Battery system

Abstract

The invention relates to a battery system. This battery system equalizes the capacity of each cell included in a battery in which a plurality of cells having a stationary region in a charge / discharge curve are connected in series, and is provided with: an equalization means for adjusting the capacity of each cell; and an ECU that controls charging and discharging of the battery. The ECU controls the equalization means by determining which one of the first control method and the second control method is to be used in accordance with a predetermined determination condition for determining which one of the first control method and the second control method is suitable for equalization under the current condition.

Description

Technical Field

[0001] The present disclosure relates to a battery system, and more particularly to a battery system that equalizes the capacities of battery cells included in a battery pack formed by connecting a plurality of battery cells having a plateau region in a charge and discharge curve. Background Art

[0002] In the past, there was a technology that equalized the voltage difference of each cell based on the SOC (State of Charge)-OCV (Open Circuit Voltage) characteristics unique to LFP (Li, Fe, P: lithium iron phosphate) batteries (for example, refer to Japanese Patent Publication No. 2019-92276). In this technology, the voltage difference of each cell is equalized based on the time difference required for the voltage of each cell of a battery pack formed by connecting multiple cells of LFP batteries in series to pass through the measurement points Pa and Pb of the two voltage steps of the SOC-OCV curve. Summary of the invention

[0003] However, if the voltage of each cell does not pass through the measurement points Pa and Pb, there is no opportunity to ensure equalization for improving the estimation accuracy of the internal state of the cell.

[0004] The present disclosure provides a battery system capable of ensuring equalization opportunities.

[0005] The battery system disclosed herein is a system for equalizing the capacities of the battery cells included in a battery pack formed by connecting a plurality of battery cells in series and having a plateau region in the charge and discharge curves, wherein the battery system comprises:

[0006] an adjustment unit that adjusts the capacity of each battery cell; and

[0007] A control device controls the charging and discharging of the battery pack.

[0008] The control device determines which control method to use according to a predetermined determination condition for determining which of the first control method and the second control method is suitable for equalization under current conditions.

[0009] When it is determined that the first control method is to be used, the control adjustment unit is controlled to equalize the capacities of the battery cells using the first control method.

[0010] When it is determined that the second control method is to be used, the adjustment unit is controlled to equalize the capacities of the battery cells using the second control method.

[0011] According to such a configuration, the capacities of the battery cells included in the battery pack can be equalized using a control method suitable for the current situation. As a result, a battery system capable of ensuring an opportunity for equalization can be provided.

[0012] The battery system may further include a sensor for detecting the voltage of each battery cell included in the battery pack.

[0013] The first control method is a control method using the open circuit voltage, which is the voltage of the battery cell detected by the sensor when no power is output from the battery pack to the outside.

[0014] The second control method is a control method using a closed-circuit voltage, which is a voltage of a battery cell detected by a sensor when electric power is output from the battery pack to the outside.

[0015] According to such a configuration, equalization can be performed using a control method suitable for equalization under the current situation, out of any of the control methods using the open circuit voltage and the closed circuit voltage.

[0016] The judgment condition may also be the following condition: when the current situation is a predetermined situation that prioritizes opportunity ensuring over ensuring equalization accuracy, the second control method is used in preference to the first control method; on the other hand, when the current situation is not a predetermined situation, the first control method is used in preference to the second control method.

[0017] According to such a configuration, equalization can be performed by preferentially using either the first control method suitable for ensuring accuracy or the second control method suitable for ensuring opportunity, depending on whether the current situation prioritizes ensuring accuracy or ensuring opportunity for equalization.

[0018] The predetermined condition may also be a condition in which a predetermined period has passed since the last equalization. According to such a configuration, when the predetermined period has passed since the last equalization, the equalization can be performed by using the second control method suitable for ensuring the opportunity with priority to ensure the opportunity. On the other hand, when the predetermined period has not passed since the last equalization, the equalization can be performed by using the first control method suitable for ensuring the accuracy with priority to ensure the accuracy.

[0019] The predetermined condition may also be a condition where the capacity difference of the battery cells is greater than a predetermined threshold value. According to such a structure, when the capacity difference of the battery cells is greater than the predetermined threshold value, the equalization can be performed by preferentially using the second control method suitable for ensuring the opportunity with priority to ensure the opportunity. On the other hand, when the capacity difference of the battery cells is not greater than the predetermined threshold value, the equalization can be performed by preferentially using the first control method suitable for ensuring the accuracy with priority to ensure the accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will be described below with reference to the accompanying drawings, in which like reference numerals represent like elements, and in which:

[0021] Figure 1 is an overall structural diagram of an electric vehicle equipped with a battery system according to this embodiment;

[0022] Figure 2 is a diagram showing an example of an equalization unit;

[0023] Figure 3 is a flowchart showing the flow of equalization control processing in the first embodiment;

[0024] Figure 4 is a graph showing a SOC-OCV curve of a single battery;

[0025] Figure 5 is a flowchart showing the flow of equalization control processing in the second embodiment; and

[0026] Figure 6 : is a flowchart showing the flow of the equalization control process in the modification example. DETAILED DESCRIPTION

[0027] Figure 1 1 is an overall structural diagram of an electric vehicle 1 equipped with a battery system S of this embodiment. In this embodiment, the electric vehicle 1 is, for example, a battery electric vehicle. The electric vehicle 1 includes a motor generator (MG) 10 as a rotating electric machine, a power transmission gear 20, a drive wheel 30, a power control unit (PCU) 40, a system main relay (SMR) 50, a battery 100, a monitoring unit 200, and an electronic control unit (ECU) 300. The electronic control unit is an example of a control device.

[0028] MG 10 is, for example, an embedded permanent magnet synchronous motor (IPM motor) and has a function as an electric motor and a generator. Output torque of MG 10 is transmitted to drive wheels 30 via a power transmission gear 20 including a speed reducer and a differential device.

[0029] When the electric vehicle 1 brakes, the MG 10 is driven by the driving wheel 30 and operates as a generator. Thus, the MG 10 also functions as a braking device for performing regenerative braking that converts the kinetic energy of the electric vehicle 1 into electric power. The regenerative electric power generated by the regenerative braking force in the MG 10 is stored in the battery 100 .

[0030] PCU 40 is a power conversion device that converts electric power bidirectionally between MG 10 and battery 100. PCU 40 includes, for example, an inverter and a converter that operate based on a control signal from ECU 300.

[0031] The converter boosts the voltage supplied from the battery 100 and supplies the voltage to the inverter when the battery 100 is discharged. The inverter converts the DC power supplied from the converter into AC power to drive the MG 10 .

[0032] On the other hand, the inverter converts AC power generated by MG 10 into DC power and supplies it to the converter when charging battery 100. The converter steps down the voltage supplied from the inverter to a voltage suitable for charging battery 100 and supplies it to battery 100.

[0033] The SMR 50 is electrically connected to the power line connecting the battery 100 and the PCU 40. When the SMR 50 is closed (ON) (i.e., in the conductive state) according to the control signal from the ECU 300, power can be transferred between the battery 100 and the PCU 40. On the other hand, when the SMR 50 is opened (OFF) (i.e., in the disconnected state) according to the control signal from the ECU 300, the electrical connection between the battery 100 and the PCU 40 is disconnected.

[0034] The battery 100 stores electric power for driving the MG 10. The battery 100 is a rechargeable DC power source (secondary battery), and is a battery pack composed of a plurality (n) of single cells (battery units) 101 stacked and electrically connected in series, for example. The single cell 101 can be composed of a lithium ion battery, for example. In this embodiment, a lithium iron phosphate ion battery (LFP battery) using lithium iron phosphate as a positive electrode active material is used as the single cell 101.

[0035] The monitoring unit 200 includes a voltage detection unit 210, a current sensor 220, and a temperature sensor 230. The voltage detection unit 210 detects the voltage VB of the cell 101 (the voltage VB between the terminals of the cell 101). The current sensor 220 detects the current IB input to and output from the battery 100 (cell 101). The temperature sensor 230 detects the temperature TB of each cell 101. Each detection unit outputs its detection result to the ECU 300.

[0036] The electric vehicle 1 is provided with a DC inlet 60, and the battery 100 can be quickly charged from an external direct current (DC) power supply as a charging device. The DC inlet 60 is configured to be connected to a connector 420 provided at the front end of a charging cable 410 of an external DC power supply (charging device) 400. The charging relay 70 is electrically connected to a power line connecting the DC inlet 60 and the battery 100. The charging relay 70 switches the supply and disconnection of power between the DC inlet 60 and the battery 100 according to a control signal from the ECU 300. By closing the charging relay 70, external charging (quick charging) of the battery 100 is performed.

[0037] The electric vehicle 1 is provided with an AC inlet 80, and the battery 100 can be normally charged from an external alternating current (AC) power source as a charging device. The AC inlet 80 is configured to be connected to a connector 520 provided at the front end of a charging cable 510 of an external AC power source (charging device) 500. A vehicle charger 130 is provided on the power line between the AC inlet 80 and the battery 100, and the AC power supplied from the external AC power source is converted into DC power, and is converted into a voltage capable of charging the battery 100. The charging relay 90 is electrically connected to the power line connecting the vehicle charger 130 and the battery 100. The charging relay 90 switches the supply and disconnection of power between the vehicle charger 130 and the battery 100 according to a control signal from the ECU 300. When the charging relay 90 is closed, external charging (normal) of the battery 100 is performed.

[0038] ECU300 includes a CPU (Central Processing Unit) 301 and a memory (e.g., including a ROM (Read Only Memory) and a RAM (Random Access Memory)) 302. ECU300 controls each device based on information such as signals received from the monitoring unit 200, signals from various sensors not shown (e.g., accelerator opening signals, vehicle speed signals, etc.), and mappings and programs stored in the memory 302, so as to bring the electric vehicle 1 into the desired state. In addition, ECU300 uses an equalization unit (equalization circuit) 250 to perform equalization processing on the single battery 101. It should be noted that the battery system S is composed of a battery 100 (single battery 101), a monitoring unit 200, an equalization unit 250, and ECU300.

[0039] Figure 2: is a diagram showing an example of an equalization unit 250. In this embodiment, the equalization unit 250 is assembled in the voltage detection unit (voltage detection circuit) 210 of the monitoring unit 200 as an equalization circuit. In the battery 100, a plurality of (n) single cells (battery cells) 101A to 101N (representatively also referred to as "single cells 101") are connected in series. The voltage detection unit 210 detects the voltage of the single cells 101A to 101N via a plurality of voltage detection lines L1, branch lines L11, and branch lines L12. The first voltage detection line L1 is connected to the positive terminal of the single cell 101A. In addition, the second to n+1th voltage detection lines L1 are connected to the negative terminal of one single cell and the positive terminal of another single cell between each adjacent single cell of the single cells 101A to 101N.

[0040] The voltage detection line L1 is provided with a fuse F and a chip bead Cb. The fuse F melts when an overcurrent occurs to protect the circuit. The chip bead Cb reduces the applied stress when a surge voltage is applied instantaneously.

[0041] A Zener diode D is connected in parallel to each of the cells 101A to 101N via the adjacent voltage detection line L1. The cathode of the Zener diode D is connected to the positive terminal side of the corresponding cell, and the anode is connected to the negative terminal side of the corresponding cell. When an overvoltage is applied from the battery 100 (cell 101) to the voltage detection unit 210, current flows through the Zener diode D, thereby protecting the voltage detection unit 210 from the overvoltage.

[0042] The voltage detection line L1 is branched into a branch line L11 and a branch line L12 at a position closer to the monitoring unit 200 than the Zener diode D. The branch line L11 is connected to the comparator 211 via the switch So, and the branch line L12 is connected to the comparator 211 via the switch Sh. The switch So and the switch Sh can use, for example, a photoelectric MOS (Metal Oxide Semiconductor) relay. It should be noted that the branch line L11 branched from the voltage detection line L1 connected to the positive terminal of the single cell 101A configured on the positive output terminal side of the battery 100 is not connected to the comparator 211. In addition, the voltage detection line L1 connected to the negative terminal of the single cell 101N configured on the negative output terminal side of the battery 100 does not have a branch line L12.

[0043] A resistor R1 is provided in the branch line L12. A capacitor (flying capacitor) C is provided between the branch line L12 connected to the positive terminal of each single cell and the branch line L11 connected to the negative terminal. In the branch line L12, the capacitor C is connected between the resistor R1 and the switch Sh, and an RC low-pass filter is formed by the resistor R1 and the capacitor C. Each capacitor C is connected in parallel with the corresponding single cell 101A~101N. The charge of the corresponding single cell 101A~101N is charged into the capacitor C, and the voltage value of the capacitor C is equal to the voltage value of the corresponding single cell 101A~101N. By turning on (closing) the switch Sh and the switch So corresponding to the specific single cell 101A~101N, the comparator 211 outputs the voltage (cell voltage) VB of the specific single cell 101A~101N. Thus, the monitoring unit 200 can detect the voltage VB of each of the cells 101A to 101N using the voltage detection unit 210 by sequentially turning on the switches Sh and So corresponding to the cells 101A to 101N. In addition, the voltage Vb of the battery 100 can be detected by turning on (closing) the switch Sh of the cell 101A and the switch So connected to the negative terminal of the cell 101N.

[0044] The equalization unit 250 is composed of a discharge resistor Rd provided in the branch line L11 and a switch S1 for connecting (closing) and disconnecting (opening) adjacent branch lines L11. The switch S1 switches between ON (closing) and OFF (opening) by receiving a control signal from the ECU 300. Figure 2 In FIG. 1 , the arrows of the single-dot-dashed lines indicate the flow of current when equalization control is performed to eliminate the uneven SOC of the single cells 101. The figure shows a case where the SOC of the single cell 101B is large, and discharge is performed from the single cell 101B, and equalization control is performed. When the SOC of the single cell 101B is large, the switch S1 corresponding to the single cell 101B is turned on (closed). When the switch S1 corresponding to the single cell 101B is turned on (closed), as shown by the arrows of the single-dot-dashed lines, the current discharged from the single cell 101B is consumed by the two discharge resistors Rd, the SOC of the single cell 101B is reduced, and equalization of the SOC is performed. In this way, equalization is performed between the single cells 101 of the battery 100 (battery pack).

[0045] Conventionally, there is a technology that equalizes the voltage difference of each cell based on the time difference required for the voltage of each cell of a battery pack formed by connecting a plurality of LFP cells in series to pass through the measurement points Pa and Pb of two voltage steps on the SOC-OCV curve. However, if the voltage of each cell does not pass through the measurement points Pa and Pb, there is no opportunity to ensure equalization for improving the estimation accuracy of the internal state of the cell.

[0046] Therefore, ECU300 determines which control method to use according to a predetermined determination condition for determining which of the first control method and the second control method is suitable for equalization under the current situation. When ECU300 determines that the first control method is to be used, it controls the equalization unit 250 in a manner that the capacities of the individual cells 101 are equalized using the first control method. When ECU300 determines that the second control method is to be used, it controls the equalization unit 250 in a manner that the capacities of the individual cells 101 are equalized using the second control method. Thus, it is possible to perform equalization of the capacities of the individual cells 101 included in the battery 100 using a control method that is suitable for the current situation. As a result, it is possible to ensure the opportunity for equalization. First Embodiment

[0047] Figure 3 : is a flowchart showing the flow of the equalization control process in the first embodiment. Figure 3 , the equalization control process is periodically called and executed by the CPU 301 of the ECU 300 from the upper processing. The CPU 301 determines whether it is Ready OFF after the power switch of the electric vehicle 1 has just become Ready OFF due to the user's operation (S111). When it is determined to be Ready OFF (YES in S111), the CPU 301 determines whether a predetermined trip (for example, 10 trips) has passed since the last equalization control was executed (S112). The trip refers to one trip from being operated to Ready ON to being operated to Ready OFF after the electric vehicle 1 is driven.

[0048] When it is determined that the predetermined distance has not passed since the last equalization control was executed (No in S112), CPU301 stores a flag indicating that equalization based on OCV is executed as an equalization execution flag in memory 302 (S113). Equalization based on OCV refers to equalization control of the SOC of the cells 101A to 101N included in the battery 100 using OCV. On the other hand, when it is determined that the predetermined distance has passed since the last equalization control was executed (YES in S112), CPU301 stores a flag indicating that equalization based on CCV (Closed Circuit Voltage) is executed as an equalization execution flag in memory 302 (S114). Equalization based on CCV refers to equalization control of the SOC of the cells 101A to 101N included in the battery 100 using CCV.

[0049] After S113 or S114, CPU301 determines whether it is in ReadyOFF (for example, ReadyOFF after external charging is completed, ReadyOFF without external charging) (S131). When it is determined to be in ReadyOFF (YES in S131), CPU301 determines whether the equalization execution flag stored in memory 302 is a flag indicating the execution of OCV-based equalization (S132). When it is determined to be a flag indicating the execution of OCV-based equalization (YES in S132), CPU301 obtains the open circuit voltages V1 to Vn of all the cells 101A to 101N contained in battery 100 (S141). It should be noted that in Figure 1 and Figure 2 In the circuit shown, even when the SMR 50 and the charging relays 70 and 90 are turned on, current flows through the monitoring unit 200 when measuring the voltage of the cells 101A to 101N. Therefore, the voltage of the cells 101A to 101N detected in this state is not strictly OCV, but is handled as OCV.

[0050] Figure 4 It is a graph showing the SOC-OCV curve of a single battery. Figure 4 The vertical axis of the graph represents OCV (unit: V) and the horizontal axis represents SOC (unit: %). The solid line graph represents the SOC-OCV curve of the single cell 101 of the LFP battery used in this embodiment. The dotted line graph represents the SOC-OCV curve of the single cell of the ternary battery used in the past.

[0051] return Figure 3 , CPU301 uses Figure 4 The SOC-OCV curve shown calculates the SOC of the cell having the lowest voltage Vmin among the cells 101A to 101N included in the battery 100 ( S142 ). The CPU 301 determines whether the calculated SOC is equal to or greater than a threshold value Th.

[0052] Refer again Figure 4, the SOC-OCV curve of the single cell 101 disclosed in the present invention includes a portion of range A with SOC=0~a, a portion of range B with SOC=a~c, a portion of range C with SOC=c~d, a portion of range D with SOC=d~f, and a portion of range E with SOC=f~100. In the portion of range A, OCV rises sharply as SOC increases. In the portion of range B, the rise of OCV with the increase of SOC is slow. In the portion of range C, there is a "step" of the rise of OCV with the increase of SOC. Even if the single cell 101 deteriorates and the full charge capacity of the single cell 101 decreases (the capacity retention rate of the single cell 101 decreases), the position of the "step" does not change. Even if the single cell 101 deteriorates, the value of the remaining capacity where the "step" appears does not change. In the portion of range D, OCV hardly rises with the increase of SOC. This range D is called a stable (flat) area. Range B is sometimes also called a stable area. In the portion of range E, OCV rises sharply as SOC increases. It should be noted that, in the SOC-OCV curve of a conventional ternary battery, the OCV increases proportionally over almost the entire range as the SOC increases.

[0053] In the range B to the range D, the change in OCV relative to the change in SOC is small compared to the range A and the range E. Therefore, in the range B to the range D, it is difficult to perform equalization based on OCV. Therefore, in the range E, that is, in the range where SOC is greater than f, equalization based on OCV is performed. Therefore, the threshold value Th of S143 is set to f.

[0054] return Figure 3 , when it is determined that the SOC is above the threshold value Th (YES in S143), the CPU 301 starts the equalization based on OCV (S144). The equalization based on OCV is specifically performed as follows. With the SMR 50 and the charging relays 70 and 90 opened, the OCV of each single cell 101 is measured by the monitoring unit 200. Based on the OCV, the SOC of each single cell 101 is calculated using the SOC-OCV curve. For the single cell 101 whose SOC difference relative to the minimum SOC is greater than a predetermined value, the corresponding switch S1 is turned on (closed) during a period corresponding to the difference. Thus, the power corresponding to the difference is consumed by the discharge resistor Rd. As a result, the SOC of the single cell 101 is reduced by an amount corresponding to the difference, and the equalization of the SOC is performed.

[0055] After S144, CPU 301 stores a flag indicating that equalization is turned off as an equalization execution flag in memory 302 (S145). When it is determined that the SOC is less than the threshold value Th (NO in S143), or after S145, CPU 301 returns the executed process to the upper process of the call source of the equalization control process.

[0056] When it is determined that the vehicle is not in ReadyOFF (NO in S131), for example, the vehicle is in motion or is parked in ReadyON, or when it is determined that the equalization execution flag is not a flag indicating that equalization based on OCV is to be executed (NO in S132), CPU 301 determines whether the equalization execution flag stored in memory 302 is a flag indicating that equalization based on CCV is to be executed (S151). When it is determined that the flag indicates that equalization based on CCV is to be executed (YES in S151), CPU 301 starts equalization based on CCV (S152). In this way, equalization based on CCV can be executed not only when the vehicle is not in ReadyOFF, but also when the vehicle is in ReadyOFF, as shown in the process flow of S131 and S132.

[0057] Refer again Figure 4 The equalization based on CCV is specifically performed as follows. When the SMR 50 is closed (ReadyON state) or when any one of the charging relays 70 and 90 is closed (external charging is performed), the CCV of each battery cell 101 is measured by the monitoring unit 200. Based on the CCV, the temporary SOC of each battery cell 101 is calculated using the SOC-OCV curve.

[0058] When the battery 100 is in ReadyON and regeneration from the MG 10 is in progress, or when the battery 100 is in ReadyOFF and external charging is in progress, the SOC of each cell 101 increases. In this case, the SOC difference between the cell 101 that first exceeds the "step" of SOC=c~d, that is, the cell F, and the cell 101 that last exceeds the "step" of SOC=c~d, that is, the cell L, is calculated. Specifically, if the SOC of the cell L when the cell F exceeds the "step" is set to b, and the SOC of the cell F when the cell L exceeds the "step" is set to e, then the SOC difference=ed≈db can be calculated. The SOC difference between the cell that exceeds the "step" between the cell F and the cell L and the cell L is calculated in the same manner. For the SOC cells 101 whose SOC differences are equal to or greater than a predetermined value, the corresponding switch S1 is turned on (closed) for a period corresponding to the difference. Thus, regenerative power or charging power is charged to all the cells 101A to 101N included in the battery 100, and on the other hand, for the cells 101 whose SOC difference is greater than or equal to a predetermined value, power corresponding to the difference is consumed by the discharge resistor Rd. As a result, the SOC of the cells 101 whose SOC difference is greater than or equal to the predetermined value is reduced by an amount corresponding to the difference, and the SOC is equalized.

[0059] When the battery 100 is in the ReadyON state and power is being output from the battery 100 to the MG 10, the SOC of each cell 101 decreases. In this case, the SOC difference between the cell 101 that first exceeds the "step" of SOC=d~c, i.e., the cell F, and the cell 101 that last exceeds the "step" of SOC=d~c, i.e., the cell L, is calculated. The SOC difference between the cell that exceeds the "step" between the cell F and the cell L and the cell L is calculated in the same manner. For the cells 101 whose SOC difference is greater than or equal to a predetermined value, the corresponding switch S1 is turned on (closed) during a period corresponding to the difference. Thus, the power output to the MG 10 is consumed for all the cells 101A~101N included in the battery 100. In addition, for the cells 101 whose SOC difference is greater than or equal to a predetermined value, the power corresponding to the difference is further consumed by the discharge resistor Rd. As a result, the SOC of the battery cell 101 having an SOC difference equal to or greater than a predetermined value is reduced by an amount corresponding to the difference, and the SOC is equalized.

[0060] return Figure 3After S152, CPU 301 stores a flag indicating that equalization is turned off as an equalization execution flag in memory 302 (S153). When it is determined that the equalization execution flag is not a flag indicating that equalization based on CCV is executed (No in S151), or after S153, CPU 301 returns the executed processing to the upper processing of the calling source of the equalization control processing. Second Embodiment

[0061] Figure 5 : is a flowchart showing the flow of the equalization control process in the second embodiment. Figure 5 The equalization control process is periodically called and executed by the CPU 301 of the ECU 300 from the upper processing. Figure 3 The equalization control process in the first embodiment described in the above is common, so it will not be described repeatedly. The CPU 301 determines whether it is the time for the first single cell 101 to pass through the "step" (S121). If it is determined that it is the time to pass (YES in S121), the CPU 301 starts to integrate the current of the unit (S122).

[0062] When it is determined that it is not the first time for the single cell 101 to pass the "step" (No in S121), or after S122, the CPU 301 determines whether it is the last time for the single cell 101 to pass the "step" (S123). When it is determined that it is the time to pass (Yes in S123), the CPU 301 determines whether the accumulated capacity of the current accumulated in S122 is greater than or equal to a threshold value Cth (for example, 5 Ah) (S124). When it is determined that the accumulated capacity is less than the threshold value Cth (No in S124), the CPU 301 stores a flag indicating that equalization based on OCV is executed as an equalization execution flag in the memory 302 (S125). On the other hand, when it is determined that the accumulated capacity is greater than or equal to the threshold value Cth (Yes in S124), the CPU 301 stores a flag indicating that equalization based on CCV is executed as an equalization execution flag in the memory 302 (S126). After S125 or S126, CPU 301 resets the accumulated capacity (S127). Figure 3 The equalization control process of the first embodiment described in is similarly executed in the steps S131 and thereafter.

[0063] Modifications

[0064] (1) As described in the first and second embodiments, equalization based on OCV or equalization based on CCV is preferentially performed according to the situation. However, the present invention is not limited thereto, and the equalization control process may be performed as described below. Figure 6 : is a flowchart showing the flow of equalization control processing in a modified example. Figure 6 , CPU301 performs processing for determining the method of equalization control (S211). Based on the result of determination in S211, CPU301 determines which of control method I or control method II is to be set (S212). When it is determined that control method I is to be set, CPU301 executes control method I (for example, equalization control based on OCV) (S213). On the other hand, when it is determined that control method II is to be set, CPU301 executes control method II (for example, equalization control based on CCV) (S214).

[0065] In S211, it is also possible to determine which control method to set based on which equalization control method is suitable. For example, when the opportunity of equalization is prioritized, it is determined that control method II is set to be more suitable for ensuring the opportunity than control method I. When the accuracy of equalization is prioritized, it is determined that control method I is set to be more suitable for ensuring the accuracy than control method II. Other indicators may be used in addition to or instead of opportunity and accuracy.

[0066] (2) In the aforementioned embodiment, when it is determined that OCV-based equalization is appropriate, OCV-based equalization is performed with a frequency of 100%, and when it is determined that CCV-based equalization is appropriate, CCV-based equalization is performed with a frequency of 100%. However, this is not limited to this, and when it is determined that OCV-based equalization is appropriate, OCV-based equalization may be performed with priority over CCV-based equalization. When it is determined that CCV-based equalization is appropriate, CCV-based equalization may be performed with priority over OCV-based equalization. For example, when it is determined that OCV-based equalization is appropriate, OCV-based equalization may be performed with a higher frequency than CCV-based equalization. When it is determined that CCV-based equalization is appropriate, CCV-based equalization may be performed with a higher frequency than OCV-based equalization.

[0067] Summarize

[0068] (1) If Figure 1 and Figure 2As shown in FIG. 1 , the battery system S is a system that equalizes the capacities of the individual cells 101 included in the battery 100 formed by connecting a plurality of cells 101A to 101N in series and having a plateau region in the charge and discharge curve. The battery system S includes an equalization unit 250 that adjusts the capacities of the individual cells 101 and an ECU 300 that controls the charge and discharge of the battery 100. Figures 3 to 6 As shown, the ECU 300 determines which control method to use according to a predetermined determination condition for determining which of the first control method (e.g., equalization based on OCV) and the second control method (e.g., equalization based on CCV) is suitable for equalization under the current situation. When the ECU 300 determines that the first control method is to be used, the ECU 300 controls the equalization unit 250 so that the capacities of the cells 101 are equalized using the first control method. When the ECU 300 determines that the second control method is to be used, the ECU 300 controls the equalization unit 250 so that the capacities of the cells 101 are equalized using the second control method.

[0069] Thus, the capacities of the cells 101 included in the battery 100 can be equalized using a control method suitable for the current situation. As a result, an opportunity for equalization can be ensured.

[0070] (2) If Figures 3 to 6 As shown, a monitoring unit 200 for detecting the voltage of each cell 101 included in the battery 100 may be further provided. The first control method may be a control method using the voltage of the cell 101 detected by the monitoring unit 200 when no power is output from the battery 100 to the outside, that is, the OCV. The second control method may be a control method using the voltage of the cell 101 detected by the monitoring unit 200 when power is output from the battery 100 to the outside, that is, the CCV.

[0071] Thus, equalization can be performed using a control method suitable for equalization under the current situation, among any of the control methods using OCV and CCV.

[0072] (3) If Figures 3 to 6 As shown, the determination condition may be a condition that, when the current situation is a predetermined situation that prioritizes opportunity assurance over equalization accuracy assurance, the second control method is used with priority over the first control method, and, on the other hand, when the current situation is not a predetermined situation, the first control method is used with priority over the second control method. The second control method may be used with priority, either only the second control method is used, or the second control method is used more frequently than the first control method. The first control method may be used with priority, either only the first control method is used, or the first control method is used more frequently than the second control method.

[0073] Thus, equalization can be performed by preferentially using either the first control method suitable for ensuring accuracy or the second control method suitable for ensuring opportunity, depending on whether the current situation prioritizes ensuring accuracy or ensuring opportunity for equalization.

[0074] (4) If Figure 3 As shown, the predetermined condition may also be a condition in which a predetermined period has passed since the last equalization. The predetermined period may be, for example, a period until a predetermined number of trips are completed or a period during which the vehicle is in motion. In the case of not being limited to being mounted on a vehicle, it may be a period until a predetermined number of power-on times or a period during which the battery is in use. Thus, in the case in which a predetermined period has passed since the last equalization, the second control method suitable for ensuring the opportunity can be used to perform the equalization with priority to ensure the opportunity. In the case in which the predetermined period has not passed since the last equalization, the first control method suitable for ensuring the accuracy can be used to perform the equalization with priority to ensure the accuracy.

[0075] (5) If Figure 5 As shown, the predetermined condition may also be a condition where the capacity difference of the single battery 101 is greater than a predetermined threshold value. Thus, when the capacity difference of the single battery 101 is greater than the predetermined threshold value, the second control method suitable for ensuring the opportunity can be used to perform equalization with priority to ensure the opportunity. When the capacity difference of the single battery 101 is not greater than the predetermined threshold value, the first control method suitable for ensuring the accuracy can be used to perform equalization with priority to ensure the accuracy.

[0076] The embodiments disclosed this time should be considered as illustrative in all aspects and not restrictive. The scope of the present disclosure is indicated by the claims rather than the description of the embodiments described above, and is intended to include all modifications within the meaning and scope equivalent to the claims.

Claims

1. A battery system that equalizes the capacities of the battery cells included in a battery pack formed by connecting a plurality of battery cells in series and having a plateau region in the charge and discharge curve, wherein: The battery system has: an adjustment unit, for adjusting the capacity of each of the battery cells; as well as A control device controls the charging and discharging of the battery pack, The control device determines which control method to use according to a predetermined determination condition for determining which of the first control method and the second control method is suitable for equalization under current conditions. When it is determined that the first control method is to be used, the adjustment unit is controlled to equalize the capacities of the battery cells using the first control method. When it is determined that the second control method is to be used, the adjustment unit is controlled to equalize the capacities of the battery cells using the second control method.

2. The battery system according to claim 1, wherein: The battery system further includes a sensor for detecting a voltage of each battery cell included in the battery pack. The first control method is a control method using an open circuit voltage, which is a voltage of the battery cell detected by the sensor when no power is output from the battery pack to the outside. The second control method is a control method using a closed-circuit voltage, which is the voltage of the battery cell detected by the sensor when the battery pack outputs electric power to the outside.

3. The battery system according to claim 2, wherein: The judgment condition is as follows: when the current situation is a predetermined situation that prioritizes opportunity ensuring over ensuring equalization accuracy, the second control method is used in preference to the first control method; on the other hand, when the current situation is not the predetermined situation, the first control method is used in preference to the second control method.

4. The battery system according to claim 3, wherein: The predetermined status is a status in which a predetermined period of time has passed since the previous equalization.

5. The battery system according to claim 3, wherein: The predetermined condition is a condition in which the capacity difference of the battery cells is equal to or larger than a predetermined threshold value.

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