Power conversion device

Abstract

A power conversion device (4) comprises inverters (8, 9), a switch (10), a power supply line (5), and a snubber circuit (11). The inverter (8) is connected to one end of the winding of a rotating electrical machine (3), and the inverter (9) is connected to the other end of the winding. The switch (10) includes a changeover switch (101) that connects a DC power supply (2) and the inverter (9) in a closed state and cuts off the connection in an open state. The snubber circuit (11) has a capacitor (11C) and is connected in parallel to the inverter (9). The power supply line (5) has: a wiring (51) that connects the inverter (8) and the changeover switch (101); and wiring (52) that connects the changeover switch (101) and the inverter (9). Of said wirings (51, 52), the wiring (51) is connected to the snubber circuit (11).

Description

Power Conversion Device CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based on Patent Application No. 2024-8239 filed in Japan on January 23, 2024, and the contents of the original application are incorporated by reference in their entirety.

[0002] The disclosure herein relates to power conversion devices.

[0003] Patent Document 1 discloses a power conversion device including a first inverter connected to one end of a winding of a rotating electric machine, a second inverter connected to the other end of the winding, and a changeover switch. The changeover switch is disposed between a DC power source and the second inverter, and connects the DC power source and the second inverter in a closed state and disconnects the DC power source and the second inverter in an open state. The contents of the prior art document are incorporated by reference as explanations of the technical elements in this specification.

[0004] Japanese Patent Application Laid-Open No. 2022-177342

[0005] To reduce inductance, a configuration in which a snubber circuit is connected in parallel to the inverter can be considered. However, when the changeover switch is open, there is a risk that the capacitor of the snubber circuit connected in parallel to the second inverter may be charged or discharged. In other words, there is a problem of low power conversion efficiency. In terms of the above and other aspects not mentioned, further improvements are required in power conversion devices.

[0006] One disclosed object is to provide a power conversion device capable of improving power conversion efficiency.

[0007] One aspect of the disclosure is a power conversion device comprising: a first inverter connected to one end of a winding of a rotating electric machine; a second inverter connected to the other end of the winding; a switch disposed between a DC power source and the second inverter, the switch having a change-over switch that connects the DC power source and the second inverter in a closed state and cuts off the connection between the DC power source and the second inverter in an open state; wiring constituting a power line electrically connected to the DC power source, the first wiring connecting the first inverter and the change-over switch, and a second wiring connecting the change-over switch and the second inverter; and a snubber circuit having a capacitor and connected in parallel to the second inverter, wherein the snubber circuit is connected to the first wiring of the first wiring and the second wiring.

[0008] In the disclosed power conversion device, the snubber circuit is connected to the first wiring of the power supply line that connects the first inverter and the selector switch. This clamps the voltage across the capacitor of the snubber circuit to the power supply voltage, thereby suppressing the charging and discharging of the capacitor when the selector switch is open. This improves power conversion efficiency.

[0009] The various aspects disclosed in this specification employ different technical means to achieve their respective objectives. The reference numerals in parentheses in the claims and in this section are intended to exemplify correspondences with the following embodiments and are not intended to limit the technical scope. The objectives, features, and advantages disclosed in this specification will become more apparent by reference to the following detailed description and the accompanying drawings.

[0010] Fig. 1 is a diagram showing a power conversion device and a drive system according to a first embodiment; Fig. 2 is a diagram showing an example of an operating point map of a rotating electric machine; Fig. 3 is a diagram showing star connection drive; Fig. 4 is a diagram showing an open connection drive; Fig. 5 is a diagram showing a reference example; Fig. 6 is a diagram showing a power conversion device according to a second embodiment; Fig. 7 is a diagram showing a power conversion device according to a third embodiment; Fig. 8 is a diagram showing a power conversion device according to a fourth embodiment;

[0011] Hereinafter, several embodiments will be described with reference to the drawings. Note that in each embodiment, corresponding components are designated by the same reference numerals, and redundant description may be omitted. When only a portion of the configuration is described in each embodiment, the configuration of another embodiment previously described may be applied to the remaining portion of the configuration. Furthermore, in addition to the combinations of configurations explicitly stated in the description of each embodiment, configurations of several embodiments may be partially combined together even if not explicitly stated, provided that there is no particular problem with the combination.

[0012] The power conversion device of this embodiment is applied to, for example, a mobile body using a rotating electric machine as a drive source, such as an electric vehicle (BEV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), an aircraft such as an electric vertical take-off and landing aircraft or a drone, a ship, a construction machine, an agricultural machine, etc.

[0013] First Embodiment First, a schematic configuration of a drive system for a moving body will be described with reference to FIG.

[0014] <Drive System for a Moving Body> As shown in FIG. 1 , a drive system 1 for a moving body includes a DC power supply 2 , a rotating electric machine 3 , and a power conversion device 4 .

[0015] The DC power supply 2 may be, for example, a rechargeable secondary battery such as a lithium ion battery, a nickel-metal hydride battery, etc. The DC power supply 2 may also be one that converts AC power into DC power and outputs it.

[0016] The rotating electric machine 3 is a three-phase open-winding type rotating electric machine with an open neutral point. The rotating electric machine 3 has a U-phase winding 3U, a V-phase winding 3V, and a W-phase winding 3W. Hereinafter, the U-phase winding 3U, the V-phase winding 3V, and the W-phase winding 3W may be simply referred to as windings 3U, 3V, and 3W.

[0017] The rotating electric machine 3 functions, for example, as a drive source for a moving body, that is, as an electric motor. If the moving body is a vehicle, the rotating electric machine 3 generates torque for driving drive wheels (not shown). The rotating electric machine 3 is not limited to an electric motor. The rotating electric machine 3 may be a motor generator that functions as both an electric motor and a generator, or may be a generator.

[0018] The power conversion device 4 performs power conversion between the DC power source 2 and the rotating electric machine 3. The drive system 1 is a system of a common power source type in which power is supplied from a common DC power source 2 to two inverters 8 and 9, which will be described later. The drive system 1 may include only one common DC power source 2 as illustrated in FIG. 1 , or may include multiple common DC power sources 2. The drive system 1 may also include a power supply switch (not shown), such as an SMR, between the DC power source 2 and the power conversion device 4. SMR is an abbreviation for System Main Relay. Turning the power supply switch on enables power supply from the DC power source 2 to the rotating electric machine 3, and turning the power supply switch off cuts off the power supply from the DC power source 2 to the rotating electric machine 3.

[0019] 1 shows an example circuit configuration of a power conversion device 4. The power conversion device 4 (power conversion circuit) shown in FIG. 1 includes power lines 5 and 6, a smoothing capacitor 7, inverters 8 and 9, a switch 10, and snubber circuits 11 and 12.

[0020] The power supply line 5 is a high-potential power line. The power supply line 5 is connected to the positive electrode of the DC power supply 2. The power supply line 5 may be referred to as a positive power supply line, a P line, etc. The power supply line 6 is a low-potential power line. The power supply line 6 is connected to the negative electrode of the DC power supply 2. The power supply line 6 may be referred to as a negative power supply line, an N line, etc. The power supply lines 5 and 6 are configured to include bus bars that are, for example, metal plates.

[0021] The power supply line 5 has wirings 51 and 52. The wirings 51 and 52 are part of the wiring that constitutes the power supply line 5. The wiring 51 is a part of the power supply line 5 that connects the inverter 8 and a changeover switch 101 (described later). The wiring 52 is a part of the power supply line 5 that connects the changeover switch 101 and the inverter 9. The wiring 51 corresponds to the first wiring, and the wiring 52 corresponds to the second wiring.

[0022] The smoothing capacitor 7 mainly smoothes the DC voltage supplied from the DC power supply 2. The smoothing capacitor 7 is provided between the power supply lines 5 and 6. The positive electrode of the smoothing capacitor 7 is connected to the power supply line 5 between the DC power supply 2 and the inverters 8 and 9. The negative electrode of the smoothing capacitor 7 is connected to the power supply line 6 between the DC power supply 2 and the inverters 8 and 9. The smoothing capacitor 7 is connected in parallel to the inverters 8 and 9.

[0023] The inverters 8 and 9 are DC-AC conversion circuits. The inverter 8 corresponds to a first inverter, and the inverter 9 corresponds to a second inverter. The inverter 8 is configured with upper and lower arm circuits 8HL for three phases. The upper and lower arm circuits 8HL are sometimes referred to as legs. The upper and lower arm circuit 8HL has an upper arm 8H and a lower arm 8L. The upper arm 8H and the lower arm 8L are connected in series between the power supply lines 5 and 6, with the upper arm 8H on the power supply line 5 side.

[0024] The connection point between the upper arm 8H and the lower arm 8L is connected to the winding of the corresponding phase in the rotating electric machine 3 via an output line 13. The inverter 8 has six arms. Each arm is configured with a switching element. The number of switching elements constituting each arm is not particularly limited. There may be one or more. When there are more than one switching elements, the multiple switching elements connected in parallel to each other are turned on and off at the same timing by a common gate drive signal (drive voltage).

[0025] In the example shown in Fig. 1, an n-channel MOSFET 8S is used as the switching element constituting each arm. MOSFET is an abbreviation for Metal Oxide Semiconductor Field Effect Transistor. In the upper arm 8H, the drain terminal of the MOSFET 8S is connected to the power supply line 5. In the lower arm 8L, the source terminal of the MOSFET 8S is connected to the power supply line 6. The source terminal of the MOSFET 8S in the upper arm 8H and the drain terminal of the MOSFET 8S in the lower arm 8L are connected to each other.

[0026] A freewheeling diode 8D is connected in antiparallel to each MOSFET 8S. The diode 8D may be a parasitic diode (body diode) of the MOSFET 8S or may be provided separately from the parasitic diode. The anode terminal of the diode 8D is connected to the source terminal of the corresponding MOSFET 8S, and the cathode terminal is connected to the drain terminal.

[0027] The inverter 9 has the same configuration as the inverter 8. The inverter 9 is configured with upper and lower arm circuits 9HL for three phases. The upper and lower arm circuits 9HL have an upper arm 9H and a lower arm 9L. The upper arm 9H and the lower arm 9L are connected in series between the power supply lines 5 and 6, with the upper arm 9H on the power supply line 5 side.

[0028] The connection point between the upper arm 9H and the lower arm 9L is connected to the winding of the corresponding phase in the rotating electric machine 3 via an output line 14. The inverter 9 also has six arms. Each arm is configured with a switching element. The number of switching elements constituting each arm is not particularly limited. It may be one or more.

[0029] 1, an n-channel MOSFET 9S is used as the switching element constituting each arm. In the upper arm 9H, the drain terminal of the MOSFET 9S is connected to the power supply line 5. In the lower arm 9L, the source terminal of the MOSFET 9S is connected to the power supply line 6. The source terminal of the MOSFET 9S in the upper arm 9H and the drain terminal of the MOSFET 9S in the lower arm 9L are connected to each other. A freewheeling diode 9D is connected in antiparallel to each MOSFET 9S.

[0030] As described above, the high-potential terminals (drain terminals) of the upper arms 8H, 9H of the inverters 8, 9 are connected to the power supply line 5. The low-potential terminals (source terminals) of the lower arms 8L, 9L are connected to the power supply line 6. A node connecting the upper arm 8H and the lower arm 8L is connected to one end of the corresponding phase winding via an output line 13, and a node connecting the upper arm 9H and the lower arm 9L is connected to the other end of the corresponding phase winding via an output line 14. Specifically, one end of the U-phase winding 3U is connected to a node U1 of the U-phase upper and lower arm circuit 8HL, and the other end of the U-phase winding 3U is connected to a node U2 of the U-phase upper and lower arm circuit 9HL. One end of the V-phase winding 3V is connected to a node V1 of the V-phase upper and lower arm circuit 8HL, and the other end of the V-phase winding 3V is connected to a node V2 of the V-phase upper and lower arm circuit 9HL. One end of the W-phase winding 3W is connected to a node W1 of the W-phase upper and lower arm circuit 8HL, and the other end of the W-phase winding 3W is connected to a node W2 of the W-phase upper and lower arm circuit 9HL.

[0031] The switching elements constituting the inverters 8 and 9 are not limited to the above-described MOSFETs. For example, IGBTs may be used. IGBT is an abbreviation for Insulated Gate Bipolar Transistor. In the case of an IGBT, a freewheeling diode is connected in antiparallel. The types of switching elements constituting the inverters 8 and 9 may be the same or different. For example, one of the inverters 8 and 9 may be composed of a MOSFET and the other of an IGBT. The types (materials) of the semiconductor substrates may be different.

[0032] The switch 10 is provided between the inverter 8 and the inverter 9 on at least one of the power supply lines 5, 6. The switch 10 is provided on the power supply line. When the switch 10 is closed, it connects the high-potential side terminal of the upper arm 9H of the inverter 9 to the smoothing capacitor 7 (DC power supply 2). When the switch 10 is open, it cuts off the connection between the high-potential side terminal of the upper arm 9H and the smoothing capacitor 7 (DC power supply 2).

[0033] The switch 10 includes at least a changeover switch 101. The changeover switch 101 is a semiconductor switch, i.e., a switching element formed on a semiconductor chip. The switching element is not particularly limited. It may have the same configuration as or a different configuration from the switching element constituting at least one of the inverters 8 and 9. The changeover switch 101 illustrated in FIG. 1 is a MOSFET. A wire 51 is connected to the drain terminal of the changeover switch 101 (MOSFET), and a wire 52 is connected to the source terminal. A diode is connected in antiparallel to the MOSFET. The diode is, for example, a parasitic diode. When the changeover switch 101 is turned on and the switch 10 is in a closed state, the high-potential side terminal of the upper arm 9H is electrically connected to the smoothing capacitor 7. When the changeover switch 101 is turned off and the switch 10 is in an open state, the electrical connection between the high-potential side terminal of the upper arm 9H and the smoothing capacitor 7 is interrupted.

[0034] The snubber circuit 11 is connected in parallel to the inverter 9, i.e., the upper and lower arm circuits 9HL. The snubber circuits 11 shown in FIG. 1 are provided collectively for the three-phase upper and lower arm circuits 9HL. The snubber circuits 11 reduce the inductance of the upper and lower arm circuits 9HL. In other words, the snubber circuits 11 absorb transient high voltages, so-called switching surges, that occur when the switching elements (MOSFETs 9S) that make up the upper and lower arm circuits 9HL are switched. This enables the inverter 9 to perform high-speed switching.

[0035] The snubber circuit 11 includes at least a capacitor 11C. The snubber circuit 11 may be, for example, a C snubber circuit including a capacitor, or an RC snubber circuit including a capacitor and a resistor. It may also be an RCD snubber circuit including a capacitor, a resistor, and a diode. The snubber circuit 11 shown in FIG. 1 is an RC snubber circuit in which a capacitor 11C and a resistor 11R are connected in series. One end of the snubber circuit 11 is connected to the power supply line 5. One end of the snubber circuit 11 is connected to a wiring 51 of the power supply line 5. The other end of the snubber circuit 11 is connected to the power supply line 6. The snubber circuit 11 is electrically connected to the smoothing capacitor 7 and the DC power supply 2 without passing through the selector switch 101.

[0036] The snubber circuit 12 is connected in parallel to the inverter 8, i.e., the upper and lower arm circuits 8HL. The snubber circuits 12 shown in FIG. 1 are provided for the three-phase upper and lower arm circuits 8HL together. The snubber circuits 12 reduce the inductance of the upper and lower arm circuits 8HL. This enables the inverter 8 to perform high-speed switching.

[0037] The snubber circuit 12 includes at least a capacitor 12C. The snubber circuit 12 may be, for example, a C snubber circuit, an RC snubber circuit, or an RCD snubber circuit. The snubber circuit 12 shown in FIG. 1 is an RC snubber circuit in which a capacitor 12C and a resistor 12R are connected in series. One end of the snubber circuit 12 is connected to the power supply line 5. The other end of the snubber circuit 12 is connected to the power supply line 6.

[0038] As illustrated in FIG. 1 , the power conversion device 4 may further include a control unit (CTR) 15. The control unit 15 may be configured to include, for example, a processor, a memory, a storage, and the like. The processor executes various processes by accessing the memory. The memory is a rewritable volatile storage medium. The memory is, for example, RAM. RAM is an abbreviation for Random Access Memory. The storage is, for example, a rewritable non-volatile storage medium. The storage stores a program executed by the processor. The program constructs multiple functional units by causing the processor to execute multiple instructions. The processes executed by the control unit 15 may be realized by software processing in which the processor executes the above-mentioned program, or may be realized by hardware processing using a dedicated electronic circuit. They may also be realized by a combination of software processing and hardware processing.

[0039] The control unit 15 may include, for example, a drive command generation unit and a drive circuit unit (not shown). The drive command generation unit controls the inverters 8 and 9. The drive command generation unit generates drive commands (command signals) for controlling the on / off of the MOSFETs 8S and 9S and outputs them to the drive circuit unit. The drive command generation unit generates drive commands based on drive requests for the rotating electric machine 3, such as torque command values ​​input from a higher-level ECU (not shown), and signals detected by various sensors. The various sensors may include current sensors, rotation angle sensors, voltage sensors, and the like (not shown). The current sensors detect phase currents flowing through the windings 3U, 3V, and 3W of each phase. The rotation angle sensors detect the rotation angle of the rotor of the rotating electric machine 3. The voltage sensor detects the voltage across the smoothing capacitor 7.

[0040] The drive command generating unit controls the switch 10. The drive command generating unit generates a drive command for controlling the on / off of the changeover switch 101 that constitutes the switch 10.

[0041] The drive circuit unit is sometimes referred to as a driver. Based on drive commands, the drive circuit unit can independently control the on / off of six MOSFETs 8S, six MOSFETs 9S, and one selector switch 101. For convenience, signal lines for transmitting drive signals from the control unit 15 to each switching element are omitted from FIG. 1.

[0042] <Star Connection Drive and Open Connection Drive> Next, star connection drive and open connection drive will be described with reference to Figures 2, 3, and 4. Figure 2 shows an example of an operating point map of a rotating electric machine, with the horizontal axis representing rotation speed and the vertical axis representing torque. Figure 3 is a diagram showing star connection drive. Figure 4 is a diagram showing open connection drive. For convenience, the control unit 15 is omitted from Figures 3 and 4.

[0043] As shown in Figure 2, the driving range of the rotating electric machine 3 is divided into two ranges depending on the rotation speed and torque. One of the driving ranges is the star connection driving range. The star connection driving range is a normal use range. The other driving range is the open connection driving range. The open connection driving range is a range of higher rotation speeds or higher torques than the star connection driving range.

[0044] When the operating point is in the star connection drive region, the control unit 15 executes star connection drive control. Star connection drive is sometimes referred to as Y drive. The control unit 15 controls the MOSFETs 8S and 9S and the changeover switch 101 so that the windings 3U, 3V, and 3W are in a star connection state. Specifically, as shown in FIG. 3, the switch 10 is opened, i.e., the changeover switch 101 is turned off. The inverter 9 is also neutralized. As shown in FIG. 3, for example, the MOSFETs 9S of the upper arms 9H of all phases may be turned on and the MOSFETs 9S of the lower arms 9L of all phases may be turned off. The MOSFETs 9S of the upper arms 9H of all phases may be turned off and the MOSFETs 9S of the lower arms 9L of all phases may be turned on. The MOSFETs 8S of the inverter 8 are then controlled according to drive requirements, etc.

[0045] FIG. 3 shows one current conduction pattern in star-connection drive. The dashed-dotted arrows in FIG. 3 indicate an example of a current path. FIG. 3 shows the current path when the MOSFET 8S in the U-phase upper arm 8H and the MOSFET 8S in the W-phase lower arm 8L are turned on. In the example shown in FIG. 3, the upper arm 9H of the inverter 9 is turned on and the lower arm 9L is turned off. Current flows in the following order: U-phase upper arm 8H → node U1 → U-phase winding 3U → node U2 → U-phase upper arm 9H → W-phase upper arm 9H → node W2 → W-phase winding 3W → node W1 → W-phase lower arm 8L. In this way, current flows without passing through the changeover switch 101 (switchgear 10).

[0046] When the operating point is in the open connection drive region, the control unit 15 executes open connection drive control. Open connection drive is sometimes referred to as H drive. The control unit 15 closes the switch 10, i.e., turns on the changeover switch 101, and opens the neutral point of the inverter 9. Opening the neutral point forms an open connection circuit of the U-phase upper and lower arm circuits 8HL, 9HL via the U-phase winding 3U. Similarly, an open connection circuit of the V-phase upper and lower arm circuits 8HL, 9HL via the V-phase winding 3V is formed. An open connection circuit of the W-phase upper and lower arm circuits 8HL, 9HL via the W-phase winding 3W is formed. The control unit 15 regards each phase as an independent open connection circuit and controls the applied voltage for each phase.

[0047] Figure 4 shows one current conduction pattern in open connection drive. The two-dot chain arrow in Figure 4 indicates an example of a current path. Figure 4 shows the current path when MOSFET 8S in W-phase lower arm 8L and MOSFET 9S in W-phase upper arm 9H are turned on. Current flows in the following order: changeover switch 101 → W-phase upper arm 9H → node W2 → W-phase winding 3W → node W1 → W-phase lower arm 8L. In this way, current flows via changeover switch 101 (switchgear 10).

[0048] As described above, the inverters 8 and 9 can switch between star connection drive and open connection drive. By performing open connection drive instead of star connection drive, it is possible to output a higher rotation speed range or a higher torque range.

[0049] Summary of First Embodiment Figures 5 and 6 show a reference example of a power conversion device. Figure 5 shows an example of a current conduction pattern when star-connected driving is performed in the reference example. Figure 6 shows a current conduction pattern with different timing from that in Figure 5 when star-connected driving is performed. In the reference example, the reference symbols of related elements shown in this embodiment are indicated by adding r to the end of their reference symbols.

[0050] The control unit performs star connection drive while switching between multiple current conduction patterns. The control unit performs star connection drive using, for example, a PWM control method. PWM is an abbreviation for Pulse Width Modulation. The multiple current conduction patterns include the zero vector current conduction patterns shown in FIGS. 5 and 6. The current conduction pattern shown in FIG. 5 is a zero vector pattern in which all upper arms 8Hr of the inverter 8r are turned on and all lower arms 8Lr are turned off. The current conduction pattern shown in FIG. 6 is a zero vector pattern in which all lower arms 8Lr of the inverter 8r are turned on and all upper arms 8Hr are turned off.

[0051] As shown in Figures 5 and 6, in a power conversion device 4r of the reference example, a snubber circuit 11r connected in parallel to an inverter 9r is connected to a wiring 52r of a power supply line 5r that connects a changeover switch 101r and the inverter 9r. One end of the snubber circuit 11r is connected to the wiring 52r of the power supply line 5r, and the other end is connected to a power supply line 6r. For convenience, Figures 5 and 6 omit the smoothing capacitor and the snubber circuit connected in parallel to the inverter 8r. The rest of the configuration is the same as that of the power conversion device 4 of the present embodiment.

[0052] In the examples shown in Figures 5 and 6, all three-phase upper arms 9Hr of inverter 9r are turned on to neutralize inverter 9r. In this state, as shown in Figure 5, when all three-phase upper arms 8Hr of inverter 8r are turned on, the voltage across capacitor 11Cr becomes approximately equal to the supply voltage of DC power supply 2r, i.e., power supply voltage Vdc. Furthermore, as shown in Figure 6, when all three-phase lower arms 8Lr of inverter 8r are turned on, the voltage across capacitor 11Cr becomes approximately 0 V (zero volts).

[0053] As described above, star connection driving is performed while switching between multiple current patterns, so the voltage across the capacitor 11Cr of the snubber circuit 11r fluctuates during star connection driving. The voltage across the capacitor 11Cr fluctuates within a range from 0 V to Vdc. As such, the capacitor 11Cr is charged and discharged during star connection driving, resulting in a low power conversion efficiency. The resistor 11Rr of the snubber circuit 11r consumes the energy stored in the capacitor 11Cr and generates heat. This heat affects the capacitor 11Cr.

[0054] In the power conversion device 4 of this embodiment, the snubber circuit 11 connected in parallel to the inverter 9 is connected to the wiring 51 (first wiring) connecting the inverter 8 and the changeover switch 101, rather than to the wiring 52 (second wiring). This causes the voltage across the capacitor 11C of the snubber circuit 11 to be clamped to the power supply voltage of the DC power supply 2 (the voltage across the smoothing capacitor 7). Therefore, when the changeover switch 101 is off (open state), that is, when the star connection is in operation, the charging and discharging operation of the capacitor 11C can be suppressed. This improves the power conversion efficiency.

[0055] As illustrated, a changeover switch 101 may be provided on the power supply line 5 electrically connected to the positive electrode of the DC power supply 2. During star connection driving, the changeover switch 101 is turned off. That is, the switch 10 is in an open state. The changeover switch 101 cuts off the connection between the DC power supply 2 (smoothing capacitor 7) and the inverter 9. During open connection driving, the changeover switch 101 is turned on. That is, the switch 10 is in a closed state. The changeover switch 101 connects the DC power supply 2 (smoothing capacitor 7) and the inverter 9.

[0056] In the present embodiment, an example has been shown in which the power conversion device 4 includes the snubber circuit 12, but the present invention is not limited to this. A configuration without the snubber circuit 12 may also be used.

[0057] Second Embodiment This embodiment is a modification of the preceding embodiment, and the description of the preceding embodiment can be used. In the preceding embodiment, one changeover switch 101 and one snubber circuit 11 are provided for each of the three-phase upper and lower arm circuits 9HL that constitute the inverter 9. Alternatively, a changeover switch 101 and a snubber circuit 11 may be provided for each of the upper and lower arm circuits 9HL.

[0058] FIG. 7 shows a power conversion device 4 and a drive system 1 according to this embodiment. In the power conversion device 4, a changeover switch 101 and a snubber circuit 11 are provided for each phase of the upper and lower arm circuits 9HL. The switchgear 10 has three changeover switches 101. The drain terminal of each changeover switch 101 is connected to a wiring 51, and the source terminal is connected to a wiring 52. One of the changeover switches 101 is connected in series to the upper and lower arm circuits 9HL of the U phase. The other changeover switch 101 is connected in series to the upper and lower arm circuits 9HL of the V phase. The other changeover switch 101 is connected in series to the upper and lower arm circuits 9HL of the W phase. The source terminals of the three changeover switches 101 are electrically connected to each other by the wiring 52. The source terminals of the three changeover switches 101 are commonly connected.

[0059] The power conversion device 4 includes three snubber circuits 11 in addition to the three changeover switches 101 described above. One end of each snubber circuit 11 is connected to the wiring 51, and the other end is connected to the power supply line 6. Each snubber circuit 11 includes a capacitor 11C and a resistor 11R. One of the snubber circuits 11 is connected in parallel to the U-phase upper and lower arm circuit 9HL. The other snubber circuit 11 is connected in parallel to the V-phase upper and lower arm circuit 9HL. The other snubber circuit 11 is connected in parallel to the W-phase upper and lower arm circuit 9HL.

[0060] As shown in FIG. 7 , the power conversion device 4 may include three snubber circuits 12. One end of each snubber circuit 12 is connected to the power supply line 5, and the other end is connected to the power supply line 6. Each snubber circuit 12 includes a capacitor 12C and a resistor 12R. One of the snubber circuits 12 is connected in parallel to the U-phase upper and lower arm circuit 8HL. The other snubber circuit 12 is connected in parallel to the V-phase upper and lower arm circuit 8HL. The other snubber circuit 12 is connected in parallel to the W-phase upper and lower arm circuit 8HL. The other configuration is the same as that of the power conversion device 4 shown in the preceding embodiment.

[0061] Summary of Second Embodiment As illustrated, the changeover switch 101 and the snubber circuit 11 may be provided for each phase of the upper and lower arm circuits 9HL that constitute the inverter 9. This makes it possible to reduce the area of ​​the current loop formed by the upper and lower arm circuits 9HL and the snubber circuit 11 compared to a configuration in which a single changeover switch 101 and snubber circuit 11 are provided common to three phases. This reduces the wiring inductance of the upper and lower arm circuits 9HL, thereby improving power conversion efficiency.

[0062] The total chip area of ​​the three changeover switches 101 can be made smaller than the chip area of ​​a single changeover switch 101 common to the three phases shown in the preceding embodiment. Also, the total capacitance of the capacitors 11C of the three snubber circuits 11 can be made smaller than the capacitance of a single capacitor 11C common to the three phases. Therefore, the size of the power conversion device 4 can be reduced.

[0063] As shown in the example, the source terminals (low potential side terminals) of the changeover switches 101 provided for each phase may be electrically connected to each other. This allows, for example, if one of the changeover switches 101 fails, the other changeover switches 101 to be used in place. Note that the source terminals of the changeover switches 101 provided for each phase may not be electrically connected to each other. In other words, the source terminal of the changeover switch 101 may be electrically connected only to the upper and lower arm circuits 9HL of the corresponding phase.

[0064] In the present embodiment, an example has been shown in which the power conversion device 4 includes the snubber circuit 12, but the present invention is not limited to this. A configuration without the snubber circuit 12 may also be used.

[0065] Third Embodiment This embodiment is a modification of the preceding embodiment, and the description of the preceding embodiment can be used. In the preceding embodiment, the changeover switch 101 and the snubber circuit 11 are provided for each phase of the upper and lower arm circuits 9HL. Alternatively, the changeover switch 101 may be provided for each phase of the upper and lower arm circuits 9HL, and the snubber circuit 11 may be commonly disposed for the three-phase upper and lower arm circuits 9HL.

[0066] Fig. 8 shows the power conversion device 4 and the drive system 1 according to this embodiment. In the example shown in Fig. 8, a changeover switch 101 is provided for each phase of the upper and lower arm circuits 9HL. That is, the switchgear 10 has three changeover switches 101. The source terminals of the three changeover switches 101 are electrically connected to one another by wiring 52. The source terminals of the three changeover switches 101 are commonly connected.

[0067] The snubber circuit 11 has a capacitor 11C and a resistor 11R, as in the previous embodiment. One end of the snubber circuit 11 is connected to the wiring 51, and the other end is connected to the power line 6. The power conversion device 4 has a single snubber circuit 11 common to the three-phase upper and lower arm circuits 9HL. The power conversion device 4 has a single snubber circuit 12 common to the three-phase upper and lower arm circuits 8HL. The other configurations are the same as those of the power conversion device 4 shown in the previous embodiment.

[0068] Summary of Third Embodiment As illustrated, the changeover switch 101 may be provided for each phase of the upper and lower arm circuits 9HL, and the snubber circuit 11 may be commonly disposed for the upper and lower arm circuits 9HL of each phase. Even with this configuration, the voltage across the capacitor 11C of the snubber circuit 11 is clamped to the power supply voltage of the DC power supply 2 (the voltage across the smoothing capacitor 7) in star-connected drive. Therefore, the same effect as in the configurations shown in the preceding embodiments, that is, improved power conversion efficiency, can be achieved.

[0069] As shown in the example, the source terminals (low potential side terminals) of the changeover switches 101 provided for each phase may be electrically connected to each other. This allows, for example, if one of the changeover switches 101 fails, the other changeover switches 101 to be used in place. Note that the source terminals of the changeover switches 101 provided for each phase may not be electrically connected to each other. In other words, the source terminal of the changeover switch 101 may be electrically connected only to the upper and lower arm circuits 9HL of the corresponding phase.

[0070] In the present embodiment, an example has been shown in which the power conversion device 4 includes the snubber circuit 12, but the present invention is not limited to this. A configuration without the snubber circuit 12 may also be used.

[0071] Fourth Embodiment This embodiment is a modification of the preceding embodiment, and the description of the preceding embodiment can be used. In the preceding embodiment, the changeover switch 101 is provided on the power supply line 5. Alternatively, or instead of this, the changeover switch 101 may be provided on the power supply line 6.

[0072] 9 shows a power conversion device 4 and a drive system 1 according to this embodiment. In the power conversion device 4, a switch 10 has a changeover switch 101 provided on a power supply line 6. The power supply line 6 has a wire 61 connecting the inverter 8 and the changeover switch 101, and a wire 62 connecting the changeover switch 101 and the inverter 9. The wire 61 corresponds to the first wire, and the wire 62 corresponds to the second wire.

[0073] The changeover switch 101 has a MOSFET and a diode, as in the preceding embodiment. The source terminal of the changeover switch 101 is connected to a wiring 61, and the drain terminal is connected to a wiring 62. The lower arm 9L (source terminal) of the upper and lower arm circuit 9HL of each phase is connected to the wiring 62. One end of the snubber circuit 11 is connected to the power supply line 5, and the other end is connected to the wiring 61. The other configuration is the same as that of the power conversion device 4 (see FIG. 1) shown in the preceding embodiment.

[0074] Summary of Fourth Embodiment As illustrated, a changeover switch 101 may be provided on the power supply line 6 electrically connected to the negative electrode of the DC power supply 2. During star connection driving, the changeover switch 101 is turned off. That is, the switch 10 is in an open state. The changeover switch 101 cuts off the connection between the DC power supply 2 (smoothing capacitor 7) and the inverter 9. During open connection driving, the changeover switch 101 is turned on. That is, the switch 10 is in a closed state. The changeover switch 101 connects the DC power supply 2 (smoothing capacitor 7) and the inverter 9. In addition, the snubber circuit 11 connected in parallel to the inverter 9 is connected to the wiring 61 (first wiring) connecting the inverter 8 and the changeover switch 101, rather than the wiring 62 (second wiring). As a result, the voltage across the capacitor 11C of the snubber circuit 11 is clamped to the power supply voltage of the DC power supply 2 (the voltage across the smoothing capacitor 7). Therefore, when the changeover switch 101 is turned off (open state), that is, when the star connection is in operation, the charging and discharging operation of the capacitor 11C is suppressed, and the power conversion efficiency can be improved.

[0075] In the present embodiment, an example has been shown in which the power conversion device 4 includes the snubber circuit 12, but the present invention is not limited to this. A configuration without the snubber circuit 12 may also be used.

[0076] The configuration of the switch 10 including the changeover switch 101 and the snubber circuit 11 is not limited to the example shown in Fig. 9. A configuration similar to the configurations shown in the second and third embodiments realized in the power supply line 5 may be realized in the power supply line 6.

[0077] Although an example has been shown in which the switch 10 having the changeover switch 101 is provided only on the power supply line 6, the present invention is not limited to this. The configuration shown in this embodiment and the configuration shown in the preceding embodiment may be combined. That is, the switch 10 may have a changeover switch 101 provided on the power supply line 5 and a changeover switch 101 provided on the power supply line 6. In this configuration, one end of the snubber circuit 11 may be connected to the wiring 51, and the other end may be connected to the wiring 61.

[0078] (Other Embodiments) The disclosure in this specification and drawings, etc. is not limited to the exemplified embodiments. The disclosure encompasses the exemplified embodiments and modifications thereto by those skilled in the art. For example, the disclosure is not limited to the combinations of parts and / or elements shown in the embodiments. The disclosure can be implemented in various combinations. The disclosure can have additional parts that can be added to the embodiments. The disclosure encompasses the omission of parts and / or elements from the embodiments. The disclosure encompasses the substitution or combination of parts and / or elements between one embodiment and another embodiment. The disclosed technical scope is not limited to the description of the embodiments. Some disclosed technical scopes are defined by the claims, and should be interpreted as including all modifications within the meaning and scope equivalent to the claims.

[0079] The disclosure in the specification, drawings, etc. is not limited by the claims. The disclosure in the specification, drawings, etc. encompasses the technical ideas described in the claims, and extends to more diverse and broader technical ideas than the technical ideas described in the claims. Therefore, various technical ideas can be extracted from the disclosure in the specification, drawings, etc. without being bound by the claims.

[0080] When an element or layer is referred to as being "on," "coupled," "connected," or "bonded," it may be directly coupled, connected, or bonded to another element or layer, and intervening elements or layers may be present. In contrast, when an element is referred to as being "directly on," "directly coupled," "directly connected," or "directly bonded" to another element or layer, no intervening elements or layers are present. Other terms used to describe relationships between elements should be construed in a similar manner (e.g., "between" vs. "directly between," "adjacent" vs. "directly adjacent," etc.). As used in this specification, the term "and / or" includes any and all combinations of one or more of the associated listed items. That is, a reference to A and / or B means at least one of A and B, and can include A only, B only, or both A and B.

[0081] Spatially relative terms such as "inside," "outside," "back," "below," "low," "top," "top," and the like are used herein to facilitate the description of one element or feature's relationship to other elements or features, as illustrated. Spatially relative terms may be intended to encompass different orientations of the device during use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures were turned over, elements described as "below" or "directly below" other elements or features would then be oriented "above" the other elements or features. Thus, the term "bottom" can encompass both an orientation of top and bottom. The device may also be oriented in other ways (rotated 90 degrees or at other orientations), and the spatially relative descriptors used in this specification would be interpreted accordingly.

[0082] (Disclosure of Technical Ideas) This specification discloses multiple technical ideas described in the following multiple clauses. Some clauses may be described in a multiple dependent form, with the subsequent clause alternatively referring to the preceding clause. Furthermore, some clauses may be described in a multiple dependent form, with the subsequent clause referring to another multiple dependent clause. These multiple dependent clauses define multiple technical ideas.

[0083] <Technical Idea 1> A power conversion device comprising: a first inverter (8) connected to one end of a winding of a rotating electric machine (3); a second inverter (9) connected to the other end of the winding; a switch (10) arranged between a DC power source (2) and the second inverter, the switch having a change-over switch (101) that connects the DC power source and the second inverter in a closed state and cuts off the connection between the DC power source and the second inverter in an open state; wiring constituting a power supply line (5, 6) electrically connected to the DC power source, the first wiring (51, 61) connecting the first inverter and the change-over switch and a second wiring (52, 62) connecting the change-over switch and the second inverter; and a snubber circuit (11) having a capacitor (11C) and connected in parallel to the second inverter, wherein the snubber circuit is connected to the first wiring of the first wiring and the second wiring.

[0084] <Technical Concept 2> The power conversion device according to Technical Concept 1, wherein the second inverter has a three-phase upper and lower arm circuit (9HL), and the changeover switch and the snubber circuit are provided for each phase of the upper and lower arm circuit.

[0085] <Technical Idea 3> The power conversion device according to Technical Idea 1, wherein the second inverter has three-phase upper and lower arm circuits (9HL), the changeover switch is provided for each phase with respect to the upper and lower arm circuits, and the snubber circuit is commonly disposed for the upper and lower arm circuits of each phase.

[0086] <Technical Concept 4> The power conversion device according to Technical Concept 2 or 3, wherein the low-potential side terminals of the changeover switches provided for each phase are electrically connected to each other.

[0087] <Technical Concept 5> The power conversion device according to any one of Technical Concepts 1 to 4, wherein the power supply line includes a positive power supply line electrically connected to a positive electrode of the DC power supply.

[0088] <Technical Concept 6> The power conversion device according to any one of Technical Concepts 1 to 5, wherein the power supply line includes a negative power supply line electrically connected to a negative electrode of the DC power supply.

Claims

1. A first inverter (8) connected to one end of the winding of a rotating electrical machine (3), a second inverter (9) connected to the other end of the winding, a switch (101) disposed between a DC power source (2) and the second inverter, which connects the DC power source and the second inverter in a closed state and disconnects the connection between the DC power source and the second inverter in an open state, and a switchgear (10) having the switch; wirings constituting power lines (5, 6) electrically connected to the DC power source, including a first wiring (51, 61) connecting the first inverter and the switch, and a second wiring (52, 62) connecting the switch and the second inverter; and a snubber circuit (11) having a capacitor (11C) and connected in parallel to the second inverter. The snubber circuit is a power conversion device connected to the first wiring among the first wiring and the second wiring.

2. The second inverter has three-phase upper and lower arm circuits (9HL), and the switch and the snubber circuit are provided for each phase with respect to the upper and lower arm circuits. The power conversion device according to claim 1.

3. The second inverter has three-phase upper and lower arm circuits (9HL), the switch is provided for each phase with respect to the upper and lower arm circuits, and the snubber circuit is commonly arranged for the upper and lower arm circuits of each phase. The power conversion device according to claim 1.

4. Terminals on the low-potential side of the switches provided for each phase are electrically connected to each other. The power conversion device according to claim 2 or 3.

5. The power line includes a positive-pole side power line electrically connected to the positive pole of the DC power source. The power conversion device according to any one of claims 1 to 3.

6. The power line includes a negative-pole side power line electrically connected to the negative pole of the DC power source. The power conversion device according to any one of claims 1 to 3.

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