Battery charge / discharge control system and battery charge / discharge control method

Abstract

To appropriately select a battery to be preferentially used from among a plurality of batteries.SOLUTION: A battery charging / discharging control method is provided for controlling a first battery 7 and a second battery 8 that supply power to an electric motor 2, charge power supplied from the electric motor 2, and are connected in parallel with the electric motor 2. The battery charging / discharging control method includes steps of: acquiring respective internal resistances of the first battery 7 and the second battery 8; and selecting, as a battery to be preferentially used, a battery that has the smaller inner resistance between the first battery 7 and the second battery 8.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a battery charge / discharge control system and a battery charge / discharge control method for controlling the charging and discharging of a battery. [Background technology]

[0002] Conventionally, vehicles equipped with multiple batteries have been proposed to improve the running performance of vehicles using electric motors as a driving source. It is generally known that the charge / discharge characteristics of a battery deteriorate when its temperature decreases. Therefore, a technology has been proposed in which the temperatures of two batteries are compared and the battery with the lower temperature is used preferentially (for example, see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2009-240094 A Summary of the Invention [Problem to be solved by the invention]

[0004] Generally, the internal resistance of a battery increases when the battery temperature is low due to the charging and discharging characteristics of the battery. Therefore, when a battery with a low temperature is selected as the battery to be used preferentially as in the above-mentioned conventional technology, the internal resistance of the battery is relatively high, so that the amount of heat generated by the battery increases, and the energy loss of the battery due to the heat generation increases. Therefore, it is important to appropriately select the battery to be used preferentially, taking into account the energy loss of the battery.

[0005] An object of the present invention is to appropriately select a battery to be used preferentially from among a plurality of batteries. [Means for solving the problem]

[0006] One aspect of the present invention is a battery charge / discharge control method for supplying power to an electric motor, charging the electric power supplied from the electric motor, and controlling a plurality of batteries connected in parallel to the electric motor. In this battery charge / discharge control method, The plurality of batteries are configured with a first battery using cells with high internal resistance and high capacity density, and a second battery using cells with low internal resistance and high output density, and the first battery and the second battery are selected based on the battery temperature and SOC. The internal resistance of each Estimation death, First and second batteries From these, the battery with the smallest energy loss based on the internal resistance is selected as the battery to be used preferentially. Even if charging and discharging is possible using only one of the first and second batteries, both the first and second batteries are used for charging and discharging, and the charging and discharging power of one of the first and second batteries selected as the battery to be used preferentially is controlled to be greater than the charging and discharging power of the other battery. Effect of the Invention

[0007] According to the present invention, it is possible to appropriately select a battery to be used preferentially from among a plurality of batteries. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a block diagram showing an example of the configuration of a battery charge / discharge control system according to the first embodiment. [Diagram 2] FIG. 2 is a diagram showing an example of charge / discharge characteristics of the first battery. [Diagram 3] FIG. 3 is a diagram showing an example of charge / discharge characteristics of the second battery. [Figure 4] FIG. 4 is a flowchart showing an example of a procedure of a battery charge / discharge control process performed by the battery charge / discharge control system. [Diagram 5] FIG. 5 is a block diagram showing an example of the configuration of a battery charge / discharge control system according to the second embodiment. [Figure 6] FIG. 6 is a flowchart showing an example of a procedure of a battery charge / discharge control process performed by the battery charge / discharge control system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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

[0010] [First embodiment] [Example of battery charge / discharge control system configuration] 1 is a block diagram showing an example of the configuration of a battery charge / discharge control system 1 in the first embodiment. The battery charge / discharge control system 1 includes, for example, an electric motor 2 (travel motor) that functions as a drive source for traveling an electric vehicle. Note that the electric vehicle includes an electric vehicle (EV) or a hybrid electric vehicle (HEV).

[0011] Fig. 2 is a diagram showing an example of charge / discharge characteristics (charge / discharge performance) of the first battery 7. Fig. 3 is a diagram showing an example of charge / discharge characteristics of the second battery 8. In Figs. 2 and 3, the left side shows the relationship between internal resistance (DCR (Direct Current Resistance)) and temperature, and the right side shows the relationship between internal resistance and SOC (States Of Charge).

[0012] Generally, the characteristics of battery temperature and internal resistance are such that the internal resistance of the battery decreases in inverse proportion to the increase in battery temperature. In addition, upper and lower limits of the usable battery temperature are set for each battery, and there are restrictions on use outside the range set by these upper and lower limits. In addition, upper and lower limits of the usable SOC are set for each battery, and there are restrictions on use outside the range set by these upper and lower limits.

[0013] As shown in FIG. 1, the battery charge / discharge control system 1 includes an electric motor 2, an inverter 3, a controller 4, DC / DC converters 5 and 6, a first battery 7, and a second battery 8.

[0014] The electric motor 2 is driven to rotate by AC current supplied from the inverter 3, and transmits driving force to the drive wheels of the vehicle. The electric motor 2 is also configured to recover the kinetic energy of the vehicle as electric energy to the first battery 7 and the second battery 8 when the vehicle is decelerating, etc. In this way, the electric motor 2 functions as both a drive motor and a generator motor.

[0015] The inverter 3 is electrically connected to the electric motor 2, the first battery 7, and the second battery 8. Based on the control of the controller 4, the inverter 3 converts AC power generated by the electric motor 2 into DC power and supplies it to at least one of the first battery 7 and the second battery 8. Based on the control of the controller 4, the inverter 3 also converts DC power output from at least one of the first battery 7 and the second battery 8 into AC power and supplies it to the electric motor 2.

[0016] The controller 4 is a computer including, for example, a central processing unit (CPU), a read-only memory (ROM), a random access memory (RAM), and an input / output interface (I / O interface). The controller 4 also controls each part. For example, the controller 4 estimates the internal resistance of each battery based on the battery temperature and SOC, and executes control to select a battery to be used preferentially based on the comparison result of the internal resistance of each battery.

[0017] The DC / DC converters 5 and 6 are installed to match the output voltages of the first battery 7 and the second battery 8. Specifically, the DC / DC converter 5 performs voltage conversion to adjust and output the DC voltage exchanged between the inverter 3 and the first battery 7 based on the control of the controller 4. Also, the DC / DC converter 6 performs voltage conversion to adjust and output the DC voltage exchanged between the inverter 3 and the second battery 8 based on the control of the controller 4. Note that, although an example in which a DC / DC converter is provided in both the first battery 7 and the second battery 8 is shown in the first embodiment, a DC / DC converter may be provided in either one of the batteries. Note that an example in which a DC / DC converter is provided in one of the batteries will be shown in the second embodiment.

[0018] The first battery 7 is an energy-specialized battery pack that uses cells with high internal resistance and high capacity density. In other words, the first battery 7 is a battery pack with high capacity characteristics. In FIG. 2, the relationship between the internal resistance and temperature and the relationship between the internal resistance and SOC are shown as examples of the charge and discharge characteristics of the first battery 7.

[0019] The second battery 8 is a power-specialized battery pack using cells with low internal resistance and high output density. In other words, the second battery 8 is a battery pack with high output characteristics. FIG. 3 shows the relationship between internal resistance and temperature and the relationship between internal resistance and SOC as an example of charge / discharge characteristics of the second battery 8. Note that the high and low internal resistances of the first battery 7 and the second battery 8 shown here mean inherent values ​​when the first battery 7 and the second battery 8 are compared under the same conditions. That is, they mean characteristics that are determined according to the individual differences of the first battery 7 and the second battery 8, regardless of the operating conditions (temperature, SOC, etc.) of the first battery 7 and the second battery 8. For example, as shown in FIG. 2 and FIG. 3, the internal resistances of the first battery 7 and the second battery 8 change depending on the operating conditions such as the temperature and SOC of the battery, so it is assumed that the high and low measured internal resistances of the first battery 7 and the second battery 8 may be reversed depending on these changes.

[0020] In the first embodiment, for ease of explanation, an example is shown in which the relationship between the internal resistance and the temperature (i.e., a two-axis relationship) and the relationship between the internal resistance and the SOC (i.e., a two-axis relationship) are used separately. However, the relationship between the temperature and the SOC and the internal resistance (i.e., a three-axis relationship) may be used.

[0021] Furthermore, the first battery 7 and the second battery 8 are connected in parallel to the electric motor 2. Furthermore, the electric motor 2 is supplied with power from at least one of the first battery 7 and the second battery 8 based on the control of the controller 4.

[0022] In this way, the first embodiment shows an example of a battery pack consisting of two battery packs with different internal resistances when compared under the same conditions. Also, by using a first battery 7 with high capacity characteristics and a second battery 8 with high output characteristics in parallel, a vehicle equipped with a battery with high capacity characteristics and high output characteristics can be realized.

[0023] The first battery 7 is also provided with a temperature sensor that detects the temperature related to the first battery 7. Temperature information detected by this temperature sensor is output to the controller 4. One or more temperature sensors can be installed in the first battery 7. The installation location of the temperature sensor in the first battery 7 can be appropriately set based on experimental data or the like. Similarly, the second battery 8 is also provided with one or more temperature sensors that detect the temperature related to the second battery 8.

[0024] As shown in Figures 2 and 3, the internal resistance of each battery changes depending on the temperature and SOC of the battery. The amount of heat W generated when the battery is charged or discharged can be calculated from the following formula 1 using the current value I [A] when the battery is charged or discharged and the internal resistance value R [Ω] of the battery. W=I 2 ×R…Formula 1

[0025] For example, if a battery with a high internal resistance is used preferentially, the amount of heat generated by the battery with the high internal resistance will be large, resulting in a large energy loss in the battery due to the heat generated. Specifically, according to the above-mentioned formula 1, when the required current for each battery is the same, the amount of heat generated W during charging and discharging by the battery will be smaller for a battery with a low internal resistance. Here, the required power means the charging and discharging power required for each battery in the vehicle, and is calculated by the controller 4. Furthermore, the required voltage and the required current are calculated by the controller 4 based on the required power. In this embodiment, the required power for the electric motor 2 will be described as an example of the required power required for each battery in the vehicle.

[0026] Therefore, in the first embodiment, an example is shown in which a battery to be used preferentially is selected in consideration of the energy loss of the battery. Specifically, when the battery temperatures of both the first battery 7 and the second battery 8 are within the range of the upper limit and lower limit of the battery temperature, the internal resistances of the first battery 7 and the second battery 8 are compared, and the battery with the smaller internal resistance is selected as the battery to be used preferentially. According to the above-mentioned formula 1, a battery with a smaller internal resistance means a battery with a smaller energy loss based on the internal resistance. That is, selecting the battery with the smaller internal resistance as the battery to be used preferentially from among the first battery 7 and the second battery 8 means selecting the battery with the smaller energy loss based on the internal resistance as the battery to be used preferentially. Note that, when the battery temperature of at least one of the first battery 7 and the second battery 8 is not within the range of the upper limit and lower limit of the battery temperature, the battery to be used preferentially is selected based on a preset condition. Here, the range of the upper limit and lower limit of the battery temperature is a range that specifies the temperature at which charging and discharging of the battery needs to be restricted. In addition, the upper limit and lower limit of the battery temperature are appropriately set according to the battery.

[0027] Also, the battery selected as the battery to be used with priority is made to cover the power required for charging and discharging more than the other batteries. For example, the power that can be charged and discharged by the first battery 7 is set to 100, and the power that can be charged and discharged by the second battery 8 is set to 50. In this case, it is assumed that the first battery 7 is selected as the battery to be used with priority, and the power required for charging and discharging is 100. In this case, charging and discharging are performed using only the first battery 7 selected as the battery to be used with priority. Also, it is assumed that the first battery 7 is selected as the battery to be used with priority, and the power required for charging and discharging is 120. In this case, charging and discharging of 100 is performed using the first battery 7 selected as the battery to be used with priority, and charging and discharging of 20 is performed using the second battery 8. In this way, when charging and discharging is possible using only the battery selected as the battery to be used with priority, only the selected battery is used. On the other hand, when charging and discharging cannot be performed using only the battery selected as the battery to be used with priority, the selected battery is used, and the power that cannot be covered by the selected battery is covered by other batteries. In this way, when the maximum power of the battery selected as the battery to be preferentially used is insufficient relative to the power required by the electric motor 2, the difference in power is supplied from another battery.

[0028] In addition, even if charging and discharging can be performed using only one of the batteries, two batteries may be used. For example, assume that the first battery 7 is selected as the battery to be used with priority, and the power required for charging and discharging is 100. In this case, 90% of charging and discharging can be performed using the first battery 7 selected as the battery to be used with priority, and 10% of charging and discharging can be performed using the second battery 8. Also assume that the first battery 7 is selected as the battery to be used with priority, and the power required for charging and discharging is 120. In this case, 90% of charging and discharging can be performed using the first battery 7 selected as the battery to be used with priority, and 30% of charging and discharging can be performed using the second battery 8. In this way, when the first battery 7 is selected as the battery to be used with priority, the charge and discharge power of the first battery 7 with respect to the required power of the electric motor 2 is controlled to be larger than the charge and discharge power of the second battery 8 with respect to the required power. On the other hand, when the second battery 8 is selected as the battery to be used with priority, the charge and discharge power of the second battery 8 with respect to the required power is controlled to be larger than the charge and discharge power of the first battery 7 with respect to the required power. In this manner, in this embodiment, the charge / discharge power of the battery selected as the battery to be preferentially used is controlled to be greater than the charge / discharge power of the other batteries.

[0029] [Example of battery charge / discharge control system operation] 4 is a flowchart showing an example of a procedure for battery charge / discharge control processing by the battery charge / discharge control system 1. This procedure is executed based on a program stored in a storage unit (not shown). This procedure is also executed repeatedly at a predetermined calculation cycle.

[0030] In step S201, the controller 4 acquires the temperatures of the first battery 7 and the second battery 8. That is, the controller 4 acquires a temperature T1 detected by a temperature sensor attached to the first battery 7 and a temperature T2 detected by a temperature sensor attached to the second battery 8.

[0031] In step S202, the controller 4 determines whether or not each of the temperatures T1 and T2 is higher than the lower limit of the battery temperature and lower than the upper limit of the battery temperature. If each of the temperatures T1 and T2 is within the range of the upper and lower limits of the battery temperature, the process proceeds to step S203. On the other hand, if at least one of the temperatures T1 and T2 is not within the range of the upper and lower limits of the battery temperature, the process proceeds to step S205.

[0032] In step S203, the controller 4 estimates the internal resistance R1 of the first battery 7 based on the temperature T1, and estimates the internal resistance R2 of the second battery 8 based on the temperature T2. Specifically, the internal resistance R1 of the first battery 7 is estimated based on the relationship between the internal resistance and the temperature shown on the left side of Fig. 2, and the internal resistance R2 of the second battery 8 is estimated based on the relationship between the internal resistance and the temperature shown on the left side of Fig. 3.

[0033] In step S204, the controller 4 compares the estimated internal resistance R1 of the first battery 7 with the internal resistance R2 of the second battery 8, and determines whether the internal resistance R1 is greater than the internal resistance R2. If the internal resistance R1 is greater than the internal resistance R2, the process proceeds to step S206. On the other hand, if the internal resistance R1 is less than the internal resistance R2, the process proceeds to step S207.

[0034] In step S206, the controller 4 selects and uses the second battery 8 as the battery to be preferentially used.

[0035] In step S207, the controller 4 selects and uses the first battery 7 as the battery to be preferentially used. In this manner, in the first embodiment, from among the first battery 7 and the second battery 8, the battery having a smaller internal resistance (i.e., the battery having a smaller energy loss due to the internal resistance) is selected as the battery to be preferentially used.

[0036] In step S205, the controller 4 selects a battery to be used preferentially based on the temperatures T1 and T2. For example, it is preferable to select a battery included in a predetermined temperature range where a desired charge / discharge characteristic can be obtained as a battery to be used preferentially. Therefore, for example, when either the temperatures T1 or T2 is included in the range of the upper limit value and the lower limit value of the battery temperature, the controller 4 can select a battery having a battery temperature within the range of the upper limit value and the lower limit value as a battery to be used preferentially. On the other hand, when both the temperatures T1 and T2 are not included in the range of the upper limit value and the lower limit value of the battery temperature, the controller 4 can select a battery having a battery temperature closest to the range of the upper limit value and the lower limit value as a battery to be used preferentially. Note that in order to suppress heat generation of the battery with the higher battery temperature, the use of the battery with the higher battery temperature may be restricted. In this case, the controller 4 can select a battery with a lower battery temperature as a battery to be used preferentially. Then, when the first battery 7 is selected, the process proceeds to step S207. On the other hand, when the second battery 8 is selected, the process proceeds to step S206.

[0037] Although Fig. 4 shows an example in which the internal resistance of each battery is estimated using only the battery temperature, the internal resistance of each battery may be estimated using only the SOC. Specifically, the internal resistance R1 of the first battery 7 is estimated based on the relationship between the internal resistance and the SOC shown on the right side of Fig. 2, and the internal resistance R2 of the second battery 8 is estimated based on the relationship between the internal resistance and the SOC shown on the right side of Fig. 3. The internal resistance of each battery may also be estimated using the battery temperature and the SOC.

[0038] As described above, the upper and lower limits of the SOC of the battery are set. Even if the SOC of each battery is within the range of the upper and lower limits of the SOC, the charging and discharging of each battery is controlled so as to optimize the battery capacity. That is, the charging and discharging of each battery is controlled based on the SOC of each battery. Furthermore, as shown on the right side of Figs. 2 and 3, the internal resistance of the battery increases with both an increase and a decrease in the SOC, and therefore changes in a U-shape according to the increase and decrease in the SOC.

[0039] For example, if only one of the first battery 7 and the second battery 8 continues to be used, the SOC of the battery that has been used decreases. For example, if the SOC of the battery that has been used decreases below the median SOC of the battery, the internal resistance of the battery increases as shown on the right side of FIG. 2 and FIG. 3. In this case, it is assumed that the internal resistance of the battery that has been used will be greater than the internal resistance of the battery that has not been used. That is, it is assumed that the magnitude of the internal resistance of the two batteries will be reversed as a result of continuing to use only one battery. In such a case, at a predetermined timing, the battery that has not been used is selected as the battery to be used preferentially. In this way, in the first embodiment, in addition to the charge / discharge control based on the SOC of the battery, charge / discharge control based on the internal resistance can be executed, so that the efficiency of the system can be improved.

[0040] 4 shows an example in which the SOC of the first battery 7 and the second battery 8 is within the range of the lower limit and upper limit of the SOC. If the SOC of the first battery 7 or the second battery 8 is not within the range of the lower limit and upper limit of the SOC, a battery whose SOC is within the range of the lower limit and upper limit is selected and used. If the SOC of both the first battery 7 and the second battery 8 is not within the range of the lower limit and upper limit of the SOC, a battery is selected and used based on a preset condition.

[0041] In the first embodiment, the battery charge / discharge control system 1 including two batteries (first battery 7, second battery 8) has been described as an example, but the first embodiment can also be applied to a battery charge / discharge control system including three or more batteries. For example, assume a battery charge / discharge control system including a battery A with the highest internal resistance, a battery B with the second highest internal resistance, and a battery C with the lowest internal resistance when the battery temperature and SOC are the same. When the first embodiment is applied to this battery charge / discharge control system, the battery with the lowest internal resistance (battery C under the same conditions) is selected as the battery to be used with priority. That is, based on the internal resistances of the multiple batteries, the battery with the lowest internal resistance (the battery with the lowest energy loss due to the internal resistance) is selected from among the multiple batteries as the battery to be used with priority.

[0042] [Configuration and Effects of the First Embodiment] The battery charge / discharge control method according to the first embodiment is a battery charge / discharge control method that supplies power to an electric motor 2, charges the power supplied from the electric motor 2, and controls a first battery 7 and a second battery 8 (one example of a plurality of batteries) connected in parallel to the electric motor 2. In this battery charge / discharge control method, in step S203, the internal resistances of the first battery 7 and the second battery 8 are obtained, and in steps S204, S206, and S207, from among the first battery 7 and the second battery 8, a battery with the smallest energy loss based on the internal resistance is selected as the battery to be preferentially used.

[0043] According to this battery charge / discharge control method, the battery with the smallest energy loss based on the internal resistance, i.e., the battery with the smallest internal resistance (heat generation) can be selected as the battery to be used preferentially. Therefore, a control logic is realized that can appropriately select the battery to be used preferentially so as to reduce the energy loss per total charge / discharge power of the first battery 7 and the second battery 8.

[0044] In the battery charge / discharge control method according to the first embodiment, in step S203, the internal resistance of each of the first battery 7 and the second battery 8 (an example of a plurality of batteries) is estimated based on at least one of the battery temperature and the SOC.

[0045] According to this battery charge / discharge control method, the internal resistance of each battery can be estimated by calculation using the battery temperature and SOC, thereby improving the accuracy of the internal resistance of each battery and enabling more efficient control.

[0046] In the first embodiment, the multiple batteries are composed of a first battery and a second battery. In the battery charge / discharge control method according to the first embodiment, the internal resistance of the first battery 7 is compared with the internal resistance of the second battery 8 in step S204. If the internal resistance of the first battery 7 is greater than the internal resistance of the second battery 8, the second battery 8 is selected in step S206 as the battery with the smallest energy loss based on the internal resistance. On the other hand, if the internal resistance of the first battery 7 is less than the internal resistance of the second battery 8, the first battery 7 is selected in step S207 as the battery with the smallest energy loss based on the internal resistance.

[0047] According to this battery charge / discharge control method, a specific control logic can be realized for selecting a battery with the smallest energy loss based on the internal resistance. In particular, the internal resistance of a battery is directly related to the magnitude of the battery's energy loss (Equation 1). Therefore, by selecting a battery with the smallest energy loss based on the comparison result of the internal resistance of the batteries, the load of the battery charge / discharge control can be reduced.

[0048] Furthermore, in the battery charge / discharge control method according to the first embodiment, when the first battery 7 is selected in step S207 as the battery to be preferentially used, the charge / discharge power of the first battery 7 with respect to the power required by the electric motor 2 is controlled to be greater than the charge / discharge power of the second battery 8 with respect to the required power. On the other hand, when the second battery 8 is selected in step S206 as the battery to be preferentially used, the charge / discharge power of the second battery 8 with respect to the power required by the electric motor 2 is controlled to be greater than the charge / discharge power of the first battery 7 with respect to the required power.

[0049] According to this battery charge / discharge control method, it is possible to realize a specific control logic for giving priority to the use of a battery with a small internal resistance. As described above, the magnitude of the charge / discharge power to be set is directly linked to the magnitude of energy loss via the internal resistance (Equation 1). Therefore, by setting the priority relationship of the battery to be used based on the magnitude of the charge / discharge power, a control mode that can more reliably reduce energy loss is realized.

[0050] In particular, in the battery charge / discharge control method according to the first embodiment, when the maximum power of the battery selected as the battery to be preferentially used is insufficient relative to the power required by the electric motor 2, the difference in power is supplied from another battery.

[0051] According to this battery charge / discharge control method, the charge / discharge power of the battery with the small internal resistance is basically maximized, and the shortage of the required power is covered by the charge / discharge power of the battery with the large internal resistance, thereby making it possible to further reduce energy loss while satisfying the required power.

[0052] Moreover, the battery charge / discharge control system 1 according to the first embodiment includes a first battery 7 and a second battery 8 (one example of a plurality of batteries) that supply power to the electric motor 2, charge the electric motor 2 with the power supplied from the electric motor 2, and are connected in parallel to the electric motor 2, and a controller 4 that controls the charging and discharging of the first battery 7 and the second battery 8. The controller 4 acquires the internal resistances of the first battery 7 and the second battery 8, and executes control to select the battery with the smallest internal resistance from the first battery 7 and the second battery 8 as the battery to be preferentially used.

[0053] This makes it possible to realize a specific system configuration suitable for use with the battery charge / discharge control method.

[0054] [Second embodiment] In the first embodiment, an example is shown in which a battery is selected for preferential use by using the internal resistances of multiple batteries (using energy loss based on the internal resistance). In the second embodiment, an example is shown in which a battery is selected for preferential use by taking into consideration the energy loss of a DC / DC converter through which power passes as well as the energy loss of multiple batteries. This makes it possible to systematically improve the efficiency of the battery charge / discharge control system.

[0055] [Example of battery charge / discharge control system configuration] Fig. 5 is a block diagram showing a configuration example of a battery charge / discharge control system 10 in the second embodiment. The battery charge / discharge control system 10 is similar to the battery charge / discharge control system 1 shown in Fig. 1 except that the DC / DC converter 5 connected to the first battery 7 is omitted. Therefore, the following description will focus on the parts that are different from the battery charge / discharge control system 1, and parts corresponding to those in Fig. 1 will be denoted by the same reference numerals as in Fig. 1 and some of the description will be omitted.

[0056] As shown in FIG. 5, the battery charge / discharge control system 10 includes an electric motor 2, an inverter 3, a controller 4, a DC / DC converter 6, a first battery 7, and a second battery 8.

[0057] In general, a battery with high capacity characteristics is often used during normal vehicle running. Furthermore, if a DC / DC converter is provided in a battery that is used frequently, the amount of power passing through the DC / DC converter increases, resulting in a large power loss in the DC / DC converter. For this reason, when a DC / DC converter is provided in either the first battery 7 or the second battery 8, it is preferable to provide the DC / DC converter in the second battery 8 rather than in the first battery 7 that is used frequently. Therefore, in the second embodiment, an example in which the DC / DC converter 6 is provided in the second battery 8 is shown.

[0058] [Example of battery charge / discharge control system operation] Fig. 6 is a flowchart showing an example of a processing procedure of a battery charge / discharge control process by the battery charge / discharge control system 10. This processing procedure is executed based on a program stored in a storage unit (not shown). This processing procedure is executed repeatedly at a predetermined calculation period. The processing shown in Fig. 6 is an example in which a part of the processing shown in Fig. 4 is modified, and parts common to the processing shown in Fig. 4 are given the same reference numerals as in Fig. 4, and some of the explanations thereof will be omitted.

[0059] In step S211, the controller 4 estimates the internal resistance R1 of the first battery 7 based on the temperature T1, and estimates the internal resistance R2 of the second battery 8 based on the temperature T2. As described above, the internal resistance of each battery may be estimated using the battery temperature and SOC, or the internal resistance of each battery may be estimated using the SOC.

[0060] In step S212, the controller 4 calculates the energy losses W1 and W2 in each battery relative to the required power of the electric motor 2, based on the internal resistance and required current of each battery. Specifically, the controller 4 calculates the energy loss W1 (=I1 2In addition, the controller 4 calculates the energy loss W2 (=I2 2 × R2).

[0061] In step S213, the controller 4 calculates a required voltage and a required current for the DC / DC converter 6. The required voltage and the required current for the DC / DC converter 6 are calculated by the controller 4 based on the required power of the electric motor 2.

[0062] In step S214, the controller 4 calculates an energy loss W3 related to the required power in the DC / DC converter 6 based on the required voltage and current for the DC / DC converter 6 and the temperature of the DC / DC converter 6. Specifically, the controller 4 holds a loss map according to the required voltage, the required current, and the temperature. Then, the controller 4 uses the loss map to obtain the energy loss of the DC / DC converter corresponding to the required voltage and current for the DC / DC converter 6 and the temperature of the DC / DC converter 6. Note that, for the temperature of the DC / DC converter 6, a temperature sensor for detecting the temperature related to the DC / DC converter 6 may be provided inside or outside the DC / DC converter 6, and the temperature detected by the temperature sensor may be used. Alternatively, a temperature detected by another temperature sensor capable of detecting the temperature related to the DC / DC converter 6 may be used.

[0063] In step S215, the controller 4 compares the energy loss W1 of the first battery 7 with the sum (W2+W3) of the energy loss W2 of the second battery 8 and the energy loss W3 in the DC / DC converter 6, and determines whether the energy loss W1 is greater than the sum (W2+W3). If the energy loss W1 is greater than the sum (W2+W3), the process proceeds to step S206. On the other hand, if the energy loss W1 is less than the sum (W2+W3), the process proceeds to step S207.

[0064] As described in the first embodiment, if only one battery continues to be used, it is assumed that the magnitudes of the internal resistances of the two batteries are reversed. In such a case, in the first embodiment, the battery that has not been used is selected as the battery to be used preferentially at a predetermined timing based on the magnitude of the internal resistances (energy loss based on the internal resistance) of the two batteries. In contrast, in the second embodiment, the battery to be used preferentially is not selected based on the magnitude of the internal resistances of the two batteries, but the battery to be used preferentially is selected taking into consideration the influence of energy loss of the peripheral devices of the batteries (the DC / DC converter 6 in the second embodiment). In this way, in the second embodiment, charge and discharge control can be performed taking into consideration the influence of energy loss of the peripheral devices of the batteries (the DC / DC converter 6), so that the efficiency of the system can be improved.

[0065] Although an example in which a DC / DC converter is provided for one of the two batteries has been described above, the second embodiment can also be applied to cases in which a DC / DC converter is provided for both of the two batteries. When a DC / DC converter is provided for both of the two batteries, the sum of the battery energy loss and the energy loss in the DC / DC converter is calculated for both of the two batteries, and the battery to be preferentially used is selected based on the result of comparing the two sums.

[0066] In the second embodiment, the battery charge / discharge control system 10 including two batteries (the first battery 7 and the second battery 8) has been described as an example, but the second embodiment can also be applied to a battery charge / discharge control system including three or more batteries. For example, a battery charge / discharge control system including three batteries is assumed. When the second embodiment is applied to this battery charge / discharge control system, for each of the three batteries, the sum of the energy loss of the battery and the energy loss in the DC / DC converter is calculated, and the battery to be used preferentially is selected based on the comparison result of the three sums. That is, based on each energy loss calculated for a combination of a plurality of batteries and a DC / DC converter, the battery related to the combination with the smallest energy loss is selected as the battery to be used preferentially from among the plurality of batteries. In this case, for a battery to which a DC / DC converter is not connected, only the energy loss of the battery is compared.

[0067] [Configuration and Effects of the Second Embodiment] In the second embodiment, the DC / DC converter 6 is connected to at least one of the first battery 7 and the second battery 8 (an example of a plurality of batteries) (only the second battery 8 in the second embodiment). In the battery charge / discharge control method according to the second embodiment, in steps S213 and S214, an energy loss W3 generated in the DC / DC converter 6 due to the power required by the electric motor 2 for the second battery 8 to which the DC / DC converter 6 is connected is calculated. When a DC / DC converter is connected to a plurality of batteries, the energy loss for each DC / DC converter is calculated for each battery. In addition, for the second battery 8 to which the DC / DC converter 6 is connected among the first battery 7 and the second battery 8 (an example of a plurality of batteries), the calculation result (W2+W3) of the energy loss W3 calculated for the DC / DC converter 6 and the energy loss W2 based on the internal resistance of the second battery 8 is compared with the energy loss W1 based on the internal resistance of the first battery 7 to which the DC / DC converter is not connected. Then, in steps S215, S206, and S207, the battery with the smallest energy loss is selected as the battery to be used preferentially, based on the energy loss W1 based on the internal resistance of the first battery 7 not connected to a DC / DC converter and the calculation result (W2+W3) of the energy loss obtained for the second battery 8 connected to the DC / DC converter 6.

[0068] According to this battery charge / discharge control method, it is possible to select a battery to be used preferentially after considering the energy loss of the first battery 7 and the second battery 8 as well as the impact of the energy loss of the DC / DC converter 6. Therefore, more accurate control is possible, taking into consideration the impact of the energy loss of not only the battery itself but also the surrounding DC / DC converter 6.

[0069] In the second embodiment, the plurality of batteries are composed of a first battery 7 and a second battery 8. The first battery 7 and the second battery 8 are configured so that the internal resistance of the second battery 8 is smaller than that of the first battery 7 when the battery temperature and SOC are the same. That is, the second battery 8 is configured so that the inherent internal resistance determined based on the design or the like is lower than that of the first battery 7. The DC / DC converter 6 is connected to the second battery 8. In the battery charge / discharge control method of the second embodiment, in step S215, a first energy loss W1 based on the internal resistance of the first battery 7 is compared with a second energy loss (W2+W3) which is a calculation result of an energy loss W2 based on the internal resistance of the second battery 8 and an energy loss W3 calculated for the DC / DC converter 6. If the first energy loss W1 is larger than the second energy loss (W2+W3), in step S206, the second battery 8 is selected as the battery to be preferentially used. On the other hand, if the first energy loss W1 is smaller than the second energy loss (W2+W3), in step S207, the first battery 7 is selected as the battery to be used preferentially.

[0070] According to this battery charge / discharge control method, by comparing the energy loss W1 of the first battery 7 with the total value (W2+W3) of the energy loss W2 of the second battery 8 and the energy loss W3 of the DC / DC converter 6, a specific control logic can be realized for selecting the optimal battery, taking into account the effects of energy loss not only of the battery itself but also of the surrounding DC / DC converter 6.

[0071] Each process shown in each embodiment is executed based on a program for causing a computer to execute each processing procedure. Therefore, each embodiment can also be understood as an embodiment of a program for realizing a function for executing each process, and a recording medium for storing the program. For example, the program can be stored in a storage device of the vehicle by an update operation for adding a new function to the vehicle. This makes it possible to execute each process shown in each embodiment on the updated vehicle. The update can be performed, for example, during a regular inspection of the vehicle. The program may also be updated by wireless communication.

[0072] Although the embodiments of the present invention have been described above, the above-mentioned embodiments merely show some of the application examples of the present invention, and it is not intended that the technical scope of the present invention be limited to the specific configurations of the above-mentioned embodiments. [Explanation of symbols]

[0073] 1, 10 Battery charge / discharge control system, 2 Electric motor, 3 Inverter, 4 Controller, 5, 6 DC / DC converter, 7 First battery, 8 Second battery

Claims

1. 1. A battery charge / discharge control method for supplying power to an electric motor, charging the electric motor with the power supplied thereto, and controlling a plurality of batteries connected in parallel to the electric motor, comprising: The plurality of batteries include a first battery using cells having a high internal resistance and a high capacity density, and a second battery using cells having a low internal resistance and a high output density, Estimating an internal resistance of each of the first battery and the second battery based on a battery temperature and an SOC; selecting a battery having the smallest energy loss based on the internal resistance as a battery to be preferentially used from the first battery and the second battery; Even if charging and discharging can be performed using only one of the first battery and the second battery, charging and discharging are performed using both the first battery and the second battery, and controlling the charging and discharging power of one of the first battery and the second battery, selected as a battery to be preferentially used, to be greater than the charging and discharging power of the other battery; A method for controlling battery charging and discharging.

2. 2. A battery charge / discharge control method according to claim 1, comprising: When a DC / DC converter is connected to one of the first battery and the second battery, an energy loss caused in the DC / DC converter due to a power demand of the electric motor for the battery to which the DC / DC converter is connected is calculated for each DC / DC converter; for one of the first battery and the second battery to which the DC / DC converter is connected, a calculation result of the energy loss obtained for the DC / DC converter and an energy loss based on an internal resistance of the battery is compared with an energy loss based on an internal resistance of a battery to which the DC / DC converter is not connected; selecting a battery having the smallest energy loss among an energy loss based on an internal resistance of a battery not connected to the DC / DC converter and an energy loss obtained as a result of the calculation for a battery connected to the DC / DC converter, as the battery to be preferentially used; A method for controlling battery charging and discharging.

3. 3. The battery charge / discharge control method according to claim 2, the DC / DC converter is connected to the second battery; comparing a first energy loss based on an internal resistance of the first battery with a second energy loss which is the calculation result of an energy loss based on an internal resistance of the second battery and the energy loss obtained for the DC / DC converter, and selecting the second battery as the battery to be preferentially used when the first energy loss is larger than the second energy loss, and selecting the first battery as the battery to be preferentially used when the first energy loss is smaller than the second energy loss; A method for controlling battery charging and discharging.

4. A battery charge / discharge control system including: a plurality of batteries that supply power to an electric motor, charge the electric power supplied from the electric motor, and are connected in parallel to the electric motor; and a controller that controls charging and discharging of the plurality of batteries, The plurality of batteries include a first battery using cells having a high internal resistance and a high capacity density, and a second battery using cells having a low internal resistance and a high output density, The controller: Estimating an internal resistance of each of the first battery and the second battery based on a battery temperature and an SOC; selecting a battery having the smallest internal resistance from the first battery and the second battery as a battery to be preferentially used; Even if charging and discharging can be performed using only one of the first battery and the second battery, charging and discharging are performed using both the first battery and the second battery, and controlling the charging and discharging power of one of the first battery and the second battery, selected as a battery to be preferentially used, to be greater than the charging and discharging power of the other battery; Battery charge / discharge control system.

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