Battery control device for electric vehicles

Abstract

Provided is a battery control device for an electric vehicle that can reduce temporary deterioration of battery performance caused by temperature differences between multiple battery groups. The battery control device for an electric vehicle is mounted on an electric vehicle that includes a battery that includes a first battery group and a second battery group connected in parallel and stores power for running, and a variable resistor electrically connected to the battery, and includes a controller that controls the variable resistor, and the controller executes a resistance adjustment process based on the difference between the temperature of the first battery group and the temperature of the second battery group, and the resistance adjustment process controls the variable resistor so that the current per unit capacity of the first battery group and the current per unit capacity of the second battery group are closer to being equal than when the resistance adjustment process is not executed.

Description

[Technical field]

[0001] The present invention relates to a battery control device for an electric vehicle. [Background technology]

[0002] Patent Document 1 shows a configuration in which a variable resistance circuit is connected to two battery groups in an on-board power storage system. The variable resistance circuit is set so that a smaller discharge current flows through the battery group with a smaller SOC. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2017-175758 A Summary of the Invention [Problem to be solved by the invention]

[0004] The present inventors have found that when a temperature difference occurs among multiple battery groups in a battery mounted on an electric vehicle, the temperature difference increases, and it may happen that the battery cannot perform as intended.

[0005] An object of the present invention is to provide a battery control device for an electric vehicle that can reduce temporary deterioration of battery performance caused by temperature differences between multiple battery groups. [Means for solving the problem]

[0006] (1) The present invention In one aspect The battery control device for an electric vehicle is A battery control device for an electric vehicle, which is mounted on an electric vehicle, the battery including a first battery group and a second battery group connected in parallel and storing power for driving the vehicle, and a variable resistor electrically connected to the battery, A controller for controlling the variable resistor, the controller performs a resistance adjustment process based on a difference between a temperature of the first battery group and a temperature of the second battery group; The resistance adjustment process is a process for controlling the variable resistor so that a current per unit capacity of the first battery group and a current per unit capacity of the second battery group become closer to equal than when the resistance adjustment process is not performed. the law of nature, The controller does not execute the resistance adjustment process when the driving power is output from the battery. It is characterized by the above. (2) A battery control device for an electric vehicle according to another aspect of the present invention includes: A battery control device for an electric vehicle, which is mounted on an electric vehicle, the battery including a first battery group and a second battery group connected in parallel and storing power for driving the vehicle, and a variable resistor electrically connected to the battery, A controller for controlling the variable resistor, the controller performs a resistance adjustment process based on a difference between a temperature of the first battery group and a temperature of the second battery group; the resistance adjustment process is a process of controlling the variable resistor so that a current per unit capacity of the first battery group and a current per unit capacity of the second battery group become closer to equal than when the resistance adjustment process is not executed, the controller starts the resistance adjustment process when a difference between a temperature of the first battery group and a temperature of the second battery group is equal to or greater than a first threshold value; The resistance adjustment process is terminated when the difference between the temperature of the first battery group and the temperature of the second battery group becomes equal to or less than a second threshold value. (3) A battery control device for an electric vehicle according to another aspect of the present invention includes: A battery control device for an electric vehicle, which is mounted on an electric vehicle, the battery including a first battery group and a second battery group connected in parallel and storing power for driving the vehicle, and a variable resistor electrically connected to the battery, A controller for controlling the variable resistor, the controller executes a resistance adjustment process when there is a difference between a temperature of the first battery group and a temperature of the second battery group during regeneration in which regenerative power is sent to the battery; The resistance adjustment process is characterized in that it is a process of controlling the variable resistor so that the current per unit capacity of the first battery group and the current per unit capacity of the second battery group become closer to equal than when the resistance adjustment process is not performed. Effect of the Invention

[0007] According to the present invention, it is possible to reduce temporary deterioration of battery performance caused by temperature variations between the first cell group and the second cell group. [Brief description of the drawings]

[0008] [Figure 1] 1 is a block diagram showing an electric vehicle equipped with a battery control device according to an embodiment of the present invention. [Diagram 2] 5 is a time chart showing an example of control for suppressing over-discharging of a battery. [Diagram 3] FIG. 4 is a diagram illustrating the output performance of a battery. [Figure 4] FIG. 1 is a diagram illustrating an example of a battery of a comparative example. [Figure 5A]FIG. 4 is a diagram showing an example of changes in SOC and temperature of each battery group during discharge. [Figure 5B] FIG. 11 is a diagram showing an example of changes in SOC and temperature of each battery group during charging. [Figure 6] 4 is a flowchart showing an example of a battery control process executed by a controller of the battery control device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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

[0010] <Electric vehicles> Fig. 1 is a block diagram showing an electric vehicle equipped with a battery control device according to an embodiment of the present invention. The electric vehicle 1 in Fig. 1 includes drive wheels 2, a braking device 3 that generates a braking force by friction, an electric motor 20 that drives the drive wheels 2, a battery system 10 including a battery 11 that stores electric power for traveling, an operation unit 26 that performs operations for traveling, a vehicle controller 22 that controls traveling, an inverter 24 that drives the electric motor 20, and a battery control device 40 that controls the battery system 10.

[0011] The operation unit 26 is a mechanism operated by the driver to drive the electric vehicle 1. The operation unit 26 includes an accelerator operation unit (e.g., an accelerator pedal) 26a for transmitting an acceleration command, a brake operation unit (e.g., a brake pedal) 26b for transmitting a braking command, and a steering operation unit (e.g., a steering wheel) 26c for steering. Note that the operation unit 26 may be configured to be operated by an automatic driving device, and the accelerator operation unit 26a and the brake operation unit 26b may be configured as software.

[0012] The vehicle controller 22 receives an operation signal from an operation unit 26, and controls the inverter 24 so as to obtain acceleration or deceleration according to the operation, thereby causing the electric motor 20 to perform power running or regenerative operation. During regenerative operation, regenerative power is sent to the battery 11. The vehicle controller 22 is a microcomputer that operates according to a control program.

[0013] The vehicle controller 22 further confirms the discharge capacity and charge capacity of the battery 11 by exchanging information with the battery control device 40. The discharge capacity of the battery 11 is represented, for example, by dischargeable power Wout. The charge capacity of the battery 11 is represented, for example, by chargeable power Win. The dischargeable power Wout represents the upper limit of the dischargeable power at that time. The chargeable power Win represents the upper limit of the chargeable power at that time.

[0014] Then, the vehicle controller 22 adjusts the drive torque of the electric motor so that the power of the power running operation of the electric motor 20 does not exceed the discharge capacity of the battery 11. Similarly, the vehicle controller 22 adjusts the regenerative torque of the electric motor 20 so that the charging power by the regenerative operation of the electric motor 20 does not exceed the charging capacity of the battery 11. There may be cases where the charging capacity of the battery 11 becomes low and the braking force required for the electric vehicle 1 cannot be obtained by the regenerative braking of the electric motor 20 alone. In such a case, the vehicle controller 22 generates the required braking force by operating the brake device 3 in addition to the regenerative operation of the electric motor 20.

[0015] The vehicle controller 22 further performs control to suppress over-discharge of the battery 11. That is, the vehicle controller 22 performs control to stop discharging the battery 11 when the discharge capacity of the battery 11 is significantly reduced.

[0016] FIG. 2 is a time chart showing an example of control for suppressing over-discharge of the battery. As shown in FIG. 2, the control for suppressing over-discharge may be performed, for example, based on the voltage of the battery 11. That is, when the voltage of the battery 11 reaches the lower limit voltage Vlow (timing t1), the vehicle controller 22 stops the discharge current of the battery 11. Although not shown, the vehicle controller 22 may also perform control for gradually decreasing the discharge of the battery 11 when the output voltage of the battery 11 approaches the lower limit voltage Vlow. Here, the output voltage of the battery 11 is monitored by the battery control device 40, and information that the output voltage approaches the lower limit voltage Vlow and that the output voltage has reached the lower limit voltage Vlow may be sent from the battery control device 40 to the vehicle controller 22.

[0017] Alternatively, the vehicle controller 22 may perform similar control based on information on the dischargeable power Wout of the battery 11 instead of the output voltage. In this case, the vehicle controller 22 controls the inverter 24 so that discharging of the battery 11 stops when the dischargeable power Wout becomes zero. The vehicle controller 22 may also use control to gradually reduce the discharge of the battery 11 as the dischargeable power Wout approaches zero.

[0018] <Battery system and battery control device> 1, the battery 11 includes a first battery group 11A having a plurality of battery cells, and a second battery group 11B having a plurality of battery cells. The first battery group 11A may be a battery cell string in which a plurality of battery cells are connected in series, or may be a configuration in which a plurality of battery cell strings are connected in parallel. The same is true for the second battery group 11B. The first battery group 11A and the second battery group 11B are connected in parallel. The plurality of battery cells are, for example, lithium ion secondary batteries or nickel metal hydride secondary batteries.

[0019] In the following, a case will be described where the storage capacity of the first battery group 11A is the same as the storage capacity of the second battery group 11B. In this case, when the current of the first battery group 11A is the same as the current of the second battery group 11B, it means that the current per unit capacity of the first battery group 11A is the same as the current per unit capacity of the second battery group 11B. The unit capacity means unit storage capacity.

[0020] The battery system 10 further includes a variable resistor 12 electrically connected to the battery 11, a first temperature sensor 13a for estimating the temperature of the first battery group 11A, and a second temperature sensor 13b for estimating the temperature of the second battery group 11B.

[0021] The variable resistor 12 is a circuit including a plurality of electric resistors and a plurality of switches for switching the connections of the plurality of electric resistors, and the resistance value on the current path changes by switching the plurality of switches. Note that the variable resistor 12 may have various circuit configurations as long as the resistance value can be changed by control. The variable resistor 12 includes a first variable resistor 12A connected in series to the first battery group 11A and a second variable resistor 12B connected in series to the second battery group 11B. ,

[0022] The first temperature sensor 13a may directly detect the temperature of the first battery group 11A, or may detect the temperature of a location whose temperature correlates with that of the first battery group 11A, and the controller 41 may estimate the temperature of the first battery group 11A based on the detection result. The second temperature sensor 13b may directly detect the temperature of the second battery group 11B, or may detect the temperature of a location whose temperature correlates with that of the second battery group 11B, and the controller 41 may estimate the temperature of the second battery group 11B based on the detection result. When estimating the temperature, a data table correlating the detection result with the temperature is provided to the controller 41 in advance. The controller 41 can estimate the temperature from the data table and the detection result.

[0023] The battery control device 40 includes a controller 41 that controls the variable resistor 12. The controller 41 is a microcomputer that operates according to a control program. The detection results of the first temperature sensor 13a and the second temperature sensor 13b are sent to the controller 41. Furthermore, information on the operation amount of the accelerator operation unit 26a and information on the operation amount of the brake operation unit 26b are sent to the controller 41. The information on the operation amount may be sent to the controller 41 via the vehicle controller 22.

[0024] <Battery characteristics> FIG. 3 is a diagram for explaining the output performance (i.e., dischargeable power Wout) of a general battery. Map M1 in FIG. 3 is a general map for calculating dischargeable power Wout from the temperature and SOC of the battery. As shown in map M1, the value of dischargeable power Wout varies depending on the battery temperature and SOC. In the temperature range in which the battery can be used, dischargeable power Wout has a tendency to increase as the battery temperature increases and as the SOC increases. Although not shown in the figure, chargeable power Win similarly has a tendency to increase as the battery temperature increases and as the SOC decreases in the temperature range in which the battery 11 can be used.

[0025] The battery control device 40 measures the temperature, voltage, and current of the battery 11, and manages the SOC, dischargeable power Wout, and chargeable power Win of the battery 11.

[0026] <Effects due to temperature variations> Here, the influence of temperature variations occurring among the multiple battery groups in a battery 81 of a comparative example will be described. FIG. 4 is a diagram showing an example of a battery 81 of a comparative example. FIG. 5A is a diagram showing an example of changes in SOC and temperature of each battery group during discharging. FIG. 5B is a diagram showing an example of changes in SOC and temperature of each battery group during charging. The battery 81 of the comparative example has a configuration in which the first battery group 11A and the second battery group 11B are connected in parallel, and does not have the variable resistor 12 of this embodiment. The first battery group 11A and the second battery group 11B have internal resistances R1 and R2, respectively.

[0027] First, assume that there is a temperature variation between the first battery group 11A and the second battery group 11B, and that the SOCs are the same as each other, as an initial state (see "Initial State" in Figs. 5A and 5B). The temperature variation is such that the temperature of the first battery group 11A, 0°C, is lower than the temperature of the second battery group 11B, 5°C.

[0028] The first battery group 11A and the second battery group 11B have a characteristic that the lower the temperature, the higher the internal resistances R1, R2. Therefore, when there is temperature variation in the initial state, as shown in FIG. 4, the internal resistance R1 of the first battery group 11A is larger than the internal resistance R2 of the second battery group 11B. In this state, when a current I flows through the battery 81, the current I2 of the second battery group 11B is smaller than the current I1 of the first battery group 11A due to the difference between the internal resistances R1, R2. Furthermore, the heat generation amount W2 of the second battery group 11B is larger than the heat generation amount W1 of the first battery group 11A due to the difference between the current and the internal resistance.

[0029] Therefore, when a discharge current occurs, the temperature difference between the first battery group 11A and the second battery group 11B increases, as shown in "After Discharge" in Fig. 5A. Furthermore, the SOC of the second battery group 11B, which has a higher temperature, decreases faster, resulting in a difference in SOC between the first battery group 11A and the second battery group 11B.

[0030] Furthermore, when a charging current is generated, the temperature difference between the first battery group 11A and the second battery group 11B increases, as shown in "After charging" in Fig. 5B. Furthermore, the increase in SOC of the first battery group 11A, which has a lower temperature, decreases, and a difference in SOC occurs between the first battery group 11A and the second battery group 11B.

[0031] That is, if there is a temperature difference between the first battery group 11A and the second battery group 11B, the temperature difference will be further increased by the current flow. If the temperature difference is large, for example, the first battery group 11A and the second battery group 11B may become very low in temperature compared to the other. In this case, if a charging current flows through one of the battery groups that has become low in temperature, there is a risk that the deterioration of the battery group will progress due to deposition of metallic lithium on the internal electrodes, etc. In addition, if the temperature difference is large, there is a risk that only one of the first battery group 11A and the second battery group 11B may become very high in temperature. In this case, there is a risk that the material decomposition and structural deterioration in the cell of the one battery group that has become high in temperature will progress. As a result, there is an influence that the deterioration will be biased between the first battery group 11A and the second battery group 11B.

[0032] Furthermore, if there is a temperature variation between the first battery group 11A and the second battery group 11B, a current will flow, causing a difference in SOC, as shown in Figures 5A and 5B. If there is a difference in SOC, even if one of the first battery group 11A and the second battery group 11B has a margin for discharge or charge, the other will not have the margin, which will have the effect of restricting discharge or charge from the battery 81.

[0033] Furthermore, as shown in FIG. 5B, after charging, in addition to the temperature difference becoming wider, the SOC of the first battery group 11A, which has a lower temperature, becomes lower than the SOC of the second battery group 11B, which has a higher temperature. As described above, the dischargeable power Wout tends to decrease as the temperature decreases and also decreases as the SOC decreases. Therefore, as both the temperature and the SOC decrease in the first battery group 11A, the dischargeable power Wout of the first battery group 11A becomes lower than the dischargeable power Wout of the second battery group 11B. In this case, even if the second battery group 11B has a surplus, the dischargeable power Wout of the first battery group 11A becomes a low value (for example, zero), and this causes an output restriction on the battery 81. In particular, at low temperatures (such as 10° C. or lower) at which the value of the dischargeable power Wout becomes small, the possibility of the above-mentioned output restriction occurring increases.

[0034] <Control action> The controller 41 of the battery control device 40 performs the following control operation in order to reduce the effects of the temperature variations described above.

[0035] That is, first, the controller 41 estimates the temperature of the first battery group 11A and the temperature of the second battery group 11B based on the outputs of the first temperature sensor 13a and the second temperature sensor 13b. Note that if the temperatures can be estimated, the controller 41 may estimate the above temperatures from other conditions without using the outputs of the temperature sensors.

[0036] When there is a temperature difference between the first battery group 11A and the second battery group 11B, the controller 41 performs a resistance adjustment process. The resistance adjustment process is a process for controlling the resistance value of the variable resistor 12 so that the current flowing through the first battery group 11A and the current flowing through the second battery group 11B become closer to equal compared to the case where the resistance adjustment process is not performed.

[0037] By performing the resistance adjustment process, even if a temperature difference occurs between the first battery group 11A and the second battery group 11B, the currents of both become equal, so that the amounts of self-generated heat of the first battery group 11A and the second battery group 11B become equal or the magnitudes are reversed. This makes it possible to reduce the increase in the temperature difference between the first battery group 11A and the second battery group 11B. This makes it possible to suppress the effects caused by the increase in the temperature difference described above.

[0038] Specifically, in the resistance adjustment process, when the temperature of the first battery group 11A is higher than the temperature of the second battery group 11B, the controller 41 makes the resistance value of the first variable resistor 12A greater than the resistance value of the second variable resistor 12B. Similarly, when the temperature of the first battery group 11A is lower than the temperature of the second battery group 11B, the controller 41 makes the resistance value of the first variable resistor 12A smaller than the resistance value of the second variable resistor 12B. Through this control, the current of the first battery group 11A and the current of the second battery group 11B can be made closer to equal.

[0039] The controller 41 may be configured to perform the resistance adjustment process under the above conditions, particularly during regenerative operation when a charging current is sent to the battery 11. By performing the resistance adjustment process when a charging current is sent, it is possible to reduce the occurrence of a situation such as that shown in "After charging" in FIG. 5B. This situation is a situation in which both the temperature and SOC are low in one of the first battery group 11A and the second battery group 11B, resulting in a lower dischargeable power Wout compared to the other. Therefore, by performing the resistance adjustment process when a charging current is sent, it is possible to reduce the phenomenon in which the dischargeable power Wout of one battery group decreases first, resulting in an output limit for the entire battery 11.

[0040] Furthermore, the controller 41 may be configured to not execute the resistance adjustment process during driving when a discharge current is output from the battery 11. In the electric vehicle 1, a larger current tends to flow to the battery 11 during acceleration than during braking. This is because braking of the electric vehicle 1 is achieved by a combination of regenerative braking and braking by the brake device 3. On the other hand, acceleration of the electric vehicle 1 is mainly achieved by power running of the electric motor 20. Therefore, by not executing the resistance adjustment process during driving as described above, the probability that the resistance adjustment process will be not executed when a large current flows increases. Therefore, during a driving period when the influence of temperature variations is small, the power loss occurring in the variable resistor 12 can be suppressed.

[0041] In addition, by not executing the resistance adjustment process during operation, the discharge current of the lower-temperature battery group out of the first battery group 11A and the second battery group 11B is reduced, so that the decrease in SOC of the lower-temperature battery group can be suppressed. Therefore, it is possible to suppress a decrease in both temperature and SOC in one battery group. This makes it possible to reduce the phenomenon in which the dischargeable power Wout of one battery group becomes smaller before the other battery group, resulting in an output limit for the entire battery 11.

[0042] The controller 41 may determine whether or not the vehicle is in regenerative driving mode in which a charging current is being sent, or whether or not the vehicle is in driving mode in which driving power is being output from the battery 11, based on information on the operation amount of the brake operation unit 26b and information on the operation amount of the accelerator operation unit 26a. Alternatively, the controller 41 may detect the current flowing through the power line connected to the battery 11, and determine whether the vehicle is in a period in which a charging current is being sent, or a period in which a discharging current is being output.

[0043] The phenomenon that the dischargeable power Wout of one of the first battery group 11A and the second battery group 11B decreases first, resulting in output restriction of the entire battery 11, is more likely to occur at low temperatures. Therefore, the controller 41 may add a condition of low temperature to the conditions for executing the resistance adjustment process. A low temperature may be 25° C. or lower, 10° C. or lower, or 0° C. or lower. A low temperature may also be defined as a temperature at which the dischargeable power Wout is 20% or lower of the maximum value when the SOC is 10%.

[0044] The controller 41 may be configured to start the resistance adjustment process when the temperature difference between the first battery group 11A and the second battery group 11B is equal to or greater than a first threshold, and to end the resistance adjustment process when the temperature difference becomes less than a second threshold. The first threshold is not particularly limited, but can be set to a value within a range of 5°C to 15°C, for example. The second threshold is not particularly limited, but can be set to a value lower than the first threshold, between 0°C and 15°C. Such a configuration makes it easy to execute the resistance adjustment process at an appropriate timing such that the advantages of the resistance adjustment process outweigh the disadvantages of the resistance adjustment process (such as the occurrence of power loss).

[0045] <Battery control processing> Next, an example of the battery control process executed by the controller of the battery control device will be described with reference to a flowchart. Fig. 6 is a flowchart showing an example of the battery control process. The battery control process is repeatedly executed while the electric vehicle 1 is activated.

[0046] When the battery control process is started, the controller 41 estimates the temperature difference between the first battery group 11A and the second battery group 11B based on the outputs of the first temperature sensor 13a and the second temperature sensor 13b (step S1).

[0047] Next, the controller 41 determines whether the temperature difference between the first battery group 11A and the second battery group 11B is equal to or greater than a first threshold value Tth1 (step S2). The temperature difference means the absolute value of the difference between the two temperatures. If the determination result is No, the controller 41 ends one battery control process.

[0048] On the other hand, if the determination result of step S2 is YES, the controller 41 determines whether the temperature is lower, the first battery group 11A or the second battery group 11B (step S3). Then, if the temperature of the first battery group 11A is lower, the controller 41 prepares to set a first switching state in which the resistance value of the second variable resistor 12B is higher than that of the first variable resistor 12A (step S4). On the other hand, if the temperature of the second battery group 11B is lower, the controller 41 prepares to set a second switching state in which the resistance value of the first variable resistor 12A is higher than that of the second variable resistor 12B (step S5). Each of the first switching state and the second switching state may be a switching state of the variable resistor 12 that is previously determined. Alternatively, each of the first switching state and the second switching state may be a switching state in which the resistance value changes depending on the temperature difference. In either case, by setting the first or second switching state, the currents flowing through the first battery group 11A and the second battery group 11B become closer to being equal, compared to a case where the first or second switching state is not set.

[0049] Next, the controller 41 determines whether a charging current is being generated (for example, during regeneration when regenerative power is being generated) (step S6). Specifically, the controller 41 determines whether the operation amount of the accelerator operation unit 26a is decreasing or the operation amount of the brake operation unit 26b is greater than zero, thereby determining whether the electric motor 20 is in a regenerative operation.

[0050] As a result, if a charging current is generated (e.g., during regenerative operation), the controller 41 switches the variable resistor 12 to the first switching state or the second switching state prepared in step S4 or S5 (step S7). On the other hand, if a charging current is not generated, the controller 41 cancels the switching of the variable resistor 12 (step S8). Canceling the switching means that the resistance value of the first variable resistor 12A and the resistance value of the second variable resistor 12B are both set to zero. Alternatively, canceling the switching of the variable resistor 12 may mean that the resistance value of the first variable resistor 12A and the resistance value of the second variable resistor 12B are set to a predetermined value (e.g., an equal predetermined value).

[0051] Furthermore, the controller 41 counts the time elapsed in the loop process of steps S6 to S9, and determines whether a preset time (for example, 10 seconds) has elapsed (step S9). If the time has not elapsed, the controller 41 returns the process to step S6 and continues the loop process of steps S6 to S9.

[0052] On the other hand, if it is determined in step S9 that the time has elapsed, the controller 41 estimates the temperature difference between the first battery group 11A and the second battery group 11B based on the outputs of the first temperature sensor 13a and the second temperature sensor 13b (step S10).

[0053] Then, the controller 41 determines whether the temperature difference between the first battery group 11A and the second battery group 11B is less than a second threshold value Tth2 (step S11). If the result of the determination is No, the controller 41 returns to the process of step S6 and continues the loop process of steps S6 to S11. On the other hand, if the result of the determination in step S11 is YES, the controller 41 ends one iteration of the battery control process.

[0054] By the above-described battery control process, an example of the control operation of the battery system 10 described above can be realized.

[0055] The condition for transitioning to steps S4 and S5, or to step S7, may include a condition that the battery 11 is at a low temperature. The controller 41 may determine whether the battery 11 is at a low temperature based on the temperature of the battery 11 (average temperature, maximum temperature, minimum temperature, etc.) or the environmental temperature of the battery 11 (air temperature, coolant temperature, etc.). The low temperature is as described above. According to this configuration, switching of the variable resistor 12 is reduced at high temperatures when the influence due to temperature variations is small. Therefore, it is possible to reduce losses caused by the resistance of the variable resistor 12 when the influence due to temperature variations is small.

[0056] The program for the battery control process is stored in a non-transitory storage medium (non-transitory computer readable medium) 41a built into the controller 41. The controller 41 may be configured to read the program stored in the portable non-transitory storage medium and execute the program. The portable non-transitory storage medium may store the program for the battery control process described above.

[0057] The above describes the embodiments of the present invention. However, the present invention is not limited to the above embodiments. For example, in the above embodiments, the first battery group 11A and the second battery group 11B have the same storage capacity. However, the storage capacity of the first battery group 11A and the storage capacity of the second battery group 11B may be different. In that case, in the description of the section [Mode for carrying out the invention], the current (i.e., the discharge current and the charge current) flowing through the first battery group 11A or the second battery group 11B may be read as the current per unit capacity. Furthermore, the resistance value of the first variable resistor 12A or the second variable resistor 12B may be read as the resistance value per unit capacity. Furthermore, the heat generation amount of the first battery group 11A or the second battery group 11B may be read as the heat generation amount per unit capacity.

[0058] In the above embodiment, the battery 11 has two battery groups, the first battery group 11A and the second battery group 11B, but the battery 11 may have three or more battery groups connected in parallel with each other. In that case, any one of the battery groups may be regarded as the first battery group and the other battery group as the second battery group.

[0059] In addition, in the above embodiment, an EV (Electric Vehicle) that does not have an internal combustion engine is shown as the electric vehicle, but the electric vehicle may be an HEV (Hybrid Electric Vehicle) or a PHEV (Plug-in Hybrid Electric Vehicle). Other details shown in the embodiment may be appropriately changed without departing from the spirit of the invention. [Industrial Applicability]

[0060] The present invention can be used in a battery control device for an electric vehicle. [Explanation of symbols]

[0061] 1 Electric vehicles 2 Drive wheels 3 Braking device 10 Battery System 11 Battery 11A 1st battery group 11B 2nd battery group 12 Variable resistor 12A First Variable Resistor 12B Second variable resistor 13a First temperature sensor 13b Second temperature sensor 20 Electric motor 22 Vehicle Controller 24 Inverter 26 Control section 26a Accelerator operation part 26b Brake operation unit 40 Battery control device 41 Controller 41a Storage medium

Claims

1. A battery control device for an electric vehicle is mounted on an electric vehicle including a battery including a first battery group and a second battery group connected in parallel and storing power for driving the vehicle, and a variable resistor electrically connected to the battery, A controller for controlling the variable resistor, the controller performs a resistance adjustment process based on a difference between a temperature of the first battery group and a temperature of the second battery group; the resistance adjustment process is a process of controlling the variable resistor so that a current per unit capacity of the first battery group and a current per unit capacity of the second battery group become closer to equal than when the resistance adjustment process is not executed, The battery control device for an electric vehicle, wherein the controller does not execute the resistance adjustment process when the vehicle is being driven and driving power is being output from the battery.

2. the variable resistor includes a first variable resistor connected in series to the first battery group and a second variable resistor connected in series to the second battery group; The resistance adjustment process includes: When the temperature of the first battery group is higher than the temperature of the second battery group, The resistance value of the first variable resistor is made larger than the resistance value of the second variable resistor; When the temperature of the first battery group is lower than the temperature of the second battery group, 2. The battery control device for an electric vehicle according to claim 1, wherein the resistance value of the first variable resistor is made smaller than the resistance value of the second variable resistor.

3. When there is a difference between a temperature of the first battery group and a temperature of the second battery group during regeneration in which regenerative power is sent to the battery, the controller 2. The battery control device for an electric vehicle according to claim 1, wherein the resistance adjustment process is executed.

4. the controller starts the resistance adjustment process when a difference between a temperature of the first battery group and a temperature of the second battery group is equal to or greater than a first threshold value; 2. The battery control device for an electric vehicle according to claim 1, wherein the resistance adjustment process is terminated when a difference between the temperature of the first battery group and the temperature of the second battery group becomes equal to or less than a second threshold value.

5. A battery control device for an electric vehicle is mounted on an electric vehicle including a battery including a first battery group and a second battery group connected in parallel and storing power for driving the vehicle, and a variable resistor electrically connected to the battery, A controller for controlling the variable resistor, the controller performs a resistance adjustment process based on a difference between a temperature of the first battery group and a temperature of the second battery group; the resistance adjustment process is a process of controlling the variable resistor so that a current per unit capacity of the first battery group and a current per unit capacity of the second battery group become closer to equal than when the resistance adjustment process is not executed, the controller starts the resistance adjustment process when a difference between a temperature of the first battery group and a temperature of the second battery group is equal to or greater than a first threshold value; 23. A battery control device for an electric vehicle, comprising: a control unit for controlling a resistance of a battery that is electrically connected to a first battery group and a second battery group;

6. the variable resistor includes a first variable resistor connected in series to the first battery group and a second variable resistor connected in series to the second battery group; The resistance adjustment process includes: When the temperature of the first battery group is higher than the temperature of the second battery group, The resistance value of the first variable resistor is made larger than the resistance value of the second variable resistor; When the temperature of the first battery group is lower than the temperature of the second battery group, 6. The battery control device for an electric vehicle according to claim 5, wherein the process comprises making the resistance value of the first variable resistor smaller than the resistance value of the second variable resistor.

7. When there is a difference between a temperature of the first battery group and a temperature of the second battery group during regeneration in which regenerative power is sent to the battery, the controller 6. The battery control device for an electric vehicle according to claim 5, wherein the resistance adjustment process is executed.

8. A battery control device for an electric vehicle is mounted on an electric vehicle including a battery including a first battery group and a second battery group connected in parallel and storing power for driving the vehicle, and a variable resistor electrically connected to the battery, A controller for controlling the variable resistor, the controller executes a resistance adjustment process when there is a difference between a temperature of the first battery group and a temperature of the second battery group during regeneration in which regenerative power is sent to the battery; a current per unit capacity of the first battery group and a current per unit capacity of the second battery group that are closer to equal than when the resistance adjustment process is not performed, the current per unit capacity of the first battery group being closer to equal than when the resistance adjustment process is not performed, the battery control device for an electric vehicle being characterized in that

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