Battery equalization control device

Abstract

To provide an equalization controller capable of suppressing expansion of a voltage difference between a plurality of battery cells by charging processing of the battery cells performed after completion of equalization even when the plurality of battery cells are equalized in a low SOC range.SOLUTION: A battery equalization controller comprises: an acquisition unit for acquiring a full charge capacity and a voltage value of a first cell and a second cell included in a plurality of battery cells about a battery having a flat range; and a control unit for controlling equalization of the plurality of battery cells on the basis of the value acquired by the acquisition unit. If an absolute value of a difference between a full charge capacity of the first cell and a full charge capacity of the second cell is a first threshold value or more, the control unit performs equalization so that an absolute value of a difference between a charging rate of the first cell and a charging rate of the second cell at the time of full charge becomes less than a second threshold value. If an absolute value of a difference between a voltage of the first cell and a voltage of the second cell is a third threshold value or more, the control unit performs equalization so that the absolute value of the difference between the voltage of the first cell and the voltage of the second cell becomes less than a third threshold value.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to an equalization control device for controlling a battery (battery pack) composed of a plurality of battery cells.

Background Art

[0002] Patent Document 1 discloses a technique for equalizing a plurality of battery cells in a battery (battery pack) composed of a plurality of battery cells, which has a "flat region" in which the rate of change of the open circuit voltage (OCV) with respect to the state of charge (SOC) in the SOC-OCV characteristic curve is equal to or less than a predetermined value. In the technique described in this Patent Document 1, after performing a charging rate lowering process or a charging rate raising process to transition the state of the battery to a "non-flat region" other than the flat region, equalization of a plurality of battery cells based on the open circuit voltage is performed in the non-flat region.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When equalization of a plurality of battery cells based on the open circuit voltage is performed in a "low SOC region" which is a region on the low charging rate side in the non-flat region, depending on the variation in the full charge capacity among the plurality of battery cells, in the charging process after equalization is completed, the battery cell with a small full charge capacity reaches a high charging rate earlier, resulting in an increase in the voltage difference from the battery cell with a large full charge capacity, and there is a possibility that equalization needs to be performed again.

[0005] The present disclosure has been made in view of the above problems, and an object thereof is to provide an equalization control device capable of suppressing an increase in the voltage difference between a plurality of battery cells due to the charging process of the battery cells performed after the completion of equalization even when equalization of the plurality of battery cells is performed in a low SOC region.

Means for Solving the Problems

[0006] In order to solve the above problems, one aspect of the disclosed technology is an equalization control device for equalizing a plurality of battery cells in a battery configured by a plurality of battery cells and having a flat region in an SOC-OCV characteristic curve where the rate of change of the open-circuit voltage with respect to the state of charge is equal to or less than a predetermined value. The equalization control device includes an acquisition unit that acquires the values of the full charge capacity and voltage of a first cell and a second cell included in the plurality of battery cells, and a control unit that controls the equalization of the plurality of battery cells based on the values acquired by the acquisition unit. When the absolute value of the difference between the full charge capacity of the first cell and the full charge capacity of the second cell is equal to or greater than a first threshold value, the control unit performs equalization so that the absolute value of the difference between the state of charge of the first cell and the state of charge of the second cell at full charge is less than a second threshold value. When the absolute value of the difference between the voltage of the first cell and the voltage of the second cell is equal to or greater than a third threshold value, the control unit performs equalization so that the absolute value of the difference between the voltage of the first cell and the voltage of the second cell is less than the third threshold value.

Advantages of the Invention

[0007] According to the battery equalization control device of the present disclosure, even when equalization of a plurality of battery cells is performed in a low SOC region, it is possible to suppress an increase in the voltage difference between the plurality of battery cells due to the charging process of the battery cells performed after the completion of equalization.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Embodiment for Carrying out the Invention

[0009] The equalization control device of the present disclosure controls the equalization process to be performed based on the full charge capacity and voltage of two or more battery cells to be equalized for a battery having a flat region in the SOC-OCV characteristic curve composed of a plurality of battery cells. The increase in the voltage difference between a plurality of battery cells can be suppressed only by the equalization process of the battery cells in the low SOC region. Hereinafter, an embodiment of the present disclosure will be described in detail with reference to the drawings.

[0010] <Embodiment> [Configuration] FIG. 1 is a block diagram showing a schematic configuration of a power supply system 1 including an equalization control device 50 according to an embodiment of the present disclosure. The power supply system 1 illustrated in FIG. 1 includes a first battery 10, a DCDC converter 20, a second battery 30, a plurality of in-vehicle devices 40, and the equalization control device 50 of the present embodiment.

[0011] The power supply system 1 shown in FIG. 1 can be mounted on a vehicle. In the following embodiments, the case where the power supply system 1 is mounted on a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), an electric vehicle (BEV), etc., which uses an electric motor as a power source, will be taken as an example to explain the control of the equalization control device 50 according to the present embodiment.

[0012] The first battery 10 is a high-voltage battery for supplying power to an electric motor (not shown) or a DCDC converter 20. A typical first battery 10 mounted on a vehicle is, for example, a drive battery. Further, the first battery 10 may be configured to be able to obtain power from an external power source via a plug-in charger (not shown) connectable to the external power source. A secondary battery such as a lithium-ion battery configured to be chargeable and dischargeable is used for the first battery 10.

[0013] The DCDC converter 20 connects the first battery 10, the second battery 30, and a plurality of in-vehicle devices 40, and supplies the power of the first battery 10 to the second battery 30 and the plurality of in-vehicle devices 40. When supplying power, the DCDC converter 20 can convert the high voltage of the first battery 10, which is the input voltage, into a predetermined low voltage and output it.

[0014] The second battery 30 is a low-voltage battery that charges the power output from the DCDC converter 20 or discharges the power it stores. A typical second battery 30 mounted on a vehicle is, for example, an auxiliary battery. The second battery 30 of the present embodiment is a battery pack composed of a plurality of battery cells. The second battery 30 is typically configured by connecting a plurality of battery cells in series. Also, the second battery 30 may be configured by connecting two or more cell blocks in which some battery cells are connected in parallel in series.

[0015] Each battery cell of this second battery 30 uses a battery having a so-called flat region, that is, a region where the absolute value of the change rate of the open-circuit voltage OCV with respect to the state of charge SOC is equal to or less than a predetermined value, in the SOC-OCV characteristic curve showing the relationship between the state of charge SOC and the open-circuit voltage OCV of the battery. This predetermined value is a value determined based on the specifications of the battery and the like. As a battery having a flat region, a lithium iron phosphate-based lithium-ion battery (LFP battery) can be exemplified. FIG. 2 shows an example of the SOC-OCV characteristic curve of a lithium iron phosphate-based lithium-ion battery.

[0016] The plurality of in-vehicle devices 40 are various devices mounted on a vehicle that operate with the power output from the DCDC converter 20 or the power of the second battery 30. The plurality of in-vehicle devices 40 include, for example, actuators such as motors and solenoids, lighting devices such as headlamps and interior lights, air conditioners such as heaters and coolers, electronic control units (ECUs: Electronic Control Unit) for steering, brakes, and automatic driving and advanced driving assistance, and other devices.

[0017] The equalization control device 50 includes an acquisition unit 510 and a control unit 520, and controls the second battery 30. This equalization control device 50 can typically be configured as an electronic control unit (ECU) including a processor, a memory, an input / output interface, and the like. The electronic control unit realizes all or part of the functions performed by the acquisition unit 510 and the control unit 520 by the processor reading and executing a program stored in the memory.

[0018] The acquisition unit 510 acquires the states of a plurality of battery cells constituting the second battery 30, respectively. Examples of the state of the battery cell can include the full charge capacity and the voltage value. The voltage of the battery cell is the voltage value between the positive electrode terminal and the negative electrode terminal, and can be acquired, for example, via a detection element such as a voltage sensor provided in the battery cell. The full charge capacity of the battery cell can be acquired, for example, when the second battery 30 is inspected or replaced at a dealer or a repair shop, or can be acquired using a well-known technique for measuring or estimating the full charge capacity.

[0019] Based on the states of a plurality of battery cells constituting the second battery 30 acquired by the acquisition unit 510, the control unit 520 controls a process of equalizing the variations in voltage and charge rate occurring between the plurality of battery cells. The voltage variation between the plurality of battery cells is caused by, for example, the variation in the self-discharge amount of each battery cell. When the voltage varies between the plurality of battery cells, the deterioration of a specific battery cell may progress acceleratively, or the available energy amount may decrease. Therefore, the control unit 520 discharges the battery cell with a high voltage as needed to lower the voltage and align it with the voltages of other battery cells, thereby avoiding these effects.

[0020] [Control] Next, with further reference to FIG. 3, the control performed by the equalization control device 50 according to an embodiment of the present disclosure will be described. FIG. 3 is a flowchart showing a processing procedure of equalization control performed on a plurality of battery cells constituting the second battery 30 executed by the equalization control device 50.

[0021] Note that FIG. 3 shows an example of control for equalizing between cells, targeting the first cell and the second cell among the plurality of battery cells constituting the second battery 30. However, equalization control between cells targeting three or more battery cells can also be similarly implemented according to the procedure of FIG. 3.

[0022] The equalization control of the battery cells illustrated in FIG. 3 is started at a timing that does not affect the operation of the plurality of in-vehicle devices 40. As an example, the equalization control of the battery cells is started at the timing when the vehicle power is turned off (for example, the timing when the ignition switch is switched from on to off).

[0023] (Step S301) The acquisition unit 510 of the equalization control device 50 acquires the full charge capacity FCC1 of the first cell, the voltage V1 of the first cell, the full charge capacity FCC2 of the second cell, and the voltage V2 of the second cell, respectively.

[0024] When the full charge capacity and voltage of each cell are acquired by the acquisition unit 510, the process proceeds to step S302.

[0025] (Step S302) The control unit 520 of the equalization control device 50 determines whether both the voltage V1 of the first cell and the voltage V2 of the second cell acquired by the acquisition unit 510 are in the low SOC region on the side where the charge rate is lower than the flat region on the SOC-OCV characteristic curve. That is, it is determined whether both the voltage V1 of the first cell and the voltage V2 of the second cell are lower than the lower limit voltage of the flat region. The lower limit voltage for determining that it is in the low SOC region is predetermined based on the specifications of the second battery 30 and the like.

[0026] When the control unit 520 determines that both the voltage V1 of the first cell and the voltage V2 of the second cell are in the low SOC region (step S302, yes), the process proceeds to step S303. On the other hand, when the control unit 520 determines that both the voltage V1 of the first cell and the voltage V2 of the second cell are not in the low SOC region (step S302, no), the process proceeds to step S301 without performing the equalization process.

[0027] (Step S303) The control unit 520 of the equalization control device 50 determines whether the full charge capacity difference ΔFCC between the first cell and the second cell is equal to or greater than the first threshold. This full charge capacity difference ΔFCC is the absolute value of the difference between the full charge capacity FCC1 of the first cell and the full charge capacity FCC2 of the second cell (ΔFCC = |FCC1 - FCC2|). This determination is made to determine whether it is necessary to perform equalization between the first cell and the second cell. Therefore, the first threshold is appropriately set based on the characteristics of the second battery 30 and the performance required for the vehicle, etc., from the viewpoint of suppressing the progress of deterioration of the second battery 30.

[0028] When the control unit 520 determines that the full charge capacity difference ΔFCC between the first cell and the second cell is equal to or greater than the first threshold (step S303, yes), the process proceeds to step S304. On the other hand, when the control unit 520 determines that the full charge capacity difference ΔFCC between the first cell and the second cell is less than the first threshold (step S303, no), the process proceeds to step S307.

[0029] (Step S304) The control unit 520 of the equalization control device 50 calculates the equalization capacity EQC1 of the first cell and the equalization capacity EQC2 of the second cell, respectively. The equalization capacity EQC1 [Ah] of the first cell can be derived by the following formula [1] based on the full charge capacity FCC1 [Ah] of the first cell and the state of charge SOC_V1 [%] derived from the voltage V1 [V] according to the SOC-OCV characteristic curve. Also, the equalization capacity EQC2 [Ah] of the second cell can be derived by the following formula [2] based on the full charge capacity FCC2 [Ah] of the second cell and the state of charge SOC_V2 [%] derived from the voltage V2 [V] according to the SOC-OCV characteristic curve.

[0030] EQC1=(100 - SOC_V1)×FCC1 … [1] EQC2=(100 - SOC_V2)×FCC2 … [2]

[0031] When the equalization capacity of each cell is calculated by the control unit 520, the process proceeds to step S305.

[0032] (Step S305) The control unit 520 of the equalization control device 50 determines (estimates) whether or not the state of charge difference ΔSOC between the first cell and the second cell becomes equal to or greater than the second threshold value when a charging process is performed to fully charge the current second battery 30. This state of charge difference ΔSOC is the difference in the state of charge between one cell that has reached the fully charged state earlier due to the variation in the battery cells and the other cell that has not reached the fully charged state, and can be derived based on the equalization capacity EQC1 of the first cell and the equalization capacity EQC2 of the second cell.

[0033] As an example, when the first cell has a full charge capacity FCC1 = "30 Ah" and SOC_V1 = "10%", the equalization capacity EQC1 = "27.0 Ah" of the first cell is calculated by the above formula [1]. On the other hand, when the second cell has a full charge capacity FCC 2 = "29 Ah" and SOC_V 2When it is 「20%」, the equalization capacity EQC2 of the second cell is calculated as 「23.2 Ah」 by the above formula [2]. When charging the second battery 30 including such first and second cells in the configuration, when 23.2 Ah is supplied to the second cell, the second cell reaches a fully charged state of 100%, but the first cell only reaches about 87% (=10 + 23.2 / 30 × 100) with the supply of 23.2 Ah, and a charging rate difference ΔSOC ≒ 「13%」 occurs between the first cell and the second cell. The second threshold is set according to how much this charging rate difference ΔSOC is allowed.

[0034] When the control unit 520 determines that the charging rate difference ΔSOC between the first cell and the second cell at full charge is equal to or greater than the second threshold (step S305, yes), the process proceeds to step S306. On the other hand, when the control unit 520 determines that the charging rate difference ΔSOC between the first cell and the second cell at full charge is less than the second threshold (step S305, no), the process proceeds to step S301 without performing the equalization process.

[0035] (Step S306) The control unit 520 of the equalization control device 50 performs the equalization process based on the charging rate difference ΔSOC between the first cell and the second cell at full charge. Specifically, the control unit 520 discharges the power stored in the cell with the lower equalization capacity so that the equalization capacity EQC1 of the first cell and the equalization capacity EQC2 of the second cell match.

[0036] For example, when the equalization capacity EQC1 of the first cell is 「27.0 Ah」 and the equalization capacity EQC2 of the second cell is 「23.2 Ah」, the power of the second cell is discharged by 3.8 Ah to make the equalization capacity EQC2 of the second cell the same as the equalization capacity EQC1 of the first cell, which is 「27.0 Ah」. It should be noted that the first cell may also be charged by 3.8 Ah to make the equalization capacity EQC1 of the first cell the same as the equalization capacity EQC2 of the second cell, which is 「23.2 Ah」.

[0037] When the equalization process based on the charge rate difference ΔSOC between the first cell and the second cell at full charge is performed by the control unit 520, the process proceeds to step S301.

[0038] (Step S307) The control unit 520 of the equalization control device 50 determines whether the voltage difference ΔV between the first cell and the second cell is equal to or greater than a third threshold value. This voltage difference ΔV is the absolute value of the difference between the voltage V1 of the first cell and the voltage V2 of the second cell (ΔV = |V1 - V2|). This determination is made to determine whether it is necessary to perform equalization between the first cell and the second cell. Therefore, the third threshold value is appropriately set based on the characteristics of the second battery 30 and the performance required for the vehicle, etc., from the viewpoint of suppressing the progress of deterioration of the second battery 30.

[0039] When the control unit 520 determines that the voltage difference ΔV between the first cell and the second cell is equal to or greater than the third threshold value (step S307, yes), the process proceeds to step S308. On the other hand, when the control unit 520 determines that the voltage difference ΔV between the first cell and the second cell is less than the third threshold value (step S307, no), the process proceeds to step S301 without performing the equalization process.

[0040] (Step S308) The control unit 520 of the equalization control device 50 performs an equalization process based on the voltage difference ΔV between the first cell and the second cell. Specifically, the control unit 520 discharges the power stored in the cell with the higher voltage so that the voltage V1 of the first cell and the voltage V2 of the second cell match.

[0041] For example, when the voltage V1 of the first cell is "3.2V" and the voltage V2 of the second cell is "3.3V", the power of the second cell is discharged until the voltage V2 drops to 3.2V, and the voltage V2 of the second cell is made the same as the voltage V1 of the first cell, which is "3.2V". Note that the first cell may be charged with power so that the voltage V1 of the first cell is made the same as the voltage V2 of the second cell, which is "3.3V".

[0042] When the equalization process based on the voltage difference ΔV between the first cell and the second cell is performed by the control unit 520, the process proceeds to step S301.

[0043] <Operation and Effect> As described above, according to the equalization control device 50 according to an embodiment of the present disclosure, for the second battery 30 having a flat region in the SOC-OCV characteristic curve composed of a plurality of battery cells, an equalization process based on the full charge capacity and voltage of two or more battery cells to be equalized is appropriately performed.

[0044] Specifically, when the full charge capacity difference ΔFCC between the first cell and the second cell is equal to or greater than the first threshold, an equalization process is performed so that the charge rate difference ΔSOC between the first cell and the second cell at full charge is less than the second threshold. Also, when the voltage difference ΔV between the first cell and the second cell is equal to or greater than the third threshold, an equalization process is performed so that the voltage difference ΔV between the first cell and the second cell is less than the third threshold.

[0045] By such control, even when the equalization process of a plurality of battery cells is performed in the low SOC region, it is possible to suppress an increase in the voltage difference between the plurality of battery cells due to the charging process of the battery cells performed after the completion of the equalization process.

[0046] As described above, although one embodiment of the present disclosure has been described, the present disclosure can be understood not only as the above-described equalization control device but also as an equalization control method executed by an equalization control device including a processor and a memory, a control program for the equalization control method, a computer-readable non-temporary recording medium storing the control program, or a vehicle equipped with the equalization control device.

Industrial Applicability

[0047] The battery equalization control device of the present disclosure can be used when controlling a battery composed of a plurality of battery cells.

Explanation of Reference Numerals

[0048] 1 Power supply system 10 First battery 20 DC-DC converter 30 Second battery 40 In-vehicle equipment 50 Equalization control device 510 Acquisition unit 520 Control unit

Claims

1. A battery composed of a plurality of battery cells and having a flat region in the SOC-OCV characteristic curve where the rate of change of the open-circuit voltage with respect to the state of charge is equal to or less than a predetermined value, and an equalization control device for equalizing the plurality of battery cells, an acquisition unit that acquires the values of the full charge capacity and voltage of a first cell and a second cell included in the plurality of battery cells; a control unit that controls the equalization of the plurality of battery cells based on the values acquired by the acquisition unit, wherein when the voltage of the first cell and the voltage of the second cell are lower than the lower limit voltage of the flat region, if the absolute value of the difference between the full charge capacity of the first cell and the full charge capacity of the second cell is equal to or greater than a first threshold value, equalization is performed so that the absolute value of the difference between the state of charge of the first cell and the state of charge of the second cell at full charge of the battery is less than a second threshold value; an equalization control device.

2. wherein when the voltage of the first cell and the voltage of the second cell are lower than the lower limit voltage of the flat region, if the absolute value of the difference between the full charge capacity of the first cell and the full charge capacity of the second cell is less than the first threshold value, equalization is performed so that the absolute value of the difference between the voltage of the first cell and the voltage of the second cell is less than a third threshold value; The equalization control device according to claim 1.

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