Power conversion device, drive system, control device, and control program

Abstract

In steps (S110-S113) of rotation control processing, a control unit controls a first inverter and a second inverter in a star mode so as to drive a rotary electric machine by star driving in which the second inverter is neutralized. In steps (S114-S117), the control unit controls the first inverter and the second inverter in an open mode so as to drive the rotary electric machine by open driving in which the second inverter is not neutralized. In steps (S103-S106), the control unit controls the first inverter and the second inverter in a boost mode so as to drive the rotary electric machine by star driving and increase a zero-phase current flowing through a second capacitor as compared with the star mode.

Description

Power conversion device, drive system, control device, and control program CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based on Patent Application No. 2024-071969 filed in Japan on April 25, 2024, and the contents of the original application are incorporated by reference in their entirety.

[0002] The disclosure in this specification relates to a power conversion device, a drive system, a control device, and a control program.

[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 and a second inverter connected to the other end of the winding. The power conversion device also includes a first capacitor connected in parallel to the first inverter and a second capacitor connected in parallel to the second inverter. The power conversion device is capable of star drive or open drive of the rotating electric machine. The contents of the prior art documents are incorporated by reference as explanations of the technical elements in this specification.

[0004] Japanese Patent Application Laid-Open No. 2021-125922

[0005] However, in the above-mentioned Patent Document 1, there is a concern that when the drive of the rotating electric machine is switched from star drive to open drive, an inrush current may flow into the second capacitor, etc., due to a voltage increase in the second capacitor. In this case, the inrush current may cause an abnormality in the power conversion device. In terms of the above and other aspects not mentioned, further improvements are required in power conversion devices, drive systems, control devices, and control programs.

[0006] One disclosed object is to provide a power conversion device, a drive system, a control device, and a control program that can suppress the occurrence of abnormalities in the power conversion device.

[0007] One aspect of the disclosure is a power conversion device that converts power supplied from a power supply unit to a rotating electric machine, the power conversion device comprising: a first inverter connected to one end of a winding of the rotating electric machine; a second inverter connected to the other end of the winding; a first capacitor connected in parallel to the first inverter; a second capacitor connected in parallel to the second inverter; a star control unit that controls the first inverter and the second inverter in star mode so as to drive the rotating electric machine by star drive with the second inverter as a neutral point; an open control unit that controls the first inverter and the second inverter in open mode so as to drive the rotating electric machine by open drive with the second inverter not as a neutral point; and a boost control unit that controls the first inverter and the second inverter in boost mode so as to drive the rotating electric machine and so that zero-phase current flows in the windings.

[0008] According to the above power conversion device, in the boost mode, the rotating electric machine is driven so that the zero-phase current flowing through the second capacitor is larger than in the star mode. In this configuration, the second capacitor is charged by the zero-phase current, so the voltage of the second capacitor in the boost mode is more likely to rise than the voltage of the second capacitor in the star mode. Therefore, by switching the control mode of the power conversion device from the star mode to the open mode via the boost mode, the voltage rise of the second capacitor can be mitigated. This makes it possible to suppress inrush currents from flowing through the second capacitor, etc. This makes it possible to suppress abnormalities in the power conversion device caused by inrush currents.

[0009] One aspect of the disclosure is a drive system that includes: a rotating electric machine; and a power conversion device that converts power supplied to the rotating electric machine from a power supply unit, and drives the rotating electric machine using the power conversion device, the drive system including: a first inverter connected to one end of a winding of the rotating electric machine; a second inverter connected to the other end of the winding; a first capacitor connected in parallel to the first inverter; a second capacitor connected in parallel to the second inverter; a star control unit that controls the first inverter and the second inverter in star mode so as to drive the rotating electric machine by star drive with the second inverter at the neutral point; an open control unit that controls the first inverter and the second inverter in open mode so as to drive the rotating electric machine by open drive with the second inverter not at the neutral point; and a boost control unit that controls the first inverter and the second inverter in boost mode so as to drive the rotating electric machine and so that a zero-phase current flows in the windings.

[0010] According to the drive system, similar to the power conversion device, it is possible to prevent an abnormality from occurring in the power conversion device due to an inrush current.

[0011] One aspect of the disclosure is a control device that controls a power conversion device that converts power supplied from a power supply unit to a rotating electric machine, the 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 first capacitor connected in parallel to the first inverter; and a second capacitor connected in parallel to the second inverter, the control device comprising: a star control unit that controls the first inverter and the second inverter in star mode so as to drive the rotating electric machine by star drive with the second inverter at the neutral point; an open control unit that controls the first inverter and the second inverter in open mode so as to drive the rotating electric machine by open drive with the second inverter not at the neutral point; and a boost control unit that controls the first inverter and the second inverter in boost mode so as to drive the rotating electric machine and so that zero-phase current flows in the winding.

[0012] According to the control device, similarly to the power conversion device, it is possible to prevent an abnormality from occurring in the power conversion device due to an inrush current.

[0013] One aspect of the disclosure is a control program for controlling a power conversion device that converts power supplied from a power supply unit to a rotating electric machine, the 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 first capacitor connected in parallel to the first inverter; and a second capacitor connected in parallel to the second inverter, the control program causing at least one processing unit to: control the first inverter and the second inverter in star mode so as to drive the rotating electric machine by star drive with the second inverter at the neutral point; control the first inverter and the second inverter in open mode so as to drive the rotating electric machine by open drive with the second inverter not at the neutral point; and control the first inverter and the second inverter in boost mode so as to drive the rotating electric machine and so that zero-phase current flows in the winding.

[0014] According to the control program, similar to the power conversion device, it is possible to prevent an abnormality from occurring in the power conversion device due to an inrush current.

[0015] 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.

[0016] 1 is a diagram illustrating a power conversion circuit and a drive system. FIG. 2 is a diagram illustrating an example of an operating point map of a rotating electric machine. FIG. 3 is a diagram illustrating star drive. FIG. 4 is a diagram illustrating open drive. FIG. 5 is a diagram illustrating boost drive in the bottom-on state. FIG. 6 is a diagram illustrating boost drive in the top-on state. A flowchart illustrating the procedure of a rotation control process. A flowchart illustrating the procedure of a boost drive process. A timing chart illustrating how a capacitor current changes. A flowchart illustrating the procedure of a boost drive process according to a second embodiment. A diagram illustrating star drive in the top-on state. FIG. 2 is a diagram illustrating a power conversion circuit and a drive system according to a second embodiment. A flowchart illustrating the procedure of a rotation control process.

[0017] 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.

[0018] The power conversion module of this embodiment is applied to, for example, a mobile object powered by a rotating electric machine, 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, or an agricultural machine.

[0019] First Embodiment First, a schematic configuration of a drive system for a moving body will be described with reference to FIG.

[0020] <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 circuit 4 .

[0021] The DC power supply 2 may be, for example, a rechargeable secondary battery such as a lithium ion battery or a nickel-metal hydride battery. The DC power supply 2 may also be one that converts AC power to DC and outputs it. The DC power supply 2 supplies power to the rotating electrical machine 3. The DC power supply 2 corresponds to a power supply unit.

[0022] 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.

[0023] 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. The rotating electric machine 3 is sometimes referred to as a motor.

[0024] The power conversion circuit 4 converts power between the DC power source 2 and the rotating electric machine 3. The power conversion circuit 4 corresponds to a power conversion device. The power conversion circuit 4 is a three-phase power conversion device. The drive system 1 is a system of a common power source type in which a common DC power source 2 supplies power to two inverters 8 and 9 (described later) to drive the rotating electric machine 3. 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 include a power supply switch (not shown), such as an SMR, between the DC power source 2 and the power conversion circuit 4. SMR is an abbreviation for System Main Relay. Turning on the power supply switch enables power supply from the DC power source 2 to the rotating electric machine 3, and turning off the power supply switch cuts off the power supply from the DC power source 2 to the rotating electric machine 3.

[0025] <Power Conversion Circuit> Next, the power conversion circuit 4 will be described with reference to Fig. 1. Fig. 1 shows an example of the power conversion circuit 4. The power conversion circuit 4 illustrated in Fig. 1 includes power supply lines 5 and 6, smoothing capacitors 71 and 72, inverters 8 and 9, switches 10P and 10N, and snubber circuits 11 and 12.

[0026] 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. In the DC power supply 2, the positive electrode is sometimes referred to as the high-potential side. The power supply line 5 is a current path through which current flows. The power supply line 5 is sometimes referred to as a P line. The power supply line 5 has wiring 5A. The wiring 5A is a part of the wiring that makes up the power supply line 5. The wiring 5A is a part of the power supply line 5 that connects the inverter 8 and the inverter 9.

[0027] The power supply line 6 is a low-potential side power line. The power supply line 6 is connected to the negative electrode of the DC power supply 2. In the DC power supply 2, the negative electrode is sometimes referred to as the low-potential side. The power supply line 6 is a current path through which current flows. The power supply line 6 is sometimes referred to as an N-line. The power supply line 6 has wiring 6A. The wiring 6A is a part of the wiring that makes up the power supply line 6. The wiring 6A is a part of the power supply line 6 that connects the inverter 8 and the inverter 9. The power supply lines 5 and 6 are configured to include a bus bar that is, for example, a metal plate material.

[0028] The smoothing capacitors 71 and 72 mainly smooth the DC voltage supplied from the DC power supply 2. The smoothing capacitors 71 and 72 are provided between the power supply lines 5 and 6. The positive electrodes of the smoothing capacitors 71 and 72 are connected to the power supply line 5 and the negative electrodes are connected to the power supply line 6. The smoothing capacitor 71 is connected in parallel to the inverter 8. The smoothing capacitor 71 corresponds to the first capacitor. The smoothing capacitor 71 may be referred to as the first smoothing capacitor. For example, the smoothing capacitor 71 is connected to the power supply lines 5 and 6 at a position opposite the inverter 9 with the inverter 8 therebetween. The smoothing capacitor 72 is connected in parallel to the inverter 9. The smoothing capacitor 72 corresponds to the second capacitor. The smoothing capacitor 72 may be referred to as the second smoothing capacitor. For example, the smoothing capacitor 72 is connected to the power supply lines 5 and 6 at a position opposite the inverter 8 with the inverter 9 therebetween.

[0029] The inverters 8 and 9 are DC-AC conversion circuits. The inverters 8 and 9 are three-phase inverter circuits. The inverter 8 corresponds to the first inverter, and the inverter 9 corresponds to the 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.

[0030] 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).

[0031] In the example shown in FIG. 1 , arm switches 8HS and 8LS are used as switching elements constituting each arm. The arm switches 8HS and 8LS are, for example, n-channel MOSFETs. MOSFET is an abbreviation for Metal Oxide Semiconductor Field Effect Transistor. The upper arm switch 8HS is a switching element of the upper arm 8H. The upper arm switch 8HS is electrically connected to the high-potential side of the DC power supply 2. The upper arm switch 8HS is sometimes referred to as a first upper switch. In the upper arm 8H, the drain terminal of the upper arm switch 8HS is connected to the power line 5.

[0032] The lower arm switch 8LS is a switching element of the lower arm 8L. The lower arm switch 8LS is electrically connected to the low potential side of the DC power supply 2. The lower arm switch 8LS is sometimes referred to as a first lower switch. In the lower arm 8L, the source terminal of the lower arm switch 8LS is connected to the power supply line 6. The source terminal of the upper arm switch 8HS in the upper arm 8H and the drain terminal of the lower arm switch 8LS in the lower arm 8L are connected to each other.

[0033] A freewheeling diode 8HD is connected in anti-parallel to the upper arm switch 8HS. A freewheeling diode 8LD is connected in anti-parallel to the lower arm switch 8LS. The diodes 8HD and 8LD may be parasitic diodes (body diodes) of the arm switches 8HS and 8LS, or may be provided separately from the parasitic diodes. The anode terminals of the diodes 8HD and 8LD are connected to the source terminals of the corresponding arm switches 8HS and 8LS, and the cathode terminals are connected to the drain terminals.

[0034] 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.

[0035] 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.

[0036] In the example shown in FIG. 1 , arm switches 9HS and 9LS are used as the switching elements constituting each arm. The arm switches 9HS and 9LS are, for example, n-channel MOSFETs. The upper arm switch 9HS is the switching element of the upper arm 9H. The upper arm switch 9HS is electrically connected to the positive electrode, which is the high-potential side of the DC power supply 2. The upper arm switch 9HS corresponds to the upper arm switch. The upper arm switch 9HS is sometimes referred to as a second upper switch. In the upper arm 9H, the drain terminal of the upper arm switch 9HS is connected to the power supply line 5.

[0037] The lower arm switch 9LS is a switching element of the lower arm 9L. The lower arm switch 9LS is electrically connected to the negative electrode, which is the low potential side, of the DC power supply 2. The lower arm switch 9LS corresponds to the lower arm switch. The lower arm switch 9LS is sometimes referred to as a second lower switch. In the lower arm 9L, the source terminal of the lower arm switch 9LS is connected to the power supply line 6. The source terminals of the arm switches 9HS, 9LS in the upper arm 9H and the drain terminals of the arm switches 9HS, 9LS in the lower arm 9L are connected to each other.

[0038] A freewheeling diode 9HD is connected in anti-parallel to the upper arm switch 9HS. A freewheeling diode 9LD is connected in anti-parallel to the lower arm switch 9LS. The diodes 9HD and 9LD may be parasitic diodes (body diodes) of the arm switches 9HS and 9LS, or may be provided separately from the parasitic diodes. The anode terminals of the diodes 9HD and 9LD are connected to the source terminals of the corresponding arm switches 9HS and 9LS, and the cathode terminals are connected to the drain terminals.

[0039] As described above, the high-potential terminals (drain terminals) of the upper arms 8H and 9H are connected to the power supply line 5. The low-potential terminals (source terminals) of the lower arms 8L and 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.

[0040] The switching elements constituting the inverters 8 and 9 are not limited to the MOSFETs described above. 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 also connected in anti-parallel.

[0041] The switch 10P is provided on the power supply line 5 between the inverter 8 and the inverter 9. For example, the switch 10P is provided on the wiring 5A. The power supply line 5 is a path connecting the high-potential side of the DC power supply 2 and the smoothing capacitor 72. The power supply line 5 corresponds to the high-voltage power supply path. The switch 10P can be switched between a closed state and an open state. When the switch 10P is in the closed state, it can pass current from the DC power supply 2 and the smoothing capacitor 71 to the inverter 9 and the smoothing capacitor 72. When the switch 10P is in the open state, it cuts off current from the DC power supply 2 and the smoothing capacitor 71 to the inverter 9 and the smoothing capacitor 72. On the other hand, when the switch 10P is in the open state, it can pass current from the smoothing capacitor 72 to the DC power supply 2 and the smoothing capacitor 71. The switch 10P corresponds to a high-voltage switch.

[0042] The switch 10P has a changeover switch 10PS and a diode 10PD. The changeover switch 10PS is, for example, a semiconductor switch. The semiconductor switch is formed by forming a switching element on a semiconductor chip. The switching element is, for example, a MOSFET or an IGBT. The diode 10PD is connected in parallel to the changeover switch 10PS. The diode 10PD is oriented to block current from the inverter 8 to the inverter 9 and to allow current to flow from the inverter 9 to the inverter 8. The diode 10PD may be a parasitic diode of the changeover switch 10PS or may be a diode provided separately from the parasitic diode. Note that the diode 10PD may be any rectifying element.

[0043] The switch 10P is opened and closed in response to the driving of the changeover switch 10PS. When the changeover switch 10PS is turned on, the switch 10P transitions to a closed state. When the changeover switch 10PS is turned off, the switch 10P transitions to an open state. When the switch 10P is in an open state, the changeover switch 10PS cuts off current from the DC power supply 2 and the smoothing capacitor 71 to the smoothing capacitor 72 and the inverter 9. In this case, the diode 10PD allows current to flow from the smoothing capacitor 72 to the DC power supply 2 and the smoothing capacitor 71.

[0044] The switch 10N is provided on the power supply line 6 between the inverter 8 and the inverter 9. For example, the switch 10N is provided on the wiring 6A. The power supply line 6 is a path connecting the low potential side of the DC power supply 2 and the smoothing capacitor 72. The power supply line 6 corresponds to the low power supply path. The switch 10N can be switched between a closed state and an open state. When the switch 10N is in the closed state, it is possible for a current to flow from the smoothing capacitor 72 to the DC power supply 2 or the smoothing capacitor 71. When the switch 10N is in the open state, it cuts off the current from the smoothing capacitor 72 to the DC power supply 2 or the smoothing capacitor 71. On the other hand, when the switch 10N is in the open state, it is possible for a current to flow from the DC power supply 2 or the smoothing capacitor 71 to the smoothing capacitor 72. The switch 10N corresponds to the low voltage switch.

[0045] The switch 10N has a changeover switch 10NS and a diode 10ND. The changeover switch 10NS is, for example, a semiconductor switch. The changeover switch 10NS is formed in the same manner as the changeover switch 10PS. The diode 10ND is connected in parallel to the changeover switch 10NS. The diode 10ND is oriented to block current from the inverter 9 to the inverter 8 and to allow current to flow from the inverter 8 to the inverter 9. The diode 10ND may be a parasitic diode of the changeover switch 10NS or may be a diode provided separately from the parasitic diode. The diode 10ND may also be a rectifying element.

[0046] The switch 10N is opened and closed in response to the driving of the changeover switch 10NS. When the changeover switch 10NS is turned on, the switch 10N transitions to a closed state. When the changeover switch 10NS is turned off, the switch 10N transitions to an open state. When the switch 10N is in an open state, the changeover switch 10NS cuts off the current from the smoothing capacitor 72 to the DC power supply 2 and the smoothing capacitor 71. In this case, the diode 10ND allows current to flow from the DC power supply 2 and the smoothing capacitor 71 to the smoothing capacitor 72.

[0047] The snubber circuit 11 is connected in parallel to the inverter 9, i.e., the upper and lower arm circuits 9HL. The snubber circuit 11 reduces the inductance of the upper and lower arm circuits 9HL. In other words, the snubber circuit 11 absorbs 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.

[0048] 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, an RC snubber circuit including a capacitor and a resistor, or 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. The other end of the snubber circuit 11 is connected to the power supply line 6.

[0049] In the power conversion circuit 4 illustrated in FIG. 1 , a snubber circuit 11 is provided for each phase of the upper and lower arm circuits 9HL. The power conversion circuit 4 includes three snubber circuits 11. One end of each snubber circuit 11 is connected to the power supply line 5, 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.

[0050] The snubber circuit 12 is connected in parallel to the inverter 8, i.e., the upper and lower arm circuits 8HL. The snubber circuit 12 reduces the inductance of the upper and lower arm circuits 8HL, thereby enabling high-speed switching of the inverter 8. 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.

[0051] In the power conversion circuit 4 illustrated in FIG. 1 , a snubber circuit 12 is provided for each phase of the upper and lower arm circuits 8HL. The power conversion circuit 4 includes 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.

[0052] As illustrated in FIG. 1 , the power conversion circuit 4 may include a control unit (CTR) 15. The control unit 15 corresponds to a control device. The control unit 15 may include, for example, a processor 15a, a memory 15b, and a storage 15c. The processor 15a accesses the memory 15b to perform various processes. The memory 15b is a rewritable volatile storage medium. The memory 15b is, for example, a RAM. RAM is an abbreviation for Random Access Memory. The storage 15c is a rewritable nonvolatile memory. The storage 15c may be realized by at least one type of non-transitory tangible storage medium, such as a semiconductor memory, a magnetic medium, or an optical medium. The storage 15c may include multiple types of storage media, such as a ROM and a flash memory. ROM is an abbreviation for Read Only Memory.

[0053] The storage 15c stores a program 15d executed by the processor 15a. The program 15d configures multiple functional units by causing the processor 15a to execute multiple instructions. The processing performed by the control unit 15 may be realized by software processing in which the processor 15a executes the program 15d described above, or may be realized by hardware processing using a dedicated electronic circuit. It may also be realized by a combination of software processing and hardware processing. The program 15d includes a program for executing the rotation control processing described below. The processor 15a corresponds to the processing unit, and the program 15d corresponds to the control program.

[0054] 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 arm switches 8HS, 8LS, 9HS, and 9LS, and outputs the drive commands 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 sensors detect the voltages across smoothing capacitors 71 and 72.

[0055] The drive command generation unit controls the switches 10P and 10N. The drive command generation unit generates drive commands for controlling the on / off of the changeover switches 10PS and 10NS and outputs the drive commands to the drive circuit unit. The drive circuit unit is sometimes referred to as a driver. Based on the drive commands, the drive circuit unit can independently control the on / off of the arm switches 8HS, 8LS, 9HS, and 9LS and the changeover switches 10PS and 10NS. For convenience, signal lines for transmitting drive signals from the control unit 15 to each switching element are omitted in FIG. 1 .

[0056] <Star Drive and Open Drive> Next, star drive and open 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 drive. Figure 4 is a diagram showing open drive. For convenience, the control unit 15 is omitted from Figures 3 and 4.

[0057] As shown in FIG. 2, the driving region of the rotating electric machine 3 is divided into two regions depending on the rotation speed and torque. One of the driving regions is the star driving region. The star driving region is a normal range. The other driving region is the open driving region. The open driving region is a region with higher rotation speeds or higher torque than the star driving region. The star driving and the star driving region are sometimes referred to as star connection driving and the star connection driving region. The open driving and the open driving region are sometimes referred to as open connection driving and the open connection driving region.

[0058] When the operating point is in the star drive region, the control unit 15 executes star drive control. Star drive is sometimes called Y drive. The control unit 15 controls the arm switches 8HS, 8LS, 9HS, and 9LS and the changeover switches 10PS and 10NS so that the windings 3U, 3V, and 3W are in a star connection state. Specifically, as shown in FIG. 3, the control unit 15 turns off the changeover switches 10PS and 10NS and opens the switches 10P and 10N. The control unit 15 also neutralizes the inverter 9. The control unit 15 then controls the arm switches 8HS and 8LS of the inverter 8 in accordance with drive requirements, etc.

[0059] As shown in Fig. 3, the inverter 9 may be placed in an upper on state to establish a neutral point. The upper on state of the inverter 9 is a state in which the upper arm switches 9HS of the upper arms 9H of all phases are turned on and the lower arm switches 9LS of the lower arms 9L of all phases are turned off. Note that the inverter 9 may be placed in a lower on state to establish a neutral point. The lower on state of the inverter 9 is a state in which the upper arm switches 9HS of the upper arms 9H of all phases are turned off and the lower arm switches 9LS of the lower arms 9L of all phases are turned on.

[0060] FIG. 3 shows one current conduction pattern in star drive. The dashed-dotted arrows in FIG. 3 indicate an example of a current path. FIG. 3 shows the current path when the upper arm switch 8HS of the U-phase upper arm 8H and the lower arm switch 8LS of the W-phase lower arm 8L are turned on. In the example shown in FIG. 3, the inverter 9 is in the upper-on state. 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, in star drive, current flows without passing through switches 10P and 10N.

[0061] When the operating point is in the open drive region, the control unit 15 executes open drive control. Open drive is sometimes referred to as H drive. The control unit 15 turns on the changeover switches 10PS and 10NS and closes the switches 10P and 10N. The control unit 15 also 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 and 9HL via the U-phase winding 3U. Similarly, an open connection circuit of the V-phase upper and lower arm circuits 8HL and 9HL via the V-phase winding 3V is formed. An open connection circuit of the W-phase upper and lower arm circuits 8HL and 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.

[0062] Figure 4 shows one current conduction pattern in open drive. The two-dot chain arrow in Figure 4 indicates an example of a current path. Figure 4 shows the current path when the lower arm switch 8LS of the W-phase lower arm 8L and the upper arm switch 9HS of the W-phase upper arm 9H are turned on. Current flows in the following order: switches 10P, 10N → W-phase upper arm 9H → node W2 → W-phase winding 3W → node W1 → W-phase lower arm 8L. In this way, in open drive, current flows via switches 10P, 10N.

[0063] As described above, the power conversion circuit 4 is configured to be switchable between star drive and open drive. The power conversion circuit 4 is configured to be able to execute star drive. The power conversion circuit 4 is configured to be able to execute open drive. By executing open drive instead of star drive, it is possible to output a higher rotation speed range or a higher torque range.

[0064] <Boost Mode> The control unit 15 can set star mode, open mode, and boost mode as control modes for controlling the rotating electric machine 3. The control modes are control processes for the control unit 15 to control the rotating electric machine 3. The star mode is sometimes referred to as star process, the open mode is sometimes referred to as open process, and the boost mode is sometimes referred to as boost process. The control modes are sometimes referred to as control modes of the drive system 1, the rotating electric machine 3, and the power conversion circuit 4.

[0065] The star mode is a control mode for star-driving the rotating electric machine 3. In the star mode, the rotating electric machine 3 is star-driven with both the switch 10P and the switch 10N in the open state. In the star mode, the power supply voltage Vdc is applied to the smoothing capacitor 72 via the windings 3U, 3V, and 3W, and therefore the capacitor voltage Vc is smaller than the power supply voltage Vdc. For example, the capacitor voltage Vc is approximately half the value of the power supply voltage Vdc (see FIG. 9 ). The capacitor voltage Vc is the voltage of the smoothing capacitor 72. The power supply voltage Vdc is the voltage of the DC power supply 2.

[0066] The open mode is a control mode for open-circuit driving the rotating electric machine 3. In the open mode, the rotating electric machine 3 is open-circuit driven with both the switch 10P and the switch 10N in the closed state. In the open mode, the power supply voltage Vdc is applied directly without passing through the windings 3U, 3V, and 3W, and therefore the capacitor voltage Vc has approximately the same value as the power supply voltage Vdc (see FIG. 9 ).

[0067] For example, when the control mode is switched from star mode to open mode, the power supply voltage Vdc is likely to increase sharply at the timing when both the switch 10P and the switch 10N are switched to the closed state. In this case, an inrush current is likely to flow through the switch 10P and the smoothing capacitor 72 in response to the sudden increase in the power supply voltage Vdc. This inrush current is likely to cause a sudden increase in the capacitor current Ic flowing through the smoothing capacitor 72 (see FIG. 9 ). When an inrush current occurs, there is a concern that an abnormality may occur in the switch 10P or the smoothing capacitor 72 in the power conversion circuit 4.

[0068] In response to this, the control mode is switched from the star mode to the open mode via the boost mode. The boost mode is a control mode for boosting the rotating electric machine 3 while mitigating the increase in the capacitor voltage Vc. In the boost mode, the capacitor voltage Vc gradually increases. In the boost mode, the smoothing capacitor 72 is slowly charged over a certain period of time. In the boost mode, the rotating electric machine 3 is boost-driven with the switch 10P in an open state and the switch 10N in a closed state. Boost driving is driving the rotating electric machine 3 in the boost mode.

[0069] In the boost mode, the inverter 9 is switched between an upper-side ON state and a lower-side ON state. Boost driving of the rotating electric machine 3 includes boost driving in the upper-side ON state and boost driving in the lower-side ON state. In boost driving in the upper-side ON state, the inverter 8 is controlled so that the rotating electric machine 3 is driven when the inverter 9 is in the upper-side ON state. In boost driving in the lower-side ON state, the inverter 8 is controlled so that the rotating electric machine 3 is driven when the inverter 9 is in the lower-side ON state.

[0070] When the inverter 9 is in the low-side on state in the boost mode, the motor current Im flowing through the rotating electric machine 3 star-drives the rotating electric machine 3 and stores electrical energy in the windings 3U, 3V, and 3W. The motor current Im is a current flowing through the rotating electric machine 3. The motor current Im flows through the windings 3U, 3V, and 3W. In the boost drive in the low-side on state, the inverter 8 is driven so that the motor current Im includes both the three-phase currents Iu, Iv, and Iw and the zero-phase current I0. The three-phase currents Iu, Iv, and Iw are currents for star-driving the rotating electric machine 3. The three-phase currents Iu, Iv, and Iw include currents of multiple phases. For example, the three-phase currents Iu, Iv, and Iw include a U-phase current Iu, a V-phase current Iv, and a W-phase current Iw. For example, as shown in FIG. 5 , the U-phase current Iu flows through the U-phase winding 3U. Furthermore, the V-phase current Iv flows through the V-phase winding 3V, and the W-phase current Iw flows through the W-phase winding 3W.

[0071] The zero-phase current I0 is a current that stores electrical energy in the windings 3U, 3V, and 3W when the inverter 9 is in the low-side on state in the boost mode. The zero-phase current I0 flows through each of the multiple phases. For example, the zero-phase current I0 flows through the U-phase winding 3U, the V-phase winding 3V, and the W-phase winding 3W. The zero-phase current I0 is the sum of the three-phase currents Iu, Iv, and Iw. That is, the zero-phase current I0 is the sum of the U-phase current Iu, the V-phase current Iv, and the W-phase current Iw. In the boost drive in the low-side on state, the inverter 8 is driven so as to increase the zero-phase current I0 flowing through the windings 3U, 3V, and 3W. In the rotating electric machine 3, the electrical energy stored in the windings 3U, 3V, and 3W increases as the zero-phase current I0 increases.

[0072] When the inverter 9 is in the high-side ON state in the step-up mode, the motor current Im flowing through the rotary electric machine 3 star-drives the rotary electric machine 3 while supplying energy from the windings 3U, 3V, and 3W to the smoothing capacitor 72. In step-up driving in the high-side ON state, the inverter 8 is driven so that the motor current Im includes three-phase currents Iu, Iv, and Iw. For example, as shown in FIG. 6 , the U-phase current Iu flows through the U-phase winding 3U, and the W-phase current Iw flows through the W-phase winding 3W.

[0073] When the inverter 9 is in the high-side on state in the boost mode, the zero-phase current I0 flows from the windings 3U, 3V, and 3W to the smoothing capacitor 72. This zero-phase current I0 supplies the electrical energy stored in the windings 3U, 3V, and 3W during boost driving in the low-side on state to the smoothing capacitor 72. When the inverter 9 is in the high-side on state in the boost mode, the electrical energy stored in the smoothing capacitor 72 increases due to the zero-phase current I0, thereby increasing the capacitor voltage Vc. During boost driving in the high-side on state, the inverter 8 is driven so that the zero-phase current I0 flows from the windings 3U, 3V, and 3W to the smoothing capacitor 72. In other words, the inverter 8 is driven so that the zero-phase current I0 flowing through the windings 3U, 3V, and 3W decreases. When the inverter 9 is in the high-side on state in the boost mode, the smoothing capacitor 72 is charged by the zero-phase current I0.

[0074] In the drive system 1, when the rotating electric machine 3 is star-driven in star mode, the zero-phase current I0 flowing through the windings 3U, 3V, and 3W is approximately zero. Also, when the rotating electric machine 3 is open-driven in open mode, the zero-phase current I0 flowing through the windings 3U, 3V, and 3W is approximately zero.

[0075] The control unit 15 performs rotation control, which is control of the rotating electric machine 3. The rotation control includes control of the power conversion circuit 4. The control of the power conversion circuit 4 includes control of the inverters 8 and 9 and control of the switches 10P and 10N. The control unit 15 performs rotation control by executing a rotation control process. The control unit 15 repeatedly executes the rotation control process at a predetermined control period. The control unit 15 has a function of executing the processing of each step of the rotation control process. The rotation control process will be described with reference to the flowchart in FIG. 7. In FIGS. 7, 9, etc., the selector switch 10PS is illustrated as PSW, and the selector switch 10NS is illustrated as NSW.

[0076] In step S101 shown in FIG. 7 , the control unit 15 acquires drive information related to the drive system 1. The drive information includes information acquired from detection signals of various sensors. The drive information includes a current detection value calculated using the detection signal of a current sensor, a rotation detection value calculated using the detection signal of a rotation angle sensor, and a voltage detection value calculated using the detection signal of a voltage sensor. The current detection values ​​include three-phase currents Iu, Iv, and Iw and a capacitor current Ic. The voltage detection values ​​include a capacitor voltage Vc and a power supply voltage Vdc.

[0077] In step S102, the control unit 15 determines whether to start the boost mode. For example, the control unit 15 determines whether to end the star mode. That is, the control unit 15 determines whether to switch the drive of the rotating electric machine 3 from star drive to open drive. When the drive of the rotating electric machine 3 is switched from star drive to open drive, the control unit 15 determines to end the star mode and start the boost mode. The control unit 15 also determines whether the operating point of the rotating electric machine 3 moves from the star region to the open region. When the operating point of the rotating electric machine 3 moves from the star region to the open region, the control unit 15 determines to end the star mode and start the boost mode. The control unit 15 acquires the position of the operating point in the drive region of the rotating electric machine 3 by, for example, acquiring the torque and rotation speed of the rotating electric machine 3 using the drive information.

[0078] If the step-up mode is not to be started, the control unit 15 proceeds to step S109. In step S109, the control unit 15 determines whether or not the operating point of the rotating electric machine 3 is in the star region. If the operating point of the rotating electric machine 3 is in the star region, the control unit 15 performs star control processing in steps S110 to S113. The star control processing is processing for star-driving the rotating electric machine 3 in star mode. The function of the control unit 15 for executing the processing of steps S110 to S113 corresponds to a star control unit.

[0079] In step S110 of the star control process, the control unit 15 sets the control mode to star mode. For example, the control unit 15 sets a star flag indicating that the control mode is star mode in the memory 15b, etc. In step S111, the control unit 15 turns off the changeover switch 10PS to open the switch 10P. If the switch 10P is already in the open state, the open state of the switch 10P is maintained. In step S112, the control unit 15 turns off the changeover switch 10NS to open the switch 10N. If the switch 10N is already in the open state, the open state of the switch 10P is maintained.

[0080] In step S113, the control unit 15 performs star drive processing. In the star drive processing, processing for neutralizing the inverter 9 and processing for star driving the rotating electric machine 3 by the inverter 8 are performed. In the processing for neutralizing the inverter 9, processing for putting the inverter 9 into the upper-on state or the lower-on state is performed. In the processing for star driving the rotating electric machine 3 by the inverter 8, motor control such as vector control is performed on the inverter 8. If the star drive processing is already being performed, the star drive processing is continued. In star mode, the drive of the inverters 8 and 9 is controlled so that the zero-phase current I0 becomes zero. This makes it possible to reduce power loss, vibration, and noise in star driving of the rotating electric machine 3.

[0081] If the operating point of the rotating electric machine 3 is not in the star region in step S109, the control unit 15 performs open control processing in steps S114 to S117. The open control processing is processing for open driving the rotating electric machine 3 in open mode. The function of the control unit 15 for executing the processing of steps S114 to S117 corresponds to an open control unit.

[0082] In step S114 of the open control process, the control unit 15 sets the control mode to the open mode. For example, the control unit 15 sets an open flag indicating that the control mode is the open mode in the memory 15b, etc. In step S115, the control unit 15 turns on the changeover switch 10PS to close the switch 10P. If the switch 10P is already in the closed state, the switch 10P is maintained in the closed state. In step S112, the control unit 15 turns off the changeover switch 10NS to close the switch 10N. If the switch 10N is already in the closed state, the switch 10N is maintained in the closed state.

[0083] In step S117, the control unit 15 performs open drive processing. In the open drive processing, processing is performed to open drive the rotating electric machine 3 using the inverters 8 and 9. For example, in the open drive processing, motor control such as vector control is performed on the inverters 8 and 9. If the open drive processing is already being performed, the open drive processing is continued. In the open mode, the drive of the inverters 8 and 9 is controlled so that the zero-phase current I0 becomes zero. This makes it possible to reduce power loss, vibration, and noise when the rotating electric machine 3 is open driven.

[0084] When the voltage step-up mode is started in step S102, the control unit 15 performs voltage step-up control processing in steps S103 to S106. The voltage step-up control processing is processing for star driving the rotating electric machine 3 in the voltage step-up mode. The function of the control unit 15 for executing the processing in steps S103 to S106 corresponds to a voltage step-up control unit.

[0085] In step S103 of the voltage boost control process, the control unit 15 sets the control mode to the voltage boost mode. For example, the control unit 15 sets a voltage boost flag indicating that the control mode is the voltage boost mode in the memory 15b or the like.

[0086] In step S104, the control unit 15 turns off the changeover switch 10PS to open the switch 10P. If the switch 10P was in the open state in the star mode, the switch 10P is maintained in the open state. The function of the control unit 15 to execute the process of step S104 corresponds to an open control unit.

[0087] In step S105, the control unit 15 turns on the changeover switch 10NS to close the switch 10N. If the switch 10N was in the open state in the star mode, the control unit 15 switches the switch 10N from the open state to the closed state. The function of the control unit 15 to execute the process of step S105 corresponds to the closing control unit.

[0088] In step S106, the control unit 15 performs a boost drive process. The boost drive process is a process for boost-driving the rotating electric machine 3 in the boost mode. The boost drive process is a process for increasing the capacitor voltage Vc to a voltage threshold value JVc, which will be described later. The control unit 15 continues to perform the boost drive process until the capacitor voltage Vc reaches the voltage threshold value JVc. Details of the boost drive process will be described later. The control unit 15 temporarily stops repeatedly executing the rotation control process until the boost drive process is completed.

[0089] After the boost drive process is completed, the control unit 15 proceeds to step S107. In step S107, the control unit 15 performs open control process similar to steps S114 to S117. In this open control process, processes for switching the control mode from star mode to boost mode, for switching the switch 10P from an open state to a closed state, and for switching the drive of the rotating electrical machine 3 from boost drive to open drive are performed. The function of the control unit 15 for executing the process of step S107 corresponds to an open control unit.

[0090] Next, the boost drive process will be described with reference to the flowchart of FIG.

[0091] The control unit 15 performs first inverter processing in steps S201 to S204. The first inverter processing is processing for controlling the drive of the inverter 8. The first inverter processing is also torque control processing for controlling the output torque of the rotating electric machine 3 in the step-up mode. In the first inverter processing, motor control such as vector control is performed on the inverter 8 so that a zero-phase current I0 flows. Furthermore, in the first inverter processing, the drive of the inverter 8 is controlled so that the output torque of the rotating electric machine 3 is the same as the output torque in the star mode. The function of the control unit 15 for executing the processing in steps S201 to S204 corresponds to a zero-phase control unit.

[0092] In step S201 of the first inverter process, the control unit 15 performs a dq transformation process. In the dq transformation process, the three-phase currents Iu, Iv, and Iw are subjected to a dq transformation to calculate the d-axis current and the q-axis current. In this dq transformation, the three-phase currents Iu, Iv, and Iw in the three-phase AC coordinate system are converted into the d-axis current and the q-axis current in the dq coordinate system. The dq transformation is sometimes referred to as a three-phase to two-phase transformation.

[0093] In step S202, the control unit 15 performs a command conversion process. The command conversion process is a process for calculating a voltage command value in a three-phase coordinate system. The command conversion process includes a process for calculating a current command value in a dq coordinate system according to a command torque, etc., and a process for calculating a voltage command value in the dq coordinate system so that the d-axis current and the q-axis current match the current command values ​​in the dq coordinate system. The command conversion process converts the voltage command value in the dq coordinate system into a voltage command value in the three-phase coordinate system, thereby calculating the voltage command value in the three-phase coordinate system.

[0094] In step S203, the control unit 15 calculates a first duty ratio. The first duty ratio is a duty ratio for performing PWM control of the inverter 8. The control unit 15 calculates the first duty ratio in accordance with the voltage command value in the three-phase coordinate system, the capacitor voltage Vc, and the like. The control unit 15 generates a first PWM signal for driving the inverter 8 using the first duty ratio.

[0095] In step S204, the control unit 15 calculates a first switching pattern for driving the inverter 8. For example, the control unit 15 calculates the first switching pattern using a first duty ratio and a first PWM signal. The first switching pattern is information for turning on and off the arm switches 8HS and 8LS in each of the multiple phases. The control unit 15 drives the inverter 8 by turning on and off the arm switches 8HS and 8LS in accordance with the first switching pattern.

[0096] The control unit 15 performs second inverter processing in steps S205 to S208. The second inverter processing is processing for controlling the driving of the inverter 9. The second inverter processing is also processing for boosting the capacitor voltage Vc. In the second inverter processing, processing is performed for switching the inverter 9 between the lower on state and the upper on state. This processing is processing for switching the switching element that forms the neutral point in the inverter 9 between the upper arm switch 8HS and the lower arm switch 8LS. The function of the control unit 15 that executes the processing of steps S205 to S208 corresponds to a neutral point control unit.

[0097] In step S205 of the second inverter process, the control unit 15 calculates the zero-phase current I0. The control unit 15 calculates the zero-phase current I0 using the U-phase current Iu, the V-phase current Iv, and the W-phase current Iw. The control unit 15 also calculates the d-axis current and the q-axis current by performing dq transformation on the zero-phase current I0. In step S206, the control unit 15 performs command conversion processing similar to step S202.

[0098] In step S207, the control unit 15 calculates a second duty ratio. The second duty ratio is a duty ratio for performing PWM control of the inverter 9. The control unit 15 calculates the second duty ratio in accordance with the voltage command value in the three-phase coordinate system, the capacitor voltage Vc, and the like. The control unit 15 generates a second PWM signal for driving the inverter 9 using the second duty ratio.

[0099] The control unit 15 calculates the second duty ratio to set the upper on-time TH and the lower on-time TL (see FIG. 9 ). The upper on-time TH is the time during which the inverter 9 is held in the upper on state. The lower on-time TL is the time during which the inverter 9 is held in the lower on state. The upper on-time TH and the lower on-time TL are set according to the second duty ratio. The control unit 15 can set the second duty ratio so that one of the upper on-time TH and the lower on-time TL is longer than the other, or can set the second duty ratio so that the upper on-time TH and the lower on-time TL are the same.

[0100] In step S208, the control unit 15 calculates a second switching pattern for driving the inverter 9. For example, the control unit 15 calculates the second switching pattern using a second duty ratio or a second PWM signal. The second switching pattern is information for turning on and off the arm switches 9HS and 9LS for each of the multiple phases. The control unit 15 drives the inverter 9 by turning on and off the arm switches 9HS and 9LS in accordance with the second switching pattern.

[0101] In drive system 1, when inverter 9 is set to the low-side on state by the second switching pattern, electrical energy is stored in windings 3U, 3V, and 3W by zero-phase current I0. On the other hand, when inverter 9 is set to the high-side on state by the second switching pattern, electrical energy is supplied from windings 3U, 3V, and 3W to smoothing capacitor 72 by zero-phase current I0, and capacitor voltage Vc increases.

[0102] In step S209, the control unit 15 determines whether the capacitor voltage Vc has reached the voltage threshold JVc. For example, the voltage threshold JVc is set to a value equal to or lower than the power supply voltage Vdc. The voltage threshold JVc may be variably set depending on the power supply voltage Vdc or the like, or may be set to a value determined in advance through testing or the like. The voltage threshold JVc may also be set to a value higher than the power supply voltage Vdc. The voltage threshold JVc may also be set depending on the rated voltage of the smoothing capacitor 72 or the like.

[0103] The control unit 15 repeatedly executes the first inverter process and the second inverter process in steps S201 to S208 until the capacitor voltage Vc reaches the voltage threshold JVc. Therefore, the process of switching the inverter 9 between the upper-side ON state and the lower-side ON state in steps S205 to S208 is executed multiple times until the capacitor voltage Vc reaches the voltage threshold JVc.

[0104] When the capacitor voltage Vc reaches the voltage threshold JVc, the control unit 15 ends the boost drive process. Returning to FIG. 7 , after the boost drive process, the control unit 15 proceeds to step S107. In step S107, the control unit 15 performs a process for ending the boost mode in addition to the open control process. The process for ending the boost mode may include a process for changing the control mode of the control unit 15 from the boost mode to the open mode. For example, the control unit 15 clears the boost flag and sets the open flag. The function of the control unit 15 that executes the process of step S107 corresponds to a boost end unit.

[0105] Next, the manner in which the capacitor current Ic changes in the boost mode will be described. As shown in FIG. 9 , at time t1 when the control mode is switched from star mode to boost mode, the inverter 9 is in the low-side on state. While the inverter 9 is maintained in the low-side on state, the zero-phase current I0 flowing through the windings 3U, 3V, and 3W tends to increase. During this period, the electrical energy stored in the windings 3U, 3V, and 3W tends to increase. Furthermore, during this period, the zero-phase current I0 does not easily flow from the windings 3U, 3V, and 3W to the smoothing capacitor 72. Therefore, the capacitor voltage Vc tends to be maintained at approximately half the power supply voltage Vdc.

[0106] Furthermore, in the boost mode, because the switch 10P is in the open state, a sudden increase in the capacitor current Ic due to an inrush current is unlikely to occur. For example, the capacitor current Ic begins to increase at timing t1, and after increasing to a certain level, is maintained at a substantially constant value. In the boost mode, a sudden increase in the capacitor current Ic is limited by the windings 3U, 3V, and 3W. For example, the capacitor current Ic is limited so as not to exceed the rated current value IswR of the switch 10P. Furthermore, the capacitor current Ic is limited so as not to exceed the rated current value of the smoothing capacitor 72.

[0107] At time t2, which is the elapsed time TL from time t1, the inverter 9 is switched from the low-side on state to the high-side on state. While the inverter 9 is maintained in the high-side on state, the zero-phase current I0 tends to flow from the windings 3U, 3V, and 3W into the smoothing capacitor 72. During this period, the zero-phase current I0 flowing through the windings 3U, 3V, and 3W tends to decrease. At time t2, the zero-phase current I0 starts to flow into the smoothing capacitor 72, which tends to increase the capacitor voltage Vc.

[0108] At time t3, which is the time the upper-side on time TH has elapsed since time t2, the inverter 9 is switched from the upper-side on state to the lower-side on state. The inverter 9 is repeatedly switched between the upper-side on state and the lower-side on state until the capacitor voltage Vc reaches a voltage threshold JVc such as the power supply voltage Vdc. For example, if the capacitor voltage Vc reaches the power supply voltage Vdc at time t9, the control mode is switched from the boost mode to the open mode at time t9.

[0109] 9 illustrates an example in which the top on-time TH and the bottom on-time TL are the same length for convenience of explanation. This example includes an example in which the top on-time TH is the same length in multiple top on-states and the bottom on-time TL is the same length in multiple bottom on-states.

[0110] Summary of First Embodiment According to this embodiment, in the boost mode, the rotating electric machine 3 is driven so that the zero-phase current I0 flowing through the smoothing capacitor 72 is larger than in the star mode. In this configuration, the smoothing capacitor 72 is charged by the zero-phase current I0, so the capacitor voltage Vc in the boost mode is more likely to rise than the capacitor voltage Vc in the star mode. Therefore, by switching the control mode of the control unit 15 from the star mode to the open mode via the boost mode, the rise in the capacitor voltage Vc can be mitigated. This makes it possible to prevent an inrush current from flowing through the smoothing capacitor 72, the switch 10P, the power line 5, etc. As a result, the drive system 1, the power conversion circuit 4, the control unit 15, and the program 15d can prevent an abnormality in the power conversion circuit 4 due to an inrush current.

[0111] According to this embodiment, the control unit 15 switches the inverter 9 between a low-phase-on state and a high-phase-on state in the boost mode. In the boost mode, the inverter 9 is in the low-phase-on state, which allows electrical energy to be stored in the windings 3U, 3V, and 3W by the zero-phase-sequence current I0. Furthermore, the inverter 9 is in the high-phase-on state, which allows the electrical energy stored in the windings 3U, 3V, and 3W to be supplied to the smoothing capacitor 72 by the zero-phase-sequence current I0. Therefore, in the boost mode, the capacitor voltage Vc can be gradually increased. Therefore, the zero-phase-sequence current I0 can suppress a sudden increase in the capacitor current Ic due to an inrush current.

[0112] According to this embodiment, the control unit 15 switches the inverter 9 between the low-side on state and the high-side on state multiple times in the boost mode. In this configuration, electrical energy is stored in the windings 3U, 3V, and 3W, and electrical energy is supplied from the windings 3U, 3V, and 3W to the smoothing capacitor 72 multiple times. This allows the voltage of the smoothing capacitor 72 to be increased in stages. This prevents the zero-phase current I0 flowing from the windings 3U, 3V, and 3W into the smoothing capacitor 72 from becoming too large. This prevents the power conversion circuit 4 and the rotating electric machine 3 from being burdened when the voltage of the smoothing capacitor 72 is increased.

[0113] According to this embodiment, when the inverter 9 is in the low-side on state in the boost mode, the control unit 15 controls the inverter 8 so that the zero-phase current I0 in the windings 3U, 3V, and 3W increases. In this case, electrical energy can be efficiently stored in the windings 3U, 3V, and 3W. Furthermore, when the inverter 9 is in the high-side on state in the boost mode, the control unit 15 controls the inverter 8 so that the zero-phase current I0 in the windings 3U, 3V, and 3W decreases. In this case, the zero-phase current I0 flows from the windings 3U, 3V, and 3W to the smoothing capacitor 72, thereby efficiently boosting the capacitor voltage Vc of the smoothing capacitor 72. Therefore, the boost mode can be shortened in time.

[0114] According to this embodiment, the control unit 15 terminates the boost mode when the capacitor voltage Vc reaches the voltage threshold JVc. This prevents the capacitor voltage Vc from being boosted excessively. This prevents the smoothing capacitor 72 from being abnormally charged due to excessive charging.

[0115] According to this embodiment, the control unit 15 opens the switch 10P in the boost mode. In this configuration, the switch 10P can prevent an inrush current from flowing from the DC power supply 2 or the smoothing capacitor 71 to the smoothing capacitor 72 in the boost mode.

[0116] According to this embodiment, the control unit 15 closes the switch 10N in the voltage step-up mode. In this configuration, the motor current Im, such as three-phase currents Iu, Iv, and Iw, is allowed to flow through the power supply line 6 via the switch 10N, which makes it easier for the zero-phase current I0 to be generated in the windings 3U, 3V, and 3W. As a result, the voltage across the smoothing capacitor 72 is easily boosted by the zero-phase current I0.

[0117] Second Embodiment This embodiment is a modification based on the preceding embodiment, and the description of the preceding embodiment can be used. In the preceding embodiment, the boost mode is terminated when the capacitor voltage Vc reaches the voltage threshold JVc. However, the present invention is not limited to this. In this embodiment, the boost mode may be terminated regardless of the capacitor voltage Vc.

[0118] In this embodiment, the boost drive process will be described with reference to the flowchart of FIG.

[0119] The control unit 15 performs the processes of steps S201 to S208 in the same manner as in the first embodiment. After step S208, the control unit 15 proceeds to step S301. In step S301, the control unit 15 determines whether the boost period Tmode has reached the period threshold JTmode. The boost period Tmode is the time elapsed since the boost mode was initiated. The control unit 15 measures the time elapsed since the boost mode was initiated in step S103 or the like. The period threshold JTmode is a value determined in advance by testing or the like, and is stored in the memory 15b or the like. The period threshold JTmode is set according to the time required for the capacitor voltage Vc to reach the voltage threshold JVc after the boost mode is initiated.

[0120] The control unit 15 repeatedly executes the first inverter process and the second inverter process in steps S201 to S208 until the voltage step-up period Tmode reaches the period threshold JTmode.

[0121] In this embodiment, the boost mode is ended at a timing corresponding to the boost period Tmode, so there is a possibility that the capacitor voltage Vc may exceed the voltage threshold JVc or the power supply voltage Vdc. In response to this, the switch 10P, in its open state, is able to pass current from the smoothing capacitor 72 to the DC power supply 2. This makes it possible to prevent the capacitor voltage Vc from becoming excessively high and exceeding the voltage threshold JVc or the power supply voltage Vdc.

[0122] For example, if the boost mode continues after the capacitor voltage Vc reaches the power supply voltage Vdc, the inverter 9 switches from the low-side on state to the high-side on state, causing an excess current Iex to flow through the switch 10P, as shown in FIG. 11 . The excess current Iex is a current flowing from the smoothing capacitor 72 toward the DC power supply 2. After the capacitor voltage Vc reaches the power supply voltage Vdc, the inverter 9 is in the low-side on state, causing the zero-phase current I0 to rise and exceed the power supply voltage Vdc. Then, when the inverter 9 switches from the low-side on state to the high-side on state, the power that exceeds the power supply voltage Vdc in the smoothing capacitor 72 flows out of the smoothing capacitor 72 as the excess current Iex. The excess current Iex flows through the diode 10PD of the switch 10P into the smoothing capacitor 71 and the DC power supply 2.

[0123] According to this embodiment, when the switch 10P is in an open state, it is possible for a current to flow from the smoothing capacitor 72 to the DC power supply 2. In this configuration, the excess current Iex is likely to be released from the smoothing capacitor 72 through the switch 10P to the DC power supply 2 or the smoothing capacitor 71. Therefore, the switch 10P can suppress an excessive rise in the capacitor voltage Vc.

[0124] In this embodiment, the number of state changes of the inverter 9 and the capacitor potential difference may be used as parameters for determining whether to terminate the boost mode, in addition to or instead of the capacitor voltage Vc and the boost period Tmode. The number of state changes of the inverter 9 is the number of times the inverter 9 is switched between the high-side on state and the low-side on state in the boost mode. For example, the boost mode may be terminated when the number of state changes reaches a count threshold. The capacitor potential difference is the difference between the voltage of the smoothing capacitor 71 and the capacitor voltage Vc of the smoothing capacitor 72. For example, when the capacitor potential difference becomes smaller than a potential difference threshold, it may be determined that the capacitor voltage Vc has risen sufficiently, and the boost mode may be terminated. The count threshold and the potential difference threshold may be predetermined values ​​or variably set values.

[0125] Third Embodiment This embodiment is a modification based on the preceding embodiment, and the description of the preceding embodiment can be used. In the preceding embodiment, the switch 10N is provided on the power line 6, but this is not limited thereto. In this embodiment, the switch 10N does not have to be provided on the power line 6.

[0126] In this embodiment, as shown in FIG. 12, the drive system 1 does not include the switch 10N. In this configuration, the control unit 15 does not need to open or close the switch 10N depending on the control mode. For example, as shown in FIG. 13, unlike the first embodiment, the control unit 15 does not perform the processes of steps S105, S112, and S116 in the rotation control process. However, when the control mode is in star mode, the control unit 15 needs to place the inverter 9 in the upper on state in the star drive process of step S113.

[0127] (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.

[0128] 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.

[0129] When an element or layer is referred to as being "on," "coupled," "connected," or "bonded," it may be directly on, coupled, connected, or bonded to the other 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, there are no intervening elements or layers present. Other language used to describe relationships between elements should be construed in a similar manner (e.g., "between" vs. "directly between," "adjacent" vs. "directly adjacent," etc.).

[0130] As used in this specification, the term "and / or" includes any and all combinations of one or more of the associated listed items, i.e., reference to A and / or B means at least one of A and B, and may include A only, B only, or both A and B.

[0131] 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.

[0132] In each of the above embodiments, the control unit 15 does not need to use a duty ratio as long as it can set the upper on-time TH and the lower on-time TL. For example, the control unit 15 may set the upper on-time TH and the lower on-time TL according to predetermined parameters. Examples of these parameters include the capacitor voltage Vc, the power supply voltage Vdc, and the three-phase currents Iu, Iv, and Iw. The control unit 15 may set the upper on-time TH and the lower on-time TL so that the total time of one upper on-time TH and one lower on-time TL is long, or may set the upper on-time TH and the lower on-time TL so that the total time is short. The control unit 15 may also set at least one of the upper on-time TH and the lower on-time TL to a predetermined value.

[0133] In each of the above embodiments, the switches 10P and 10N may include any type of switches or switches that can be switched between an open state and a closed state. For example, in the switches 10P and 10N, the changeover switches 10PS and 10NS may be mechanical switches. A mechanical switch is a switch that has mechanical contacts.

[0134] In each of the above embodiments, the power supply lines 5 and 6 may directly or indirectly connect the inverter 8 and the inverter 9. For example, the power supply lines 5 and 6 may electrically connect the inverter 9 and the DC power supply 2 without passing through the inverter 8. In this configuration, the power supply lines 5 and 6 also indirectly connect the inverter 8 and the inverter 9 via the DC power supply 2.

[0135] In each of the above embodiments, in the step-up mode, the inverters 8 and 9 may be controlled in any manner as long as the rotating electric machine 3 is driven and the zero-phase current I0 flows through the windings 3U, 3V, and 3W and the smoothing capacitor 72. Furthermore, in the step-up mode, the output torque of the rotating electric machine 3 may be smaller than the output torque in the star mode or open mode as long as the zero-phase current I0 flows through the windings 3U, 3V, and 3W.

[0136] In each of the above embodiments, the control unit 15 is provided by a control system including at least one computer. The control system includes at least one processor that is hardware. This processor corresponds to the processing unit. If this processor is referred to as a hardware processor, the hardware processor can be provided by the following (i), (ii), or (iii):

[0137] (i) A hardware processor may be a hardware logic circuit. In this case, the computer is provided by a digital circuit including a large number of programmed logic units (gate circuits). The digital circuit may include a memory that stores at least one of a program and data. The computer may be provided by an analog circuit. The computer may be provided by a combination of a digital circuit and an analog circuit.

[0138] (ii) The hardware processor may be at least one processor core that executes a program stored in at least one memory. In this case, a computer is provided by at least one memory and at least one processor core. The processor core is referred to as a CPU, for example. The memory is also referred to as a storage medium. The memory is a non-transitory, tangible storage medium that non-temporarily stores "at least one of a program and data" that can be read by the processor.

[0139] (iii) The hardware processor may be a combination of (i) above and (ii) above, where (i) and (ii) are located on different chips or on a common chip.

[0140] That is, at least one of the means and functions provided by the control unit 15 can be provided by hardware only, software only, or a combination thereof.

[0141] (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.

[0142] (Technical Idea 1) A power conversion device (4) that converts power supplied from a power supply unit (2) to a rotating electric machine (3), comprising: a first inverter (8) connected to one end of a winding of the rotating electric machine; a second inverter (9) connected to the other end of the winding; a first capacitor (71) connected in parallel to the first inverter; and a second capacitor (72) connected in parallel to the second inverter. A star control unit (S110 to S113) that controls the first inverter and the second inverter in a star mode so as to drive the rotating electric machine by star drive with the second inverter at a neutral point; an open control unit (S107, S114 to S117) that controls the first inverter and the second inverter in an open mode so as to drive the rotating electric machine by open drive with the second inverter not at a neutral point; and a boost control unit (S103 to S106) that controls the first inverter and the second inverter in a boost mode so as to drive the rotating electric machine and so that a zero-phase current (I0) flows in the winding. A power conversion device comprising:

[0143] (Technical Idea 2) The second inverter has an upper arm switch (9HS) connected to the high potential side of the power supply unit and a lower arm switch (9LS) connected to the low potential side of the power supply unit, and the boost control unit has a neutral point control unit (S205 to S208) that switches the second inverter between a lower on state where the neutral point is set by the lower arm switch and an upper on state where the neutral point is set by the upper arm switch, in this power conversion device according to Technical Idea 1.

[0144] (Technical Concept 3) The power conversion device according to Technical Concept 2, wherein the neutral point control unit switches the second inverter between the low-side on state and the high-side on state multiple times in the boost mode.

[0145] (Technical Idea 4) The power conversion device according to Technical Idea 2 or 3, wherein the boost control unit has a zero-phase control unit (S201 to S204) that controls the first inverter so that the zero-phase current flowing through the winding increases when the second inverter is in the low-side on state, and controls the first inverter so that the zero-phase current flowing through the second capacitor increases when the second inverter is in the high-side on state.

[0146] (Technical Idea 5) The power conversion device according to any one of Technical Ideas 1 to 4, further comprising a boost termination unit (S107) that terminates the boost mode when the voltage (Vc) of the second capacitor reaches a voltage threshold (JVc) that is equal to or lower than the voltage (Vdc) of the power supply unit.

[0147] (Technical Idea 6) A power conversion device according to any one of Technical Ideas 1 to 5, comprising: a high-voltage switch (10P) provided in a high-voltage power path (5) connecting the high-potential side of the power supply unit and the second capacitor, the high-voltage switch (10P) being in a closed state to pass current from the power supply unit to the second capacitor and being in an open state to cut off current from the power supply unit to the second capacitor; and an opening control unit (S104) that sets the high-voltage switch to the open state when the boost control unit controls the first inverter and the second inverter in the boost mode.

[0148] (Technical Concept 7) The power conversion device according to Technical Concept 6, wherein the high-voltage switch allows a current to flow from the second capacitor to the power supply unit side in the open state.

[0149] (Technical Idea 8) A power conversion device according to any one of Technical Ideas 1 to 7, comprising: a low voltage switch (10N) provided in a low voltage power path (6) connecting the low potential side of the power supply unit and the second capacitor, the low voltage switch (10N) being in a closed state to pass current from the second capacitor to the power supply unit side and being in an open state to cut off current from the second capacitor to the power supply unit side; and a closing control unit (S105) that closes the low voltage switch when the boost control unit controls the first inverter and the second inverter in the boost mode.

[0150] (Technical Idea 9) A drive system (1) comprising: a rotating electric machine (3); and a power conversion device (4) that converts power supplied to the rotating electric machine from a power supply unit (2), and drives the rotating electric machine using the power conversion device, comprising: a first inverter (8) connected to one end of a winding of the rotating electric machine; a second inverter (9) connected to the other end of the winding; a first capacitor (71) connected in parallel to the first inverter; and a second capacitor (72) connected in parallel to the second inverter. A star control unit (S110 to S113) that controls the first inverter and the second inverter in a star mode so as to drive the rotating electric machine by star drive with the second inverter at a neutral point; and an open control unit (S107, S114 to S117) that controls the first inverter and the second inverter in an open mode so as to drive the rotating electric machine by open drive with the second inverter not at a neutral point. a boost control unit (S103 to S106) that controls the first inverter and the second inverter in a boost mode so as to drive the rotating electric machine and so that a zero-phase current (I0) flows through the windings.

[0151] (Technical Idea 10) A control device (15) for controlling a power conversion device (4) that converts power supplied to the rotating electric machine from a power supply unit (2), the control device (15) 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 first capacitor (71) connected in parallel to the first inverter; and a second capacitor (72) connected in parallel to the second inverter, the control device (15) comprising: a star control unit (S110 to S113) that controls the first inverter and the second inverter in a star mode so as to drive the rotating electric machine by star drive with the second inverter at a neutral point; and an open control unit (S107, S114 to S117) that controls the first inverter and the second inverter in an open mode so as to drive the rotating electric machine by open drive with the second inverter not at a neutral point. a boost control unit (S103 to S106) that controls the first inverter and the second inverter in a boost mode so as to drive the rotating electric machine and so as to cause a zero-phase current (I0) to flow through the windings.

[0152] (Technical Idea 11) A control program (15d) for controlling a power conversion device (4) that converts power supplied to a rotating electric machine from a power supply unit (2), the power conversion device (4) 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 first capacitor (71) connected in parallel to the first inverter; and a second capacitor (72) connected in parallel to the second inverter, the control program (15d) causing at least one processing unit (15a) to: control the first inverter and the second inverter in a star mode so as to drive the rotating electric machine by star driving with the second inverter at a neutral point (S110 to S113); and control the first inverter and the second inverter in an open mode so as to drive the rotating electric machine by open driving with the second inverter not at a neutral point (S107, S114 to S117). a control program for controlling the first inverter and the second inverter in a boost mode so as to drive the rotating electric machine and so as to cause a zero-phase current (I0) to flow through the windings (S103 to S106).

Claims

1. A power conversion device (4) that converts power supplied from a power supply unit (2) to a rotating electric machine (3), comprising: a first inverter (8) connected to one end of a winding of the rotating electric machine; a second inverter (9) connected to the other end of the winding; a first capacitor (71) connected in parallel to the first inverter; a second capacitor (72) connected in parallel to the second inverter; a star control unit (S110 to S113) that controls the first inverter and the second inverter in star mode so as to drive the rotating electric machine by star drive with the second inverter at a neutral point; an open control unit (S107, S114 to S117) that controls the first inverter and the second inverter in open mode so as to drive the rotating electric machine by open drive without neutralizing the second inverter; and a boost control unit (S103 to S106) that controls the first inverter and the second inverter in boost mode so as to drive the rotating electric machine and cause a zero-phase current (I0) to flow in the winding.

2. The power conversion device according to claim 1, wherein the second inverter has an upper arm switch (9HS) connected to the high potential side of the power supply unit and a lower arm switch (9LS) connected to the low potential side of the power supply unit, and the boost control unit has a neutral point control unit (S205 to S208) that switches the second inverter between a lower on state in which the neutral point is established by the lower arm switch and an upper on state in which the neutral point is established by the upper arm switch.

3. The power conversion device according to claim 2, wherein the neutral point control unit switches the second inverter between the low-side on state and the high-side on state multiple times in the boost mode.

4. The power conversion device according to claim 2 or 3, wherein the boost control unit includes a zero-phase control unit (S201 to S204) that controls the first inverter so that the zero-phase current flowing through the winding increases when the second inverter is in the low-on state, and controls the first inverter so that the zero-phase current flowing through the winding decreases when the second inverter is in the high-on state.

5. A power conversion device as described in any one of claims 1 to 3, further comprising a boost termination unit (S107) that terminates the boost mode when the voltage (Vc) of the second capacitor reaches a voltage threshold (JVc) that is equal to or lower than the voltage (Vdc) of the power supply unit.

6. A power conversion device according to any one of claims 1 to 3, comprising: a high-voltage switch (10P) provided in a high-voltage power path (5) connecting the high-potential side of the power supply unit and the second capacitor, the high-voltage switch (10P) being closed to pass current from the power supply unit to the second capacitor and being open to cut off current from the power supply unit to the second capacitor; and an open control unit (S104) that opens the high-voltage switch when the boost control unit controls the first inverter and the second inverter in the boost mode.

7. The power conversion device according to claim 6, wherein the high-voltage switch allows current to flow from the second capacitor to the power supply unit side in the open state.

8. A power conversion device according to any one of claims 1 to 3, comprising: a low voltage switch (10N) provided in a low voltage power path (6) connecting the low potential side of the power supply unit and the second capacitor, the low voltage switch (10N) being closed to allow current to flow from the second capacitor to the power supply unit side and being open to cut off current from the second capacitor to the power supply unit side; and a closing control unit (S105) that closes the low voltage switch when the boost control unit controls the first inverter and the second inverter in the boost mode.

9. A drive system (1) comprising: a rotating electric machine (3); and a power conversion device (4) that converts power supplied to the rotating electric machine from a power supply unit (2), and drives the rotating electric machine using the power conversion device, comprising: a first inverter (8) connected to one end of a winding of the rotating electric machine; a second inverter (9) connected to the other end of the winding; a first capacitor (71) connected in parallel to the first inverter; and a second capacitor (72) connected in parallel to the second inverter. A star control unit (S110 to S113) that controls the first inverter and the second inverter in star mode so as to drive the rotating electric machine by star drive with the second inverter at the neutral point; and an open control unit (S107, S114 to S117) that controls the first inverter and the second inverter in open mode so as to drive the rotating electric machine by open drive with the second inverter not at the neutral point. a boost control unit (S103 to S106) that controls the first inverter and the second inverter in a boost mode so as to drive the rotating electric machine and so that a zero-phase current (I0) flows through the windings.

10. A control device (15) for controlling a power conversion device (4) for converting power supplied from a power source unit (2) to the rotating electric machine, the control device (15) 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 first capacitor (71) connected in parallel to the first inverter; and a second capacitor (72) connected in parallel to the second inverter, the control device (15) comprising: a star control unit (S110 to S113) for controlling the first inverter and the second inverter in star mode so as to drive the rotating electric machine by star drive with the second inverter at the neutral point; and an open control unit (S107, S114 to S117) for controlling the first inverter and the second inverter in open mode so as to drive the rotating electric machine by open drive with the second inverter not at the neutral point. a boost control unit (S103 to S106) that controls the first inverter and the second inverter in a boost mode so as to drive the rotating electric machine and so as to cause a zero-phase current (I0) to flow through the windings.

11. A control program (15d) for controlling a power conversion device (4) for converting power supplied to a rotating electric machine from a power supply unit (2), the power conversion device (4) 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 first capacitor (71) connected in parallel to the first inverter; and a second capacitor (72) connected in parallel to the second inverter, the control program (15d) causing at least one processing unit (15a) to: control the first inverter and the second inverter in star mode so as to drive the rotating electric machine by star drive with the second inverter at the neutral point (S110 to S113); and control the first inverter and the second inverter in open mode so as to drive the rotating electric machine by open drive with the second inverter not at the neutral point (S107, S114 to S117); a control program for controlling the first inverter and the second inverter in a boost mode so as to drive the rotating electric machine and so as to cause a zero-phase current (I0) to flow through the windings (S103 to S106).

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