Power supply system for electric vehicle

Abstract

Provided is a power supply system for an electric vehicle, the system being capable of accurately obtaining the insulation resistance of a power supply line after the electric vehicle collides. The power supply system for an electric vehicle includes: a first battery for storing power for traveling; a power supply line through which the power of the first battery is transmitted; a relay capable of disconnecting the first battery and the power supply line; a second battery capable of supplying a power supply voltage lower than the voltage of the first battery; a DC / DC converter capable of boosting the voltage of the second battery and outputting the voltage to the power supply line; a controller for detecting the occurrence of a collision of the electric vehicle; and a measuring instrument for measuring a leakage current through the power supply line. The controller, when detecting the occurrence of a collision, after the relay disconnects the first battery and the power supply line, causes the DC / DC converter to output the voltage boosted to a first voltage to the power supply line, and measures the electric leakage with the measuring instrument.

Description

Electric vehicle power supply system

[0001] The present invention relates to a power supply system for an electric vehicle.

[0002] Patent Document 1 describes a method of detecting whether or not the insulation resistance of equipment has decreased when a vehicle collides, using an insulation resistance decrease detector.

[0003] JP 2011-155743 A

[0004] Even if a vehicle crashes, it would be convenient if high-voltage electrical equipment could be used even if it was partially damaged. However, in order to use high-voltage electrical equipment even if it was partially damaged, it is necessary to accurately determine the degree to which the insulation resistance of the high-voltage power supply line has decreased.

[0005] An object of the present invention is to provide a power supply system for an electric vehicle that can accurately measure a decrease in insulation resistance after a vehicle collision.

[0006] One aspect of the present invention provides a power supply system for an electric vehicle comprising: a first battery that stores power for driving; a power supply line through which the power of the first battery is transmitted; a relay capable of disconnecting the first battery from the power supply line; a second battery that can supply a power supply voltage lower than that of the first battery; a DC / DC converter that can boost the voltage of the second battery and output it to the power supply line; a controller that detects the occurrence of a vehicle collision; and a measuring instrument that measures leakage current through the power supply line, wherein when the controller detects the occurrence of a collision, the relay disconnects the first battery from the power supply line, and then the controller outputs a voltage boosted to a first voltage via the DC / DC converter to the power supply line, and measures the leakage current using the measuring instrument.

[0007] According to the present invention, the first voltage obtained by boosting the voltage of the second battery is output to the power supply line and the leakage current is measured, so that the insulation resistance of the power supply line after a vehicle collision can be accurately determined.

[0008] It is a block diagram showing an electric vehicle equipped with a power supply system according to an embodiment of the present invention. It is a circuit diagram showing details of the periphery of a power supply line. It is a flowchart showing the procedure of a collision handling process executed by a controller. It is a circuit diagram showing a state when measuring insulation resistance after a collision. It is a circuit diagram showing a power transmission state after a collision.

[0009] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0010] Fig. 1 is a block diagram showing an electric vehicle equipped with a power supply system according to an embodiment of the present invention. In Fig. 1, the peripheral circuitry of a power supply line L1 is shown in a simplified form. Fig. 2 is a circuit diagram showing details of the periphery of the power supply line in Fig. 1.

[0011] 1 includes drive wheels 2, a traction motor 3 that generates power for the drive wheels 2, a traction inverter 4 that drives the traction motor 3, a first battery 6 that supplies power to the traction inverter 4, an air conditioner 7 that is driven by the power of the first battery 6, and a controller 10 that controls each component. The electric vehicle 1 further includes a power supply line L1 through which power from the first battery 6 is transmitted, a DC / DC converter 8 connected to the power supply line L1, an SMR relay provided on the power supply line L1, a second battery 9 that outputs a voltage lower than the output voltage of the first battery 6, and a measuring instrument 11 that measures leakage current through the power supply line L1. The electric vehicle 1 further includes a driving operation unit 15 that receives driving operations from a driver, a collision sensor 12 that detects a collision of the electric vehicle 1, and an operation panel 13 through which a passenger inputs an operation command for the air conditioner 7.

[0012] The power supply system 20 of this embodiment corresponds to the configuration including the power supply line L1, the relay SMR, the driving inverter 4, the first battery 6, the air conditioning device 7, the DC / DC converter 8, the second battery 9, the controller 10, the measuring instrument 11, and the collision sensor 12, among the above-mentioned components.

[0013] The first battery 6 is connected to the power supply line L1 via a relay SMR. As shown in FIG. 2 , the power supply line L1 has a pair of electrical paths to which the anode and cathode of the first battery 6 are respectively connected. The relay SMR is a so-called system main relay, and is controlled to open and close by a controller 10. The relay SMR includes a pair of switches re1 and re2, each of which is provided on the pair of electrical paths of the power supply line L1. The relay SMR also includes a pre-charge resistor R and a pre-charge switch re3 for reducing inrush current from the first battery 6 to the power supply line L1 when switching from an open state to a closed state. The power supply line L1 is also connected to a traction inverter 4, an air conditioner 7, and a DC / DC converter 8. Both of the pair of electrical paths of the power supply line L1 are insulated from the vehicle frame.

[0014] The first battery 6 outputs a high power supply voltage of 100 V or 200 V. The first battery 6 is, for example, a lithium ion secondary battery, a nickel-metal hydride secondary battery, or the like, but the type is not particularly limited.

[0015] The second battery 9 outputs a power supply voltage, such as 12 V or 24 V, that is lower than the voltage of the first battery 6. The second battery 9 is, for example, a lead battery, but the type is not particularly limited. The second battery 9 supplies power to low-voltage devices such as the controller 10, but a separate battery may be provided to supply power to the low-voltage devices, and the second battery 9 may be an auxiliary battery.

[0016] The DC / DC converter 8 steps down the power supply voltage of the first battery 6 and sends it to the second battery 9, thereby charging the second battery 9 or supplying the power supply voltage to low-voltage devices. Furthermore, the DC / DC converter 8 is a bidirectional converter capable of stepping up and down, and when the first battery 6 is disconnected from the power supply line L1, it can step up the voltage of the second battery 9 and output the stepped-up voltage (hereinafter referred to as the "step-up voltage") to the power supply line L1. The voltage value of the step-up voltage of the DC / DC converter 8 can be controlled by the controller 10.

[0017] The DC / DC converter 8 has two terminals t1 and t2 to which the power supply line L1 is connected and two terminals t3 and t4 to which the low-voltage power supply line L2 is connected. Both terminals t1 and t2 are insulated from the vehicle frame, while terminal t4 is grounded to the vehicle frame. When the relay SMR is open and a boosted voltage is supplied from the DC / DC converter 8 to the power supply line L1, if there is no leakage current in the power supply line L1 or the devices connected to the power supply line L1, the currents flowing through the terminals t1 and t2 will be opposite in direction but identical in magnitude. On the other hand, if there is leakage current in the power supply line L1 or the devices connected to the power supply line L1, the currents flowing through the terminals t1 and t2 will differ in magnitude by the amount of the leakage current. The leakage current is recovered from terminal t4, for example, via the vehicle frame. However, the DC / DC converter 8 may have a dedicated terminal for recovering the leakage current.

[0018] The leakage current measuring instrument 11 corresponds to a configuration having a first ammeter i1 that measures the current at terminal t1 and a second ammeter i2 that measures the current at terminal t2 of the DC / DC converter 8. When the relay SMR is open and power is being supplied from the DC / DC converter 8 to the power supply line L1, the leakage current from the power supply line L1 or a device connected to the power supply line L1 can be measured based on the difference between the measurement value of the first ammeter i1 and the measurement value of the second ammeter i2.

[0019] The air conditioner 7 includes a heater device for heating the vehicle cabin, a heat pump device for cooling the vehicle cabin, or both. The vehicle cabin refers to the space in which passengers sit in the electric vehicle 1. The air conditioner 7 is electrically driven.

[0020] The driving operation unit 15 (see FIG. 1) includes a steering unit 15a such as a steering wheel, a braking operation unit 15b such as a brake pedal, and an acceleration operation unit 15c such as an accelerator pedal. The driving operation unit 15 is configured to be operable by a driver, but may also be configured to be operated by an automated driving system.

[0021] The collision sensor 12 (see FIG. 1) is, for example, a sensor that detects the deployment of an airbag, but may be any other sensor capable of detecting a collision, such as an acceleration sensor for impact detection.

[0022] The controller 10 is a microcomputer such as an ECU (Electronic Control Unit), and operates according to a control program stored in a storage unit 10a. The controller 10 receives signals from a driving operation unit 15 and controls the driving inverter 4 to drive the electric vehicle 1. In addition, the controller 10 receives input from an operation panel 13 and controls the operation of the air conditioning device 7 in accordance with the input. In addition, if a collision of the electric vehicle 1 occurs, the controller 10 performs processing to deal with the collision.

[0023] <Collision handling process> Fig. 3 is a flowchart showing the procedure of the collision handling process executed by the controller. Fig. 4 is a circuit diagram showing the state when the insulation resistance is measured after a collision. Fig. 5 is a circuit diagram showing the power transmission state after a collision.

[0024] The controller 10 starts a collision handling process when the system of the electric vehicle 1 is started. When the collision handling process starts, the controller 10 monitors whether a collision has occurred in the electric vehicle 1 based on the output of the collision sensor 12 (step S1), and if a collision is detected, proceeds to the next step.

[0025] When a collision occurs and the process proceeds to the next step, the controller 10 switches the relay SMR from a closed state to an open state, thereby disconnecting the first battery 6 from the power supply line L1 (step S2). Next, the controller 10 performs a discharge process by activating a discharge function that removes high voltage remaining in the power supply line L1 (step S3). The discharge function may be provided, for example, in the power supply line L1 or in each device connected to the power supply line L1. The discharge function is realized, for example, by a circuit that connects a current path between a pair of power supply lines L1 via a large resistance. The discharge process in step S3 releases charge accumulated in input capacitors and other components of the devices connected to the power supply line L1, thereby reducing the voltage on the power supply line L1.

[0026] When the discharge process is completed, the controller 10 causes the DC / DC converter 8 to perform a boost operation, thereby boosting the voltage of the second battery 9 to the first voltage V1 [V] and outputting the boosted voltage to the power supply line L1 (step S4), as shown in Fig. 4. If the output of the first voltage V1 reduces the insulation resistance Rx of the power supply line L1, as shown in Fig. 4, a leakage current ΔI occurs.

[0027] The first voltage V1 [V] is lower than the voltage of the first battery 6 and higher than the voltage of the second battery 9. More specifically, the first voltage V1 is set to a voltage below a level at which direct contact with the human body is dangerous (for example, a voltage exceeding 60 V DC). The above-mentioned dangerous voltage may be set lower by the manufacturer with a margin. On the other hand, the first voltage V1 should be set not too low (for example, 20 V or higher, preferably 30 V or higher, more preferably 40 V or higher) so that small leakage currents can be accurately measured. As an example, in this embodiment, the first voltage V1 is set to 48 V DC.

[0028] Next, the controller 10 calculates the difference between the currents at the terminals t1 and t2 as the leakage current ΔI [A] based on the measurement values ​​of the first ammeter i1 and the second ammeter i2 of the DC / DC converter 8, and measures the insulation resistance Rx [Ω] of the power supply line L1 (step S5). The insulation resistance Rx [Ω] can be calculated as Rx = ΔI / V1.

[0029] Next, the controller 10 calculates the value of the second voltage V2 that can be output to the power line L1 based on the insulation resistance Rx measured in step S5 (step S6). A voltage that satisfies a preset insulation resistance standard (unit: Ω / V) can be applied as the second voltage V2. The insulation resistance standard is a reference value set to suppress the occurrence of abnormalities and is an index indicating a standard for how many ohms of insulation resistance are required for a given applied voltage. The insulation resistance standard is, for example, 500 Ω / V, but may be set higher by the manufacturer to allow for a margin, or may be set lower to take into account the effects of other leakage current countermeasures.

[0030] For example, if the insulation resistance standard A is 500 [Ω / V] and the insulation resistance Rx calculated in step S5 is 60,000 Ω, then in step S6, the second voltage V2 is calculated as follows: V2 = Rx / A = 60,000 / 500 = 120 [V]. Note that if the maximum voltage that satisfies the insulation resistance standard is greater than the voltage of the first battery 6 or greater than the maximum voltage that can be generated by the first battery 6 and the DC / DC converter 8, the controller 10 may set the above maximum voltage as the second voltage V2.

[0031] Once the second voltage V2 is determined, as shown in FIG. 5, the controller 10 drives the DC / DC converter 8 to cause the DC / DC converter 8 to output the second voltage V2 to the power supply line L1 (step S7).

[0032] As shown in FIG. 5 , when the driver operates the electric vehicle 1, the traction inverter 4 is driven using the second voltage V2 as a power supply voltage, thereby operating the traction motor 3. Because the second voltage V2 output to the power supply line L1 is lower than the normal voltage before the collision, the traction motor 3 cannot be driven with high output, but the low-output traction motor 3 can be driven to allow the electric vehicle 1 to evacuate the scene of the collision. Furthermore, when the passenger operates the air conditioning device 7, the air conditioning device 7 is driven using the second voltage V2 as a power supply voltage, and the air conditioning device 7 can regulate the cabin temperature even though it cannot output a large amount of power. This prevents the cabin temperature from becoming extremely low in extremely cold regions or extremely high in the hot sun.

[0033] The program for the collision handling process described above is stored in a non-transitory computer readable medium such as the storage unit 10a of the controller 10. The controller 10 may be configured to read and execute a program stored in a portable non-transitory recording medium. The portable non-transitory recording medium may store the program for the collision handling process described above.

[0034] As described above, according to the power supply system 20 of the electric vehicle 1 of this embodiment, when the controller 10 detects the occurrence of a collision, after the relay SMR disconnects the first battery 6 from the power supply line L1, the controller 10 outputs a voltage obtained by boosting the voltage of the second battery 9 to the first voltage V1 via the DC / DC converter 8 to the power supply line L1, and measures the leakage current with the measuring instrument 11. In this way, by using the first voltage V1 obtained by boosting the voltage of the second battery 9, it is possible to accurately measure a small leakage current, and therefore it is possible to accurately determine the insulation resistance of the power supply line L1 and the devices connected to the power supply line L1 after the collision.

[0035] Furthermore, according to the power supply system 20 of the electric vehicle 1 of this embodiment, the first voltage V1 is set to a voltage of not more than 60 V. Therefore, even if the insulation resistance of the power supply line L1 or the devices connected to the power supply line L1 is reduced due to a collision of the electric vehicle 1, it is possible to prevent adverse effects from occurring due to the first voltage V1 applied to the power supply line L1.

[0036] Furthermore, according to the power supply system 20 of the electric vehicle 1 of this embodiment, after measuring the leakage current, the DC / DC converter 8 outputs to the power supply line L1 a second voltage V2 corresponding to the insulation resistance of the power supply line L1 calculated from the leakage current. The output of the second voltage V2 prevents a large leakage current from occurring even if the insulation resistance of the power supply line L1 is reduced due to a collision. Furthermore, the second voltage V2 supplies power to devices connected to the power supply line L1, enabling the devices to be driven, even if imperfectly. In addition, since the second voltage V2 is generated by boosting the voltage of the second battery 9 using the DC / DC converter 8, the first voltage V1 for measuring the insulation resistance after a collision and the second voltage V2 for driving the devices after a collision can be generated using the same DC / DC converter 8 and second battery 9. This allows the overall volume of the power supply system 20 to be reduced.

[0037] Furthermore, in the power supply system 20 of the electric vehicle 1 of this embodiment, the measuring instrument 11 that measures the earth leakage current is the first ammeter i1 and the second ammeter i2 that measure the currents at the terminals t1 and t2 of the DC / DC converter 8, respectively. This configuration makes it possible to omit providing a separate component for earth leakage detection, thereby enabling the downsizing of the power supply system 20. Furthermore, the earth leakage current can be accurately measured.

[0038] Furthermore, according to the power supply system 20 of the electric vehicle 1 of this embodiment, the traction inverter 4 and the air conditioner 7 are connected to the power supply line L1 and can operate by receiving the second voltage as the power supply voltage. Therefore, after a collision occurs in the electric vehicle 1, the driving of the traction inverter 4 enables the electric vehicle 1 to travel to safety, and the driving of the air conditioner 7 can reduce the harsh environment inside the vehicle cabin due to weather outside the vehicle.

[0039] The above describes an embodiment of the present invention. However, the present invention is not limited to the above embodiment. For example, in the above embodiment, a battery that supplies power supply voltage to low-voltage devices is used as the second battery. However, for example, some of the battery cells included in the first battery may be used as the second battery. After a collision of the electric vehicle, the battery cells included in the first battery 6 may be diagnosed, and if any battery cells are found to be usable, they may be used as the second battery.

[0040] Furthermore, in the above embodiment, an example has been shown in which the measuring instruments for measuring the earth leakage current are the first ammeter i1 and the second ammeter i2, which measure the currents at the terminals t1 and t2 of the DC / DC converter 8, respectively. However, the measuring instruments for measuring the earth leakage current are not limited to the above example, and various configurations may be applied as long as they can measure the earth leakage current that occurs in a state in which the first voltage V1 is output.

[0041] In the above embodiment, an example was shown in which, after a collision occurs, the first voltage V1 is output to the power supply line L1 after the power supply line L1 is discharged. However, by starting the output of the first voltage V1 to the power supply line L1 during the discharge process, the voltage of the power supply line L1 may be maintained at the first voltage V1 without being temporarily reduced to near zero, and the process may proceed to the insulation resistance measurement. In addition, in the above embodiment, when the first voltage V1 is output to the power supply line L1 to perform the insulation resistance measurement process, the device connected to the power supply line L1 may be switched off before the insulation resistance measurement process is performed. Other details shown in the embodiment may be modified as appropriate without departing from the spirit of the invention.

[0042] The present invention can be used in a power supply system for an electric vehicle.

[0043] REFERENCE SIGNS LIST 1 Electric vehicle 2 Drive wheels 3 Traction motor 4 Traction inverter 6 First battery 7 Air conditioner 8 DC / DC converter 9 Second battery 10 Controller 10a Memory unit 11 Measuring instrument 12 Collision sensor 13 Operation panel 15 Driving operation unit 20 Power supply system L1 Power supply line SMR relay V1 First voltage V2 Second voltage

Claims

1. A power supply system for an electric vehicle comprising: a first battery that stores power for driving; a power supply line through which the power of the first battery is transmitted; a relay that can disconnect the first battery from the power supply line; a second battery that can supply a power supply voltage lower than that of the first battery; a DC / DC converter that can boost the voltage of the second battery and output it to the power supply line; a controller that detects the occurrence of a collision of the electric vehicle; and a measuring instrument that measures leakage current through the power supply line, wherein when the controller detects the occurrence of a collision, the relay disconnects the first battery from the power supply line, and then the controller outputs a voltage that has been boosted to a first voltage via the DC / DC converter to the power supply line, and the measuring instrument measures the leakage current.

2. The power supply system for an electric vehicle according to claim 1, wherein the first voltage is lower than the voltage of the first battery and is a voltage of 60V or less.

3. The power supply system for an electric vehicle according to claim 1, wherein after measuring the leakage current, the controller supplies a voltage boosted to a second voltage via the DC / DC converter to the power supply line, the second voltage being a voltage according to the insulation resistance of the power supply line corresponding to the measurement result of the leakage current.

4. The power supply system for an electric vehicle according to claim 1, wherein the measuring instruments are a first ammeter and a second ammeter that measure the current at two terminals of the DC / DC converter that outputs the boosted voltage.

5. The power supply system for an electric vehicle according to claim 3, wherein a driving inverter and an air conditioning device are connected to the power supply line, and the driving inverter and the air conditioning device are operable by receiving the second voltage as a power supply voltage.

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