Battery system

Abstract

To secure an opportunity of equalization.SOLUTION: A battery system is a system for equalizing capacities of electric cells included in a battery in which a plurality of electric cells each including a plateau region in a charge / discharge curve are connected in series. The battery system comprises: an equalization unit for adjusting the capacity of each of the electric cells; and an ECU for controlling charge / discharge of the battery. In accordance with a predetermined determination condition for determining which one of a first control method (e.g., equalization by OCV) and a second control method (e.g., equalization by CCV) is suitable for equalization in a present situation, the ECU determines which control method is to be used. In a case where the first control method is determined to be used, the equalization unit is controlled so as to equalize the capacity of each of the electric cells using the first control method and in a case where the second control method is determined to be used, the equalization unit is controlled so as to equalize the capacity of each of the electric cells using the second control method.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present disclosure relates to a battery system, and more particularly to a battery system that equalizes the capacity of each battery cell included in a battery pack in which a plurality of battery cells having plateau regions in their charge / discharge curves are connected in series. [Background technology]

[0002] In the past, there was a technology that, based on the SOC (State of Charge)-OCV (Open Circuit Voltage) characteristics specific to LFP (Li,Fe,P) batteries, equalized the voltage difference between each cell in an assembled battery in which multiple LFP battery cells are connected in series, according to the time difference required for the voltage of each cell to pass between measurement points Pa and Pb of the two voltage steps on the SOC-OCV curve (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2019-92276 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, if the voltage of each cell does not pass through the measurement points Pa and Pb, it is not possible to ensure an opportunity to perform equalization for improving the accuracy of estimating the internal state of the cells.

[0005] This disclosure has been made to solve the above-mentioned problems, and its purpose is to provide a battery system that can ensure an opportunity for equalization. [Means for solving the problem]

[0006] A battery system according to the present disclosure is a system for equalizing the capacity of each battery cell included in a battery pack in which multiple battery cells having plateau regions in their charge / discharge curves are connected in series, and includes an adjustment unit that adjusts the capacity of each battery cell, and a control device that controls charging and discharging of the battery pack. The control device determines which of a first control method and a second control method is to be used according to a predetermined determination condition for determining which of the first control method and the second control method is suitable for equalization in a current situation, and when it is determined that the first control method is to be used, controls the adjustment unit to equalize the capacity of each battery cell using the first control method, and when it is determined that the second control method is to be used, controls the adjustment unit to equalize the capacity of each battery cell using the second control method.

[0007] According to this configuration, the capacities of the battery cells included in the battery pack can be equalized using a control method suitable for the current situation, thereby providing a battery system that can ensure an opportunity for equalization.

[0008] The battery may further include a sensor that detects the voltage of each battery cell included in the assembled battery, and the first control method may be a control method that uses an open circuit voltage, which is the voltage of the battery cell detected by the sensor when no power is being output from the assembled battery to the outside, and the second control method may be a control method that uses a closed circuit voltage, which is the voltage of the battery cell detected by the sensor when power is being output from the assembled battery to the outside.

[0009] According to this configuration, equalization can be performed using either the control method using the open circuit voltage or the closed circuit voltage, whichever is more suitable for equalization under the current situation.

[0010] The judgment condition may be such that when the current situation is a specified situation in which securing opportunities is prioritized over ensuring the accuracy of equalization, the second control method is used in preference to the first control method, whereas when the current situation is not the specified situation, the first control method is used in preference to the second control method.

[0011] With this configuration, equalization can be performed by preferentially using either the first control method, which is suitable for ensuring accuracy, or the second control method, which is suitable for securing opportunities, depending on whether the current situation requires priority to ensure the accuracy of equalization or to secure opportunities.

[0012] The predetermined situation may be a situation in which a predetermined period of time has passed since the previous equalization. According to this configuration, if a predetermined period of time has passed since the previous equalization, equalization can be performed by giving priority to securing opportunities and preferentially using the second control method suitable for securing opportunities, whereas if a predetermined period of time has not passed, equalization can be performed by giving priority to securing accuracy and preferentially using the first control method suitable for securing accuracy.

[0013] The predetermined situation may be a situation in which the capacity difference between the battery cells is equal to or greater than a predetermined threshold. According to this configuration, when the capacity difference between the battery cells is equal to or greater than the predetermined threshold, it is possible to prioritize securing opportunities and perform equalization by preferentially using the second control method suitable for securing opportunities, whereas when the capacity difference is not equal to or greater than the predetermined threshold, it is possible to prioritize securing accuracy and perform equalization by preferentially using the first control method suitable for securing accuracy. [Brief description of the drawings]

[0014] [Figure 1] 1 is an overall configuration diagram of an electric vehicle equipped with a battery system according to this embodiment. [Diagram 2] FIG. 2 illustrates an example of an equalization unit. [Diagram 3] 5 is a flowchart showing a flow of an equalization control process in the first embodiment. [Figure 4] FIG. 2 is a diagram showing the SOC-OCV curve of a single battery. [Diagram 5] 10 is a flowchart showing a flow of an equalization control process in the second embodiment. [Figure 6] 13 is a flowchart showing a flow of an equalization control process in a modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] 1 is an overall configuration diagram of an electric vehicle 1 equipped with a battery system S according to this embodiment. In this embodiment, the electric vehicle 1 is, for example, an electric car. The electric vehicle 1 includes a motor generator (MG) 10, which is a rotating electric machine, a power transmission gear 20, drive wheels 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, which is an example of a control device.

[0016] The MG 10 is, for example, an interior permanent magnet synchronous motor (IPM motor) and has a function as an electric motor (motor) and a function as a generator (generator). The output torque of the MG 10 is transmitted to the drive wheels 30 via a power transmission gear 20 configured to include a reduction gear, a differential device, etc.

[0017] When braking the electric vehicle 1, the MG 10 is driven by the drive wheels 30 and operates as a generator. This allows the MG 10 to function as a braking device that performs regenerative braking to convert the kinetic energy of the electric vehicle 1 into electric power. The regenerative power generated by the regenerative braking force of the MG 10 is stored in the battery 100.

[0018] PCU 40 is a power conversion device that converts power bidirectionally between MG 10 and battery 100. PCU 40 includes an inverter and a converter that operate based on a control signal from ECU 300, for example.

[0019] The converter boosts the voltage supplied from the battery 100 and supplies the boosted voltage to the inverter when the battery 100 is discharging. The inverter converts the DC power supplied from the converter into AC power to drive the MG 10.

[0020] On the other hand, when charging the battery 100, the inverter converts the AC power generated by the MG 10 into DC power and supplies it to the converter. The converter steps down the voltage supplied from the inverter to a voltage suitable for charging the battery 100 and supplies it to the battery 100.

[0021] The SMR 50 is electrically connected to a power line connecting the battery 100 and the PCU 40. When the SMR 50 is closed (ON) in response to a control signal from the ECU 300 (i.e., in a conductive state), power can be exchanged between the battery 100 and the PCU 40. On the other hand, when the SMR 50 is opened (OFF) in response to a control signal from the ECU 300 (i.e., in a cut-off state), the electrical connection between the battery 100 and the PCU 40 is cut off.

[0022] The battery 100 stores power for driving the MG 10. The battery 100 is a rechargeable DC power source (secondary battery) and is an assembled battery in which a plurality (n pieces) of single cells (battery cells) 101 are stacked and, for example, electrically connected in series. The single cells 101 may be, for example, lithium ion batteries. In this embodiment, a lithium iron phosphate ion battery (LFP battery) that uses lithium iron phosphate as the positive electrode active material is adopted as the single cells 101.

[0023] 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 cells 101 (the voltage VB between each terminal of the cells 101). The current sensor 220 detects the current IB input to and output from the battery 100 (cells 101). The temperature sensor 230 detects the temperature TB of each of the cells 101. Each detection unit outputs the detection result to the ECU 300.

[0024] The electric vehicle 1 includes a DC inlet 60, and the battery 100 can be rapidly charged from an external direct current (DC) power source, which is a charging facility. The DC inlet 60 is configured to be connectable to a connector 420 provided at the end of a charging cable 410 of an external DC power source (charging facility) 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 between supplying and cutting off power between the DC inlet 60 and the battery 100 in response to a control signal from the ECU 300. When the charging relay 70 is closed, external charging (rapid charging) of the battery 100 is performed.

[0025] The electric vehicle 1 includes an AC inlet 80, and the battery 100 can be normally charged from an external alternating current (AC) power source, which is a charging facility. The AC inlet 80 is configured to be connectable to a connector 520 provided at the tip of a charging cable 510 of an external AC power source (charging facility) 500. An on-board charger 130 is provided on a power line between the AC inlet 80 and the battery 100, and converts AC power supplied from the external AC power source into DC power and also converts it into a voltage that can charge the battery 100. A charging relay 90 is electrically connected to the power line connecting the on-board charger 130 and the battery 100. The charging relay 90 switches between supplying and cutting off power between the on-board charger 130 and the battery 100 in response to a control signal from the ECU 300. When the charging relay 90 is closed, external charging (normal) of the battery 100 is performed.

[0026] The ECU 300 includes a CPU (Central Processing Unit) 301 and a memory (including, for example, a ROM (Read Only Memory) and a RAM (Random Access Memory)) 302. The ECU 300 controls each device so that the electric vehicle 1 is in a desired state, based on information such as signals received from the monitoring unit 200, signals from various sensors (not shown) (for example, an accelerator opening signal, a vehicle speed signal, etc.), and maps and programs stored in the memory 302. The ECU 300 also performs an equalization process on the single cells 101 using an equalization unit (equalization circuit) 250. The battery system S is composed of the battery 100 (single cells 101), the monitoring unit 200, the equalization unit 250, the ECU 300, etc.

[0027] FIG. 2 is a diagram showing an example of the equalization unit 250. In this embodiment, the equalization unit 250 is incorporated as an equalization circuit in the voltage detection section (voltage detection circuit) 210 of the monitoring unit 200. In the battery 100, a plurality (n pieces) of single cells (battery cells) 101A to 101N (representatively referred to as "single cells 101") are connected in series. The voltage detection section 210 detects the voltages of the single cells 101A to 101N via a plurality of voltage detection lines L1, a branch line L11, and a branch line L12. The first voltage detection line L1 is connected to the positive electrode terminal of the single cell 101A. In addition, the second to n+1th voltage detection lines L1 are connected between adjacent single cells of the single cells 101A to 101N, between the negative electrode terminal of one single cell and the positive electrode terminal of the other single cell.

[0028] The voltage detection line L1 is provided with a fuse F and chip beads Cb. The fuse F melts when an overcurrent occurs to protect the circuit. The chip beads Cb reduce the applied stress when a surge voltage is applied instantaneously.

[0029] A Zener diode D is connected in parallel to each of the cells 101A-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, a current flows through the Zener diode D, thereby protecting the voltage detection unit 210 from the overvoltage.

[0030] The voltage detection line L1 branches into a branch line L11 and a branch line L12 on the monitoring unit 200 side of the Zener diode D. The branch line L11 is connected to the comparator 211 via a switch So, and the branch line L12 is connected to the comparator 211 via a switch Sh. For example, a photo MOS (Metal Oxide Semiconductor) relay can be used for the switch So and the switch Sh. Note that the branch line L11 branched from the voltage detection line L1 connected to the positive terminal of the cell 101A arranged 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 cell 101N arranged on the negative output terminal side of the battery 100 does not include the branch line L12.

[0031] A resistor R1 is provided on the branch line L12. A capacitor (flying capacitor) C is provided between the branch line L12 connected to the positive electrode terminal of each cell and the branch line L11 connected to the negative electrode terminal. In the branch line L12, the capacitor C is connected between the resistor R1 and the switch Sh, and the resistor R1 and the capacitor C form an RC low-pass filter. Each of the capacitors C is connected in parallel with the corresponding cell 101A-101N, and the charge of the corresponding cell 101A-101N is charged to the capacitor C, and the voltage value of the capacitor C becomes equal to the voltage value of the corresponding cell 101A-101N. By turning on (closing) the switch Sh and the switch So corresponding to a specific cell 101A-101N, the comparator 211 outputs the voltage (cell voltage) VB of the specific cell 101A-101N. Thus, the monitoring unit 200 can detect the voltage VB of each of the cells 101A-101N by sequentially turning on the switches Sh and So corresponding to each of the cells 101A-101N using the voltage detection section 210. Also, by turning on (closing) the switch Sh of the cell 101A and the switch So connected to the negative terminal of the cell 101N, the voltage Vb of the battery 100 can be detected.

[0032] The equalization unit 250 is composed of a discharge resistor Rd provided in the branch line L11 and a switch S1 that connects (closes) / disconnects (opens) between adjacent branch lines L11. The switch S1 switches between ON (closed) and OFF (open) upon receiving a control signal from the ECU 300. In FIG. 2, the dashed arrow indicates the flow of current when equalization control is executed to eliminate the unevenness of the SOC of the cells 101. This shows a case where the SOC of the cell 101B is large, and the cell 101B is discharged and equalization control is executed. When the SOC of the cell 101B is large, the switch S1 corresponding to the cell 101B is turned ON (closed). When the switch S1 corresponding to the cell 101B is turned ON (closed), the current discharged from the cell 101B is consumed by the two discharge resistors Rd, as indicated by the dashed arrow, and the SOC of the cell 101B decreases, and SOC equalization is executed. In this manner, the cells 101 of the battery 100 (battery pack) are equalized.

[0033] Previously, there was a technology that, based on the SOC-OCV characteristics specific to LFP batteries, equalized the voltage difference between each cell in an assembled battery consisting of multiple LFP battery cells connected in series, according to the time difference required for the voltage of each cell to pass between the measurement points Pa and Pb of the two voltage steps on the SOC-OCV curve. However, if the voltage of each cell does not pass the measurement points Pa and Pb, it becomes impossible to secure an opportunity to perform equalization to improve the estimation accuracy of the internal state of the cells.

[0034] Therefore, the ECU 300 determines which control method to use according to a predetermined determination condition for determining whether the first control method or the second control method is suitable for equalization in the current situation, and when it is determined that the first control method is to be used, it controls the equalization unit 250 to equalize the capacities of the single cells 101 using the first control method, and when it is determined that the second control method is to be used, it controls the equalization unit 250 to equalize the capacities of the single cells 101 using the second control method. This makes it possible to execute the equalization of the capacities of the single cells 101 included in the battery 100 using a control method suitable for the current situation. As a result, it is possible to ensure an opportunity for equalization.

[0035] [First embodiment] Fig. 3 is a flowchart showing the flow of the equalization control process in the first embodiment. Referring to Fig. 3, the equalization control process is periodically called from a higher-level process and executed by the CPU 301 of the ECU 300. The CPU 301 judges whether or not it is Ready-OFF immediately after the power switch of the electric vehicle 1 is operated by the user to set it to Ready-OFF (step S111). If it is determined that it is Ready-OFF (YES in step S111), the CPU 301 judges whether or not a predetermined trip (for example, 10 trips) has elapsed since the previous execution of the equalization control (step S112). A trip refers to one run from when the electric vehicle 1 runs after an operation to set it to Ready-ON until an operation to set it to Ready-OFF.

[0036] When it is determined that a predetermined trip has not elapsed since the previous execution of equalization control (NO in step S112), the CPU 301 stores a flag indicating that equalization by OCV is to be executed in the memory 302 as an equalization execution flag (step S113). Equalization by OCV refers to equalization control of the SOC of the cells 101A to 101N included in the battery 100 using the OCV. On the other hand, when it is determined that a predetermined trip has elapsed since the previous execution of equalization control (YES in step S112), the CPU 301 stores a flag indicating that equalization by CCV (Closed Circuit Voltage) is to be executed in the memory 302 as an equalization execution flag (step S114). Equalization by CCV refers to equalization control of the SOC of the cells 101A to 101N included in the battery 100 using the CCV.

[0037] After step S113 or step S114, the CPU 301 judges whether or not the battery is in Ready-OFF (for example, in Ready-OFF after completion of external charging, in Ready-OFF without external charging) (step S131). If it is judged that the battery is in Ready-OFF (YES in step S131), the CPU 301 judges whether or not the equalization execution flag stored in the memory 302 is a flag indicating that equalization by OCV is to be executed (step S132). If it is judged that the flag indicates that equalization by OCV is to be executed (YES in step S132), the CPU 301 acquires the open circuit voltages V1 to Vn of all the single cells 101A to 101N included in the battery 100 (step S141). Note that in the circuit shown in FIG. 1 and FIG. 2, even if the SMR 50 and the charging relays 70 and 90 are in an open state, a current flows through the monitoring unit 200 when the voltages of the single cells 101A to 101N are measured. Therefore, the voltages of the cells 101A to 101N detected in this state are not OCVs in the strict sense, but are treated as OCVs.

[0038] Fig. 4 is a diagram showing the SOC-OCV curve of a single cell. Referring to Fig. 4, the vertical axis of this graph indicates OCV (unit: V), and the horizontal axis indicates SOC (unit: %). The solid line graph shows the SOC-OCV curve of a single cell 101 of the LFP battery used in this embodiment. The dashed line graph shows the SOC-OCV curve of a single cell of a conventionally used ternary battery.

[0039] 3, the CPU 301 calculates the SOC of the cell having the lowest voltage Vmin among the cells 101A-101N included in the battery 100 using the SOC-OCV curve shown in Fig. 4 (step S142). The CPU 301 determines whether the calculated SOC is equal to or higher than the threshold value Th.

[0040] Referring again to FIG. 4, the SOC-OCV curve of the cell 101 of this disclosure includes a range A of SOC=0 to a, a range B of SOC=a to c, a range C of SOC=c to d, a range D of SOC=d to f, and a range E of SOCf to 100. In the range A, the OCV rises rapidly with an increase in SOC. In the range B, the OCV rises slowly with an increase in SOC. In the range C, there is a "step" in the increase in OCV with an increase in SOC. Even if the cell 101 deteriorates and the full charge capacity of the cell 101 decreases (the capacity maintenance rate of the cell 101 decreases), the position of the "step" does not change. Even if the cell 101 deteriorates, the remaining capacity value at which the "step" appears does not change. In the range D, there is almost no increase in OCV with an increase in SOC. This range D is called a plateau (flat) region. The range B may also be called a plateau region. In the range E, the OCV rises sharply with an increase in SOC. Note that in the SOC-OCV curve of a conventional ternary battery, the OCV rises proportionally over almost the entire range with an increase in SOC.

[0041] In range B to range D, the change in OCV relative to the change in SOC is smaller than in range A and range E. For this reason, equalization by OCV is difficult in range B to range D. For this reason, equalization by OCV is performed in range E, that is, in the range where SOC is equal to or greater than f. For this reason, the threshold value Th in step S143 is set to f.

[0042] Returning to FIG. 3, when it is determined that the SOC is equal to or greater than the threshold value Th (YES in step S143), the CPU 301 starts equalization by the OCV (step S144). Specifically, equalization by the OCV is performed as follows. With the SMR 50 and the charging relays 70, 90 open, the monitoring unit 200 measures the OCV of each cell 101. Based on the OCV, the SOC of each cell 101 is calculated using the SOC-OCV curve. For cells 101 whose SOC difference from the minimum SOC is equal to or greater than a predetermined value, the corresponding switch S1 is turned ON (closed) for a period according to the difference. This causes the discharge resistor Rd to consume power according to the difference. As a result, the SOC of the cells 101 drops by an amount according to the difference, and SOC equalization is performed.

[0043] After step S144, CPU 301 stores a flag indicating that equalization is turned off as an equalization execution flag in memory 302 (step S145). If CPU 301 determines that SOC is less than threshold value Th (NO in step S143) or after step S145, CPU 301 returns the process to be executed to the upper process that called this equalization control process.

[0044] If it is determined that the vehicle is not in ReadyOFF (NO in step S131), for example, that the vehicle is running or is stopped in ReadyON, or if it is determined that the equalization execution flag is not a flag indicating that equalization by the OCV is to be executed (NO in step S132), the CPU 301 determines whether or not the equalization execution flag stored in the memory 302 is a flag indicating that equalization by the CCV is to be executed (step S151). If it is determined that the flag indicates that equalization by the CCV is to be executed (YES in step S151), the CPU 301 starts equalization by the CCV (step S152). In this way, equalization by the 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 steps S131 and S132.

[0045] 4 again, the equalization by CCV is specifically performed as follows: With the SMR 50 closed (ReadyON state) or with either the charging relay 70, 90 closed (external charging being performed), the monitoring unit 200 measures the CCV of each cell 101. Based on the CCV, a tentative SOC of each cell 101 is calculated using the SOC-OCV curve.

[0046] When ReadyON and regeneration from MG10 to battery 100 is in progress, or when ReadyOFF and external charging is in progress, the SOC of each cell 101 increases. In this case, the SOC difference between cell F, which is the cell 101 that first exceeded the "step" of SOC=c-d among the cells 101A-101N included in the battery 100, and cell L, which is the cell 101 that last exceeded the "step" of SOC=c-d, is calculated. Specifically, if the SOC of cell L when cell F exceeded the "step" is set to b, and the SOC of cell F when cell L exceeded the "step" is set to e, the SOC difference=ed≒db can be calculated. The SOC difference between the cell that exceeded the "step" between cell F and cell L and cell L is calculated in the same manner. For the cells 101 whose SOC difference is equal to or greater than a predetermined value, the corresponding switch S1 is turned ON (closed) for a period according to the difference. As a result, all the cells 101A-101N included in the battery 100 are charged with regenerative power or charging power, while for the cells 101 whose SOC difference is equal to or greater than a predetermined value, power according to the difference is consumed by the discharge resistor Rd. As a result, the SOC of the cells 101 whose SOC difference is equal to or greater than the predetermined value is reduced by an amount according to the difference, and SOC equalization is performed.

[0047] When ReadyON is in progress and power is being output from the battery 100 to the MG10, the SOC of each cell 101 decreases. In this case, the SOC difference between cell F, which is the cell 101 that was the first cell 101 to exceed the "step" of SOC=d to c among the cells 101A to 101N included in the battery 100, and cell L, which is the cell 101 that was the last cell to exceed the "step" of SOC=d to c, is calculated. The SOC difference between the cell that exceeded the "step" between cell F and cell L and cell L is also calculated in the same manner. For the cells 101 whose SOC difference is equal to or greater than a predetermined value, the corresponding switch S1 is turned ON (closed) for a period according to the difference. As a result, in addition to the power output to the MG10 being consumed for all the cells 101A to 101N included in the battery 100, for the cells 101 whose SOC difference is equal to or greater than a predetermined value, power according to the difference is further consumed by the discharge resistor Rd. As a result, the SOC of the cells 101 whose SOC difference is equal to or greater than the predetermined value is reduced by an amount corresponding to the difference, and the SOCs are equalized.

[0048] 3, after step S152, CPU 301 stores a flag indicating that equalization is turned off as an equalization execution flag in memory 302 (step S153). If CPU 301 determines that the equalization execution flag is not a flag indicating that equalization by CCV is to be executed (NO in step S151), or after step S153, CPU 301 returns the process to be executed to the higher-level process that called this equalization control process.

[0049] [Second embodiment] Fig. 5 is a flowchart showing the flow of the equalization control process in the second embodiment. Referring to Fig. 5, this equalization control process is periodically called from a higher-level process by CPU 301 of ECU 300 and executed. Steps S131 to S153 are common to the equalization control process in the first embodiment described with reference to Fig. 3, and therefore overlapping descriptions will not be repeated. CPU 301 determines whether or not it is the timing when the first cell 101 has passed through the "step" (step S121). If it is determined that it has passed through (YES in step S121), CPU 301 starts current integration of the cell (step S122).

[0050] If it is determined that the first cell 101 has not passed through the "step" (NO in step S121), or after step S122, the CPU 301 determines whether the last cell 101 has passed through the "step" (step S123). If it is determined that the last cell 101 has passed through the "step" (YES in step S123), the CPU 301 determines whether the integrated capacity of the current whose integration started in step S122 is equal to or greater than a threshold Cth (for example, 5 Ah) (step S124). If it is determined that the integrated capacity is less than the threshold Cth (NO in step S124), the CPU 301 stores a flag indicating that equalization by the OCV is to be executed as an equalization execution flag in the memory 302 (step S125). On the other hand, if it is determined that the accumulated capacity is equal to or greater than the threshold Cth (YES in step S124), the CPU 301 stores a flag indicating that equalization by CCV is to be executed as an equalization execution flag in the memory 302 (step S126). After step S125 or step S126, the CPU 301 resets the accumulated capacity (step S127). After step S127, the CPU 301 executes the processes from step S131 onwards, similar to the equalization control process of the first embodiment described in FIG.

[0051] [Variations] (1) As shown in the first and second embodiments described above, equalization by OCV or equalization by CCV is preferentially performed depending on the situation. However, the present invention is not limited to this, and an equalization control process may be performed as described below. FIG. 6 is a flowchart showing the flow of the equalization control process in the modified example. Referring to FIG. 6, the CPU 301 executes a process for determining the equalization control method (step S211). As a result of the determination in step S211, the CPU 301 determines whether control method I or control method II should be used (step S212). If it is determined that control method I should be used, the CPU 301 executes control method I (e.g., equalization control by OCV) (step S213). On the other hand, if it is determined that control method II should be used, the CPU 301 executes control method II (e.g., equalization control by CCV) (step S214).

[0052] In step S211, it may be determined which control method to use depending on which equalization control method is more suitable. For example, if priority is given to the opportunity for equalization, it is determined that control method II is used, which is more suitable for ensuring the opportunity than control method I. If priority is given to the accuracy of equalization, it is determined that control method I is used, which is more suitable for ensuring the accuracy than control method II. Other indices may be used in addition to or instead of the opportunity and accuracy.

[0053] (2) In the above-described embodiment, if it is determined that equalization by OCV is appropriate, the equalization by OCV is executed 100% of the time, and if it is determined that equalization by CCV is appropriate, the equalization by CCV is executed 100% of the time. However, the present invention is not limited to this, and if it is determined that equalization by OCV is appropriate, the equalization by OCV may be executed in preference to equalization by CCV, and if it is determined that equalization by CCV is appropriate, the equalization by CCV may be executed in preference to equalization by OCV. For example, if it is determined that equalization by OCV is appropriate, the equalization by OCV may be executed more frequently than the equalization by CCV, and if it is determined that equalization by CCV is appropriate, the equalization by CCV may be executed more frequently than the equalization by OCV.

[0054] [summary] (1) As shown in Fig. 1 and Fig. 2, the battery system S is a system for equalizing the capacity of each of the cells 101 included in a battery 100 in which a plurality of cells 101A-101N having plateau regions in their charge / discharge curves are connected in series, and includes an equalization unit 250 that adjusts the capacity of each of the cells 101, and an ECU 300 that controls the charging and discharging of the battery 100. As shown in Fig. 3 to Fig. 6, the ECU 300 determines which of a first control method (e.g., equalization by OCV) and a second control method (e.g., equalization by CCV) is to be used according to a predetermined determination condition for determining whether the first control method is suitable for equalization in a current situation, and when it is determined that the first control method is to be used, the ECU 300 controls the equalization unit 250 to equalize the capacity of each of the cells 101 using the first control method, and when it is determined that the second control method is to be used, the ECU 300 controls the equalization unit 250 to equalize the capacity of each of the cells 101 using the second control method.

[0055] This makes it possible to use a control method suited to the current situation to equalize the capacities of the cells 101 included in the battery 100. As a result, it is possible to ensure an opportunity for equalization.

[0056] (2) As shown in Figures 3 to 6, the battery 100 may further include a monitoring unit 200 that detects the voltage of each cell 101 included in the battery 100, and the first control method may be a control method using an OCV, which is the voltage of the cell 101 detected by the monitoring unit 200 when the battery 100 is not outputting power to the outside, and the second control method may be a control method using a CCV, which is the voltage of the cell 101 detected by the monitoring unit 200 when the battery 100 is outputting power to the outside.

[0057] This allows equalization to be performed using either the control method using the OCV or the control method using the CCV, whichever is more suitable for equalization in the current situation.

[0058] (3) As shown in Figures 3 to 6, the judgment condition may be such that when the current situation is a specified situation in which securing opportunities is prioritized over ensuring the accuracy of equalization, the second control method is used in preference to the first control method (only the second control method may be used, or the second control method may be used more frequently than the first control method), whereas when the current situation is not the specified situation, the first control method is used in preference to the second control method (only the first control method may be used, or the first control method may be used more frequently than the second control method).

[0059] This allows equalization to be performed by preferentially using either the first control method, which is suitable for ensuring accuracy, or the second control method, which is suitable for ensuring opportunities, depending on whether the current situation requires priority to ensure the accuracy of equalization or to ensure opportunities.

[0060] (4) As shown in Fig. 3, the predetermined situation may be a situation in which a predetermined period has passed since the previous equalization (for example, it may be a period until a predetermined number of trips have occurred, or it may be a period during which the vehicle is running, or if it is not limited to being mounted on a vehicle, it may be a period until the power is turned on a predetermined number of times, or it may be a period during which the battery is used). As a result, if the predetermined period has passed since the previous equalization, it is possible to prioritize securing opportunities and perform equalization by preferentially using the second control method suitable for securing opportunities, whereas if the predetermined period has not passed, it is possible to prioritize securing accuracy and perform equalization by preferentially using the first control method suitable for securing accuracy.

[0061] (5) As shown in Fig. 5, the predetermined situation may be a situation in which the capacity difference between the cells 101 is equal to or greater than a predetermined threshold. In this way, when the capacity difference between the cells 101 is equal to or greater than the predetermined threshold, it is possible to prioritize securing opportunities and perform equalization by preferentially using the second control method suitable for securing opportunities, whereas when the capacity difference is not equal to or greater than the predetermined threshold, it is possible to prioritize securing accuracy and perform equalization by preferentially using the first control method suitable for securing accuracy.

[0062] The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the disclosure is defined by the claims, not by the description of the embodiments described above, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0063] 1 electric vehicle, 10 MG, 20 power transmission gear, 30 drive wheel, 40 PCU, 50 SMR, 60, 80 inlet, 70, 90 charging relay, 100 battery, 101, 101A to 101N single cell, 130 on-board charger, 200 monitoring unit, 210 voltage detection unit, 211 comparator, 220 current sensor, 230 temperature sensor, 250 equalization unit, 300 ECU, 301 CPU, 302 memory, 410, 510 charging cable, 420, 520 connector, S battery system.

Claims

1. A battery system that equalizes the capacity of each battery cell included in a battery pack in which a plurality of battery cells having a plateau region in a charge / discharge curve are connected in series, comprising: An adjustment unit that adjusts the capacity of each of the battery cells; a control device for controlling charging and discharging of the battery pack, The control device includes: determining which of the first and second control techniques is to be used according to a predetermined determination condition for determining whether the first or second control technique is suitable for equalization in a current situation; 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. 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 being output from the battery pack to an outside; The battery system according to claim 1 , wherein the second control method is a control method using a closed circuit voltage, which is a voltage of the battery cells detected by the sensor when power is being output from the assembled battery to an outside.

3. The battery system of claim 2, wherein the judgment condition is a condition that when the current situation is a specified situation in which securing opportunities is prioritized over ensuring the accuracy of equalization, the second control method is used in preference to the first control method, and when the current situation is not the specified 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 state is a state in which a predetermined period of time has elapsed since the previous equalization.

5. The battery system according to claim 3 , wherein the predetermined situation is a situation in which a capacity difference between the battery cells is equal to or greater than a predetermined threshold value.

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