagram showing a power conversion device including power modules according to a first embodiment and a comparative example; FIG. 2 is a schematic circuit diagram showing the configuration of a control unit and power modules connected in parallel, indicated by dashed line A in FIG. 1; FIG. 3 is a waveform diagram showing time variations in voltage and current of power modules connected in parallel, indicated by dashed line A; FIG. 4 is a partial circuit diagram showing a power module and control unit of a comparative example, enlarging a part of dashed line A in FIG. 2; FIG. 5 is a partial circuit diagram showing the configuration of a power module and control unit of a power conversion device according to a first embodiment; FIG. 6 is a partial circuit diagram showing the configuration of a power module and control unit of a power conversion device according to a first embodiment;

[0011] Hereinafter, preferred embodiments of a power conversion device according to the present disclosure will be described with reference to the drawings. Note that the same reference numerals are used to designate the same contents and corresponding parts, and detailed description thereof will be omitted.

[0012] Embodiment 1 <Configuration of Comparative Example and Embodiment 1> FIG. 1 is a configuration diagram of a power conversion device for driving a three-phase AC motor according to a comparative example and embodiment 1. In this embodiment, a three-phase inverter circuit is shown as an example of a power conversion circuit. Power conversion device 1 includes a DC power supply 101 and a three-phase AC motor 109. DC power supply 101 is connected to a smoothing capacitor 102 for smoothing a DC voltage. A three-phase inverter circuit is connected downstream of smoothing capacitor 102, and the three-phase inverter circuit includes a U-phase leg formed by a series connection of power modules 103 and 104, a V-phase leg formed by a series connection of power modules 105 and 106, and a W-phase leg formed by a series connection of power modules 107 and 108. The connection points of the upper and lower arms of each leg are connected to three-phase AC motor 109. A control unit 10 controls the on / off of power modules 103 to 108 of each phase arm in a predetermined order to generate three-phase AC current and drive three-phase AC motor 109.

[0013] The switching elements used in the power modules 103 to 108 are configured, for example, by MOSFETs. Note that the switching elements may be self-extinguishing semiconductor switching elements, such as IGBTs with diodes connected in antiparallel. Furthermore, wide bandgap semiconductors, such as SiC (silicon carbide) or GaN (gallium nitride), may be used instead of Si (silicon) as the semiconductor material constituting the switching elements. In this embodiment, a case where MOSFETs are used as the switching elements will be described.

[0014] <Explanation of Circuit Configuration and Operation of Comparative Example> (1) Drain-Source Voltage Potential Difference Due to Timing Deviation of Switching First, the circuit configuration and operation of a comparative example will be described with reference to FIGS. 2 and 3 regarding the drain-source voltage potential difference due to timing deviation of switching between power modules connected in parallel in a power conversion device configured as shown in FIG. 1 . FIG. 2 is an enlarged view of the U-phase leg of the portion A indicated by the dashed line in FIG. 1 . The upper arm power modules 103a and 103b and the lower arm power modules 104a and 104b of the U-phase leg in FIG. 2 are connected in parallel. The control unit 10 controls the switching operation of the power modules 103a, 103b, 104a, and 104b via control lines 20 and 21 based on information from sensors (current, voltage, rotation angle sensors, etc.) not shown. While the U-phase leg will be described here, the V-phase leg and the W-phase leg may also be configured in a similar manner.

[0015] The power modules 103a and 103b have a drain terminal and a source terminal as a terminal pair, and the drain terminals are connected to each other via parasitic inductances L103a and L103b of the wiring. Note that a parasitic inductance of the wiring also exists between the connected source terminals, but this is omitted in FIG. 2 . The power modules 104a and 104b have a drain terminal and a source terminal as a terminal pair, and the source terminals are connected to each other via parasitic inductances L104a and L104b of the wiring. Note that a parasitic inductance of the wiring also exists between the connected drain terminals, but this is omitted in FIG. 2 . Parasitic capacitances exist between the drain and source, between the drain and gate, and between the gate and source of the power modules 103a, 103b, 104a, and 104b, respectively.

[0016] The operation will be described when the power modules 103a and 103b on the upper arm side are off and the power modules 104a and 104b on the lower arm side are turned on. When the power modules 104a and 104b are off, current flows through the internal diodes of the power modules 103a and 103b in the direction of the solid arrows in Figure 2. When the power modules 104a and 104b are turned on, the current gradually switches to the direction of the dotted arrows in Figure 2.

[0017] FIG. 3 is a waveform diagram of the drain-source voltage and drain current of the power modules 103a and 103b. The vertical axis represents the magnitude of the voltage or current, and the horizontal axis represents the time transition. When the power modules 104a and 104b are turned on, if the parasitic inductances of the wiring are L103a ≠ L103b and L104a ≠ L104b, even if the power modules 104a and 104b are switched on at the same time, the difference in the parasitic inductances of the wiring, i.e., the impedance, causes a current imbalance. For example, in FIG. 3, at time t0, the current I103b flowing through the internal diode of the power module 103b is smaller than the current I103a flowing through the internal diode of the power module 103a. Therefore, the current flowing through the internal diode of the power module 103b reaches zero first, causing reverse recovery in the internal diode. Subsequently, the parasitic capacitance between the drain and source of the power module 103b is charged, and the drain-source voltage Vds2 rises.

[0018] On the other hand, because the internal diode of power module 103a is in a conductive state, the drain-source voltage Vds1 is approximately 0 V (forward voltage VF). For example, at time t1 when Vds2 reaches its peak, Vds1 is approximately 0, so a potential difference occurs between power module 103a and power module 103b.

[0019] (2) Resonance phenomenon occurring between power modules in the comparative example The resonance phenomenon between power modules caused by the potential difference occurring between the power modules will be described with reference to Fig. 4. Fig. 4 is a partial circuit diagram of Fig. 2, and shows the power modules 103a and 103b and the gate circuit configuration connected to the control unit 10.

[0020] The power modules 103a and 103b have drain-source parasitic capacitances Cds1 and Cds2, drain-gate parasitic capacitances Cdg1 and Cdg2, and gate-source parasitic capacitances Cgs1 and Cgs2.

[0021] The control unit 10 functions as a gate drive circuit that drives the power modules 103a and 103b on and off. The control unit 10 includes a gate-on switch element 201 such as a transistor and a gate-off switch element 202. The control unit 10 is connected by wiring to a power supply Vcc that provides a gate-on voltage Vcc and a power supply Vee that provides a gate-off voltage Vee, with a reference potential 200 (source potential in the case of a MOSFET) of the semiconductor elements that make up the power modules 103a and 103b as the reference. A gate-on signal is output from an output terminal 301, and a gate-off signal is output from an output terminal 302. A resistive element 203a is connected between the output terminal 301 and a control signal input terminal 103ag of the power module 103a, and a resistive element 204a is connected between the output terminal 302 and the control signal input terminal 103ag. A resistive element 203b is connected between the output terminal 301 and the control signal input terminal 103bg of the power module 103b, and a resistive element 204b is connected between the output terminal 302 and the control signal input terminal 103bg. The gate-on voltage Vcc will be described as a positive bias potential with respect to a reference potential 200, and the gate-off voltage Vee will be described as a negative bias potential with respect to the reference potential 200. Note that the gate-off voltage Vee may be the same potential as the reference potential 200. In Fig. 4, resistive elements 203a and 203b for the gate-on signal and resistive elements 204a and 204b for the gate-off signal are provided separately, but they may be provided as a common resistive element for gate-on and gate-off.

[0022] Furthermore, a switch element 205a is connected between a wiring connected to the control signal input terminal 103ag and the resistance elements 203a and 204a and a wiring to which a gate-off voltage Vee is applied, and a switch element 205b is connected between a wiring connected to the control signal input terminal 103bg and the resistance elements 203b and 204b and a wiring to which a gate-off voltage Vee is applied. The switch elements 205a and 205b switch in accordance with the on / off of the power modules 103a and 103b, and in order to accommodate the high-speed switching and high-frequency of the power modules 103a and 103b, the switch elements 205a and 205b between the gate and source are configured with fast-switching MOSFETs.

[0023] By turning on the switch elements 205a and 205b when the power modules 103a and 103b are off, a low impedance is created between the gates of the power modules 103a and 103b and the wiring for the gate-off voltage Vee (between the gate and gate-off voltage Vee). That is, the control unit 10 detects the gate-source voltages of the power modules 103a and 103b, and when the gate-source voltages fall below a predetermined value, an ON signal is output from the output terminals 303 and 304 to turn on the switch elements 205a and 205b. Note that the gate-source voltage detection circuit is not shown in FIG. 4.

[0024] In this way, when the switch elements 205a and 205b are turned on to set a low impedance between the gates of the power modules 103a and 103b and the gate-off voltage Vee, the gates of the power modules 103a and 103b are also connected at a low impedance via the gate-off voltage Vee.

[0025] Here, the potential difference between the power modules 103a and 103b described in FIG. 3 causes a resonance phenomenon due to the parasitic inductances L103a and L103b between the power modules 103a and 103b and their parasitic capacitances, and the inductance components of the control lines (not shown, for example, the gate or source lines of the transistors that make up the power modules). For example, at time t1 in FIG. 3 , Vds2 > Vds1, and a portion of the current generated by this potential difference flows between the gates of the power modules 103a and 103b, as indicated by the solid arrows in FIG. 4 . More specifically, if the switch elements 205a and 205b are configured using bidirectional elements such as MOSFETs, current flows into the parasitic capacitance Cgs2 of the power module 103b via the parasitic capacitance Cdg1 of the power module 103a and the switch elements 205a and 205b, causing the gate voltage of the power module 103b to rise and resulting in a false turn-on. The lower the gate-to-gate impedance between the power modules 103a and 103b, the larger the current that flows in and the larger the rise in gate voltage.

[0026] <Circuit Configuration and Operation of Power Conversion Device According to First Embodiment> Next, the circuit configuration and operation of the power conversion device according to the first embodiment will be described with reference to Fig. 5. In addition to the configuration of Fig. 4 for the comparative example, Fig. 5 further includes a diode 206a with its anode connected to control signal input terminal 103ag and resistance elements 203a and 204a and its cathode connected to switch element 205a, and a diode 206b with its anode connected to control signal input terminal 103bg and resistance elements 203b and 204b and its cathode connected to switch element 205b. Note that while the upper arm of the U-phase leg will be described here, the lower arm of the U-phase leg, the V-phase leg, and the W-phase leg may also be configured in a similar manner.

[0027] In this way, by providing diodes 206a and 206b facing each other between the gates, for example, at time t1 in Fig. 3, a reverse bias is applied to diode 206b, making it possible to block the current along the path indicated by the solid arrow in Fig. 4. In other words, while maintaining a low impedance between the gate and gate-off voltage Vee of power modules 103a and 103b, a high impedance is created between the gates of power modules 103a and 103b, making it possible to block the current flowing between the gates due to the potential difference between power modules 103a and 103b, suppressing an increase in gate voltage and preventing false turn-on.

[0028] The connection points of diodes 206a and 206b may be the points shown in Fig. 6. Specifically, diode 206a is provided with the side connected to switch element 205a as the anode and the side connected to the wiring for gate-off voltage Vee as the cathode, and diode 206b is provided with the side connected to switch element 205b as the anode and the side connected to the wiring for gate-off voltage Vee as the cathode. Even with the configuration in Fig. 6, by providing diodes 206a and 206b facing each other between gates, high impedance is achieved between the gates, thereby achieving the same effect as in Fig. 5.

[0029] 5 and 6 may be configured as a single switch element 205 as shown in Figures 7 and 8, and the circuit can be made smaller while still achieving the same effect even if the switch elements 205 are included in the control unit 10 as shown in Figure 8. In this case, the switch element 205 and diodes 206a and 206b are connected via terminal 305.

[0030] Furthermore, by using a negative bias potential based on the reference potential 200 as the gate-off voltage Vee, even if the gate voltage rises, a margin can be provided up to the threshold voltage required for turning on, making it less likely that the device will turn on erroneously.

[0031] Similarly, by using Schottky barrier diodes with a small forward voltage (VF) for the diodes 206a and 206b, the voltage drop due to the VF of the gate-off voltage can be reduced, and a margin can be provided up to the threshold voltage required for turning on, making it less likely that the diodes will turn on erroneously.

[0032] The smaller the junction capacitance Cak of diodes 206a and 206b, the higher the impedance when a reverse bias is applied, so a smaller capacitance is desirable. When current flows between the gates, the junction capacitance Cak and the gate-source parasitic capacitance Cgs of the power module (input capacitance, Cgs1 or Cgs2 in Figures 5 to 8) are connected in series. For example, if a diode having a junction capacitance Cak with the same capacitance as the parasitic capacitance Cgs is connected, the combined capacitance of the parasitic capacitance Cgs and the junction capacitance Cak is half of the parasitic capacitance Cgs, and the impedance is doubled, making it more difficult for current to flow, compared to when no diode is connected. In other words, as long as the capacitance of the junction capacitance Cak is smaller than the parasitic capacitance Cgs, which is the input capacitance, sufficient effect can be obtained.

[0033] In addition to the configuration of FIG. 5 , FIG. 9 includes a diode 207a oriented such that the side connected to resistance element 203a is the anode and the side connected to control signal input terminal 103ag is the cathode; a diode 207b oriented such that the side connected to resistance element 203b is the anode and the side connected to control signal input terminal 103bg is the cathode; a diode 208a oriented such that the side connected to control signal input terminal 103ag is the anode and the side connected to resistance element 204a is the cathode; and a diode 208b oriented such that the side connected to control signal input terminal 103bg is the anode and the side connected to resistance element 204b is the cathode.

[0034] Here, as a current path flowing into the parasitic capacitance Cgs2 of the power module 103b, in addition to the path via the switch elements 205a and 205b, there are also paths via the resistor elements 203a and 203b and the resistor elements 204a and 204b, as shown by the dotted lines in Figure 4. By providing diodes 207a, 207b, 208a, and 208b as shown in Figure 9, the current paths via the resistor elements 203a and 203b and the resistor elements 204a and 204b can be blocked, thereby further suppressing the rise in gate voltage. It goes without saying that the same effect as in Figure 9 can be obtained by connecting diodes 207a, 207b, 208a, and 208b in Figures 5 to 8.

[0035] Furthermore, if the resistance values ​​of the resistive elements 203a and 203b on the gate-on side are greater than the resistance values ​​of the resistive elements 204a and 204b on the gate-off side, the diodes 208a and 208b may be provided only on the resistive elements 204a and 204b side where the impedance is lower.

[0036] As described above, in the first embodiment, by providing a diode in each of the first and second bypass circuits connected in parallel and arranging the diodes to face each other between the gates of the power module, it is possible to reduce the resonant current that flows and suppress false turn-on due to resonance of the power module.

[0037] In the above embodiment, the switching elements used in the power module have been described as MOSFETs using Si as the semiconductor material. However, they may also be configured using wide-bandgap semiconductor materials such as SiC or GaN, which are capable of high-frequency operation, have fast switching speeds (dv / dt, di / dt), and reduce losses. The faster the switching speed, the larger the potential difference that occurs between the power modules, making the gate voltage more likely to be turned on erroneously. In other words, by configuring this embodiment using wide-bandgap semiconductors, it is possible to suppress false gate turn-on while further reducing the size and increasing the efficiency of the power conversion device.

[0038] Although exemplary embodiments are described in the present disclosure, the various features, aspects, and functions described in the embodiments are not limited to the application of a particular embodiment, but may be applied to the embodiments alone or in various combinations. Therefore, countless variations not illustrated are anticipated within the scope of the technology disclosed in this specification. For example, variations in, addition to, or omission of at least one component are included.

[0039] Various aspects of the present disclosure are summarized below as appendices.

[0040] (Supplementary Note 1) A power conversion device comprising: a control unit that switches between an on voltage and an off voltage and outputs a switching control signal; first and second power modules connected in parallel and performing switching based on the switching control signal; a first control wiring that connects the control unit and the first power module; a second control wiring that connects the control unit and the second power module; a first bypass circuit having a first diode connected between the first control wiring and the off voltage wiring, with the first control wiring on its anode side and the off voltage wiring on its cathode side; a second bypass circuit having a second diode connected between the second control wiring and the off voltage wiring, with the second control wiring on its anode side and the off voltage wiring on its cathode side; and a switch that turns on and off the first bypass circuit and the second bypass circuit. (Supplementary Note 2) The power conversion device according to Supplementary Note 1, characterized in comprising: a third diode connected between the control unit and the first power module, with the wiring connected to the first power module on its anode side and the wiring connected to the control unit on its cathode side; and a fourth diode connected between the control unit and the second power module, with the wiring connected to the control unit on its anode side and the wiring connected to the second power module on its cathode side. (Supplementary Note 3) The power conversion device according to Supplementary Note 1 or 2, characterized in that the switches are provided in the first bypass circuit and the second bypass circuit, respectively. (Supplementary Note 4) The power conversion device according to any one of Supplements 1 to 3, characterized in that the off-voltage is a negative potential with respect to the reference potentials of the first and second power modules. (Supplementary Note 5) The power conversion device according to any one of Supplements 1 to 4, characterized in that the junction capacitance of the first and second diodes is smaller than the input capacitance of semiconductor switching elements constituting the power modules. (Supplementary Note 6) The power conversion device according to any one of Supplementary Notes 1 to 5, wherein the first and second diodes are Schottky barrier diodes.(Supplementary Note 7) The power conversion device according to any one of Supplementary Notes 1 to 6, wherein the first and second power modules are wide bandgap semiconductor elements.

[0041] 1: power conversion device, 10: control unit, 20, 21: control line, 101: DC power supply, 102: smoothing capacitor, 103, 103a, 103b, 104, 104a, 104b, 105, 106, 107, 108: power module, 109: three-phase AC motor, 200: reference potential, 201, 202: switch element, 203a, 203b, 204a, 204b: resistance element, 205, 205a, 205b: switch element, 301, 302, 303, 304: output terminal, 305: terminal, 206a, 206b, 207a, 207b, 208a, 208b: diodes.

Claims

1. A power conversion device comprising: a control unit that switches between an on voltage and an off voltage and outputs a switching control signal; first and second power modules connected in parallel and performing switching based on the switching control signal; a first control wiring that connects the control unit and the first power module; a second control wiring that connects the control unit and the second power module; a first bypass circuit having a first diode connected between the first control wiring and the off voltage wiring in an orientation where the first control wiring is on the anode side and the off voltage wiring is on the cathode side; a second bypass circuit having a second diode connected between the second control wiring and the off voltage wiring in an orientation where the second control wiring is on the anode side and the off voltage wiring is on the cathode side; and a switch that turns on and off the first bypass circuit and the second bypass circuit.

2. The power conversion device according to claim 1, further comprising: a third diode connected between the control unit and the first power module, with a wiring connected to the first power module being its anode side and a wiring connected to the control unit being its cathode side; and a fourth diode connected between the control unit and the second power module, with a wiring connected to the control unit being its anode side and a wiring connected to the second power module being its cathode side.

3. The power conversion device according to claim 1 or 2, wherein the switch is provided in each of the first bypass circuit and the second bypass circuit.

4. A power conversion device according to any one of claims 1 to 3, wherein the off-voltage is a negative potential with respect to the reference potentials of the first and second power modules.

5. A power conversion device according to any one of claims 1 to 4, characterized in that the junction capacitance of the first and second diodes is smaller than the input capacitance of the semiconductor switching elements constituting the first and second power modules.

6. A power conversion device according to any one of claims 1 to 5, wherein the first and second diodes are Schottky barrier diodes.

7. A power conversion device according to any one of claims 1 to 6, characterized in that the first and second power modules are wide band gap semiconductor elements.

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