Battery system

Abstract

To estimate SOC variations of a unit battery, and reduce the SOC variations by executing an equalization control using an irregular point that is a maximum value of a voltage-changing amount.SOLUTION: A maximum value M2 of a voltage-changing amount ΔVB of a unit battery is detected during external charging of a battery. An equalization current-integration value q is calculated in a period until a last unit battery detects a maximum value M2 (tn) from when the maximum value M2 is detected for each unit battery. Equalization processing by which discharging is carried out from each unit battery is executed, based on the equalization current-integration value q of each unit battery thereof.SELECTED DRAWING: Figure 3

Description

[Technical field]

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

[0002] Japanese Patent Laid-Open No. 2014-167457 (Patent Document 1) describes detecting a singular point, which is a maximum value of the amount of voltage change of a secondary battery during charging and discharging, and estimating the capacity of the secondary battery based on this singular point. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2014-167457 A Summary of the Invention [Problem to be solved by the invention]

[0004] Patent Document 1 estimates the capacity of secondary batteries (single cells) that make up a battery pack. In a battery pack in which single cells are connected in series, there is a concern that some cells may be overcharged if the capacity of the single cells decreases (the capacity maintenance rate decreases) due to, for example, degradation, causing variations in the SOC (State of Charge) of each single cell.

[0005] An object of the present disclosure is to reduce the SOC variation among the cells by estimating the SOC variation among the cells using a singular point that is a maximum value of the amount of voltage change and performing equalization control. [Means for solving the problem]

[0006] The battery system disclosed herein is a battery system including a battery pack in which a plurality of cells are connected in series, and a control device. The control device includes a maximum value detection unit that detects a maximum value of the voltage change of the cells when the battery pack is charged, and a current integration unit that calculates an integrated current value that is an integrated value of the charging current of the cells. The control device calculates an integrated current value for each cell for a predetermined period from when the maximum value was detected, and executes an equalization process in which each cell is discharged based on the integrated current value for each cell.

[0007] In each cell, the maximum value of the voltage change is detected at approximately the same remaining capacity (charge capacity). With this configuration, the current integration value is calculated for each cell as the integration value of the charging current for a predetermined period from when the maximum value was detected. Therefore, the current integration value of each cell corresponds to the SOC variation of each cell. Based on this current integration value, each cell is discharged and an equalization process is performed. This makes it possible to reduce the SOC variation.

[0008] Preferably, the predetermined period of time may be a period of time until the maximum values ​​of all the unit cells are detected in the group of unit cells on which the equalization process is performed.

[0009] The equalization process of the cells may be performed for each group (division) of cells. For example, the equalization process may be performed for each battery module (stack), or for the entire battery pack. Furthermore, the equalization process may be performed for each monitoring unit or equalization circuit.

[0010] According to this configuration, the specified period is set to a period until the maximum values ​​of all the cells in the group of cells on which the equalization process is performed are detected, thereby making it possible to reduce the SOC variation of all the cells included in the group (division).

[0011] Preferably, the single battery has a characteristic in which there are multiple maximum values, and the control device may start calculating the current integrated value when it detects a maximum value among the multiple maximum values ​​where the voltage of the single battery is on the high-voltage side.

[0012] According to this configuration, calculation of the current integrated value begins when the voltage of the single cell detects a maximum value on the high-voltage side, thereby reducing SOC variations on the side of the single cell close to full charge and effectively preventing the single cell from being overcharged.

[0013] Preferably, the control device may perform the equalization process by discharging the unit cells whose current integrated values ​​are equal to or greater than a set value.

[0014] According to this configuration, by setting the set value based on the detection error of the maximum value or the like, it is possible to suppress discharge from cells that do not require discharge.

[0015] Preferably, the control device executes the equalization process after charging of the battery pack is completed, and may not execute the equalization process if the maximum values ​​of all the cells in the group of cells are not detected before charging of the battery pack is completed.

[0016] There may be a case where a maximum value of a battery cannot be detected due to noise, disturbance, etc. With this configuration, if the maximum values ​​of all the batteries in a group of batteries are not detected by the time charging of the battery pack is completed, the equalization process is not executed. This makes it possible to prevent the degree of variation in SOC of the batteries for which the maximum value is not detected from increasing. Effect of the Invention

[0017] According to the present disclosure, the SOC variation of the cells can be estimated using a singular point that is a maximum value of the amount of voltage change, and equalization control can be performed to reduce the SOC variation. [Brief description of the drawings]

[0018] [Figure 1] 1 is an overall configuration diagram of an electric vehicle equipped with a battery system according to an embodiment of the present invention. [Diagram 2] FIG. 2 illustrates an example of an equalization unit. [Diagram 3] 1A, 1B, 1C, and 1D are diagrams showing the relationship between OCV and remaining capacity in a single cell (LFP battery) according to the present embodiment. [Figure 4] 5 is a flowchart showing an example of an equalization current integration process executed by an ECU. [Diagram 5] 10 is a flowchart showing an example of an equalization process executed by the ECU. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference characters and their description will not be repeated.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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 configured by stacking a plurality (M pieces) of single cells (battery cells) 10m (m is a positive integer from 1 to M) and, for example, electrically connecting them in series. The single cells 10m may be configured, for example, as lithium ion batteries. In this embodiment, a lithium iron phosphate ion battery (LFP battery) using lithium iron phosphate as the positive electrode active material is adopted as the single cells 10m.

[0028] 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 10m (the voltage VB between each terminal of the cell 10m). The current sensor 220 detects the current IB input to and output from the battery 100 (cell 10m). The temperature sensor 230 detects the temperature TB of each cell 10m. Each detection unit outputs the detection result to the ECU 300.

[0029] 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.

[0030] 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.

[0031] 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 uses an equalization unit (equalization circuit) 250 to perform an equalization process on the single cells 10m. The battery system S is composed of the battery 100 (single cells 10m), the monitoring unit 200, the equalization unit 250, the ECU 300, etc.

[0032] 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 a voltage detection section (voltage detection circuit) 210 of the monitoring unit 200. In the battery 100, a plurality of single cells (battery cells) 101 to 10M are connected in series. The voltage detection section 210 detects the voltages of the single cells 101 to 10M via a plurality of voltage detection lines L1, a branch line L11, and a branch line L12. The voltage detection line L1 is connected to the positive terminal of the single cell 101 and the negative terminal of the single cell 10m. In addition, the voltage detection line L1 is connected to the negative terminal of one of the single cells and the negative terminal of the other of the single cells between the single cells 101 to 10M.

[0033] 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 momentarily applied.

[0034] A Zener diode D is connected in parallel to the cells 101-10M via a 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 10m) to the voltage detection unit 210, a current flows through the Zener diode D, thereby protecting the voltage detection unit 210 from the overvoltage.

[0035] 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 21a via a switch So, and the branch line L12 is connected to the comparator 21a 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 101 arranged on the positive output terminal side of the battery 100 is not connected to the comparator 21a. In addition, the voltage detection line L1 connected to the negative terminal of the cell 10M arranged on the negative output terminal side of the battery 100 does not include the branch line L12.

[0036] 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. The capacitor C is connected in parallel with the corresponding cell 101-10M, and the electric charge of the corresponding cell 101-10M is charged to the capacitor C, and the voltage value of the capacitor C becomes equal to the voltage value of the corresponding cell 101-10M. By turning on (closing) the switch Sh and the switch So corresponding to a specific cell 101-10M, the comparator 21a outputs the voltage (cell voltage) VB of the specific cell 101-10M. Thus, the monitoring unit 200 can detect the voltage VB of each of the cells 101-10M by sequentially turning on the switches Sh and So corresponding to each of the cells 101-10M using the voltage detection section 210. Also, by turning on (closing) the switch Sh of the cell 101 and the switch So connected to the negative terminal of the cell 10M, the voltage Vb of the battery 100 can be detected.

[0037] 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 SOC imbalance of the cells 10m. This shows a case where the SOC of the cell 102 is large, and the cell 102 is discharged and equalization control is executed. When the SOC of the cell 102 is large, the switch S1 corresponding to the cell 102 is turned ON (closed). When the switch S1 corresponding to the cell 102 is turned ON (closed), the current discharged from the cell 102 is consumed by the discharge resistors Rd, Rd, as indicated by the dashed arrow, and the SOC of the cell 102 decreases, and SOC equalization is executed. In this manner, equalization between the cells 10m of the battery 100 (battery pack) is achieved.

[0038] FIG. 3 is a diagram showing the relationship between the OCV (Open Circuit Voltage) and the remaining capacity in the cell 10m (LFP battery) of this embodiment. In FIG. 3(A), the vertical axis is the OCV [V] of the cell 10m, and the horizontal axis is the remaining capacity (charge capacity) [Ah] of the cell 10m. As shown in FIG. 2(A), the relationship between the OCV and the remaining capacity (hereinafter, this relationship is also referred to as the OCV curve) has a wide region (voltage plateau region) where the change in the OCV curve is minute. If a point where the OCV curve increases from the voltage plateau region and returns to the voltage plateau region is referred to as a step, then there are two steps P1 and P2 in the cell 10m of this embodiment.

[0039] The step P1 in the first step (OCV on the low voltage side) exists when the SOC of the cell 10m when new is approximately 30% (for example, when the remaining capacity is C1). The step P2 in the second step (OCV on the high voltage side) exists when the SOC of the cell 10m when new is approximately 60% (for example, when the remaining capacity is C2). As shown by the dashed lines in FIG. 3(A), the positions of these steps do not change even if the cell 10m deteriorates and the full charge capacity of the cell 10m decreases (if the capacity maintenance rate of the cell 10m decreases). Even if the cell 10m deteriorates, the remaining capacity value at which the steps appear does not change.

[0040] Fig. 3(B) shows the relationship between the voltage change ΔVB of the voltage VB and the remaining capacity when charging the battery 100, and shows the relationship when charging at a constant current. The voltage change ΔVB is the amount of change [V / Ah] of the voltage VB with respect to the remaining capacity (charge capacity) or the amount of change [V / s] of the voltage VB with respect to time (charging time). As shown in Fig. 3(B), the voltage change ΔVB reaches a maximum value M1 at a remaining capacity C1 corresponding to a step P1, and reaches a maximum value M2 at a remaining capacity C2 corresponding to a step P2.

[0041] In a battery (battery pack) 100 in which cells 10m are connected in series, the SOC of each cell 10m may gradually vary due to the progression of deterioration, temperature differences, differences in self-discharge rates, and the like. In a battery having an OCV curve that does not have a voltage plateau region as shown in FIG. 3(A), the SOC of each cell can be estimated using the SOC-OCV characteristics (SOC-OCV curve) to eliminate the SOC variation of the cells. However, in a battery having an OCV curve that has a voltage plateau region, such as the cell 10m of the present embodiment, it is difficult to determine the SOC of the cell 10m based on the SOC-OCV characteristics.

[0042] FIG. 3C shows the step P2 of each cell 10m during external charging. In FIG. 3C, the vertical axis is the voltage VB [V] of the cell 10m, and the horizontal axis is the integrated value [Ah] of the charging current or the charging time [s]. If the SOC of each cell 10m constituting the battery 100 is the same, the timing of occurrence of the step P2 will be approximately the same. If there is variation in the SOC of the cells 10m, as shown in FIG. 3C, the timing of occurrence of the step P2 in each cell 10m will differ due to the variation in the SOC of the cells 10m. Therefore, in this embodiment, the charging current is integrated from the time when the step P2 (maximum value M2) of each cell 10m is detected, and the SOC variation between the cells 10m is estimated using the integrated value.

[0043] In this embodiment, as shown in FIG. 3(D), for each cell 10m, the charging current is integrated from the time when the maximum value M2 (step P2) is detected, and the equalization current integrated value q is calculated. The charging current is integrated until all the maximum values ​​M2 of the cells 10m included in the battery 100 are detected, and the equalization current integrated value q is calculated. The charging current of the cell 10m whose polar body value M2 is last detected is not integrated, and the equalization current integrated value q of the cell 10m is 0 (zero). The variation in the equalization current integrated value q of the cells 10m corresponds to the variation in the SOC of the cells 10m. In FIG. 3(D), t1 is the timing when the maximum value M2 of the cell 10m is first detected. t2 is the timing when the maximum value M2 of the cell 10m is last detected (the timing when all the maximum values ​​M2 of the cells 10m included in the battery 100 are detected).

[0044] 4 is a flowchart showing an example of an equalization current integration process executed by the ECU 300. This flowchart is executed when external charging of the battery 100 is started, and is executed for each of the single cells 10m. When the connector 420 is connected to the DC inlet 60, or the connector 520 is connected to the AC inlet 80, and external charging of the battery 100 is started, the ECU 300 determines in step (hereinafter, step is abbreviated as "S") 10 whether or not a maximum value M2 of a voltage change amount ΔVB of the voltage VB of each of the single cells 10m has been detected. The voltage change amount ΔVB may be the amount of change [V / Ah] of the voltage VB with respect to the remaining capacity (charging capacity), or may be the amount of change [V / s] of the voltage VB with respect to time (charging time).

[0045] The detection of the maximum value of the voltage change amount ΔVB may be determined as the detection of the maximum value when the current voltage change amount ΔVB becomes smaller than the previous voltage change amount ΔVB. Alternatively, the detection of the maximum value may be determined as the detection of the maximum value when the sign of the differential value of the voltage change amount ΔVB becomes negative from positive. As shown in FIG. 2(A), the maximum value of the voltage change amount ΔVB includes a low-voltage side maximum value M1 (step P1) and a high-voltage side maximum value M2 (step P2). Therefore, if the voltage VB when the maximum value of the voltage change amount ΔVB is detected is equal to or higher than a predetermined voltage, it may be determined that the maximum value M2 (maximum value on the high-voltage side) is detected. Alternatively, the integrated current threshold value Qs may be calculated based on the voltage VB and temperature TB at the start of external charging, and the detection of the maximum value of the voltage change amount ΔVB may be started after the integrated value of the charging current exceeds the integrated current threshold value Qs. This makes it possible to mask the detection of the maximum value M1 (maximum value on the low-voltage side). The process of S10 corresponds to an example of a "maximum value detection unit" in the present disclosure.

[0046] When the maximum value M2 of the voltage change amount ΔVB of the cell 10m is detected, the process proceeds to S11, and when the maximum value M2 is not detected, the process proceeds to S14. In S11, it is determined whether the currently detected maximum value M2 is the last maximum value M2. When the maximum values ​​M2 of all the cells 10m constituting the battery 100 have been detected, it is determined that the last maximum value M2 has been detected, and the process proceeds to S13. When the currently detected maximum value M2 is not the last maximum value M2, the process proceeds to S12.

[0047] In S12, the process starts to accumulate the equalization current accumulated value q of the battery 10m in which the maximum value M2 was detected, and then the process proceeds to S14. The equalization current accumulated value q is accumulated by accumulating the charging current detected by the current sensor 220. The process of S12 corresponds to an example of a "current accumulation unit" in the present disclosure.

[0048] In S14, it is determined whether or not external charging of the battery 100 has been completed. When the battery 100 is fully charged, it may be determined that external charging has been completed. Alternatively, it may be determined that external charging has been completed when a charging stop operation is performed before full charging and the connector 420 is disconnected from the DC inlet 60 or when the connector 520 is disconnected from the AC inlet 80. If external charging has not been completed, the process returns to S10. If external charging has been completed, the process proceeds to S15, where the accumulation of the equalization current integrated value q is stopped, and the flag Fd is set to 0, and the current routine is terminated. In this case, the equalization current integrated value q of each cell 10m may be reset.

[0049] When the maximum values ​​M2 of all the cells 10m constituting the battery 100 have been detected before the external charging is completed, it is determined in S11 that the last maximum value M2 has been detected, and the process proceeds to S13. In S13, the accumulation of the equalization current integrated value q is stopped, and the flag Fd is set to 1, and the current routine is terminated. In this case, the equalization current integrated value q of each cell 10m is stored in the memory 302.

[0050] 5 is a flowchart showing an example of an equalization process executed by ECU 300. This flowchart is executed, for example, when IG switch (power switch) 240 is turned on. When IG switch 240 is turned on and battery system S is started, in S20, it is determined whether or not flag Fd is 1. When S13 (FIG. 4) is processed and flag Fd is set to 1, the process proceeds to S21. When flag Fd is 0, a negative determination is made and the current routine is terminated.

[0051] In S21, the discharge amount of each cell 10m is calculated based on the equalization current integrated value q of each cell 10m. As shown in FIG. 3(D), the earlier the cell 10m is for detecting the maximum value M2, the larger the equalization current integrated value q of the cell 10m is, and the equalization current integrated value q of the cell 10m for which the maximum value M2 was detected last is 0. The discharge amount of each cell 10m may be the equalization current integrated value q of each cell 10m. In this embodiment, the discharge time th of each cell 10m is calculated based on the equalization current integrated value q so that the equalization current integrated value q becomes 0 (zero).

[0052] In the next S23, each cell 10m is discharged (equalization process), the flag Fd is set to 0, and the current routine is terminated. The equalization process is performed by sequentially turning on (closing) the switch S1 (see FIG. 2) corresponding to each cell 10m for a discharge time th to discharge each cell 10m. This reduces the variation in SOC of each cell 10m.

[0053] According to this embodiment, the battery 100 is an assembled battery in which the cells 10m are connected in series. The ECU 300 includes a maximum value detection unit (S10) that detects the maximum value of the voltage change amount ΔVB of the cells 10m when charging the battery 100, and a current integration unit (S12) that calculates an equalization current integration value q, which is an integration value of the charging current of the cells 10m. The ECU 300 calculates the equalization current integration value q for each cell 10m for a predetermined period from when the maximum value is detected, and performs an equalization process to discharge each cell 10m based on the equalization current integration value q for each cell 10m. The equalization current integration value q is calculated as an integration value of the charging current for each cell 10m for a predetermined period from when the maximum value is detected. Therefore, the equalization current integration value q for each cell 10m corresponds to the SOC variation of each cell 10m. Based on this equalization current integrated value q, each of the cells 10m is discharged to execute equalization processing, thereby reducing SOC variations among the cells 10m.

[0054] In the above embodiment, the predetermined period is set to the period from when the maximum value of the cell 10m is detected until the maximum values ​​of all the cells 10m included in the battery 100 are detected, and the equalization current integrated value q of each cell 10m is calculated. If the maximum values ​​of all the cells 10m are not detected, the equalization process is not executed. Therefore, the cells 10m for which the maximum value is not detected are not equalized, so that the SOC variation can be prevented from increasing and the SOC variation of all the cells 10m included in the battery 100 can be reduced.

[0055] When a battery pack is formed by connecting a plurality of battery modules (stacks), each of which has a plurality of unit cells connected in series, and the battery pack is used as the battery 100, the equalization process may be performed for each battery module, or may be performed for the entire battery pack. Also, the equalization process may be performed for each monitoring unit 200 or equalization unit 250. In this manner, the group of unit cells on which the equalization process is performed may be selected arbitrarily.

[0056] In the above embodiment, calculation of the equalization current integrated value q starts when the maximum value M2 on the high-voltage side of the cell 10m is detected, so that SOC variations on the side of the cell 10m close to full charge can be reduced and overcharging of the cell 10m can be effectively prevented. However, calculation of the equalization current integrated value q may start after the maximum value M1 on the low-voltage side of the cell 10m is detected, and the equalization process may be performed using the equalization current integrated value q.

[0057] In addition, a set value may be set in consideration of the detection accuracy of the maximum value M2, and the equalization process may be performed by discharging from the cell 10m whose equalization current integrated value q is equal to or greater than the set value. This makes it possible to reduce SOC variations and suppress unnecessary discharge.

[0058] In the above embodiment, a lithium iron phosphate battery (LFP battery) is used as the cell 10m. However, the cell 10m may be another type of battery as long as it has a region (voltage plateau region) where the change in the OCV curve is minute and the maximum value of the voltage change amount ΔVB can be detected.

[0059] Vehicles to which the battery system S of the present disclosure can be applied are not limited to the electric vehicle 1 shown in Fig. 1. For example, the present disclosure can also be applied to a plug-in hybrid vehicle equipped with an engine and a motor generator, and to a fuel cell vehicle equipped with a storage battery and capable of being charged externally. It may also be an industrial vehicle such as a forklift. The battery system S may also be a stationary battery.

[0060] The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention 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]

[0061] 1 electric vehicle, 10 motor generator (MG), 20 drive transmission gear, 30 drive wheel, 40 PCU, 50 SMR, 60 DC inlet, 80 AC inlet 100 battery, 10m single cell, 200 monitoring unit, 210 voltage detection section, 220 current sensor, 230 temperature sensor, 240 IG switch, 250 equalization unit, 300 ECU, 400 DC power supply, 420 connector, 500 AC power supply, 520 connector, S battery system.

Claims

1. A battery system including a battery pack in which a plurality of single cells are connected in series and a control device, The control device includes: a maximum value detection unit that detects a maximum value of a voltage change amount of the single battery during charging of the battery pack; a current integration unit that calculates a current integration value that is an integration value of the charging current of the battery, determining, for each of the single cells, the current integrated value for a predetermined period from when the maximum value is detected; The battery system executes an equalization process of discharging each of the unit cells based on the current integrated value for each of the unit cells.

2. 2 . The battery system according to claim 1 , wherein the predetermined period is a period until the maximum values ​​of all the cells in the group of cells on which the equalization process is performed are detected.

3. The battery has a characteristic in which a plurality of maximum values ​​exist, The control device includes: 3 . The battery system according to claim 1 , wherein calculation of the current integrated value is started when a maximum value that exists on a high voltage side of the voltage of the unit cell is detected among the plurality of maximum values.

4. The control device includes: The battery system according to claim 3 , wherein the equalization process is performed by discharging the unit cells whose current integrated values ​​are equal to or greater than a set value.

5. The control device includes: After the charging of the battery pack is completed, the equalization process is executed; 3 . The battery system according to claim 2 , wherein the equalization process is not executed if the maximum values ​​of all the cells in the group of cells are not detected by the time charging of the assembled battery is completed.

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