Battery switching device

Abstract

To prevent a backflow of current from a battery to be used to a used battery in processing for switching a connection state between an exchange type battery and a drive system of an electric vehicle while supplying power to the drive system.SOLUTION: A battery switching device 10 switches connection states, to a drive system 3 of an electric vehicle C, of a first bank B1 and a second bank B2 including exchange type batteries 1H, 1L, 2H and 2L and connected in parallel with the drive system 3. The battery switching device comprises a first switch 11 which controls an electrification direction of the first bank B1, a second switch 12 which controls an electrification direction of the second bank B2, and an ECU 13. When switching from one of the used first bank B1 and second bank B2 to the second bank B2 to be used, the ECU 13 controls the first switch 11 or the second switch 12 corresponding to one of the first bank B1 and the second bank B2 in such a manner that the electrification direction of one of the first bank B1 and the second bank B2 becomes a discharge direction.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a battery switching device.

Background Art

[0002] As an electric vehicle that drives a running electric drive device with power from a replaceable battery pack, when the remaining battery level of the battery pack in use falls below a threshold value, a battery pack with a remaining battery level exceeding the threshold value is connected to the running electric drive device. There is known a device that switches as described above (see, for example, Patent Document 1). Further, as a power supply switching device that switches a replaceable battery connected to a first power supply port and a second power supply port, for a switch circuit, a conduction state, a cutoff state, and a diode operation state that allows only one-way power supply from the power supply port side to the load side when the voltage on the power supply port side is higher than the voltage on the load side. There is known a device that executes a switching process in three states (see, for example, Patent Document 2).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] Consider a case where a process of switching a battery pack or battery whose remaining battery level has fallen below a threshold value (hereinafter, a used battery pack, etc.) to a battery pack, etc. whose remaining battery level exceeds the threshold value (hereinafter, a battery pack, etc. to be used hereinafter) is performed while supplying power to a running electric drive device. In this case, during the switching process, a relatively high-voltage battery pack, etc. to be used hereinafter and a relatively low-voltage battery pack, etc. after use are connected. Therefore, a reverse current flows from the battery pack to be used hereinafter to the used battery pack.

[0005] In view of the above circumstances, an object of the present invention is to provide a battery switching device that can prevent a reverse flow of current from a battery to be used to a used battery in a process of switching the connection state between a replaceable battery and a drive system of an electric vehicle while supplying power to the drive system.

Means for Solving the Problems

[0006] The battery switching device of the present invention is a battery switching device that switches the connection state of a first battery unit and a second battery unit, which are provided with replaceable batteries and connected in parallel to the drive system of an electric vehicle, to the drive system, and includes a first energization control unit that controls the energization direction of the first battery unit, a second energization control unit that controls the energization direction of the second battery unit, and a control unit that switches from a first state in which one of the first battery unit and the second battery unit is connected to the drive system, the other of the first battery unit and the second battery unit is disconnected from the drive system, and the remaining amount of the one of the first battery unit and the second battery unit is less than the remaining amount of the other of the first battery unit and the second battery unit, to a second state in which one of the first battery unit and the second battery unit is disconnected from the drive system and the other of the first battery unit and the second battery unit is connected to the drive system. When switching from the first state to the second state, the control unit controls the first energization control unit or the second energization control unit corresponding to the one of the first battery unit and the second battery unit so that the energization direction of the one of the first battery unit and the second battery unit becomes the discharge direction.

Effects of the Invention

[0007] According to the present invention, in a process of switching the connection state between a replaceable battery and a drive system of an electric vehicle while supplying power to the drive system, a reverse flow of current from a battery to be used to a used battery can be prevented.

Brief Description of the Drawings

[0008]

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Embodiments for Carrying Out the Invention

[0009] Hereinafter, the present invention will be described along with preferred embodiments. Note that the present invention is not limited to the embodiments shown below, and the embodiments shown below can be appropriately changed without departing from the gist of the present invention. Further, in the embodiments shown below, there are some places where the illustration and description of some configurations are omitted. Regarding the details of the omitted technology, well-known or well-understood technologies are appropriately applied within the range where there is no contradiction with the content described below.

[0010] FIG. 1 is a circuit diagram showing a battery switching device 10 according to an embodiment of the present invention. The battery switching device 10 shown in this figure switches the connection state between the replaceable batteries 1H, 1L, 2H, 2L and the drive system 3 of the electric vehicle C. In particular, while supplying power to the drive system 3, the battery switching device 10 switches from a state (first state) in which a used battery (one of 1H, 1L, and 2H, 2L) is connected to the drive system 3 to a state (second state) in which a battery to be used next (the other of 1H, 1L, and 2H, 2L) is connected to the drive system 3.

[0011] The electric vehicle C equipped with the battery switching device 10 includes a drive system 3 such as an inverter motor, and a first bank B1 and a second bank B2 connected in parallel to the drive system 3. The first bank B1 includes batteries 1H and 1L connected in series, and the second bank B2 includes batteries 2H and 2L connected in series.

[0012] The batteries 1H, 1L, 2H, and 2L are secondary batteries such as lithium-ion storage batteries. Before being mounted on the first bank B1 and the second bank B2, they are charged by an external charging device (not shown). After being mounted on the first bank B1 and the second bank B2, they are charged by the regenerative power of the drive system 3. The battery 1H is connected to the high-potential side of the first bank B1, and the battery 1L is connected to the low-potential side of the first bank B1. Also, the battery 2H is connected to the high-potential side of the second bank B2, and the battery 2L is connected to the low-potential side of the second bank B2. Switches S1, S2, S3, and S4 are provided for the batteries 1H, 1L, 2H, and 2L respectively. The switches S1, S2, S3, and S4 are controlled to be ON / OFF by a control device (not shown) provided for the batteries 1H, 1L, 2H, and 2L respectively.

[0013] The battery switching device 10 includes a first switch 11, a second switch 12, voltage sensors VS1, VS2, VS3, and VS4, a current sensor AS, and an ECU (Electronic Control Unit) 13. The first switch 11 is provided on the power line PL1 connected to the negative electrode side of the first bank B1. Also, the second switch 12 is provided on the power line PL2 connected to the negative electrode side of the second bank B2. The power line PL1 and the power line PL2 branch from the power line PL4 connected to the drive system 3.

[0014] The first switch 11 and the second switch 12 are N-channel MOSFETs (Metal-Oxide-Semiconductor Field Effect Transistors). The drain of the first switch 11 is connected to the negative electrode side of the first bank B1 via the power line PL1, and the source of the first switch 11 is connected to the drive system 3 via the power lines PL1 and PL4. Also, the drain of the second switch 12 is connected to the negative electrode side of the second bank B2 via the power line PL2, and the source of the second switch 12 is connected to the drive system 3 via the power lines PL2 and PL4.

[0015] When the applied voltage between the gate and the source of the first switch 11 is at the L level, the first switch 11 turns OFF, and current flows from the source to the drain, and no current flows from the drain to the source. In this case, energization in the discharging direction of the batteries 1H and 1L is possible, while energization in the charging direction of the batteries 1H and 1L is impossible.

[0016] When the applied voltage between the gate and the source of the first switch 11 is at the H level, the first switch 11 turns ON, and current flows bidirectionally between the source and the drain. In this case, bidirectional energization in both the discharging and charging directions of the batteries 1H and 1L is possible.

[0017] When the applied voltage between the gate and the source of the second switch 12 is at the L level, the second switch 12 turns OFF, and current flows from the source to the drain, and no current flows from the drain to the source. In this case, energization in the discharging direction of the batteries 2H and 2L is possible, while energization in the charging direction of the batteries 2H and 2L is impossible.

[0018] When the applied voltage between the gate and the source of the second switch 12 is at the H level, the second switch 12 turns ON, and current flows bidirectionally between the source and the drain. In this case, bidirectional energization in both the discharging and charging directions of the batteries 2H and 2L is possible.

[0019] The voltage sensor VS1 detects the voltage across the terminals of battery 1H and outputs a detection signal to the ECU13. Also, the voltage sensor VS2 detects the voltage across the terminals of battery 1L and outputs a detection signal to the ECU13. Further, the voltage sensor VS3 detects the voltage across the terminals of battery 2H and outputs a detection signal to the ECU13. Additionally, the voltage sensor VS4 detects the voltage across the terminals of battery 2L and outputs a detection signal to the ECU13. Also, the current sensor AS detects the current input to and output from the drive system 3 and outputs a detection signal to the ECU13.

[0020] Based on the detection signals of the voltage sensors VS1, VS2, VS3, and VS4, the ECU13 controls the first switch 11 and the second switch 12 to switch the connection state between the batteries 1H, 1L, 2H, 2L and the drive system 3. Specifically, when the batteries 1H, 1L are connected to the drive system 3 and are in a state of charge and discharge, the ECU13 compares the voltages across the terminals of the batteries 1H, 1L detected by the voltage sensors VS1, VS2 with a predetermined threshold value. When the voltages across the terminals of the batteries 1H, 1L exceed the predetermined threshold value, the ECU13 maintains the first switch 11 in the ON state and the second switch 12 in the OFF state. In contrast, when the voltages across the terminals of the batteries 1H, 1L drop below the predetermined threshold value, the ECU13 switches the first switch 11 to OFF, making it possible to conduct electricity in the discharging direction but not in the charging direction between the batteries 1H, 1L and the batteries 2H, 2L. Thereafter, the ECU13 maintains the first switch 11 in the OFF state, switches the second switch 12 to ON, maintains the batteries 1H, 1L in a state where electricity can be conducted in the discharging direction but not in the charging direction, and switches the batteries 2H, 2L to a state where bidirectional electricity conduction in both the discharging and charging directions is possible. The "predetermined threshold value" is a voltage value set to determine whether the batteries 1H, 1L, 2H, 2L are in a power shortage state. Note that it is not essential to determine whether the batteries 1H, 1L, 2H, 2L are in a power shortage state based on the voltages across the terminals of the batteries 1H, 1L, 2H, 2L, and this determination may also be made based on the SOC (State of Charge) estimated from current values, terminal voltages, etc.

[0021] On the other hand, when the batteries 2H and 2L are connected to the drive system 3 and are in a state of charging and discharging, the ECU 13 compares the inter-terminal voltage of the batteries 2H and 2L detected by the voltage sensors VS3 and VS4 with a predetermined threshold value. When the inter-terminal voltage of the batteries 2H and 2L exceeds the predetermined threshold value, the ECU 13 maintains the second switch 12 in the ON state and the first switch 11 in the OFF state. On the contrary, when the inter-terminal voltage of the batteries 2H and 2L drops below the predetermined threshold value, the ECU 13 switches the second switch 12 to OFF, making the batteries 2H and 2L in a state where conduction in the discharging direction is possible and conduction in the charging direction is impossible. Thereafter, the ECU 13 maintains the second switch 12 in the OFF state, switches the first switch 11 to ON, maintains the batteries 2H and 2L in a state where conduction in the discharging direction is possible and conduction in the charging direction is impossible, and switches the batteries 1H and 1L to a state where bidirectional conduction in both the discharging and charging directions is possible.

[0022] Figure 2 is a circuit diagram showing the operation of the battery switching device 10 shown in Figure 1. This figure shows a state where the inter-terminal voltage of the batteries 1H and 1L in the first bank B1 has dropped below a predetermined threshold value, and the inter-terminal voltage of the batteries 2H and 2L in the second bank B2 has exceeded the predetermined threshold value. That is, this figure shows a case where the batteries 1H and 1L are the batteries after use, and the batteries 2H and 2L are the batteries to be used hereafter.

[0023] As shown in Figure 2, when the inter-terminal voltage of the batteries 1H and 1L in the first bank B1 drops below a predetermined threshold value, the ECU 13 switches the first switch 11 from ON to OFF. Before and after the timing when the first switch 11 switches from ON to OFF, the ECU 13 maintains the second switch 12 in the OFF state.

[0024] Here, the batteries 1H and 1L of the first bank B1 and the batteries 2H and 2L of the second bank B2 are connected so as to be energizable through the diodes of the first switch 11 and the second switch 12. Also, the voltage between the terminals of the batteries 1H and 1L of the first bank B1 is lower than the voltage between the terminals of the batteries 2H and 2L of the second bank B2. On the other hand, the batteries 1H and 1L of the first bank B1 can be energized in the discharging direction through the diode of the first switch 11, but are in a state where energization in the charging direction is impossible due to the diode of the first switch 11. Thereby, when switching from the first bank B1 to the second bank B2 while continuing the power supply to the drive system 3, a reverse flow of current from the relatively high-voltage batteries 2H and 2L to the relatively low-voltage batteries 1H and 1L is prevented.

[0025] Although illustration is omitted, when the voltage between the terminals of the batteries 2H and 2L of the second bank B2 drops below a predetermined threshold value, the ECU 13 switches the second switch 12 from ON to OFF. Before and after the timing when the second switch 12 switches from ON to OFF, the ECU 13 maintains the first switch 11 in the OFF state.

[0026] Here, the batteries 1H and 1L of the first bank B1 and the batteries 2H and 2L of the second bank B2 are connected so as to be energizable through the diodes of the first switch 11 and the second switch 12. Also, the voltage between the terminals of the batteries 2H and 2L of the second bank B2 is lower than the voltage between the terminals of the batteries 1H and 1L of the first bank B1. On the other hand, the batteries 2H and 2L of the second bank B2 can be energized in the discharging direction through the diode of the second switch 12, but are in a state where energization in the charging direction is impossible due to the diode of the second switch 12. Thereby, when switching from the second bank B2 to the first bank B1 while continuing the power supply to the drive system 3, a reverse flow of current from the relatively high-voltage batteries 1H and 1L to the relatively low-voltage batteries 2H and 2L is prevented.

[0027] FIG. 3 is a graph showing changes in the load voltage of the drive system 3 when manually switching the connection state between the first bank B1 and the second bank B2 and the drive system 3. Here, when the energization directions of the first bank B1 and the second bank B2 cannot be controlled, when switching the connection state between the first bank B1 and the second bank B2 and the drive system 3, current flows backward from the relatively high-voltage bank to the relatively low-voltage bank. As a result, the load voltage of the drive system 3 is interrupted. Therefore, it is necessary to turn off the power supply of the electric vehicle C before switching the connection state between the first and second banks B2 and the drive system 3, and then turn on the power supply of the electric vehicle C again after switching the connection state between the first and second banks B2 and the drive system 3, and parking of the electric vehicle C is required.

[0028] FIG. 4 is a graph showing changes in the load voltage of the drive system 3 when automatically switching the connection state between the first bank B1 and the second bank B2 and the drive system 3 by the battery switching device 10 shown in FIGS. 1 and 2. Here, according to the battery switching device 10 of the present embodiment, when switching the connection state between the first bank B1 and the second bank B2 and the drive system 3, it is possible to prevent the backward flow of current from the relatively high-voltage bank to the relatively low-voltage bank. As a result, as shown in the graph of FIG. 4, when switching the connection state between the first bank B1 and the second bank B2 and the drive system 3, it is possible to prevent the interruption of the load voltage of the drive system 3. Therefore, it is possible to switch the connection state between the first bank B1 and the second bank B2 and the drive system 3 while the power supply of the electric vehicle C is turned on and the running of the electric vehicle C is continued.

[0029] FIG. 5 is a circuit diagram showing a battery switching device 20 according to another embodiment of the present invention. Note that the same reference numerals are given to the same configurations as those in the above-described embodiment, and the description of the above-described embodiment is incorporated herein.

[0030] As shown in FIG. 5, the battery switching device 20 includes a first switch 21, a second switch 22, voltage sensors VS1, VS2, VS3, VS4, a current sensor AS, and an ECU 23. The first switch 21 is provided on the power line PL1. The second switch 22 is provided on the power line PL2.

[0031] The first switch 21 includes FET21A and FET21B. FET21A and 21B are N-channel MOSFETs. The drains of FET21A and FET21B are connected, the source of FET21A is connected to the drive system 3 via power lines PL1 and PL4, and the source of FET21B is connected to the negative side of the first bank B1 via power line PL1.

[0032] When the voltage applied between the gates and sources of FET21A and 21B is at the L level, FET21A and 21B turn OFF, and current flows from the source to the drain and no current flows from the drain to the source. When both FET21A and FET21B are OFF, since the directions of the diodes of FET21A and FET21B are opposite, bidirectional energization in both the discharge direction and the charge direction of the batteries 1H and 1L of the first bank B1 becomes impossible.

[0033] When the voltage applied between the gates and sources of FET21A and 21B is at the H level, FET21A and 21B turn ON, and current flows bidirectionally between the source and the drain. When both FET21A and FET21B are ON, bidirectional energization in both the discharge direction and the charge direction of the batteries 1H and 1L of the first bank B1 becomes possible. On the other hand, when FET21A is OFF and FET21B is ON, energization in the discharge direction of the batteries 1H and 1L is possible, but energization in the charge direction of the batteries 1H and 1L becomes impossible. Also, when FET21A is ON and FET21B is OFF, energization in the charge direction of the batteries 1H and 1L is possible, but energization in the discharge direction of the batteries 1H and 1L becomes impossible.

[0034] The second switch 22 includes FET22A and FET22B. FET22A and 22B are N-channel MOSFETs. The drains of FET22A and FET22B are connected, the source of FET22A is connected to the drive system 3 via power lines PL2 and PL4, and the source of FET22B is connected to the negative side of the second bank B2 via power line PL2.

[0035] When the applied voltage between the gates and sources of FET22A and 22B is at the L level, FET22A and 22B turn OFF, current flows from the source to the drain, and no current flows from the drain to the source. When both FET22A and FET22B are OFF, since the directions of the diodes of FET22A and FET22B are opposite, it becomes impossible to conduct current in both the discharge direction and the charge direction of the batteries 2H and 2L in the second bank B2.

[0036] When the applied voltage between the gates and sources of FET22A and 22B is at the H level, FET22A and 22B turn ON, and current flows bidirectionally between the source and the drain. When both FET22A and FET22B are ON, it becomes possible to conduct current in both the discharge direction and the charge direction of the batteries 2H and 2L. On the other hand, when FET22A is OFF and FET22B is ON, it is possible to conduct current in the discharge direction of the batteries 2H and 2L, but it becomes impossible to conduct current in the charge direction of the batteries 2H and 2L. Also, when FET22A is ON and FET22B is OFF, it is possible to conduct current in the charge direction of the batteries 2H and 2L, but it becomes impossible to conduct current in the discharge direction of the batteries 2H and 2L.

[0037] Based on the detection signals of voltage sensors VS1, VS2, VS3, and VS4, ECU23 controls FET21A, 21B of the first switch 21 and FET22A, 22B of the second switch 22 to switch the connection state between batteries 1H, 1L, 2H, 2L and the drive system 3. When the batteries 1H, 1L of the first bank B1 are connected to the drive system 3 and are in a charge / discharge state, ECU23 compares the inter-terminal voltage of batteries 1H, 1L detected by voltage sensors VS1, VS2 with a predetermined threshold value. When the inter-terminal voltage of batteries 1H, 1L exceeds the predetermined threshold value, ECU23 keeps FET21A, 21B of the first switch 21 ON and FET22A, 22B of the second switch 22 OFF. In contrast, when the inter-terminal voltage of batteries 1H, 1L drops below the predetermined threshold value, ECU23 switches FET21A of the first switch 21 to OFF, keeps FET21B of the first switch 21 ON, keeps FET22A of the second switch 22 OFF, and controls FET22B of the second switch 22 to be ON / OFF by PWM (Pulse Width Modulation). Thereafter, ECU23 keeps FET21A of the first switch 21 OFF, switches FET21B of the first switch 21 to OFF, and switches FET22A, 22B of the second switch 22 to ON.

[0038] On the other hand, when the batteries 2H and 2L of the second bank B2 are connected to the drive system 3 and are being charged and discharged, the ECU 23 compares the inter-terminal voltages of the batteries 2H and 2L detected by the voltage sensors VS3 and VS4 with a predetermined threshold value. When the inter-terminal voltage of the batteries 2H and 2L exceeds the predetermined threshold value, the ECU 23 maintains the FETs 22A and 22B of the second switch 22 in the ON state and the FETs 21A and 21B of the first switch 21 in the OFF state. On the contrary, when the inter-terminal voltage of the batteries 2H and 2L drops below the predetermined threshold value, the ECU 23 switches the FET 22A of the second switch 22 to OFF, maintains the FET 22B of the second switch 22 in the ON state, maintains the FET 21A of the first switch 21 in the OFF state, and turns the FET 21B of the first switch 21 ON / OFF by PWM control. Thereafter, the ECU 23 maintains the FET 22A of the second switch 22 in the OFF state, switches the FET 22B of the second switch 22 to OFF, and switches the FETs 21A and 21B of the first switch 21 to ON.

[0039] FIG. 6 is a timing chart showing the relationship between the ON / OFF of the switches and the change in the load voltage when switching the connection state between the relatively high-voltage bank and the drive system 3 from disconnection to connection by the battery switching device 20 shown in FIG. 5. This timing chart shows the relationship between the ON / OFF of the FETs 22A and 22B of the second switch 22 and the change in the load voltage when switching the connection state between the relatively high-voltage second bank B2 and the drive system 3 from disconnection to connection. Note that the timing of switching the ON / OFF of the FETs 21A and 21B of the first switch 21 when switching the connection state between the relatively high-voltage first bank B1 and the drive system 3 from disconnection to connection is the same.

[0040] As shown in the timing chart of FIG. 6, when switching the connection state between the relatively high-voltage second bank B2 and the drive system 3 from disconnection to connection, the FET22A of the second switch 22 is maintained in the OFF state, while the FET22B of the second switch 22 is turned ON / OFF by PWM control. Specifically, the FET22B of the second switch 22 repeats ON / OFF so that the ON time gradually becomes longer and is finally maintained in the ON state. Thereby, the load voltage of the drive system 3 gradually increases and finally reaches a constant value.

[0041] FIG. 7 is a circuit diagram showing the operation of the battery switching device 20 shown in FIG. 5. This figure shows a state where the voltage between the terminals of the batteries 1H and 1L of the first bank B1 has dropped below a predetermined threshold value, and the voltage between the terminals of the batteries 2H and 2L of the second bank B2 has exceeded the predetermined threshold value. That is, this figure shows a case where the batteries 1H and 1L are the used batteries and the batteries 2H and 2L are the batteries to be used next.

[0042] As shown in FIG. 7, when the voltage between the terminals of the batteries 1H and 1L of the first bank B1 drops below a predetermined threshold value, the ECU 23 switches the FET21A of the first switch 21 from ON to OFF, maintains the FET21B of the first switch 21 in the ON state, maintains the FET22A of the second switch 22 in the OFF state, and turns the FET22B of the second switch 22 ON / OFF by PWM control.

[0043] Here, with the FET21A of the first switch 21 and the FET22A of the second switch 22 being OFF, and the FET21B of the first switch 21 and the FET22B of the second switch 22 being ON, the batteries 1H and 1L of the first bank B1 and the batteries 2H and 2L of the second bank B2 are connected so as to be energizable through the diodes of the FETs 21A and 22A. Also, the voltage between the terminals of the batteries 1H and 1L of the first bank B1 is lower than the voltage between the terminals of the batteries 2H and 2L of the second bank B2. In contrast, the batteries 1H and 1L of the first bank B1 can be energized in the discharging direction through the diode of the FET21A of the first switch 21, but are in a state where energization in the charging direction is impossible due to the diode of the FET21A of the first switch 21. Thereby, the reverse flow of current from the relatively high-voltage batteries 2H and 2L to the relatively low-voltage batteries 1H and 1L is prevented.

[0044] Although illustration is omitted, when the voltage between the terminals of the batteries 2H and 2L of the second bank B2 drops below a predetermined threshold value, the ECU 23 switches the FET22A of the second switch 22 to OFF, maintains the FET22B of the second switch 22 in the ON state, maintains the FET21A of the first switch 21 in the OFF state, and turns the FET21B of the first switch 21 ON / OFF by PWM control.

[0045] Here, with the FET21A of the first switch 21 and the FET22A of the second switch 22 being OFF, and the FET21B of the first switch 21 and the FET22B of the second switch 22 being ON, the batteries 1H and 1L of the first bank B1 and the batteries 2H and 2L of the second bank B2 are connected so as to be energizable through the diodes of the FETs 21A and 22A. Also, the voltage between the terminals of the batteries 2H and 2L of the second bank B2 is lower than the voltage between the terminals of the batteries 1H and 1L of the first bank B1. In contrast, the batteries 2H and 2L of the second bank B2 can be energized in the discharging direction through the diode of the FET22A of the second switch 22, but are in a state where energization in the charging direction is impossible due to the diode of the FET22A of the second switch 22. Thereby, the reverse flow of current from the relatively high-voltage batteries 1H and 1L to the relatively low-voltage batteries 2H and 2L is prevented.

[0046] FIG. 8 is a graph showing changes in the load voltage of the drive system 3 when the connection state between the first bank B1 and the second bank B2 and the drive system 3 is automatically switched by the battery switching device 20 shown in FIGS. 5 and 7. Here, according to the battery switching device 20 of the present embodiment, when switching the connection state between the first bank B1 and the second bank B2 and the drive system 3, it is possible to prevent the reverse flow of current from the relatively high-voltage bank to the relatively low-voltage bank. Thereby, as shown in the graph of FIG. 8, when switching the connection state between the first bank B1 and the second bank B2 and the drive system 3, momentary interruption of the load voltage of the drive system 3 can be prevented. Therefore, it is possible to switch the connection state between the first bank B1 and the second bank B2 and the drive system 3 while the power supply of the electric vehicle C is turned on and the running of the electric vehicle C is continued.

[0047] Furthermore, in the battery switching device 20 of the present embodiment, when switching the connection state between the first bank B1 and the second bank B2 and the drive system 3, the FET21B or FET22B connecting the relatively high-voltage bank to the drive system 3 is turned on / off by PWM control. Thereby, as shown in the graph of FIG. 8, the load voltage of the drive system 3 can be gradually increased, sudden fluctuations in the load voltage of the drive system 3 can be prevented, and the running state of the electric vehicle C can be stabilized.

[0048] FIGS. 9 to 12 are circuit diagrams showing the operation of the battery switching device 30 according to another embodiment of the present invention. As shown in this figure, the configuration of the battery switching device 30 according to the present embodiment is the same as that of the battery switching device 20 according to the above-described embodiment. The battery switching device 30 according to the present embodiment is obtained by adding a function of charging the batteries 1H, 1L, 2H, and 2L with regenerative power immediately after switching the banks to the battery switching device 20 according to the above-described embodiment.

[0049] Fig. 9 shows the state after switching from the first bank B1 to the second bank B2. In this state, the batteries 2H and 2L of the second bank B2 connected to the drive system 3 are in a fully charged state, and the connection between the power-deficient batteries 1H and 1L of the first bank B1 and the drive system 3 is interrupted. Note that both FETs 21A and 21B of the first switch 21 are OFF, and both FETs 22A and 22B of the second switch 22 are ON.

[0050] Here, in the electric vehicle C, when the battery connected to the drive system 3 is in a fully charged state, charging of the battery by regenerative power is not performed, and braking is performed only by the mechanical brake, so losses due to regenerative failure occur. Therefore, in the battery switching device 30 according to the present embodiment, immediately after switching the bank, the power-deficient battery is temporarily connected to the drive system 3 to enable charging of the battery by regenerative power.

[0051] Fig. 10 shows the state in which the first process for enabling charging by regenerative power is executed after switching from the first bank B1 to the second bank B2. In this state, the FETs 21A and 21B of the first switch 21 corresponding to the power-deficient batteries 1H and 1L are maintained OFF. On the other hand, the FET 22B of the second switch 22 corresponding to the fully charged batteries 2H and 2L is switched from ON to OFF, and the FET 22A is maintained ON. As a result, the fully charged batteries 2H and 2L are switched from a state where bidirectional energization in both the discharge direction and the charging direction is possible to a state where energization in the charging direction is possible through the diode of the FET 22B of the second switch 22 and energization in the discharge direction is not possible due to the diode.

[0052] FIG. 11 shows a state in which a second process for enabling charging by regenerative power is executed after switching from the first bank B1 to the second bank B2. Shifting from the first process to the second process, the FET21A of the first switch 21 corresponding to the power-deficient batteries 1H and 1L is switched from OFF to ON. The FET21B of the first switch 21 is maintained in the OFF state, the FET22A of the second switch 22 corresponding to the fully charged batteries 2H and 2L is maintained in the ON state, and the FET22B is maintained in the OFF state. As a result, the power-deficient batteries 1H and 1L are in a state where energization in the charging direction is possible through the diode of the FET21B of the first switch 21, and energization in the discharging direction is impossible due to the diode. Also, the fully charged batteries 2H and 2L are maintained in a state where energization in the charging direction is possible through the diode of the FET22B of the second switch 22, and energization in the discharging direction is impossible due to the diode. Thereby, charging of the power-deficient batteries 1H and 1L by regenerative power is performed, and losses due to regeneration invalidation are suppressed.

[0053] FIG. 12 shows a state in which a third process for enabling charging by regenerative power is executed after switching from the first bank B1 to the second bank B2. Shifting from the second process to the third process, the FET22A of the second switch 22 corresponding to the fully charged batteries 2H and 2L is switched from ON to OFF. The FET22B of the second switch 22 is maintained in the OFF state, the FET21A of the first switch 21 corresponding to the power-deficient batteries 1H and 1L is maintained in the ON state, and the FET21B is maintained in the OFF state. As a result, the connection between the fully charged batteries 2H and 2L and the drive system 3 is cut off, and charging of the power-deficient batteries 1H and 1L by regenerative power is continued.

[0054] FIGS. 13 to 15 are circuit diagrams showing the operation of the battery switching device 40 according to another embodiment of the present invention. As shown in this figure, the configuration of the battery switching device 40 according to the present embodiment is the same as that of the battery switching devices 20 and 30 according to the above-described embodiment. The battery switching device 40 according to the present embodiment is obtained by adding an assist mode function during power running and regeneration to the battery switching devices 20 and 30 according to the above-described embodiment.

[0055] Figure 13 shows a state in which there is a shortage of discharge power from the batteries 1H and 1L of the first bank B1 to the drive system 3 during the power running of the electric vehicle C. In this state, the fully charged batteries 2H and 2L of the second bank B2 are waiting to be used. Here, in the first bank B1, a battery 1H with a relatively fast progress of deterioration and a battery 1L with a relatively slow progress of deterioration are mixed. Therefore, a difference occurs in the SOC of the batteries 1H and 1L, and there is a shortage of discharge power from the batteries 1H and 1L of the first bank B1 to the drive system 3. In this case, there is also a shortage in the charging of the batteries 1H and 1L of the first bank B1 by the regenerative power, and there is a possibility that regenerative failure may occur.

[0056] Therefore, in the battery switching device 40 according to the present embodiment, when there is a shortage of discharge power from the battery in use to the drive system 3 during the power running of the electric vehicle C, if the unused battery is not in a power-off state, a discharge assist mode is executed in which the battery is connected to the drive system 3 and discharged. Further, in the battery switching device 40, when regenerative failure occurs during the regeneration of the electric vehicle C, if there is remaining charge capacity in the unused battery, a charge assist mode is executed in which the battery is connected to the drive system 3 and charged by the regenerative power.

[0057] FIG. 14 shows a state in which a discharge assist mode is executed when there is a shortage in the discharge power from the batteries 1H and 1L of the first bank B1 to the drive system 3. In this state, the FET 21A of the first switch 21 corresponding to the batteries 1H and 1L in use is switched from ON to OFF, and the FET 21B is maintained in the ON state. On the other hand, the FET 22A of the second switch 22 corresponding to the fully charged batteries 2H and 2L is maintained in the OFF state, and the FET 22B is switched from OFF to ON. As a result, the batteries 1H and 1L with insufficient discharge power are switched from a state where bidirectional energization in both the discharge direction and the charge direction is possible to a state where energization in the discharge direction is possible through the diode of the FET 21A of the first switch 21 and energization in the charge direction is impossible due to the diode. Also, the fully charged batteries 2H and 2L are switched from a state where bidirectional energization in both the discharge direction and the charge direction is impossible to a state where energization in the discharge direction is possible through the diode of the FET 22A of the second switch 22 and energization in the charge direction is impossible due to the diode. Thereby, by discharging from the fully charged batteries 2H and 2L to the drive system 3, the shortage of the discharge power of the batteries 1H and 1L is compensated for, and a decrease in the output of the drive system 3 is suppressed.

[0058] FIG. 15 shows a state in which a charge assist mode is executed when a regeneration failure occurs during the use of the batteries 1H and 1L of the first bank B1. In this state, the FET21B of the first switch 21 corresponding to the batteries 1H and 1L in use is switched from ON to OFF, and the FET21A is maintained in the ON state. On the other hand, the FET22B of the second switch 22 corresponding to the batteries 2H and 2L waiting to be used is maintained in the OFF state, and the FET22A is switched from OFF to ON. As a result, the batteries 1H and 1L with insufficient charge capacity are switched from a state where bidirectional energization in both the charging direction and the discharging direction is possible to a state where energization in the charging direction is possible through the diode of the FET21B of the first switch 21 and energization in the discharging direction is impossible due to the diode. Also, the batteries 2H and 2L waiting to be used are switched from a state where energization in both the charging direction and the discharging direction is impossible to a state where energization in the charging direction is possible through the diode of the FET22B of the second switch 22 and energization in the discharging direction is impossible due to the diode. Thereby, when the batteries 2H and 2L waiting to be used are charged by regenerative power, the shortage of the charge capacity of the batteries 1H and 1L is compensated, and the regeneration failure is suppressed.

[0059] FIG. 16 is a circuit diagram showing a battery switching device 50 according to another embodiment of the present invention. In addition, the same components as those in the above-described embodiment are denoted by the same reference numerals, and the description of the above-described embodiment is incorporated herein.

[0060] As shown in FIG. 16, in addition to the configurations of the battery switching devices 20, 30, and 40, the battery switching device 50 includes a switching circuit 51 that switches the connection states of the batteries 1H, 1L, 2H, and 2L to the first to eighth connection states described later. The switching circuit 51 includes a third switch 53, a fourth switch 54, a fifth switch 55, a sixth switch 56, a seventh switch 57, an eighth switch 58, and a ninth switch 59, and power lines PL9, PL10, and PL11. The third switch 53, the fourth switch 54, the fifth switch 55, the sixth switch 56, the seventh switch 57, the eighth switch 58, and the ninth switch 59 enable bidirectional energization in both the discharging direction and the charging direction in the ON state, and disable bidirectional energization in both the discharging direction and the charging direction in the OFF state.

[0061] The electric vehicle C includes power lines PL3, PL4 connected to the drive system 3, power lines PL5, PL6 branched from PL3, power lines PL1, PL2 branched from power line PL4, a power line PL7 connecting the batteries 1H, 1L, and a power line PL8 connecting the batteries 2H, 2L. The power line PL5 is connected to the high potential side of the first bank B1. A third switch 53 is provided on this power line PL5. Also, the power line PL1 is connected to the low potential side of the first bank B1. A first switch 21 is provided on this power line PL1. Further, the power line PL6 is connected to the high potential side of the second bank B2. A fourth switch 54 is provided on this power line PL6. Also, the power line PL2 is connected to the low potential side of the second bank B2. A second switch 22 is provided on this power line PL2. Additionally, a fifth switch 55 is provided on the power line PL7, and a sixth switch 56 is provided on the power line PL8.

[0062] The power line PL9 connects between the fifth switch 55 on the power line PL7 and the battery 1H and between the fourth switch 54 on the power line PL6 and the battery 2H. A seventh switch 57 is provided on this power line PL9. Also, the power line PL10 connects between the fifth switch 55 on the power line PL7 and the battery 1H and between the sixth switch 56 on the power line PL8 and the battery 2L. An eighth switch 58 is provided on this power line PL10. Furthermore, the power line PL11 connects between the first switch 21 on the power line PL1 and the battery 1L and between the sixth switch 56 on the power line PL8 and the battery 2L. A ninth switch 59 is provided on this power line PL11.

[0063] Here, due to the difference in the degree of progress of battery degradation within the bank in use, there may be a difference in the SOC and SOH (State of Health) of the batteries within the bank, and it is conceivable that there may be a mixture of batteries with depleted discharge capacity and batteries with remaining discharge capacity within the bank. In this case, since the discharge capacity of the batteries within the bank cannot be exhausted, it is conceivable to equalize the discharge capacity of the batteries within the bank by the same process as cell balancing. However, in this embodiment, since battery replacement is performed and the difference in charge capacity between the batteries within the bank may increase, the same process as cell balancing is not suitable.

[0064] Therefore, in the battery switching device 50 of the bank switching method, the battery with remaining discharge capacity is connected to the fully charged battery of the other bank waiting for use, and discharge to the drive system 3 is performed to exhaust the remaining discharge capacity.

[0065] Figs. 17 to 20 are circuit diagrams showing the operation of the battery switching device 50 shown in Fig. 16. Fig. 17 shows a state where the discharge capacity of the battery 1L of the first bank B1 remains. When the batteries 1H and 1L of the first bank B1 perform charge and discharge and the batteries 2H and 2L of the second bank B2 are in a waiting state for use, the FETs 21A and 21B of the first switch 21, the third switch 53, the fourth switch 54, the fifth switch 55, and the sixth switch 56 are ON. Also, in this state, the FETs 22A and 22B of the second switch 22, the seventh switch 57, the eighth switch 58, and the ninth switch 59 are OFF.

[0066] Fig. 18 shows a state where, after the discharge capacity of the battery 1L of the first bank B1 remains, the battery 1L and the battery 2H of the second bank B2 are connected and discharge to the drive system 3 is being performed. In this state, the third switch 53 is switched from ON to OFF, and the eighth switch 58 is switched from OFF to ON. As a result, the positive electrode of the battery 1L of the first bank B1 is connected to the negative electrode of the battery 2H of the second bank B2, and the negative electrode of the battery 1L and the positive electrode of the battery 2H are connected to the drive system 3, and discharge is performed by the serially connected battery 1L and battery 2H.

[0067] Figure 19 shows a state in which after the discharge capacities of battery 1L and battery 2H have decreased due to the discharge by the batteries 1L and 2H connected in series, battery 1L and battery 2L of the second bank B2 are connected and discharge to the drive system 3 is being performed. In this state, the FETs 21A and 21B of the first switch 21 are switched from ON to OFF, the FETs 22A and 22B of the second switch 22 are switched from OFF to ON, the sixth switch 56 and the eighth switch 58 are switched from ON to OFF, and the seventh switch 57 and the ninth switch 59 are switched from OFF to ON. As a result, the negative electrode of battery 1L of the first bank B1 is connected to the positive electrode of battery 2L of the second bank B2, and the positive electrode of battery 1L and the negative electrode of battery 2L are connected to the drive system 3, and discharge by the batteries 1L and 2L connected in series is performed.

[0068] Figure 20 shows a state in which after the discharge capacity of battery 1L has been used up due to the discharge by the directly connected batteries 1L and 2L, battery 2H and battery 2L are connected and discharge to the drive system 3 is being performed. In this state, the third switch 53 and the sixth switch 56 are switched from OFF to ON, and the seventh switch 57 and the ninth switch 59 are switched from ON to OFF. As a result, in the second bank B2, the negative electrode of battery 2H is connected to the positive electrode of battery 2L, and the positive electrode of battery 2H and the negative electrode of battery 2L are connected to the drive system 3, and discharge by the batteries 2H and 2L connected in series is performed.

[0069] The ECU 23 estimates the remaining discharge capacities of the batteries 1H, 1L, 2H, and 2L from the inter-terminal voltages of the batteries 1H, 1L, 2H, and 2L and the charge / discharge history obtained from the control devices in the batteries 1H, 1L, 2H, and 2L. For example, when the estimated value of the remaining discharge capacity of battery 1H is the smallest when the batteries 1H and 1L of the first bank B1 perform discharge, and when the remaining discharge capacity of this battery 1H is used up, the remaining discharge capacity (r1L) of battery 1L at this time is used up via battery 2H or battery 2L of the second bank B2.

[0070] Here, when discharging by connecting the battery 2H or 2L of the second bank B2 and the battery 1L of the first bank B1, a difference (d2) occurs in the remaining discharge capacity between the battery 2H and the battery 2L. Therefore, the ECU 23 adjusts the selection of the batteries 2H and 2L of the second bank B2 and the discharge power amount so that this difference (d2) decreases. Specifically, when d2 ≧ r1L, the ECU 23 discharges by connecting the battery with the relatively larger remaining discharge capacity among the batteries 2H and 2L and the battery 1L. On the other hand, when d2 < r1L, the ECU 23 discharges by an amount D1 (= d2 + (r1L - d2) / 2) by connecting the battery with the relatively larger remaining discharge capacity among the batteries 2H and 2L and the battery 1L, and then discharges by an amount D2 (= (r1L - d2) / 2) by connecting the other battery among the batteries 2H and 2L and the battery 1L.

[0071] Figures 21(A) to (H) are a list of the energization modes of the battery switching device 50 shown in FIG. 16. As shown in this figure, the battery switching device 50 can realize eight patterns of energization modes. The energization modes shown in FIGS. 21(A) and (B) are energization modes for discharging or charging by connecting the batteries of the first bank B1 or the second bank B2 in series. The energization mode shown in FIG. 21(A) is an energization mode for discharging or charging in a first connection state in which the batteries 1H and 1L of the first bank B1 are connected to the drive system 3. The energization mode shown in FIG. 21(B) is an energization mode for discharging or charging in a second connection state in which the batteries 2H and 2L of the second bank B2 are connected to the drive system 3.

[0072] The energization modes shown in FIGS. 21(C) to (F) are energization modes in which one of the batteries 1H and 1L of the first bank B1 and one of the batteries 2H and 2L of the second bank B2 are connected in series to perform discharge or charging. The energization mode shown in FIG. 21(C) is an energization mode in which discharge or charging is performed in a third connection state in which the battery 1H of the first bank B1 and the battery 2L of the second bank B2 are connected to the drive system 3. Further, the energization mode shown in FIG. 21(D) is an energization mode in which discharge or charging is performed in a fourth connection state in which the battery 2H of the second bank B2 and the battery 1L of the first bank B1 are connected to the drive system 3. Further, the energization mode shown in FIG. 21(E) is an energization mode in which discharge or charging is performed in a fifth connection state in which the battery 1H of the first bank B1 and the battery 2H of the second bank B2 are connected to the drive system 3. Furthermore, the energization mode shown in FIG. 21(F) is an energization mode in which discharge or charging is performed in a sixth connection state in which the battery 1L of the first bank B1 and the battery 2L of the second bank B2 are connected to the drive system 3.

[0073] The energization modes shown in FIGS. 21(G) and (H) are energization modes in which the batteries 1H and 1L of the first bank B1 and the batteries 2H and 2L of the second bank B2 are connected to an in-vehicle charger (not shown) and charged by an external charger (not shown). The energization mode shown in FIG. 21(G) is an energization mode in which charging is performed in a seventh connection state in which the batteries 1H and 1L of the first bank B1 connected in series and the batteries 2H and 2L of the second bank B2 connected in series are connected in parallel to the in-vehicle charger. Further, the energization mode shown in FIG. 21(H) is an energization mode in which charging is performed in an eighth connection state in which the batteries 1H and 1L of the first bank B1 connected in series and the batteries 2H and 2L of the second bank B2 connected in series are connected in parallel to the in-vehicle charger, and the negative electrodes of the batteries 1H and 2H and the positive electrodes of the batteries 1L and 2L are connected.

[0074] When the battery 1H is in a power failure state and the remaining discharge capacity exists in the battery 1L in the first connection state, the ECU 23 switches the switching circuit 51 to the fourth connection state or the sixth connection state. Further, when the battery 1L is in a power failure state and the remaining discharge capacity exists in the battery 1H in the first connection state, the ECU 23 switches the switching circuit 51 to the third connection state or the fifth connection state. Further, when the battery 2H is in a power failure state and the remaining discharge capacity exists in the battery 2L in the second connection state, the ECU 23 switches the switching circuit 51 to the third connection state or the sixth connection state. Furthermore, when the battery 2L is in a power failure state and the remaining discharge capacity exists in the battery 2H in the second connection state, the ECU 23 switches the switching circuit 51 to the fourth connection state or the fifth connection state.

[0075] As described above, the present invention has been described based on the above embodiments. However, the present invention is not limited to the above embodiments, and modifications may be made to the above embodiments without departing from the spirit of the present invention, or known and well-known techniques may be appropriately combined.

[0076] For example, in the above embodiment, the drains of the FETs 21A and 22B of the first switch 21 are connected to each other, and the drains of the FETs 22A and 22B of the second switch 22 are connected to each other, but this is not essential. The sources of the FETs 21A and 22B of the first switch 21 may be connected to each other, and the sources of the FETs 22A and 22B of the second switch 22 may be connected to each other.

Explanation of reference numerals

[0077] 1H: Battery (replaceable battery, first battery) 1L: Battery (replaceable battery, second battery) 2H: Battery (replaceable battery, third battery) 2L: Battery (replaceable battery, fourth battery) 3: Drive system 10: Battery switching device 11: First switch (first energization control unit) 12: Second switch (second energization control unit) 13: ECU (control unit) 20: Battery switching device 21: First Switch (First Energization Control Unit) 21A: FET (First Switch) 21B: FET (Second Switch) 22: Second Switch (Second Energization Control Unit) 22A: FET (First Switch) 22B: FET (Second Switch) 23: ECU (Control Unit) 30: Battery Switching Device 40: Battery Switching Device 50: Battery Switching Device 51: Switching Circuit B1: First Bank (First Battery Unit) B2: Second Bank (Second Battery Unit) C: Electric Vehicle

Claims

1. A battery switching device that switches the connection state of a first battery unit and a second battery unit, which are provided with rechargeable batteries and connected in parallel to the drive system of an electric vehicle, to the drive system, comprising: a first energization control unit that controls the energization direction of the first battery unit; a second energization control unit that controls the energization direction of the second battery unit; a control unit that switches from a first state in which one of the first battery unit and the second battery unit is connected to the drive system, the other of the first battery unit and the second battery unit is disconnected from the drive system, and the remaining amount of the one of the first battery unit and the second battery unit is less than the remaining amount of the other of the first battery unit and the second battery unit, to a second state in which the one of the first battery unit and the second battery unit is disconnected from the drive system and the other of the first battery unit and the second battery unit is connected to the drive system; and when switching from the first state to the second state, the control unit controls the first energization control unit or the second energization control unit corresponding to the one of the first battery unit and the second battery unit so that the energization direction of the one of the first battery unit and the second battery unit becomes the discharge direction. A battery switching device.

2. The first energization control unit and the second energization control unit each include: a first switch that has an OFF state and an energization direction of a discharge direction; a second switch that has an OFF state and an energization direction of a charge direction; and when switching from the first state to the second state, the control unit executes energization control to turn OFF the first switch corresponding to the one of the first battery unit and the second battery unit and turn ON the second switch corresponding to the one of the first battery unit and the second battery unit so that the energization direction of the one of the first battery unit and the second battery unit becomes the discharge direction. The battery switching device according to Claim 1.

3. During execution of the energization control, the control unit turns OFF the first switch corresponding to the other of the first battery unit and the second battery unit and performs PWM control on the second switch corresponding to the other of the first battery unit and the second battery unit so that the connection between the other of the first battery unit and the second battery unit and the drive system becomes intermittent. The battery switching device according to Claim 2.

4. After switching from the first state to the second state, when regenerative power is generated in the drive system, the control unit turns on the first switch corresponding to one of the first battery unit and the second battery unit and turns off the second switch corresponding to one of the first battery unit and the second battery unit so that the energization direction of one of the first battery unit and the second battery unit becomes the charging direction. The battery switching device according to claim 2 or 3.

5. When the discharge power of one of the first battery unit and the second battery unit is equal to or less than a threshold value in the first state, the control unit turns off the first switch corresponding to the other of the first battery unit and the second battery unit and turns on the second switch corresponding to the other of the first battery unit and the second battery unit so that the energization direction of the other of the first battery unit and the second battery unit becomes the discharge direction. The battery switching device according to claim 2 or 3.

6. When regenerative power is generated in the drive system in the first state and the charging power of one of the first battery unit and the second battery unit is equal to or less than a threshold value, the control unit turns on the first switch corresponding to the other of the first battery unit and the second battery unit and turns off the second switch corresponding to the other of the first battery unit and the second battery unit so that the energization direction of the other of the first battery unit and the second battery unit becomes the charging direction. The battery switching device according to claim 2 or 3.

7. The first battery unit includes a first battery and a second battery. The second battery unit includes a third battery and a fourth battery. A switching circuit is provided for switching the connection states of the first battery, the second battery, the third battery, and the fourth battery to the drive system among a first connection state in which the first battery and the second battery are connected to the drive system, a second connection state in which the third battery and the fourth battery are connected to the drive system, a third connection state in which the first battery and the fourth battery are connected to the drive system, a fourth connection state in which the third battery and the second battery are connected to the drive system, a fifth connection state in which the first battery and the third battery are connected to the drive system, and a sixth connection state in which the second battery and the fourth battery are connected to the drive system. The battery switching device according to claim 1.

8. The control unit When the first battery is in a power failure state and the second battery has remaining discharge capacity in the first connection state, the switching circuit is switched to the fourth connection state or the sixth connection state. When, in the first connection state, the second battery is in a discharged state and the first battery has remaining discharge capacity, the switching circuit is switched to the third connection state or the fifth connection state. When, in the second connection state, the third battery is in a discharged state and the fourth battery has remaining discharge capacity, the switching circuit is switched to the third connection state or the sixth connection state. When, in the second connection state, the fourth battery is in a discharged state and the third battery has remaining discharge capacity, the switching circuit is switched to the fourth connection state or the fifth connection state. The battery switching device according to claim 7.

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