Power supply system for electric vehicle

Abstract

The present invention accurately ascertains the resistance value of a power line that transmits power of a battery, thereby enabling accurate prediction of the amount of heat generated when a large current flows through the power line. This power supply system for an electric vehicle comprises: an electric motor that drives a drive wheel; a battery that accumulates power; an inverter that drives the electric motor on the basis of the power of the battery; a power line that transmits the power between the battery and the inverter; a plurality of sensors that measure the current flowing through the power line and the voltage between a plurality of points on the power line; and a control circuit. The plurality of sensors include a battery current sensor that measures the current of the battery and a battery voltage sensor that measures the voltage of the battery. The control circuit calculates the resistance value of the power line on the basis of the outputs of the plurality of sensors.

Description

Power supply system for electric vehicle

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

[0002] Patent Document 1 discloses measuring a resistance value of a bus bar that connects a plurality of battery modules in series in an electric vehicle. The control device determines that the battery is abnormal when the resistance value is equal to or higher than a threshold value.

[0003] Japanese Unexamined Patent Application Publication No. 2020-161315

[0004] In an electric vehicle, high power is obtained by passing a large current through a power line. Furthermore, if a large current can be passed through the power line, faster battery charging can be achieved. On the other hand, since the power line has a slight resistance, heat is generated when a large current flows therethrough.

[0005] In conventional electric vehicles, the resistance value of a power line that transmits power from a battery has not been accurately grasped. Therefore, there has been a problem that the amount of heat generation when a large current flows cannot be accurately predicted. If accurate prediction cannot be performed, an excessive safety margin is set, the power of the electric vehicle is restricted more than necessary, and high-speed charging is restricted more than necessary.

[0006] An object of the present invention is to accurately grasp the resistance value of a power line that transmits power from a battery, and to enable accurate prediction of the amount of heat generation when a large current flows through the power line.

[0007] A power supply system for an electric vehicle according to one aspect of the present invention comprises: an electric motor that drives drive wheels; a battery that stores electric power; an inverter that drives the electric motor based on the electric power from the battery; a power line that transmits electric power between the battery and the inverter; a plurality of sensors that respectively measure a current flowing through the power line and voltages between a plurality of points on the power line; and a control circuit, wherein the plurality of sensors include a battery current sensor that measures a current of the battery and a battery voltage sensor that measures a voltage of the battery, and the control circuit calculates a resistance value of the power line based on outputs from the plurality of sensors.

[0008] According to the present invention, the resistance value of power lines can be measured even after the electric vehicle has been shipped. Therefore, the resistance value of the power lines can be accurately determined, and the amount of heat generated when a large current flows through the power lines can be accurately predicted.

[0009] This is a block diagram showing an electric vehicle equipped with a power supply system according to an embodiment of the present invention. This is a block diagram showing a power supply system according to Embodiment 1 of the present invention. This is a flowchart showing the procedure for resistance measurement processing in Embodiment 1. This is a flowchart showing the resistance measurement processing in Embodiment 2 of the present invention. This is a flowchart showing the resistance measurement processing in Embodiment 3 of the present invention. This is a flowchart showing the resistance measurement processing in Embodiment 4 of the present invention. This is a block diagram showing a power supply system according to Embodiment 5 of the present invention. This is the first part of a flowchart showing the procedure for resistance measurement processing in Embodiment 5. This is the second part of a flowchart showing the procedure for resistance measurement processing in Embodiment 5. This is a block diagram showing a power supply system according to Embodiment 6 of the present invention. This is a diagram illustrating each section of the power line in Embodiment 6. This is a diagram illustrating each section of the power line in Embodiment 6. This is a flowchart showing the procedure for resistance measurement processing in Embodiment 6. This is a diagram illustrating the resistance value of the power line obtained by the resistance calculation processing. This is a flowchart showing the procedure for temperature control processing.

[0010] Hereinafter, each embodiment of the present invention will be described in detail with reference to the drawings. Figure 1 is a block diagram showing an electric vehicle 1 equipped with a power supply system 20 according to an embodiment of the present invention. Figure 2 is a block diagram showing the power supply system 20. The electric vehicle 1 in Figure 1 comprises two sets of drive wheels 2A and 2B, a first electric motor 3A that drives one of the drive wheels 2A (for example, the front wheel), a second electric motor 3B that drives the other drive wheel 2B (for example, the rear wheel), a driver-operated control device 5, and a vehicle control circuit 6 that receives an operation signal from the driver-operated control device 5 and outputs driving commands for the first electric motor 3A and the second electric motor 3B. The electric vehicle 1 further comprises a power supply system 20.

[0011] As shown in Figures 1 and 2, the power supply system 20 includes a battery 21 for storing power for driving, a first motor control circuit 22 for controlling the drive of the first electric motor 3A, and a second motor control circuit 23 for controlling the drive of the second electric motor 3B. The power supply system 20 further includes power lines 24 for transmitting power between the battery 21, the first motor control circuit 22, and the second motor control circuit 23, a battery management circuit 25 for managing the battery 21, and main relays 26p and 26n that can disconnect the power lines 24. Furthermore, the power supply system 20 includes a control circuit 28 for managing the power lines 24.

[0012] The battery 21 outputs a high voltage, for example, 100V or more to 800V or more. The battery 21 is, for example, a lithium-ion secondary battery or a nickel-metal hydride secondary battery, but various other secondary batteries may also be used.

[0013] The first motor control circuit 22 includes a first inverter 221 that drives the first electric motor 3A, a first inverter current sensor 222 that detects the input current of the first inverter 221, a first inverter voltage sensor 223 that detects the input voltage of the first inverter 221 (i.e., the voltage between input terminals tp1 and tn1), and a first inverter control circuit 224 that controls the first inverter 221. The first inverter control circuit 224 is an ECU (Electronic Control Unit) that executes a control program and communicates with the vehicle control circuit 6. Communication is performed via a communication network NE, such as a CAN (Controller Area Network). The communication described below is also performed via the same method.

[0014] The second motor control circuit 23 includes a second inverter 231 that drives the second electric motor 3B, a second inverter current sensor 232 that detects the input current of the second inverter 231, a second inverter voltage sensor 233 that detects the input voltage of the second inverter 231 (i.e., the voltage between input terminals tp2 and tn2), and a second inverter control circuit 234 that controls the second inverter 231. The second inverter control circuit 234 is an ECU that executes a control program and communicates with the vehicle control circuit 6.

[0015] The first inverter 221 includes a first capacitor 225 that stores the voltage supplied from the power line 24. The first capacitor 225 may be, for example, an input capacitor or a smoothing capacitor. The second inverter 231 includes a second capacitor 235 that stores the voltage supplied from the power line 24. The second capacitor 235 may be, for example, an input capacitor or a smoothing capacitor.

[0016] The vehicle control circuit 6 is an ECU that executes a control program and controls the driving of the electric vehicle 1. The vehicle control circuit 6 communicates with other ECUs and cooperates with them. The driving operation device 5 includes steering members 5a such as a steering wheel, acceleration operation members 5b such as an accelerator pedal, and braking operation members 5c such as a brake pedal. The vehicle control circuit 6 receives signals from the driving operation device 5. In response to these signals, the vehicle control circuit 6 calculates the torque and other parameters required for the first electric motor 3A and the second electric motor 3B. Then, the vehicle control circuit 6 sends commands to the first inverter control circuit 224 and the second inverter control circuit 234 to realize the torque and other parameters. Based on these commands, the first inverter control circuit 224 and the second inverter control circuit 234 drive the first inverter 221 and the second inverter 231, respectively, to perform powered driving or regenerative driving of the first electric motor 3A and the second electric motor 3B. Through this control, the electric vehicle 1 is driven in accordance with the driving operation. Furthermore, the driving control device 5 may be operated by the automated driving system rather than the driver.

[0017] The battery management circuit 25 may be a Battery Management System (BMC) that monitors the voltage, temperature, and other conditions of multiple battery cells in the battery 21 and maintains the voltage balance of the multiple battery cells. Alternatively, the battery management circuit 25 may be a Battery Control Unit (BCU) that estimates the State of Charge (SOC) and State of Health (SOH) of the battery 21, and manages the output power and input power of the battery 21. Alternatively, the battery management circuit 25 may be a BMC equipped with the functions of a BCU.

[0018] The battery management circuit 25 includes a battery current sensor 251 that detects the input and output currents of the battery 21, and a battery voltage sensor 252 that detects the voltage across the battery 21.

[0019] The power line 24 includes branching points Nap and NAn, a pair of first power lines 241, a pair of second power lines 242, and a pair of common power lines 243. Here, "a pair" means a pair of anode and cathode lines. The common power line 243 extends from the battery 21 to branching points Nap and NAn. The first power line 241 extends from branching points Nap and NAn to the first inverter 221. The second power line 242 extends from branching points Nap and NAn to the second inverter 231. The first power line 241 and the second power line 242 branch off from branching points Nap and NAn.

[0020] The main relays 26p and 26n are provided on a pair of common power lines 243, respectively, and are switched between an open state and a closed state by the control of the vehicle control circuit 6. When switched to the open state, the pair of common power lines 243 are disconnected. On the other hand, when switched to the closed state, the battery 21 is connected to the first inverter 221 and the second inverter 231.

[0021] The power supply system 20 further includes a charging connector (e.g., a charging inlet) 291 for taking in DC charging power from an external source, a pair of charging power lines 292 for transmitting power from the charging connector 291 to the battery 21, and a charging control circuit 293. The charging connector 291 has a sensor 294 that detects whether or not a power supply connector 301 of the charging equipment (e.g., a charging gun, see Figure 1) is attached, and the output of the sensor 294 is sent to the charging control circuit 293. The pair of charging power lines 292 are provided with charging relays 295p and 295n, which can disconnect the pair of charging power lines 292, respectively.

[0022] The control circuit 28 is an ECU that executes a control program stored in the storage device 28a. The storage device 28a is, for example, a non-volatile memory. The control circuit 28 communicates with other ECUs and cooperates with them. The control circuit 28 uses data on the resistance value of the power line 24 to estimate the amount of heat generated by the power line 24 and manages the power line 24. In this management, the control circuit 28 keeps the temperature of the power line 24 below the allowable temperature. The allowable temperature is a temperature set so that no abnormalities occur due to the heat generated by the power line 24. The allowable temperature may be a different value depending on whether the power line generates heat for a long period of time or generates a large amount of heat temporarily. The control circuit 28 may predict the temperature of the power line 24 based on the stored resistance value, and if the predicted temperature is expected to exceed the allowable temperature, it may perform a process to limit the current flowing through the power line 24.

[0023] In this embodiment, a configuration is shown that includes a dedicated control circuit 28 for managing the power lines 24. However, the control circuit 28 may be integrated into, for example, the vehicle control circuit 6, or into another ECU. Furthermore, the control circuit 28 may include multiple ECUs, and the processing of the control circuit 28 may be realized by the cooperation of multiple ECUs.

[0024] <Resistance Measurement Process> The control circuit 28 performs a resistance measurement process to measure the resistance of the power line 24. The control circuit 28 then stores the measured resistance in the storage device 28a. In the resistance measurement process, the control circuit 28 receives measured values ​​from multiple sensors that measure the current flowing through the power line 24 and the voltage between multiple points on the power line 24, and calculates the resistance based on these measured values. These multiple sensors include a battery current sensor 251 and a battery voltage sensor 252. These multiple sensors may further include several sensors described later.

[0025] In the resistance measurement process of Embodiments 1 to 4, the control circuit 28 measures the resistance R3 of a pair of common power lines 243, the resistance R1 of a pair of first power lines 241, and the resistance R2 of a pair of second power lines 242. In the figure, resistances R1 to R3 are shown only in part of the power lines, but resistance R1 is the sum of the resistance of the entire section of the first power line 241 on the anode side and the resistance of the entire section of the first power line 241 on the cathode side. The same applies to resistances R2 and R3.

[0026] Furthermore, in order to measure the resistance value, the control circuit 28 receives the outputs of the first inverter current sensor 222, the first inverter voltage sensor 223, the second inverter current sensor 232, and the second inverter voltage sensor 233, in addition to the battery current sensor 251 and the battery voltage sensor 252. Here, the control circuit 28 may also receive the output values ​​of each sensor via communication with an ECU that directly receives the output of that sensor. In the following, even if the control circuit 28 receives the sensor output values ​​via communication with another ECU, the involvement of other ECUs will be omitted.

[0027] Furthermore, in embodiments 1 to 4, the control circuit 28 causes current to flow through the power line 24 by outputting a discharge command that releases the charge accumulated in the capacitors of the electrical equipment connected to the power line 24. The resistance value of the power line 24 is then measured using this current. In embodiments 1 to 4, the first capacitor 225 of the first inverter 221 and the second capacitor 235 of the second inverter 231 are used as the capacitors of the electrical equipment.

[0028] Furthermore, the control circuit 28 outputs a first discharge command to output a discharge current from the first capacitor 225 and a second discharge command to output a discharge current from the second capacitor 235, respectively, during different first and second periods. The control circuit 28 then calculates the values ​​of resistors R1 to R3 based on the current and voltage values ​​measured at multiple locations during the first and second periods.

[0029] <Resistance Measurement Process in Embodiment 1> Next, the specific procedure for the resistance measurement process will be explained. Figure 3 is a flowchart of the resistance measurement process in Embodiment 1. The control circuit 28 performs the resistance measurement process while the electric vehicle 1 is running. Various conditions may be applied for execution, such as after each predetermined distance traveled, after each predetermined time traveled, or after each predetermined trip. A trip refers to the period from when the electric vehicle 1's system is started, through the period of travel, until the system is shut down.

[0030] When the resistance value measurement process begins, the control circuit 28 first switches to either the front driving mode or the rear driving mode (step S1). The front driving mode is a mode in which the vehicle operates with torque output from the first electric motor 3A (i.e., power driving and regenerative driving) and without torque output from the second electric motor 3B. The rear driving mode is a mode in which the vehicle operates with torque output from the second electric motor 3B and without torque output from the first electric motor 3A. The control circuit 28 can switch between driving modes by communicating with the vehicle control circuit 6 to request the driving mode.

[0031] Next, the control circuit 28 measures the terminal voltage VB of the battery 21 based on the output of the battery voltage sensor 252 (step S2).

[0032] Next, the control circuit 28 outputs a first discharge command to perform a discharge process on the first capacitor 225, causing the first capacitor 225 to output a discharge current (step S3). The discharge process is a process that releases the charge accumulated in the first capacitor 225 to the first electric motor 3A in a manner that does not generate a large torque. The current released to the first electric motor 3A by the discharge process is smaller than the current that flows during traction operation for driving. Specifically, the control circuit 28 sends a first discharge command to the first inverter control circuit 224, and the first inverter control circuit 224 drives the first inverter 221 so that the discharge is performed in the manner described above, thereby carrying out the discharge process.

[0033] The original discharge process is performed when the electric vehicle 1 system is shut down, by releasing the remaining charge in the first inverter 221 and the second inverter 231, thereby reducing the high voltage remaining in the power line 24. The original discharge process is performed after the main relays 26p and 26n are switched to the open state.

[0034] On the other hand, the discharge process in step S3 is performed when the electric vehicle 1 is running and the main relays 26p and 26n are closed. Therefore, when a discharge current flows from the first capacitor 225 to the first electric motor 3A due to the discharge process, the voltage of the battery 21 is applied to the first capacitor 225, and a current equivalent to the discharge current flows into the first capacitor 225. In other words, a current equivalent to the relatively small current released to the first electric motor 3A due to the discharge process also flows through the power line 24.

[0035] Next, the control circuit 28 measures the voltage VN (=VNp - VNn) between the branch points Nap and NAn based on the output of the second inverter voltage sensor 233 of the second motor control circuit 23 (step S4). Here, the control circuit 28 measures the voltage VN when the input current i2 of the second inverter 231 is zero. That is, since the current i2 of the second power line 242 is zero, the input voltage of the second inverter 231 and the voltage VN at the branch points Nap and NAn are the same, and the voltage VN can be measured by the second inverter voltage sensor 233.

[0036] Furthermore, the control circuit 28 measures the current i3 of the common power line 243 using the battery current sensor 251 (step S5). Then, it calculates the resistance R3 of the common power line 243 from the voltages VB, VN and current i3 as shown in the following equation (1) (step S6). R3 = (VB - VN) / i3 ... (1)

[0037] Next, the control circuit 28 measures the input voltage V1 of the first inverter 221 and the current i1 of the first power line 241 using the first inverter current sensor 222 and the first inverter voltage sensor 223 (step S7). Then, it calculates the resistance R1 of the first power line 241 from the voltage V1, VN and current i1 as shown in the following equation (2) (step S8). R1 ​​= (VN - V1) / i1 ... (2)

[0038] During steps S4 to S8 described above, the current flowing through the power line 24 is a relatively small current generated by the discharge process of the first capacitor 225. This current is small enough not to cause significant heat generation in the power line 24 and flows stably. Therefore, the control circuit 28 can obtain stable current and voltage values ​​by measuring the current and voltage in steps S4, S5, and S7. Thus, by calculating in steps S6 and S8, the control circuit 28 can obtain the values ​​of resistors R1 and R3 with high accuracy.

[0039] Next, the control circuit 28 outputs a second discharge command to perform a discharge process on the second capacitor 235, causing the second capacitor 235 to output a discharge current (step S9). The discharge process is a process that releases the charge accumulated in the second capacitor 235 to the second electric motor 3B in a manner that does not generate a large torque. The current released to the second electric motor 3B by the discharge process is smaller than the current that flows during traction operation for driving. Specifically, the control circuit 28 sends a second discharge command to the second inverter control circuit 234, and the second inverter control circuit 234 drives the second inverter 231 so that the discharge is performed in the manner described above, thereby carrying out the discharge process.

[0040] Next, the control circuit 28 measures the voltage VN (=VNp - VNn) between the branch points Nap and NAn based on the output of the first inverter voltage sensor 223 of the first motor control circuit 22 (step S10). Here, the control circuit 28 measures the voltage VN when the input current of the first inverter 221 is zero. That is, since the current of the first power line 241 is zero, the input voltage of the first inverter 221 and the voltage VN at the branch points Nap and NAn are the same, and the voltage VN can be measured by the first inverter voltage sensor 223.

[0041] Next, the control circuit 28 measures the input voltage V2 of the second inverter 231 and the current i2 of the second power line 242 by means of the second inverter current sensor 232 and the second inverter voltage sensor 233 (step S11). Then, the resistance R2 of the second power line 242 is calculated from the voltages V2, VN and the current i2 according to the following equation (3) (step S12). R2 = (VN-V2) / i2 ...(3)

[0042] During steps S10 to S12 described above, the current flowing through the power line 24 is a relatively small current generated by the discharge processing of the second capacitor 235. This current is a small current that does not cause significant heat generation in the power line 24, and flows stably. Therefore, the control circuit 28 can obtain stable current values and stable voltage values through the measurement of current and voltage in steps S10 and S11. Accordingly, through the calculation in step S12, the control circuit 28 can obtain the value of the resistance R2 with high accuracy.

[0043] When the values of resistances R1 to R3 have been calculated, the control circuit 28 learns the resistances R1 to R3 based on the calculated values, and stores the learned values in the storage device 28a (step S13). The stored values may be the calculated values themselves. Alternatively, the stored values may be values obtained through a learning process that reduces measurement errors based on the values of resistances R1 to R3 that have been previously calculated and stored at a plurality of timings and the current values. The learning process may include statistical processing for reducing measurement errors.

[0044] Then, the control circuit 28 updates the resistance value used in the temperature management control processing of the power line 24, and applies the value stored in the storage device 28a in step S13 as the resistance value (step S14). Then, the resistance value measurement processing is ended.

[0045] <Resistance Value Measurement Processing of Embodiment 2> Figure 4 is a flowchart showing the resistance value measurement processing of Embodiment 2. When the resistance value measurement processing of Embodiment 2 is started, the control circuit 28 repeatedly determines whether or not a power supply connector 301 (for example, a charging gun, see FIG. 1) is attached to the charging connector 291 (step S21). Then, when it is attached, the control circuit 28 executes the processing from step S2. The processing after step S2 is the same as the processing from step S2 to step S14 in FIG. 3.

[0046] In Embodiment 2, the processing from step S2 to S14 may be executed before the input of charging power from the charging connector is started, or may be executed during the input of charging power.

[0047] <Resistance Value Measurement Processing of Embodiment 3> Figure 5 is a flowchart showing the resistance value measurement processing of Embodiment 3. When the resistance value measurement processing of Embodiment 3 is started, the control circuit 28 repeatedly determines whether the traveling of the electric vehicle 1 has stopped (step S22). Then, when it is determined that the traveling has stopped, the control circuit 28 executes the processing from step S2. The processing after step S2 is the same as the processing from step S2 to step S14 in FIG. 3.

[0048] <Resistance Value Measurement Processing of Embodiment 4> Figure 6 is a flowchart showing the resistance value measurement processing of Embodiment 4. When the resistance value measurement processing of Embodiment 4 is started, the control circuit 28 repeatedly determines whether there is a system suspension request from a user (step S23). The system suspension refers to a state in which the main relays 26p and 26n are opened while the electric vehicle 1 is parked, and each ECU is suspended. The system suspension request may also be referred to as a ready-off request. The system suspension request is generated, for example, by an off operation of a power button of the electric vehicle 1 or an off operation of an ignition key.

[0049] As a result of the determination in step S23, if there is a system suspension request, the control circuit 28 executes the processing from step S2. The processing after step S2 is the same as the processing from step S2 to step S14 in FIG. 3. The resistance value measurement processing is executed at a stage when the main relays 26p and 26n are in a closed state.

[0050] The resistance measurement processing program in Embodiments 1 to 4 is stored in a non-transient storage medium, such as the storage device 28a of the control circuit 28. The control circuit 28 may be configured to read a program stored in a portable non-transient recording medium and execute the program. The portable non-transient storage medium may store the resistance measurement processing program described above.

[0051] <Characteristics of the Resistance Measurement Process in Embodiments 1 to 4> Comparing the resistance measurement processes in Embodiments 1 to 4, Embodiment 1, which is performed while driving, has an inferiority in drivability because there is a period during driving when the output of the first electric motor 3A and the second electric motor 3B is suppressed. However, the resistance measurement process in Embodiment 1 has the advantage of a high degree of freedom in the frequency of updating the resistance value. On the other hand, the resistance measurement processes in Embodiments 2 to 4 have an advantage in drivability because there are no restrictions during driving, but the degree of freedom in the frequency of updating the resistance value is low, and among them, the resistance measurement process in Embodiment 4, which is performed when a pause request is made, has the disadvantage of having an even lower and more restricted update frequency. In terms of energy consumption, since power is consumed separately from the power used for driving due to the discharge process, Embodiments 1 to 3, which are performed at times when there is no need to perform the discharge process, have an inferiority. On the other hand, they have an advantage when a pause request is made and the discharge process is necessary. However, since the discharge amount is suppressed during the resistance measurement process while driving, the resistance measurement process of Embodiment 1 has an advantage in terms of energy efficiency compared to resistance measurement processes during charging or while stationary.

[0052]

[0053] (Embodiment 5) Figure 7 is a block diagram of the power supply system 20A of Embodiment 5. The power supply system 20A of Embodiment 5 is the same as the power supply system 20 of Embodiment 1, except for the components related to charging. In the power supply system 20A of Embodiment 5, the anode-side charging power line 292p is connected between the anode-side main relay 26p and the first inverter 221 and the second inverter 231. Furthermore, the cathode-side charging power line 292n is connected between the cathode-side main relay 26n and the first inverter 221 and the second inverter 231. More specifically, the pair of charging power lines 292p and 292n may be connected to branching points Nap and Nan. One charging power line 292p is connected to the anode terminal of the charging connector 291, and the other charging power line 292n is connected to the cathode terminal of the charging connector 291.

[0054] A pair of charging power lines 292p and 292n are connected to charging relays 295p and 295n, which can disconnect the power lines. A charging control circuit 293 is connected to the charging power lines 292p and 292n on the charging connector 291 side of the charging relays 295p and 295n. The charging control circuit 293 includes a charging voltage sensor 297 that measures the input voltage of the charging connector 291.

[0055] The charging connector (specifically, the inlet) 291 is located inside a lid 298 provided on the exterior of the vehicle body. Furthermore, the power supply system 20A includes an open / close sensor 299 that detects the opening and closing of the lid 298, and the output of the open / close sensor 299 is sent to the control circuit 28 from another ECU, either directly or via communication.

[0056] The charging control circuit 293 is an ECU and is communicated with other ECUs in the electric vehicle 1.

[0057] <Resistance Measurement Process in Embodiment 5> In the resistance measurement process of Embodiment 5, the control circuit 28 outputs an ON command to switch the charging relays 295p and 295n to the closed state when the external power supply connector 301 (see Figure 1) is not attached to the charging connector 291. The ON command is sent to the vehicle control circuit 6 by communication, and the vehicle control circuit 6 may switch the charging relays 295p and 295n. When the charging relays 295p and 295n are in the closed state, the control circuit 28 causes the charging voltage sensor 297 to measure the voltage. This allows the voltage between the connection point of the power line 24 and the charging power lines 292p and 292n (between branch points Nap and Nan in the example in Figure 7) to be measured. That is, since the current flowing through the pair of charging power lines 292p and 292n is zero, the voltage measured by the charging voltage sensor 297 is the above voltage. The control circuit 28 then uses the measurement result of this voltage to calculate the resistance of the power line 24.

[0058] When the charging relays 295p and 295n are closed while the power supply connector 301 (see Figure 1) is not attached to the charging connector 291, the high voltage from the battery 21 is output to the terminals of the charging connector 291. Therefore, if any object touches these terminals, the high voltage will be transmitted to that object. To avoid this, the control circuit 28 performs the resistance measurement process only when the lid 298 of the charging connector 291 is closed. Furthermore, to prevent the lid 298 from being opened while the resistance measurement process is running, the control circuit 28 performs the resistance measurement process only when the electric vehicle 1 is traveling at a predetermined speed or higher. These execution conditions prevent any object from touching the terminals of the charging connector 291, even if a high voltage is output to the charging connector 291.

[0059] Next, the procedure flow for the resistance measurement process in Embodiment 5 will be explained. Figures 8 and 9 are flowcharts of the resistance measurement process according to Embodiment 5. In Embodiment 5, the control circuit 28 starts the resistance measurement process when the system of the electric vehicle 1 is started. First, the control circuit 28 repeatedly determines whether the main relays 26p and 26n are in a closed state (step S31). If the result is YES, the control circuit 28 determines whether the lid 298 covering the charging connector 291 is closed (step S32). If the result is YES, the control circuit 28 further determines whether the vehicle speed is above a threshold that indicates the vehicle is in motion (step S33). If the result of either step S32 or S33 is NO, the control circuit 28 terminates the resistance measurement process without measuring the resistance value. In this case, the control circuit 28 may start the resistance measurement process again after a predetermined time has elapsed.

[0060] On the other hand, if the determination result in steps S32 and S33 is YES, the control circuit 28 performs the processing in steps S34 to S44 and simultaneously performs the stopping response processing in steps S47 to S49.

[0061] When the process moves to step S34, the control circuit 28 first closes the charging relays 295p and 295n (step S34). Then, the control circuit 28 measures the terminal voltage VB of the battery 21 based on the output of the battery voltage sensor 252, and further measures the voltage between the branch points Nap and Nan based on the output of the charging voltage sensor 297 (step S35). This allows the control circuit 28 to calculate the voltage applied to the pair of common power lines 243.

[0062] Furthermore, the control circuit 28 measures the current i3 of the common power line 243 using the battery current sensor 251 (step S36). Then, the control circuit 28 calculates the resistance R3 of the common power line 243 as shown in the following equation (4) (step S37): R3 = (VB - VN) / i3 ... (4)

[0063] Next, the control circuit 28 calculates the voltage applied to the pair of first power lines 241 by measuring the input voltage V1 of the first inverter voltage sensor 223 and the voltage VN between the branch points Nap and Nan (step S38). Furthermore, the control circuit 28 measures the current i1 flowing through the first power line 241 by measuring the first inverter current sensor 222 (step S39). Then, from these, the resistance R1 of the first power line 241 is calculated as shown in the following equation (5) (step S40). R1 ​​= (VN - V1) / i1 ... (5)

[0064] Next, the control circuit 28 calculates the voltage applied to the pair of second power lines 242 based on the measurement of the input voltage V2 of the second inverter voltage sensor 233 and the voltage VN between the branch points Nap and Nan (step S41). Furthermore, the control circuit 28 measures the current i2 flowing through the second power line 242 by measuring the second inverter current sensor 232 (step S42). Then, from these, the resistance R2 of the second power line 242 is calculated as shown in the following equation (6) (step S43). R2 = (VN - V2) / i2 ... (6)

[0065] Once the values ​​of resistors R1 to R3 have been calculated, the control circuit 28 learns the values ​​of resistors R1 to R3 based on these values ​​and stores the learned values ​​in the memory device 28a (step S44). The values ​​to be stored may be the calculated values ​​themselves. Alternatively, the values ​​to be stored may be values ​​that have undergone a learning process to reduce measurement errors, based on the values ​​of resistors R1 to R3 that have been calculated and stored at multiple timings in the past, and the current values. This learning process may include statistical processing to reduce measurement errors.

[0066] Next, the control circuit 28 opens the charging relays 295p and 295n (step S45). This process releases the high voltage output to the charging connector 291.

[0067] Then, the control circuit 28 applies the value stored in the memory device 28a in step S13 as the resistance value used in the temperature control process of the power line 24 (step S46). Then, the resistance value measurement process is terminated.

[0068] Next, the stopping response processing in steps S47 to S49, which is performed in parallel with the processing in steps S34 to S42 described above, will be explained. In the stopping response processing, the control circuit 28 repeatedly determines whether the vehicle speed of the electric vehicle 1 has fallen below a threshold that indicates it is in motion (step S47). If the result of this determination is YES, the processing in steps S34 to S44, which is being executed in parallel, is interrupted (step S48), and the charging relays 295p and 295n are opened (step S49). Then, the control circuit 28 terminates the resistance value measurement processing. This stopping response processing prevents the electric vehicle 1 from stopping and the lid 298 from opening while a high voltage is being output to the charging connector 291 during the resistance value measurement processing.

[0069] The resistance measurement processing program in Embodiment 5 is stored in a non-transient storage medium, such as the storage device 28a of the control circuit 28. The control circuit 28 may be configured to read a program stored in a portable non-transient recording medium and execute the program. The portable non-transient storage medium may store the resistance measurement processing program described above.

[0070] (Embodiment 6) Figure 10 is a block diagram of the power supply system 20B of Embodiment 6. Figures 11A and 11B are diagrams illustrating each section of the power line. The power supply system 20B of Embodiment 6 includes a power line 31, a first battery 21A and a second battery 21B as batteries for storing power for driving, and two sets of main relays 26Ap, 26An, 26Bp, and 26Bn. The vehicle control circuit 6 can supply power to the first inverter 221 from either the first battery 21A or the second battery 21B, or from both selected, by switching the main relays 26Ap, 26An, 26Bp, and 26Bn.

[0071] The power line 31 further includes charging connectors 291p and 291n to which charging power is input from an external source, and two sets of charging relays 295Ap, 295An, 295Bp, and 295Bn. The vehicle control circuit 6 can supply charging power to one or both of the first battery 21A and the second battery 21B by switching the charging relays 295Ap, 295An, 295Bp, and 295Bn. In Figure 10, the charging connectors 291p and 291n are shown far apart, but in reality, they are located close together to form a pair of connectors that can be connected to one power supply connector 301 (e.g., a charging gun, see Figure 1).

[0072] The power line 31 includes a pair of third power lines 311p, 311n (shown as short dashed lines in Figure 11A) that transmit power between the first battery 21A and the first inverter 221, and a pair of fourth power lines 312p, 312n (shown as short dashed lines in Figure 11B) that transmit power between the second battery 21B and the first inverter 221. Furthermore, the power line 31 includes a pair of first charging power lines 313p, 313n (shown as dashed lines in Figure 11B) that transmit power between the first battery 21A and the charging connectors 291p, 291n, and a pair of second charging power lines 314p, 314n (shown as dashed lines in Figure 11A) that transmit power between the second battery 21B and the charging connectors 291p, 291n. The third power lines 311p and 311n and the fourth power lines 312p and 312n have overlapping sections 316p and 316n. The third power lines 311p and 311n, the fourth power lines 312p and 312n, the first charging power lines 313p and 313n, and the second charging power lines 314p and 314n have overlapping sections 317p, 317n, 318p, and 318n. Each of the overlapping sections 316p to 318p and 316n to 318p is composed of a single power line.

[0073] The main relays 26Ap and 26An of the first system are provided to disconnect a pair of third power lines 311p and 311n, respectively. The main relays 26Bp and 26Bn of the second system are provided to disconnect a pair of fourth power lines 312p and 312n, respectively. The system may also include the cathode-side main relays 26An and 26Bn, a relay Re for switching between disconnecting and connecting the power lines, and a pre-charge relay PRe for slowly supplying current through a pre-charge resistor Rp when connecting the power lines.

[0074] The first charging relays 295Ap and 295An are configured to disconnect the first charging power lines 313p and 313n, respectively. The second charging relays 295Bp and 295Bn are configured to disconnect the second charging power lines 314p and 314n, respectively.

[0075] The power supply system 20B further includes a first battery management circuit 25A for managing the first battery 21A and a second battery management circuit 25B for managing the second battery 21B. The first battery management circuit 25A includes a battery current sensor 251A for detecting the input and output current of the first battery 21A and a battery voltage sensor 252A for detecting the voltage between both terminals of the first battery 21A. The second battery management circuit 25B includes a battery current sensor 251B for detecting the input and output current of the second battery 21B and a battery voltage sensor 252B for detecting the voltage between both terminals of the second battery 21B.

[0076] In Embodiment 6, the first inverter 221 is also provided in the first motor control circuit 22. The first motor control circuit 22 includes a first inverter current sensor 222 for detecting the input current of the first inverter 221 and a first inverter voltage sensor 223 for detecting the input voltage of the first inverter 221. Figure 10 shows an example in which there is only one first electric motor 3A, but the power supply system 20B in Embodiment 6 may also have two electric motors, similar to Embodiments 1 to 5, and further include a second motor control circuit for controlling the second electric motor.

[0077] The power supply system 20B further includes a DC / DC converter 41 that converts the voltages of the first battery 21A and the second battery 21B to a lower voltage for equipment, such as a 12V or 24V system. The DC / DC converter 41 is connected downstream of the main relays 26Ap, 26Bp, 26An, and 26Bn in the power line 31.

[0078] <Resistance Measurement Process in Embodiment 6> In the resistance measurement process of Embodiment 6, the control circuit 28 outputs an all-on command to close all of the charging relays 295Ap to 295Bn when the potential difference between the first battery 21A and the second battery 21B is small. The above potential difference refers to the difference in anode potential when the cathode potentials are equal. When all of the charging relays 295Ap to 295Bn are switched to the closed state, the first battery 21A and the second battery 21B are connected in parallel. The control circuit 28 then measures the resistance of the power line 31 using the current that flows between the first battery 21A and the second battery 21B as a result of this parallel connection.

[0079] Next, the procedure flow for the resistance measurement process in Embodiment 6 will be explained. Figure 12 is a flowchart of the resistance measurement process according to Embodiment 6. In Embodiment 6, the control circuit 28 starts the resistance measurement process when a system shutdown request for the electric vehicle 1 occurs. A shutdown request is a request to switch the main relays 26Ap to 26Bn to the open state and to shut down each ECU, for example, when the electric vehicle 1 is stopped and the user turns off the power button or the ignition key.

[0080] When a pause request is received and the resistance measurement process begins, the control circuit 28 determines whether the potential difference between the first battery 21A and the second battery 21B is below a threshold (step S51). This threshold is set to a value such that an abnormally large current does not flow even when the first battery 21A and the second battery 21B are connected in parallel.

[0081] If the result of the determination in step S51 is YES, the control circuit 28 proceeds with the resistance value measurement process. On the other hand, if it is NO, the control circuit 28 does not perform the resistance value measurement process and notifies the vehicle control circuit 6, which then performs the normal pause transition process (step S52). The electric vehicle 1 then transitions to the pause state.

[0082] If the determination result in step S51 is YES and the resistance measurement process proceeds, the control circuit 28 outputs a full ON command to close all of the two charging relays 295Ap to 295Bn. Furthermore, the control circuit 28 outputs a command to open the first main relay 26Ap and 26An and close the second main relay 26Bp and 26Bn (step S53). Then, the control circuit 28 causes the first battery management circuit 25A, the second battery management circuit 25B and the first motor control circuit 22 to measure the current and voltage (step S54).

[0083] By switching the relay in step S53, the first battery 21A, the second battery 21B, and the first inverter 221 are connected in parallel via the first charging power lines 313p, 313n, the second charging power lines 314p, 314n, and the fourth power lines 312p, 312n. As a result, current flows between the first battery 21A and the second battery 21B, between the first battery 21A and the first inverter 221, and further, between the second battery 21B and the first inverter 221.

[0084] Then, in step S54, the combined current of the three currents is measured at three locations. Furthermore, in step S54, the control circuit 28 calculates the difference between the voltages measured at the three locations. As a result, the control circuit 28 determines the voltage applied to the first charging power lines 313p, 313n and the second charging power lines 314p, 314n, the voltage applied to the first charging power lines 313p, 313n, the second charging power lines 314p, 314n and the fourth power line 312p, 312n, and the voltage applied to the fourth power line 312p, 312n. Here, the voltage applied to the power lines means the sum of the voltage across the ends of the anode power line and the voltage across the ends of the cathode power line. Then, the control circuit 28 derives a system of equations based on the superposition theorem from the above current and voltage, and solves these equations to calculate the resistance values ​​of the first charging power lines 313p, 313n and the second charging power lines 314p, 314n, and the resistance values ​​of the fourth power line 312p, 312n (step S55).

[0085] Next, the control circuit 28 outputs a full-on command to close both of the two charging relays 295Ap to 295Bn. Furthermore, the control circuit 28 outputs a command to close the first main relay 26Ap and 26An and to open the second main relay 26Bp and 26Bn (step S56). Then, the control circuit 28 causes the first battery management circuit 25A, the second battery management circuit 25B and the first motor control circuit 22 to measure the current and voltage (step S57).

[0086] By switching the relay in step S56, the first battery 21A, the second battery 21B, and the first inverter 221 are connected in parallel via the first charging power lines 313p, 313n, the second charging power lines 314p, 314n, and the third power lines 311p, 311n. As a result, current flows between the first battery 21A and the second battery 21B, between the second battery 21B and the first inverter 221, and further, between the first battery 21A and the first inverter 221.

[0087] Then, in step S57, the combined current of the three currents is measured at three locations. Furthermore, in step S57, the control circuit 28 calculates the difference between the voltages measured at the three locations. As a result, the control circuit 28 determines the voltage applied to the first charging power lines 313p, 313n and the second charging power lines 314p, 314n, the voltage applied to the first charging power lines 313p, 313n and the second charging power lines 314p, 314n and the third power lines 311p, 311n, and the voltage applied to the third power lines 311p, 311n. Here, the voltage applied to the power lines means the sum of the voltage across both ends of the anode-side power line and the voltage across both ends of the cathode-side power line. Then, the control circuit 28 derives a system of equations based on the superposition theorem from the above current and voltage, and solves these equations to calculate the resistance values ​​of the first charging power lines 313p, 313n and the second charging power lines 314p, 314n, and the resistance values ​​of the third power lines 311p, 311n (step S58).

[0088] Once the resistance values ​​of the first charging power lines 313p, 313n and the second charging power lines 314p, 314n, the resistance values ​​of the third power line 311p, 311n, and the resistance values ​​of the fourth power line 312p, 312n have been calculated, the control circuit 28 learns the resistance of each section based on these values ​​and stores the learned values ​​in the memory device 28a (step S59). The value to be stored may be the calculated value itself. Alternatively, the value to be stored may be a value that has undergone a learning process to reduce measurement errors, based on resistance values ​​that have been calculated and stored at multiple timings in the past and the current value. This learning process may include statistical processing to reduce measurement errors.

[0089] Then, the control circuit 28 notifies the vehicle control circuit 6, which then performs the normal pause transition process (step S60), and the electric vehicle 1 transitions to the pause state.

[0090] The resistance measurement processing program of Embodiment 6 is stored in a non-transient storage medium, such as the storage device 28a of the control circuit 28. The control circuit 28 may be configured to read a program stored in a portable non-transient recording medium and execute the program. The portable non-transient storage medium may store the resistance measurement processing program described above.

[0091] <Temperature control processing of power lines according to Embodiments 1 to 6> Figure 13 is a diagram illustrating the value of the resistance R1 of the power line 24 obtained by the resistance value calculation process in Embodiment 1. The vertical axis of the bar graph in Figure 13 shows the value of the resistance R1 of the first power line 241. The horizontal axis shows the worst value such as the specification value and the measured values ​​for "Vehicle A" to "Vehicle C" of the three identical electric vehicles 1, respectively.

[0092] As shown in Figure 13, the measured resistance R1 of the power line 24 is lower than the worst-case value such as the specification value (resistance R1 of "Vehicle A" to "Vehicle C"). Furthermore, even with the same type of electric vehicle 1, the resistance R1 may vary from one electric vehicle 1 to another ("Vehicle A" to "Vehicle C"). Therefore, by actually measuring, the control circuit 28 can determine the value of the resistance R1 of the power line 24 with minimal error. On the other hand, if the resistance R1 is not measured, the worst-case value will be applied as the resistance R1. In this case, due to errors A to C between the actual value of resistance R1 and the estimated value, the amount of heat generated and the temperature of the power line 24 will be estimated to be higher than the actual values. On the other hand, by using the value of resistance R1 measured for each individual electric vehicle 1, it is possible to estimate the amount of heat generated and the temperature with less error.

[0093] In the example shown in Figure 13, the resistance R1 of the power line 24 in Embodiment 1 is shown, but the same effect occurs for resistors R2 and R3. Furthermore, the same effect occurs for each resistor of the power line 24 in Embodiments 2 to 6.

[0094] Figure 14 is a flowchart showing the procedure for temperature control processing performed by the control circuit 28. The temperature control processing is performed repeatedly during the system operation of the electric vehicle 1. In the temperature control processing, the control circuit 28 acquires the measured value of the current flowing through the power line 24 (step S71). If there is a branch point in the power line 24 and the current value differs in the section before and after the branch point, the control circuit 28 acquires the measured value of the current in each section.

[0095] Next, the control circuit 28 calculates the amount of heat generated in each section of the power line 24 by multiplying the values ​​of resistors R1 to R3 stored in the memory device 28a by the current values ​​of each section obtained in step S71 (step S72).

[0096] Next, the control circuit 28 calculates the magnitude of the cooling effect applied to each section of the power line 24 (step S73). The magnitude of the cooling effect may be calculated from the ambient air temperature and ambient air flow rate if air cooling is performed by ambient air, or from the water temperature if water cooling or the like is performed.

[0097] Then, the control circuit 28 calculates the estimated temperature of each section of the power line 24 based on the estimated temperature of each section of the power line 24 calculated in the previous step, the amount of heat generated in step S72, and the magnitude of the cooling effect in step S73 (step S74).

[0098] Next, the control circuit 28 determines whether the estimated temperature has exceeded a threshold temperature indicating an abnormality (step S75), and if there is a section where the temperature exceeds the threshold, it performs current limiting, such as lowering the upper limit of the current passing through that section (step S76).

[0099] Furthermore, the control circuit 28 identifies any sections where current is being limited (step S77), and if so, determines whether the estimated temperature in that section has fallen below the threshold temperature indicating the normal temperature (step S78). If it has, the control circuit 28 releases the current limit, such as by restoring the upper limit of the current in that section to its original value (step S79).

[0100] Then, after steps S75 to S79, the control circuit 28 completes one temperature control process and repeats the process from step S71 in the next control cycle. By repeating this temperature control process, it is prevented from the power line 24, through which a large current flows, rising to an abnormal temperature.

[0101] If the worst-case values ​​are applied as the values ​​for resistors R1 to R3, the current limit in step S76 will be performed with an excessive safety margin. On the other hand, by applying the measured values ​​for resistors R1 to R3, the current limit in step S76 can be performed with an appropriate safety margin. Therefore, it is possible to prevent the power of the electric vehicle 1 from being restricted more than necessary, or the high-speed charging from being restricted more than necessary.

[0102] In the example shown in Figure 13, temperature control based on the resistances R1 to R3 of the power line 24 in Embodiments 1 to 5 is demonstrated. However, the same effect can be obtained for the power line 31 in Embodiment 6 by the same control method.

[0103] The temperature control processing program is stored in a non-transient storage medium, such as the storage device 28a of the control circuit 28. The control circuit 28 may be configured to read a program stored in a portable non-transient recording medium and execute the program. The portable non-transient storage medium may store the temperature control processing program described above.

[0104] As described above, the power supply systems 20, 20A, and 20B of the electric vehicle 1 according to embodiments 1 to 6 provide power lines 24 and 31 through which the drive current for the electric motors (first electric motor 3A and second electric motor 3B) flows. The control circuit 28 measures the resistance values ​​of the power lines 24 and 31 based on the measured values ​​of the current and voltage of the power line 24. Therefore, even if there are individual differences in the resistance values ​​of the power lines 24 and 31 among the electric vehicle 1, the control circuit 28 can obtain accurate resistance values ​​including these individual differences. Consequently, even when current limiting is performed in the temperature control process for the power lines 24 and 31 to prevent them from reaching abnormally high temperatures, it is possible to eliminate current limiting with an excessive margin and perform appropriate current limiting. As a result, it becomes possible to output greater power from the electric motors (first electric motor 3A and second electric motor 3B), thereby improving the drivability of the electric vehicle 1.

[0105] Furthermore, according to the power supply system 20 of the electric vehicle 1 according to Embodiments 1 to 4, the control circuit 28 outputs a discharge command to release the charge stored in the first capacitor 225 and the second capacitor 235 of the electrical equipment (first inverter 221, second inverter 231) connected to the power line 24. Then, using the stable, small current that flows through the power line 24 as a result of this discharge command, the control circuit 28 calculates the resistance value of the power line 24. Therefore, the power line 24 does not generate a large amount of heat due to the current used to measure the resistance value, and the control circuit 28 can measure the resistance value of the power line 24 more accurately.

[0106] In embodiments 1 to 4, examples were shown in which the first inverter 221 and the second inverter 231 were used as electrical equipment for discharging electric charge. However, as the above-mentioned electrical equipment, various devices that have a capacitor for storing high voltage and operate by receiving power from the power line 24 may be used, such as air conditioners and heaters.

[0107] In the power supply system 20 of the electric vehicle 1 according to Embodiments 1 to 4, a first inverter 221 and a second inverter 231 are used as electrical devices that output discharge current. The control circuit 28 outputs a first discharge command to the first inverter 221 to output discharge current and a second discharge command to the second inverter 231 to output discharge current, respectively, in different first and second periods. The control circuit 28 then calculates the resistance value of the power line 24 based on the current and voltage values ​​measured in the first period and the current and voltage values ​​measured in the second period. With this configuration, the path of the current flowing through the power line 24 can be made different in the first and second periods due to the discharge current. Therefore, even when the power line 24 is branched into multiple sections, the control circuit 28 can easily determine the resistance value of each section.

[0108] More specifically, the power supply system 20 of the electric vehicle 1 according to Embodiments 1 to 4 includes a power line 24 comprising a first power line 241 and a second power line 242 that are branched from each other, and a common power line 243. The voltage and current of the pair of first power lines 241 can be measured by the first motor control circuit 22, and the voltage and current of the pair of second power lines 242 can be measured by the second motor control circuit 23. With this configuration, and with a configuration that outputs the first discharge command and the second discharge command at different time periods, the control circuit 28 can calculate the values ​​of the resistances R1 to R3 of the branched first power line 241, the second power line 242, and the common power line 243.

[0109] Furthermore, according to the power supply system 20 of the electric vehicle 1 according to Embodiments 1 to 4, the control circuit 28 performs a process of measuring resistance values ​​while the electric vehicle 1 is running, stopped, charging, or in a pause transition process. By appropriately selecting these execution conditions, it is possible to realize resistance value measurement processing that meets various requirements, such as avoiding a decrease in drivability, improving the frequency of resistance value measurement, and suppressing a decrease in energy consumption.

[0110] According to the power supply system 20A of the electric vehicle 1 in Embodiment 5, the control circuit 28 outputs an ON command to close the charging relays 295p and 295n during periods when no current flows through the charging power lines 292p and 292n. The control circuit 28 then uses the charging voltage sensor 297 to measure the voltage at the branching points Nap and Nan of the power line 24. Therefore, by using the measured voltage, the control circuit 28 can easily determine the resistance value of each section, even when the power line 24 has multiple branches at branching points Nap and Nan.

[0111] More specifically, in the power supply system 20A of the electric vehicle 1 according to Embodiment 5, the power line 24 branches into a first power line 241 and a second power line 242 from branching points Nap and NAn. However, the control circuit 28 can calculate the resistances R1 and R2 of the branched first power line 241 and second power line 242 using the voltage measured by the charging voltage sensor 297.

[0112] Furthermore, according to the power supply system 20A of the electric vehicle 1 in Embodiment 5, the control circuit 28 outputs an ON command to close the charging relays 295p and 295n while the electric vehicle 1 is running. Therefore, it is possible to prevent the charging connector 291, which outputs the voltage of the battery 21, from being exposed to the outside.

[0113] According to the power supply system 20B of the electric vehicle 1 in Embodiment 6, the control circuit 28 outputs an all-on command that closes all charging relays 295Ap to 295Bn, and connects the first battery 21A and the second battery 21B in parallel. The control circuit 28 then uses the current flowing through this parallel connection to measure the resistance of the power line 31. Therefore, when voltage adjustment is required to make the voltages of the first battery 21A and the second battery 21B equal, by performing the above parallel connection and measuring the resistance, the current that would otherwise be wasted during voltage adjustment can be effectively utilized and used to measure the resistance of the power line 31.

[0114] Furthermore, according to the power supply system 20B of the electric vehicle 1 according to Embodiment 6, the control circuit 28 outputs an all-on command to close all charging relays 295Ap to 295Bn when the voltage difference between the first battery 21A and the second battery 21B is below a threshold. The control circuit 28 then measures the resistance value of the power line 31. Therefore, it is possible to suppress the flow of an abnormally large current due to the parallel connection of the first battery 21A and the second battery 21B.

[0115] The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments. For example, the above embodiments show a specific example of controlling the temperature of a power line using the values ​​of the resistances R1 to R3 of the power line 24, but the temperature control method is not limited to the above example, and various methods may be applied. Furthermore, the details shown in the embodiments can be modified as appropriate without departing from the spirit of the invention.

[0116] This invention can be used in power supply systems for electric vehicles.

[0117] 1. Electric vehicle 2A, 2B Drive wheels 3A First electric motor 3B Second electric motor 5. Driving control device 6. Vehicle control circuit 20, 20A, 20B Power system 21. Battery 21A First battery 21B Second battery 22. First motor control circuit 23. Second motor control circuit 24. Power lines 241 First power line 242 Second power line 243 Common power line Nap, Nan Branch point 25. Battery management circuit 25A First battery management circuit 25B Second battery management circuit 251, 251A, 251B Battery current sensor 252, 252A, 252B Battery voltage sensor 26p, 26n, 26Ap, 26An, 26Bp, 26Bn Main relay 28. Control circuit 28a Memory device 221 First inverter 222 First inverter current sensor 223 First inverter voltage sensor 224 First inverter control circuit 225 First capacitor 231 Second inverter 232 Second inverter current sensor 233 Second inverter voltage sensor 234 Second inverter control circuit 235 Second capacitor 291, 291p, 291n Charging connector 292, 292p, 292n Charging power line 293 Charging control circuit 294 Sensor 295p, 295n, 295Ap, 295An, 295Bp, 295Bn Charging relay 297 Charging voltage sensor 298 Lid 299 Switching sensor 31 Power line 311p, 311n Third power line 312p, 312n Fourth power line 313p, 313n First charging power line 314p, 314n Second charging power line R1, R2, R3 Resistors

Claims

1. A power supply system for an electric vehicle comprising: an electric motor for driving the drive wheels; a battery for storing power; an inverter for driving the electric motor based on the power of the battery; a power line for transmitting power between the battery and the inverter; a plurality of sensors for measuring the current flowing through the power line and the voltage between multiple points on the power line; and a control circuit, wherein the plurality of sensors include a battery current sensor for measuring the current of the battery and a battery voltage sensor for measuring the voltage of the battery, and the control circuit calculates the resistance value of the power line based on the outputs of the plurality of sensors.

2. The power supply system for an electric vehicle according to claim 1, further comprising an electrical device that includes a capacitor for storing voltage and is connected to the power line, wherein the control circuit is capable of outputting a discharge command to release charge from the capacitor, and the control circuit calculates the resistance value of the power line based on the outputs of the plurality of sensors obtained during the period in which a discharge current is output from the capacitor based on the output of the discharge command.

3. The electric motor includes a first electric motor and a second electric motor; the inverter includes a first inverter for driving the first electric motor and a second inverter for driving the second electric motor; the capacitor includes a first capacitor included in the first inverter and a second capacitor included in the second inverter; the control circuit is capable of outputting a first discharge command for outputting a discharge current from the first capacitor and a second discharge command for outputting a discharge current from the second capacitor; the control circuit outputs the first discharge command and the second discharge command in mutually different first and second periods, respectively, and calculates the resistance value of the power line based on the outputs of the plurality of sensors obtained in the first period and the outputs of the plurality of sensors obtained in the second period, the power supply system for an electric vehicle according to claim 2.

4. The power lines include a pair of common power lines extending from the battery to a pair of branching points, a pair of first power lines extending from the pair of branching points to the first inverter, and a pair of second power lines extending from the pair of branching points to the second inverter; the plurality of sensors further include a first inverter current sensor for measuring the input current of the first inverter, a first inverter voltage sensor for measuring the input voltage of the first inverter, a second inverter current sensor for measuring the input current of the second inverter, and a second inverter voltage sensor for measuring the input voltage of the second inverter; and the control circuit calculates the resistance value of the common power lines, the resistance value of the first power lines, and the resistance value of the second power lines based on the outputs of the plurality of sensors; the power supply system for an electric vehicle according to claim 3.

5. The power supply system for an electric vehicle according to claim 3, wherein the control circuit outputs the first discharge command and the second discharge command and acquires the outputs of the plurality of sensors while the electric vehicle is running, stopped, charging, or undergoing a pause transition process.

6. A power supply system for an electric vehicle according to claim 1, further comprising: a charging connector for taking in DC charging power from an external source; a pair of charging power lines connecting the charging connector and the power line; a pair of charging relays capable of disconnecting each of the pair of charging power lines; and a charging voltage sensor for measuring the voltage of the charging power line, wherein the plurality of sensors include the charging voltage sensor; the control circuit is capable of outputting an ON command to switch the pair of charging relays to a closed state; the control circuit outputs the ON command during a period when no current flows through the pair of charging power lines, and calculates the resistance value based on the outputs of the plurality of sensors obtained when the pair of charging relays are in a closed state.

7. The electric motor includes a first electric motor and a second electric motor; the inverter includes a first inverter for driving the first electric motor and a second inverter for driving the second electric motor; the power lines include a pair of common power lines extending from the battery to a pair of branching points, a pair of first power lines extending from the pair of branching points to the first inverter, and a pair of second power lines extending from the pair of branching points to the second inverter; and the control circuit calculates the resistance values ​​of the common power lines, the first power lines, and the second power lines based on the outputs of the plurality of sensors, the power supply system for an electric vehicle according to claim 6.

8. The power supply system for an electric vehicle according to claim 6, wherein the control circuit outputs the ON command and acquires the output of the charging voltage sensor while the electric vehicle is running.

9. A power supply system for an electric vehicle according to claim 1, further comprising: a charging connector for taking in DC power to charge the battery; a charging power line connecting the charging connector and the power line; and a charging relay capable of disconnecting the pair of charging power lines, wherein the battery includes a first battery and a second battery; the charging power line includes a pair of first charging power lines connecting the charging connector and the first battery, and a pair of second charging power lines connecting the charging connector and the second battery; the charging relay includes a first system of charging relays capable of disconnecting each of the pair of first charging power lines, and a second system of charging relays capable of disconnecting each of the pair of second charging power lines; the control circuit is capable of outputting an all-on command to switch all of the first system of charging relays and the second system of charging relays to a closed state; and the control circuit calculates the resistance value based on the output of the plurality of sensors obtained when all of the first system of charging relays and the second system of charging relays are in a closed state.

10. The power supply system for an electric vehicle according to claim 9, wherein the control circuit determines whether the difference between the voltage of the first battery and the voltage of the second battery is below a threshold, and outputs the all-on command when it is determined to be below the threshold.

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