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 Art

[0002] Japanese Patent Application Laid-Open No. 2014-167457 (Patent Document 1) describes detecting a singular point that is the maximum value of the voltage change amount of a secondary battery during charge and discharge, and estimating the capacity of the secondary battery based on this singular point.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In Patent Document 1, the capacity of a secondary battery (single cell) constituting a battery pack is estimated. In a battery pack in which single cells are connected in series, for example, due to deterioration or the like, if the capacity of a single cell decreases (the capacity retention rate decreases) and the SOC (State of Charge) of each single cell varies, there is a concern that a single cell may be overcharged.

[0005] An object of the present disclosure is to estimate the SOC variation of a single cell using a singular point that is the maximum value of the voltage change amount, and to reduce the SOC variation by performing equalization control.

Means for Solving the Problems

[0006] The battery system of this disclosure is a battery system comprising a battery pack in which a plurality of individual cells are connected in series, and a control device. The control device includes a maximum value detection unit that detects the maximum value of the voltage change of an individual cell when the battery pack is being charged, and a current integration unit that calculates a current integration value which is the cumulative value of the charging current of the individual cells. For each individual cell, the control device obtains the current integration value for a predetermined period from the time the maximum value was detected, and performs an equalization process that discharges each individual cell based on the current integration value for each individual cell.

[0007] In each cell, the maximum value of the voltage change is detected at approximately the same remaining capacity (charging capacity). With this configuration, the integrated current value is calculated for each cell as the integrated value of the charging current over a predetermined period from the time the maximum value is detected. Therefore, the integrated current value of each cell corresponds to the state of charge (SOC) variation of each cell. Based on this integrated current value, discharge is performed from each cell to equalize the SOC. This reduces the SOC variation.

[0008] Preferably, the predetermined period may be the period until a maximum value is detected for all cells in the group of cells on which the equalization process is performed.

[0009] The equalization process for individual cells may be performed for each group (section) of individual 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] With this configuration, the predetermined period is set to the period until the maximum value is detected for all single cells in the group of single cells on which the equalization process is performed, thereby reducing the SOC variation of all single cells included in the group (category).

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

[0012] With this configuration, the calculation of the integrated current value begins when a maximum value is detected in the high-voltage side of the single cell's voltage. This reduces SOC variation on the side where the single cell is close to fully charged, and effectively suppresses overcharging of the single cell.

[0013] Preferably, the control device may discharge a single cell whose integrated current value is equal to or greater than a set value and perform an equalization process.

[0014] With this configuration, by setting the set value based on the detection error of the maximum value, etc., it is possible to suppress discharge from single cells that do not need to be discharged.

[0015] Preferably, the control device performs an equalization process after the battery pack has finished charging, but may refrain from performing the equalization process if no maximum values ​​are detected for all individual cells in the group of individual cells before the battery pack has finished charging.

[0016] In some cases, due to noise or disturbances, there may be individual cells whose maximum values ​​cannot be detected. With this configuration, if the maximum values ​​of all individual cells in a group are not detected by the time the battery pack is fully charged, the equalization process is not performed. This helps to suppress the large degree of variation in the state of charge (SOC) of individual cells whose maximum values ​​were not detected. [Effects of the Invention]

[0017] According to this disclosure, by using singularities, which are the maximum values ​​of the voltage change, the SOC variation of a single cell can be estimated and equalization control can be implemented to reduce the SOC variation. [Brief explanation of the drawing]

[0018] [Figure 1] This is an overall configuration diagram of an electric vehicle equipped with the battery system according to this embodiment. [Figure 2] This figure shows an example of an equalization unit. [Figure 3] (A), (B), (C), and (D) are diagrams showing the relationship between OCV and remaining capacity, etc. in the single cell (LFP cell) of this embodiment. [Figure 4] It is a flowchart showing an example of the equalization current integration process executed by the ECU. [Figure 5] It is a flowchart showing an example of the equalization process executed by the ECU.

Embodiments for Carrying out the Invention

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

[0020] FIG. 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 rotary 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] MG10 is, for example, an embedded structure permanent magnet synchronous motor (IPM motor), and has functions as a motor and a generator. The output torque of MG10 is transmitted to the drive wheels 30 via a power transmission gear 20 configured to include a reduction gear and a differential device, etc.

[0022] When the electric vehicle 1 is braked, the MG10 is driven by the drive wheels 30, and the MG10 operates as a generator. As a result, the MG10 also functions as a braking device that performs regenerative braking, converting the kinetic energy of the electric vehicle 1 into electrical power. The regenerative power generated by the regenerative braking force in the MG10 is stored in the battery 100.

[0023] The PCU40 is a power converter that converts power bidirectionally between the MG10 and the battery 100. The PCU40 includes, for example, an inverter and a converter that operate based on control signals from the ECU300.

[0024] The converter, when battery 100 is discharged, boosts the voltage supplied from battery 100 and supplies it to the inverter. The inverter converts the DC power supplied from the converter into AC power to drive MG10.

[0025] Meanwhile, when charging the battery 100, the inverter converts the AC power generated by the MG10 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 SMR50 is electrically connected to the power line connecting the battery 100 and the PCU 40. When the SMR50 is closed (ON) (i.e., conducting) in response to a control signal from the ECU 300, power can be exchanged between the battery 100 and the PCU 40. On the other hand, when the SMR50 is open (OFF) (i.e., disconnected) in response to a control signal from the ECU 300, the electrical connection between the battery 100 and the PCU 40 is disconnected.

[0027] Battery 100 stores power to drive MG10. Battery 100 is a rechargeable DC power source (secondary battery) and is a battery pack composed of multiple (M) single cells 10m (where m is a positive integer from 1 to M) stacked and electrically connected in series, for example. The single cells 10m may be composed of lithium-ion batteries, for example. In this embodiment, lithium iron phosphate batteries (LFP batteries) are used as single cells 10m, with lithium iron phosphate used as the positive electrode active material.

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

[0029] The electric vehicle 1 is equipped with a DC inlet 60, and the battery 100 is capable of rapid charging from an external DC power source, which is a charging device. The DC inlet 60 is configured to be connectable to a connector 420 located at the end of the charging cable 410 of the external DC power source (charging device) 400. The charging relay 70 is electrically connected to the 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 is equipped with an AC inlet 80, and the battery 100 is capable of normal charging from an external AC power source, which is a charging facility. The AC inlet 80 is configured to be connectable to a connector 520 located at the end of the charging cable 510 of the external AC power source (charging facility) 500. An onboard charger 130 is provided in the power line between the AC inlet 80 and the battery 100, which converts the AC power supplied from the external AC power source into DC power and also converts it to a voltage that allows the battery 100 to be charged. A charging relay 90 is electrically connected to the power line connecting the onboard charger 130 and the battery 100. The charging relay 90 switches between supplying and cutting off power between the onboard 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, ROM (Read Only Memory) and RAM (Random Access Memory)) 302. Based on signals received from the monitoring unit 200, signals from various sensors (not shown) (for example, accelerator opening signal, vehicle speed signal, etc.), and information such as maps and programs stored in the memory 302, the ECU 300 controls each device so that the electric vehicle 1 reaches a desired state. The ECU 300 also performs equalization processing of the single cell 10m using an equalization unit (equalization circuit) 250. The battery system S consists of a battery 100 (single cell 10m), a monitoring unit 200, an equalization unit 250, the ECU 300, etc.

[0032] Figure 2 shows an example of the equalization unit 250. In this embodiment, the equalization unit 250 is incorporated as an equalization circuit into the voltage detection unit (voltage detection circuit) 210 of the monitoring unit 200. In the battery 100, multiple single cells 101 to 10M are connected in series. The voltage detection unit 210 detects the voltage of the single cells 101 to 10M via multiple voltage detection lines L1, branch line L11, and branch line L12. Voltage detection line L1 is connected to the positive terminal of single cell 101 and the negative terminal of single cell 10M. Also, voltage detection line L1 is connected between the negative terminal of one single cell and the negative terminal of the other single cell between single cells 101 to 10M.

[0033] The voltage detection line L1 is equipped with a fuse F and a chip bead Cb. The fuse F blows when an overcurrent occurs, protecting the circuit. The chip bead Cb reduces applied stress when a surge voltage is applied instantaneously.

[0034] A Zener diode D is connected in parallel to each cell 101-10M via a voltage detection line L1. The cathode of the Zener diode D is connected to the positive terminal of the corresponding cell, and the anode is connected to the negative terminal of the corresponding cell. When an overvoltage is applied to the voltage detection unit 210 from battery 100 (cell 10m), current flows through the Zener diode D, protecting the voltage detection unit 210 from the overvoltage.

[0035] The voltage detection line L1 branches into branch line L11 and branch line L12 on the monitoring unit 200 side from the Zener diode D. Branch line L11 is connected to comparator 21a via switch So, and branch line L12 is connected to comparator 21a via switch Sh. Switches So and Sh can be, for example, photoMOS (Metal Oxide Semiconductor) relays. Note that branch line L11, which branches off from the voltage detection line L1 connected to the positive terminal of single cell 101 located on the positive output terminal side of battery 100, is not connected to comparator 21a. Also, the voltage detection line L1 connected to the negative terminal of single cell 10M located on the negative output terminal side of battery 100 does not have branch line L12.

[0036] A resistor R1 is provided in branch line L12. A capacitor (flying capacitor) C is provided between branch line L12, which is connected to the positive terminal of each cell, and branch line L11, which is connected to the negative terminal. In branch line L12, capacitor C is connected between resistor R1 and switch Sh, and resistor R1 and capacitor C form an RC low-pass filter. Capacitor C is connected in parallel with the corresponding cell 101~10M, and the charge of the corresponding cell 101~10M charges capacitor C, so that the voltage value of capacitor C becomes equal to the voltage value of the corresponding cell 101~10M. By turning ON (closing) switches Sh and So corresponding to a specific cell 101~10M, comparator 21a outputs the voltage (cell voltage) VB of that specific cell 101~10M. As a result, the monitoring unit 200 can detect the voltage VB of each cell 101 to 10M using the voltage detection unit 210 by sequentially turning on switches Sh and So corresponding to each cell 101 to 10M. In addition, the voltage Vb of battery 100 can be detected by turning on (closing) switch Sh of cell 101 and switch So connected to the negative terminal of cell 10M.

[0037] The equalization unit 250 consists of a discharge resistor Rd provided on the branch line L11 and a switch S1 that conducts (closes) / interrupts (opens) the connection between adjacent branch lines L11. Switch S1 switches between ON (closed) and OFF (open) in response to a control signal from the ECU 300. In Figure 2, the dashed-dotted arrows indicate the current flow when equalization control is performed to eliminate the unevenness of the SOC of the single cell 10m. This shows the case where the SOC of single cell 102 is large, and discharge is performed from single cell 102 to perform equalization control. When the SOC of single cell 102 is large, the switch S1 corresponding to single cell 102 is turned ON (closed). When the switch S1 corresponding to single cell 102 is turned ON (closed), as shown by the dashed-dotted arrows, the current discharged from single cell 102 is consumed by the discharge resistors Rd, Rd, the SOC of single cell 102 decreases, and SOC equalization is performed. In this way, the individual cells of battery 100 (battery pack) are equalized over a distance of 10m.

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

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

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

[0041] In a battery (battery pack) 100 consisting of 10m individual cells connected in series, the State of Charge (SOC) of each 10m cell may gradually vary due to factors such as degradation, temperature differences, and differences in self-discharge rates. In batteries with characteristics where the OCV curve does not have a voltage flat region as shown in Figure 3(A), the SOC-OCV characteristic (SOC-OCV curve) can be used to estimate the SOC of each individual cell and eliminate the variation in SOC of the individual cells. However, in batteries like the 10m individual cells in this embodiment, where the OCV curve has a voltage flat region, it is difficult to determine the SOC of each 10m individual cell based on the SOC-OCV characteristic.

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

[0043] In this embodiment, as shown in Figure 3(D), the charging current is integrated from the time a maximum value M2 (step difference P2) is detected for every 10m of individual cells, and the integrated equalization current value q is calculated. The integration of the charging current is carried out until all maximum values ​​M2 of the 10m of individual cells contained in the battery 100 are detected, and the integrated equalization current value q is calculated. Finally, the pole large The charging current of a single cell 10m in which value M2 is detected is not integrated, and the integrated equalization current value q for that single cell 10m is 0 (zero). The variation in the integrated equalization current value q for a single cell 10m corresponds to the variation in the state of charge (SOC) of the single cell 10m. In Figure 3(D), t1 is the timing when the maximum value M2 of a single cell 10m is first detected. t2 is the timing when the maximum value M2 of a single cell 10m is last detected (the timing when all maximum values ​​M2 of the single cells 10m contained in battery 100 are detected).

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

[0045] The detection of the maximum value of the voltage change ΔVB may be considered when the current voltage change ΔVB is small compared to the previous voltage change ΔVB. Alternatively, the maximum value may be considered when the sign of the derivative of the voltage change ΔVB changes from positive to negative. As shown in Figure 2(A), there are two maximum values ​​of the voltage change ΔVB: a low-voltage maximum M1 (step P1) and a high-voltage maximum M2 (step P2). Therefore, if the voltage VB at the time the maximum value of the voltage change ΔVB is detected is above a predetermined voltage, it may be determined that the maximum value M2 (high-voltage maximum) has been detected. Alternatively, the cumulative current threshold Qs may be determined 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 ΔVB may be started only after the cumulative value of the charging current exceeds the cumulative current threshold Qs. This makes it possible to mask the detection of the maximum value M1 (low-voltage maximum). The processing in S10 corresponds to an example of the "maximum value detection unit" in this disclosure.

[0046] If a maximum value M2 of the voltage change ΔVB of a single cell 10m is detected, proceed to S11. If no maximum value M2 is detected, proceed to S14. In S11, it is determined whether the maximum value M2 detected this time is the last maximum value M2. When the maximum value M2 of all single cells 10m constituting the battery 100 is detected, it is determined that the last maximum value M2 has been detected, and proceed to S13. If the maximum value M2 detected this time is not the last maximum value M2, proceed to S12.

[0047] In S12, after starting the integration of the equalization current integration value q of the single cell 10m where the maximum value M2 was detected, the process proceeds to S14. The integration of the equalization current integration value q is performed by integrating the charging current detected by the current sensor 220. The process in S12 corresponds to an example of the "current integration unit" in this disclosure.

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

[0049] If a maximum value M2 is detected for all individual cells 10m that make up the battery 100 before external charging is completed, S11 determines that the last maximum value M2 has been detected and proceeds to S13. In S13, the integration of the equalization current integration value q is stopped, the flag Fd is set to 1, and then the routine is terminated. In this case, the equalization current integration value q for each individual cell 10m is stored in memory 302.

[0050] Figure 5 is a flowchart showing an example of the equalization process performed by the ECU 300. This flowchart is executed, for example, when the IG switch (power switch) 240 is turned ON. When the IG switch 240 is turned ON and the battery system S starts up, in S20 it is determined whether the flag Fd is 1 or not. S13 (Figure 4) is processed and if the flag Fd is set to 1, the process proceeds to S21. If the flag Fd is 0, the condition is negated and the routine ends.

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

[0052] In the subsequent S23, each 10m cell is discharged (equalized), and the flag Fd is set to 0, ending the routine. The equalization process is performed by sequentially turning on (closing) the switch S1 (see Figure 2) corresponding to each 10m cell for the discharge time th, thereby discharging from each 10m cell. This reduces the variation in the state of charge (SOC) of each 10m cell.

[0053] According to this embodiment, the battery 100 is a battery pack in which 10m individual cells 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 individual cells 10m when the battery 100 is being charged, and a current integration unit (S12) that calculates an equalization current integration value q, which is the integrated value of the charging current of the individual cells 10m. For each individual cell 10m, the ECU 300 determines the equalization current integration value q for a predetermined period from the time the maximum value is detected, and performs an equalization process to discharge each individual cell 10m based on the equalization current integration value q for each individual cell 10m. The equalization current integration value q is calculated for each individual cell 10m as the integrated value of the charging current for a predetermined period from the time the maximum value is detected. Therefore, the equalization current integration value q for each individual cell 10m corresponds to the state of charge variation of each individual cell 10m. Based on this integrated current value q for equalization, discharge is performed from each 10m cell to carry out the equalization process. This reduces the SOC variation of the 10m cells.

[0054] In the above embodiment, the predetermined period is set to the period from when the maximum value of a single cell 10m is detected until the maximum values ​​of all single cells 10m contained in the battery 100 are detected, and the integrated current value q for equalization of each single cell 10m is calculated. If the maximum values ​​of all single cells 10m are not detected, the equalization process is not performed. Therefore, since single cells 10m for which no maximum value was detected are not subjected to equalization processing, the expansion of SOC variation can be suppressed, and the SOC variation of all single cells 10m contained in the battery 100 can be reduced.

[0055] When a battery pack is constructed by connecting multiple battery modules (stacks) in which multiple single cells are connected in series, and this battery pack is adopted as battery 100, the equalization process may be performed for each battery module, or the equalization process may be performed for the entire battery pack. Furthermore, the equalization process may be performed for each unit of the monitoring unit 200 or the equalization unit 250. Thus, the groups of single cells on which the equalization process is performed may be selected arbitrarily.

[0056] In the above embodiment, the calculation of the equalization current integration value q is started when the maximum value M2 present on the high-voltage side of the single cell 10m is detected. This reduces SOC variation on the side of the single cell 10m that is close to fully charged, and effectively suppresses overcharging of the single cell 10m. However, the calculation of the equalization current integration value q may be started after detecting the maximum value M1 present on the low-voltage side of the single cell 10m, and the equalization process may be performed using this equalization current integration value q.

[0057] Alternatively, a setting value can be established that takes into account the detection accuracy of the maximum value M2, and the equalization process can be performed by discharging from a single cell 10m whose integrated equalization current value q is equal to or greater than the setting value. This reduces SOC variation while suppressing unnecessary discharge.

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

[0059] The vehicles to which the battery system S of this disclosure can be applied are not limited to the electric vehicle 1 shown in Figure 1. For example, this disclosure can also be applied to plug-in hybrid vehicles equipped with an engine and a motor generator, and to fuel cell vehicles equipped with a battery that can be externally charged. It can also be applied to industrial vehicles such as forklifts. Furthermore, the battery system S may be a stationary battery.

[0060] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims rather than by the description of the embodiments above, and all modifications within the meaning and scope equivalent to the claims are intended to be included. [Explanation of Symbols]

[0061] 1 Electric vehicle, 10 Motor generator (MG), 20 Drive transmission gear, 30 Drive wheels, 40 PCU, 50 SMR, 60 DC inlet, 80 AC inlet, 100 Battery, 10m Single cell, 200 Monitoring unit, 210 Voltage detection unit, 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 comprising a battery pack in which multiple single cells are connected in series, and a control device, The control device is A maximum value detection unit detects the maximum value of the voltage change of the single cell when the battery pack is being charged, The unit includes a current integration unit that calculates a current integration value which is the integrated value of the charging current of the single cell, For each of the single cells, the integrated current value over a predetermined period from the time the maximum value was detected is calculated. A battery system that performs an equalization process on each of the individual cells, based on the integrated current value for each cell, by discharging the cells so that the integrated current value becomes zero.

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

3. The aforementioned single cell has the characteristic of having multiple maximum values, The control device is The battery system according to claim 1 or claim 2, wherein the calculation of the current integrated value is started when the maximum value among the multiple maximum values ​​is detected in which the voltage of the single cell is on the high-voltage side.

4. The control device is The battery system according to claim 3, wherein discharge is performed from the single cell whose integrated current value is equal to or greater than a set value, and the equalization process is executed.

5. The control device is After the charging of the aforementioned battery pack is completed, the equalization process is performed. The battery system according to claim 2, wherein if the maximum value of all single cells in the group of single cells is not detected before the charging of the battery pack is completed, the equalization process is not performed.

Images