Battery switching method and electric vehicle

Abstract

To provide a battery switching method capable of switching between a state in which one of two batteries is used and a state in which the one battery is not used without providing a power converter.SOLUTION: The first battery 11 and the second battery 21 are connected in parallel to the inverter 50 that supplies electric power to the motor 60. The control device (the first and second battery management systems 12 and 22, and the integrated controller 30) controls the inverter 50 such that a non-torque current, which is a current of a phase component that does not generate torque in the motor 60 by the inverter 50, flows when switching to the connection state in which the first electric power of the first battery 11 is supplied to the inverter 50. The control device controls the switch 40 such that the switch 40 is connected at a timing when the voltage difference between the first voltage of the first battery 11 and the second voltage of the second battery 21 becomes less than a threshold value at which the switch 40 causes arc discharge.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a battery switching method and an electric vehicle. [Background technology]

[0002] Patent Document 1 describes that a power converter is provided for each of a plurality of batteries. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-39821 Summary of the Invention [Problem to be solved by the invention]

[0004] The battery switching method and electric vehicle that can switch between using one battery and not using another battery without using a power converter are desired. [Means for solving the problem]

[0005] According to one aspect of the present invention, when the switch is in a disconnected state in which the first power from the first battery is not supplied to the inverter and is switched to a connected state in which the first power is supplied to the inverter, the control device controls the inverter to flow a non-torque current, which is a current of a phase component that does not generate torque in the motor by the inverter, and controls the switch to connect when the voltage difference between the first voltage and the second voltage of the second battery becomes less than a threshold at which the switch causes arc discharge. [Effects of the Invention]

[0006] According to the battery switching method and electric vehicle of the present invention, it is possible to switch between a state in which one of the two batteries is used and a state in which it is not used, without providing a power converter. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a block diagram showing an electric vehicle that executes a battery switching method according to one embodiment, in which a switch that switches whether or not a first power from a first battery is supplied to an inverter is in a cut-off state, and a second power from a second battery is supplied to the inverter. [Figure 2] FIG. 2 is a diagram for explaining a switching procedure when switching the switch from the disconnected state shown in FIG. 1 to the connected state shown in FIG. 3 in which the first power from the first battery is supplied to the inverter. [Figure 3] FIG. 3 is a block diagram showing a state in which the switches are in a connected state and first and second powers are supplied from first and second batteries to an inverter. [Figure 4] FIG. 4 is a diagram for explaining a switching procedure when the switch is switched from the connected state shown in FIG. 3 to the disconnected state shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0008] A battery switching method and an electric vehicle according to one embodiment will be described below with reference to the accompanying drawings. In Fig. 1, the electric vehicle includes a first battery 11, a first battery management system (hereinafter referred to as first BMS) 12, a second battery 21, a second battery management system (hereinafter referred to as second BMS) 22, an integrated control unit 30, a switch 40, an inverter 50, and a motor 60. The motor 60 drives the driving wheels (not shown) of the electric vehicle. In Fig. 1, lines for a high-power system are indicated by thick solid lines, and lines for a signal system are indicated by thin solid lines.

[0009] A first BMS 12 is connected to the first battery 11. A switch 40 is connected to the first battery 11. The switch 40 is a component that switches between a connected state in which the first power from the first battery 11 is supplied to the inverter 50 and a disconnected state in which the first power is not supplied. The switch 40 also includes a component called a relay. A second BMS 22 is connected to the second battery 21.

[0010] The series circuit of the first battery 11 and the switch 40 and the second battery 21 are connected in parallel to the inverter 50. The inverter 50 is connected to the motor 60. The inverter 50 and the motor 60 are synchronous. The first BMS 12 and the second BMS 22 are connected to the integrated control unit 30. The first BMS 12, the second BMS 22 and the integrated control unit 30 execute a battery switching method according to one embodiment.

[0011] The first BMS 12 and the second BMS 22 control the charging and discharging of the first battery 11 and the second battery 21. The first BMS 12 and the second BMS 22 can be configured, for example, by a microcomputer including a central processing unit (CPU), a read-only memory (ROM), a random access memory (RAM), and an input / output (I / O) interface. The first BMS 12 and the second BMS 22 control the charging and discharging of the first battery 11 and the second battery 21 by executing a specific computer program.

[0012] The integrated control unit 30 controls the first BMS 12 and the second BMS 22 in an integrated manner. The integrated control unit 30 can also be configured with a microcomputer similar to the above. The integrated control unit 30 may be a computer called a VCU (Vehicle Control Unit). The first BMS 12, the second BMS 22, and the integrated control unit 30 may be configured with a single computer. The first BMS 12, the second BMS 22, and the integrated control unit 30 function as a control device that controls switching between supplying and not supplying the first power from the first battery 11 to the inverter 50. The control device may be configured in any manner.

[0013] The first battery 11 is a battery with low internal impedance and high output. The second battery 21 is a battery with high internal impedance and low output. The second battery 21 has a lower unit price per capacity than the first battery 11. By providing the electric vehicle with the first battery 11 and the second battery 21, it is possible to ensure both the required driving distance and the instantaneously required high output at a relatively low cost.

[0014] If the first battery 11 and the second battery 21 were always connected in parallel, a loop current would flow due to the voltage difference between the first battery 11 and the second battery 21, making it impossible to maintain the appropriate SOC (state of charge) of each battery. Furthermore, the loop current would result in loss or heat generation. Therefore, a switch 40 switches between a state in which the first battery 11 and the second battery 21 are connected in parallel to the inverter 50 and a state in which only the second battery 21 is connected. In one embodiment, a power converter such as that described in Patent Document 1 is not provided, so there is no loss due to the power converter, and the cost of providing a power converter can be reduced.

[0015] FIG. 1 shows a state in which the switch 40 is in an OFF state and the second power from the second battery is being supplied to the inverter 50. If the switch 40 is in a ON state, the first power from the first battery 11 and the second power from the second battery can be supplied to the inverter 50. If the switch 40 is connected or disconnected while a voltage is being applied to the switch 40 and a current is flowing, the contacts of the switch 40 will be worn and damaged by arc discharge. Therefore, when the switch 40 is in the OFF state as shown in FIG. 1, the control device switches the switch 40 to the ON state as follows.

[0016] The first BMS 12 and the second BMS 22 measure and monitor the first voltage V1 of the first battery 11 and the second voltage V2 of the second battery 21. As shown in Fig. 2(a), the second voltage V2 is higher than the first voltage V1.

[0017] As shown in FIG. 2(b), at time t1, the integrated control unit 30 controls the inverter 50 to pass a no-torque current. The no-torque current means that, of the two-axis current, the d-axis current and the q-axis current, which are approximately 90 degrees out of phase with each other, that is passed through the motor 60, only the d-axis current that does not generate torque to move the electric vehicle is passed. When the inverter 50 passes a no-torque current through the motor 60, the second voltage V2, which has a high internal impedance, drops, as shown in FIG. 2(a). This voltage drop is due to the internal resistance of the second battery 21, and does not mean that the SOC is decreasing.

[0018] As the integrated control unit 30 further increases the no-torque current, the second voltage V2 gradually decreases. At time t2, the voltage difference between the first voltage V1 and the second voltage V2 becomes less than the threshold at which the switch 40 causes an arc discharge. The integrated control unit 30 closes the switch 40 at time t2. This allows the switch 40 to transition to the connected state without causing an arc discharge. In this way, the electric vehicle can switch from a state in which only the second battery 21 shown in FIG. 1 is used to a state in which both the first battery 11 and the second battery 21 are used as shown in FIG. 3.

[0019] The integrated control unit 30 may determine the timing (here, time t2) to close the switch 40 in the following manner. In a first method, the integrated control unit 30 gradually increases the no-torque current while monitoring the second voltage V2. The integrated control unit 30 closes the switch 40 at the timing (time t2) when the voltage difference between the first voltage V1 and the second voltage V2 becomes less than the threshold value. In the first method, the integrated control unit 30 executes feedback control to determine the timing to close the switch 40.

[0020] The second method is as follows. The internal resistance of the second battery 21 can be obtained in advance as a characteristic from the SOC, SOH (state of health), and temperature of the second battery 21. From the voltage difference between the first voltage V1 and the second voltage V2 and the SOC, SOH, and temperature of the second battery 21, it is possible to calculate the amount of voltage drop required for the second voltage V2 so that the voltage difference between the first voltage V1 and the second voltage V2 is less than a threshold value. The integrated control unit 30 controls the inverter 50 to flow a no-torque current sufficient to achieve this amount of voltage drop, and closes the switch 40 at the timing (time t2) when the no-torque current is flowing. In the second method, the integrated control unit 30 executes feedforward control to determine the timing to close the switch 40.

[0021] The integrated control unit 30 may combine the first and second methods to determine the timing to close the switch 40. The power of the phase component that does not generate torque, adjusted in this manner, is used the next time the switch 40 is closed. The integrated control unit 30 causes a constant no-torque current to flow from time t2 to time t3, and then gradually reduces the no-torque current until it becomes zero at time t4.

[0022] As described above, the first battery 11 has a higher output than the second battery 21. When a high output is needed instantaneously, the required high output can be obtained by switching from a state in which only the second battery 21 is used to a state in which both the first battery 11 and the second battery 21 are used.

[0023] When the switch 40 is in the connected state as shown in Figure 3, the control device disconnects the switch 40 as follows: The first BMS 12 and the second BMS 22 measure and monitor the first voltage V1 and the second voltage V2, respectively. As shown in Figure 4(a), since the switch 40 is in the connected state, the first voltage V1 and the second voltage V2 are equal.

[0024] The voltage at which the current of the first battery 11 and the second battery 21 becomes zero is defined as the open-circuit voltage. The open-circuit voltage can be obtained in advance as a function of the SOC as a battery characteristic. As shown in FIG. 4(b), the integrated control unit 30 controls the inverter 50 to pass a no-torque current at time t11. When the inverter 50 passes a no-torque current to the motor 60, the first voltage V1 and the second voltage V2 decrease, as shown in FIG. 4(a).

[0025] As the unified control unit 30 further increases the no-torque current, the first voltage V1 and the second voltage V2 decrease sequentially. At time t12, the voltage difference between the first voltage V1 and the second voltage V2 and the open-circuit voltage becomes less than the threshold value for causing arc discharge. The unified control unit 30 turns off the switch 40 at time t12. This allows the switch 40 to transition to the cut-off state without causing arc discharge.

[0026] The integrated control unit 30 flows a constant no-torque current from time t12 to time t13, and then gradually reduces the no-torque current until it becomes zero at time t14. As shown in (a) of FIG. 4, the second voltage V2 gradually increases after time t13 and becomes a constant value after time t14. In this way, the electric vehicle can switch from a state in which both the first battery 11 and the second battery 21 shown in FIG. 3 are used to a state in which only the second battery 21 is used as shown in FIG. 1.

[0027] The present invention is not limited to the above-described embodiment, and various modifications are possible without departing from the gist of the present invention. [Explanation of symbols]

[0028] 11 First Battery 12 First Battery Management System 21 Second Battery 22 Second Battery Management System 30 Integrated Control Unit 40 Switch 50 inverters 60 motor

Claims

1. a first battery and a second battery connected in parallel to an inverter that supplies power to a motor, and a switch that switches whether or not the first power from the first battery is supplied to the inverter is provided; a control device that controls switching between supplying the first power to the inverter, When the switch is in a disconnection state in which the first power is not supplied to the inverter and is switched to a connection state in which the first power is supplied to the inverter in a state in which the second power is supplied to the inverter by the second battery, controlling the inverter so that a non-torque current, which is a current of a phase component that does not generate torque in the motor, flows through the inverter; The switch is controlled to close when a voltage difference between a first voltage of the first battery and a second voltage of the second battery becomes less than a threshold at which the switch causes arc discharge. Battery switching method.

2. The control device When the switch is in the connected state and supplies the first and second powers to the inverter, the switch is switched to the disconnected state. controlling the inverter so that the non-torque current flows through the inverter; The switch is controlled to be turned off at a timing when a voltage difference between the first and second voltages and an open circuit voltage at which the currents of the first and second batteries become zero becomes less than the threshold value. The battery switching method of claim 1 .

3. 3. The battery switching method according to claim 1, wherein the first battery has a higher output than the second battery.

4. a motor for driving the drive wheels; an inverter that supplies power to the motor; first and second batteries connected in parallel to the inverter; a switch for switching whether or not the first power from the first battery is to be supplied to the inverter; a control device that controls to switch whether or not the first power is supplied to the inverter; Equipped with When the switch is in a disconnection state in which the first power is not supplied to the inverter and is switched to a connection state in which the first power is supplied to the inverter in a state in which the second power is supplied to the inverter by the second battery, The control device controlling the inverter so that a non-torque current, which is a current of a phase component that does not generate torque in the motor, flows through the inverter; controlling the switch to close the switch when a voltage difference between a first voltage of the first battery and a second voltage of the second battery becomes less than a threshold at which the switch causes arc discharge; When the switch is in the connected state and supplies the first and second powers to the inverter, the switch is switched to the disconnected state. controlling the inverter so that the non-torque current flows through the inverter; The switch is controlled to be turned off at a timing when a voltage difference between the first and second voltages and an open circuit voltage at which the currents of the first and second batteries become zero becomes less than the threshold value. Electric car.

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