Fuel cell vehicle and control method thereof

Abstract

The present invention relates to a fuel cell vehicle and a control method thereof. The controller of the fuel cell vehicle is configured to drive a power consumption device until the voltage measurement value falls below the overvoltage threshold value when the measurement value of a first voltage sensor measuring the voltage at the DC terminal of a converter exceeds an overvoltage threshold value and a battery cannot be charged. The controller is configured to estimate the voltage at the DC terminal using a second voltage sensor measuring the output voltage of a fuel cell group or a third voltage sensor measuring the output voltage of a battery to continue driving the fuel cell vehicle when the voltage measurement value exceeds the overvoltage threshold value and the battery can be charged.

Description

Technical Field

[0001] The technology disclosed in this specification relates to a fuel cell vehicle and a control method thereof. Background Art

[0002] In addition to the fuel cell, the fuel cell vehicle also has a battery. The battery stores the surplus power of the fuel cell and the regenerative power generated by the electric generator. Here, the structure of the electric generator is the same as that of a normal electric motor. The electric generator can use the power of the fuel cell and the battery to output torque for driving and can use the inertia of the vehicle to generate electricity. The fuel cell and the battery supply power to the electric generator via the converter.

[0003] If the power is too much for the battery to absorb, the voltage of the power line between the converter and the fuel cell may exceed the overvoltage threshold. In the technique of Japanese Patent Application Laid-Open No. 2010-273496, the output of the fuel cell stack is adjusted to avoid overvoltage. Summary of the invention

[0004] A fuel cell vehicle is provided with a voltage sensor for measuring the voltage at the DC end of a converter. The controller of the fuel cell vehicle determines whether an overvoltage has occurred based on the measured value of the voltage sensor. However, in the event that an abnormality occurs in the voltage sensor, the following situation may occur: although an overvoltage has not actually occurred, the voltage sensor outputs a measured value higher than an overvoltage threshold. In this case, the controller may mistakenly determine that an overvoltage has occurred. The present specification provides a fuel cell vehicle and a control method thereof that can continue to travel using an alternative voltage sensor even when an abnormality occurs in the voltage sensor when the measured value of the voltage sensor exceeds the overvoltage threshold.

[0005] The fuel cell vehicle disclosed in this specification includes a fuel cell stack, a battery, an electric generator, a converter, a first voltage sensor, a power consuming device and a controller. The electric generator is configured to use the power of the fuel cell stack and the battery to output a torque for driving and is configured to use the inertia of the fuel cell vehicle to generate electricity. The fuel cell stack and the battery are connected to the DC end of the converter, and the electric generator is connected to the AC end of the converter. The first voltage sensor is configured to measure the voltage at the DC end of the converter. The power consuming device is connected to the DC end. An example of a power consuming device is a device for operating the fuel cell stack (fuel cell auxiliary machine).

[0006] The controller is configured to drive the power consuming device until the voltage measurement value falls below the overvoltage threshold value when the measured value of the first voltage sensor (voltage measurement value) exceeds the overvoltage threshold value and the battery is in a non-chargeable state. The controller is configured to determine that an abnormality has occurred in the first voltage sensor when the voltage measurement value exceeds the overvoltage threshold value and the battery is in a chargeable state. The controller is configured to drive the motor generator while estimating the voltage at the DC terminal using the second voltage sensor measuring the output voltage of the fuel cell stack or the third voltage sensor measuring the output voltage of the battery (using a voltage sensor different from the first voltage sensor) when it is determined that an abnormality has occurred in the first voltage sensor.

[0007] If the battery is in a rechargeable state, the remaining power is absorbed by the battery, so no overvoltage is generated. In the event that the measured value of the first voltage sensor indicates an overvoltage threshold value despite this, it can be determined that an abnormality has occurred in the first voltage sensor. In such a case, the controller is configured to drive the electric generator while using the second voltage sensor or the third voltage sensor to estimate the voltage at the DC end of the converter. That is, the fuel cell vehicle can continue to travel. On the other hand, when the battery is in a non-rechargeable state, an overvoltage may occur, so it can be determined that the measured value of the first voltage sensor is correct. In this case, the controller is configured to drive the power consuming equipment to eliminate the overvoltage.

[0008] A typical case where the battery is in an unchargeable state is when the battery is electrically disconnected from the DC terminal of the converter. The controller may be configured to determine that the battery is in an unchargeable state when the measured value of the current sensor for measuring the current flowing into and out of the battery is zero. The controller may also be configured to determine that the battery is in an unchargeable state when the voltage of the battery exceeds the voltage of the DC terminal of the converter.

[0009] In the fuel cell vehicle of the present disclosure, the upper limit value of the allowable voltage set for the power consuming device may be higher than the upper limit value of the output voltage of the fuel cell stack.

[0010] In the fuel cell vehicle of the present disclosure, the DC end of the inverter may be connected to the fuel cell stack via a boost converter, and the controller may be configured to estimate the voltage of the DC end by multiplying a measurement value of the second voltage sensor by a boost ratio of the boost converter.

[0011] In the fuel cell vehicle of the present disclosure, the battery and the inverter may be connected without a voltage converter, and the controller may be configured to use a measurement value of the third voltage sensor as an estimated value of the voltage at the DC end of the inverter.

[0012] The fuel cell vehicle of the control method of the fuel cell vehicle disclosed in the specification comprises: a fuel cell stack; a battery; an electric generator configured to output torque for driving using the power of the fuel cell stack and the battery and to generate electricity using the inertia of the fuel cell vehicle; an inverter connected to the fuel cell stack and the battery at the DC end and the electric generator at the AC end; a first voltage sensor configured to measure the voltage at the DC end; a power consumption device connected to the DC end; and a controller. The control method of the fuel cell vehicle disclosed in the present invention comprises the following steps: when the measured value of the first voltage sensor exceeds the overvoltage threshold, using the controller to determine whether the battery is in a non-chargeable state or a chargeable state; when it is determined that the battery is in a non-chargeable state, using the controller to drive the power consumption device until the measured value is lower than the overvoltage threshold; and when it is determined that the battery is in a chargeable state, using the controller to drive the electric generator while estimating the voltage at the DC end using a second voltage sensor measuring the output voltage of the fuel cell stack or a third voltage sensor measuring the output voltage of the battery.

[0013] In the control method of the fuel cell vehicle of the present disclosure, the controller may be configured to determine that the battery is in a non-chargeable state when the battery is electrically disconnected from the DC terminal.

[0014] In the control method of the fuel cell vehicle of the present disclosure, the controller may be configured to determine that the battery is in an unchargeable state when a measurement value of a current sensor configured to measure current flowing into and out of the battery indicates zero.

[0015] The details and further improvements of the technology disclosed in this specification will be described in the following “Detailed Description of the Invention”. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Features, advantages and technical and industrial significance of exemplary embodiments of the present invention will be described below with reference to the accompanying drawings, in which like numerals represent like elements, and in which:

[0017] Figure 1 It is a block diagram of the electric power system of the fuel cell vehicle of the embodiment.

[0018] Figure 2 This is a flowchart of processing when the measured value of the first voltage sensor exceeds the overvoltage threshold value. DETAILED DESCRIPTION

[0019] The fuel cell vehicle 2 of the embodiment will be described with reference to the accompanying drawings. Figure 1, a block diagram of the power system of the fuel cell vehicle 2 is shown. The fuel cell vehicle 2 of the embodiment includes a fuel cell stack 3, a boost converter 6, an inverter 10, a motor generator 11 for traveling, a main battery 13, and a controller 30. The fuel cell vehicle 2 drives the motor generator 11 for traveling using the power of the fuel cell stack 3 and the main battery 13 to travel.

[0020] The motor generator 11 can not only use the power of the fuel cell stack 3 and the main battery 13 to output torque for driving, but also use the inertia of the fuel cell vehicle 2 to generate electricity. The structure of the motor generator 11 is no different from that of a normal electric motor. As is well known, a normal electric motor generates electricity when it is reverse driven. The electricity generated by the motor generator 11 is called regenerative power. The regenerative power (AC) generated by the motor generator 11 is converted into DC power by the converter 10 and charged into the main battery 13.

[0021] The converter 10 converts the DC power of the fuel cell stack 3 and the main battery 13 into three-phase AC power for driving the motor generator 11. As described above, the converter 10 sometimes converts the regenerative power (AC) generated by the motor generator 11 into DC power and outputs it from the DC terminal 10a. The fuel cell stack 3 is connected to the DC terminal 10a of the converter 10 via the FC relay 7 and the boost converter 6. The boost converter 6 boosts the output power of the fuel cell stack 3 and supplies it to the converter 10.

[0022] The FC relay 7 is disconnected when the main switch of the fuel cell vehicle 2 is off, and the fuel cell stack 3 is electrically disconnected from the converter 10. The FC relay 7 is controlled by the controller 30. If the main switch of the fuel cell vehicle 2 is turned on, the controller 30 starts the fuel cell stack 3. If the output of the fuel cell stack 3 reaches a specified voltage (starting voltage), the controller 30 closes the FC relay 7 to connect the fuel cell stack 3 to the converter 10. When the fuel cell stack 3 is stopped or an abnormality occurs in the fuel cell stack 3, the controller 30 disconnects the FC relay 7 to electrically disconnect the fuel cell stack 3 from the converter 10. The DC terminal 10a of the converter 10, the fuel cell stack 3 and the main battery 13 are connected by a power line 8.

[0023] The converter 10 has two converter circuits. The two converter circuits have a common DC terminal 10a. The AC terminal of one converter circuit is connected to the electric generator 11, and the AC terminal of the other converter circuit is connected to the air compressor 12. The air compressor 12 is a device for supplying air to the fuel cell stack 3. The converter 10 is controlled by a controller 30. The controller 30 determines the target output of the electric generator 11 according to the throttle opening and the vehicle speed, and controls the converter circuit of one side of the converter 10 in a manner to achieve the target output. In addition, the controller 30 determines the target output of the fuel cell stack 3, and controls the converter circuit of the other side in a manner to achieve the target output.

[0024] A smoothing capacitor 31 and a voltage sensor 9 (an example of a first voltage sensor) are connected to the DC terminal 10a of the converter 10. The smoothing capacitor 31 suppresses pulsation of power input to the converter 10. The voltage sensor 9 measures the voltage at the DC terminal 10a of the converter 10. The measured value of the voltage sensor 9 is sent to the controller 30.

[0025] A voltage sensor 4 (an example of a second voltage sensor) and a current sensor 5 are connected to the output end of the fuel cell stack 3. The voltage sensor 4 measures the output voltage of the fuel cell stack 3, and the current sensor 5 measures the output current of the fuel cell stack 3. The measured values ​​of the voltage sensor 4 and the current sensor 5 are sent to the controller 30. Figure 1 In the figure, communication lines for transmitting sensor information such as measured values ​​and signal lines for transmitting commands sent from the controller 30 to the inverter 10 and the like are omitted from the figure.

[0026] The main battery 13 is connected to the DC end 10a of the converter 10 via the system main relay 17. When the main switch of the fuel cell vehicle 2 is turned on, the controller 30 closes the system main relay 17 to connect the main battery 13 to the converter 10. When the main switch is turned off, the controller 30 opens the system main relay 17 to electrically disconnect the main battery 13 from the converter 10 (power line 8).

[0027] The main battery 13 is rechargeable and is typically a lithium-ion battery. The response speed of the main battery 13 is faster than that of the fuel cell stack 3. If the accelerator pedal is stepped on, the target torque of the motor generator 11 suddenly increases. When the output of the fuel cell stack 3 is insufficient to achieve the target torque, the power of the main battery 13 is used.

[0028] The aforementioned regenerative power is charged into the main battery 13. The surplus power of the fuel cell stack 3 is also charged into the main battery 13. Other electrical devices are also connected to the power line 8 connecting the DC terminal 10a of the converter 10, the fuel cell stack 3 and the main battery 13. The surplus power means the surplus power of the power generated by the fuel cell stack 3 and the aforementioned regenerative power that is not consumed by the electrical devices (including the converter 10) connected to the power line 8.

[0029] A voltage sensor 14 (an example of a third voltage sensor) and a current sensor 15 are also connected to the main battery 13. The voltage sensor 14 measures the output voltage of the main battery 13, and the current sensor 15 measures the current entering and exiting the main battery 13. The measured values ​​of the voltage sensor 14 and the current sensor 15 are also sent to the controller 30. The main battery 13 is also provided with a fuse 18.

[0030] The electrical equipment connected to the power line 8 includes, in addition to the converter 10, a hydrogen pump 21, a cooler pump 22, a heater 23, an air conditioner 24, a voltage converter 25, and the like. The hydrogen pump 21 is a device for delivering hydrogen to the fuel cell stack 3, and the cooler pump 22 is a device for circulating cooling water of the fuel cell stack 3. The heater 23 is a device for heating the fuel cell stack 3 when the temperature of the fuel cell stack 3 is low. The air conditioner 24 is a device for adjusting the temperature in the cabin of the fuel cell vehicle 2.

[0031] The voltage converter 25 steps down the voltage of the fuel cell stack 3 or the main battery 13 and supplies the voltage to low-power equipment such as the audio equipment 27. The sub-battery 26 is charged by the output of the voltage converter 25.

[0032] exist Figure 1 In the figure, the hydrogen pump 21, the cooler pump 22, and the air conditioner 24 are each depicted as a rectangle, but these devices have actuators such as pumps and drivers that drive the actuators. The driver has a switching element called a power transistor, and a withstand voltage is determined for these switching elements. The voltage converter 25 that receives power supply via the power line 8 and the boost converter 6 connected between the fuel cell stack 3 and the converter 10 also have switching elements, and a withstand voltage is also determined for these switching elements. If the voltage applied to these switching elements exceeds the withstand voltage, the switching elements may be damaged.

[0033] Therefore, the controller 30 monitors the voltage of the power line 8 (in other words, the voltage of the DC terminal 10a of the converter 10) and controls the fuel cell stack 3 and the boost converter 6 in such a way that the voltage of the DC terminal 10a does not exceed the prescribed overvoltage threshold. Alternatively, the controller 30 drives the electrical devices that receive power supply from the fuel cell stack 3 and the converter 10 (the converter 10 when outputting regenerative power) via the power line 8. That is, the controller 30 consumes the power transmitted through the power line 8 by the above-mentioned electrical devices, thereby reducing the voltage of the DC terminal 10a. Hereinafter, for the sake of convenience, the electrical devices that receive power supply from the fuel cell stack 3 and the converter 10 (the converter 10 when outputting regenerative power) via the power line 8 are collectively referred to as power consumption devices 20. The power consumption devices 20 include a hydrogen pump 21, a cooler pump 22, a heater 23, an air conditioner 24, a voltage converter 25, and a boost converter 6.

[0034] An upper limit of an allowable voltage is determined for the power consuming device 20. The upper limit of the allowable voltage is set to a value higher than the upper limit of the output voltage of the fuel cell stack 3 and the converter 10 (the converter 10 when outputting regenerative power). The upper limit of the allowable voltage is lower than the previous withstand voltage and is set to a value that does not cause damage to the power consuming device 20 due to overvoltage. The upper limit of the allowable voltage may also be the same as the previous overvoltage threshold.

[0035] The controller 30 uses the measured value of the voltage sensor 9 to monitor the voltage of the DC terminal 10a (power line 8) of the converter 10. However, if an abnormality occurs in the voltage sensor 9, the following state may occur: although the actual voltage of the DC terminal 10a does not exceed the overvoltage threshold, the measured value of the voltage sensor 9 exceeds the overvoltage threshold. When the measured value of the voltage sensor 9 exceeds the overvoltage threshold, the controller 30 can determine whether an abnormality has occurred in the voltage sensor 9 and take appropriate measures according to the presence or absence of the abnormality.

[0036] Since the DC terminal 10a and the main battery 13 are connected, if the main battery 13 can be charged, the voltage of the DC terminal 10a will not exceed the overvoltage threshold. In the case where the measured value of the voltage sensor 9 exceeds the overvoltage threshold despite the main battery 13 being connected to the DC terminal 10a, it can be determined that an abnormality has occurred in the voltage sensor 9. On the other hand, if the main battery 13 cannot be charged, the voltage of the DC terminal 10a may exceed the overvoltage threshold. In this case, the measured value of the voltage sensor 9 is likely to be correct.

[0037] Therefore, when the main battery 13 is in a chargeable state and the measured value of the voltage sensor 9 exceeds the overvoltage threshold, the controller 30 determines that an abnormality has occurred in the voltage sensor 9. In this case, the controller 30 estimates the voltage of the DC terminal 10a using another voltage sensor (for example, the voltage sensor 4 measuring the voltage of the fuel cell stack 3 or the voltage sensor 14 measuring the voltage of the main battery 13).

[0038] The process when the measured value of the voltage sensor 9 exceeds the overvoltage threshold value is Figure 2 As shown in . When the measured value of the voltage sensor 9 exceeds the overvoltage threshold, the controller 30 checks the state of the main battery 13 (step S2). When the main battery 13 is in an unchargeable state (step S2: yes), the controller 30 disconnects the system main relay 17 (step S3). An example of the main battery 13 being in an unchargeable state is a case where the main battery 13 is electrically disconnected from the fuel cell stack 3 and the converter 10. For example, when the fuse 18 is disconnected, the main battery 13 is disconnected from the fuel cell stack 3 and the converter 10 and cannot be charged. Even in such a case, the controller 30 preventively disconnects the system main relay 17. It should be noted that in this case, the voltage sensor 9 is likely to be normal.

[0039] Next, the controller 30 drives the power consuming device 20 until the measured value of the voltage sensor 9 (voltage measured value) becomes lower than the overvoltage threshold value (step S4 ).

[0040] After step S4, the controller 30 continues the driving of the fuel cell vehicle 2. It should be noted that since the system main relay 17 is disconnected (step S3), the controller 30 continues the driving of the fuel cell vehicle 2 without using the main battery 13. In this case, since the excess power cannot be absorbed, the controller 30 reduces the output of the fuel cell stack 3 compared to the normal case.

[0041] On the other hand, when the main battery 13 is in a chargeable state in step S2 (step S2: No), the controller 30 determines that an abnormality has occurred in the voltage sensor 9. In this case, the controller 30 estimates the voltage of the DC terminal 10a of the converter 10 using another voltage sensor (for example, the voltage sensor 4 that measures the voltage of the fuel cell stack 3 or the voltage sensor 14 that measures the voltage of the main battery 13) (step S5). If the measured value of the voltage sensor 4 is multiplied by the boost ratio of the boost converter 6, the estimated voltage value of the DC terminal 10a is obtained. In addition, the measured value of the voltage sensor 14 (the voltage of the main battery 13) can be used directly as the estimated voltage value of the DC terminal 10a.

[0042] The controller 30 uses the voltage estimation value to continue the driving of the fuel cell vehicle 2. Specifically, the controller 30 controls the fuel cell stack 3 and the boost converter 6 in such a way as to prevent the voltage estimation value (the estimated value of the voltage at the DC terminal 10a) from exceeding the overvoltage threshold. After step S5, the controller 30 drives the motor generator 11 while estimating the voltage at the DC terminal 10a using another voltage sensor that measures the output voltage of the fuel cell stack 3 or the main battery 13, and the fuel cell vehicle 2 drives.

[0043] It should be noted that the controller 30 determines that the main battery 13 cannot be charged if it detects any of the following (1) to (3). (1) The main battery 13 is electrically disconnected from the fuel cell stack 3 and the converter 10. This is equivalent to the case where the fuse 18 is disconnected or the system main relay 17 is disconnected.

[0044] (2) When the current sensor 15 measuring the current flowing through the main battery 13 shows a value of zero. When the current sensor 15 shows a value of zero, it also means that the main battery 13 is electrically disconnected from the fuel cell stack 3 and the converter 10 .

[0045] (3) When the voltage of the main battery 13 exceeds the voltage of the DC terminal 10a. In this case, the main battery 13 cannot absorb the power applied to the DC terminal 10a.

[0046] As described above, the fuel cell vehicle 2 of the embodiment can continue to travel using a substitute voltage sensor (voltage sensor 4 or voltage sensor 14) even when the measured value of the voltage sensor 9 exceeds the overvoltage threshold value and an abnormality occurs in the voltage sensor 9. In addition, when it can be determined that the voltage sensor 9 is normal, the power consuming device 20 is driven until the voltage of the DC terminal 10a is lower than the overvoltage threshold value. Through this process, the overvoltage state is quickly eliminated, and damage to the device connected to the power line 8 can be suppressed.

[0047] The following describes the points of attention related to the technology described in the embodiment. Figure 2 In step S2, if the main battery 13 is connected to the DC terminal 10a and the voltage of the main battery 13 is the same as the voltage of the DC terminal 10a, it is determined that the battery is chargeable.

[0048] In the fuel cell vehicle 2 of the embodiment, a voltage converter is not connected between the main battery 13 and the converter 10. In other words, the drive voltage of the converter 10 is substantially equal to the output voltage of the main battery 13. In this case, the resistance value of the power line between the DC terminal 10a of the converter 10 and the main battery 13 is small. Therefore, if the voltage of the main battery 13 is the same as the voltage of the DC terminal 10a, the surplus voltage is quickly charged into the main battery 13.

[0049] Although the specific examples of the present invention are described in detail above, they are merely illustrative and do not limit the claims. The technologies described in the claims include technologies that are variously modified and altered to the specific examples illustrated above. The technical elements described in this specification or the drawings exert technical usefulness in the form of a single or various combinations, and are not limited to the combinations recorded in the claims at the time of application. In addition, the technologies illustrated in this specification or the drawings can achieve multiple purposes at the same time, and achieving one of the purposes itself has technical usefulness.

Claims

1. A fuel cell vehicle, characterized in that: include: Fuel cell stack; Batteries; a motor generator configured to output a torque for traveling using the electric power of the fuel cell stack and the battery and to generate electric power using the inertia energy of the fuel cell vehicle; A converter, connected to the fuel cell group and the battery at a DC end and connected to the motor generator at an AC end; a first voltage sensor configured to measure the voltage at the DC terminal; A power consumption device connected to the DC terminal; and The controller is configured to drive the power consuming device until the measured value falls below the overvoltage threshold when the measured value of the first voltage sensor exceeds the overvoltage threshold and the battery is in a non-rechargeable state, and to drive the electric generator while estimating the voltage of the DC terminal using a second voltage sensor (4) measuring the output voltage of the fuel cell stack or a third voltage sensor measuring the output voltage of the battery when the measured value exceeds the overvoltage threshold and the battery is in a rechargeable state.

2. The fuel cell vehicle according to claim 1, characterized in that: The controller determines that the battery is in an unchargeable state when the battery is electrically disconnected from the DC terminal.

3. The fuel cell vehicle according to claim 1, characterized in that: It also includes a current sensor configured to measure current flowing into and out of the battery. The controller is configured to determine that the battery is in a non-chargeable state when the measured value of the current sensor indicates zero.

4. The fuel cell vehicle according to claim 1, characterized in that: The controller is configured to determine that the battery is in an unchargeable state when the voltage of the battery exceeds the voltage of the DC terminal.

5. The fuel cell vehicle according to any one of claims 1 to 4, characterized in that: The permissible voltage upper limit value set for the power consuming device is higher than the output voltage upper limit value of the fuel cell stack.

6. The fuel cell vehicle according to any one of claims 1 to 5, characterized in that: The DC end is connected to the fuel cell stack via a boost converter. The controller is configured to estimate the voltage at the DC end by multiplying a measurement value of the second voltage sensor by a boost ratio of the boost converter.

7. The fuel cell vehicle according to any one of claims 1 to 5, characterized in that: The battery and the converter are connected without a voltage converter. The controller is configured to use a measurement value of the third voltage sensor as an estimated value of the voltage at the DC terminal.

8. A control method for a fuel cell vehicle, the fuel cell vehicle comprising: Fuel cell stack; Batteries; a motor generator configured to output torque for traveling using the electric power of the fuel cell stack and the battery and to generate electric power using inertia energy of the fuel cell vehicle; A converter, connected to the fuel cell group and the battery at a DC end and connected to the motor generator at an AC end; a first voltage sensor configured to measure the voltage at the DC terminal; A power consumption device connected to the DC terminal; and Controller, The control method of the fuel cell vehicle is characterized by comprising the following steps: When the measured value of the first voltage sensor exceeds the overvoltage threshold, the controller is used to determine whether the battery is in a non-chargeable state or a chargeable state; When it is determined that the storage battery is in an unchargeable state, the controller drives the power consuming device until the measured value falls below the overvoltage threshold value; and When it is determined that the battery is in a chargeable state, the controller drives the motor generator while estimating the voltage at the DC end using a second voltage sensor (4) measuring the output voltage of the fuel cell stack or a third voltage sensor measuring the output voltage of the battery.

9. The control method according to claim 8, characterized in that: The controller is configured to determine that the battery is in an unchargeable state when the battery is electrically disconnected from the DC terminal.

10. The control method according to claim 8, characterized in that: The controller is configured to determine that the battery is in an unchargeable state when a measurement value of a current sensor configured to measure current flowing into and out of the battery indicates zero.

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