Electric circuit and control program

Abstract

The present invention bidirectionally transfers power even when a first battery (31) and a second battery (32) are not connected in series. This electric circuit comprises a battery unit (30) including a first battery and a second battery, a three-phase motor (40), an inverter circuit (10), and a switch circuit (20). In a first boost power transfer operation, power is transferred from the first battery to the second battery by repeating ON and OFF of second lower reverse conduction switching elements (24UL, 24VL, 24WL) of specific second series switch circuits (22U, 22V, 22W) in a state where a positive electrode of the first battery is connected to first high potential wiring, a positive electrode of the second battery is connected to second high potential wiring, and negative electrodes of the first battery and the second battery are connected to first low potential wiring and second low potential wiring. In a second boost power transfer operation, power is transferred from the second battery to the first battery by repeating ON and OFF of first lower reverse conduction switching elements (14UL, 14VL, 14WL) of specific first series switch circuits (12U, 12V, 12W) in the above state.

Description

Electrical circuit and control programs

[0001] (Cross-reference to related applications) This application is a related application of Japanese Patent Application No. 2024-010540 filed on January 26, 2024, and claims priority based on this Japanese patent application, the entire contents of which are incorporated herein by reference.

[0002] The technology disclosed in this specification relates to an electric circuit and a control program.

[0003] Japanese Patent Publication No. 2020-120566 (hereinafter referred to as Patent Document 1) discloses an electric circuit having two batteries connected in series. This electric circuit has an inverter that converts DC power output by the batteries into AC power and supplies it to a motor. This electric circuit can also perform a power transfer operation that transfers power between the two batteries using the motor windings. According to the technology of Patent Document 1, power can be transferred in both directions between the two batteries connected in series.

[0004] According to the power transfer operation of Patent Document 1, power can be transferred between two batteries connected in series. On the other hand, if the two batteries are not connected in series, the power transfer operation of Patent Document 1 cannot transfer power. This specification proposes a technology that can transfer power bidirectionally between two batteries by using the windings of a motor, even if the two batteries are not connected in series.

[0005] The electric circuit disclosed in this specification includes a battery unit, a three-phase motor, an inverter circuit, and a switch circuit. The battery unit includes a first battery and a second battery. The three-phase motor has three windings: a U-phase winding, a V-phase winding, and a W-phase winding. Each of the three windings has a first connection terminal at one end and a second connection terminal at the other end. The inverter circuit is connected to the battery unit, the first connection terminal of the U-phase winding, the first connection terminal of the V-phase winding, and the first connection terminal of the W-phase winding. The switch circuit changes the connection of the second connection terminal of the U-phase winding, the second connection terminal of the V-phase winding, and the second connection terminal of the W-phase winding. The inverter circuit has a first high-potential wiring, a first low-potential wiring, and three first series switch circuits provided for each of the three windings. The first series switch circuit has a first upper reverse-conducting switching element that is a reverse-conducting switching element connected between the first connection terminal of the corresponding winding and the first high-potential wiring, and a first lower reverse-conducting switching element that is a reverse-conducting switching element connected between the first connection terminal of the corresponding winding and the first low-potential wiring. The switch circuit has a second high-potential wiring, a second low-potential wiring, and at least one second series switch circuit. The second series switch circuit has a second upper reverse-conducting switching element that is a reverse-conducting switching element connected between the second connection terminal of the corresponding winding and the second high-potential wiring, and a second lower reverse-conducting switching element that is a reverse-conducting switching element connected between the second connection terminal of the corresponding winding and the second low-potential wiring. One of the three windings is a specific winding, the first series switch circuit connected to the specific winding among the three first series switch circuits is a specific first series switch circuit, and the second series switch circuit connected to the specific winding among the at least one second series switch circuit is a specific second series switch circuit. The electric circuit is capable of performing a first boost power transfer operation and a second boost power transfer operation.The first boost power transfer operation is an operation of transferring power from the first battery to the second battery by repeatedly turning on and off the second lower side reverse conducting switching element of the specific second series switch circuit in a state in which the positive electrode of the first battery is connected to the first high potential wiring, the negative electrode of the first battery is connected to the first low potential wiring and the second low potential wiring, the positive electrode of the second battery is connected to the second high potential wiring, the negative electrode of the second battery is connected to the first low potential wiring and the second low potential wiring, the first upper side reverse conducting switching element of the specific first series switch circuit is turned on, and the first lower side reverse conducting switching element of the specific first series switch circuit is turned off. The second boost power transfer operation is an operation of transferring power from the second battery to the first battery by repeatedly turning on and off the first lower side reverse conducting switching element of the specific first series switch circuit in a state in which the positive electrode of the first battery is connected to the first high potential wiring, the negative electrode of the first battery is connected to the first low potential wiring and the second low potential wiring, the positive electrode of the second battery is connected to the second high potential wiring, the negative electrode of the second battery is connected to the first low potential wiring and the second low potential wiring, the second upper side reverse conducting switching element is turned on, and the second lower side reverse conducting switching element is turned off.

[0006] In this specification, a reverse-conducting switching element refers to an element in which a switch and a diode are connected in parallel, with the cathode of the diode connected to the high-potential terminal of the switch and the anode of the diode connected to the low-potential terminal of the switch. The switch may be a semiconductor switching element such as a field-effect transistor or an insulated gate bipolar transistor. The diode may be a pn diode or a Schottky barrier diode. The switch and the diode may be provided on a common semiconductor substrate or on different semiconductor substrates. In this specification, "on" of a reverse-conducting switching element means "on" of the switch constituting the reverse-conducting switching element, and "off" of a reverse-conducting switching element means "off" of the switch constituting the reverse-conducting switching element.

[0007] 26 and 27 show equivalent circuits of the electric circuit in the first boost power transfer operation and the second boost power transfer operation. 26 and 27 , reference numeral 901 denotes a first battery, reference numeral 902 denotes a second battery, reference numeral 911H denotes a first high-potential wiring, reference numeral 911L denotes a first low-potential wiring, reference numeral 912H denotes a second high-potential wiring, reference numeral 912L denotes a second low-potential wiring, reference numeral 921 denotes a specific first series switch circuit, reference numeral 921U denotes a first upper reverse-conducting switching element of the specific first series switch circuit, reference numeral 921L denotes a first lower reverse-conducting switching element of the specific first series switch circuit, reference numeral 922 denotes a specific second series switch circuit, reference numeral 922U denotes a second upper reverse-conducting switching element of the specific second series switch circuit, reference numeral 922L denotes a second lower reverse-conducting switching element of the specific second series switch circuit, reference numeral 930 denotes a specific winding, reference numeral 931 denotes a first connecting terminal of the specific winding, and reference numeral 932 denotes a second connecting terminal of the specific winding.

[0008] 26 , in the first boost power transfer operation, the first upper reverse-conducting switching element 921U of the specific first series switch circuit 921 is controlled to be ON, and the first lower reverse-conducting switching element 921L of the specific first series switch circuit 921 is controlled to be OFF. Furthermore, the second lower reverse-conducting switching element 922L of the specific second series switch circuit 922 is controlled to be repeatedly ON and OFF. When the second lower reverse-conducting switching element 922L is turned ON, current flows from the first high-potential wiring 911H to the low-potential wirings 911L and 912L via the first upper reverse-conducting switching element 921U, the specific winding 930, and the second lower reverse-conducting switching element 922L, as indicated by arrow 940. When the second lower reverse-conducting switching element 922L is then turned OFF, an induced voltage is generated in the specific winding 930 in a direction such that the second terminal 932 side has a high potential. Therefore, as shown by arrow 942, a current flows from the first high potential wiring 911H to the second high potential wiring 912H via the first upper reverse conducting switching element 921U, the specific winding 930, and the diode of the second upper reverse conducting switching element 922U. As a result, power is transferred from the first battery 901 to the second battery 902. In this way, in the first boost power transfer operation, the electric circuit functions as a boost converter that transfers power from the first battery 901 to the second battery 902.

[0009] 27 , in the second boost power transfer operation, the second upper reverse-conducting switching element 922U of the specific second series switch circuit 922 is controlled to be ON, and the second lower reverse-conducting switching element 922L of the specific second series switch circuit 922 is controlled to be OFF. Furthermore, the first lower reverse-conducting switching element 921L of the specific first series switch circuit 921 is controlled to be repeatedly ON and OFF. When the first lower reverse-conducting switching element 921L is turned ON, current flows from the second high-potential wiring 912H to the low-potential wirings 911L and 912L via the second upper reverse-conducting switching element 922U, the specific winding 930, and the first lower reverse-conducting switching element 921L, as indicated by arrow 950. When the first lower reverse-conducting switching element 921L is then turned OFF, an induced voltage is generated in the specific winding 930 in a direction such that the first terminal 931 side has a high potential. Therefore, as indicated by arrow 952, a current flows from the second high potential wiring 912H to the first high potential wiring 911H via the second upper reverse conducting switching element 922U, the specific winding 930, and the diode of the first upper reverse conducting switching element 921U. As a result, power is transferred from the second battery 902 to the first battery 901. In this way, in the second boost power transfer operation, the electric circuit functions as a boost converter that transfers power from the second battery 902 to the first battery 901.

[0010] As described above, the electrical circuit disclosed in this specification can transfer power bidirectionally between the first battery and the second battery using the windings of a three-phase motor, even if the first battery and the second battery are not connected in series.

[0011] 1 is a circuit diagram of an electric circuit according to an embodiment; FIG. 2 is a circuit diagram of an electric circuit in which the positions of diodes 71 and 73 are interchanged; FIG. 3 is an explanatory diagram of a first inverter operation; FIG. 4 is an explanatory diagram of a second inverter operation; and FIG. 5 is a graph showing execution regions of the first inverter operation and the second inverter operation.. FIG. 4 is an explanatory diagram of a series charging operation; FIG. 5 is an explanatory diagram of a series power supply operation; and FIG. 6 is an explanatory diagram of a series power transfer operation.. An equivalent circuit diagram of an electric circuit in a series power transfer operation. A graph showing a battery current when an SOC adjustment operation is performed alone; A graph showing a battery current when a battery warming operation is performed alone; A graph showing a battery current when an SOC adjustment operation and a charging operation are performed simultaneously; A graph showing a battery current when a battery warming operation and a charging operation are performed simultaneously; A graph showing a battery current when an SOC adjustment operation and a power supply operation are performed simultaneously; A graph showing a battery current when a battery warming operation and a power supply operation are performed simultaneously; A graph showing a battery current when a battery warming operation and a power supply operation are performed simultaneously. An explanatory diagram of a parallel charging operation; An explanatory diagram of a parallel power supply operation; An explanatory diagram of a non-series power transfer operation (first step-up power transfer operation); An explanatory diagram of a non-series power transfer operation (first step-down power transfer operation). 1 is an explanatory diagram of a non-series power transfer operation (second step-up power transfer operation); 2 is an explanatory diagram of a non-series power transfer operation (second step-down power transfer operation); 3 is a circuit diagram of an electric circuit of a modified example; 4 is a circuit diagram of an electric circuit of a modified example; 5 is a circuit diagram of an electric circuit of a modified example; 6 is a circuit diagram of an electric circuit of a modified example; 7 is a circuit diagram illustrating a first step-up power transfer operation; 8 is a circuit diagram illustrating a second step-up power transfer operation.

[0012] When the configuration of the electric circuit disclosed in this specification is referred to as configuration 1, additional configurations of the electric circuit will be described below.

[0013] (Configuration 2) The electric circuit according to Configuration 1, wherein the electric circuit is capable of performing a first inverter operation, and the first inverter operation is an operation in which the inverter circuit supplies AC current to the three-phase motor in a state in which the second connection terminal of the U-phase winding, the second connection terminal of the V-phase winding, and the second connection terminal of the W-phase winding are short-circuited by the switch circuit.

[0014] (Configuration 3) The electric circuit according to Configuration 2, wherein, in the first inverter operation, the positive electrode of the first battery is connected to the first high potential wiring, the negative electrode of the first battery is connected to the positive electrode of the second battery, and the negative electrode of the second battery is connected to the first low potential wiring.

[0015] (Configuration 4) The electric circuit according to configuration 2 or 3, wherein in the first inverter operation, the positive electrode of the second battery is insulated from the second high potential wiring.

[0016] (Configuration 5) The electric circuit according to configuration 2, wherein the switch circuit has three of the second series switch circuits provided for each of three of the windings.

[0017] (Configuration 6) The electric circuit according to Configuration 5, wherein the electric circuit is capable of performing a second inverter operation, and the second inverter operation is an operation of supplying AC current to the three-phase motor by controlling a current in the U-phase winding with the first series switch circuit and the second series switch circuit connected to the U-phase winding, controlling a current in the V-phase winding with the first series switch circuit and the second series switch circuit connected to the V-phase winding, and controlling a current in the W-phase winding with the first series switch circuit and the second series switch circuit connected to the W-phase winding, with the first high potential wiring connected to the second high potential wiring and the first low potential wiring connected to the second low potential wiring.

[0018] According to this configuration, the three-phase motor can be rotated in a higher speed or higher torque range in the second inverter operation than in the first inverter operation.

[0019] (Configuration 7) The electric circuit according to any one of configurations 2 to 4, wherein the switch circuit has three second series switch circuits provided one for each of three of the windings, and in the first inverter operation, the second upper reverse-conducting switching elements of the three second series switch circuits are turned on and the second lower reverse-conducting switching elements of the three second series switch circuits are turned off.

[0020] According to this configuration, in the first inverter operation, the second connection terminals of the windings of the three-phase motor can be short-circuited to form a neutral point by the short-circuited portion.

[0021] (Configuration 8) The electric circuit according to any one of configurations 2 to 4, wherein the switch circuit has three of the second series switch circuits provided for each of three of the windings, and further has a low-potential wiring switch connected between the first low-potential wiring and the second low-potential wiring, and in the first inverter operation, the second upper reverse-conducting switching elements of the three second series switch circuits are turned on, the second lower reverse-conducting switching elements of the three second series switch circuits are turned on, and the low-potential wiring switch is turned off.

[0022] According to this configuration, in the first inverter operation, the second connection terminals of the windings of the three-phase motor can be short-circuited to form a neutral point by the short-circuited portion.

[0023] (Configuration 9) The electric circuit according to any one of configurations 2 to 4, wherein the switch circuit has three of the second series switch circuits provided for each of three of the windings, and further has a low-potential wiring switch connected between the first low-potential wiring and the second low-potential wiring, and in the first inverter operation, the second upper reverse-conducting switching elements of the three second series switch circuits are turned off, the second lower reverse-conducting switching elements of the three second series switch circuits are turned on, and the low-potential wiring switch is turned off.

[0024] According to this configuration, in the first inverter operation, the second connection terminals of the windings of the three-phase motor can be short-circuited to form a neutral point by the short-circuited portion.

[0025] (Configuration 10) An electric circuit comprising: a first diode and a second diode connected in series between the first high potential wiring and the second high potential wiring; a first switch connected in parallel to the first diode; and a second switch connected in parallel to the second diode; wherein the first diode is oriented such that the first high potential wiring side is the anode, and the second diode is oriented such that the first high potential wiring side is the cathode; the switch circuit has three second series switch circuits provided for each of three of the windings; and the electric circuit is capable of performing a second inverter operation. 5. The electric circuit according to any one of configurations 2 to 4, wherein the second inverter operation is an operation in which, with the first high potential wiring connected to the second high potential wiring and the first low potential wiring connected to the second low potential wiring, a current in the U-phase winding is controlled by the first series switch circuit and the second series switch circuit connected to the U-phase winding, a current in the V-phase winding is controlled by the first series switch circuit and the second series switch circuit connected to the V-phase winding, and a current in the W-phase winding is controlled by the first series switch circuit and the second series switch circuit connected to the W-phase winding, thereby supplying an AC current to the three-phase motor; wherein, in the second inverter operation, the first switch and the second switch are turned on; and, in the first inverter operation, the first switch is turned on and the second switch is turned off, or the first switch and the second switch are turned off.

[0026] This configuration can suppress a rise in the potential of the neutral point due to a surge.

[0027] (Configuration 11) The electric circuit according to configuration 1 or 2, further comprising a high-potential external connection terminal and a low-potential external connection terminal, wherein the electric circuit is capable of performing a parallel charging and power supply operation, and the parallel charging and power supply operation is an operation of performing at least one of charging and power supply to the first battery and the second battery in parallel via the high-potential external connection terminal and the low-potential external connection terminal, in a state where the positive electrode of the first battery is connected to the high-potential external connection terminal via the first high-potential wiring, the negative electrode of the first battery is connected to the low-potential external connection terminal via the first low-potential wiring, the positive electrode of the second battery is connected to the high-potential external connection terminal via the second high-potential wiring, and the negative electrode of the second battery is connected to the low-potential external connection terminal via the first low-potential wiring.

[0028] (Configuration 12) The electric circuit according to configuration 11, wherein at least one of the first boost power transfer operation and the second boost power transfer operation and the parallel charging operation can be performed simultaneously.

[0029] (Configuration 13) The electric circuit according to configuration 1 or 2, further comprising a high-potential external connection terminal and a low-potential external connection terminal, wherein the electric circuit is capable of performing a series charging and power supply operation, and the series charging and power supply operation is an operation of at least one of charging and power supplying the first battery and the second battery in series via the high-potential external connection terminal and the low-potential external connection terminal, with the positive electrode of the first battery connected to the high-potential external connection terminal via the first high-potential wiring, the negative electrode of the first battery connected to the positive electrode of the second battery, and the negative electrode of the second battery connected to the low-potential external connection terminal via the first low-potential wiring.

[0030] (Configuration 14) The electric circuit according to configuration 1 or 2, wherein a battery temperature raising operation is performed to raise the temperatures of the first battery and the second battery by alternately repeating the first voltage boost power transfer operation and the second voltage boost power transfer operation.

[0031] (Configuration 15) The electric circuit according to configuration 1 or 2, wherein an SOC adjustment operation is performed to adjust the charging rates of the first battery and the second battery by performing at least one of the first boost power transfer operation and the second boost power transfer operation.

[0032] (Configuration 16) The electric circuit according to Configuration 1 or 2, wherein in the first boost power transfer operation, the second lower reverse-conducting switching element of the specific second series switch circuit and the second upper reverse-conducting switching element of the specific second series switch circuit are alternately turned on.

[0033] (Configuration 17) The electric circuit according to configuration 1 or 2, wherein the second upper reverse-conducting switching element of the specific second series switch circuit is maintained in an off state in the first boost power transfer operation.

[0034] (Configuration 18) The electric circuit according to Configuration 1 or 2, wherein, in the second boost power transfer operation, the first lower reverse-conducting switching element of the specific first series switch circuit and the first upper reverse-conducting switching element of the specific first series switch circuit are alternately turned on.

[0035] The electric circuit of the embodiment shown in Fig. 1 is mounted on a vehicle. The electric circuit of the embodiment includes a battery unit 30, a first inverter circuit 10, a second inverter circuit 20, and a three-phase motor 40. The three-phase motor 40 is a motor for driving the vehicle. The electric circuit converts DC power output by the battery unit 30 into AC power and supplies it to the three-phase motor 40 to drive the vehicle.

[0036] The battery unit 30 has a first battery 31, a second battery 32, and a relay switch 50. The relay switch 50 is connected between the negative electrode of the first battery 31 and the positive electrode of the second battery 32. When the relay switch 50 is turned on, the first battery 31 and the second battery 32 are connected in series. The first battery 31 and the second battery 32 each output a DC voltage of 400 V. When the first battery 31 and the second battery 32 are connected in series, the battery unit 30 outputs a DC voltage of 800 V.

[0037] The three-phase motor 40 has a U-phase winding 40U, a V-phase winding 40V, and a W-phase winding 40W. Each of the windings 40U, 40V, and 40W is provided on a stator of the three-phase motor 40. A rotor (not shown) of the three-phase motor 40 rotates as the current flowing through the windings 40U, 40V, and 40W changes. A first connection terminal 41 is provided at one end of each of the windings 40U, 40V, and 40W, and a second connection terminal 42 is provided at the other end of each of the windings 40U, 40V, and 40W.

[0038] The first inverter circuit 10 is connected to the battery unit 30 and the first connection terminals 41 of the windings 40U, 40V, and 40W. The first inverter circuit 10 has a high-potential wiring 10H, a low-potential wiring 10L, and three output wirings 10U, 10V, and 10W. The high-potential wiring 10H is connected to the positive electrode of the first battery 31 via a relay switch 51. The low-potential wiring 10L is connected to the negative electrode of the second battery 32 via a relay switch 52. A smoothing capacitor 10C is connected between the high-potential wiring 10H and the low-potential wiring 10L. The output wiring 10U is connected to the first connection terminal 41 of the winding 40U. The output wiring 10V is connected to the first connection terminal 41 of the winding 40V. The output wiring 10W is connected to the first connection terminal 41 of the winding 40W.

[0039] The first inverter circuit 10 includes three series switch circuits 12U, 12V, and 12W. Each of the series switch circuits 12U, 12V, and 12W is a circuit configured with two reverse-conducting switching elements 14 connected in series. Each reverse-conducting switching element 14 has a structure in which a switch (e.g., an insulated gate bipolar transistor or a field-effect transistor) and a diode (e.g., a pn diode or a Schottky barrier diode) are connected in antiparallel. In each reverse-conducting switching element 14, the cathode of the diode is connected to the high-potential terminal (i.e., the collector or drain) of the switch, and the anode of the diode is connected to the low-potential terminal (i.e., the emitter or source) of the switch.

[0040] The series switch circuit 12U is provided for the winding 40U. The series switch circuit 12U has a reverse-conducting switching element 14UU and a reverse-conducting switching element 14UL. The high-potential terminal of the reverse-conducting switching element 14UU is connected to the high-potential wiring 10H. The low-potential terminal of the reverse-conducting switching element 14UU and the high-potential terminal of the reverse-conducting switching element 14UL are connected to the first connection terminal 41 of the winding 40U via the output wiring 10U. The low-potential terminal of the reverse-conducting switching element 14UL is connected to the low-potential wiring 10L.

[0041] The series switch circuit 12V is provided for the winding 40V. The series switch circuit 12V has a reverse-conducting switching element 14VU and a reverse-conducting switching element 14VL. The high-potential terminal of the reverse-conducting switching element 14VU is connected to the high-potential wiring 10H. The low-potential terminal of the reverse-conducting switching element 14VU and the high-potential terminal of the reverse-conducting switching element 14VL are connected to the first connection terminal 41 of the winding 40V via the output wiring 10V. The low-potential terminal of the reverse-conducting switching element 14VL is connected to the low-potential wiring 10L.

[0042] The series switch circuit 12W is provided for the winding 40W. The series switch circuit 12W has a reverse-conducting switching element 14WU and a reverse-conducting switching element 14WL. The high-potential terminal of the reverse-conducting switching element 14WU is connected to the high-potential wiring 10H. The low-potential terminal of the reverse-conducting switching element 14WU and the high-potential terminal of the reverse-conducting switching element 14WL are connected to the first connection terminal 41 of the winding 40W via the output wiring 10W. The low-potential terminal of the reverse-conducting switching element 14WL is connected to the low-potential wiring 10L.

[0043] The second inverter circuit 20 is connected to the second connection terminals 42 of the windings 40U, 40V, and 40W. The second inverter circuit 20 has a high-potential wiring 20H, a low-potential wiring 20L, and three output wirings 20U, 20V, and 20W. The low-potential wiring 20L is connected to the low-potential wiring 10L. The output wiring 20U is connected to the second connection terminal 42 of the winding 40U. The output wiring 20V is connected to the second connection terminal 42 of the winding 40V. The output wiring 20W is connected to the second connection terminal 42 of the winding 40W.

[0044] The second inverter circuit 20 has three series switch circuits 22U, 22V, and 22W. Each of the series switch circuits 22U, 22V, and 22W is a circuit configured with two reverse-conducting switching elements 24 connected in series. Similar to each reverse-conducting switching element 14, each reverse-conducting switching element 24 has a structure in which a switch and a diode are connected in anti-parallel.

[0045] The series switch circuit 22U is provided for the winding 40U. The series switch circuit 22U has a reverse-conducting switching element 24UU and a reverse-conducting switching element 24UL. The high-potential terminal of the reverse-conducting switching element 24UU is connected to the high-potential wiring 20H. The low-potential terminal of the reverse-conducting switching element 24UU and the high-potential terminal of the reverse-conducting switching element 24UL are connected to the second connection terminal 42 of the winding 40U via the output wiring 20U. The low-potential terminal of the reverse-conducting switching element 24UL is connected to the low-potential wiring 20L.

[0046] The series switch circuit 22V is provided for the winding 40V. The series switch circuit 22V has a reverse-conducting switching element 24VU and a reverse-conducting switching element 24VL. The high potential terminal of the reverse-conducting switching element 24VU is connected to the high potential wiring 20H. The low potential terminal of the reverse-conducting switching element 24VU and the high potential terminal of the reverse-conducting switching element 24VL are connected to the second connection terminal 42 of the winding 40V via the output wiring 20V. The low potential terminal of the reverse-conducting switching element 24VL is connected to the low potential wiring 20L.

[0047] The series switch circuit 22W is provided for the winding 40W. The series switch circuit 22W has a reverse-conducting switching element 24WU and a reverse-conducting switching element 24WL. The high-potential terminal of the reverse-conducting switching element 24WU is connected to the high-potential wiring 20H. The low-potential terminal of the reverse-conducting switching element 24WU and the high-potential terminal of the reverse-conducting switching element 24WL are connected to the second connection terminal 42 of the winding 40W via the output wiring 20W. The low-potential terminal of the reverse-conducting switching element 24WL is connected to the low-potential wiring 20L.

[0048] The electric circuit includes a wiring 60, relay switches 53, 54, and 55, and a smoothing capacitor 20C. The relay switch 53 is provided between the wiring 60 and the positive electrode of the second battery 32. When the relay switch 53 is turned on, the wiring 60 is connected to the positive electrode of the second battery 32. The relay switch 54 is provided between the wiring 60 and the high-potential wiring 20H. When the relay switch 54 is turned on, the wiring 60 is connected to the high-potential wiring 20H. The relay switch 55 is provided between the negative electrode of the first battery 31 and the negative electrode of the second battery 32. When the relay switch 55 is turned on, the negative electrode of the first battery 31 is connected to the negative electrode of the second battery 32. The smoothing capacitor 20C is connected between the wiring 60 and the low-potential wiring 20L.

[0049] The electric circuit includes a diode 71, a switch element 72, a diode 73, and a switch element 74. The diodes 71 and 73 are connected in series between the high-potential wiring 10H and the high-potential wiring 20H. The anode of the diode 71 is connected to the high-potential wiring 10H, the cathode of the diode 71 is connected to the cathode of the diode 73, and the anode of the diode 73 is connected to the high-potential wiring 20H. That is, the diode 71 is oriented such that its anode faces the high-potential wiring 10H, and the diode 73 is oriented such that its cathode faces the high-potential wiring 10H. The switch element 72 is connected in parallel to the diode 71. The switch element 72 and the diode 71 may be configured as reverse-conducting switching elements. The switch element 74 is connected in parallel to the diode 73. The switch element 74 and the diode 73 may be configured as reverse-conducting switching elements. As shown in FIG. 2, the positions of the set of diode 71 and switch element 72 and the set of diode 73 and switch element 74 may be interchanged.

[0050] When the switch elements 72 and 74 are both turned on, a short circuit occurs between the high potential wiring 10H and the high potential wiring 20H. When the switch elements 72 and 74 are both turned off, the high potential wiring 10H and the high potential wiring 20H are insulated from each other. When the switch element 72 is turned on and the switch element 74 is turned off, a current can flow from the high potential wiring 20H to the high potential wiring 10H via the diode 73 and the switch element 72, but a current cannot flow in the opposite direction.

[0051] The electric circuit has a high-potential external connection terminal 80H, a low-potential external connection terminal 80L, and relay switches 57 and 58. The high-potential external connection terminal 80H is connected to the high-potential wiring 10H via the relay switch 57. The low-potential external connection terminal 80L is connected to the low-potential wiring 10L via the relay switch 58. The high-potential external connection terminal 80H and the low-potential external connection terminal 80L are connected to equipment outside the vehicle.

[0052] The electric circuit has a control circuit 90. The control circuit 90 is connected to the gates of the switching elements that make up each of the reverse-conducting switching elements 14 and 24, and controls these switching elements. The control circuit 90 also controls the switch elements 72 and 74 and the relay switches 50, 51, 52, 53, 54, 55, 57, and 58. The control circuit 90 has a CPU, memory, etc. The memory of the control circuit 90 stores a program that controls each part of the electric circuit. The control circuit 90 performs each operation described below in accordance with the program.

[0053] Next, various operations of the electric circuit will be described. Note that in Figures 3 to 4, 6 to 8, 16 to 17, and 22 to 24, switches that are controlled to be always off are indicated by dotted hatching, and switches that are controlled to be always on are indicated by diagonal hatching. Switches that are not hatched in Figures 3 to 4, 6 to 8, 16 to 17, and 22 to 24 are switches that are appropriately controlled by the control circuit 90.

[0054] (First Inverter Operation) The electric circuit can perform a first inverter operation to drive the three-phase motor 40. In the first inverter operation, the control circuit 90 controls the relay switches 50, 51, and 52, the switch element 72, and the reverse-conducting switching elements 24UU, 24VU, and 24VW to be on, and controls the relay switches 53, 54, 55, 57, and 58, the switch element 74, and the reverse-conducting switching elements 24UL, 24VL, and 24WL to be off, as shown in FIG. 3 . In this state, the control circuit 90 switches on and off each of the reverse-conducting switching elements 14 of the first inverter circuit 10, thereby supplying AC current to the three-phase motor 40.

[0055] When the relay switch 51 is turned on, the positive electrode of the first battery 31 is connected to the high-potential wiring 10H. When the relay switch 50 is turned on, the negative electrode of the first battery 31 is connected to the positive electrode of the second battery 32. When the relay switch 52 is turned on, the negative electrode of the second battery 32 is connected to the low-potential wiring 10L. Therefore, the DC voltage (i.e., 800 V) output from the series circuit of the first battery 31 and the second battery 32 is applied between the high-potential wiring 10H and the low-potential wiring 10L. Because the reverse-conducting switching elements 24UU, 24VU, and 24VW are controlled to be on, the second connection terminals 42 of the windings 40U, 40V, and 40W are short-circuited via the high-potential wiring 20H. In other words, the high-potential wiring 20H functions as a neutral point. When the reverse-conducting switching elements 24UL, 24VL, and 24VL are turned off, the high-potential wiring 20H (i.e., the neutral point) is insulated from the low-potential wirings 10L and 20L (i.e., a potential of 0 V). When the relay switches 53 and 54 are turned off, the high-potential wiring 20H (i.e., the neutral point) is insulated from the positive electrode of the second battery 32 (i.e., a potential of 400 V). When the switch element 74 is turned off, the high-potential wiring 20H (i.e., the neutral point) is insulated from the high-potential wiring 10H (i.e., a potential of 800 V). In this way, the potential of the high-potential wiring 20H (i.e., the neutral point) is independent of the other potentials. The potential of the high-potential wiring 20H fluctuates between 0 V and 800 V. If the potential of the high-potential wiring 20H exceeds 800 V due to a surge, the diode 73 turns on, and a current flows from the high-potential wiring 20H to the high-potential wiring 10H via the diode 73 and the switch element 72. This prevents the potential of the high-potential wiring 20H from becoming excessively high.

[0056] If it is not necessary to release current from the high potential wiring 20H to the high potential wiring 10H when the potential of the high potential wiring 20H rises, both the switch elements 72 and 74 may be controlled to be turned off in the first inverter operation.

[0057] As described above, in the first inverter operation, the control circuit 90 switches on and off each reverse-conducting switching element 14 of the first inverter circuit 10. The operation of the first inverter circuit 10 in the first inverter operation is similar to that of a general inverter. For example, as shown by arrow 110 in FIG. 3 , when the reverse-conducting switching elements 14UU and 14WL are turned on, current flows from the high-potential wiring 10H to the low-potential wiring 10L via the winding 40U, the neutral point, and the winding 40W. The control circuit 90 switches on and off each reverse-conducting switching element 14 of the first inverter circuit 10, thereby controlling the current flowing through the windings 40U, 40V, and 40W and supplying three-phase AC current to the three-phase motor 40. This drives the three-phase motor 40. Note that in the first inverter operation, the current path passes through two windings, as illustrated by arrow 110.

[0058] (Second Inverter Operation) The electric circuit can perform a second inverter operation to drive the three-phase motor 40. The second inverter operation is an inverter operation for driving the three-phase motor 40 at a higher rotation speed or torque than the first inverter operation. In the second inverter operation, the control circuit 90 controls the relay switches 50, 51, and 52 and the switch elements 72 and 74 to be on and controls the relay switches 53, 54, 55, 57, and 58 to be off, as shown in FIG. 4 . In this state, the control circuit 90 switches on and off the reverse-conducting switching elements 14 of the first inverter circuit 10 and the reverse-conducting switching elements 24 of the second inverter circuit 20, thereby supplying AC current to the three-phase motor 40.

[0059] When the relay switches 50, 51, and 52 are turned on, a DC voltage (i.e., 800 V) output from the series circuit of the first battery 31 and the second battery 32 is applied between the high-potential wiring 10H and the low-potential wiring 10L. When the switch elements 72 and 74 are turned on, the high-potential wiring 10H and the high-potential wiring 20H are short-circuited. That is, the high-potential wiring 20H has the same potential as the high-potential wiring 10H.

[0060] As described above, in the second inverter operation, the control circuit 90 switches on and off the reverse-conducting switching elements 14 of the first inverter circuit 10 and the reverse-conducting switching elements 24 of the second inverter circuit 20. The control circuit 90 controls the current flowing through the winding 40U using the series switch circuit 12U and the series switch circuit 22U. When the reverse-conducting switching elements 14UU and 24UL are turned on and the reverse-conducting switching elements 24UU and 14UL are turned off, a current flows through the winding 40U from the first connection terminal 41 to the second connection terminal 42, as shown by arrow 120 in FIG. 4 . When the reverse-conducting switching elements 24UU and 14UL are turned on and the reverse-conducting switching elements 14UU and 24UL are turned off, a current flows through the winding 40U from the second connection terminal 42 to the first connection terminal 41. In this way, the control circuit 90 controls the current flowing through the winding 40U using the two series switch circuits 12U and 22U (i.e., the reverse-conducting switching elements 14UU, 14UL, 24UU, and 24UL). Similarly, the control circuit 90 controls the current flowing through the winding 40V using the two series switch circuits 12V and 22V, and controls the current flowing through the winding 40W using the two series switch circuits 12W and 22W. In this way, the control circuit 90 controls the currents flowing through the windings 40U, 40V, and 40W by switching the reverse-conducting switching elements 14 and 24 of the first inverter circuit 10 and the second inverter circuit 20, thereby supplying three-phase AC current to the three-phase motor 40. This drives the three-phase motor 40.

[0061] In the second inverter operation, the current path passes through one winding, as illustrated by arrow 120 in FIG. 4 . On the other hand, in the first inverter operation, the current path passes through two windings, as illustrated by arrow 110 in FIG. 3 . Therefore, in the second inverter operation, a higher voltage can be applied to each winding than in the first inverter operation. As illustrated in FIG. 5 , the control circuit 90 executes the first inverter operation when the rotation speed and torque of the three-phase motor 40 are low, and executes the second inverter operation when at least one of the rotation speed and torque of the three-phase motor 40 is high. When the rotation speed of the three-phase motor 40 is high, a high back electromotive force is generated in each of the windings 40U, 40V, and 40W. By executing the second inverter operation when the rotation speed of the three-phase motor 40 is high, a voltage even higher than the back electromotive force can be applied to each of the windings 40U, 40V, and 40W. This allows the three-phase motor 40 to be driven at a higher rotation speed.

[0062] (Series Charging Operation) An external rapid charging device may be connected to the high-potential external connection terminal 80H and the low-potential external connection terminal 80L. The rapid charging device applies a high voltage of more than 800 V between the high-potential external connection terminal 80H and the low-potential external connection terminal 80L. When the rapid charging device is connected to the high-potential external connection terminal 80H and the low-potential external connection terminal 80L, the control circuit 90 performs a series charging operation. In the series charging operation, as shown in FIG. 6 , the control circuit 90 controls the relay switches 50, 51, 52, 57, and 58 to be on and the relay switches 53, 54, and 55 to be off. When the relay switch 51 is on, the positive electrode of the first battery 31 is connected to the high-potential wiring 10H. When the relay switch 50 is on, the negative electrode of the first battery 31 is connected to the positive electrode of the second battery 32. When the relay switch 52 is on, the negative electrode of the second battery 32 is connected to the low-potential wiring 10L. When relay switches 57 and 58 are turned on, the high voltage output by the rapid charging equipment is applied between high potential wiring 10H and low potential wiring 10L. Therefore, current flows as shown by arrow 130 in Figure 6, and batteries 31 and 32 connected in series are charged.

[0063] The control circuit 90 can perform the series charging operation alone, or can perform the series charging operation in combination with an SOC adjustment operation or a battery warming operation, which will be described later. When performing the series charging operation alone, the control circuit 90 controls all of the reverse-conducting switching elements 14 and 24 to be turned off, and controls all of the switch elements 72 and 74 to be turned off, as shown in FIG.

[0064] (Series Power Supply Operation) External power supply target equipment (e.g., a home storage battery) may be connected to the high-potential external connection terminal 80H and the low-potential external connection terminal 80L. When the voltage used by the power supply target equipment is high, the control circuit 90 performs series power supply operation. In series power supply operation, as shown in Fig. 7 , the control circuit 90 controls relay switches 50, 51, 52, 57, and 58 to be on and relay switches 53, 54, and 55 to be off. Then, the voltage output from the series circuit of the first battery 31 and the second battery 32 is applied to the power supply target equipment, and a current flows as shown by arrow 140 in Fig. 7 , supplying power to the power supply target equipment.

[0065] The control circuit 90 can perform the series power supply operation alone, or can perform the series power supply operation in combination with an SOC adjustment operation or a battery temperature increase operation, which will be described later. When performing the series power supply operation alone, the control circuit 90 controls all of the reverse-conducting switching elements 14 and 24 to be turned off, and controls all of the switch elements 72 and 74 to be turned off, as shown in FIG.

[0066] (Series Power Transfer Operation) The series power transfer operation is an operation for transferring power between the first battery 31 and the second battery 32 when the first battery 31 and the second battery 32 are connected in series. In the series power transfer operation, the control circuit 90 controls the relay switches 50, 51, 52, 53, and 54, the switch element 72, and the reverse-conducting switching elements 24UU, 24VU, and 24WU to be on, and controls the relay switch 55, the switch element 74, and the reverse-conducting switching elements 24UL, 24VL, and 24WL to be off, as shown in FIG. 8 . In this state, the control circuit 90 switches on and off the reverse-conducting switching elements 14 of the first inverter circuit 10. In the series power transfer operation, the electric circuit operates as a step-up / step-down converter using the windings 40U, 40V, and 40W, respectively. If it is not necessary to release current from the high potential wiring 20H to the high potential wiring 10H when the potential of the high potential wiring 20H rises, both the switch elements 72 and 74 may be controlled to be turned off in the series power transfer operation.

[0067] FIG. 9 shows an equivalent circuit of a portion that functions as a step-up / step-down converter using the winding 40U in series power transfer operation. The control circuit 90 controls the current flowing through the winding 40U by switching the reverse-conducting switching elements 14UU and 14UL. The control circuit 90 repeatedly turns the reverse-conducting switching elements 14UU and 14UL on and off. For example, the control circuit 90 alternately turns the reverse-conducting switching elements 14UU and 14UL on and off. When the reverse-conducting switching element 14UL is turned on, current flows from the positive electrode of the second battery 32 to the negative electrode of the second battery 32 through the winding 40U and the reverse-conducting switching element 14UL, as shown by arrow 151. Then, when the reverse-conducting switching element 14UL is turned off, an induced electromotive force is generated in the winding 40U in a direction that causes the first connection terminal 41 to have a higher potential. As a result, as shown by arrow 152, current flows from the negative electrode of the first battery 31 to the positive electrode of the first battery 31 via the winding 40U and the diode of the reverse conducting switching element 14UU. Therefore, when current flows alternately through the paths of arrows 151 and 152, power is transferred from the second battery 32 to the first battery 31. Furthermore, when the reverse conducting switching element 14UU is turned on, current flows from the positive electrode of the first battery 31 to the negative electrode of the first battery 31 via the reverse conducting switching element 14UU and the winding 40U, as shown by arrow 153. Thereafter, when the reverse conducting switching element 14UU is turned off, an induced electromotive force is generated in the winding 40U in a direction that causes the second connection terminal 42 side to have a high potential. As a result, as shown by arrow 154, current flows from the negative electrode of the second battery 32 to the positive electrode of the second battery 32 via the diode of the reverse conducting switching element 14UL and the winding 40U. Therefore, when current flows alternately through the paths of arrows 153 and 154 , power is transferred from the first battery 31 to the second battery 32 .

[0068] The control circuit 90 can also perform the power transfer described in Fig. 9 using the windings 40V and 40W. For example, power transfer may be performed simultaneously among the windings 40U, 40V, and 40W, or the timing of power transfer may be staggered among the windings 40U, 40V, and 40W. The control circuit 90 may also perform the power transfer described in Fig. 9 using one or two of the three windings 40U, 40V, and 40W.

[0069] The control circuit 90 can perform an SOC adjustment operation and a battery temperature increase operation as the series power transfer operation.

[0070] In the SOC adjustment operation, the control circuit 90 adjusts the SOCs (State Of Charge, also referred to as charging rates) of the first battery 31 and the second battery 32 to target values ​​by transferring power between the first battery 31 and the second battery 32 using the power transfer described in FIG. 9 . In the SOC adjustment operation, the control circuit 90 may transfer power between the first battery 31 and the second battery 32 from the battery with a higher SOC to the battery with a lower SOC, or from the battery with a lower SOC to the battery with a higher SOC. As illustrated in FIG. 10 , in the SOC adjustment operation, the control circuit 90 controls the current so that the current I1 flowing through the first battery 31 and the current I2 flowing through the second battery 32 are substantially constant. Note that the current I1 flowing through the first battery 31 and the current I2 flowing through the second battery 32 are each shown with the charging direction being positive.

[0071] In the battery warming operation, the control circuit 90 alternately transfers power from the first battery 31 to the second battery 32 and from the second battery 32 to the first battery 31 using the power transfer described in FIG. 9 . FIG. 11 shows the currents I1 and I2 during the battery warming operation. As shown in FIG. 11 , the control circuit 90 varies the current I1 of the first battery 31 and the current I2 of the second battery 32 in a sinusoidal waveform. By varying the currents in this manner, the first battery 31 and the second battery 32 are repeatedly charged and discharged, respectively, and the temperatures of the first battery 31 and the second battery 32 increase. If the performance of the batteries 31 and 32 has deteriorated due to low temperatures, the battery warming operation can restore the performance of the batteries 31 and 32.

[0072] The control circuit 90 can perform a series charging operation or a series power supply operation in addition to the series power transfer operation (i.e., the above-described SOC adjustment operation or battery warming operation). When simultaneously performing the series power transfer operation and the series charging operation, the control circuit 90 turns on the relay switches 57 and 58 while an external quick charging device is connected to the high-potential external connection terminal 80H and the low-potential external connection terminal 80L, and then performs the series power transfer operation (i.e., the SOC operation or the battery warming operation). Then, a current flows as indicated by arrow 130 in FIG. 6 , and simultaneously, a current generated by the windings 40U, 40V, and 40W flows. When simultaneously performing the series charging operation and the SOC adjustment operation, the currents I1 and I2 shift upward by the amount of the externally supplied current Is, as shown in FIG. 12 . When simultaneously performing the series charging operation and the battery warming operation, the currents I1 and I2 shift upward by the amount of the externally supplied current Is, as shown in FIG. 13 . When the series power transfer operation and the series power supply operation are performed simultaneously, the control circuit 90 turns on the relay switches 57 and 58 while the external power supply target equipment is connected to the high-potential external connection terminal 80H and the low-potential external connection terminal 80L, and then performs the series power transfer operation (i.e., the SOC adjustment operation or the battery heating operation). Then, a current flows as indicated by the arrow 140 in FIG. 7 , and simultaneously, a current generated by the windings 40U, 40V, and 40W flows. When the series power supply operation and the SOC adjustment operation are performed simultaneously, the currents I1 and I2 shift downward by the amount of the current Is supplied to the outside, as shown in FIG. 14 . When the series power supply operation and the battery heating operation are performed simultaneously, the currents I1 and I2 shift downward by the amount of the current Is supplied to the outside, as shown in FIG. 15 .

[0073] As described above, the electric circuit of the embodiment can perform the SOC adjustment operation or the battery warming operation while performing the series charging operation or the series power supply operation. Note that the control circuit 90 can also perform the series power transfer operation (i.e., the SOC adjustment operation or the battery warming operation) alone. In this case, the control circuit 90 controls the relay switches 57 and 58 to be turned off.

[0074] (Parallel Charging Operation) External general charging equipment may be connected to the high-potential external connection terminal 80H and the low-potential external connection terminal 80L. The general charging equipment applies a voltage higher than 400 V and lower than 800 V between the high-potential external connection terminal 80H and the low-potential external connection terminal 80L. When the general charging equipment is connected to the high-potential external connection terminal 80H and the low-potential external connection terminal 80L, the control circuit 90 performs parallel charging operation. In parallel charging operation, as shown in FIG. 16 , the control circuit 90 controls the relay switches 51, 52, 53, 54, 55, 57, and 58 and the reverse-conducting switching elements 14UU, 14VU, 14WU, 24UU, 24VU, and 24WU to be on, and controls the relay switch 50, the switch elements 72 and 74, and the reverse-conducting switching elements 14UL, 14VL, 14WL, 24UL, 24VL, and 24WL to be off. The positive electrode of the first battery 31 is connected to the high-potential external connection terminal 80H via relay switches 51 and 57. The negative electrode of the first battery 31 is connected to the low-potential external connection terminal 80L via relay switches 55, 52, and 58. The positive electrode of the second battery 32 is connected to the high-potential external connection terminal 80H via relay switches 53 and 54, reverse-conducting switching elements 24UU-24WU, windings 40U-40W, reverse-conducting switching elements 14UU-14WU, and relay switch 57. The negative electrode of the second battery 32 is connected to the low-potential external connection terminal 80L via relay switches 52 and 58. In other words, the first battery 31 and the second battery 32 are connected in parallel between the high-potential external connection terminal 80H and the low-potential external connection terminal 80L. Therefore, a current flows as indicated by arrow 160 in FIG. 16 , charging the parallel-connected batteries 31 and 32. In FIG. 16, only the path passing through the winding 40U is shown as the charging path for the second battery 32.

[0075] The control circuit 90 can perform the parallel charging operation alone, but can also perform the parallel charging operation in combination with an SOC adjustment operation or a battery temperature increase operation, which will be described later.

[0076] (Parallel Power Supply Operation) External power supply target equipment may be connected to the high-potential external connection terminal 80H and the low-potential external connection terminal 80L. When the operating voltage of the power supply target equipment is low, the control circuit 90 executes parallel power supply operation. In parallel power supply operation, as shown in FIG. 17 , the control circuit 90 controls the relay switches 51, 52, 53, 54, 55, 57, and 58 and the reverse-conducting switching elements 14UU, 14VU, 14WU, 24UU, 24VU, and 24WU to be on, and controls the relay switch 50, the switch elements 72 and 74, and the reverse-conducting switching elements 14UL, 14VL, 14WL, 24UL, 24VL, and 24WL to be off. Therefore, the first battery 31 and the second battery 32 are connected in parallel between the high-potential external connection terminal 80H and the low-potential external connection terminal 80L. Therefore, current flows as indicated by arrow 170 in Fig. 17, and power is supplied to the power supply target facility from the parallel-connected batteries 31 and 32. Note that Fig. 17 shows only the path passing through winding 40U as the power supply path from second battery 32.

[0077] The control circuit 90 can perform the parallel power supply operation alone, but can also perform the parallel power supply operation in combination with an SOC adjustment operation or a battery temperature increase operation, which will be described later.

[0078] (Non-series power transfer operation) The non-series power transfer operation is an operation for transferring power between the first battery 31 and the second battery 32 when the first battery 31 and the second battery 32 are not connected in series. In the non-series power transfer operation, the control circuit 90 controls the relay switches 51, 52, 53, 54, and 55 to be on, and controls the relay switch 50 and the switch elements 72 and 74 to be off. When the relay switch 51 is turned on, the positive electrode of the first battery 31 is connected to the high potential wiring 10H. When the relay switches 55 and 52 are turned on, the negative electrode of the first battery 31 is connected to the low potential wiring 10L and the low potential wiring 20L. When the relay switches 53 and 54 are turned on, the positive electrode of the second battery 32 is connected to the high potential wiring 20H. When the relay switch 52 is turned on, the negative electrode of the second battery 32 is connected to the low potential wiring 10L and the low potential wiring 20L. In this connection state, the electric circuit operates as a buck-boost converter using windings 40U, 40V, and 40W. The buck-boost converter using winding 40U (hereinafter referred to as the first buck-boost converter) is composed of reverse-conducting switching elements 14UU, 14UL, 24UU, and 24UL, and winding 40U. The buck-boost converter using winding 40V (hereinafter referred to as the second buck-boost converter) is composed of reverse-conducting switching elements 14VU, 14VL, 24VU, and 24VL, and winding 40V. The buck-boost converter using winding 40W (hereinafter referred to as the third buck-boost converter) is composed of reverse-conducting switching elements 14WU, 14WL, 24WU, and 24WL, and winding 40W. The first to third buck-boost converters can operate synchronously, or only one or two of them can operate. Since the first to third buck-boost converters operate in the same manner, the first buck-boost converter will be described below.

[0079] FIG. 18 shows an equivalent circuit of the first buck-boost converter. As shown in FIG. 18, the first battery 31 is connected between the high-potential wiring 10H and the low-potential wiring 10L, and the second battery 32 is connected between the high-potential wiring 20H and the low-potential wiring 20L. Furthermore, when switch elements 72 and 74 are turned off, the high-potential wiring 10H is insulated from the high-potential wiring 20H. The buck-boost converter can perform a first step-up power transfer operation, a first step-down power transfer operation, a second step-up power transfer operation, and a second step-down power transfer operation as non-series power transfer operations. The first step-up power transfer operation is an operation of transferring power from the first battery 31 to the second battery 32 while stepping down the voltage. The first step-down power transfer operation is an operation of transferring power from the first battery 31 to the second battery 32 while stepping down the voltage. The second step-up power transfer operation is an operation of transferring power from the second battery 32 to the first battery 31 while stepping up the voltage. The second step-down power transfer operation is an operation of transferring power from the second battery 32 to the first battery 31 while stepping down the voltage.

[0080] As shown in FIG. 18 , in the first boost power transfer operation, the control circuit 90 controls the reverse conducting switching element 14UU to be on and the reverse conducting switching element 14UL to be off. The control circuit 90 also repeatedly turns the reverse conducting switching element 24UL on and off. The duty ratio of the reverse conducting switching element 24UL is appropriately changed according to the control target value. Over a short period of time, the duty ratio of the reverse conducting switching element 24UL may be 0% or 100%. The reverse conducting switching element 24UU may be controlled in any manner as long as it is off during the period when the reverse conducting switching element 24UL is on. For example, the reverse conducting switching element 24UU may be always off, or the reverse conducting switching element 24UU and the reverse conducting switching element 24UL may be alternately on.

[0081] When the reverse conducting switching element 24UL is turned on, current flows from the positive electrode of the first battery 31 through the reverse conducting switching element 14UU, the winding 40U, and the reverse conducting switching element 24UL to the negative electrode of the second battery 32, as shown by arrow 181. Thereafter, when the reverse conducting switching element 24UL is turned off, an induced electromotive force is generated in the winding 40U in a direction such that the second connection terminal 42 side has a higher potential. As a result, current flows from the positive electrode of the first battery 31 to the positive electrode of the second battery 32 through the reverse conducting switching element 14UU, the winding 40U, and the diode of the reverse conducting switching element 24UU, as shown by arrow 182. In the first boost power transfer operation, current flows alternately as shown by arrows 181 and 182, thereby transferring power from the first battery 31 to the second battery 32. Since the voltage applied to the second battery 32 is the sum of the output voltage of the first battery 31 and the induced voltage generated in the winding 40U, a voltage higher than the output voltage of the first battery 31 is applied to the second battery 32. In this way, the first voltage-boost power transfer operation is an operation of transferring power from the first battery 31 to the second battery 32 while boosting the voltage.

[0082] As shown in FIG. 19 , in the first step-down power transfer operation, the control circuit 90 controls the reverse-conducting switching element 24UU to be on and the reverse-conducting switching element 24UL to be off. The control circuit 90 also repeatedly turns the reverse-conducting switching element 14UU on and off. The duty ratio of the reverse-conducting switching element 14UU is appropriately changed according to the control target value. Over a short period of time, the duty ratio of the reverse-conducting switching element 14UU may be 0% or 100%. The reverse-conducting switching element 14UL may be controlled in any manner as long as it is off during the period when the reverse-conducting switching element 14UU is on. For example, the reverse-conducting switching element 14UL may be always off, or the reverse-conducting switching element 14UL and the reverse-conducting switching element 14UU may be alternately on.

[0083] When the reverse conducting switching element 14UU is turned on, current flows from the positive electrode of the first battery 31 through the reverse conducting switching element 14UU, the winding 40U, and the reverse conducting switching element 24UU to the positive electrode of the second battery 32, as shown by arrow 183. When the reverse conducting switching element 14UU is then turned off, an induced electromotive force is generated in the winding 40U in a direction such that the second connection terminal 42 side has a higher potential. As a result, as shown by arrow 184, current flows from the negative electrode of the second battery 32 to the positive electrode of the second battery 32 through the diode of the reverse conducting switching element 14UL, the winding 40U, and the reverse conducting switching element 24UU. In the first step-down power transfer operation, current flows alternately as shown by arrows 183 and 184, thereby transferring power from the first battery 31 to the second battery 32. Since the output voltage of the first battery 31 is divided between the winding 40U and the second battery 32, a voltage lower than the output voltage of the first battery 31 is applied to the second battery 32. In this way, the first step-down power transfer operation is an operation of transferring power from the first battery 31 to the second battery 32 while stepping down the voltage.

[0084] As shown in FIG. 20 , in the second boost power transfer operation, the control circuit 90 controls the reverse conducting switching element 24UU to be on and the reverse conducting switching element 24UL to be off. The control circuit 90 also repeatedly turns the reverse conducting switching element 14UL on and off. The duty ratio of the reverse conducting switching element 14UL is appropriately changed according to the control target value. Over a short period of time, the duty ratio of the reverse conducting switching element 14UL may be 0% or 100%. The reverse conducting switching element 14UU may be controlled in any manner as long as it is off during the period when the reverse conducting switching element 14UL is on. For example, the reverse conducting switching element 14UU may be always off, or the reverse conducting switching element 14UU and the reverse conducting switching element 14UL may be alternately on.

[0085] When the reverse conducting switching element 14UL is turned on, current flows from the positive electrode of the second battery 32 through the reverse conducting switching element 24UU, the winding 40U, and the reverse conducting switching element 14UL to the negative electrode of the second battery 32, as shown by arrow 191. Thereafter, when the reverse conducting switching element 14UL is turned off, an induced electromotive force is generated in the winding 40U in a direction such that the first connection terminal 41 side has a higher potential. As a result, as shown by arrow 192, current flows from the positive electrode of the second battery 32 to the positive electrode of the first battery 31 through the reverse conducting switching element 24UU, the winding 40U, and the diode of the reverse conducting switching element 14UU. In the second boost power transfer operation, current flows alternately as shown by arrows 191 and 192, thereby transferring power from the second battery 32 to the first battery 31. Since the voltage applied to the first battery 31 is the sum of the output voltage of the second battery 32 and the induced voltage generated in the winding 40U, a voltage higher than the output voltage of the second battery 32 is applied to the first battery 31. In this way, the second boost power transfer operation is an operation of transferring power from the second battery 32 to the first battery 31 while boosting the voltage.

[0086] As shown in FIG. 21 , in the second step-down power transfer operation, the control circuit 90 controls the reverse-conducting switching element 14UU to be on and the reverse-conducting switching element 14UL to be off. The control circuit 90 also repeatedly turns the reverse-conducting switching element 24UU on and off. The duty ratio of the reverse-conducting switching element 24UU is appropriately changed according to the control target value. Over a short period of time, the duty ratio of the reverse-conducting switching element 24UU may be 0% or 100%. The reverse-conducting switching element 24UL may be controlled in any manner as long as it is off during the period when the reverse-conducting switching element 24UU is on. For example, the reverse-conducting switching element 24UL may be always off, or the reverse-conducting switching element 24UL and the reverse-conducting switching element 24UU may be alternately on.

[0087] When the reverse conducting switching element 24UU is turned on, current flows from the positive electrode of the second battery 32 through the reverse conducting switching element 24UU, the winding 40U, and the reverse conducting switching element 14UU to the positive electrode of the first battery 31, as shown by arrow 193. Thereafter, when the reverse conducting switching element 24UU is turned off, an induced electromotive force is generated in the winding 40U in a direction such that the first connection terminal 41 side has a higher potential. As a result, as shown by arrow 194, current flows from the negative electrode of the first battery 31 to the positive electrode of the first battery 31 through the diode of the reverse conducting switching element 24UL, the winding 40U, and the reverse conducting switching element 14UU. In the second step-down power transfer operation, current flows alternately as shown by arrows 193 and 194, thereby transferring power from the second battery 32 to the first battery 31. Since the output voltage of the second battery 32 is divided between the winding 40U and the first battery 31, a voltage lower than the output voltage of the second battery 32 is applied to the first battery 31. In this way, the second step-down power transfer operation is an operation of transferring power from the second battery 32 to the first battery 31 while stepping down the voltage.

[0088] In the non-series power transfer operation, the control circuit 90 appropriately performs the first step-up power transfer operation, the first step-down power transfer operation, the second step-up power transfer operation, and the second step-down power transfer operation according to the current and target values ​​of the output voltage of each battery. When transferring power from the first battery 31 to the second battery 32, the control circuit 90 performs the first step-up power transfer operation if the target value of the output voltage of the second battery 32 is greater than the current value of the output voltage of the first battery 31, and performs the first step-down power transfer operation if the target value of the output voltage of the second battery 32 is equal to or less than the current value of the output voltage of the first battery 31. Furthermore, when transferring power from the second battery 32 to the first battery 31, the control circuit 90 performs the second step-down power transfer operation if the target value of the output voltage of the second battery 32 is greater than the current value of the output voltage of the first battery 31, and performs the second step-up power transfer operation if the target value of the output voltage of the second battery 32 is equal to or less than the current value of the output voltage of the first battery 31.

[0089] The control circuit 90 can perform an SOC adjustment operation and a battery temperature increase operation as non-series power transfer operations.

[0090] In the SOC adjustment operation, the control circuit 90 adjusts the SOCs of the first battery 31 and the second battery 32 to target values ​​by transferring power between the first battery 31 and the second battery 32. In the SOC adjustment operation, the control circuit 90 may transfer power from the first battery 31 to the second battery 32, either from the battery with a higher SOC to the battery with a lower SOC, or from the battery with a lower SOC to the battery with a higher SOC. In the SOC adjustment operation, the control circuit 90 performs a first step-up power transfer operation, a first step-down power transfer operation, a second step-up power transfer operation, and a second step-down power transfer operation depending on the situation. As illustrated in FIG. 10 , in the SOC adjustment operation, the control circuit 90 controls the current so that the current I1 flowing through the first battery 31 and the current I2 flowing through the second battery 32 are substantially constant.

[0091] In the battery warming operation, the control circuit 90 alternately transfers power from the first battery 31 to the second battery 32 and from the second battery 32 to the first battery 31. In the power transfer from the first battery 31 to the second battery 32, the control circuit 90 performs a first voltage-boosting power transfer operation and a first voltage-decreasing power transfer operation depending on the situation. In the power transfer from the second battery 32 to the first battery 31, the control circuit 90 performs a second voltage-boosting power transfer operation and a second voltage-decreasing power transfer operation depending on the situation. For example, as shown in FIG. 11 , the control circuit 90 sinusoidally changes the current I1 of the first battery 31 and the current I2 of the second battery 32. By changing the current in this manner, the first battery 31 and the second battery 32 are repeatedly charged and discharged, respectively, and the temperatures of the first battery 31 and the second battery 32 increase. If the performance of the batteries 31 and 32 has deteriorated due to low temperatures, the battery warming operation can restore the performance of the batteries 31 and 32.

[0092] The control circuit 90 can perform a parallel charging operation or a parallel power supply operation in addition to the non-series power transfer operation (i.e., the above-described SOC adjustment operation or battery warming operation). When the non-series power transfer operation and the parallel charging operation are performed simultaneously, the control circuit 90 turns on the relay switches 57 and 58 while the high-potential external connection terminal 80H and the low-potential external connection terminal 80L are connected to external general charging equipment, and then performs the non-series power transfer operation (i.e., the SOC adjustment operation or the battery warming operation). Then, in addition to the current generated by the non-series power transfer operation, a current indicated by an arrow 160 in FIG. 16 (i.e., a current supplied from the external general charging equipment) flows. Therefore, when the parallel charging operation and the SOC adjustment operation of the non-series power transfer operation are performed simultaneously, the currents I1 and I2 are shifted upward by the amount of the externally supplied current Is, as shown in FIG. 12 . When the parallel charging operation and the battery warming operation of the non-series power transfer operation are performed simultaneously, the currents I1 and I2 are shifted upward by the amount of the current Is supplied from the outside, as shown in FIG. 13 . When the non-series power transfer operation and the parallel power supply operation are performed simultaneously, the control circuit 90 turns on the relay switches 57 and 58 while the external power supply target equipment is connected to the high-potential external connection terminal 80H and the low-potential external connection terminal 80L, and then performs the non-series power transfer operation (i.e., the SOC adjustment operation or the battery warming operation). Then, in addition to the current generated by the non-series power transfer operation, the current indicated by the arrow 170 in FIG. 17 (i.e., the current supplied to the external power supply target equipment) flows. Therefore, when the parallel power supply operation and the SOC adjustment operation of the non-series power transfer operation are performed simultaneously, the currents I1 and I2 are shifted downward by the amount of the current Is supplied from the outside, as shown in FIG. 14 . When the parallel power supply operation and the battery temperature raising operation of the non-series power transfer operation are performed simultaneously, as shown in FIG. 15, the currents I1 and I2 are shifted downward by the amount of the current Is supplied to the outside.

[0093] As described above, the electric circuit of the embodiment can perform the SOC adjustment operation and the battery warming operation while performing the parallel charging operation or the parallel power supply operation. Note that the control circuit 90 can also perform the non-series power transfer operation (i.e., the SOC adjustment operation or the battery warming operation) alone. In this case, the control circuit 90 controls the relay switches 57 and 58 to be turned off.

[0094] The first inverter circuit of the embodiments is an example of an inverter circuit. The series switch circuits 12U, 12V, and 12W of the embodiments are examples of first series switch circuits. The reverse-conducting switching elements 14UU, 14WU, and 14VU of the embodiments are examples of first upper reverse-conducting switching elements. The reverse-conducting switching elements 14UL, 14WL, and 14VL of the embodiments are examples of first lower reverse-conducting switching elements. The second inverter circuit of the embodiments is an example of a switch circuit. The series switch circuits 22U, 22V, and 22W of the embodiments are examples of second series switch circuits. The reverse-conducting switching elements 24UU, 24WU, and 24VU of the embodiments are examples of second upper reverse-conducting switching elements. The reverse-conducting switching elements 24UL, 24WL, and 24VL of the embodiments are examples of second lower reverse-conducting switching elements. Each of the windings 40U, 40V, and 40W in the embodiment is an example of a specific winding. If the winding 40U is considered to be a specific winding, the series switch circuit 12U is an example of a specific first series switch circuit, and the series switch circuit 22U is an example of a specific second series switch circuit. If the winding 40V is considered to be a specific winding, the series switch circuit 12V is an example of a specific first series switch circuit, and the series switch circuit 22V is an example of a specific second series switch circuit. If the winding 40W is considered to be a specific winding, the series switch circuit 12W is an example of a specific first series switch circuit, and the series switch circuit 22W is an example of a specific second series switch circuit.

[0095] In the electric circuit described above, the low-potential wiring 10L and the low-potential wiring 20L are always connected. However, as shown in FIG. 22 , a switch element 100 may be provided between the low-potential wiring 10L and the low-potential wiring 20L to insulate the low-potential wiring 10L from the low-potential wiring 20L. In this case, during first inverter operation, a neutral point where the second connection terminals 42 of the windings 40U, 40V, and 40W are connected to each other can be formed by various control methods. For example, as shown in FIG. 22 , the switch element 100 may be controlled to be off, and the reverse-conducting switching elements 24UU, 24VU, 24WU, 24UL, 24VL, and 24WL may be controlled to be on. Alternatively, as shown in FIG. 23 , the switch element 100 may be controlled to be off, and the upper reverse-conducting switching elements 24UU, 24VU, and 24WU may be controlled to be off, and the lower reverse-conducting switching elements 24UL, 24VL, and 24WL may be controlled to be on. Alternatively, as shown in FIG. 24 , the upper reverse-conducting switching elements 24UU, 24VU, and 24WU may be controlled to be on, and the lower reverse-conducting switching elements 24UL, 24VL, and 24WL may be controlled to be off. In this case, the switch element 100 may be off or on. In any of the control methods shown in FIGS. 22 to 24 , the second connection terminals 42 of the windings 40U, 40V, and 40W can be connected to each other by the second inverter circuit 20. When the switch element 100 is provided, the switch element 100 is turned on to short-circuit the low-potential wiring 10L and the low-potential wiring 20L in the second inverter operation, series power transfer operation, parallel charging operation, parallel power supply operation, and non-series power transfer operation. In the series charging operation and series power supply operation, the switch element 100 may be on or off.

[0096] In the above-described embodiment, the relay switch 54 is provided between the high-potential wiring 20H and the wiring 60. However, as shown in FIG. 25 , the high-potential wiring 20H may be directly connected to the wiring 60. That is, a smoothing capacitor 20C may be constantly connected between the high-potential wiring 20H and the low-potential wiring 20L. In this configuration, when attempting to perform the first inverter operation, the smoothing capacitor 20C is connected between the neutral point (i.e., the high-potential wiring 20H) and the low-potential wiring 20L, making it difficult to fluctuate the potential at the neutral point. This makes it difficult to properly perform the first inverter operation. However, even with this configuration, the second inverter operation can be performed. That is, the configuration of FIG. 25 is a circuit configuration applicable when driving the three-phase motor 40 in the second inverter operation.

[0097] Although the embodiments have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and variations of the specific examples exemplified above. The technical elements described in this specification or drawings exhibit technical utility alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. Furthermore, the technology exemplified in this specification or drawings simultaneously achieves multiple objectives, and achieving one of these objectives itself has technical utility.

Claims

1. An electric circuit, comprising: a battery unit including a first battery and a second battery; a three-phase motor having three windings, namely a U-phase winding, a V-phase winding, and a W-phase winding, each of the three windings having a first connection terminal provided at one end thereof and a second connection terminal provided at the other end thereof; an inverter circuit connected to the battery unit, the first connection terminal of the U-phase winding, the first connection terminal of the V-phase winding, and the first connection terminal of the W-phase winding; a switch circuit for changing the connection of the second connection terminal of the U-phase winding, the second connection terminal of the V-phase winding, and the second connection terminal of the W-phase winding. The inverter circuit includes a first high-potential wiring, a first low-potential wiring, and three first series switch circuits provided for each of the three windings. The first series switch circuit includes a first upper-side reverse-conducting switching element, which is a reverse-conducting switching element connected between the first connection terminal of the corresponding winding and the first high-potential wiring, and a first lower-side reverse-conducting switching element, which is a reverse-conducting switching element connected between the first connection terminal of the corresponding winding and the first low-potential wiring. The switch circuit includes a second high-potential wiring, a second low-potential wiring, and at least one second series switch circuit. The second series switch circuit includes a second upper-side reverse-conducting switching element, which is a reverse-conducting switching element connected between the second connection terminal of the corresponding winding and the second high-potential wiring, and a second lower-side reverse-conducting switching element, which is a reverse-conducting switching element connected between the second connection terminal of the corresponding winding and the second low-potential wiring. One of the three windings is a specific winding, the first series switch circuit connected to the specific winding among the three first series switch circuits is a specific first series switch circuit, and the second series switch circuit connected to the specific winding among at least one of the second series switch circuits is a specific second series switch circuit. The electric circuit is capable of performing a first boost power transfer operation and a second boost power transfer operation.The first step-up power transfer operation is an operation of transferring power from the first battery to the second battery by repeating turning on and off the second lower reverse-conducting switching element of the specific second series switch circuit in a state where the positive electrode of the first battery is connected to the first high-potential wiring, the negative electrode of the first battery is connected to the first low-potential wiring and the second low-potential wiring, the positive electrode of the second battery is connected to the second high-potential wiring, the negative electrode of the second battery is connected to the first low-potential wiring and the second low-potential wiring, the first upper reverse-conducting switching element of the specific first series switch circuit is on, and the first lower reverse-conducting switching element of the specific first series switch circuit is off. The second step-up power transfer operation is an operation of transferring power from the second battery to the first battery by repeating turning on and off the first lower reverse-conducting switching element of the specific first series switch circuit in a state where the positive electrode of the first battery is connected to the first high-potential wiring, the negative electrode of the first battery is connected to the first low-potential wiring and the second low-potential wiring, the positive electrode of the second battery is connected to the second high-potential wiring, the negative electrode of the second battery is connected to the first low-potential wiring and the second low-potential wiring, the second upper reverse-conducting switching element is on, and the second lower reverse-conducting switching element is off. Electrical circuit.

2. The electrical circuit is capable of executing a first inverter operation, and the first inverter operation is an operation of supplying an alternating current to the three-phase motor by the inverter circuit in a state where the second connection terminal of the U-phase winding, the second connection terminal of the V-phase winding, and the second connection terminal of the W-phase winding are short-circuited by the switch circuit. The electrical circuit according to claim 1.

3. In the first inverter operation, the positive electrode of the first battery is connected to the first high-potential wiring, the negative electrode of the first battery is connected to the positive electrode of the second battery, and the negative electrode of the second battery is connected to the first low-potential wiring. The electrical circuit according to claim 2.

4. In the first inverter operation, the positive electrode of the second battery is insulated from the second high-potential wiring. The electrical circuit according to claim 2 or 3.

5. The switch circuit has three second series switch circuits provided for each of the three windings. The electrical circuit according to claim 1 or 2.

6. The electrical circuit is capable of executing a second inverter operation, and the second inverter operation is an operation of supplying an alternating current to the three-phase motor by controlling the current of the U-phase winding by the first series switch circuit and the second series switch circuit connected to the U-phase winding, controlling the current of the V-phase winding by the first series switch circuit and the second series switch circuit connected to the V-phase winding, and controlling the current of the W-phase winding by the first series switch circuit and the second series switch circuit connected to the W-phase winding in a state where the first high-potential wiring is connected to the second high-potential wiring and the first low-potential wiring is connected to the second low-potential wiring. The electrical circuit according to claim 5.

7. The switch circuit has three second series switch circuits provided for each of the three windings. In the first inverter operation, the second upper reverse-conducting switching elements of the three second series switch circuits are turned on, and the second lower reverse-conducting switching elements of the three second series switch circuits are turned off. The electrical circuit according to claim 2 or 3.

8. The switch circuit has three second series switch circuits provided for each of the three windings, and further has a low potential wiring switch connected between the first low potential wiring and the second low potential wiring. In the first inverter operation, the second upper reverse conduction switching elements of the three second series switch circuits are turned on, the second lower reverse conduction switching elements of the three second series switch circuits are turned on, and the low potential wiring switch is turned off. The electric circuit according to claim 2 or 3.

9. The switch circuit has three second series switch circuits provided for each of the three windings, and further has a low potential wiring switch connected between the first low potential wiring and the second low potential wiring. In the first inverter operation, the second upper reverse conduction switching elements of the three second series switch circuits are turned off, the second lower reverse conduction switching elements of the three second series switch circuits are turned on, and the low potential wiring switch is turned off. The electric circuit according to claim 2 or 3.

10. A first diode and a second diode connected in series between the first high-potential wiring and the second high-potential wiring; a first switch connected in parallel to the first diode; and a second switch connected in parallel to the second diode. The first diode is provided with the anode on the first high-potential wiring side, and the second diode is provided with the cathode on the first high-potential wiring side. The switch circuit has three of the second series switch circuits provided for each of the three windings. The electric circuit is capable of performing a second inverter operation. The second inverter operation is an operation of supplying an alternating current to the three-phase motor by controlling the current of the U-phase winding by the first series switch circuit and the second series switch circuit connected to the U-phase winding, controlling the current of the V-phase winding by the first series switch circuit and the second series switch circuit connected to the V-phase winding, and controlling the current of the W-phase winding by the first series switch circuit and the second series switch circuit connected to the W-phase winding, in a state where the first high-potential wiring is connected to the second high-potential wiring and the first low-potential wiring is connected to the second low-potential wiring. In the second inverter operation, the first switch and the second switch are turned on. In the first inverter operation, the first switch is turned on and the second switch is turned off, or the first switch and the second switch are turned off. The electric circuit according to claim 2 or 3.

11. Further comprising a high-potential external connection terminal and a low-potential external connection terminal, wherein the electric circuit is capable of performing a parallel charge and discharge operation, and the parallel charge and discharge operation is such that the positive electrode of the first battery is connected to the high-potential external connection terminal via the first high-potential wiring, the negative electrode of the first battery is connected to the low-potential external connection terminal via the first low-potential wiring, the positive electrode of the second battery is connected to the high-potential external connection terminal via the second high-potential wiring, and the negative electrode of the second battery is connected to the low-potential external connection terminal via the first low-potential wiring, and at least one of charging and discharging is performed in parallel with respect to the first battery and the second battery via the high-potential external connection terminal and the low-potential external connection terminal. The electric circuit according to claim 1 or 2.

12. The electric circuit according to claim 11, capable of simultaneously performing at least one of the first boost power transfer operation and the second boost power transfer operation and the parallel charge and discharge operation.

13. Further comprising a high-potential external connection terminal and a low-potential external connection terminal, wherein the electric circuit is capable of performing a series charge and discharge operation, and the series charge and discharge operation is such that the positive electrode of the first battery is connected to the high-potential external connection terminal via the first high-potential wiring, the negative electrode of the first battery is connected to the positive electrode of the second battery, and the negative electrode of the second battery is connected to the low-potential external connection terminal via the first low-potential wiring, and at least one of charging and discharging is performed in series with respect to the first battery and the second battery via the high-potential external connection terminal and the low-potential external connection terminal. The electric circuit according to claim 1 or 2.

14. The electric circuit according to claim 1 or 2, capable of performing a battery temperature increase operation for increasing the temperatures of the first battery and the second battery by alternately repeating the first boost power transfer operation and the second boost power transfer operation.

15. The electric circuit according to claim 1 or 2, capable of performing an SOC adjustment operation for adjusting the state of charge of the first battery and the second battery by performing at least one of the first boost power transfer operation and the second boost power transfer operation.

16. In the first step-up power transfer operation, the second lower reverse-conducting switching element of the specific second series switch circuit and the second upper reverse-conducting switching element of the specific second series switch circuit are alternately turned on. The electric circuit according to claim 1 or 2.

17. In the first step-up power transfer operation, the second upper reverse-conducting switching element of the specific second series switch circuit is maintained in the off state. The electric circuit according to claim 1 or 2.

18. In the second step-up power transfer operation, the first lower reverse-conducting switching element of the specific first series switch circuit and the first upper reverse-conducting switching element of the specific first series switch circuit are alternately turned on. The electric circuit according to claim 1 or 2.

19. In the second step-up power transfer operation, the first upper reverse-conducting switching element of the specific first series switch circuit is maintained in the off state. The electric circuit according to claim 1 or 2.

20. A program executed by an electric circuit, comprising: a battery unit including a first battery and a second battery; a three-phase motor having three windings, namely a U-phase winding, a V-phase winding, and a W-phase winding, each of the three windings having a first connection terminal provided at one end thereof and a second connection terminal provided at the other end thereof; an inverter circuit connected to the battery unit, the first connection terminal of the U-phase winding, the first connection terminal of the V-phase winding, and the first connection terminal of the W-phase winding; a switch circuit for changing the connection of the second connection terminal of the U-phase winding, the second connection terminal of the V-phase winding, and the second connection terminal of the W-phase winding. The inverter circuit includes a first high-potential wiring, a first low-potential wiring, and three first series switch circuits provided for each of the three windings. The first series switch circuit includes a first upper reverse-conducting switching element, which is a reverse-conducting switching element connected between the first connection terminal of the corresponding winding and the first high-potential wiring, and a first lower reverse-conducting switching element, which is a reverse-conducting switching element connected between the first connection terminal of the corresponding winding and the first low-potential wiring. The switch circuit includes a second high-potential wiring, a second low-potential wiring, and at least one second series switch circuit. The second series switch circuit includes a second upper reverse-conducting switching element, which is a reverse-conducting switching element connected between the second connection terminal of the corresponding winding and the second high-potential wiring, and a second lower reverse-conducting switching element, which is a reverse-conducting switching element connected between the second connection terminal of the corresponding winding and the second low-potential wiring. One of the three windings is a specific winding, the first series switch circuit connected to the specific winding among the three first series switch circuits is a specific first series switch circuit, and the second series switch circuit connected to the specific winding among at least one of the second series switch circuits is a specific second series switch circuit. The program causes the control circuit to execute a first boost power transfer operation and a second boost power transfer operation.The first step-up power transfer operation is an operation of transferring power from the first battery to the second battery by connecting the positive electrode of the first battery to the first high-potential wiring, connecting the negative electrode of the first battery to the first low-potential wiring and the second low-potential wiring, connecting the positive electrode of the second battery to the second high-potential wiring, connecting the negative electrode of the second battery to the first low-potential wiring and the second low-potential wiring, turning on the first upper reverse-conducting switching element of the specific first series switch circuit, turning off the first lower reverse-conducting switching element of the specific first series switch circuit, and repeatedly turning on and off the second lower reverse-conducting switching element of the specific second series switch circuit. The second step-up power transfer operation is an operation of transferring power from the second battery to the first battery by connecting the positive electrode of the first battery to the first high-potential wiring, connecting the negative electrode of the first battery to the first low-potential wiring and the second low-potential wiring, connecting the positive electrode of the second battery to the second high-potential wiring, connecting the negative electrode of the second battery to the first low-potential wiring and the second low-potential wiring, turning on the second upper reverse-conducting switching element, turning off the second lower reverse-conducting switching element, and repeatedly turning on and off the first lower reverse-conducting switching element of the specific first series switch circuit. Program.

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