Power conversion device and drive system

Abstract

Provided is a power conversion device (2) that receives power supplied from a DC power supply (1) and controls an AC rotary electric machine (5). The power conversion device (2) comprises: a drive circuit (11) that drives a semiconductor switching element (4b); a power supply circuit (13) that receives the power supplied from the DC power supply (1) via a reverse conduction prevention diode (50) and supplies the power to the drive circuit (11); and a control circuit board (10) on which the drive circuit (11) and the power supply circuit (13) are mounted, wherein the control circuit board (10) is provided with a restriction element (60) that suppresses an input current in an electrical path (38b) that avoids or suppresses the flow, toward the drive circuit (11), of an input current that flows from the reverse conduction prevention diode (50) to the power supply circuit (13), or in a closed circuit through which the input current flows.

Description

Power conversion device and drive system

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

[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 that includes a DC power supply, an AC rotating electric machine for propelling the vehicle, a power conversion device that receives power from the DC power supply and controls the AC rotating electric machine, and a low-voltage battery that supplies power to a control circuit board that constitutes the power conversion device.

[0003] Furthermore, the power conversion device has legs in which an upper-stage semiconductor switching element connected to the positive side of the DC power supply and a lower-stage semiconductor switching element connected to the negative side are connected in series, and these semiconductor switching elements are controlled to be turned on and off by a drive circuit on a control circuit board to perform power conversion. Meanwhile, in the power conversion device of an electric vehicle, in the event of a vehicle collision or when it is determined that an abnormality has occurred in the power conversion device, active short circuit control (ASC control) is executed in which one of the upper-stage semiconductor switching elements or the lower-stage semiconductor switching elements is forcibly switched on and the other is forcibly switched off in order to quickly protect the power conversion device and the AC rotating electric machine.

[0004] However, in the event of a vehicle collision, for example, a disconnection may occur in the wiring between the low-voltage battery and the control circuit board. In such a state, the control circuit board loses power and is unable to perform ASC control. Therefore, a configuration has been proposed in which a power supply circuit called a backup power supply is added to continue supplying power to the control circuit board and ensure ASC control even if the power supply from the low-voltage battery to the control circuit board drops for some reason, resulting in a voltage drop (see, for example, Patent Document 1).

[0005] Patent No. 6291899

[0006] According to Patent Document 1, a power supply circuit powered by a DC power supply is mounted on the same control circuit board as a drive circuit for a semiconductor switching element, and they are connected to a common reference potential. However, a new problem has been discovered: when a surge voltage occurs during switching operation of the semiconductor switching element, the surge voltage causes the input current flowing through the power supply circuit to flow to the reference potential of the drive circuit, and the inductance component of the reference potential causes voltage fluctuations in the gate-source or base-emitter voltage of the semiconductor switching element on the lower stage. Such voltage fluctuations are undesirable for a power conversion device because they cause unstable on-off control of the semiconductor switching element.

[0007] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a power conversion device that can stably control the on / off of semiconductor switching elements even when a power supply circuit using a DC power supply as a power source is installed on the same control circuit board as a drive circuit for the semiconductor switching elements.

[0008] The power conversion device according to the present disclosure receives power from a DC power supply to control an AC rotating electric machine, and includes: a smoothing capacitor connected in parallel to the DC power supply; at least one pair of legs each including an upper-stage semiconductor switching element connected to the positive electrode of the DC power supply and a lower-stage semiconductor switching element connected to the negative electrode of the DC power supply, connected in series; a drive circuit that turns on or off the upper-stage semiconductor switching element or the lower-stage semiconductor switching element, respectively; a power supply circuit that receives power from the DC power supply via a reverse conduction prevention diode and supplies power to the drive circuit; and a control circuit board on which the drive circuit, the reverse conduction prevention diode, and the power supply circuit are mounted, wherein the control circuit board is provided with an electrical path that prevents an input current flowing from the reverse conduction prevention diode to the power supply circuit from flowing to the drive circuit, or a limiting element or electrical path that suppresses the input current.

[0009] According to the present disclosure, even when a power supply circuit using a DC power source as a power source is mounted on the same control circuit board as a drive circuit for a semiconductor switching element, by providing an electrical path on the control circuit board that prevents the input current flowing into the power supply circuit from flowing to the drive circuit, or a limiting element or electrical path that suppresses such input current, it is possible to obtain a power conversion device that can stably control the on / off of the semiconductor switching element.

[0010] 1 is a block diagram showing an entire drive system for a rotating electric machine equipped with a power conversion device according to each embodiment. FIG. 2 is a schematic configuration diagram showing a main part of a power conversion device according to embodiment 1. FIG. 3 is a schematic configuration diagram showing a comparative example for explaining the operating principle of the power conversion device according to embodiment 1. FIG. 4 is a waveform diagram showing the voltage and current of a comparative example for explaining the operating principle of the power conversion device according to embodiment 1. FIG. 5 is a waveform diagram showing the voltage and current of the power conversion device according to embodiment 1. FIG. 6 is a configuration diagram showing a first modified example of the power conversion device according to embodiment 1. FIG. 7 is a configuration diagram showing a second modified example of the power conversion device according to embodiment 1. FIG. 8 is a configuration diagram showing a third modified example of the power conversion device according to embodiment 1. FIG. 9 is a configuration diagram showing a fourth modified example of the power conversion device according to embodiment 1. FIG. 10 is a schematic configuration diagram showing a main part of a power conversion device according to embodiment 2. FIG. 11 is a waveform diagram showing the voltage and current of the power conversion device according to embodiment 2. FIG. 12 is a schematic configuration diagram showing a main part of a power conversion device according to embodiment 3. FIG. 13 is a configuration diagram showing a first modified example of the power conversion device according to embodiment 3. FIG. 14 is a configuration diagram showing a second modified example of the power conversion device according to embodiment 3. FIG. 15 is a schematic configuration diagram showing a main part of a power conversion device according to embodiment 4. FIG. 16 is a waveform diagram showing the voltage and current of the power conversion device according to embodiment 4. Fig. 10 is a schematic configuration diagram showing a main part of a power conversion device according to embodiment 5. Fig. 11 is a waveform diagram showing the voltage and current of the power conversion device according to embodiment 5. Fig. 12 is a schematic configuration diagram showing a main part of a power conversion device according to embodiment 6. Fig. 13 is a waveform diagram showing the voltage and current of the power conversion device according to embodiment 6.

[0011] Hereinafter, an embodiment will be described with reference to Figures 1 to 21. In each figure, the same reference numerals indicate the same or corresponding parts. Note that Figures 1 to 21 relate to one embodiment, and the present disclosure is not limited to these figures.

[0012] Embodiment 1. Figure 1 is a block diagram showing the entire drive system of a rotating electric machine on which a power conversion device according to each embodiment is mounted, and in Figure 1, the drive system of a rotating electric machine for an electric vehicle includes a DC power source 1, which is a high-voltage battery of, for example, 400 to 800 [V], an AC rotating electric machine 5 that serves as a load device for propelling the vehicle, a power conversion device 2 that receives power supply from the DC power source 1 and controls the AC rotating electric machine 5, and a low-voltage battery 14 that is electrically independent of the DC power source 1 and supplies power of, for example, 12 to 24 [V] to a control circuit board 10 that constitutes the power conversion device 2. The power conversion device 2 is provided with three sets of legs, each set having 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 side of the DC power supply 1, and lower-stage semiconductor switching elements 4b, 4d, and 4f connected to the negative electrode side, connected in series, and the semiconductor switching elements 4a to 4f are controlled to be turned on and off by a drive circuit 11 on a control circuit board 10, thereby performing power conversion.

[0013] The control circuit board 10 receives power from a low-voltage battery 14 to generate a drive power supply 12, and the voltage of the drive power supply 12 is transmitted as a gate drive signal 31 from the drive circuit 11 via gate drive signal lines 21a to 21f to control the on / off states of the semiconductor switching elements 4a to 4f. Furthermore, even if the power supply from the low-voltage battery 14 to the control circuit board 10 drops for some reason and the voltage of the drive power supply 12 drops, a power supply circuit 13 is mounted, which uses a DC power supply 1 as a backup power source, so that the power supply to the control circuit board 10 can continue. The drive circuit 11 receives power from the drive power supply 12, the power supply circuit 13, and the low-voltage battery 14 via control power supply lines 32a to 32d, respectively.

[0014] Next, the configuration and operation of the control circuit board 10 will be described. Fig. 2 is a schematic diagram showing the main components of the power conversion device 2 according to the first embodiment. In Fig. 2, the control circuit board 10 is mounted with a drive circuit 11 for controlling the on / off of the lower-stage semiconductor switching elements 4b and a power supply circuit 13 using a DC power supply 1 as a power source, and a reference potential 38a of the drive circuit 11 and a reference potential 38b of the power supply circuit 13 are independently provided on the control circuit board 10. Note that the drive power supply 12 generated by receiving power from a low-voltage battery 14 and the drive circuit 11 for controlling the on / off of the upper-stage semiconductor switching elements 4a are omitted from the illustration.

[0015] The control circuit board 10 has connection points 39a, 39b, 39c, and 39d for connecting circuits, and the reference potential 38a of the drive circuit 11 is connected to the source or emitter terminal 33 of the semiconductor switching element 4b via the source or emitter wiring 35 at connection point 39b, and the reference potential 38b of the power supply circuit 13 is connected to the negative terminal 37 of the conductor connecting the negative side of the DC power supply 1 and the negative side of the smoothing capacitor 3 at connection point 39c. The control circuit board 10 is also provided with a reverse conduction prevention diode 50, the anode of which is connected to the positive terminal 36 of the conductor connecting the positive side of the DC power supply 1 and the positive side of the smoothing capacitor 3 at connection point 39a, and the cathode of which is connected to the positive side of the input capacitor 40 that constitutes the power supply circuit 13 at connection point 39d.

[0016] Furthermore, the drive circuit 11 includes a drive IC, and the power supply circuit 13 is composed of an input capacitor 40, a power supply control IC, a semiconductor switching element, a transformer, etc. The dotted arrows in the figure indicate the route of an input current Iin flowing to the power supply circuit 13 due to a surge voltage of the semiconductor switching element 4b (described later), through an electrical path formed by a reverse conduction prevention diode 50 and a reference potential 38b of the power supply circuit 13, etc. While a metal oxide semiconductor field effect transistor (MOSFET) is shown as an example of the semiconductor switching element, a bipolar transistor or the like may also be used. The control terminal and the pair of main terminals may be equivalently referred to as source terminals, for example, by replacing the source terminal with an emitter terminal, and therefore, hereinafter, the respective terminals and wiring will not be shown together.

[0017] Here, when power supply circuit 13 using DC power supply 1 as a power source is provided on the same control circuit board 10 as drive circuit 11 for semiconductor switching element 4b, the operating principle of unstable on / off control of semiconductor switching element 4b and countermeasures for this will be described by comparing the solution in embodiment 1 with a hypothetical comparative example. First, Fig. 3 is a schematic configuration diagram showing a comparative example for explaining the operating principle of power conversion device 2 according to embodiment 1, and Fig. 4 is a waveform diagram showing voltages and currents of the comparative example in Fig. 3. Finally, Fig. 5 is a waveform diagram showing voltages and currents of power conversion device 2 according to embodiment 1.

[0018] 3, it is assumed that the reference potential 38a of the drive circuit 11 and the reference potential 38b of the power supply circuit 13 are connected on the control circuit board 20. 4 and 5 illustrate, in order, the switching waveforms when the semiconductor switching element 4b switches from the on state to the off state, including the gate-source voltage of the semiconductor switching element 4b, the induced voltage between the source terminal 33 and the source wiring 35, the input current of the power supply circuit 13, the cathode-anode voltage of the reverse conduction prevention diode 50, and the drain-source voltage of the semiconductor switching element 4b.

[0019] Now, if a surge voltage occurs during the switching operation of turning semiconductor switching element 4b on or off, there may be an instantaneous fluctuation in the input voltage of power supply circuit 13. In the comparative example of Fig. 3, for example, when semiconductor switching element 4b switches from the on state to the off state, during the interval t1 to t2 in Fig. 4, the route of input current Iin flowing to power supply circuit 13 is as shown in Fig. 3, from reverse conduction prevention diode 50 via power supply circuit 13 to drive circuit 11, and the direction of induced voltage ΔV generated between source terminal 33 and source wiring 35 of semiconductor switching element 4b is positive and then negative in the direction of the flow of input current Iin.

[0020] At this time, an induced voltage is generated in the wiring inductance of the closed-loop circuit including the legs formed by the smoothing capacitor 3 and the semiconductor switching elements 4a and 4b, depending on the time change d(Id) / dt of the main current Id (not shown) flowing through the semiconductor switching element 4b, causing a voltage overshoot known as a surge voltage to occur in the drain-source voltage of the semiconductor switching element 4b. Meanwhile, during the interval t0 to t1 in FIG. 4 , the voltage across the input capacitor 40 constituting the power supply circuit 13 is equal to the voltage of the DC power supply 1, and the potential difference between the cathode and anode of the reverse conduction prevention diode 50 is 0 V. From this state, when a surge voltage occurs during the interval t1 to t2, a potential difference is generated between the cathode and anode of the reverse conduction prevention diode 50, and an input current Iin corresponding to this potential difference flows through the power supply circuit 13.

[0021] Furthermore, in accordance with the time change d(Iin) / dt of this input current Iin, an induced voltage ΔV (=Ls×d(Iin) / dt) is generated in the wiring inductance Ls of the source terminal 33 and the source wiring 35. The source terminal 33 and the source wiring 35 serve as signal wiring with which the drive circuit 11 controls the on / off of the semiconductor switching element 4b, and when the induced voltage ΔV is generated, the gate-source voltage of the semiconductor switching element 4b drops instantaneously.

[0022] Next, during the period from t2 to t3 in Figure 4, the route of the input current Iin flowing to the power supply circuit 13 is as shown in Figure 3, flowing to the drive circuit 11 via the power supply circuit 13, but the direction of the induced voltage ΔV generated between the source terminal 33 and the source wiring 35 reverses from negative to positive in the direction of the flow of the input current Iin. This is because, during the period from t1 to t2, the input current Iin flowing to the power supply circuit 13 causes charge to accumulate in the input capacitor 40, and the potential difference between the cathode and anode of the reverse conduction prevention diode 50 changes from increasing to decreasing. At this time, the input current Iin changes according to the potential difference between the cathode and anode of the reverse conduction prevention diode 50, so the input current Iin also changes from increasing to decreasing, and the direction of the time change d(Iin) / dt of the input current Iin is reversed. As a result, the sign of the induced voltage ΔV generated in the wiring inductance Ls between the source terminal 33 and the source wiring 35 is reversed, and the gate-source voltage of the semiconductor switching element 4b increases.

[0023] However, during the interval t3 to t4 in Figure 4, the route of the input current Iin (inverted Iin in the figure) flowing to the power supply circuit 13 reverses its flow direction, and flows from the drive circuit 11 to the reverse conduction prevention diode 50 via the power supply circuit 13 as shown in Figure 3, and the direction of the induced voltage ΔV generated between the source terminal 33 and the source wiring 35 becomes positive and negative in the direction of the input current Iin (inverted Iin in the figure). Here, it is known that a typical diode characteristic is that even if an attempt is made to turn the diode off by applying a reverse voltage between the cathode and anode of the diode from an on state in which a forward current flows through the diode, the current does not immediately converge to 0 [A], and a reverse current called a recovery current flows.

[0024] That is, at time t3, the potential difference between the cathode and anode of the reverse conduction prevention diode 50 becomes 0 V, but due to the diode characteristics, a recovery current flows in the section from t3 to t4. Therefore, the time change d(Iin) / dt of the input current Iin (inverted Iin in the figure) does not change, and therefore the induced voltage ΔV generated in the wiring inductance Ls between the source terminal 33 and the source wiring 35 and the gate-source voltage of the semiconductor switching element 4b also continue to rise.

[0025] Furthermore, during the interval t4 to t5 in FIG. 4, the route of the input current Iin (reversed Iin in the figure) flowing to the power supply circuit 13 is as shown in FIG. 3, from the drive circuit 11 via the power supply circuit 13 to the reverse conduction prevention diode 50, but the direction of the induced voltage ΔV generated between the source terminal 33 and the source wiring 35 reverses from negative to positive in the direction of the flow of the input current Iin (reversed Iin in the figure). In other words, at time t4, the recovery current begins to decrease, and the direction of the time change d(Iin) / dt of the input current Iin (reversed Iin in the figure) reverses again. At this time, the positive and negative of the induced voltage ΔV generated across the wiring inductance Ls between the source terminal 33 and the source wiring 35 also reverses again, causing an instantaneous drop in the gate-source voltage of the semiconductor switching element 4b.

[0026] Incidentally, a fast recovery diode (FRD) with a short reverse recovery time, which is the conduction time of the recovery current, may be used as the reverse conduction prevention diode 50 in order to minimize losses that occur when starting up the power supply circuit 13. When an FRD is used as the reverse conduction prevention diode 50, the time change d(Iin) / dt of the input current Iin (inverted Iin in the figure) in the section t4 to t5 increases, and as a result, the instantaneous voltage drop in the gate-source voltage of the semiconductor switching element 4b tends to become more pronounced.

[0027] Although the switching operation of the lower-stage semiconductor switching element 4b switching from an ON state to an OFF state has been exemplified as an example of a case in which the input voltage of the power supply circuit 13 fluctuates instantaneously due to a surge voltage generated during the switching operation of the semiconductor switching elements 4a, 4b constituting one leg, fluctuations in the gate-source voltage of the semiconductor switching element 4b occur in any of the following cases: when the lower-stage semiconductor switching element 4b switches from an OFF state to an ON state; when the upper-stage semiconductor switching element 4a switches from an ON state to an OFF state; and when the upper-stage semiconductor switching element 4a switches from an OFF state to an ON state. The same applies to the semiconductor switching elements 4c to 4f constituting the other legs.

[0028] 2 , according to the power conversion device 2 of embodiment 1, the reference potential 38b of the power supply circuit 13 is electrically independent from the reference potential 38a of the drive circuit 11 and is provided on the control circuit board 10 to configure an electrical path, so that when the semiconductor switching element 4b switches from the on state to the off state, the input current Iin flowing from the reverse conduction prevention diode 50 to the power supply circuit 13 can be prevented from flowing to the drive circuit 11. Therefore, even if the input voltage of the power supply circuit 13 fluctuates due to the switching operation of the semiconductor switching element 4b, the input current Iin will not flow between the source terminal 33 and the source wiring 35.

[0029] That is, in the interval t1 to t5 in Fig. 5, when the switching waveforms of the power conversion device 2 according to the first embodiment are compared with the switching waveforms of the comparative example in the same interval in Fig. 4, no induced voltage ΔV is generated between the source terminal 33 and the source wiring 35, and therefore no fluctuation occurs in the gate-source voltage of the semiconductor switching element 4b, and it becomes possible to stably control the on / off of the semiconductor switching element 4b. The same applies to the other semiconductor switching elements 4d and 4f.

[0030] As a modification of the first embodiment, a discharge circuit 15 that discharges the charge stored in the smoothing capacitor 3 may be mounted on the control circuit board. FIG. 6 is a configuration diagram showing a first modification of the power conversion device 2 according to the first embodiment, in which the configuration of the control circuit board 10a is changed from that of the first embodiment. In FIG. 6 , when the discharge circuit 15 is mounted on the control circuit board 10a, the reference potential 38b of the power supply circuit 13 may be connected to the negative terminal 37 of the conductor that connects the negative side of the DC power supply 1 and the negative side of the smoothing capacitor 3 to the reference potential of the discharge circuit 15, using a connection point 39c on the control circuit board 10a. With such a configuration, existing terminals can be effectively utilized and a dedicated terminal is not required, thereby minimizing the additional cost of an electrical path that prevents the input current Iin flowing through the power supply circuit 13 from flowing to the drive circuit 11.

[0031] As a modification of the first embodiment, a voltage sensor circuit 16 that monitors the voltage of the smoothing capacitor 3 may be mounted on a control circuit board. FIG. 7 is a configuration diagram showing a second modification of the power conversion device 2 according to the first embodiment, in which the configuration of the control circuit board 10b is changed from that of the first embodiment. In FIG. 7 , when the voltage sensor circuit 16 is mounted on the control circuit board 10b, the reference potential 38b of the power supply circuit 13 may be connected to a negative terminal 37 of a conductor that connects the negative side of the DC power supply 1 and the negative side of the smoothing capacitor 3 to the reference potential of the voltage sensor circuit 16, using a connection point 39c on the control circuit board 10b. This configuration makes it possible to effectively utilize existing terminals and eliminates the need for a dedicated terminal, thereby minimizing the additional cost of an electrical path that prevents the input current Iin flowing through the power supply circuit 13 from flowing to the drive circuit 11.

[0032] As a modification of the first embodiment, a noise reduction filter circuit 17 that suppresses normal mode noise having high frequency components may be mounted on the control circuit board. FIG. 8 is a configuration diagram showing a third modification of the power conversion device according to the first embodiment, in which the configuration of the control circuit board 10c is changed from that of the first embodiment. In FIG. 8, when the filter circuit 17 is mounted on the control circuit board 10c, the reference potential 38b of the power supply circuit 13 may be connected to the negative terminal 37 of the conductor that connects the negative side of the DC power supply 1 and the negative side of the smoothing capacitor 3 to the reference potential of the filter circuit 17, using a connection point 39c on the control circuit board 10c. This configuration makes it possible to effectively utilize existing terminals and eliminates the need for a dedicated terminal, thereby minimizing the additional cost of an electrical path that prevents the input current Iin flowing through the power supply circuit 13 from flowing to the drive circuit 11.

[0033] As a modification of the first embodiment, in order to improve the controllability of the semiconductor switching element and detect an abnormal state of the semiconductor switching element, a second source terminal 34 different from the first source terminal 33 to which the reference potential 38a of the drive circuit 11 is connected may be provided in the semiconductor switching element 4b. FIG. 9 is a configuration diagram showing a fourth modification of the power conversion device according to the first embodiment, in which the configuration of the control circuit board 10d is modified from that of the first embodiment. In FIG. 9, when the semiconductor switching element 4b is provided with the second source terminal 34, the reference potential 38b of the power supply circuit 13 may be connected to the second source terminal 34 of the semiconductor switching element 4b using a connection point 39c of the control circuit board 10d. This configuration makes it possible to effectively utilize existing terminals and eliminates the need for a dedicated terminal, thereby minimizing the additional cost of an electrical path that prevents the input current Iin flowing through the power supply circuit 13 from flowing to the drive circuit 11.

[0034] Second Embodiment. In the second embodiment, differences from the first embodiment will be described, focusing on the means for preventing the input current Iin flowing to the power supply circuit 13 from flowing to the drive circuit 11. FIG. 10 is a schematic diagram showing the main components of a power conversion device 2 according to the second embodiment, in which the configuration of the control circuit board 10e is changed from that of the first embodiment. FIG. 11 is a waveform diagram showing the voltage and current of the power conversion device 2 in FIG. 10. In FIG. 10, the reference potential 38a of the drive circuit 11 and the reference potential 38b of the power supply circuit 13 are electrically independent of each other on the control circuit board 10e, and an electrical path is formed by connecting them to the same source terminal 33 using a connection point 39b on the control circuit board 10e. Therefore, even if the input voltage of the power supply circuit 13 fluctuates due to the switching operation of the semiconductor switching element 4b, the input current Iin flowing to the power supply circuit 13 does not flow to the source wiring 35 of the drive circuit 11.

[0035] In other words, comparing the switching waveforms of the power conversion device 2 according to the second embodiment during the period t1 to t5 in Figure 11 with the switching waveforms of the comparative example during the same period in Figure 4, while an induced voltage ΔV is generated at the source terminal 33, no induced voltage ΔV is generated at the source wiring 35. This suppresses fluctuations in the gate-source voltage of the semiconductor switching element 4b, enabling stable on / off control of the semiconductor switching element 4b. The same applies to the other semiconductor switching elements 4d and 4f. Furthermore, because the reference potential 38b of the power supply circuit 13 is connected to the same source terminal 33 as the reference potential 38a of the drive circuit 11, there is no need to provide a dedicated terminal for connecting the reference potential 38b of the power supply circuit 13. This minimizes the additional cost of an electrical path that prevents the input current Iin flowing through the power supply circuit 13 from flowing to the drive circuit 11.

[0036] Third Embodiment. In the third embodiment, differences from the first embodiment will be described, focusing on a means for suppressing, instead of preventing, the input current Iin flowing through the power supply circuit 13 from flowing to the drive circuit 11. FIG. 12 is a schematic diagram showing the main components of a power conversion device 2 according to the third embodiment, in which the configuration of the control circuit board 10f is modified from that of the first embodiment. FIG. 13 is a waveform diagram showing the voltage and current of the power conversion device 2 in FIG. 12. In FIG. 12, a current-limiting resistor 60 is provided on the control circuit board 10f between the positive terminal 36 of the conductor connecting the positive side of the DC power supply 1 and the positive side of the smoothing capacitor 3 and the anode of the reverse conduction prevention diode 50. While the reference potential 38a of the drive circuit 11 and the reference potential 38b of the power supply circuit 13 are connected in this example, the reference potentials 38a and 38b may be provided electrically independently on the control circuit board 10f, as shown in the second embodiment.

[0037] According to the power conversion device 2 of embodiment 3, a current limiting resistor 60 is provided in the closed circuit of the input current Iin formed on the control circuit board 10f by the positive terminal 36, the reverse conduction prevention diode 50, the power supply circuit 13, the drive circuit 11, and the source terminal 33 of the semiconductor switching element 4b. Therefore, even if the input voltage of the power supply circuit 13 fluctuates due to the switching operation of the semiconductor switching element 4b, the amount of change in the input current Iin flowing to the power supply circuit 13 can be suppressed.

[0038] In other words, comparing the switching waveforms of the power conversion device 2 according to the third embodiment with the switching waveforms of the comparative example in the same period in Figure 4 during the period t1 to t5 in Figure 13, even if the input voltage of the power supply circuit 13 fluctuates momentarily when the semiconductor switching element 4b performs a switching operation, the current change in the input current Iin is suppressed, so that the induced voltage ΔV (= Ls × d(Iin) / dt) generated in the wiring inductance Ls between the source terminal 33 and the source wiring 35 is reduced, and the amount of fluctuation in the gate-source voltage of the semiconductor switching element 4b can be suppressed, thereby enabling stable on / off control of the semiconductor switching element 4b. Note that by combining the third embodiment with the second embodiment, the induced voltage ΔV at the source terminal 33 is reduced while no induced voltage ΔV is generated in the source wiring 35, making it possible to more effectively reduce fluctuations in the gate-source voltage of the semiconductor switching element 4b.

[0039] As a modification of the third embodiment, the insertion location of the current limiting resistor 60 provided in the closed circuit of the input current Iin may be changed. FIGS. 14 and 15 are configuration diagrams showing modifications 1 and 2 of the power conversion device 2 according to the third embodiment, in which the configurations of the control circuit boards 10g and 10h, respectively, are modified from the configuration of the first embodiment. In FIG. 14 , the current limiting resistor 60 is provided between the cathode of the reverse conduction prevention diode 50 and the connection point 39d on the positive side of the input capacitor 40. In FIG. 15 , the current limiting resistor 60 is provided between the reference potential 38a of the drive circuit 11 and the reference potential 38b of the power supply circuit 13. Regardless of the insertion location of the current limiting resistor 60, the current change in the input current Iin flowing through the power supply circuit 13 is suppressed, thereby reducing the induced voltage ΔV between the source terminal 33 and the source wiring 35. This suppresses fluctuations in the gate-source voltage of the semiconductor switching element 4b, enabling stable on / off control of the semiconductor switching element 4b.

[0040] Fourth Embodiment. The fourth embodiment will be described, focusing on differences from the first embodiment, as a means for suppressing, instead of preventing, the input current Iin flowing to the power supply circuit 13 from flowing to the drive circuit 11. FIG. 16 is a schematic diagram showing the main components of a power conversion device 2 according to the fourth embodiment, in which the configuration of the control circuit board 10i is modified from that of the first embodiment. FIG. 17 is a waveform diagram showing the voltage and current of the power conversion device 2 in FIG. 16. In FIG. 16, a Schottky barrier diode 50a is used as the reverse conduction prevention diode 50 provided on the control circuit board 10i. Here, the Schottky barrier diode 50a is called a unipolar device in which either electrons or holes contribute to its operation. Unlike the general diode characteristics described in the operating principle of the first embodiment, it is known that, in principle, it has no reverse recovery time.

[0041] In other words, when a Schottky barrier diode 50a is used as the reverse conduction prevention diode 50, comparing the switching waveforms of the power conversion device 2 according to the fourth embodiment during the period t1 to t5 in FIG. 17 with the switching waveforms of the comparative example during the same period in FIG. 4, fluctuations in the gate-source voltage of the semiconductor switching element 4b due to the diode recovery current during the period t3 to t5 can be suppressed, thereby enabling stable on / off control of the semiconductor switching element 4b. While the reference potential 38a of the drive circuit 11 and the reference potential 38b of the power supply circuit 13 are connected in this example, the reference potentials 38a and 38b may be electrically independent of each other on the control circuit board 10i, as shown in the second embodiment. Furthermore, by combining the fourth embodiment with the second embodiment, the induced voltage ΔV at the source terminal 33 is reduced while no induced voltage ΔV is generated in the source wiring 35, thereby more effectively reducing fluctuations in the gate-source voltage of the semiconductor switching element 4b.

[0042] Fifth Embodiment. In the fifth embodiment, differences from the first embodiment will be described, focusing on a means for suppressing, instead of preventing, the input current Iin flowing through the power supply circuit 13 from flowing to the drive circuit 11. FIG. 18 is a schematic diagram showing the main components of a power conversion device 2 according to the fifth embodiment, in which the configuration of the control circuit board 10j is modified from that of the first embodiment. FIG. 19 is a waveform diagram showing the voltage and current of the power conversion device 2 in FIG. 18. In FIG. 18, the anode of the reverse conduction prevention diode 50 is a conductor connecting the positive electrode of the DC power supply 1 and the positive electrode of the smoothing capacitor 3, and is connected to a positive terminal 36 provided at a connection point 39e closer to the DC power supply 1 than the smoothing capacitor 3, thereby forming an electrical path. Note that, although the reference potential 38a of the drive circuit 11 and the reference potential 38b of the power supply circuit 13 are connected, the reference potentials 38a and 38b may be provided electrically independently on the control circuit board 10j, as shown in the second embodiment.

[0043] As explained regarding the operating principle of the first embodiment, during switching operation of semiconductor switching element 4b, an induced voltage is generated in the wiring inductance of the closed loop circuit including smoothing capacitor 3 and the legs of semiconductor switching elements 4a and 4b, causing a surge voltage to occur in the drain-source voltage of semiconductor switching element 4b. In this case, in the comparative example shown in Figure 3, the anode of reverse conduction prevention diode 50 is connected to positive terminal 36, which is a conductor connecting the positive side of DC power supply 1 and the positive side of smoothing capacitor 3 and is provided at connection point 39a, which is closer to semiconductor switching element 4a than smoothing capacitor 3. Therefore, the induced voltage in the closed loop circuit including the legs is superimposed on the voltage of DC power supply 1, and a correspondingly larger voltage is input to power supply circuit 13, causing the input voltage of power supply circuit 13 to fluctuate instantaneously.

[0044] On the other hand, according to the fifth embodiment, the anode of the reverse conduction prevention diode 50 is connected to the positive terminal 36, which is a conductor connecting the positive side of the DC power supply 1 and the positive side of the smoothing capacitor 3 and is provided at the connection point 39e, which is closer to the DC power supply 1 than the smoothing capacitor 3. This reduces the induced voltage of the closed loop circuit superimposed on the voltage of the DC power supply 1, thereby stabilizing the input voltage of the power supply circuit 13. Comparing the switching waveforms of the power conversion device 2 according to the fifth embodiment during the interval t1 to t5 in FIG. 19 with the switching waveforms of the comparative example during the same interval in FIG. 4 reveals that, as a result, the potential difference between the cathode and anode of the reverse conduction prevention diode 50 during the interval t2 to t3 is reduced, thereby suppressing fluctuations in the gate-source voltage of the semiconductor switching element 4b. Note that by combining the fifth embodiment with the second embodiment, the induced voltage ΔV at the source terminal 33 is reduced while no induced voltage ΔV is generated in the source wiring 35, thereby more effectively reducing fluctuations in the gate-source voltage of the semiconductor switching element 4b.

[0045] Sixth Embodiment. In the sixth embodiment, differences from the first embodiment will be described, focusing on a means for suppressing, instead of preventing, the input current Iin flowing through the power supply circuit 13 from flowing to the drive circuit 11 when multiple legs are provided. FIG. 20 is a schematic diagram showing the main components of a power conversion device 2 according to the sixth embodiment, in which the configuration of the control circuit board 10k is changed from that of the first embodiment. FIG. 21 is a waveform diagram showing the voltage and current of the power conversion device 2 in FIG. 20. In FIG. 20, for example, when three legs are provided, the reference potential 38b of the power supply circuit 13 is connected to the reference potential 38a of the drive circuit 11 for the lower-stage semiconductor switching element 4b, 4d, or 4f, which is the leg of the closed-loop circuit having the smallest wiring inductance, among the three closed-loop circuits formed by the smoothing capacitor 3 and each of the three legs, thereby forming an electrical path for the three legs. Although the case where the reference potential 38a of the drive circuit 11 and the reference potential 38b of the power supply circuit 13 are connected is shown, as shown in embodiment 2, the reference potentials 38a and 38b may be provided electrically independently on the control circuit board 10k.

[0046] The power conversion device 2 may include, for example, three sets of legs, each of which is formed by connecting upper-stage semiconductor switching elements 4a, 4c, and 4e in series with lower-stage semiconductor switching elements 4b, 4d, and 4f. These legs are connected to a DC power supply 1 (high-voltage battery) and a smoothing capacitor 3 via a wiring bus bar having an inductance component. In this case, depending on the structural arrangement of the semiconductor switching elements 4a to 4f, the closed loop circuit formed by the smoothing capacitor 3 and one set of legs may have a long wiring length or a short wiring length. The longer the wiring length, the greater the value of wiring inductance, and therefore the greater the surge voltage when the semiconductor switching elements 4a to 4f perform switching operations. As a result, the fluctuation amount of the gate-source voltage of the lower-stage semiconductor switching elements 4b, 4d, and 4f increases.

[0047] In other words, reference potential 38b of power supply circuit 13 is connected to reference potential 38a of drive circuit 11, which is a leg that forms a closed loop circuit in which the surge voltage is minimized during switching operation of semiconductor switching elements 4a to 4f and controls the on / off of lower-stage semiconductor switching elements 4b, 4d, or 4f. Therefore, when the switching waveforms of power conversion device 2 according to embodiment 6 during intervals t1 to t5 in Figure 21 are compared with the switching waveforms of the comparative example during the same interval in Figure 4, it is possible to suppress fluctuations in the gate-source voltage of the corresponding semiconductor switching elements 4b, 4d, or 4f. Note that by combining embodiment 6 with embodiment 2, induced voltage ΔV at source terminal 33 is reduced while no induced voltage ΔV is generated in source wiring 35, making it possible to more effectively reduce fluctuations in the gate-source voltage of semiconductor switching elements 4b, 4d, and 4f.

[0048] In the first to sixth embodiments, the semiconductor switching elements 4a to 4f constituting the power conversion device 2 are power control semiconductor switching elements such as the MOSFETs shown as examples or insulated gate bipolar transistors (IGBTs), as well as free wheel diodes, etc. The semiconductor switching elements 4a to 4f are not limited to these, and other semiconductor switching elements such as bipolar transistors may also be used.

[0049] In addition, in the first to sixth embodiments, the semiconductor switching elements 4a to 4f have been described using diagrams illustrating the use of MOSFETs and the parasitic diodes of the MOSFETs as freewheeling diodes, but when using semiconductor switching elements that do not have parasitic diodes, such as IGBTs, a freewheeling diode may be provided in parallel. Furthermore, the semiconductor switching elements 4a to 4f are formed on a semiconductor substrate made of a material such as silicon, silicon carbide, or gallium nitride, and a wide bandgap semiconductor with a bandgap wider than that of silicon may be used for the semiconductor switching elements 4a to 4f.

[0050] The power conversion device 2 according to the first to sixth embodiments can be used as a power conversion device such as an inverter or converter in the power electronics field, particularly as an inverter for automotive, railway, and industrial equipment. For example, the power conversion device 2 is an inverter circuit that controls an AC rotating electric machine 5 using a 400-800 V high-voltage battery as a DC power source 1. The inverter for such high voltages uses a MOSFET formed of silicon carbide, a wide-bandgap semiconductor. Wide-bandgap semiconductors are generally suitable for high-speed switching and are prone to large surge voltages during switching operations. Therefore, by configuring the power conversion device 2 using wide-bandgap semiconductors as the semiconductor switching elements 4a-4f, the effects obtained from each embodiment can be more prominently demonstrated.

[0051] Although various exemplary embodiments and examples are described in this disclosure, the various features, aspects, and functions described in one or more 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, this includes cases where at least one component is modified, added, or omitted, or where at least one component is extracted and combined with components of another embodiment.

[0052] 1: DC power supply, 2: power conversion device, 3: smoothing capacitor, 4a to 4f: semiconductor switching elements, 5: AC rotating electric machine, 10, 10a to 10k, 20: control circuit board, 11: drive circuit, 13: power supply circuit, 14: low-voltage battery, 15: discharge circuit, 16: voltage sensor circuit, 17: filter circuit, 33, 34: source terminal, 35: source wiring, 36: positive terminal, 37: negative terminal, 38a, 38b: reference potential, 39a, 39b, 39c, 39d, 39e: connection points, 50: reverse conduction prevention diode, 50a: Schottky barrier diode, 60: current limiting resistor.

Claims

1. A power conversion device that receives power from a DC power source and controls an AC rotating electric machine, comprising: a smoothing capacitor connected in parallel to the DC power source; at least one pair of legs each formed by connecting in series an upper-stage semiconductor switching element connected to the positive electrode of the DC power source and a lower-stage semiconductor switching element connected to the negative electrode of the DC power source; a drive circuit that turns on or off the upper-stage semiconductor switching element or the lower-stage semiconductor switching element, respectively; a power supply circuit that receives power from the DC power source via a reverse conduction prevention diode and supplies power to the drive circuit; and a control circuit board on which the drive circuit, the reverse conduction prevention diode, and the power supply circuit are mounted, wherein the control circuit board is provided with an electrical path that prevents an input current flowing from the reverse conduction prevention diode to the power supply circuit from flowing to the drive circuit, or a limiting element or electrical path that suppresses the input current.

2. The power conversion device according to claim 1, characterized in that when the electrical path that avoids the input current is provided, the reference potential of the power supply circuit is provided on the control circuit board, electrically independent of the reference potential of the drive circuit.

3. The power conversion device according to claim 1 or 2, characterized in that, when the electrical path that avoids the input current is provided, the control circuit board has a plurality of reference potentials connected to the negative side of the DC power supply, the reference potential of the drive circuit for the semiconductor switching element on the lower side is connected to the source or emitter terminal of the semiconductor switching element on the lower side, and the reference potential of the power supply circuit is connected to a terminal of a reference potential different from the terminal to which the reference potential of the drive circuit is connected.

4. A power conversion device as described in claim 2 or 3, characterized in that the reference potential of the power supply circuit is connected to the negative terminal of the conductor connecting the negative side of the DC power supply and the negative side of the smoothing capacitor via a connection point on the control circuit board.

5. The power conversion device according to claim 4, characterized in that the control circuit board is equipped with a discharge circuit that discharges the charge stored in the smoothing capacitor, and the reference potential of the power supply circuit is connected to the negative terminal of a conductor that connects the negative side of the DC power supply and the negative side of the smoothing capacitor to the reference potential of the discharge circuit.

6. The power conversion device according to claim 4, characterized in that the control circuit board is equipped with a voltage sensor circuit that monitors the voltage of the smoothing capacitor, and the reference potential of the power supply circuit is connected to the negative terminal of a conductor that connects the negative side of the DC power supply and the negative side of the smoothing capacitor to the reference potential of the voltage sensor circuit.

7. The power conversion device according to claim 4, characterized in that the control circuit board is equipped with a noise reduction filter circuit connected in parallel with the DC power supply, and the reference potential of the power supply circuit is connected to the negative terminal of a conductor connecting the negative side of the DC power supply and the negative side of the smoothing capacitor to the reference potential of the filter circuit.

8. A power conversion device according to claim 2 or 3, characterized in that the reference potential of the power supply circuit is connected to a source or emitter terminal of the semiconductor switching element on the lower stage that is different from the source or emitter terminal to which the reference potential of the drive circuit is connected.

9. The power conversion device according to claim 2, characterized in that the reference potential of the power supply circuit is connected to the same source or emitter terminal of the semiconductor switching element on the lower stage as the source or emitter terminal to which the reference potential of the drive circuit is connected.

10. The power conversion device according to claim 1, wherein when the limiting element that suppresses the input current is provided, a current limiting resistor is inserted in a closed circuit formed on the control circuit board by the positive terminal of the conductor connecting the positive side of the DC power supply and the positive side of the smoothing capacitor, the reverse conduction prevention diode, the power supply circuit, the drive circuit, and the source or emitter terminal of the semiconductor switching element on the lower stage.

11. The power conversion device according to claim 10, wherein the current limiting resistor is inserted on the anode side or cathode side of the reverse conduction prevention diode, or between the reference potential of the drive circuit and the reference potential of the power supply circuit.

12. The power conversion device according to claim 1, wherein when the limiting element for suppressing the input current is provided, the reverse conduction prevention diode is a Schottky barrier diode.

13. The power conversion device according to claim 1, characterized in that, when the electrical path for suppressing the input current is provided, the positive terminal of the conductor connecting the positive side of the DC power supply and the positive side of the smoothing capacitor is located closer to the DC power supply than the smoothing capacitor, and the anode of the reverse conduction prevention diode is connected to the positive terminal via a connection point on the control circuit board.

14. The power conversion device according to claim 1, characterized in that when the device comprises a plurality of sets of the legs and the electrical path for suppressing the input current is provided, the reference potential of the power supply circuit is the leg of the closed loop circuit having the smallest wiring inductance among a plurality of closed loop circuits formed by the smoothing capacitor and each of the plurality of legs, and is connected to the same reference potential as or a different reference potential from the drive circuit for the semiconductor switching element on the lower side.

15. A power conversion device according to any one of claims 9 to 14, characterized in that at least two means are combined from among the electrical path that avoids the input current, and the limiting element or electrical path that suppresses the input current.

16. A power conversion device according to any one of claims 1 to 15, characterized in that the semiconductor switching element is a wide-gap semiconductor.

17. A power conversion device as claimed in any one of claims 1 to 16, characterized in that the drive circuit receives power from a low-voltage battery that is electrically independent of the DC power supply and has a lower voltage than the DC power supply, and also receives power from the power supply circuit as a backup power source for the low-voltage battery.

18. A drive system that uses a high-voltage battery and a low-voltage battery that is electrically independent of the high-voltage battery and has a lower voltage than the high-voltage battery as power sources, and converts the power from the high-voltage battery to drive a load device, comprising: a semiconductor switching element connected in parallel to the high-voltage battery for controlling the power conversion of the high-voltage battery; a drive circuit that receives power from the low-voltage battery and drives the semiconductor switching element; a power supply circuit connected in parallel to the high-voltage battery and supplies power to the drive circuit as a backup power supply for the low-voltage battery; and a control circuit board on which the drive circuit and the power supply circuit are mounted, respectively; wherein the control circuit board is provided with an electrical path that prevents an input current that flows into the power supply circuit due to the switching operation of the semiconductor switching element from flowing into the drive circuit, or a limiting element or electrical path that suppresses the input current.

19. A drive system as described in claim 18, characterized in that the drive circuit is connected between the control terminal of the semiconductor switching element and a reference potential, and when the electrical path that avoids the input current is provided, the reference potential of the power supply circuit is provided electrically independent from the reference potential of the drive circuit.

20. The drive system described in claim 18, characterized in that the drive circuit is connected between the control terminal of the semiconductor switching element and a reference potential, and when the reference potential of the power supply circuit is connected to the reference potential of the drive circuit, the limiting element or the electrical path is provided to suppress the input current.

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