Power conversion device, program, and method for controlling power conversion device

Abstract

This power conversion device can be applied to a system comprising: a first power storage unit (31, 131, 231); and a second power storage unit (32, 132, 232). The power conversion device comprises power transmission circuits (10, 20, 22H, 22L, 50, 60, 61, 73, 120A, 120B, 340, 350) and a control device (100). The control device executes a first mode on the condition that an electric parameter, which is the magnitude of a current or power transmitted via the power transmission circuits, is greater than a switching threshold (Ith, IthH), and executes a second mode on the condition that the electric parameter is equal to or less than the switching threshold. In the first mode, switching control for the power transmission circuits is continuously performed. In the second mode, changing between the switching control for the power transmission circuits and stopping of the switching control is carried out, or the number of phases of the power transmission circuits subjected to the switching control is made lower than that in the first mode.

Description

Power conversion device, program, and method for controlling power conversion device CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based on Japanese Application No. 2024-025866, filed on February 22, 2024, the contents of which are incorporated herein by reference.

[0002] The present disclosure relates to a power conversion device, a program, and a method for controlling a power conversion device.

[0003] A power conversion device applied to a system including a first power storage unit and a second power storage unit has been known. The power conversion device includes a power transfer circuit for transferring power between the first power storage unit and the second power storage unit. An example of such a power conversion device is disclosed in Patent Document 1.

[0004] Patent No. 6527785

[0005] In the above power conversion device, if the current flowing through the power transmission circuit decreases, there is a concern that the efficiency of the power transmission circuit will decrease.

[0006] A primary object of the present disclosure is to provide a power conversion device, a program, and a method for controlling a power conversion device that can suppress a decrease in efficiency of a power transmission circuit.

[0007] The present disclosure relates to a power conversion device applicable to a system including a first power storage unit and a second power storage unit, the device comprising: a power transmission circuit that is switching-controlled to transmit power between the first power storage unit and the second power storage unit; and a control device that controls the switching of the power transmission circuit, wherein the control device executes a first mode on the condition that an electrical parameter that is the magnitude of current or power transmitted through the power transmission circuit is greater than a switching threshold, and executes a second mode on the condition that the electrical parameter is equal to or less than the switching threshold, the first mode being a mode in which switching control of the power transmission circuit is continued, and the second mode being a mode in which switching control of the power transmission circuit is switched between and stopping the switching control, or the number of phases of the power transmission circuit that are subjected to switching control is reduced compared to the first mode.

[0008] The control device of the present disclosure operates in either a first mode or a second mode. The second mode switches between switching control and non-switching control of the power transfer circuit, or reduces the number of phases of the power transfer circuit that are subjected to switching control compared to the first mode. This prevents a decrease in efficiency of the power transfer circuit when an electrical parameter, such as the magnitude of the current or power transferred through the power transfer circuit, is equal to or less than a switching threshold.

[0009] The above and other objects, features and advantages of the present disclosure will become more apparent from the following detailed description taken in conjunction with the accompanying drawings. 1 is an overall configuration diagram of a system according to a first embodiment, FIG. 2 is a diagram showing the control state of switches during high-voltage charging, FIG. 3 is a diagram showing the control state of switches during low-voltage charging, FIG. 4 is a diagram showing the relationship between inverter current and inverter efficiency, FIG. 5 is a functional block diagram of a battery ECU and an EVECU, FIG. 6 is a flowchart showing the procedure of an external charging control process, FIG. 7 is a flowchart showing the procedure of a second mode, FIG. 8 is a time chart showing an external charging control mode, FIG. 9 is a time chart showing an external charging control mode according to a comparative example, FIG. 10 is a flowchart showing the procedure of an external charging control process according to a second embodiment, FIG. 11 is a flowchart showing the procedure of the second mode, FIG. 12 is a time chart showing an external charging control mode, FIG. 13 is a diagram showing the control state of switches during high-voltage power supply according to a third embodiment, FIG. 14 is a diagram showing the control state of switches during low-voltage power supply, FIG. 15 is a functional block diagram of a battery ECU and an EVECU, and FIG. 24 is a flowchart showing the procedure of the second mode, FIG. 25 is a functional block diagram of a battery ECU and an EVECU according to another embodiment, FIG. 26 is a functional block diagram of a battery ECU and an EVECU according to another embodiment, FIG. 27 is a time chart showing an example of a method of setting a command current, FIG. 28 is an overall configuration diagram of a system according to another embodiment, FIG. 29 is an overall configuration diagram of a system according to another embodiment, and FIG. 30 is an overall configuration diagram of a system according to another embodiment.

[0010] Several embodiments will be described with reference to the drawings. In several embodiments, functionally and / or structurally corresponding and / or associated parts may be designated by the same reference numerals or reference numerals that differ in the hundredth or more digit. For corresponding and / or associated parts, reference may be made to the descriptions of other embodiments.

[0011] A first embodiment of a power conversion device according to the present disclosure will now be described with reference to the drawings. The power conversion device of this embodiment is mounted on a vehicle such as an electric vehicle or a hybrid vehicle, and forms an in-vehicle system.

[0012] As shown in FIG. 1 , the power conversion device includes a motor 10, an inverter 20, a high-potential side path 22H, and a low-potential side path 22L. The motor 10 is a three-phase synchronous machine that includes star-connected armature windings 11 of U, V, and W phases, and a rotor (not shown). The armature windings 11 of each phase are arranged with an electrical angle offset of 120°. The motor 10 is, for example, a permanent magnet synchronous machine. The rotor is capable of transmitting power to the drive wheels of the vehicle. Therefore, the motor 10 serves as a source of torque for propelling the vehicle.

[0013] The inverter 20 includes three phases of series-connected upper-arm switches SWH and lower-arm switches SWL. An upper-arm diode DH, which is a freewheeling diode, is connected in antiparallel to the upper-arm switch SWH, and a lower-arm diode DL, which is also a freewheeling diode, is connected in antiparallel to the lower-arm switch SWL. In this embodiment, each of the switches SWH and SWL is an IGBT.

[0014] The inverter 20 includes a smoothing capacitor 21. A high-potential side path 22H is connected to a high-potential side terminal of the smoothing capacitor 21. A low-potential side path 22L is connected to a low-potential side terminal of the smoothing capacitor 21. The high-potential side path 22H and the low-potential side path 22L are, for example, electrical paths such as bus bars. The smoothing capacitor 21 may be provided outside the inverter 20.

[0015] In each phase, a first end of the armature winding 11 is connected to a connection point between an emitter serving as a low potential terminal of the upper arm switch SWH and a collector serving as a high potential terminal of the lower arm switch SWL via a conductive member 23 such as a bus bar. Second ends of the armature windings 11 of each phase are connected to each other at a neutral point O. In this embodiment, the armature windings 11 of each phase are set to have the same number of turns. As a result, the armature windings 11 of each phase are set to have the same inductance, for example.

[0016] A high potential side path 22H is connected to the collector of the upper arm switch SWH of each phase, and a low potential side path 22L is connected to the emitter of the lower arm switch SWL of each phase.

[0017] The system includes a first storage battery 31 (corresponding to the "first power storage unit") and a second storage battery 32 (corresponding to the "second power storage unit"). Each storage battery 31, 32 serves as a power supply source for driving the rotor of the motor 10 to rotate. Each storage battery 31, 32 is a battery pack including a series connection of multiple unit batteries. A unit battery is a single battery cell, which is a single cell, or a series connection of multiple battery cells. In this embodiment, the unit batteries constituting the first storage battery 31 and the second storage battery 32 have the same full charge capacity (specifically, for example, a rated full charge capacity) [Ah]. The positive terminal of the first storage battery 31 is connected to the high-potential-side path 22H via a first fuse 41 and a high-potential-side main switch SMRH (described later), and the negative terminal of the second storage battery 32 is connected to the low-potential-side path 22L via a second fuse 42 and a low-potential-side main switch SMRL (described later). The terminal voltages (e.g., rated voltages) of the battery cells constituting the battery pack are set to be the same, for example. The battery cells are, for example, secondary batteries such as lithium-ion batteries. In this embodiment, the terminal voltage (e.g., rated voltage) of the first storage battery 31 is higher than the terminal voltage (e.g., rated voltage) of the second storage battery 32. This configuration can be achieved, for example, by making the number of unit batteries constituting the first storage battery 31 greater than the number of unit batteries constituting the second storage battery 32.

[0018] The power conversion device includes main switches for electrically connecting or disconnecting the first and second storage batteries 31, 32 from the inverter 20. Specifically, the main switches include a high-side main switch SMRH, a low-side main switch SMRL, and a pre-charge main switch SMRP. In this embodiment, the main switches SMRH, SMRL, and SMRP are mechanical relays. When turned off, the main switches SMRH, SMRL, and SMRP block bidirectional current flow, and when turned on, allow bidirectional current flow. A series connection of the pre-charge main switch SMRP and a pre-charge resistor 40 is connected in parallel to the low-side main switch SMRL. The main switches SMRH, SMRL, and SMRP are not limited to mechanical relays and may be, for example, semiconductor switching elements.

[0019] Each of the storage batteries 31 and 32 can be charged by an external charger provided outside the vehicle through external charging control. The external charger is, for example, a stationary charger.

[0020] Each of the storage batteries 31, 32 can supply power to a power supply target outside the vehicle through external power supply control. When the power supply target is a grid power supply, the external power supply control is also called V2G (Vehicle to Grid). When the power supply target is an electrical device in a building such as a residence, the external power supply control is also called V2H (Vehicle to Home).

[0021] The power conversion device includes a high-potential-side connection switch DCRH and a low-potential-side connection switch DCRL for electrically connecting or disconnecting an external charger or a power supply target unit to or from the first and second storage batteries 31, 32. In this embodiment, each of the connection switches DCRH and DCRL is a mechanical relay. When turned off, each of the connection switches DCRH and DCRL blocks bidirectional current flow, and when turned on, each of the connection switches DCRH and DCRL allows bidirectional current flow. The high-potential-side connection switch DCRH is connected to the high-potential-side path 22H. The low-potential-side connection switch DCRL is connected to the low-potential-side path 22L. Note that each of the connection switches DCRH and DCRL is not limited to a mechanical relay, and may be, for example, a semiconductor switching element.

[0022] The power conversion device includes an inter-battery switch 50 (corresponding to an "inter-power storage unit switch"), a bypass switch 60, a first motor-side switch 71, a second motor-side switch 72, and a connection path 73 as components for switching the connection state of the first storage battery 31 and the second storage battery 32. In this embodiment, the inter-battery switch 50, the bypass switch 60, and the motor-side switches 71 and 72 are mechanical relays. When turned off, the inter-battery switch 50, the bypass switch 60, and the motor-side switches 71 and 72 block bidirectional current flow, and when turned on, allow bidirectional current flow. Note that the inter-battery switch 50, the bypass switch 60, and the motor-side switches 71 and 72 are not limited to mechanical relays and may be, for example, semiconductor switching elements.

[0023] The inter-battery switch 50 connects the negative terminal of the first storage battery 31 and the positive terminal of the second storage battery 32. When the inter-battery switch 50 is turned on, the negative terminal of the first storage battery 31 and the positive terminal of the second storage battery 32 are electrically connected. When the inter-battery switch 50 is turned off, the negative terminal of the first storage battery 31 and the positive terminal of the second storage battery 32 are electrically disconnected.

[0024] The bypass switch 60 connects the negative terminal of the first storage battery 31 and the low potential side path 22L. When the bypass switch 60 is turned on, the negative terminal of the first storage battery 31 and the negative terminal of the second storage battery 32 are electrically connected. When the bypass switch 60 is turned off, the negative terminal of the first storage battery 31 and the negative terminal of the second storage battery 32 are electrically disconnected. The connection path 73 is an electrical path that connects the positive terminal of the second storage battery 32 and the neutral point O.

[0025] In this embodiment, the armature winding 11 of the motor 10, the inverter 20, the high-potential side path 22H, the low-potential side path 22L, the inter-battery switch 50, the bypass switch 60, the bypass switch 61, and the connection path 73 correspond to a "power transmission circuit." The first storage battery 31 and the second storage battery 32 form a battery unit 30.

[0026] The connection path 73 is provided with a first motor side switch 71 and a second motor side switch 72 in this order from the second storage battery 32 .

[0027] The power conversion device includes a neutral point capacitor 74 that connects the connection path 73 and the low potential side path 22L. A first end of the neutral point capacitor 74 is connected to a portion of the connection path 73 between the first motor side switch 71 and the second motor side switch 72. A second end of the neutral point capacitor 74 is connected to the low potential side path 22L.

[0028] When the first motor-side switch 71 is turned on, the first end of the neutral point capacitor 74 is electrically connected to the positive terminal of the second storage battery 32. On the other hand, when the first motor-side switch 71 is turned off, the first end of the neutral point capacitor 74 is electrically disconnected from the positive terminal of the second storage battery 32. When the second motor-side switch 72 is turned on, the neutral point O of the armature winding 11 is electrically connected to the first end of the neutral point capacitor 74. On the other hand, when the second motor-side switch 72 is turned off, the neutral point O is electrically disconnected from the first end of the neutral point capacitor 74.

[0029] The power conversion device includes current sensors that detect the current flowing through each part of the power conversion device itself, including a first current sensor 81, a second current sensor 82, a phase current sensor 83, and a motor current sensor 84. The first current sensor 81 detects the current flowing through the first storage battery 31, and the second current sensor 82 detects the current flowing through the second storage battery 32. The phase current sensor 83 detects the current flowing through the armature winding 11 of each phase. The motor current sensor 84 detects the current flowing through the connection path 73, and in this embodiment, detects the current (hereinafter referred to as motor current IN) flowing through a portion of the connection path 73 that is closer to the neutral point O than the connection point with the neutral point capacitor 74.

[0030] The power conversion device includes a capacitor voltage sensor 85 that detects the terminal voltage of the neutral point capacitor 74, a first voltage sensor 86 that detects the terminal voltage of the first storage battery 31, and a second voltage sensor 87 that detects the terminal voltage of the second storage battery 32. The first voltage sensor 86 detects, for example, the terminal voltage of each unit battery that constitutes the first storage battery 31, and the second voltage sensor 87 detects, for example, the terminal voltage of each unit battery that constitutes the second storage battery 32. The power conversion device also includes a power supply voltage sensor 89 that detects the terminal voltage of the smoothing capacitor 21.

[0031] The power conversion device includes a battery temperature sensor 88A that detects the temperatures of the first storage battery 31 and the second storage battery 32, and an inverter temperature sensor 88B that detects the temperature of the inverter 20. The battery temperature sensor 88A detects, for example, the temperature of each unit battery that constitutes the first storage battery 31 and the temperature of each unit battery that constitutes the second storage battery 32. The inverter temperature sensor 88B detects, for example, the temperatures of the upper and lower arm switches SWH, SWL of each phase. The power conversion device also includes, as another sensor, a rotation angle sensor (not shown) that detects the rotation angle (electrical angle) of the rotor.

[0032] The system includes a battery ECU 90 that controls the battery unit 30, and an EVECU 100 that controls the inverter 20. The battery ECU 90 is an electronic control unit that mainly comprises a microcomputer 91. The EVECU 100 is an electronic control unit that mainly comprises a microcomputer 101. The battery ECU 90 and the EVECU 100 can exchange information via a communication unit such as CAN communication.

[0033] Each microcomputer 91, 101 includes a central processing unit (CPU). The functions provided by each microcomputer 91, 101 can be provided by software stored in a physical memory device and a computer executing the software, software alone, hardware alone, or a combination thereof. For example, when each microcomputer 91, 101 is provided by a hardware electronic circuit, the function can be provided by a digital circuit including multiple logic circuits or an analog circuit. For example, each microcomputer 91, 101 executes a program stored on a non-transitory tangible storage medium serving as its own storage unit. The program includes, for example, programs for the processes shown in Figures 6, 7, 10, 11, 16, 17, 21, and 24, which will be described later. A set of instructions constituting the program is executed to perform a method corresponding to the program. The storage unit is, for example, a non-volatile memory. The program stored in the storage unit can be updated via a communication network such as the Internet, for example, via OTA (Over the Air).

[0034] The battery ECU 90 receives detection values ​​from the first current sensor 81, the second current sensor 82, the first voltage sensor 86, the second voltage sensor 87, and the battery temperature sensor 88A. The battery ECU 90 calculates the SOC of each unit battery that constitutes the first storage battery 31 based on the detection values ​​of the first voltage sensor 86, the first current sensor 81, and the battery temperature sensor 88A. The battery ECU 90 calculates the SOC of each unit battery that constitutes the second storage battery 32 based on the detection values ​​of the second voltage sensor 87, the second current sensor 82, and the battery temperature sensor 88A.

[0035] The EVECU 100 receives detection values ​​from a phase current sensor 83, a motor current sensor 84, a capacitor voltage sensor 85, a power supply voltage sensor 89, an inverter temperature sensor 88B, and a rotation angle sensor. Based on the detection values ​​received from each sensor, the EVECU 100 performs switching control of the switches SWH and SWL constituting the inverter 20 to feedback control the control variable of the motor 10 to a command value. The control variable is, for example, torque. In each phase, the upper arm switch SWH and the lower arm switch SWL are alternately turned on. As a result, the rotational power of the rotor of the motor 10 is transmitted to the drive wheels, causing the vehicle to run.

[0036] The main switches SMRH, SMRL, SMRP, the connection switches DCRH, DCRL, the inter-battery switch 50, the bypass switch 60, and the motor-side switches 71, 72 may be controlled by either the battery ECU 90 or the EVECU 100. In this embodiment, for convenience, it is assumed that the main switches SMRH, SMRL, SMRP, the connection switches DCRH, DCRL, the inter-battery switch 50, the bypass switch 60, the first motor-side switch 71, and the second motor-side switch 72 are controlled by the EVECU 100.

[0037] Next, the external charging control will be described.

[0038] In this embodiment, the external charger is a high-voltage charger 200 or a low-voltage charger 210, as shown in FIGS. 2 and 3 . The charging voltage of the high-voltage charger 200 is higher than the inter-terminal voltage (specifically, the rated voltage) of the series-connected first and second storage batteries 31, 32, e.g., 800 V. The charging voltage of the low-voltage charger 210 is lower than the inter-terminal voltage of the series-connected first and second storage batteries 31, 32 and higher than the inter-terminal voltage (specifically, the rated voltage) of the first storage battery 31, e.g., 400 V. When the first and second storage batteries 31, 32 are being charged by the external charger, the high-potential-side connection switch DCRH and the low-potential-side connection switch DCRL are switched on. On the other hand, when charging by the external charger is not being performed or the external charger is not connected to the power conversion device, the high-potential-side connection switch DCRH and the low-potential-side connection switch DCRL are switched off.

[0039] 2 shows the control state of each switch during external charging control using the high-voltage charger 200. The high-voltage charger 200 is provided with a charging plug (not shown). When the EVECU 100 determines that the charging plug of the high-voltage charger 200 has been connected to the power conversion device by the vehicle user, it turns on the connection switches DCRH and DCRL to electrically connect the high-voltage charger 200 to the power conversion device. When the EVECU 100 determines that the external charger connected to the power conversion device is the high-voltage charger 200, it turns off the pre-charge main switch SMRP, the bypass switch 60, the first motor-side switch 71, the second motor-side switch 72, and the upper and lower arm switches SWH and SWL of all phases of the inverter 20, and turns on the high-potential-side main switch SMRH, the low-potential-side main switch SMRL, and the inter-battery switch 50. This results in the first storage battery 31 and the second storage battery 32 being connected in series to the high-voltage charger 200. As a result, current flows through a closed circuit including the high-voltage charger 200, the high-potential side path 22H, the first storage battery 31, the inter-battery switch 50, the second storage battery 32, and the low-potential side path 22L, and the first storage battery 31 and the second storage battery 32 are charged in a series-connected state. At this time, because the upper arm switch SWH of the inverter 20 and the second motor-side switch 72 are turned off, it is possible to prevent the charging current of the high-voltage charger 200 from flowing to the inverter 20 and the armature winding 11.

[0040] 3 shows the control states of each switch during external charging control using the low-voltage charger 210. The low-voltage charger 210 is provided with a charging plug (not shown). When the EVECU 100 determines that the charging plug of the low-voltage charger 210 has been connected to the power conversion device by the vehicle user, it turns on the connection switches DCRH and DCRL to electrically connect the low-voltage charger 210 to the power conversion device. When the EVECU 100 determines that the external charger connected to the power conversion device is the low-voltage charger 210, it turns off the pre-charge main switch SMRP and the inter-battery switch 50 and turns on the high-potential-side main switch SMRH, the low-potential-side main switch SMRL, the bypass switch 60, the first motor-side switch 71, and the second motor-side switch 72. As a result, current flows through a closed circuit including the low-voltage charger 210, the high-potential-side path 22H, the first storage battery 31, the bypass switch 60, and the low-potential-side path 22L, thereby charging the first storage battery 31.

[0041] In the external charging control by the low-voltage charger 210, the EVECU 100 performs switching control to alternately turn on the upper and lower arm switches SWH, SWL of at least one phase, or performs switching control to switch on the upper arm switch SWH of at least one phase while keeping the lower arm switches SWL of all phases of the inverter 20 off, thereby stepping down the output voltage of the low-voltage charger 210 and supplying it to the second storage battery 32. More specifically, the EVECU 100 performs the step-down operation, which is the switching control described above, to control the voltage detected by the capacitor voltage sensor 85 (hereinafter referred to as the neutral point capacitor voltage VN) to a target charging voltage. As a result, a current flows through a closed circuit including the low-voltage charger 210, the high-potential side path 22H, the upper arm switch SWH of the inverter 20, the armature winding 11, the neutral point O, the second motor-side switch 72, the first motor-side switch 71, the second storage battery 32, and the low-potential side path 22L, and the second storage battery 32 is charged. Since the terminal voltage of the second storage battery 32 is lower than the terminal voltage of the first storage battery 31, the target charging voltage of the second storage battery 32 is lower than the target charging voltage of the first storage battery 31. In this embodiment, the upper arm switch SWH of the inverter 20 corresponds to the "target switch."

[0042] By performing external charging control using the low-voltage charger 210, the first storage battery 31 is charged directly by the low-voltage charger 210, and the second storage battery 32 is charged by the low-voltage charger 210 via the inverter 20. As shown in FIG. 4 , the efficiency of the inverter 20 (specifically, power conversion efficiency) decreases as the inverter current Iinv, which is the current flowing through the inverter 20 (e.g., switches SWH and SWL), decreases. Therefore, when the output current Io of the low-voltage charger 210 is small and the inverter current Iinv is also small, there is a concern that the charging time of the low-voltage charger 210 for the storage batteries 31 and 32 may be longer than when the inverter current Iinv is large. Therefore, in this embodiment, the inverter 20 is controlled to suppress a decrease in the efficiency of the inverter 20. This control method will be described below.

[0043] FIG. 5 is a functional block diagram of the battery ECU 90 and the EVECU 100.

[0044] The battery ECU 90 is equipped with a first input power calculation unit 92A, a first output power calculation unit 92B, a second input power calculation unit 93A, and a second output power calculation unit 93B as processing units that calculate parameters related to the charging and discharging of the first storage battery 31 and the second storage battery 32.

[0045] The first input power calculation unit 92A calculates the first upper limit input power Win1 based on the battery state of the first storage battery 31. The first upper limit input power Win1 is the maximum value of power that can be input to the first storage battery 31. The battery state of the first storage battery 31 includes, for example, the temperature of the first storage battery 31 detected by the battery temperature sensor 88A and the SOC of the first storage battery 31. For example, the first input power calculation unit 92A calculates a smaller first upper limit input power Win1 as the SOC of the first storage battery 31 increases or the temperature of the first storage battery 31 decreases. The SOC of the first storage battery 31 used in subsequent processing, including the calculation of the first upper limit input power Win1, may be, for example, the maximum value of the SOC of each unit battery constituting the first storage battery 31 or the average value of the SOC of each unit battery.

[0046] The first output power calculation unit 92B calculates the first upper limit output power Wout1 based on the battery state of the first storage battery 31. The first upper limit output power Wout1 is the maximum value of power that can be output from the first storage battery 31. For example, the first output power calculation unit 92B calculates a larger first upper limit output power Wout1 as the SOC of the first storage battery 31 increases or the temperature of the first storage battery 31 detected by the battery temperature sensor 88A increases.

[0047] The second input power calculation unit 93A calculates the second upper limit input power Win2 based on the battery state of the second storage battery 32. The second upper limit input power Win2 is the maximum value of power that can be input to the second storage battery 32. The battery state of the second storage battery 32 includes, for example, the temperature of the second storage battery 32 detected by the battery temperature sensor 88A and the SOC of the second storage battery 32. For example, the second input power calculation unit 93A calculates a smaller second upper limit input power Win2 as the SOC of the second storage battery 32 increases or the temperature of the second storage battery 32 decreases. The SOC of the second storage battery 32 used in subsequent processing, including the calculation of the second upper limit input power Win2, may be, for example, the maximum value of the SOC of each unit battery constituting the second storage battery 32 or the average value of the SOC of each unit battery.

[0048] The second output power calculation unit 93B calculates the second upper limit output power Wout2 based on the battery state of the second storage battery 32. The second upper limit output power Wout2 is the maximum value of power that can be output from the second storage battery 32. For example, the second output power calculation unit 93B calculates a larger second upper limit output power Wout2 as the SOC of the second storage battery 32 increases or the temperature of the second storage battery 32 detected by the battery temperature sensor 88A increases.

[0049] The EVECU 100 includes a first charging current calculation unit 102A, a second charging current calculation unit 102B, a mode selection unit 103, an external charger instruction unit 104, and an inverter instruction unit 105.

[0050] The first charging current calculation unit 102A calculates a first command charging current Ich1, which is a command value for the charging current of the first storage battery 31, based on the calculated first upper limit input power Win1 and the first detected voltage VH, which is the voltage detected by the first voltage sensor 86. More specifically, the first charging current calculation unit 102A calculates the first command charging current Ich1 (=Win1 / VH) by dividing the first upper limit input power Win1 by the first detected voltage VH.

[0051] The second charging current calculation unit 102B calculates a second command charging current Ich2, which is a command value for the charging current of the second storage battery 32, based on the calculated second upper limit input power Win2 and the second detected voltage VL, which is the detected voltage of the second voltage sensor 87. More specifically, the second charging current calculation unit 102B calculates the second command charging current Ich2 (=Win2 / VL) by dividing the second upper limit input power Win2 by the second detected voltage VL.

[0052] The mode selection unit 103 selects either the first mode or the second mode. In this embodiment, the first mode is a mode in which the inverter 20 operates continuously, and the second mode is a mode in which the inverter 20 operates intermittently to improve the efficiency of the inverter 20. Specifically, the mode selection unit 103 selects the first mode on the condition that it determines that the inverter current Iinv (corresponding to an "electrical parameter") is greater than a current threshold Ith (corresponding to a "switching threshold"). The mode selection unit 103 selects the second mode if it determines that the inverter current Iinv is equal to or less than the current threshold Ith. In this embodiment, the inverter current Iinv is the second command charging current Ich2. Note that the inverter current Iinv may be, for example, the absolute value of the value detected by the second current sensor 82 or the absolute value of the motor current IN.

[0053] Based on the calculated first and second command charging currents Ich1, Ich2 and the first and second detected voltages VH, VL, the external charger instructing unit 104 calculates the external command charging current Icht, which is a command value for the charging current output from the low-voltage charger 210. The first and second detected voltages VH, VL are used in order to take into account the voltage drop caused by the inverter 20 functioning as a step-down chopper circuit.

[0054] The external charger instructing unit 104 first calculates the first command conversion current Ichc1 based on the second command charging current Ich2 and the first and second detected voltages VH and VL. Specifically, the external charger instructing unit 104 calculates the first command conversion current Ichc1 based on "Ichc1 = Ich2 × VL / VH." For example, if the first detected voltage VH is 400 V, the second detected voltage VL is 200 V, and the second command charging current Ich2 is 25 A, the first command conversion current Ichc1 is 12.5 A (= 25 A × 200 V / 400 V).

[0055] The external charger instructing unit 104 calculates an external command charging current Icht (e.g., 62.5 A) by adding the calculated first command conversion current Ichc1 (e.g., 12.5 A) to the first command charging current Ich1 (e.g., 50 A). The external charger instructing unit 104 transmits the calculated external command charging current Icht to the low-voltage charger 210. As a result, the low-voltage charger 210 is controlled so that the output current Io of the low-voltage charger 210 becomes the external command charging current Icht.

[0056] When the second mode is selected by the mode selection unit 103, the external charger instructing unit 104 calculates first and second estimated input powers Winc1 and Winc2 in addition to the external command charging current Icht. The first estimated input power Winc1 is an estimated value of power when the output current Io of the low-voltage charger 210 is input only to the first storage battery 31 of the first and second storage batteries 31 and 32. The second estimated input power Winc2 is an estimated value of power when the output current Io of the low-voltage charger 210 is input only to the second storage battery 32 of the first and second storage batteries 31 and 32.

[0057] When the external charger instructing unit 104 determines that the calculated first estimated input power Winc1 is greater than the first upper limit input power Win1, it imposes a condition that the input power to the first storage battery 31 be equal to or less than the first upper limit input power Win1, and reduces the external command charging current Icht. The external charger instructing unit 104 transmits the reduced external command charging current Icht to the low-voltage charger 210. As a result, the low-voltage charger 210 is controlled so that the output current Io of the low-voltage charger 210 becomes the reduced external command charging current Icht.

[0058] When the external charger instructing unit 104 determines that the calculated second estimated input power Winc2 is greater than the second upper limit input power Win2, it imposes a condition that the input power to the second storage battery 32 be equal to or less than the second upper limit input power Win2, and reduces the external command charging current Icht. The external charger instructing unit 104 transmits the reduced external command charging current Icht to the low-voltage charger 210. As a result, the low-voltage charger 210 is controlled so that the output current Io of the low-voltage charger 210 becomes the reduced external command charging current Icht.

[0059] When the first mode is selected by the mode selection unit 103, the inverter instruction unit 105 performs a step-down operation of the inverter 20 to control the current flowing through the second storage battery 32 to the calculated second command charging current Ich2. Specifically, for example, the inverter instruction unit 105 performs a step-down operation of the inverter 20 to control the detection value of the second current sensor 82 or the motor current IN to the second command charging current Ich2.

[0060] When the second mode is selected by the mode selection unit 103 and the inverter 20 is to perform a step-down operation, the inverter instruction unit 105 performs the step-down operation of the inverter 20 so as to reduce the current flowing through the first storage battery 31 to zero. Specifically, for example, the inverter instruction unit 105 performs the step-down operation of the inverter 20 so as to control the detection value of the second current sensor 82 or the motor current IN to the external command charging current Icht.

[0061] When the second mode is selected in the mode selection unit 103 and the inverter 20 is to be stopped, the inverter instruction unit 105 stops the operation of the inverter 20 by turning off the upper and lower arm switches SWH, SWL of each phase so that the current flowing through the second storage battery 32 becomes zero.

[0062] 6 is a flowchart showing the procedure of the external charging control process of the low-voltage charger 210. This process is executed repeatedly, for example, at a predetermined control period, by cooperation between the EVECU 100 and the battery ECU 90.

[0063] In step S10 , the battery ECU 90 calculates the first upper limit input power Win1 and the second upper limit input power Win2 and transmits them to the EVECU 100 .

[0064] In step S11, the EVECU 100 calculates a first command charging current Ich1 and a second command charging current Ich2. In step S12, the EVECU 100 calculates an external command charging current Icht.

[0065] In step S13, the EVECU 100 determines whether or not the inverter current Iinv is greater than the current threshold Ith in the mode selection unit 103. The inverter current Iinv is the second command charging current Ich2 calculated in step S11.

[0066] If the EVECU 100 determines that the inverter current Iinv is greater than the current threshold Ith, the EVECU 100 proceeds to step S14.

[0067] In step S14, the EVECU 100 determines whether the inverter temperature Tinv, which is the detection value of the inverter temperature sensor 88B, is lower than the temperature threshold value Tth. The process of step S14 is a process for determining whether to execute an overheat protection process for the inverter 20, which will be described later.

[0068] If the EVECU 100 determines that the inverter temperature Tinv is lower than the temperature threshold value Tth, the EVECU 100 proceeds to step S15 and executes the first mode. In the first mode, the EVECU 100 transmits the external command charging current Icht calculated in step S12 to the low-voltage charger 210 and performs a step-down operation of the inverter 20 to control the current flowing through the second storage battery 32 to the second command charging current Ich2.

[0069] On the other hand, if the EVECU 100 determines in step S13 that the inverter current Iinv is equal to or less than the current threshold Ith, the EVECU 100 proceeds to step S16 and executes the second mode. In the second mode, the EVECU 100 switches between step-down operation and stop of operation of the inverter 20 to improve the efficiency of the inverter 20.

[0070] Next, FIG. 7 shows the processing procedure of the second mode.

[0071] In step S20, the battery ECU 90 calculates the charge threshold value Sth and transmits it to the EVECU 100.

[0072] In step S21, the EVECU 100 calculates a difference value ΔSOC. In this embodiment, the difference value ΔSOC is a value obtained by subtracting the SOC of the second storage battery 32 from the SOC of the first storage battery 31.

[0073] The processes of steps S20 and S21 are processes for suppressing an increase in the difference value ΔSOC associated with the execution of the second mode. Specifically, if the operation of the inverter 20 is stopped in the second mode, there is a concern that the difference value ΔSOC will increase. For this reason, the EVECU 100 determines whether to perform the step-down operation of the inverter 20 or to stop the operation of the inverter 20 based on the calculated charge threshold value Sth and the difference value ΔSOC.

[0074] A method for calculating the charge threshold value Sth will be described. The longer the elapsed time from the start timing ta of the external charging control, the smaller the calculated charge threshold value Sth. Fig. 7 illustrates an example in which the charge threshold value Sth at the timing (e.g., timing tb) at the end of charging of each storage battery 31, 32 is calculated to be smaller than the charge threshold value Sth at the start timing ta of each storage battery 31, 32. This calculation method is used because it is desirable that the difference between the SOC of the first storage battery 31 and the SOC of the second storage battery 32 is small when the external charging control ends.

[0075] In the second mode, the inverter 20 is switched between step-down operation and non-operation to improve the efficiency of the inverter 20. Here, in the second mode, when the inverter 20 is step-down operation, the second storage battery 32 is charged, and when the inverter 20 is non-operational, the first storage battery 31 is charged. Therefore, there is a concern that the difference in SOC between the first storage battery 31 and the second storage battery 32 will increase if the non-operational state of the inverter 20 continues. When the SOC difference is large, the inter-battery switch 50 is turned on to connect the storage batteries 31 and 32 in series, and, for example, the vehicle starts traveling. In this case, if the SOC difference is large, there is a concern that the SOC of one of the first and second storage batteries 31 and 32 will reach its allowable lower limit first, making it impossible to use the storage batteries 31 and 32 in series. Therefore, by switching between step-down operation and non-operation of the inverter 20 based on the difference value ΔSOC and the charging threshold value Sth, it is possible to prevent the difference between the SOC of the first storage battery 31 and the SOC of the second storage battery 32 from becoming large.

[0076] In step S22, the EVECU 100 calculates the first and second estimated input powers Winc1 and Winc2.

[0077] In step S23, the EVECU 100 determines whether the difference value ΔSOC is greater than the charge threshold value Sth. If the EVECU 100 determines in step S23 that the difference value ΔSOC is greater than the charge threshold value Sth, the EVECU 100 proceeds to step S24.

[0078] In step S24, the EVECU 100 determines whether the first detection voltage VH is higher than the second detection voltage VL. If the EVECU 100 determines that the first detection voltage VH is higher than the second detection voltage VL, the EVECU 100 proceeds to step S25.

[0079] In step S25, the EVECU 100 determines whether the second estimated input power Winc2 is equal to or less than the second upper limit input power Win2. If the EVECU 100 determines that the second estimated input power Winc2 is equal to or less than the second upper limit input power Win2, the EVECU 100 proceeds to step S26.

[0080] In step S26, the EVECU 100 performs a step-down operation of the inverter 20 so that the output current Io of the low-voltage charger 210 is entirely supplied to the second storage battery 32 and the current flowing through the first storage battery 31 becomes zero.

[0081] When the second storage battery 32 is charged by the step-down operation of the inverter 20, the voltage of the second storage battery 32 subsequently becomes higher than the voltage of the first storage battery 31. In this case, there is a concern that current may flow from the second storage battery 32 to the first storage battery 31 via the connection path 73, the armature winding 11, and the upper-arm diode DH. Therefore, when the EVECU 100 determines that the first detected voltage VH is higher than the second detected voltage VL, it causes the inverter 20 to perform a step-down operation, thereby increasing the voltage of the second storage battery 32. This makes it possible to prevent current from flowing from the second storage battery 32 to the first storage battery 31.

[0082] If the EVECU 100 determines in step S25 that the second estimated input power Winc2 is greater than the second upper limit input power Win2, the EVECU 100 proceeds to step S27.

[0083] In step S27, the EVECU 100 reduces the external command charging current Icht so that the second estimated input power Winc2 becomes equal to or less than the second upper limit input power Win2, and transmits the reduced external command charging current Icht to the low-voltage charger 210. After completing the process of step S27, the EVECU 100 proceeds to step S26 and performs a step-down operation. Because the external command charging current Icht is reduced in step S27, the execution of the step-down operation can prevent the input power of the second storage battery 32 from exceeding the second upper limit input power Win2.

[0084] If the EVECU 100 determines in step S23 that the difference value ΔSOC is equal to or smaller than the charge threshold value Sth, or if the EVECU 100 makes a negative determination in step S24, the EVECU 100 proceeds to step S28.

[0085] In step S28, the EVECU 100 determines whether the first estimated input power Winc1 is equal to or less than the first upper limit input power Win1. If the EVECU 100 determines that the first estimated input power Winc1 is equal to or less than the first upper limit input power Win1, the EVECU 100 proceeds to step S29.

[0086] In step S29, the EVECU 100 turns off the upper and lower arm switches SWH, SWL of each phase to stop the operation of the inverter 20 so as to reduce the current flowing through the second storage battery 32 to zero.

[0087] If the EVECU 100 determines in step S28 that the first estimated input power Winc1 is greater than the first upper limit input power Win1, the EVECU 100 proceeds to step S30.

[0088] In step S30, the EVECU 100 reduces the external command charging current Icht so that the first estimated input power Winc1 becomes equal to or less than the first upper limit input power Win1, and transmits the reduced external command charging current Icht to the low-voltage charger 210. After completing the processing of step S30, the EVECU 100 proceeds to step S29 and stops the operation of the inverter 20. Because the external command charging current Icht is reduced in step S30, it is possible to prevent the input power of the first storage battery 31 from exceeding the first upper limit input power Win1 due to the stop of operation.

[0089] In step S31, the EVECU 100 calculates an average current Iave, which is a time average value of the current flowing through the inverter 20 over a predetermined period. The predetermined period is the period during which the second mode is being executed, and specifically, is the sum of the period during which the voltage step-down operation is being executed in step S26 and the period during which the voltage step-down operation is stopped in step S29. The average current Iave is calculated based on, for example, the detection value of the second current sensor 82 or the motor current IN. In the second mode, the inverter 20 switches between voltage step-down operation and operation stop. Therefore, in order to estimate the power conversion efficiency of the inverter 20, it is necessary to calculate the current flowing through the inverter 20 during the period during which the voltage step-down operation of the inverter 20 is being executed and the period during which the voltage step-down operation of the inverter 20 is stopped in the second mode.

[0090] After calculating the average current Iave in step S31, the EVECU 100 proceeds to step S17 in FIG.

[0091] In step S17, the EVECU 100 determines whether the external charging control has ended. If the EVECU 100 determines that the external charging control has ended, the EVECU 100 ends the external charging control. On the other hand, if the EVECU 100 determines that the external charging control has not ended, the EVECU 100 proceeds to step S10.

[0092] Thereafter, if it is determined in step S13 that the inverter current Iinv is equal to or less than the current threshold Ith, the second mode is continued. Here, if step S13 is executed after the second mode was executed in the previous control cycle, the inverter current Iinv used in step S13 is set to the average current Iave. As a result, the second mode is continued until it is determined in step S13 that the average current Iave exceeds the current threshold Ith.

[0093] On the other hand, if it is determined in step S13 that the inverter current Iinv is greater than the current threshold Ith and the determination in step S14 is affirmative, the mode is switched from the second mode to the first mode in step S15.

[0094] If the EVECU 100 makes a negative determination in step S14, the EVECU 100 proceeds to step S32 and performs overheat protection processing. This processing, similar to steps S28 and S29 in the second mode described above, is processing for stopping the operation of the inverter 20. When the operation of the inverter 20 is stopped, the temperature of the inverter 20 drops. Therefore, by performing the overheat protection processing when the inverter temperature Tinv is equal to or higher than the temperature threshold value Tth, overheating of the inverter 20 can be suppressed. Note that in step S14, the detection value of a temperature sensor that detects the temperature of the motor 10 may be used instead of the inverter temperature Tinv.

[0095] In the external charging control by the low-voltage charger 210, the SOC of each storage battery 31, 32 increases as charging progresses. Therefore, the inverter 20 may be controlled so that the output current Io of the low-voltage charger 210 is smaller at the end of charging than at the beginning of charging. Here, when the first mode is executed, the output current Io of the low-voltage charger 210 is distributed to the first and second storage batteries 31, 32. Therefore, the current flowing through the inverter 20 becomes smaller at the end of charging compared to the beginning of charging, which may result in a decrease in the efficiency of the inverter 20.

[0096] Therefore, a second mode is executed in which the inverter 20 performs a step-down operation or is stopped. In the second mode, when the inverter 20 is stopped, the output current Io of the low-voltage charger 210 does not flow to the second storage battery 32 but flows to the first storage battery 31. In the second mode, when the inverter 20 performs a step-down operation, the output current Io of the low-voltage charger 210 does not flow to the first storage battery 31 but flows to the second storage battery 32 via the inverter 20. In this way, when the inverter 20 performs a step-down operation or is stopped, the output current Io flows to the first storage battery 31 or the second storage battery 32. As a result, when the second mode is executed, compared to when the first mode is executed, the current flowing to the inverter 20 can be increased even if the output current Io is small, and a decrease in the efficiency of the inverter 20 can be suppressed.

[0097] Fig. 8 shows an example of waveforms when external charging control is executed for the low-voltage charger 210. In Fig. 8, SOC1 is the SOC of the first storage battery 31, and SOC2 is the SOC of the second storage battery 32. I1 is the charging current of the first storage battery 31, and I2 is the charging current of the second storage battery 32.

[0098] Between time t0 and time t1, the first mode is executed. A first command charging current Ich1 is calculated based on the first upper limit input power Win1 and the first detected voltage VH, and in the first mode, the charging current of the first storage battery 31 is controlled to the first command charging current Ich1. As the first storage battery 31 is charged, the SOC1 gradually increases.

[0099] Furthermore, the second command charging current Ich2 is calculated based on the second upper limit input power Win2 and the second detected voltage VL, and the charging current of the second storage battery 32 is controlled to the second command charging current Ich2. As the second storage battery 32 is charged, the SOC2 gradually increases.

[0100] At time t1, the inverter current Iinv becomes equal to or less than the current threshold Ith. Here, the operation of the inverter 20 is stopped on the condition that it is determined that the difference value ΔSOC, which is the value obtained by subtracting SOC2 from SOC1, is equal to or less than the charging threshold Sth. As a result, the output current Io of the low-voltage charger 210 does not flow to the second storage battery 32 but flows to the first storage battery 31, I2 becomes 0, and SOC1 gradually increases.

[0101] At time t2, the difference value ΔSOC becomes greater than the charge threshold value Sth. Here, on the condition that it is determined that the difference value ΔSOC is greater than the charge threshold value Sth, the inverter 20 performs a step-down operation. As a result, the output current Io of the low-voltage charger 210 does not flow to the first storage battery 31 but flows to the second storage battery 32, I1 becomes 0, and SOC2 gradually increases. In this way, by executing the second mode in which the inverter 20 performs a step-down operation or is stopped, the charging of each storage battery 31, 32 is completed at time t3 while suppressing a decrease in the efficiency of the inverter 20.

[0102] FIG. 9 shows an example of waveforms when external charging control according to a comparative example is executed. In the comparative example, unlike the present embodiment, the second mode is not executed, and only the first mode is executed. In this case, I1 and I2 decrease at time t1, and the efficiency of the inverter 20 decreases accordingly. In the comparative example of FIG. 9 , charging of each of the storage batteries 31 and 32 is completed at time t2. Here, the period from time t0 to time t3 in FIG. 8 is shorter than the period from time t0 to time t2 in FIG. 9 .

[0103] <Modification of First Embodiment> The first command charging current Ich1 may be calculated as a value smaller than "Win1 / VH." The second command charging current Ich2 may be calculated as a value smaller than "Win2 / VL."

[0104] Second Embodiment A second embodiment will be described below with reference to the drawings, focusing on differences from the first embodiment. In this embodiment, the number of phases of the inverter 20 that are switching-controlled is changed in the second mode.

[0105] 10 is a flowchart showing the procedure of the external charging control process of the low-voltage charger 210 according to this embodiment. This process is executed repeatedly, for example, at a predetermined control interval, by the cooperation of the EVECU 100 and the battery ECU 90.

[0106] After executing the process of step S12, the EVECU 100 determines in step S40 whether the inverter current Iinv is greater than a first threshold value IthH (corresponding to the "switching threshold value"). In this embodiment, the inverter current Iinv is the second command charging current Ich2 calculated in step S11.

[0107] When the EVECU 100 determines that the inverter current Iinv is greater than the first threshold value IthH, the EVECU 100 proceeds to step S14. The first threshold value IthH is a value corresponding to the current threshold value Ith in the first embodiment.

[0108] If the EVECU 100 determines in step S14 that the inverter temperature Tinv is lower than the temperature threshold value Tth, the EVECU 100 proceeds to step S41 and executes the first mode. In the first mode, the EVECU 100 performs a step-down operation of the inverter 20 by controlling the switching of the three-phase upper and lower arm switches SWH, SWL to control the current flowing through the second storage battery 32 to the second command charging current Ich2.

[0109] When the EVECU 100 determines in step S40 that the inverter current Iinv is equal to or less than the first threshold value IthH, the EVECU 100 proceeds to step S42 and executes the second mode. In the second mode, the EVECU 100 changes the number of phases of the inverter 20 that are subjected to switching control.

[0110] When the three-phase upper and lower arm switches SWH, SWL are switching-controlled, the output current Io of the low-voltage charger 210 is distributed to each phase. In this case, the amount of current flowing per phase is smaller than when the two-phase or one-phase upper and lower arm switches SWH, SWL are switching-controlled. As a result, the efficiency of the inverter 20 may decrease. Therefore, the number of phases of the inverter 20 that are switching-controlled is changed depending on the current flowing through the inverter 20. This increases the amount of current flowing per phase, thereby suppressing a decrease in the efficiency of the inverter 20.

[0111] Next, FIG. 11 shows the processing procedure of the second mode.

[0112] In step S50, the EVECU 100 determines whether the inverter current Iinv is greater than a second threshold value IthL, which is a value smaller than the first threshold value IthH.

[0113] If the EVECU 100 determines that the inverter current Iinv is greater than the second threshold value IthL, the process proceeds to step S51, where the EVECU 100 selects two phases as the number of phases of the inverter 20 to be switched. In this case, for example, the EVECU 100 selects the phase with the lowest detected value from the inverter temperature sensor 88B and the phase with the next lowest detected value from the inverter temperature sensor 88B, among the three phases that make up the inverter 20. Since the EVECU 100 selects the phase with the lowest temperature to perform switching control, overheating of the components that make up the inverter 20 can be suppressed.

[0114] In step S52, the EVECU 100 performs the step-down operation of the inverter 20 by controlling the switching of the selected two-phase upper and lower arm switches SWH, SWL to control the current flowing through the second storage battery 32 to the second command charging current Ich2.

[0115] If the EVECU 100 determines that the inverter current Iinv is equal to or less than the second threshold value IthL, the process proceeds to step S53. In step S53, the EVECU 100 selects one phase as the number of phases of the inverter 20 to be subjected to switching control. In this case, for example, the EVECU 100 selects the phase having the lowest detected value from the inverter temperature sensor 88B among the three phases constituting the inverter 20. As a result, the EVECU 100 selects the phase with the lowest temperature to perform switching control, thereby preventing overheating of the components constituting the inverter 20.

[0116] In step S54, the EVECU 100 performs the step-down operation of the inverter 20 by controlling the switching of the upper and lower arm switches SWH, SWL of the selected one phase to control the current flowing through the second storage battery 32 to the second command charging current Ich2.

[0117] In step S55, the EVECU 100 calculates the total current Isum, which is the current flowing through the inverter 20 when one or two of the three-phase upper and lower arm switches SWH, SWL are switched. The total current Isum is, for example, the value detected by the second current sensor 82 or the motor current IN.

[0118] After calculating the total current Isum in step S55, the EVECU 100 proceeds to step S17 in FIG.

[0119] In step S17, the EVECU 100 determines whether the external charging control has ended. If the EVECU 100 determines that the external charging control has ended, the EVECU 100 ends the external charging control. On the other hand, if the EVECU 100 determines that the external charging control has not ended, the EVECU 100 proceeds to step S10.

[0120] Thereafter, if it is determined in step S40 that the inverter current Iinv is equal to or less than the first threshold value IthH, the second mode is continued. Here, if step S40 is executed after the second mode was executed in the previous control cycle, the inverter current Iinv used in step S40 is set as the total current Isum. As a result, the second mode is continued until it is determined in step S40 that the total current Isum exceeds the first threshold value IthH.

[0121] On the other hand, if it is determined in step S40 that the inverter current Iinv is greater than the first threshold value IthH and the determination in step S14 is affirmative, the control proceeds to step S41 where the mode is switched from the second mode to the first mode.

[0122] If the EVECU 100 makes a negative determination in step S14, the EVECU 100 proceeds to step S32 and performs overheat protection processing. This processing, similar to the second mode described above, is processing for changing the number of phases of the inverter 20 that are subjected to switching control. Since the number of phases of the inverter 20 that are subjected to switching control is reduced, the temperature of the inverter 20 drops. Therefore, by performing overheat protection processing when the inverter temperature Tinv is equal to or higher than the temperature threshold value Tth, overheating of the inverter 20 can be suppressed. Note that in step S14, the detection value of a temperature sensor that detects the temperature of the motor 10 may be used instead of the inverter temperature Tinv.

[0123] FIG. 12 shows an example of each waveform when external charging control of the low-voltage charger 210 is executed.

[0124] At time t1, the inverter current Iinv becomes equal to or less than the first threshold value IthH. This starts the second mode, and the switching control of the upper and lower arm switches SWH, SWL is changed from three phases to two phases. Therefore, when the upper arm switches SWH of the selected two phases are turned on, the output current Io of the low-voltage charger 210 flows through the turned-on upper arm switches SWH. On the other hand, when the upper arm switches SWH are turned off, the current flows through the lower arm diodes DL of the two phases. When two phases are selected, the current flowing per phase is larger than when the switching control of the upper and lower arm switches SWH, SWL of three phases is performed.

[0125] At time t2, the inverter current Iinv becomes equal to or less than the second threshold value IthL. This changes the switching-controlled upper and lower arm switches SWH, SWL from two phases to one phase. Therefore, when the upper arm switch SWH of the selected one phase is turned on, the output current Io of the low-voltage charger 210 flows through the turned-on upper arm switch SWH. On the other hand, when the upper arm switch SWH is turned off, the current flows through the lower arm diode DL of the one phase. When one phase is selected, the current flowing per phase is larger than when the switching-controlled upper and lower arm switches SWH, SWL of two phases are selected.

[0126] In this way, by performing the step-down operation of the inverter 20 while changing the number of phases of the inverter 20 to be switched in accordance with the inverter current Iinv, it is possible to suppress a decrease in the efficiency of the inverter 20. At time t3, charging of each of the storage batteries 31 and 32 is completed.

[0127] According to the present embodiment described above, it is possible to obtain the same effects as those of the first embodiment, which means that, for example, the period from time t0 to time t3 in Fig. 12 can be made shorter than the period from time t0 to time t2 in Fig. 9 .

[0128] <Modification of Second Embodiment> The EVECU 100 may perform interleaving control in step S52 of Fig. 11. Specifically, the EVECU 100 shifts the timing at which each of the target switches for two phases is turned on by 180 degrees. The EVECU 100 may also perform interleaving control in step S41 of Fig. 10. Specifically, the EVECU 100 shifts the timing at which each of the target switches for three phases is turned on by 120 degrees.

[0129] Third Embodiment A third embodiment will now be described with reference to the drawings, focusing on differences from the first embodiment. In this embodiment, the second mode is executed during external power feeding control.

[0130] 13 shows the control state of each switch during external power supply control in which power is supplied from the first and second storage batteries 31, 32 to the high-voltage power supply target unit 220. When the EVECU 100 determines that the power supply target unit connected to the power conversion device is the high-voltage power supply target unit 220, it turns off the pre-charge main switch SMRP, the bypass switch 60, the first motor-side switch 71, the second motor-side switch 72, and the upper and lower arm switches SWH, SWL of all phases of the inverter 20, and turns on the connection switches DCRH, DCRL, the high-potential-side main switch SMRH, the low-potential-side main switch SMRL, and the inter-battery switch 50. This results in the first storage battery 31 and the second storage battery 32 being connected in series to the high-voltage power supply target unit 220. Therefore, current flows through a closed circuit including the first storage battery 31, the high-voltage side path 22H, the high-voltage power supply target portion 220, the low-voltage side path 22L, and the second storage battery 32, and power is supplied from the first storage battery 31 and the second storage battery 32 to the high-voltage power supply target portion 220.

[0131] 14 shows the control states of each switch during external power supply control in which power is supplied from the first and second storage batteries 31, 32 to the low-voltage power supply target unit 230. The rated voltage of the low-voltage power supply target unit 230 is lower than the rated voltage of the high-voltage power supply target unit 220. When the EVECU 100 determines that the power supply target unit connected to the power conversion device is the low-voltage power supply target unit 230, it turns off the pre-charge main switch SMRP and the inter-battery switch 50 and turns on the connection switches DCRH, DCRL, the high-potential-side main switch SMRH, the low-potential-side main switch SMRL, the bypass switch 60, the first motor-side switch 71, and the second motor-side switch 72. As a result, current flows through a closed circuit including the first storage battery 31, the high-potential-side path 22H, the low-voltage power supply target unit 230, the low-potential-side path 22L, and the bypass switch 60, and power is supplied from the first storage battery 31 to the low-voltage power supply target unit 230.

[0132] In the external power supply control for the low-voltage power supply target 230, the EVECU 100 performs switching control to alternately turn on the upper and lower arm switches SWH and SWL of at least one phase, or performs switching control to turn on the lower arm switch SWL of at least one phase while keeping the upper arm switches SWH of all phases of the inverter 20 off, thereby boosting the output voltage of the second storage battery 32 and supplying it to the low-voltage power supply target 230. Specifically, the EVECU 100 performs a boost operation, which is the switching control described above, to control the power supply voltage VB, which is the voltage detected by the power supply voltage sensor 89, to a target power supply voltage. As a result, a current flows through a closed circuit including the second storage battery 32, the connection path 73, the armature winding 11, the inverter 20, the high-potential-side path 22H, the low-voltage power supply target 230, and the low-potential-side path 22L, and power is supplied from the second storage battery 32 to the low-voltage power supply target 230. In this embodiment, the lower arm switch SWL corresponds to the "target switch."

[0133] By executing external power supply control on the low-voltage power supply target unit 230, the low-voltage power supply target unit 230 is supplied with power directly from the first storage battery 31 and from the second storage battery 32 via the inverter 20. Here, the smaller the inverter current Iinv, the lower the efficiency of the inverter 20. Therefore, when the input current Ii to the low-voltage power supply target unit 230 is small, the inverter current Iinv becomes small, and there is a concern that the efficiency of the inverter 20 will decrease. Therefore, in this embodiment, the inverter 20 is controlled to suppress the decrease in the efficiency of the inverter 20. This control method will be described below.

[0134] FIG. 15 is a functional block diagram of the battery ECU 90 and the EVECU 100.

[0135] The EVECU 100 includes a first discharge current calculation unit 106A, a second discharge current calculation unit 106B, a mode selection unit 107, an external power supply instruction unit 108, and an inverter instruction unit 109.

[0136] The first discharge current calculation unit 106A calculates, based on the first upper limit output power Wout1 and the first detected voltage VH, a first command discharge current Idis1 that is a command value for the discharge current of the first storage battery 31. More specifically, the first discharge current calculation unit 106A calculates the first command discharge current Idis1 (=Wout1 / VH) by dividing the first upper limit output power Wout1 by the first detected voltage VH.

[0137] Based on the second upper limit output power Wout2 and the second detected voltage VL, the second discharge current calculation unit 106B calculates a second command discharge current Idis2, which is a command value for the discharge current of the second storage battery 32. More specifically, the second discharge current calculation unit 106B calculates the second command discharge current Idis2 (=Wout2 / VL) by dividing the second upper limit output power Wout2 by the second detected voltage VL.

[0138] The mode selection unit 107 selects the first mode or the second mode.

[0139] Based on the calculated first and second command discharge currents Idis1 and Idis2 and the first and second detected voltages VH and VL, the external power supply instructing unit 108 calculates the external command discharge current Idist, which is a command value for the discharge current to be supplied from each of the storage batteries 31 and 32 to the low-voltage power supply target unit 230. The first and second detected voltages VH and VL are used in order to take into account the voltage increase due to the voltage boost operation.

[0140] The external power supply instructing unit 108 first calculates the first command conversion current Idisc1 based on the second command discharge current Idis2 and the first and second detected voltages VH and VL. Specifically, the external power supply instructing unit 108 calculates the first command conversion current Idisc1 based on "Idisc1 = Idis2 × VL / VH". The external power supply instructing unit 108 calculates a value obtained by adding the first command discharge current Idis1 to the calculated first command conversion current Idisc1 as the external command discharge current Idist. The external power supply instructing unit 108 transmits the calculated external command discharge current Idist to the low-voltage power supply target unit 230. As a result, the low-voltage power supply target unit 230 is controlled so that the input current Ii of the low-voltage power supply target unit 230 becomes the external command discharge current Idist.

[0141] When the second mode is selected by the mode selection unit 107, the external power supply instructing unit 108 calculates first and second estimated output powers Woutc1, Woutc2 in addition to the external command discharge current Idist. The first estimated output power Woutc1 is an estimated value of power when the input current Ii of the low-voltage power supply target unit 230 is supplied only from the first storage battery 31 of the first and second storage batteries 31, 32. The second estimated output power Woutc2 is an estimated value of power when the input current Ii of the low-voltage power supply target unit 230 is supplied only from the second storage battery 32 of the first and second storage batteries 31, 32.

[0142] When the external power supply instructing unit 108 determines that the calculated first estimated output power Woutc1 is greater than the first upper limit output power Wout1, the external power supply instructing unit 108 imposes a condition that the output power of the first storage battery 31 be equal to or less than the first upper limit output power Wout1, and reduces the external command discharge current Idist. The external power supply instructing unit 108 transmits the reduced external command discharge current Idist to the low-voltage power supply target unit 230. As a result, the low-voltage power supply target unit 230 is controlled so that the input current Ii of the low-voltage power supply target unit 230 becomes the reduced external command discharge current Idist.

[0143] When the external power supply instructing unit 108 determines that the calculated second estimated output power Woutc2 is greater than the second upper limit output power Wout2, it imposes a condition that the output power of the second storage battery 32 be equal to or less than the second upper limit output power Wout2, and reduces the external command discharge current Idist. The external power supply instructing unit 108 transmits the reduced external command discharge current Idist to the low-voltage power supply target unit 230. As a result, the low-voltage power supply target unit 230 is controlled so that the input current Ii of the low-voltage power supply target unit 230 becomes the reduced external command discharge current Idist.

[0144] When the first mode is selected by the mode selection unit 107, the inverter instruction unit 109 performs a boost operation of the inverter 20 to control the current flowing through the second storage battery 32 (e.g., the detection value of the second current sensor 82 or the motor current IN) to the calculated second command discharge current Idis2.

[0145] When the second mode is selected by the mode selection unit 107 and the inverter 20 is to perform a voltage boosting operation, the inverter command unit 109 performs the voltage boosting operation of the inverter 20 so as to reduce the current flowing through the first storage battery 31 to zero. Specifically, for example, the inverter command unit 105 performs the voltage boosting operation of the inverter 20 so as to control the detection value of the second current sensor 82 or the motor current IN to the external command discharge current Idist.

[0146] When the second mode is selected in the mode selection unit 107 and the inverter 20 is to be stopped, the inverter instruction unit 109 stops the operation of the inverter 20 by turning off the upper and lower arm switches SWH, SWL of each phase so that the current flowing through the second storage battery 32 becomes zero.

[0147] 16 is a flowchart showing the procedure of the external power supply control process for the low-voltage power supply target unit 230. This process is executed repeatedly, for example, at a predetermined control period by cooperation between the EVECU 100 and the battery ECU 90.

[0148] In step S60, the battery ECU 90 calculates the first upper limit output power Wout1 and the second upper limit output power Wout2 and transmits them to the EVECU 100.

[0149] In step S61, the EVECU 100 calculates a first command discharge current Idis1 and a second command discharge current Idis2. In step S62, the EVECU 100 calculates an external command discharge current Idist.

[0150] In step S63, the EVECU 100 determines whether the inverter current Iinv is greater than the current threshold Ith. In this embodiment, the inverter current Iinv is the second command discharge current Idis2 calculated in step S61. Note that the inverter current Iinv may be, for example, the detection value of the second current sensor 82 or the motor current IN.

[0151] If the EVECU 100 determines that the inverter current Iinv is greater than the current threshold Ith, the EVECU 100 proceeds to step S64.

[0152] In step S64, the EVECU 100 determines whether the inverter temperature Tinv is lower than the temperature threshold value Tth. The process of step S64 is a process for determining whether or not to perform an overheat protection process for the inverter 20, which will be described later.

[0153] If the EVECU 100 determines that the inverter temperature Tinv is lower than the temperature threshold Tth, the EVECU 100 proceeds to step S65 and executes the first mode. In the first mode, the EVECU 100 performs a boost operation of the inverter 20 to control the current flowing through the second storage battery 32 to the second command discharge current Idis2.

[0154] If the EVECU 100 determines in step S63 that the inverter current Iinv is equal to or less than the current threshold Ith, the EVECU 100 proceeds to step S66 and executes the second mode. In the second mode, the EVECU 100 executes the boost operation or stops the operation of the inverter 20 to improve the efficiency of the inverter 20.

[0155] Next, FIG. 17 shows the processing procedure of the second mode.

[0156] In step S70, the battery ECU 90 calculates the charge threshold value Sth and transmits it to the EVECU 100. A method for calculating the charge threshold value Sth in this embodiment will be described. The EVECU 100 calculates a smaller charge threshold value Sth as the time elapsed since the start timing ta of the external power feeding control becomes longer. Figure 17 illustrates an example in which the charge threshold value Sth at the end of the external power feeding control (for example, timing tb) is calculated to be smaller than the charge threshold value Sth at the start timing ta of the external power feeding control. This calculation method is used because it is desirable that the difference between the SOC of the first storage battery 31 and the SOC of the second storage battery 32 is small when the external power feeding control ends.

[0157] In step S71, the EVECU 100 calculates a difference value ΔSOC. In this embodiment, the difference value ΔSOC is a value obtained by subtracting the SOC of the second storage battery 32 from the SOC of the first storage battery 31.

[0158] In step S72, the EVECU 100 calculates first and second estimated output powers Woutc1 and Woutc2.

[0159] In step S73, the EVECU 100 determines whether the difference value ΔSOC is equal to or less than the charge threshold value Sth. If the EVECU 100 determines in step S73 that the difference value ΔSOC is equal to or less than the charge threshold value Sth, the EVECU 100 proceeds to step S74.

[0160] In step S74, the EVECU 100 determines whether the second estimated output power Woutc2 is equal to or less than the second upper limit output power Wout2. If the EVECU 100 determines in step S74 that the second estimated output power Woutc2 is equal to or less than the second upper limit output power Wout2, the EVECU 100 proceeds to step S75.

[0161] In step S75, the EVECU 100 supplies current to the low-voltage power supply target section 230 from only the second storage battery 32 of the first and second storage batteries 31, 32, and performs a boost operation of the inverter 20 to reduce the current flowing to the first storage battery 31 to zero.

[0162] If the EVECU 100 determines in step S74 that the second estimated output power Woutc2 is greater than the second upper limit output power Wout2, the EVECU 100 proceeds to step S76.

[0163] In step S76, the EVECU 100 reduces the external command discharge current Idist so that the second estimated output power Woutc2 is equal to or less than the second upper limit output power Wout2, and transmits the reduced external command discharge current Idist to the low-voltage power supply target unit 230. After completing the process of step S76, the EVECU 100 proceeds to step S75 and performs a boost operation. Because the external command discharge current Idist is reduced in step S76, it is possible to prevent the output power of the second storage battery 32 from exceeding the second upper limit output power Wout2 as the boost operation is performed.

[0164] On the other hand, if the EVECU 100 determines in step S73 that the difference value ΔSOC exceeds the charge threshold value Sth, the EVECU 100 proceeds to step S77.

[0165] In step S77, the EVECU 100 determines whether the first detection voltage VH is higher than the second detection voltage VL. If the EVECU 100 determines that the first detection voltage VH is higher than the second detection voltage VL, the EVECU 100 proceeds to step S78. On the other hand, if the EVECU 100 determines that the first detection voltage VH is equal to or lower than the second detection voltage VL, the EVECU 100 proceeds to step S74.

[0166] If the inverter 20 is stopped and only the first storage battery 31 of the first and second storage batteries 31, 32 is discharged, the voltage of the second storage battery 32 will then become higher than the voltage of the first storage battery 31. In this case, there is a concern that current will flow from the second storage battery 32 to the first storage battery 31 via the connection path 73, the armature winding 11, and the upper arm diode DH. Therefore, when the EVECU 100 determines that the first detected voltage VH is higher than the second detected voltage VL, it stops the inverter 20, thereby preventing current from flowing from the second storage battery 32 to the first storage battery 31.

[0167] In step S78, the EVECU 100 determines whether the first estimated output power Woutc1 is equal to or less than the first upper limit output power Wout1. If the EVECU 100 determines that the first estimated output power Woutc1 is equal to or less than the first upper limit output power Wout1, the EVECU 100 proceeds to step S79.

[0168] In step S79, the EVECU 100 turns off the upper and lower arm switches SWH, SWL of each phase to stop the operation of the inverter 20 so as to reduce the current flowing through the second storage battery 32 to zero.

[0169] If the EVECU 100 determines in step S78 that the first estimated output power Woutc1 is greater than the first upper limit output power Wout1, the EVECU 100 proceeds to step S80.

[0170] In step S80, the EVECU 100 reduces the external command discharge current Idist so that the first estimated output power Woutc1 becomes equal to or less than the first upper limit output power Wout1, and transmits the reduced external command discharge current Idist to the low-voltage power supply target unit 230. After completing the processing of step S80, the EVECU 100 proceeds to step S79 and stops the operation of the inverter 20. Because the external command discharge current Idist is reduced in step S80, it is possible to prevent the output power of the first storage battery 31 from exceeding the first upper limit output power Wout1 when the operation of the inverter 20 is stopped.

[0171] In step S81, the EVECU 100 calculates an average current Iave, which is a time average value of the current flowing through the inverter 20 over a predetermined period. The predetermined period is the period during which the second mode is being executed, and specifically, is the sum of the period during which the voltage step-up operation is being executed in step S75 and the period during which the voltage step-down operation is stopped in step S79. The average current Iave is calculated based on, for example, the detection value of the second current sensor 82 or the motor current IN. In the second mode, the inverter 20 switches between voltage step-up operation and operation stop. Therefore, in order to estimate the power conversion efficiency of the inverter 20, it is necessary to calculate the current flowing through the inverter 20 during the period during which the voltage step-up operation of the inverter 20 is being executed and the period during which the voltage step-up operation is stopped in the second mode.

[0172] After calculating the average current Iave in step S81, the EVECU 100 proceeds to step S67 in FIG.

[0173] In step S67, the EVECU 100 determines whether the external power supply control has ended. If the EVECU 100 determines that the external power supply control has ended, the EVECU 100 ends the external power supply control. On the other hand, if the EVECU 100 determines that the external power supply control has not ended, the EVECU 100 proceeds to step S60.

[0174] Thereafter, if it is determined in step S63 that the inverter current Iinv is equal to or less than the current threshold Ith, the second mode is continued. Here, if step S63 is executed after the second mode was executed in the previous control cycle, the inverter current Iinv used in step S63 is set to the average current Iave. As a result, the second mode is continued until it is determined in step S63 that the average current Iave exceeds the current threshold Ith.

[0175] On the other hand, if it is determined in step S63 that the inverter current Iinv is greater than the current threshold Ith and the determination in step S64 is affirmative, the mode is switched from the second mode to the first mode in step S65.

[0176] If the EVECU 100 makes a negative determination in step S64, the EVECU 100 proceeds to step S82 to perform overheat protection processing. This processing is processing to stop the operation of the inverter 20, similar to steps S78 and S79 in the second mode described above.

[0177] According to the present embodiment described above, it is possible to suppress a decrease in the efficiency of the inverter 20 during external power feeding control.

[0178] <Modification of Third Embodiment> The first commanded discharge current Idis1 may be calculated as a value smaller than "Wout1 / VH". The second commanded discharge current Idis2 may be calculated as a value smaller than "Wout2 / VL".

[0179] Fourth Embodiment The fourth embodiment will be described below with reference to the drawings, focusing on differences from the first embodiment. In this embodiment, as shown in Fig. 18 , a connection path 73 electrically connects the neutral point O of the armature winding 11 to the negative terminal of the first storage battery 31. A bypass switch 61 connects the positive terminal of the second storage battery 32 to the high-potential side path 22H. A first end of a neutral point capacitor 75 is connected to a portion of the connection path 73 between the first motor-side switch 71 and the second motor-side switch 72. A second end of the neutral point capacitor 75 is connected to the high-potential side path 22H.

[0180] In this embodiment, the terminal voltage (for example, rated voltage) of the first storage battery 31 is lower than the terminal voltage (for example, rated voltage) of the second storage battery 32 .

[0181] Next, the external charging control of this embodiment will be described. Figure 19 shows the control state of each switch during external charging control using the high-voltage charger 200. When the EVECU 100 determines that the external charger connected to the power conversion device is the high-voltage charger 200, it turns off the pre-charge main switch SMRP, the bypass switch 61, the first motor-side switch 71, the second motor-side switch 72, and the upper and lower arm switches SWH, SWL of all phases of the inverter 20, and turns on the high-potential side main switch SMRH, the low-potential side main switch SMRL, and the inter-battery switch 50. As a result, the first storage battery 31 and the second storage battery 32 are charged while connected in series to the high-voltage charger 200.

[0182] 20 shows the control state of each switch during external charging control using the low-voltage charger 210. When the EVECU 100 determines that the external charger connected to the power conversion device is the low-voltage charger 210, it turns off the pre-charge main switch SMRP and the inter-battery switch 50, and turns on the high-potential side main switch SMRH, the low-potential side main switch SMRL, the bypass switch 61, the first motor-side switch 71, and the second motor-side switch 72. This causes the second storage battery 32 to be charged.

[0183] In the external charging control by the low-voltage charger 210, the EVECU 100 performs switching control to alternately turn on the upper and lower arm switches SWH, SWL of at least one phase, or performs switching control to switch on the lower arm switch SWL of at least one phase while keeping the upper arm switches SWH of all phases of the inverter 20 off, thereby stepping down the output voltage of the low-voltage charger 210 and supplying it to the first storage battery 31. More specifically, the EVECU 100 performs the step-down operation, which is the switching control described above, to control the neutral point capacitor voltage VN to a target charging voltage. This charges the first storage battery 31. Because the terminal voltage of the first storage battery 31 is lower than the terminal voltage of the second storage battery 32, the target charging voltage of the first storage battery 31 is lower than the target charging voltage of the second storage battery 32.

[0184] By performing external charging control using the low-voltage charger 210, the second storage battery 32 is charged directly by the low-voltage charger 210, and the first storage battery 31 is charged by the low-voltage charger 210 via the inverter 20. When the output current Io of the low-voltage charger 210 is small and the inverter current Iinv is small, there is a concern that the charging time of each storage battery 31, 32 by the low-voltage charger 210 may be longer than when the inverter current Iinv is large. Therefore, in this embodiment, the inverter 20 is controlled to suppress a decrease in the efficiency of the inverter 20. This control method will be described below.

[0185] In this embodiment, the external charging control of the low-voltage charger 210 shown in Fig. 6 is also executed. This process is executed repeatedly, for example, at a predetermined control period by the cooperation of the EVECU 100 and the battery ECU 90.

[0186] After executing the process of step S12, the EVECU 100 determines in step S13 whether the inverter current Iinv is greater than the current threshold Ith. In this embodiment, the inverter current Iinv is the first command charging current Ich1 calculated in step S11. Note that the inverter current Iinv may be the absolute value of the value detected by the first current sensor 81 or the absolute value of the motor current IN.

[0187] If the EVECU 100 determines that the inverter current Iinv is greater than the current threshold Ith, the EVECU 100 proceeds to step S14.

[0188] If the EVECU 100 determines in step S14 that the inverter temperature Tinv is lower than the temperature threshold value Tth, the EVECU 100 proceeds to step S15 and executes the first mode. In the first mode, the EVECU 100 transmits the external command charging current Icht calculated in step S12 to the low-voltage charger 210 and performs a step-down operation of the inverter 20 to control the current flowing through the first storage battery 31 to the first command charging current Ich1.

[0189] When the EVECU 100 determines in step S13 that the inverter current Iinv is equal to or less than the current threshold Ith, the EVECU 100 proceeds to step S16 and executes the second mode. In the second mode, the EVECU 100 switches between the step-down operation and the stop of the operation of the inverter 20 to improve the efficiency of the inverter 20.

[0190] Next, FIG. 21 shows the processing procedure of the second mode.

[0191] After executing the process of step S20, the EVECU 100 calculates the difference value ΔSOC in step S21. In this embodiment, the difference value ΔSOC is a value obtained by subtracting the SOC of the first storage battery 31 from the SOC of the second storage battery 32.

[0192] After executing the process of step S22, the EVECU 100 determines in step S23 whether the difference value ΔSOC is greater than the charge threshold value Sth. If the EVECU 100 determines in step S23 that the difference value ΔSOC is greater than the charge threshold value Sth, the EVECU 100 proceeds to step S90.

[0193] In step S90, the EVECU 100 determines whether the second detection voltage VL is higher than the first detection voltage VH. If the EVECU 100 determines that the second detection voltage VL is higher than the first detection voltage VH, the EVECU 100 proceeds to step S91.

[0194] In step S91, the EVECU 100 determines whether the first estimated input power Winc1 is equal to or less than the first upper limit input power Win1. If the EVECU 100 determines that the first estimated input power Winc1 is equal to or less than the first upper limit input power Win1, the EVECU 100 proceeds to step S92.

[0195] In step S92, the EVECU 100 performs a step-down operation of the inverter 20 so that the output current Io of the low-voltage charger 210 is entirely supplied to the first storage battery 31 and the current flowing through the second storage battery 32 becomes zero.

[0196] When the first storage battery 31 is charged by the step-down operation of the inverter 20, the voltage of the first storage battery 31 may then become higher than the voltage of the second storage battery 32. In this case, there is a concern that current may flow from the first storage battery 31 to the second storage battery 32 via the bypass switch 61. Therefore, when the EVECU 100 determines that the second detected voltage VL is higher than the first detected voltage VH, it causes the inverter 20 to perform a step-down operation, thereby increasing the voltage of the first storage battery 31. This makes it possible to prevent current from flowing from the first storage battery 31 to the second storage battery 32.

[0197] If the EVECU 100 determines in step S91 that the first estimated input power Winc1 is greater than the first upper limit input power Win1, the EVECU 100 proceeds to step S93.

[0198] In step S93, the EVECU 100 reduces the external command charging current Icht so that the first estimated input power Winc1 becomes equal to or less than the first upper limit input power Win1, and transmits the reduced external command charging current Icht to the low-voltage charger 210. After completing the process of step S93, the EVECU 100 proceeds to step S92 and performs a step-down operation. Because the external command charging current Icht is reduced in step S93, the execution of the step-down operation can prevent the input power of the first storage battery 31 from exceeding the first upper limit input power Win1.

[0199] On the other hand, if the EVECU 100 determines in step S23 that the difference value ΔSOC is equal to or less than the charge threshold value Sth, or if the EVECU 100 makes a negative determination in step S90, the EVECU 100 proceeds to step S94.

[0200] In step S94, the EVECU 100 determines whether the second estimated input power Winc2 is equal to or less than the second upper limit input power Win2. If the EVECU 100 determines that the second estimated input power Winc2 is equal to or less than the second upper limit input power Win2, the EVECU 100 proceeds to step S95.

[0201] In step S95, the EVECU 100 turns off the upper and lower arm switches SWH, SWL of each phase to stop the operation of the inverter 20 so as to reduce the current flowing through the first storage battery 31 to zero.

[0202] If the EVECU 100 determines in step S94 that the second estimated input power Winc2 is greater than the second upper limit input power Win2, the EVECU 100 proceeds to step S96.

[0203] In step S96, the EVECU 100 reduces the external command charging current Icht so that the second estimated input power Winc2 becomes equal to or less than the second upper limit input power Win2, and transmits the reduced external command charging current Icht to the low-voltage charger 210. After completing the process of step S96, the EVECU 100 proceeds to step S95 and stops the operation of the inverter 20. Because the external command charging current Icht has been reduced in step S96, it is possible to prevent the input power of the second storage battery 32 from exceeding the second upper limit input power Win2 due to the stop of operation.

[0204] In step S97, the EVECU 100 calculates an average current Iave, which is a time average value of the current flowing through the inverter 20 over a predetermined period. The predetermined period is the period during which the second mode is being executed, and more specifically, is the total period of the execution period of the voltage step-down operation in step S92 and the stop period of the voltage step-down operation in step S95. The average current Iave is calculated based on, for example, the detection value of the first current sensor 81 or the motor current IN.

[0205] After calculating the average current Iave in step S97, the EVECU 100 proceeds to step S17 in FIG.

[0206] According to the present embodiment described above, the same effects as those of the first embodiment can be obtained.

[0207] Fifth Embodiment A fifth embodiment will now be described with reference to the drawings, focusing on differences from the first and fourth embodiments. In this embodiment, the second mode is executed during external power feeding control.

[0208] 22 shows the control state of each switch during external power supply control in which power is supplied from the first and second storage batteries 31, 32 to the high-voltage power supply target unit 220. When the EVECU 100 determines that the power supply target unit connected to the power conversion device is the high-voltage power supply target unit 220, it turns off the pre-charge main switch SMRP, the bypass switch 61, the first motor-side switch 71, the second motor-side switch 72, and the upper and lower arm switches SWH, SWL of all phases of the inverter 20, and turns on the connection switches DCRH, DCRL, the high-potential-side main switch SMRH, the low-potential-side main switch SMRL, and the inter-battery switch 50. As a result, power is supplied from the first storage battery 31 and the second storage battery 32 to the high-voltage power supply target unit 220.

[0209] 23 shows the control state of each switch during external power supply control in which power is supplied from the first and second storage batteries 31, 32 to the low-voltage power supply target unit 230. When the EVECU 100 determines that the power supply target unit connected to the power conversion device is the low-voltage power supply target unit 230, it turns off the pre-charge main switch SMRP and the inter-battery switch 50 and turns on the connection switches DCRH, DCRL, the high-potential side main switch SMRH, the low-potential side main switch SMRL, the bypass switch 61, the first motor-side switch 71, and the second motor-side switch 72. As a result, power is supplied from the second storage battery 32 to the low-voltage power supply target unit 230.

[0210] In the external power supply control for the low-voltage power supply target portion 230, the EVECU 100 performs switching control to alternately turn on the upper and lower arm switches SWH, SWL of at least one phase, or performs switching control of the upper arm switch SWH of at least one phase while keeping the lower arm switches SWL of all phases of the inverter 20 off, thereby boosting the output voltage of the first storage battery 31 and supplying it to the low-voltage power supply target portion 230. More specifically, the EVECU 100 performs a boost operation, which is the switching control, to control the power supply voltage VB to the target power supply voltage. As a result, power is supplied from the first storage battery 31 to the low-voltage power supply target portion 230.

[0211] By executing external power supply control for the low-voltage power supply target unit 230, the low-voltage power supply target unit 230 is supplied with power directly from the second storage battery 32 and from the first storage battery 31 via the inverter 20. Here, the smaller the inverter current Iinv, which is the current flowing through the inverter 20, the lower the efficiency of the inverter 20. Therefore, when the input current Ii to the low-voltage power supply target unit 230 is small, the inverter current Iinv becomes smaller, and the efficiency of the inverter 20 decreases. This raises the concern that the power supply time to the low-voltage power supply target unit 230 from the storage batteries 31, 32 may be longer than when the inverter current Iinv is large. Therefore, in this embodiment, the inverter 20 is controlled to suppress the decrease in the efficiency of the inverter 20. Hereinafter, this control method will be described.

[0212] In this embodiment as well, the external power supply control of the low-voltage power supply target unit 230 shown in Fig. 16 is executed. This process is executed repeatedly, for example, at a predetermined control period by cooperation between the EVECU 100 and the battery ECU 90.

[0213] After executing the process of step S62, the EVECU 100 determines in step S63 whether the inverter current Iinv is greater than the current threshold Ith. In this embodiment, the inverter current Iinv is the first command discharge current Idis1 calculated in step S61. Note that the inverter current Iinv may be the absolute value of the detection value of the first current sensor 81 or the absolute value of the motor current IN.

[0214] If the EVECU 100 determines that the inverter current Iinv is greater than the current threshold Ith, the EVECU 100 proceeds to step S64.

[0215] If the EVECU 100 determines in step S64 that the inverter temperature Tinv is lower than the temperature threshold value Tth, the EVECU 100 proceeds to step S65 and executes the first mode. In the first mode, the EVECU 100 transmits the external command discharge current Idist calculated in step S62 to the low-voltage power supply target unit 230 and performs a boost operation of the inverter 20 to control the current flowing through the first storage battery 31 to the first command discharge current Idis1.

[0216] If the EVECU 100 determines in step S63 that the inverter current Iinv is equal to or less than the current threshold Ith, the EVECU 100 proceeds to step S66 and executes the second mode. In the second mode, the EVECU 100 switches between the boost operation and the stop of the operation of the inverter 20 to improve the efficiency of the inverter 20.

[0217] Next, FIG. 24 shows the processing procedure of the second mode.

[0218] After executing the process of step S70, the EVECU 100 calculates the difference value ΔSOC in step S71. In this embodiment, the difference value ΔSOC is a value obtained by subtracting the SOC of the first storage battery 31 from the SOC of the second storage battery 32.

[0219] After executing the process of step S72, the EVECU 100 determines in step S103 whether the difference value ΔSOC is equal to or less than the charge threshold value Sth. If the EVECU 100 determines in step S103 that the difference value ΔSOC is equal to or less than the charge threshold value Sth, the EVECU 100 proceeds to step S104.

[0220] In step S104, the EVECU 100 determines whether the first estimated output power Woutc1 is equal to or less than the first upper limit output power Wout1. If the EVECU 100 determines that the first estimated output power Woutc1 is equal to or less than the first upper limit output power Wout1, the EVECU 100 proceeds to step S105.

[0221] In step S105, the EVECU 100 supplies current to the low-voltage power supply target section 230 from only the first storage battery 31 of the first and second storage batteries 31, 32, and performs a boost operation of the inverter 20 to reduce the current flowing to the second storage battery 32 to zero.

[0222] If the EVECU 100 determines in step S104 that the first estimated output power Woutc1 is greater than the first upper limit output power Wout1, the EVECU 100 proceeds to step S106.

[0223] In step S106, the EVECU 100 reduces the external command discharge current Idist so that the first estimated output power Woutc1 becomes equal to or less than the first upper limit output power Wout1, and transmits the reduced external command discharge current Idist to the low-voltage power supply target unit 230. After completing the processing of step S106, the EVECU 100 proceeds to step S105 and performs a boost operation. Because the external command discharge current Idist is reduced in step S106, it is possible to prevent the output power of the first storage battery 31 from exceeding the first upper limit output power Wout1 as the boost operation is performed.

[0224] On the other hand, if the EVECU 100 determines in step S103 that the difference value ΔSOC is greater than the charge threshold value Sth, the EVECU 100 proceeds to step S107.

[0225] In step S107, the EVECU 100 determines whether the second detection voltage VL is higher than the first detection voltage VH. If the EVECU 100 determines that the second detection voltage VL is equal to or lower than the first detection voltage VH, the EVECU 100 proceeds to step S104. On the other hand, if the EVECU 100 determines that the second detection voltage VL is higher than the first detection voltage VH, the EVECU 100 proceeds to step S108.

[0226] If the inverter 20 is stopped and only the second storage battery 32 of the first and second storage batteries 31, 32 is discharged, the voltage of the first storage battery 31 will then become higher than the voltage of the second storage battery 32. In this case, there is a concern that current will flow from the first storage battery 31 to the second storage battery 32 via the bypass switch 61. Therefore, when the EVECU 100 determines that the second detected voltage VL is higher than the first detected voltage VH, it stops the inverter 20, thereby preventing current from flowing from the first storage battery 31 to the second storage battery 32.

[0227] In step S108, the EVECU 100 determines whether the second estimated output power Woutc2 is equal to or less than the second upper limit output power Wout2. If the EVECU 100 determines that the second estimated output power Woutc2 is equal to or less than the second upper limit output power Wout2, the EVECU 100 proceeds to step S109.

[0228] In step S109, the EVECU 100 turns off the upper and lower arm switches SWH, SWL of each phase to stop the operation of the inverter 20 so as to reduce the current flowing through the first storage battery 31 to zero.

[0229] If the EVECU 100 determines in step S108 that the second estimated output power Woutc2 is greater than the second upper limit output power Wout2, the EVECU 100 proceeds to step S110.

[0230] In step S110, the EVECU 100 reduces the external command discharge current Idist so that the second estimated output power Woutc2 becomes equal to or less than the second upper limit output power Wout2, and transmits the reduced external command discharge current Idist to the low-voltage power supply target unit 230. After completing the process of step S110, the EVECU 100 proceeds to step S109 and stops the operation of the inverter 20. Because the external command discharge current Idist is reduced in step S110, it is possible to prevent the output power of the second storage battery 32 from exceeding the second upper limit output power Wout2 when the operation of the inverter 20 is stopped.

[0231] In step S111, the EVECU 100 calculates an average current Iave, which is a time average value of the current flowing through the inverter 20 over a predetermined period. The predetermined period is the period during which the second mode is operated, and specifically, is the sum of the period during which the voltage step-up operation is being performed in step S105 and the period during which the voltage step-up operation is stopped in step S109. The average current Iave is calculated based on, for example, the detection value of the first current sensor 81 or the motor current IN. In the second mode, the inverter 20 is switched between voltage step-up operation and operation stop. Therefore, in order to estimate the power conversion efficiency of the inverter 20, it is necessary to calculate the current flowing through the inverter 20 during the period during which the voltage step-up operation of the inverter 20 is being performed and the period during which the voltage step-up operation of the inverter 20 is stopped in the second mode.

[0232] After calculating the average current Iave in step S111, the EVECU 100 proceeds to step S67 in FIG.

[0233] According to the present embodiment described above, it is possible to suppress a decrease in the efficiency of the inverter 20 during external power feeding control.

[0234] Other Embodiments The above-described embodiments may be modified as follows.

[0235] The control of the second embodiment may be applied to the third to fifth embodiments.

[0236] A configuration may be adopted in which some of the functions of the EVECU 100 are provided in the battery ECU 90, rather than in the EVECU 100. For example, as shown in FIG. 25 , a first charging current calculation unit 102A and a second charging current calculation unit 102B may be provided in the battery ECU 90.

[0237] The output upper limit value and the input upper limit value calculated by the battery ECU 90 are not limited to the upper limit power, but may be the upper limit current. FIG. 26 is a functional block diagram of the battery ECU 90 and the EVECU 100.

[0238] The battery ECU 90 includes a first input current calculation unit 94A, a first output current calculation unit 94B, a second input current calculation unit 95A, and a second output current calculation unit 95B.

[0239] The first input current calculation unit 94A calculates a first upper limit input current Iin1, which is the maximum value of current that can be input to the first storage battery 31, based on the battery state of the first storage battery 31. For example, the first input current calculation unit 94A calculates a smaller first upper limit input current Iin1 as the SOC of the first storage battery 31 increases or the temperature of the first storage battery 31 detected by the battery temperature sensor 88A decreases.

[0240] The first output current calculation unit 94B calculates a first upper limit output current Iout1, which is the maximum value of the current that can be output from the first storage battery 31, based on the battery state of the first storage battery 31. For example, the first output current calculation unit 94B calculates a larger first upper limit output current Iout1 as the SOC of the first storage battery 31 increases or the temperature of the first storage battery 31 detected by the battery temperature sensor 88A increases.

[0241] The second input current calculation unit 95A calculates the second upper limit input current Iin2, which is the maximum value of the current that can be input to the second storage battery 32, based on the battery state of the second storage battery 32. For example, the second input current calculation unit 95A calculates the second upper limit input current Iin2 to be smaller as the SOC of the second storage battery 32 is higher or the temperature of the second storage battery 32 detected by the battery temperature sensor 88A is lower.

[0242] The second output current calculation unit 95B calculates a second upper limit output current Iout2, which is the maximum value of the current that can be output from the second storage battery 32, based on the battery state of the second storage battery 32. For example, the second output current calculation unit 95B calculates a larger second upper limit output current Iout2 as the SOC of the second storage battery 32 increases or the temperature of the second storage battery 32 detected by the battery temperature sensor 88A increases.

[0243] In each of the above embodiments, instead of the first upper limit input power Win1, the first upper limit output power Wout1, the second upper limit input power Win2, and the second upper limit output power Wout2, the first upper limit input current Iin1, the first upper limit output current Iout1, the second upper limit input current Iin2, and the second upper limit output current Iout2 may be used.

[0244] Taking the first embodiment as an example, the first charging current calculation unit 102A may calculate the calculated first upper limit input current Iin1 as the first command charging current Ich1.

[0245] Furthermore, the second charging current calculation unit 102B may calculate the calculated second upper limit input current Iin2 as the second command charging current Ich2.

[0246] In step S26 of Fig. 7 and step S75 of Fig. 17, the EVECU 100 does not have to set the current flowing through the first storage battery 31 to zero. In this case, the EVECU 100 performs a step-down operation or a step-up operation of the inverter 20 so that the current flowing through the first storage battery 31 is smaller than that when the first mode is executed. Specifically, for example, the EVECU 100 performs a step-down operation or a step-up operation of the inverter 20 so that the current flowing through the first storage battery 31 is equal to or less than a first predetermined current. For example, the first predetermined current is equal to or less than 1 / 20 or 1 / 10 of the current flowing through the first storage battery 31 when the first mode is executed.

[0247] 21 and step S105 in FIG. 24, the EVECU 100 does not have to set the current flowing through the second storage battery 32 to zero. In this case, the EVECU 100 performs a step-down operation or a step-up operation of the inverter 20 so that the current flowing through the second storage battery 32 is smaller than that when the first mode is executed. Specifically, for example, the EVECU 100 performs a step-down operation or a step-up operation of the inverter 20 so that the current flowing through the second storage battery 32 is equal to or less than a second predetermined current. For example, the second predetermined current is equal to or less than 1 / 20 or 1 / 10 of the current flowing through the second storage battery 32 when the first mode is executed.

[0248] The terminal voltage (e.g., rated voltage) of the first storage battery 31 may be equal to the terminal voltage (e.g., rated voltage) of the second storage battery 32. In this case, in the external charging control using the low-voltage charger 210 shown in Fig. 3 , the EVECU 100 charges the first and second storage batteries 31, 32 by turning on the upper arm switches SWH of all or some of the phases of the inverter 20 and turning off the lower arm switches SWL of all of the phases of the inverter 20. In addition, in the external charging control using the low-voltage charger 210 shown in Fig. 20 , the EVECU 100 charges the first and second storage batteries 31, 32 by turning on the lower arm switches SWL of all or some of the phases of the inverter 20 and turning off the upper arm switches SWH of all of the phases of the inverter 20.

[0249] In each of the above embodiments, the power conversion device does not necessarily have to include either the first or second motor-side switch 71, 72. Furthermore, the power conversion device does not necessarily have to include both the first and second motor-side switches 71, 72.

[0250] The switches of the inverter 20 are not limited to IGBTs and may be, for example, N-channel MOSFETs having body diodes. In this case, the high-potential terminal of the N-channel MOSFET serves as the drain, and the low-potential terminal serves as the source.

[0251] The high-potential side main switch SMRH does not have to be provided.

[0252] Instead of the low-potential side main switch SMRL, a series connection of the pre-charge main switch SMRP and the pre-charge resistor 40 may be connected in parallel to the high-potential side main switch SMRH. In this case, the low-potential side main switch SMRL may not be provided. Also, the fuses 41 and 42 may not be provided.

[0253] The motor is not limited to a star-connected motor, but may be a delta-connected motor. The motor and inverter are not limited to a three-phase motor, but may be a two-phase motor, or a four-phase or more phase motor. The motor is not limited to a permanent magnet synchronous machine having a permanent magnet as a field pole on the rotor, but may be a wound field synchronous machine having a field winding as a field pole on the rotor. In this case, the rotor may be provided with both a field winding and a permanent magnet. The motor is not limited to a synchronous machine, but may be an induction machine.

[0254] As shown in FIG. 27 , when switching from one of the voltage step-down operation (or voltage step-up operation) and the stop of the voltage step-down operation (or the stop of the voltage step-up operation) to the other in the second mode, the EVECU 100 may gradually change the current flowing through the connection path 73. Specifically, for example, when switching from one to the other, the control device may gradually change the charge current command value or the discharge current command value. FIG. 27 shows an example in which the command value is gradually increased. This makes it possible to suppress current overshoot during external charging control or external power supply control.

[0255] 6, the inverter current Iinv may be the transmitted power of the inverter 20 (hereinafter referred to as inverter power Winv, which corresponds to the "electrical parameter"). In the first embodiment, the battery ECU 90 or the EVECU 100 calculates the inverter power Winv by multiplying the detected value of the second current sensor 82 or the motor current IN by the second detected voltage VL, for example.

[0256] 7, the average current Iave calculated in step S31 or the like may be the time average value of the power transmitted by the inverter 20 (hereinafter referred to as average power Wave). In the case of the first embodiment, the battery ECU 90 or the EVECU 100 calculates the average power Wave by multiplying the average current Iave by the second detected voltage VL, for example.

[0257] The total current Isum calculated in step S55 of Fig. 11 may be the total power Wsum. The total power Wsum is, for example, a value obtained by multiplying the total current Isum by the second detection voltage VL.

[0258] The system including the power conversion device is not limited to the system shown in Fig. 1 or 18, but may be, for example, the systems shown in Fig. 28 to Fig. 30. Note that in Fig. 28 to Fig. 30, the pre-charge main switch, pre-charge resistor, control device, etc. are not shown.

[0259] 28 shows a system including two storage batteries and two inverters. The system includes a first storage battery 131, a second storage battery 132, and first and second inverters 120A and 120B (corresponding to "power transmission circuits") that constitute a power conversion device. The first storage battery 131 is an assembled battery similar to the first storage battery 31 in FIG. 1 and the like, and the second storage battery 132 is an assembled battery similar to the second storage battery 32 in FIG. 1 and the like. A positive terminal of the first storage battery 131 is electrically connected to a positive terminal of an external charger 240 via a high-side connection switch DCRH, and a negative terminal of the first storage battery 131 is electrically connected to a negative terminal of the external charger 240 via a low-side connection switch DCRL.

[0260] The first inverter 120A includes three phases of a series connection of a first upper-arm switch SWHA and a first lower-arm switch SWLA. A first upper-arm diode DHA, which is a freewheeling diode, is connected in anti-parallel to the first upper-arm switch SWHA, and a first lower-arm diode DLA, which is also a freewheeling diode, is connected in anti-parallel to the first lower-arm switch SWLA. In this embodiment, each of the switches SWHA and SWLA is an IGBT. Like the first inverter 120A, the second inverter 120B also includes a second upper-arm switch SWHB, a second lower-arm switch SWLB, a second upper-arm diode DHB, and a second lower-arm diode DLB.

[0261] The power conversion device includes a motor 110. The motor 110 includes three-phase armature windings 111. In each phase, a connection point between the emitter of the second upper arm switch SWHB and the collector of the second lower arm switch SWLB is connected via the armature winding 111 to a connection point between the emitter, which is the low potential terminal of the first upper arm switch SWHA, and the collector, which is the high potential terminal of the first lower arm switch SWLA.

[0262] The collector of the first upper arm switch SWHA of each phase is connected to the positive terminal of the first storage battery 131 via the first high-side main switch SRH1. The emitter of the first lower arm switch SWLA of each phase is connected to the negative terminal of the first storage battery 131 via the first low-side main switch SRL1. The collector of the second upper arm switch SWHB of each phase is connected to the positive terminal of the second storage battery 132 via the second high-side main switch SRH2. The emitter of the second lower arm switch SWLB of each phase is connected to the negative terminal of the second storage battery 132 via the second low-side main switch SRL2.

[0263] In external charging control using the external charger 240, a control device (not shown) of the power conversion device charges the first storage battery 131 from the external charger 240 while keeping the switches DCRH, DCRL, SRH1, SRL1, SRH2, and SRL2 on. At the same time, the control device controls the switching of the switches of the first inverter 120A and the second inverter 120B, thereby also charging the second storage battery 132 from the external charger 240 via the inverters 120A and 120B. In this case, a decrease in the current flowing through the inverters 120A and 120B (e.g., switches SWHA, SWLA, SWHB, and SWLB) can reduce the efficiency of the inverters 120A and 120B. Therefore, to suppress the reduction in the efficiency of the inverters 120A and 120B, the control device executes the second mode described in FIG. 7 of the first embodiment.

[0264] For example, the control device switches between operating and stopping the operation of the first and second inverters 120A, 120B while maintaining a constant output current of the external charger 240. The control device operates the first and second inverters 120A, 120B so that only the second storage battery 132 of the first and second storage batteries 131, 132 is charged from the external charger. On the other hand, the control device stops the operation of the first and second inverters 120A, 120B so that only the first storage battery 131 of the first and second storage batteries 131, 132 is charged from the external charger.

[0265] In external power supply control in which an external power supply target, which is a system power supply or an electrical load, is electrically connected to the first storage battery 131 instead of the external charger 240, power is supplied from the second storage battery 132 to the external power supply target via the inverters 120A, 120B by switching control of the inverters 120A, 120B. In this case, a decrease in the current flowing through the inverters 120A, 120B can reduce the efficiency of the inverters 120A, 120B. Therefore, to suppress the reduction in the efficiency of the inverters 120A, 120B, the control device executes the second mode described in FIG. 17 of the third embodiment.

[0266] The control device switches between operating and stopping the first and second inverters 120A, 120B, for example, while maintaining a constant output current from the power conversion device to the external power supply target components. The control device operates the first and second inverters 120A, 120B so that power is supplied to the external power supply target components only from the second storage battery 132 of the first and second storage batteries 131, 132. On the other hand, the control device stops the operation of the first and second inverters 120A, 120B so that power is supplied to the external power supply target components only from the first storage battery 131 of the first and second storage batteries 131, 132.

[0267] 29 shows a system including two storage batteries, one inverter, and one DCDC converter. The system includes a first storage battery 231, a second storage battery 232, an inverter 121 constituting a power conversion device, a motor 310, and a DCDC converter 340 (corresponding to a "power transmission circuit"). The first storage battery 231 is an assembled battery similar to the first storage battery 31 shown in FIG. 1 , etc., and the second storage battery 232 is an assembled battery similar to the second storage battery 32 shown in FIG. 1 , etc. The positive terminal of the first storage battery 231 is electrically connected to the positive terminal of an external charger 240 via a high-side connection switch DCRH, and the negative terminal of the first storage battery 231 is electrically connected to the negative terminal of the external charger 240 via a low-side connection switch DCRL. The motor 310 includes a three-phase armature winding 311 and a smoothing capacitor 321.

[0268] The DCDC converter 340 and the first storage battery 231 are connected via a high-side main switch SRH and a low-side main switch SRL. The DCDC converter 340 has a boost function that boosts the DC output voltage of the first storage battery 231 and outputs it to the inverter 121 side through its own switching control, and a buck function that lowers the DC input voltage from the inverter 121 side and outputs it to the first storage battery 231. The smoothing capacitor 321 and the second storage battery 232 are connected via a main switch SRS.

[0269] In external charging control using the external charger 240, a control device (not shown) of the power conversion device turns on each of the switches DCRH, DCRL, SRH, SRL, and SRS, and charges the first storage battery 231 from the external charger 240 via the DCDC converter 340, while also charging the second storage battery 232 from the external charger 240. In this case, a decrease in the current flowing through the DCDC converter 340 can reduce the efficiency of the DCDC converter 340. Therefore, in order to suppress the decrease in the efficiency of the DCDC converter 340, the control device executes the second mode described in FIG. 7 of the first embodiment.

[0270] For example, the control device switches between operating and stopping the operation of the DCDC converter 340 while maintaining a constant output current of the external charger 240. The control device stops the operation of the DCDC converter 340 so that, of the first and second storage batteries 231, 232, only the second storage battery 232 is charged from the external charger 240. On the other hand, the control device operates the DCDC converter 340 so that, of the first and second storage batteries 231, 232, only the first storage battery 231 is charged from the external charger 240.

[0271] When executing external power supply control, the control device switches between operating and stopping the operation of the DCDC converter 340 while maintaining the output current to the external power supply target components constant, for example. The control device stops the operation of the DCDC converter 340 so that power is supplied to the external power supply target components from only the second storage battery 232 of the first and second storage batteries 231, 232. On the other hand, the control device operates the DCDC converter 340 so that power is supplied to the external power supply target components from only the first storage battery 131 of the first and second storage batteries 231, 232.

[0272] Fig. 30 shows a system including two storage batteries, one inverter, and two DC-DC converters. In the configuration shown in Fig. 30, the DC-DC converter 340 will be referred to as the first DC-DC converter 340. The system also includes a second DC-DC converter 350 (corresponding to a "power transmission circuit") provided between the smoothing capacitor 321 and the second storage battery 232. The second DC-DC converter 350 has a boost function that boosts the DC output voltage of the second storage battery 232 and outputs it to the inverter 121 side, and a buck function that lowers the DC input voltage from the inverter 121 side and outputs it to the second storage battery 232, through its own switching control.

[0273] During external charging control using the external charger 240, a control device (not shown) of the power conversion device turns on the switches DCRH, DCRL, SRH, SRL, and SRS, and charges the second storage battery 232 from the external charger 240 via the second DC-DC converter 350 by controlling the switching of the second DC-DC converter 350, while also charging the first storage battery 231 from the external charger 240 via the first DC-DC converter 340 by controlling the switching of the first DC-DC converter 340. If the current flowing through at least one of the first and second DC-DC converters 340, 350 decreases, the efficiency of the first and second DC-DC converters 340 may decrease. In such a case, to suppress the decrease in the efficiency of the first and second DC-DC converters 340, the same processing as that described for the configuration of FIG. 29 may be performed. Furthermore, the same processing as that described for the configuration of FIG. 29 may be performed during external power feeding control as well.

[0274] The control devices that perform external charging and power supply control are not limited to the battery ECU 90 and the EVECU 110, and may be other control devices.

[0275] The power storage unit to be charged by the external charger is not limited to a storage battery. For example, it may be a large-capacity electric double layer capacitor, or a unit including both a storage battery and an electric double layer capacitor.

[0276] The mobile body on which the power conversion device is mounted is not limited to a vehicle, but may be, for example, an aircraft or a ship.Furthermore, the power conversion device is not limited to a mobile body, but may be a stationary device.

[0277] The control device and method described herein may be implemented by a special-purpose computer configured with a processor and memory programmed to execute one or more functions embodied in a computer program. Alternatively, the control device and method described herein may be implemented by a special-purpose computer configured with a processor comprising one or more dedicated hardware logic circuits. Alternatively, the control device and method described herein may be implemented by one or more special-purpose computers configured with a combination of a processor and memory programmed to execute one or more functions and a processor configured with one or more hardware logic circuits. Furthermore, the computer program may be stored in a computer-readable non-transitory tangible recording medium as instructions to be executed by a computer.

[0278] Characteristic configurations extracted from the above-described embodiments are described below. [Configuration 1] A power conversion device applied to a system including a first power storage unit (31, 131, 231) and a second power storage unit (32, 132, 232), comprising: a power transmission circuit (10, 20, 22H, 22L, 50, 60, 61, 73, 120A, 120B, 340, 350) whose switching is controlled to transmit power between the first power storage unit and the second power storage unit; and a control device (100) that controls the switching of the power transmission circuit, wherein the control device executes a first mode on condition that an electrical parameter that is the magnitude of current or power transmitted through the power transmission circuit is greater than a switching threshold (Ith, IthH), and executes a second mode on condition that the electrical parameter is equal to or less than the switching threshold, and the first mode is a mode in which switching control of the power transmission circuit is continuously performed. The power conversion device, wherein the second mode is a mode in which switching control of the power transmission circuit is switched between stopping the switching control and stopping the switching control, or the number of phases of the power transmission circuit that perform switching control is reduced compared to the first mode.[Configuration 2] The power transmission circuit includes: an inverter (20) having upper and lower arm switches (SWH, SWL) of a plurality of phases; a motor (10) having an armature winding (11) electrically connected to a low potential side terminal of the upper arm switch of each phase and a high potential side terminal of the lower arm switch of each phase; a high potential side path (22H) electrically connecting a positive terminal of a first power storage unit (31) to the high potential side terminal of the upper arm switch; a low potential side path (22L) electrically connecting a negative terminal of a second power storage unit (32) to the low potential side terminal of the lower arm switch; and an inter-power storage unit switch (50) that, when turned on, electrically connects the negative terminal of the first power storage unit to the positive terminal of the second power storage unit and, when turned off, electrically disconnects the negative terminal of the first power storage unit from the positive terminal of the second power storage unit. the control device performs switching control of a target switch that is at least one of the upper and lower arm switches to allow a current to flow through the connection path; executes the first mode on condition that a magnitude of the current flowing through the connection path, which is the electrical parameter, is greater than the switching threshold; and executes the second mode on condition that a magnitude of the current flowing through the connection path is equal to or less than the switching threshold; the first mode is a mode in which the switching control of the target switch is continued; and the second mode is a mode in which switching control of the target switch is switched between and stopping the switching control, or a mode in which the number of phases of the target switch to be switched is reduced compared to the first mode.the bypass switch (60) electrically connects the negative terminal of the first power storage unit and the negative terminal of the second power storage unit when turned on and electrically disconnects the negative terminal of the first power storage unit and the negative terminal of the second power storage unit when turned off; the connection path electrically connects the armature winding and the positive terminal of the second power storage unit; and the control device, when an external charger (210) is electrically connected to the high potential side path and the low potential side path, turns off the inter-power storage unit switch and turns on the bypass switch, thereby performing switching control of the upper arm switch which is the target switch, thereby performing external charging control to charge the second power storage unit by causing a current to flow in a closed circuit including the external charger, the inverter, the armature winding, the connection path, and the second power storage unit. [Configuration 4] The power conversion device according to configuration 2 or 3, wherein the second mode is a mode for switching between switching control of the target switch and stopping the switching control, and the control device, in the second mode, performs switching control of the target switch such that the input power of the first storage unit does not exceed an upper limit input power (Win1) of the first storage unit upon stopping the switching control, and performs switching control of the target switch such that the input power of the second storage unit does not exceed an upper limit input power (Win2) of the second storage unit upon starting the switching control.the bypass switch (60) electrically connects the negative terminal of the first power storage unit and the negative terminal of the second power storage unit when turned on and electrically disconnects the negative terminal of the first power storage unit and the negative terminal of the second power storage unit when turned off; the connection path electrically connects the armature winding and the positive terminal of the second power storage unit; and the control device, when an external power supply target unit (230) is electrically connected to the high potential side path and the low potential side path, turns off the inter-power storage unit switch and turns on the bypass switch, thereby performing external power supply control to supply current from the second power storage unit to the external power supply target unit via the connection path, the armature winding, and the inverter. [Configuration 6] The power conversion device according to Configuration 5, wherein the second mode is a mode for switching between switching control of the target switch and stop of the switching control, and the control device, in the second mode, performs switching control of the target switch such that, in conjunction with the stop of the switching control, the output power of the first power storage unit does not exceed an upper limit output power (Wout1) of the first power storage unit, and performs switching control of the target switch such that, in conjunction with the start of the switching control, the output power of the second power storage unit does not exceed an upper limit output power (Wout2) of the second power storage unit. [Configuration 7] The power conversion device according to any one of Configurations 3 to 6, wherein the second mode is a mode for switching between switching control of the target switch and stop of the switching control, and the control device switches between the first mode and the second mode such that the voltage of the second power storage unit does not exceed the voltage of the first power storage unit.[Configuration 8] The power conversion device according to Configuration 2, wherein the bypass switch (61) electrically connects a positive terminal of the first power storage unit and a positive terminal of the second power storage unit when turned on and electrically disconnects the positive terminal of the first power storage unit and the positive terminal of the second power storage unit when turned off, the connection path electrically connects the armature winding and a negative terminal of the first power storage unit, and the control device, when an external charger (210) is electrically connected to the high potential side path and the low potential side path, turns off the inter-power storage unit switch and turns on the bypass switch, thereby performing switching control of the lower arm switch which is the target switch, to cause a current to flow in a closed circuit including the external charger, the first power storage unit, the connection path, the armature winding, and the inverter, thereby charging the first power storage unit. [Configuration 9] The power conversion device according to Configuration 8, wherein the second mode is a mode for switching between switching control of the target switch and stop of the switching control, and the control device, in the second mode, performs switching control of the target switch such that, upon stop of the switching control, the input power of the second power storage unit does not exceed an upper limit input power (Win2) of the second power storage unit, and performs switching control of the target switch such that, upon start of the switching control, the input power of the first power storage unit does not exceed an upper limit input power (Win1) of the first power storage unit. [Configuration 10] The power conversion device according to any one of Configurations 3, 4, 8, and 9, wherein the second mode is a mode for switching between switching control of the target switch and stop of the switching control, and the control device switches between the first mode and the second mode so that a difference between a voltage of the first power storage unit and a voltage of the second power storage unit is equal to or less than a threshold (Sth). [Configuration 11] The power conversion device according to Configuration 10, wherein the control device sets the threshold to be smaller as time passes since the start of the external charging control.the bypass switch (61) electrically connects the positive terminal of the first power storage unit and the positive terminal of the second power storage unit when turned on and electrically disconnects the positive terminal of the first power storage unit and the positive terminal of the second power storage unit when turned off; the connection path electrically connects the armature winding and the negative terminal of the first power storage unit; and the control device, when an external power supply target unit (230) is electrically connected to the high potential side path and the low potential side path, turns off the inter-power storage unit switch and turns on the bypass switch, thereby performing external power supply control to supply current to the external power supply target unit via a closed circuit including the external power supply target unit, the first power storage unit, the connection path, the armature winding, and the inverter. [Configuration 13] The power conversion device according to Configuration 12, wherein the second mode is a mode for switching between switching control of the target switch and stop of the switching control, and the control device, in the second mode, performs switching control of the target switch such that, in conjunction with the stop of the switching control, the output power of the second power storage unit does not exceed an upper limit output power (Wout2) of the second power storage unit, and performs switching control of the target switch such that, in conjunction with the start of the switching control, the output power of the first power storage unit does not exceed an upper limit output power (Wout1) of the first power storage unit. [Configuration 14] The power conversion device according to any one of Configurations 5, 6, 12, and 13, wherein the second mode is a mode for switching between switching control of the target switch and stop of the switching control, and the control device switches between the first mode and the second mode so that a difference between a voltage of the first power storage unit and a voltage of the second power storage unit is equal to or less than a threshold (Sth). [Configuration 15] The power conversion device according to Configuration 14, wherein the control device sets the threshold to be smaller as time passes since the external power supply control is started.[Configuration 16] The power conversion device according to any one of configurations 8, 9, 12, and 13, wherein the second mode is a mode for switching between switching control of the target switch and stopping the switching control, and the control device switches between the first mode and the second mode so that the voltage of the first power storage unit does not exceed the voltage of the second power storage unit. [Configuration 17] The power conversion device according to any one of configurations 1 to 16, wherein the control device gradually changes the current flowing through the power transmission circuit when switching from one of the switching control and stopping the switching control to the other in the second mode. [Configuration 18] The power conversion device according to configuration 1, wherein the second mode is a mode for reducing the number of phases compared to the first mode, and the control device performs interleaved control in the second mode. [Configuration 19] The power conversion device according to configuration 18, wherein the system includes a temperature sensor (88A) for detecting switch temperatures of the upper and lower arm switches of each phase, and the control device selects a phase to be switched based on a value detected by the temperature sensor.

[0279] Although the present disclosure has been described with reference to the embodiments, it is understood that the present disclosure is not limited to the embodiments or structures. The present disclosure also encompasses various modifications and equivalent modifications. In addition, various combinations and forms, including only one element, more than one element, or less than one element, are also within the scope and spirit of the present disclosure.

Claims

1. A power conversion device applied to a system including a first power storage unit (31, 131, 231) and a second power storage unit (32, 132, 232), comprising: a power transmission circuit (10, 20, 22H, 22L, 50, 60, 61, 73, 120A, 120B, 340, 350) whose switching is controlled to transmit power between the first power storage unit and the second power storage unit; and a control device (100) that controls the switching of the power transmission circuit, wherein the control device executes a first mode on the condition that an electrical parameter that is the magnitude of current or power transmitted through the power transmission circuit is greater than a switching threshold (Ith, IthH), and executes a second mode on the condition that the electrical parameter is equal to or less than the switching threshold, and the first mode is a mode in which switching control of the power transmission circuit is continuously performed, The power conversion device, wherein the second mode is a mode in which switching control of the power transmission circuit is switched between stopping the switching control and stopping the switching control, or the number of phases of the power transmission circuit that perform switching control is reduced compared to the first mode.

2. The power transmission circuit comprises: an inverter (20) having upper and lower arm switches (SWH, SWL) of a plurality of phases; a motor (10) having an armature winding (11) electrically connected to a low potential side terminal of the upper arm switch of each phase and a high potential side terminal of the lower arm switch of each phase; a high potential side path (22H) electrically connecting a positive terminal of a first power storage unit (31) to a high potential side terminal of the upper arm switch; a low potential side path (22L) electrically connecting a negative terminal of a second power storage unit (32) to a low potential side terminal of the lower arm switch; and an inter-power storage unit switch (50) which, when turned on, electrically connects the negative terminal of the first power storage unit to the positive terminal of the second power storage unit and, when turned off, electrically disconnects the negative terminal of the first power storage unit from the positive terminal of the second power storage unit.

2. The power conversion device according to claim 1, further comprising: a bypass switch (60, 61) that electrically connects negative terminals of the first power storage unit and the second power storage unit to each other or electrically connects positive terminals of the first power storage unit and the second power storage unit to each other; and a connection path (73) that electrically connects the negative terminal of the first power storage unit or the positive terminal of the second power storage unit to the armature winding, wherein the control device: performs switching control of a target switch that is at least one of the upper and lower arm switches to flow a current to the connection path; executes the first mode on condition that a magnitude of the current flowing in the connection path, which is the electrical parameter, is greater than the switching threshold; and executes the second mode on condition that a magnitude of the current flowing in the connection path is equal to or less than the switching threshold, the first mode being a mode in which the switching control of the target switch is continued, and the second mode being a mode in which switching control of the target switch is switched between and stopping the switching control, or a mode in which a number of phases of the target switch to be subjected to switching control is reduced compared to the first mode.

3. The power conversion device according to claim 2, wherein the bypass switch (60) electrically connects the negative terminal of the first power storage unit and the negative terminal of the second power storage unit when turned on and electrically disconnects the negative terminal of the first power storage unit and the negative terminal of the second power storage unit when turned off, the connection path electrically connects the armature winding and the positive terminal of the second power storage unit, and the control device, when an external charger (210) is electrically connected to the high potential side path and the low potential side path, turns off the inter-power storage unit switch and turns on the bypass switch, thereby performing switching control of the upper arm switch, which is the target switch, to pass a current through a closed circuit including the external charger, the inverter, the armature winding, the connection path, and the second power storage unit, thereby charging the second power storage unit.

4. The power conversion device according to claim 3, wherein the second mode is a mode for switching between switching control of the target switch and stopping the switching control, and wherein the control device, in the second mode, performs switching control of the target switch so that the input power of the first storage unit does not exceed an upper limit input power (Win1) of the first storage unit when the switching control is stopped, and performs switching control of the target switch so that the input power of the second storage unit does not exceed an upper limit input power (Win2) of the second storage unit when the switching control is started.

5. The power conversion device according to claim 2, wherein the bypass switch (60) electrically connects the negative terminal of the first power storage unit and the negative terminal of the second power storage unit when turned on and electrically disconnects the negative terminal of the first power storage unit and the negative terminal of the second power storage unit when turned off, the connection path electrically connects the armature winding and the positive terminal of the second power storage unit, and the control device, when an external power supply target unit (230) is electrically connected to the high potential side path and the low potential side path, turns off the inter-power storage unit switch and turns on the bypass switch, thereby performing external power supply control to supply current from the second power storage unit to the external power supply target unit via the connection path, the armature winding and the inverter.

6. The power conversion device according to claim 5, wherein the second mode is a mode for switching between switching control of the target switch and stopping the switching control, and wherein the control device, in the second mode, performs switching control of the target switch so that the output power of the first storage unit does not exceed an upper limit output power (Wout1) of the first storage unit when the switching control is stopped, and performs switching control of the target switch so that the output power of the second storage unit does not exceed an upper limit output power (Wout2) of the second storage unit when the switching control is started.

7. A power conversion device as described in claim 3 or 5, wherein the second mode is a mode for switching between switching control of the target switch and stopping the switching control, and the control device switches between the first mode and the second mode so that the voltage of the second storage unit does not exceed the voltage of the first storage unit.

8. The power conversion device according to claim 2, wherein the bypass switch (61) electrically connects the positive terminal of the first power storage unit and the positive terminal of the second power storage unit when turned on and electrically disconnects the positive terminal of the first power storage unit and the positive terminal of the second power storage unit when turned off, the connection path electrically connects the armature winding and the negative terminal of the first power storage unit, and the control device, when an external charger (210) is electrically connected to the high potential side path and the low potential side path, turns off the inter-power storage unit switch and turns on the bypass switch, thereby performing switching control of the lower arm switch, which is the target switch, to pass a current through a closed circuit including the external charger, the first power storage unit, the connection path, the armature winding, and the inverter, thereby charging the first power storage unit.

9. The power conversion device according to claim 8, wherein the second mode is a mode for switching between switching control of the target switch and stopping of the switching control, and wherein the control device, in the second mode, performs switching control of the target switch so that the input power of the second storage unit does not exceed an upper limit input power (Win2) of the second storage unit when the switching control is stopped, and performs switching control of the target switch so that the input power of the first storage unit does not exceed an upper limit input power (Win1) of the first storage unit when the switching control is started.

10. A power conversion device as described in claim 3 or 8, wherein the second mode is a mode for switching between switching control of the target switch and stopping the switching control, and the control device switches between the first mode and the second mode so that the difference between the voltage of the first storage unit and the voltage of the second storage unit is equal to or less than a threshold value (Sth).

11. The power conversion device according to claim 10, wherein the control device sets the threshold value to be smaller as time passes since the external charging control is started.

12. The power conversion device according to claim 2, wherein the bypass switch (61) electrically connects the positive terminal of the first power storage unit and the positive terminal of the second power storage unit when turned on and electrically disconnects the positive terminal of the first power storage unit and the positive terminal of the second power storage unit when turned off, the connection path electrically connects the armature winding and the negative terminal of the first power storage unit, and the control device, when an external power supply target unit (230) is electrically connected to the high potential side path and the low potential side path, turns off the inter-power storage unit switch and turns on the bypass switch, thereby performing switching control of the upper arm switch which is the target switch, and supplies current to the external power supply target unit via a closed circuit including the external power supply target unit, the first power storage unit, the connection path, the armature winding, and the inverter.

13. The power conversion device according to claim 12, wherein the second mode is a mode for switching between switching control of the target switch and stopping the switching control, and wherein the control device, in the second mode, performs switching control of the target switch so that the output power of the second storage unit does not exceed an upper limit output power (Wout2) of the second storage unit when the switching control is stopped, and performs switching control of the target switch so that the output power of the first storage unit does not exceed an upper limit output power (Wout1) of the first storage unit when the switching control is started.

14. A power conversion device as described in claim 5 or 12, wherein the second mode is a mode for switching between switching control of the target switch and stopping the switching control, and the control device switches between the first mode and the second mode so that the difference between the voltage of the first storage unit and the voltage of the second storage unit is equal to or less than a threshold value (Sth).

15. The power conversion device according to claim 14, wherein the control device sets the threshold value to be smaller as time passes since the external power supply control is started.

16. A power conversion device as described in claim 8 or 12, wherein the second mode is a mode for switching between switching control of the target switch and stopping the switching control, and the control device switches between the first mode and the second mode so that the voltage of the first storage unit does not exceed the voltage of the second storage unit.

17. A power conversion device according to any one of claims 1 to 6, 8, 9, 12, and 13, wherein the control device gradually changes the current flowing through the power transmission circuit when switching from one of the switching control and the stop of the switching control to the other in the second mode.

18. The power conversion device according to claim 1, wherein the second mode is a mode in which the number of phases is reduced compared to the first mode, and the control device performs interleaved control in the second mode.

19. The power conversion device according to claim 18, wherein the system includes a temperature sensor (88B) for detecting the switch temperature of the upper and lower arm switches of each phase, and the control device selects the phase to be switched based on the detected value of the temperature sensor.

20. A program applied to a system including a first power storage unit (31, 131, 231) and a second power storage unit (32, 132, 232), wherein the system includes a power transmission circuit (10, 20, 22H, 22L, 50, 60, 61, 73, 120A, 120B, 340, 350) whose switching is controlled to transmit power between the first power storage unit and the second power storage unit, and causes a computer (101) that controls the switching of the power transmission circuit to execute a process of executing a first mode on condition that an electrical parameter that is the magnitude of current or power transmitted through the power transmission circuit is greater than a switching threshold (Ith, IthH), and a process of executing a second mode on condition that the electrical parameter is equal to or less than the switching threshold, wherein the first mode is a mode in which switching control of the power transmission circuit is continuously performed, The second mode is a mode in which switching control of the power transmission circuit is switched between stopping the switching control and stopping the switching control, or the number of phases of the power transmission circuit that are subjected to switching control is reduced compared to the first mode.

21. A control method for a power conversion device applied to a system including a first power storage unit (31, 131, 231) and a second power storage unit (32, 132, 232), wherein the system includes a power transmission circuit (10, 20, 22H, 22L, 50, 60, 61, 73, 120A, 120B, 340, 350) whose switching is controlled to transmit power between the first power storage unit and the second power storage unit, and the method includes the steps of: executing a first mode on condition that an electrical parameter that is the magnitude of current or power transmitted through the power transmission circuit is greater than a switching threshold (Ith, IthH); and executing a second mode on condition that the electrical parameter is equal to or less than the switching threshold, wherein the first mode is a mode in which switching control of the power transmission circuit is continuously performed, A control method for a power conversion device, wherein the second mode is a mode in which switching control of the power transmission circuit is switched between stopping the switching control, or the number of phases of the power transmission circuit that perform switching control is reduced compared to the first mode.

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