Methods and apparatus for controlling vehicle battery charging

Abstract

This invention relates to a method and apparatus for controlling vehicle battery charging. The apparatus for controlling vehicle battery charging may include: a vehicle charging device configured to generate a boost voltage higher than the charging voltage of an electric vehicle power supply device disposed externally to the vehicle, and to charge a battery storing electricity for driving the vehicle; and a vehicle control unit configured to, when charging the battery with the boost voltage, determine whether powerline communication transmitting information about charging the battery using the electric vehicle power supply device disposed externally to the vehicle and providing the charging voltage to the vehicle charging device.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority to Korean Patent Application No. 10-2020-0073734, filed on June 17, 2020, the entire contents of which are incorporated herein by reference for all purposes. Technical Field

[0003] This invention relates to vehicles, and more particularly to methods and apparatus for controlling the charging of vehicle batteries. Background Technology

[0004] Electric vehicles use battery packs as a power source and motors (motors driven by the voltage of the battery pack) to generate driving force. When powered by the battery, the motors work as motors, and when the vehicle brakes, the motors work as generators. Thus, the motors convert the regenerative energy generated during braking into electrical energy and supply the converted electrical energy to the battery pack as a charging voltage.

[0005] Battery packs installed in electric vehicles typically consist of 25 or more modules connected in series, and are charged using commercial power sources when the state of charge (SOC) of the battery pack cannot guarantee stable travel to the destination after operation or during operation.

[0006] Environmentally friendly vehicles, such as electric vehicles (EVs) or plug-in hybrid electric vehicles (PHEVs), use electric vehicle supply equipment (EVSE) provided at charging stations to charge their batteries.

[0007] The information disclosed in the background section of this invention is intended only to enhance the understanding of the general background of this invention, and should not be construed as an admission or in any way implying that the information constitutes related technology known to those skilled in the art. Summary of the Invention

[0008] Various aspects of the present invention are dedicated to providing a method and apparatus for controlling vehicle battery charging, configured to prevent the main relay of the vehicle charging device connected to the external electric vehicle power supply (EVSE) from blowing and overvoltage from occurring in a capacitor located at the neutral point of the charging device when the power line communication (PLC) between the external electric vehicle power supply (EVSE) and the vehicle controller is closed, in the case of charging the vehicle battery using a boost voltage (e.g., 800V) higher than the charging voltage (e.g., 400V) of the external electric vehicle power supply (EVSE) (e.g., a fast charger).

[0009] Various aspects of the present invention are dedicated to providing a method for controlling vehicle battery charging, the method comprising: when charging a battery storing electricity for driving the vehicle using a boost voltage higher than the charging voltage of an electric vehicle power supply device located outside the vehicle, a vehicle control unit checks whether powerline communication for transmitting information for battery charging between the electric vehicle power supply device and the vehicle control unit is closed, the electric vehicle power supply device being located outside the vehicle and providing a charging voltage to a vehicle charging device that generates the boost voltage; when the powerline communication is closed, the vehicle control unit reduces the input voltage of the vehicle charging device output from the electric vehicle power supply device located outside the vehicle by utilizing the vehicle charging device that provides the boost voltage; the vehicle control unit determines whether the input voltage of the vehicle charging device reaches a voltage at which the electric vehicle power supply device located outside the vehicle is not operating; after determining that the input voltage of the vehicle charging device reaches a voltage at which the electric vehicle power supply device is not operating, the vehicle control unit determines whether the electric vehicle power supply device located outside the vehicle is closed based on the charging current output from the electric vehicle power supply device located outside the vehicle to the vehicle charging device; when the electric vehicle power supply device located outside the vehicle is closed, the vehicle control unit shuts off the main relay of the vehicle charging device and stops charging the battery.

[0010] The vehicle control unit can reduce the input voltage of the vehicle charging device, which is output from an electric vehicle power supply device located outside the vehicle, by utilizing an inverter and the drive motor of the vehicle charging device. The inverter is connected to the main relay and the drive motor and controls the drive motor.

[0011] The vehicle control unit can reduce the input voltage of the vehicle charging device, which is located outside the vehicle, to 0 by using an inverter and the drive motor of the vehicle charging device. The inverter is connected to the main relay and the drive motor and controls the drive motor.

[0012] Electric vehicle power supply equipment located outside the vehicle may include fast chargers.

[0013] When the charging current output from the electric vehicle power supply equipment located outside the vehicle to the vehicle charging device is 0, the vehicle control unit can determine that the electric vehicle power supply equipment located outside the vehicle is turned off.

[0014] Various aspects of the present invention are dedicated to providing an apparatus for controlling the charging of a vehicle battery, comprising: a vehicle charging device configured to generate a boost voltage higher than the charging voltage of an electric vehicle power supply device disposed outside the vehicle, and to charge a battery storing electricity for driving the vehicle; and a vehicle control unit configured to, when charging the battery using the boost voltage, determine whether powerline communication transmitting information about battery charging performed using the electric vehicle power supply device disposed outside the vehicle and providing the charging voltage to the vehicle charging device, wherein, when powerline communication is off, the vehicle control unit is configured to charge the battery using the vehicle charging device providing the boost voltage. The vehicle control unit reduces the input voltage of the vehicle charging device from the external electric vehicle power supply equipment. The vehicle control unit determines whether the input voltage of the vehicle charging device reaches the voltage at which the external electric vehicle power supply equipment is not in operation. After the input voltage of the vehicle charging device reaches the voltage at which the external electric vehicle power supply equipment is not in operation, the vehicle control unit determines whether the external electric vehicle power supply equipment is turned off based on the charging current output from the external electric vehicle power supply equipment to the vehicle charging device. When the external electric vehicle power supply equipment is turned off, the vehicle control unit turns off the main relay of the charging device and stops charging the battery.

[0015] The vehicle control unit can reduce the input voltage of the vehicle charging device, which is output from an electric vehicle power supply device located outside the vehicle, by utilizing an inverter and the drive motor of the vehicle charging device. The inverter is connected to the main relay and the drive motor and controls the drive motor.

[0016] The vehicle control unit can reduce the input voltage of the vehicle charging device, which is located outside the vehicle, to 0 by using an inverter and the drive motor of the vehicle charging device. The inverter is connected to the main relay and the drive motor and controls the drive motor.

[0017] Electric vehicle power supply equipment located outside the vehicle may include fast chargers.

[0018] When the charging current output from the electric vehicle power supply equipment located outside the vehicle to the vehicle charging device is 0, the vehicle control unit can determine that the electric vehicle power supply equipment located outside the vehicle is turned off.

[0019] The method and apparatus for controlling vehicle battery charging according to an exemplary embodiment of the present invention can prevent the main relay of the vehicle charging device connected to the external electric vehicle power supply from melting and the generation of overvoltage in the capacitor installed at the neutral point of the charging device when the vehicle battery is charged using a boost voltage that is higher than the charging voltage of the electric vehicle power supply device outside the vehicle, and when the power line communication (PLC) between the external electric vehicle power supply device and the vehicle control unit is closed.

[0020] The methods and apparatus of the present invention have other features and advantages that will be apparent from or will be set forth in detail in the accompanying drawings and subsequent embodiments incorporated herein, which together serve to explain the particular principles of the invention. Attached Figure Description

[0021] Figure 1 This is a flowchart describing a method for controlling the charging of a vehicle battery according to various exemplary embodiments of the present invention.

[0022] Figure 2 It is used to describe the application Figure 1 The diagram shows a method for controlling the charging of a vehicle battery and a device for controlling the charging of a vehicle battery.

[0023] It is understood, and should be understood, that the accompanying drawings are not drawn to scale, but rather are schematic simplifications illustrating various features to demonstrate the basic principles of the invention. Specific design features of the invention disclosed herein (including, for example, specific dimensions, orientations, positions, and shapes) will be determined in part by the specific environment in which they will be applied and used.

[0024] In these figures, throughout the multiple figures in the accompanying drawings, reference numerals refer to the same or equivalent parts of the invention. Detailed Implementation

[0025] Reference will now be made in detail to various embodiments of the invention, examples of which are illustrated in the accompanying drawings and described below. Although the invention will be described in conjunction with exemplary embodiments thereof, it should be understood that this specification is not intended to limit the invention to those exemplary embodiments. On the contrary, the invention is intended to cover not only the exemplary embodiments thereof, but also various alternatives, modifications, equivalents and other embodiments that may be included within the spirit and scope of the invention as defined by the appended claims.

[0026] To fully understand the present invention and the objectives achieved by practicing the present invention, reference can be made to the accompanying drawings, which illustrate exemplary embodiments of the invention, and the contents described therein.

[0027] The invention will now be described in detail with reference to the accompanying drawings, illustrating exemplary embodiments thereof. In the following description of exemplary embodiments of the invention, detailed descriptions of known configurations or functions incorporated herein will be omitted where such detailed description would likely obscure the subject matter of the invention. Throughout this specification, the same reference numerals presented in each drawing denote the same elements.

[0028] The terminology used in the exemplary embodiments of the present invention is for describing particular embodiments only and is not intended to limit the invention. Unless specifically described to the contrary in the context, singular expressions include plural expressions. In the exemplary embodiments, it will be understood that the terms "comprising" and "having" are intended to indicate the presence of the features, numbers, steps, operations, constituent elements, and components described in the specification or a combination thereof, and do not preclude the possibility of the presence or addition of one or more other features, numbers, steps, operations, constituent elements, and components or combinations thereof.

[0029] Throughout the following description and claims, when an element is described as being “connected to” another element, the element may be “directly connected to” the other element, or “electrically connected” or “mechanically connected” to the other element via a third element.

[0030] All terms used herein (including technical or scientific terms) have the same meaning as commonly understood by those skilled in the art, unless otherwise specified. Terms defined in general dictionaries shall be interpreted as having a meaning that matches the meaning in the context of the relevant field, and shall not be interpreted as having an idealized or overly formal meaning unless expressly defined in this specification.

[0031] According to related technologies, the high-voltage battery of an electric vehicle is charged by a fast electric vehicle power supply (EVSE) located outside the vehicle. Currently used fast EVSEs operate at a voltage range of 400V. To charge the vehicle's battery at 800V in the future, a device is needed to boost the 400V voltage to 800V. This device could be a multi-charge system utilizing a motor and an inverter. The vehicle battery, including the multi-charge system, can be charged by both a 400V and an 800V EVSE.

[0032] The EVSE exchanges information with the electric vehicle via power line communication (PLC). The exchanged information includes the start and end of vehicle charging and the charging current / voltage.

[0033] During fast charging, when no PLC connection is established between the EVSE and the electric vehicle, the EVSE receives no signal from the electric vehicle, causing the current output from the EVSE to gradually decrease. Therefore, the electric vehicle begins preparations to stop charging. When communication is interrupted, the electric vehicle measures the charging current of the EVSE, and when the charging current is less than or equal to 5A, the electric vehicle shuts off the main relay used to protect the high-voltage battery. However, when the charging current is greater than 5A, the electric vehicle immediately shuts off the relay 5 seconds after the measurement point. Therefore, the vehicle's relay shuts off while the charging current is flowing. When the vehicle's relay shuts off while the charging current is flowing, the relay will experience a fuse failure. Furthermore, during charging, when the electrical path is broken by shutting off the relay, the current output from the EVSE enters the capacitor located at the neutral point of the vehicle charging device (neutral point capacitor), thereby generating an overvoltage.

[0034] Figure 1 This is a flowchart describing a method for controlling the charging of a vehicle battery according to various exemplary embodiments of the present invention. Figure 2 It is used to describe the application Figure 1 The diagram shows a method for controlling the charging of a vehicle battery and a device for controlling the charging of a vehicle battery.

[0035] refer to Figure 1 and Figure 2 During the inspection operation 100, when the vehicle control unit (VCU) or vehicle controller 220 can charge the battery 232 storing electricity for driving the vehicle using a boost voltage (e.g., 800V) that is higher than the charging voltage (e.g., 400V) of the EVSE located outside the vehicle (e.g., an electric vehicle), the vehicle charging device that generates the boost voltage provides a charging voltage and checks (determines) whether the PLC transmitting information for battery charging between the EVSE 250 located outside the vehicle and the VCU 220 is turned off.

[0036] For example, information used for charging the battery may include charging start information, charging end information, charging current, or charging voltage. For example, situations where the PLC is off (not executing PLC) may include: the VCU 220 not receiving a power line signal, the time during which no power line signal is received being equal to or longer than a predetermined time period, or the strength of the received power line signal being less than or equal to a predetermined strength.

[0037] When power line communication is off, the EVSE 250 can reduce the charging current output to the vehicle charging device through its output terminal 252. Like a fast charger performing fast charging, the EVSE 250 can perform current control for charging the battery 232.

[0038] like Figure 2 As shown, the vehicle may include: a vehicle control module (VCM) 200, a vehicle controller (VCU) 220, a battery management system (BMS) 230, and a motor control unit (or motor controller) 240. The vehicle control module (VCM) 200 includes a charging control module (CCM) 210 that uses an EVSE 250 to execute a PLC. The battery management system (BMS) 230 includes a battery (e.g., a high-voltage battery) 232 that stores electricity for driving the vehicle and manages the battery. The motor control unit (or motor controller) 240 includes a drive motor 244 that drives the vehicle and controls the drive motor.

[0039] The vehicle charging device includes a BMS 230 and an MCU 240, and can be a multi-charger for charging the battery 232 using either a boost voltage or a charging voltage. An operational embodiment of the vehicle charging device is described in Korean Patent Application Publication No. 10-2019-0040120 (US Patent Publication No. US 2019 / 0109462).

[0040] BMS 230 may include: battery 232, main relay, first relay (800V relay), second relay ((-) terminal relay), and third relay (e.g., 400V). The main relay is used to protect battery 232; the first relay (800V relay) is used to charge the battery using a boost voltage (e.g., 800V); the second relay ((-) terminal relay) is connected to the ground wire of the vehicle charging device; and the third relay (400V) is used to charge the battery using a charging voltage (e.g., 400V). In another exemplary embodiment of the invention, BMS 230 may omit (exclude) battery 232.

[0041] MCU 240 may include: inverter 242, drive motor 244, capacitor connected between the input terminals of inverter 242, and capacitor located at the neutral point of drive motor (neutral terminal capacitor). Inverter 242 may include a switch, such as an insulated gate bipolar transistor (IGBT). In another exemplary embodiment of the invention, MCU 240 may omit (exclude) drive motor 244.

[0042] The VCU 220 can communicate with the VCM 200, BMS 230, and MCU 240 via a Controller Area Network (CAN). The VCU 220 may include the VCM 200, BMS 230, and MCU 240.

[0043] The VCU 220 can function as an electronic control unit (ECU) to control the overall operation of the vehicle. For example, the VCU 220 can be one or more microprocessors or hardware including a microprocessor (e.g., a microcomputer) that is operated by a program (control logic), and the program can include a series of instructions for performing methods of controlling the charging of the vehicle battery according to various exemplary embodiments of the invention. These instructions can be stored in the memory of the vehicle or the VCU 220.

[0044] Devices that control vehicle battery charging may include VCU 220 and vehicle charging unit.

[0045] according to Figure 1 As shown in operation 120, when the PLC is off, the VCU 220 can reduce the input voltage of the vehicle charging device output from the EVSE 250 located outside the vehicle by utilizing the vehicle charging device that provides a boost voltage. For example, the VCU 220 can linearly reduce the input voltage of the vehicle charging device output from the EVSE 250 located outside the vehicle to 0V by utilizing the drive motor 244 of the vehicle charging device that provides a boost voltage and the inverter 242 that controls the drive motor (or the drive motor and the inverter connected to the drive motor).

[0046] According to operation 130, VCU 220 can determine whether the input voltage of the vehicle charging device has reached the voltage at which the EVSE 250 located outside the vehicle does not operate (the lower operating limit voltage of the EVSE). When the input voltage of the vehicle charging device decreases, the output voltage through the output terminal 252 of the EVSE 250 located outside the vehicle will also decrease.

[0047] According to operation 140, after the input voltage of the vehicle charging device reaches a voltage at which the EVSE 250 does not operate, the VCU 220 can determine whether the EVSE 250 located outside the vehicle is turned off based on the charging current output from the EVSE 250 located outside the vehicle to the vehicle charging device. For example, when the charging current output from the EVSE 250 located outside the vehicle to the vehicle charging device is 0A, the VCU 220 can determine that the EVSE 250 located outside the vehicle is turned off.

[0048] According to operation 150, when the EVSE 250 located outside the vehicle is turned off, the VCU 220 can stop (interrupt) charging of the battery 232 by turning off the main relay of the vehicle charging device. Therefore, it is possible to prevent the main relay of the vehicle charging device connected to the EVSE outside the vehicle from blowing and to prevent overvoltage from occurring in the capacitor located at the neutral point of the charging device.

[0049] In another exemplary embodiment of the invention, when the main relay is turned off, the 800V relay and the (-) terminal relay can also be turned off.

[0050] The constituent elements, "units," blocks, or modules used in exemplary embodiments of the present invention can be implemented by software or hardware, or by a combination of software and hardware. The software may include tasks, classes, subroutines, processes, objects, threads of execution, and programs executed in predetermined areas of memory. The hardware may include field-programmable gate arrays (FPGAs) or application-specific integrated circuits (ASICs). Constituent elements, "units," etc., may also be included in computer-readable storage media, and a portion thereof may be distributed across multiple computers.

[0051] Additionally, terms related to the control device, such as "controller," "control unit," "control device," or "control module," refer to a hardware device including a memory and a processor configured to execute one or more steps interpreted as an algorithmic structure. The memory stores the algorithmic steps, and the processor executes the algorithmic steps to perform one or more processes of methods according to various exemplary embodiments of the invention. A controller according to an exemplary embodiment of the invention can be implemented using non-volatile memory and a processor configured to store algorithms for controlling the operation of various components of a vehicle or data regarding software commands for executing the algorithms, the processor being configured to perform the aforementioned operations using the data stored in the memory. The memory and processor can be separate chips. Alternatively, the memory and processor can be integrated into a single chip. The processor can be implemented as one or more processors.

[0052] The control device may be at least one microprocessor operated by a predetermined program, which may include a series of commands for performing methods included in the foregoing various exemplary embodiments of the present invention.

[0053] The aforementioned invention can also be implemented as computer-readable code on a computer-readable recording medium. A computer-readable recording medium is any data storage device that can store data that can subsequently be read by a computer system. Examples of computer-readable recording media include: hard disk drives (HDDs), solid-state drives (SSDs), silicon disk drives (SDDs), read-only memory (ROM), random access memory (RAM), CD-ROMs, magnetic tapes, floppy disks, optical data storage devices, etc., and are implemented as carrier waves (e.g., transmitted over the Internet).

[0054] In various exemplary embodiments of the present invention, each of the above operations can be performed by a controller, and the controller can be configured by multiple controllers or a single integrated controller.

[0055] For ease of interpretation and precise definition of the appended claims, the terms “upper,” “lower,” “inner,” “outer,” “above,” “below,” “upward,” “downward,” “front,” “back,” “inner side,” “outer side,” “inward,” “outer,” “internal,” “external,” “inner,” “external,” “forward,” and “backward” are used to describe features of the exemplary embodiments with reference to the positions of these features shown in the accompanying drawings. It will be further understood that the term “connection” or its derivatives refer to both direct and indirect connections.

[0056] The foregoing description of specific exemplary embodiments of the present invention is for illustrative and descriptive purposes. It is not intended to be exhaustive or to limit the invention to the precise embodiments disclosed, and it will be apparent that modifications and variations can be made based on the foregoing teachings. The exemplary embodiments were chosen and described to explain the specific principles of the invention and its practical application, thereby enabling those skilled in the art to implement and utilize various exemplary embodiments of the invention, as well as their various alternatives and modifications. The scope of the invention is intended to be defined by the appended claims and their equivalents.

Claims

1. A method of controlling charging of a vehicle battery, the method comprising: checking, by a vehicle control unit, whether power line communication is off when charging a vehicle battery storing electric power for driving a vehicle with a boosted voltage higher than a charging voltage of an electric vehicle supply device, the power line communication transmitting information for charging the vehicle battery between the electric vehicle supply device and the vehicle control unit, wherein the electric vehicle supply device is disposed outside the vehicle and configured to supply the charging voltage to a vehicle charging device that generates the boosted voltage; reducing, by the vehicle control unit, an input voltage of the vehicle charging device output from the electric vehicle supply device by using the vehicle charging device when it is determined that the power line communication is off; determining, by the vehicle control unit, whether the input voltage of the vehicle charging device reaches a voltage at which the electric vehicle supply device does not operate; determining, by the vehicle control unit, whether the electric vehicle supply device is off according to a charging current output from the electric vehicle supply device to the vehicle charging device when it is determined that the input voltage of the vehicle charging device reaches the voltage at which the electric vehicle supply device does not operate; turning off, by the vehicle control unit, a main relay connected to the vehicle battery and stopping charging of the vehicle battery when it is determined that the electric vehicle supply device is off.

2. The method of claim 1, wherein, the vehicle control unit is configured to reduce the input voltage of the vehicle charging device output from the electric vehicle supply device by using a drive motor of the vehicle charging device and an inverter connected to the main relay and the drive motor and controlling the drive motor.

3. The method of claim 1, wherein, the vehicle control unit is configured to reduce the input voltage of the vehicle charging device output from the electric vehicle supply device to 0 by using the drive motor of the vehicle charging device and the inverter connected to the main relay and the drive motor and controlling the drive motor.

4. The method of claim 3, wherein, the vehicle control unit is configured to linearly reduce the input voltage to 0.

5. The method of claim 1, wherein, the electric vehicle supply device includes a fast charger.

6. The method of claim 1, wherein, the vehicle control unit is configured to determine that the electric vehicle supply device is off when the charging current output from the electric vehicle supply device to the vehicle charging device is 0.

7. The method of claim 1, wherein, the power line communication is determined to be off when the vehicle control unit does not receive a power line signal, when the vehicle control unit does not receive the power line signal for a predetermined period of time, or when the strength of the power line signal received by the vehicle control unit is less than or equal to a predetermined strength.

8. The method of claim 1, wherein, the vehicle control unit includes: a processor; and a non-volatile storage medium having recorded thereon a program for executing the method of claim 1 and executed by the processor. 9.An apparatus of controlling charging of a vehicle battery, the apparatus comprising: a vehicle charging device configured to generate a boosted voltage higher than a charging voltage of an electric vehicle supply device and to charge a vehicle battery storing electric power for driving a vehicle; a vehicle control unit including a processor and configured to determine whether power line communication is off when charging a vehicle battery with a boosted voltage, the power line communication transmitting information on charging the vehicle battery performed with an electric vehicle supply device, wherein the electric vehicle supply device is disposed outside the vehicle and configured to supply a charging voltage to a vehicle charging device, wherein, upon determining that the power line communication is off, the vehicle control unit is configured to reduce the input voltage of the vehicle charging device from the electric vehicle supply device by using the vehicle charging device, the vehicle control unit is configured to determine whether the input voltage of the vehicle charging device reaches a voltage at which the electric vehicle supply device does not operate, upon determining that the input voltage of the vehicle charging device reaches the voltage at which the electric vehicle supply device does not operate, the vehicle control unit is configured to determine whether the electric vehicle supply device is off based on a charging current output from the electric vehicle supply device to the vehicle charging device, upon determining that the electric vehicle supply device is off, the vehicle control unit is configured to turn off a main relay of the vehicle charging device and stop charging the vehicle battery, wherein the main relay is connected to the vehicle battery.

10. The apparatus for controlling charging of a vehicle battery of claim 9, wherein, the vehicle control unit is configured to reduce the input voltage of the vehicle charging device from the electric vehicle supply device by using an inverter and a drive motor of the vehicle charging device, the inverter being connected to the main relay and the drive motor and controlling the drive motor.

11. The apparatus for controlling charging of a vehicle battery of claim 9, wherein, the vehicle control unit is configured to reduce the input voltage of the vehicle charging device from the electric vehicle supply device to 0 by using an inverter and a drive motor of the vehicle charging device, the inverter being connected to the main relay and the drive motor and controlling the drive motor.

12. The apparatus for controlling charging of a vehicle battery of claim 11, wherein, the vehicle control unit is configured to linearly reduce the input voltage of the vehicle charging device from the electric vehicle supply device to 0.

13. The apparatus for controlling charging of a vehicle battery of claim 9, wherein, the electric vehicle supply device includes a fast charger.

14. The apparatus for controlling charging of a vehicle battery of claim 9, wherein, upon determining that the charging current output from the electric vehicle supply device to the vehicle charging device is 0, the vehicle control unit is configured to determine that the electric vehicle supply device is off.

15. The apparatus for controlling charging of a vehicle battery of claim 9, wherein, the power line communication is determined to be off when the vehicle control unit does not receive a power line signal, when the vehicle control unit does not receive the power line signal for a predetermined period of time, or when the strength of the power line signal received by the vehicle control unit is less than or equal to a predetermined strength.

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