Secondary battery cell balance control device, secondary battery cell balance control method, and secondary battery cell balance control program

Abstract

To easily achieve accurate and efficient passive cell balance.SOLUTION: A secondary battery cell balance control device includes: a passive cell balance circuit that equalizes states of charge of a plurality of cells each being composed of a secondary battery by discharging via a resistor; and a control unit that individually calculates an operation time of the discharging of each of discharging object cells and exerts control of individually stopping operation of the discharging for each of the discharging object cells provided that the calculated operation time of the discharging elapses.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a cell balance control device for a secondary battery, a cell balance control method for a secondary battery, and a cell balance control program for a secondary battery. [Background technology]

[0002] In energy storage systems that use secondary batteries such as lithium-ion batteries, there are known systems that include a cell balance control device that adjusts the cell balance within a battery stack (hereinafter referred to as a "cell stack") formed by connecting multiple secondary battery cells. Cell balance control devices are classified into active types that use, for example, a transformer and passive types that use, for example, a resistor.

[0003] A passive cell balance control device that performs passive cell balancing has a cell balance circuit in which a discharge circuit including a resistor and a switch is provided for each cell in the cell stack (see, for example, Patent Document 1). The cell balance circuit closes the switch of a specific cell in response to a discharge control signal, causing the energy stored in that specific cell to be discharged via a resistor. By performing this discharge individually for each cell, the cell balance circuit equalizes the state of charge (SOC) of all cells in the cell stack. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-151147 Summary of the Invention [Problem to be solved by the invention]

[0005] However, complicating control processes, etc. in order to achieve accurate and efficient cell balancing with little energy loss is undesirable, particularly in passive cell balancing control devices, which have a relatively simple configuration compared to active types.

[0006] An object of the present invention is to provide a cell balance control device for a secondary battery, an energy storage system, a cell balance control method for a secondary battery, and a cell balance control program for a secondary battery, which can easily achieve accurate and efficient passive cell balancing. [Means for solving the problem]

[0007] One aspect of the cell balance control device for a secondary battery according to the present invention is a passive cell balance circuit that equalizes the charge states of a plurality of cells, each of which is a secondary battery, by discharging the cells through a resistor; a control unit that individually calculates the discharge operation time of each discharge target cell, and performs control to stop the discharge operation for each discharge target cell on the condition that the calculated discharge operation time has elapsed; Has.

[0008] One aspect of the cell balance control method for a secondary battery according to the present invention is to A cell balance control method for a secondary battery, which is performed on a passive cell balance circuit that equalizes the charge states of a plurality of cells, each of which is a secondary battery, by discharging through a resistor, comprising: Calculating the discharge operation time of each discharge target cell individually; Control is performed to stop the discharge operation for each of the discharge target cells individually, on the condition that the calculated discharge operation time has elapsed.

[0009] One aspect of the cell balance control program for a secondary battery according to the present invention is to The above-described cell balance control method for a secondary battery is executed by a processing unit. [Effects of the Invention]

[0010] According to the present invention, accurate and efficient passive cell balancing can be easily achieved. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a circuit diagram showing a configuration of a cell balance control device according to an embodiment of the present invention. [Figure 2] FIG. 1 is a block diagram showing a configuration of a cell balance control device according to an embodiment of the present invention. [Figure 3] 1 is a flowchart illustrating a control operation of a cell balance control device according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0013] 1 and 2 are a circuit diagram and a block diagram showing the configuration of a cell balance control device according to an embodiment of the present invention.

[0014] The cell balance control device 1 according to this embodiment is a device for performing cell balancing to equalize the charging rates of cells B1, B2, B3, ..., Bn in a cell stack B in which n (n is an integer equal to or greater than 2) cells B1, B2, B3, ..., Bn are connected in series on a power supply line PL. The cells B1, B2, B3, ..., Bn are secondary battery cells, and in this embodiment, they are, for example, lithium-ion batteries. Note that the cells to be equalized may be either charging rates or battery voltages. In this embodiment, the indices to be equalized in cell balancing, such as charging rates and battery voltages, are collectively referred to as the "state of charge."

[0015] When in use, the cell stack B is electrically connected to an external power supply or a load device (neither shown) via terminals +T and -T to which its positive and negative terminals are connected, respectively. The load device is a load device (motor, electric circuit, etc.) that operates using energy discharged from the cell stack B. The cell stack B is charged by receiving power from an external power supply. Charging of the cell stack B by the external power supply and discharging from the cell stack B to the load device are controlled by a control device (not shown), but may also be controlled by a control IC (Integrated Circuit) provided in the cell balance control device 1.

[0016] The cell balancing control device 1 includes a control IC 10, a passive cell balancing circuit 20, and a voltage sensor 30.

[0017] The control IC 10 has a memory unit 11, which is realized by, for example, an arithmetic processing unit, etc. The memory unit 11 includes a storage device realized by, for example, a flash memory, etc., and a memory device realized by, for example, a RAM (Random Access Memory), etc.

[0018] The arithmetic processing device reads various control programs or instructions for realizing each function of the cell balance control device 1, as well as data such as tables related to the programs or instructions (hereinafter simply referred to as "programs, etc.") from the storage device, stores them in the memory device, and executes the various control programs or instructions while using the data.

[0019] The programs and the like may be stored in a removable storage medium such as a flash memory. In this case, the control IC 10 is configured to be able to attach and detach the removable storage medium, and reads the programs and the like from the storage medium. Note that the control IC 10 may be configured to be able to communicate with the outside, so that the programs and the like may be downloaded to the control IC 10 from the outside via a communication network.

[0020] The storage device, memory device, and removable storage medium described above are examples of non-transitory storage media.

[0021] The control IC 10 controls the state of each of the n switches SW1, SW2, SW3, ..., SWn. By controlling the states of the switches SW1, SW2, SW3, ..., SWn by the control IC 10, it is possible to equalize the charging rates of the cells B1, B2, B3, ..., Bn in the cell stack B. The control IC 10 is an example of a control unit in the present invention.

[0022] The passive cell balancing circuit 20 has n discharge circuits D1, D2, D3, ..., Dn. Each discharge circuit D1, D2, D3, ..., Dn has resistors R1, R2, R3, ..., Rn and switches SW1, SW2, SW3, ..., SWn, and is connected in parallel to the corresponding cell B1, B2, B3, ..., Bn and connected to the power supply line PL.

[0023] Unless otherwise specified, the discharge referred to in this embodiment refers to the discharge of discharge circuits D1, D2, D3, ..., Dn, which is the discharge for equalizing the charge rates of cells B1, B2, B3, ..., Bn in cell stack B, i.e., for cell balancing. This discharge is performed via resistors R1, R2, R3, ..., Rn. In other words, the cell balancing performed in this embodiment is of the passive type.

[0024] The start and end of discharge via resistors R1, R2, R3, ..., Rn are controlled by switches SW1, SW2, SW3, ..., SWn. In this embodiment, the switch elements used as switches SW1, SW2, SW3, ..., SWn are P-channel MOSFETs (Metal Oxide Semiconductor Field Effect Transistors), but other types of switch elements may be used. If the cell to be discharged is designated as discharge target cell Bk (k is an integer between 1 and n), control IC 10 applies a voltage signal as a discharge control signal to the gate of the corresponding switch SWk to turn on the switch SWk. This causes the energy stored in discharge target cell Bk to flow as a discharge current on discharge line DL, pass through switch SWk, and be consumed by resistor Rk. In this manner, discharge of discharge target cell Bk is performed.

[0025] When discharging from the cell stack B to the load device, the switches SW1, SW2, SW3, ..., SWn are turned off so that discharging is not performed in the discharge circuits D1, D2, D3, ..., Dn.

[0026] As mentioned above, cell balancing is performed to equalize the charge rates of cells B1, B2, B3, ..., Bn. Generally, when multiple cells gradually age at different rates, the more deteriorated cells tend to increase their charge rate faster and reach full charge more quickly than the less deteriorated cells (and therefore cells with a higher capacity). Therefore, cell balancing releases a small amount of energy from the highly charged cells at a low current, which is then dissipated by a discharge resistor (in the case of a passive type) to delay the increase in the charge rate or the reaching of full charge. This allows each cell to be charged to its maximum performance level.

[0027] However, if the discharge duration from the target cell, especially the timing to stop the discharge, cannot be properly controlled, the target cell will discharge more than necessary, resulting in increased energy loss and reduced cell balancing efficiency. On the other hand, if precise control of cell balancing is aimed at suppressing excessive energy loss, it becomes necessary to obtain constantly changing discharge current values ​​and aging-related changes in the internal resistance of the cells in real time and calculate the appropriate discharge amount using complex calculations.

[0028] However, this type of control increases the burden on the control IC of the cell balancing control device, necessitating measures such as the provision of a more powerful control IC. This would undermine the advantage of a passive cell balancing control device, which can be implemented at low cost due to its relatively simple circuit configuration. In light of this, this embodiment aims to easily achieve accurate and efficient passive cell balancing by determining the discharge operation time for each cell through a relatively simple calculation.

[0029] In this embodiment, the control IC 10 calculates the discharge operation time of the discharge target cell Bk individually for each cell using the following formula (1).

[0030] Tk=(CAPinit*(SOCk-SOCave)) / IkBalance ···(1) Here, Tk is the discharge operation time (unit: Hrs) of the cell Bk to be discharged, CAPinit is the reference capacity of each cell (e.g., the nominal value of the cell's maximum capacity), SOCk is the state of charge (SOC) of the cell Bk to be discharged, SOCave is the average state of charge of cells B1, B2, B3, ..., Bn, and IkBalance is the discharge current value of the cell Bk to be discharged. Note that the discharge current value of the cell Bk to be discharged is not an actual measured value during discharge, but an estimated value obtained by estimation before the start of discharge. CAPinit*(SOCk-SOCave) is the capacity to be discharged from the cell Bk to be discharged. In equation (1), the discharge operation time Tk of the cell Bk to be discharged is calculated by dividing the capacity to be discharged from the cell Bk to be discharged by the current value (estimated value) IkBalance of the discharge current of the cell Bk to be discharged.

[0031] The reference capacitance CAPinit of cells B1, B2, B3, ..., Bn may be the nominal value of the maximum capacity of cells B1, B2, B3, ..., Bn, as described above. In this case, a fixed value can be always used without depending on the actual maximum capacity of cells B1, B2, B3, ..., Bn, which changes over time, simplifying the calculation process. The control IC 10 substitutes the reference capacitance values ​​of cells B1, B2, B3, ..., Bn, which are stored in advance in the memory unit 11, for CAPinit in equation (1).

[0032] The state of charge SOCk of the cell Bk to be discharged can be calculated from the open circuit voltage (OCV) of the cell Bk to be discharged. As an example, in this embodiment, a table showing the correspondence between OCV and state of charge is created in advance and stored in memory unit 11. Then, when actually calculating the discharge operation time Tk, control IC 10 refers to the table in memory unit 11 to obtain the state of charge value corresponding to the actually measured OCV of cell Bk to be discharged, and substitutes the obtained state of charge value for SOCk in equation (1).

[0033] The OCV of each cell B1, B2, B3, ..., Bn is measured by a voltage sensor 30 when no current is flowing through each cell B1, B2, B3, ..., Bn. Although not shown in Fig. 1, the voltage sensor 30 is connected to both ends of each cell B1, B2, B3, ..., Bn and is configured to be able to measure the OCV and full charge voltage of each cell B1, B2, B3, ..., Bn.

[0034] The average charging rate of cells B1, B2, B3, ..., Bn is obtained by calculating the charging rates of all cells B1, B2, B3, ..., Bn from their respective OCVs using the above method, and then calculating their average value. Control IC 10 then substitutes the obtained average charging rate into SOCave in equation (1).

[0035] In this embodiment, the estimated value IkBalance of the discharge current of the cell Bk to be discharged is calculated by dividing the average of the OCV of the cell Bk to be discharged and the full charge voltage value previously measured for the cell Bk by the resistance value of the resistor Rk corresponding to the cell Bk to be discharged. This calculation formula allows for a rough estimate of the average discharge current value during the discharge that occurs from time to time from the time the cell Bk to be discharged is charged to the time it reaches a full charge state, without actually measuring the discharge current that changes from time to time during discharge. Therefore, a discharge current estimate with a certain degree of accuracy can be easily obtained. The control IC 10 then substitutes the estimated discharge current value thus obtained for IkBalance in equation (1).

[0036] As a result, the control IC 10 can calculate the discharge operation time Tk of the discharge target cell Bk.

[0037] Next, the control operation of the cell balance control device 1 according to this embodiment will be described with reference to the flowchart in Fig. 3. The control operation described here is realized by the control IC 10 executing a cell balance control program for the secondary battery that is stored in advance in the storage unit 11.

[0038] First, in step S1, the control IC 10 measures the OCV (unit: V) of each cell B1, B2, B3, ..., Bn using the voltage sensor 30. Then, in step S2, the control IC 10 estimates the SOC, i.e., the charging rate (unit: %), of each cell B1, B2, B3, ..., Bn from the OCV of each cell B1, B2, B3, ..., Bn, for example, by referring to a table pre-stored in the memory unit 11. Furthermore, the control IC 10 calculates the average SOC (average charging rate, unit: %) from the SOC of each cell B1, B2, B3, ..., Bn.

[0039] Then, the control IC 10 subtracts the average SOC from the SOC of each of the cells B1, B2, B3, ..., Bn and determines whether the calculated difference is greater than 5%. If the SOC of all of the cells B1, B2, B3, ..., Bn is not greater than 5% of the average SOC (NO in step S4), the control flow proceeds to step S11. If the SOC of any of the cells B1, B2, B3, ..., Bn is greater than 5% of the average SOC (YES in step S4), the control flow proceeds to step S5. Note that the "5%" used as the determination standard in step S4 is merely an example, and other reference values ​​may be used.

[0040] In step S5, the control IC 10 identifies the cell Bk to be discharged. For example, the control IC 10 identifies a cell Bk whose SOC is more than 5% higher than the average SOC. This narrows down the cell Bk to be discharged to cells whose SOC is more than 5% higher than the average SOC. As a result, unnecessary discharge can be significantly suppressed, and efficient cell balancing with low energy loss can be performed. Furthermore, accurate selection of the cell Bk to be discharged is possible and simple.

[0041] In step S6, the discharge current of the identified cell Bk is estimated. The control IC 10 calculates this by dividing the average of the OCV of the cell Bk and the previously measured full charge voltage of the cell Bk by the resistance of the resistor Rk corresponding to the cell Bk. As described above, this formula allows for a rough estimate of the average discharge current during the discharging of the cell Bk from charging to full charge, without actually measuring the discharge current, which changes from moment to moment during discharging. Therefore, a discharge current estimate with a certain degree of accuracy can be easily obtained.

[0042] Needless to say, if there are multiple discharge target cells Bk, the estimation of the discharge current in this step is performed individually for each discharge target cell Bk. This also applies to the following steps, where processing is performed individually for each discharge target cell Bk when there are multiple discharge target cells Bk.

[0043] In step S7, the control IC 10 calculates the discharge operation time (Tk) of the discharge target cell Bk using the above-mentioned formula (1). The SOC of the discharge target cell Bk was obtained in step S2. The average SOC (SOCave) was obtained in step S3. The current value (IkBalance) of the discharge current of the discharge target cell Bk was obtained in step S6.

[0044] In step S8, the control IC 10 applies a discharge control signal to the switch SWk of the discharge circuit Dk corresponding to the cell Bk to be discharged, turning on the switch SWk. This starts discharging the cell Bk to be discharged. At this time, the control IC 10 measures and monitors the elapsed time since the start of discharge.

[0045] In step S9, charging of the cell stack B is started. Note that charging control of the cell stack B may be performed by the control IC 10 provided in the cell balancing control device 1, or may be performed by another control device provided outside the cell balancing control device 1. If it is performed by another control device, it is necessary, for example, to send a signal indicating the end of step S8 from the control IC 10 to the other control device.

[0046] In step S10, the control IC 10 turns off the switch SWk of the discharge circuit Dk corresponding to the cell Bk to be discharged by stopping the application of the discharge control signal. This ends the discharge of the cell Bk to be discharged. The timing of this discharge end is the timing when the discharge operation time calculated in step S7 is confirmed by the control IC 10 through timing. Therefore, the discharge of the cell Bk to be discharged ends when the necessary and sufficient amount of discharge has been performed, so that the cell Bk to be discharged can be discharged without excess or deficiency, achieving efficient cell balancing. After step S10, the cell balancing control flow in the cell balance control device 1 ends.

[0047] In step S11, charging of the cell stack B begins. Note that charging control of the cell stack B may be performed by the control IC 10 included in the cell balancing control device 1, or may be performed by another control device provided external to the cell balancing control device 1. If it is performed by another control device, it may be necessary, for example, to send a signal indicating the end of step S4 from the control IC 10 to the other control device. After step S11, the cell balancing control flow in the cell balancing control device 1 ends.

[0048] In the control flow shown in Figure 3, charging of cell stack B begins in step S9 before discharge ends in step S10. In other words, the charging time of cell stack B and the discharging operation time of discharge-target cell Bk always overlap. This makes it possible to discharge discharge-target cell Bk, which has a high charge rate, while charging each of cells B1, B2, B3, ..., Bn, and suppress the degree to which the charge rate (average SOC) of cell stack B as a whole decreases due to discharge. Furthermore, because power is reliably supplied to control IC 10 while cell stack B is being charged, cell balance control can be stably performed.

[0049] However, the order of steps S9 and S10 may be reversed. That is, charging of the cell stack B may be started after discharging of the discharge target cell Bk is completed. In this case, there is an advantage that the charging efficiency of the cell stack B can be improved.

[0050] It is preferable that whether step S9 or step S10 is executed first be determined in advance, for example, by a user setting. For example, if the discharging operation time of the discharge target cell Bk is as long as several hours, charging of the cell stack B is started without waiting for the end of the discharging operation. On the other hand, if the discharging operation time of the discharge target cell Bk is as short as several minutes, charging of the cell stack B is started after waiting for the end of the discharging operation. In this way, by variably setting the charging start timing based on the discharging operation time Tk, user convenience can be improved.

[0051] As described above, according to this embodiment, the cell balance control device 1 for a secondary battery includes a passive cell balance circuit 20 that equalizes the charge states of multiple cells B1, B2, B3, ..., Bn, each of which is a secondary battery, by discharging through resistors R1, R2, R3, ..., Rn, and a control IC 10 that individually calculates the discharge operation time Tk for each cell Bk to be discharged and performs control to stop the discharge operation for each cell Bk to be discharged when the calculated discharge operation time Tk has elapsed. This makes it possible to easily achieve accurate and efficient passive cell balancing.

[0052] In this embodiment, the control IC 10 estimates the discharge current value IkBalance for each cell Bk to be discharged and calculates the discharge operation time Tk for each cell Bk to be discharged based on the estimated discharge current value IkBalance before the start of discharge. This reliably avoids the need to measure the discharge current, which changes from moment to moment, in real time during actual discharge and instantly reflect this in the calculation, thereby making it possible to reliably avoid the complication of the control process.

[0053] In this embodiment, the control IC 10 calculates the discharge operation time Tk by dividing the capacity to be discharged (CAPinit*(SOCk-SOCave)) by the estimated discharge current value IkBalance. This allows the discharge operation time Tk for each discharge target cell Bk to be calculated individually.

[0054] In this embodiment, the control IC 10 estimates the discharge current IkBalance by dividing the average of the open circuit voltage OCV and full charge voltage of the cell Bk to be discharged by the resistance Rk. This makes it possible to roughly calculate the discharge current IkBalance before the start of discharge without measuring the actual discharge current IkBalance.

[0055] In this embodiment, the control IC 10 variably sets the timing for starting charging of the cells B1, B2, B3, ..., Bn based on the calculated discharge operation time Tk, thereby improving user convenience.

[0056] Although the embodiments of the present invention have been specifically described above, the present invention is not limited to the specific embodiments described above. Various modifications and changes to the specific examples described in the above embodiments are possible within the scope of the gist of the present invention as defined in the claims. [Industrial Applicability]

[0057] The cell balance control device of the present invention can easily achieve accurate and efficient passive cell balancing, and is suitable for use as a cell balance control device that performs passive cell balancing in a power storage system that uses secondary batteries. [Explanation of symbols]

[0058] 1 Cell balance control device 10 Control IC 11 Storage section 20 Passive cell balancing circuit 30 Voltage Sensor B Cell stack B1, B2, B3, ..., Bn cells D1, D2, D3, ..., Dn discharge circuit DL discharge line PL power line R1, R2, R3,..., Rn resistance SW1, SW2, SW3, ..., SWn switches +T, -T terminal

Claims

1. a passive cell balance circuit that equalizes the charge states of a plurality of cells, each of which is a secondary battery, by discharging the cells through a resistor; a control unit that individually calculates the discharge operation time of each discharge target cell, and performs control to stop the discharge operation for each discharge target cell on the condition that the calculated discharge operation time has elapsed; A cell balance control device for a secondary battery having the same.

2. The control unit estimates a current value of the discharge for each of the discharge target cells individually, and calculates an operation time of the discharge for each of the discharge target cells individually based on the estimated current value of the discharge before the start of the discharge. The cell balancing control device according to claim 1 .

3. The control unit calculates the discharge operation time by dividing the capacity to be discharged by the estimated discharge current value. The cell balancing control device according to claim 2 .

4. the control unit estimates the discharge current value by dividing the average value of the open circuit voltage value and the full charge voltage value of the discharge target cell by the resistance value. The cell balancing control device according to claim 2 .

5. the control unit variably sets the timing to start charging the plurality of cells based on the calculated operation time of the discharging. The cell balancing control device according to claim 1 .

6. A cell balance control method for a secondary battery, which is performed on a passive cell balance circuit that equalizes the charge states of a plurality of cells, each of which is a secondary battery, by discharging through a resistor, comprising: Calculating the discharge operation time of each discharge target cell individually; performing control to stop the discharge operation for each of the discharge target cells individually on the condition that the calculated discharge operation time has elapsed; A method for controlling cell balance of a secondary battery.

7. A secondary battery cell balance control program for causing a processor to execute the secondary battery cell balance control method according to claim 6.

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