Battery management system

Abstract

To suppress wasteful consumption of stored electric power in a battery pack, which is caused by equalization control.SOLUTION: A vehicle 1 includes: a battery pack 10 that includes a plurality of cells B1 to Bn which are connected in series; an equalization circuit 30 configured to be capable of individually discharging each of a plurality of cells; and an ECU 100 that executes equalization control to the equalization circuit 30, which eliminates inequality in SOC among the plurality of cells B1 to Bn. The battery pack 10 is charged or discharged so that the SOC of the battery pack 10 falls within a normal SOC range. The ECU 100 estimates an equivalent SOC that is an SOC at which the SOCs of the plurality of cells become equal to each other in the case where the battery pack is charged or discharged without the equalization control being executed, based on the voltage and full charging capacity of each of the plurality of cells. The ECU 100 executes the equalization control when the equivalent SOC is within the normal SOC range, and does not execute the equalization control when the equivalent SOC is out of the normal SOC range.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present disclosure relates to a battery management system. [Background technology]

[0002] JP 2021-090349 A (Patent Document 1) discloses a control system for a battery pack. The control system includes a discharge circuit configured to be able to discharge a plurality of cells individually, and a control device configured to execute equalization control to eliminate inequality in the state of charge (SOC) of the plurality of cells by individually discharging the plurality of cells using the discharge circuit. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-090349 Summary of the Invention [Problem to be solved by the invention]

[0004] When equalization control is executed, a part of the power stored in the battery pack is consumed. Therefore, for example, if a battery management system is installed in a vehicle, the vehicle's cruising distance (so-called EV distance) may be shortened. It is desirable to suppress the wasteful consumption of stored power due to equalization control.

[0005] The present disclosure has been made to solve the above problems, and one of the objects of the present disclosure is to suppress wasteful consumption of stored power in a battery pack due to equalization control. [Means for solving the problem]

[0006] A battery management system according to an aspect of the present disclosure includes a battery pack including a plurality of cells connected in series, an electric circuit configured to be able to charge or discharge each of the plurality of cells individually, and a control device that executes equalization control to eliminate inequality in SOC among the plurality of cells using the electric circuit. The battery pack is charged or discharged so that the SOC of the battery pack falls within a predetermined SOC range. The control device estimates an equalization SOC, which is an SOC that would make the SOC of the plurality of cells equal to each other if the battery pack were charged or discharged without executing the equalization control, based on the voltage and full charge capacity of each of the plurality of cells. The control device executes the equalization control when the equalization SOC is within the predetermined SOC range, and does not execute the equalization control when the equalization SOC is outside the predetermined SOC range. Effect of the Invention

[0007] According to the present disclosure, it is possible to suppress wasteful consumption of stored power in a battery pack due to equalization control. [Brief description of the drawings]

[0008] [Figure 1] 1 is an overall configuration diagram of a vehicle equipped with a battery management system according to an embodiment of the present disclosure; [Diagram 2] FIG. 4 is a diagram for explaining changes in SOC of a cell included in a battery pack. [Diagram 3] 5 is a flowchart showing a processing procedure of equalization control in the present embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, an embodiment of the present disclosure will be described in detail with reference to the drawings. In addition, the same or corresponding parts in the drawings are given the same reference numerals, and the description thereof will not be repeated. In the following example, a battery management system according to the present disclosure is mounted on a vehicle. However, the use of the battery management system according to the present disclosure is not limited to vehicle use, and may be, for example, stationary use.

[0010] [Embodiment Mode] <System configuration> 1 is an overall configuration diagram of a vehicle equipped with a battery management system according to an embodiment of the present disclosure. In this example, the vehicle 1 is an electric vehicle (BEV) capable of EV running. The vehicle 1 includes a battery pack 10, a load 20, an equalization circuit 30, an inlet 40, a power conversion device 50, and an ECU (Electronic Control Unit) 100.

[0011] The battery pack 10 is electrically connected to the load 20 and stores power for driving the load 20. The battery pack 10 includes n cells B1 to Bn connected in series, where n is a natural number of 2 or more. Each cell is typically a secondary battery such as a lithium ion secondary battery or a nickel-metal hydride battery. The battery pack 10 is provided with a plurality of voltage sensors 111 to 11n that detect the voltages V1 to Vn of the corresponding cells, and a current sensor 12 that detects the current flowing through the battery pack 10. Each sensor outputs the detection result to the ECU 100.

[0012] The load 20 includes a motor generator that generates driving force for driving the vehicle 1 using the stored power of the battery pack 10, and a drive device for the motor generator (neither is shown). The load 20 can charge the battery pack 10 with regenerative power of the motor generator.

[0013] The equalization circuit 30 includes, for example, n bypass resistors R1 to Rn and n switches SW1 to SWn. The n bypass resistors R1 to Rn are connected in parallel to the n cells B1 to Bn, respectively. The n switches SW1 to SWn are connected in series to the n bypass resistors R1 to Rn, respectively. The equalization circuit 30 corresponds to the "discharge circuit" according to the present disclosure.

[0014] The inlet 40 is configured to be connectable to a connector 902 of an external charger 901. The power conversion device 50 charges the battery pack 10 with power received from the external charger 901 via the inlet 40 (plug-in charging) under the control of the ECU 100.

[0015] The ECU 100 includes a processor and a memory (not shown) and controls each device of the vehicle 1. In this embodiment, the ECU 100 realizes "equalization control" by controlling the equalization circuit 30 based on voltage information acquired from a plurality of voltage sensors 111-11n, current information acquired from the current sensor 12, information stored in the memory, and the like. More specifically, the ECU 100 extracts a cell having a relatively low SOC from among the n cells B1-Bn as a "reference cell" and controls the equalization circuit 30 to individually discharge each cell so that the SOC of each cell approaches the SOC of the reference cell. This makes it possible to eliminate the inequality in SOC among the cells B1-Bn. The equalization control will be described in more detail below.

[0016] <Equalization control> 2 is a diagram for explaining changes in the SOC of the cells included in the battery pack 10. The horizontal axis represents elapsed time, and the vertical axis represents the SOC of each cell. Here, an example will be described in which the battery pack 10 is discharged at a constant discharge rate (amount of discharged power per unit time). However, the battery pack 10 may be charged, or charging and discharging may be switched between as appropriate.

[0017] A lower limit LW and an upper limit UP are preset for the SOC of the battery pack 10 to prevent overcharging and overdischarging of the battery pack 10. The ECU 100 controls the load 20 and / or the power conversion device 50 so that the SOC of the battery pack 10 falls within an SOC range from the lower limit LW to the upper limit UP (hereinafter referred to as "within the normal SOC range"). The normal SOC range corresponds to the "predetermined SOC range" according to the present disclosure.

[0018] FIG. 2(A) focuses on one of the n cells B1 to Bn, and shows the change in SOC when that cell is discharged at a constant discharge rate. If equalization control is not performed (see solid line), the vehicle 1 can run in EV mode from time t0 to time t2. In contrast, if equalization control is performed before time t0 (see dashed line), the SOC of the cell at time t0 decreases. As a result, the vehicle 1 can only run in EV mode from time t0 to time t1. As a result, the EV distance becomes shorter.

[0019] In order to solve such problems, in this embodiment, the concept of "equal SOC" is introduced. The equal SOC is an SOC in which the SOCs of cells B1 to Bn are equal to each other when the battery pack 10 is charged or discharged without performing equalization control. In FIG. 2B, for ease of understanding, two cells (cells A and B) are taken as an example. At the current time t0, the SOC of cell A is higher than the SOC of cell B, so cell A is subject to equalization control, while cell B is not subject to equalization control. The SOC change of cell A when equalization control is not performed is indicated by a solid line, and the SOC change of cell B is indicated by a dashed line.

[0020] While there may be variation in full charge capacity between cells, in this example, the full charge capacity of cell A is smaller than that of cell B. Therefore, although the discharge power is the same between cell A and cell B, the slope of the line showing the SOC change is steeper for cell A (see solid line) than for cell B (see dashed line). Therefore, although the SOC of cell A is higher than that of cell B at the current time t0, the SOC difference between cell A and cell B decreases over time. Then, at time t30, the SOC of cell A and the SOC of cell B become equal to each other. The SOC at this time is the equivalent SOC. In the example of FIG. 2(B), the equivalent SOC is located within the normal SOC range.

[0021] 2C, in this example as well, the slope of the line showing the SOC change is steeper for cell A (see solid line) than for cell B (see dashed line). At time t40, the SOC of cell A and the SOC of cell B become equal. The equivalent SOC at this time is lower than the lower limit LW. In other words, the equivalent SOC is outside the normal SOC range.

[0022] In the example of FIG. 2(B), when equalization control is not performed, the SOC of cell A (see solid line) reaches the lower limit LW before the SOC of cell B (see dashed line) (see time t31). When equalization control is performed, the SOC of cell A (see dashed line) also reaches the lower limit LW before the SOC of cell B, but the time at which the SOC of cell A reaches the lower limit LW is advanced by the amount that the SOC of cell A at time t0 has decreased due to the equalization control (see time t32). That is, as in the example of FIG. 2(A), the EV distance is shortened by the equalization control.

[0023] In contrast, in the example of FIG. 2(B), when equalization control is not performed, the SOC of cell B (see dashed line) reaches the lower limit LW earlier than the SOC of cell A (see solid line) (see time t41). When equalization control is performed, the time when the SOC of cell A (see dashed line) reaches the lower limit LW is earlier (see time t42) than when equalization control is not performed. However, this time t42 is later than the time t41 when the SOC of cell B reaches the lower limit LW. Therefore, the EV distance is determined according to the SOC of cell B. The EV distance is not shortened by the equalization control of cell A. Therefore, the shortening of the equalization control can be suppressed.

[0024] Therefore, in this embodiment, when the equalization SOC is outside the normal SOC range as shown in FIG. 2(C), the ECU 100 executes the equalization control of cell A. This is because the EV distance will not be shortened even if the equalization control of cell A is executed. On the other hand, when the equalization SOC is within the normal SOC range as shown in FIG. 2(B), the ECU 100 does not execute the equalization control of cell A. This is because the EV distance will be shortened by executing the equalization control of cell A. In this way, by determining whether to execute / not execute the equalization control depending on whether the equalization SOC is inside or outside the normal SOC range, it is possible to suppress unnecessary consumption of the stored power of cell A and ensure the EV distance of vehicle 1.

[0025] <Processing flow> 3 is a flowchart showing the procedure of the equalization control in this embodiment. The process shown in this flowchart is executed when a predetermined condition is met (for example, at predetermined intervals). Hereinafter, step is abbreviated as S.

[0026] In S1, the ECU 100 determines whether a trigger for determining whether or not equalization control is required has occurred. For example, the trigger occurs when the vehicle 1 is started while IG-OFF or when ReadyON is started. If the trigger has not occurred (NO in S1), the ECU 100 ends the process without executing any subsequent processes. If the trigger has occurred (YES in S1), the ECU 100 advances the process to S2.

[0027] In S2, the ECU 100 acquires the voltages V1 to Vn of the cells B1 to Bn from the voltage sensors 111 to 11n.

[0028] In S3, the ECU 100 estimates the SOC of each cell according to a known method. For example, the ECU 100 can estimate the SOC from the voltages V1 to Vn (under conditions that can be regarded as OCV) by referring to a SOC-OCV curve prepared in advance.

[0029] In S4, the ECU 100 acquires the full charge capacity of each cell. The ECU 100 calculates the full charge capacity of each cell, for example, during plug-in charging of the vehicle 1, and stores the calculation results in memory. The ECU 100 can read out these full charge capacities.

[0030] In S5, the ECU 100 calculates the equivalent SOC of the battery pack 10 based on the SOC estimated in S3 and the full charge capacity acquired in S4. More specifically, in the example of Fig. 2, the SOC corresponds to the intercept of the line, and the full charge capacity determines the slope of the line. Therefore, the ECU 100 can calculate the equivalent SOC of the battery pack 10 by calculating a line for each cell and determining the coordinates of the intersections of those lines. If there are three or more lines, it is sufficient to select the intersection with the smallest x coordinate (the intersection located earliest in time) among the two or more intersections.

[0031] In S6, the ECU 100 determines whether the equivalent SOC estimated in S5 is outside a predetermined normal SOC range. If the equivalent SOC is outside the normal SOC range (YES in S6), the ECU 100 determines to execute equalization control of the assembled battery 10 (S7). The equalization control is executed according to a process of another flow not shown. On the other hand, if the equivalent SOC is within the normal SOC range (NO in S6), the ECU 100 determines not to execute equalization control of the assembled battery 10 (S8).

[0032] As described above, in this embodiment, when the equivalent SOC is within the normal SOC range, the equalization control of the battery pack 10 is not executed. This is because if the equalization control is executed when the equivalent SOC is within the normal SOC range, the EV distance will be shortened due to power consumption. Conversely, when the equivalent SOC is outside the normal SOC range, the EV distance will not be shortened even if power is consumed due to the equalization control, so the equalization control is executed. Therefore, according to this embodiment, it is possible to suppress wasteful consumption of the stored power of the battery pack 10.

[0033] The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present disclosure is defined by the claims, not by the description of the embodiments described above, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0034] 1 vehicle, 10 battery pack, 11n~111 voltage sensors, B1~Bn cells, 12 current sensor, 20 load, 30 equalization circuit, R1~Rn bypass resistors, SW1~SWn switches, 40 inlet, 50 power conversion device, 901 external charger, 902 connector.

Claims

[Claim 1] A battery pack including a plurality of cells connected in series; A discharge circuit configured to be able to individually discharge each of the plurality of cells; a control device that performs equalization control to eliminate inequality in SOC among the plurality of cells using the discharge circuit; The battery pack is charged or discharged so that the SOC of the battery pack falls within a predetermined SOC range; The control device includes: an equal SOC, which is an SOC at which the SOCs of the plurality of cells will be equal to each other if the battery pack is charged or discharged without executing the equalization control, is estimated based on the voltages and full charge capacities of each of the plurality of cells; When the equivalent SOC is within the predetermined SOC range, the equalization control is executed, while When the equivalent SOC is outside the predetermined SOC range, the equalization control is not executed.

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