Battery system

Abstract

To provide a battery system capable of estimating the SOC of the battery when replacing the battery.SOLUTION: The battery system includes a battery and a control unit that estimates the SOC of the battery. When battery replacement is detected (YES in S11) and when the SMR is not connected (NO in S13), the SOC is estimated based on SOC-OCV characteristics from the voltage VBs of the single battery when the battery ECU starts. When the SMR is connected (YES in S13), the SOC estimated from the voltage VBs is corrected by the current integrated value ΣQ charged or discharged through the SMR, and the SOC is estimated.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. 2018-63115 (Patent Document 1) discloses a technique for appropriately estimating SOC (State of Charge) in a secondary battery having a wide plateau region. The plateau region is a region where the OCV (Open Circuit Voltage) of the secondary battery hardly changes even when the SOC changes, and is also referred to as a "voltage flat region" in the present disclosure. In Patent Document 1, the internal resistance of a secondary battery is calculated from the current and voltage during charging and discharging, and the SOC is estimated by using the relationship between the internal resistance and the SOC. [Prior Art Literature] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2018-63115 [Summary of the Invention] [Problems to be Solved by the Invention]

[0004] The SOC of a secondary battery is generally calculated by a control device including an input device, a CPU (Central Processing Unit), a memory, and the like. In a battery system composed of a battery (secondary battery), a control device, and the like, the battery may be replaced. When replacing a battery, it is desired to estimate the SOC of the replaced battery.

[0005] In Patent Document 1, the internal resistance of the battery is obtained from the current and voltage during charging and discharging, and the SOC is estimated. However, obtaining the internal resistance of the battery requires a sufficient amount of time after battery replacement, and the SOC cannot be estimated simultaneously with the battery replacement.

[0006] The purpose of this disclosure is to estimate the State of Charge (SOC) of a battery when it is replaced. [Means for solving the problem]

[0007] The battery system of this disclosure comprises a battery, a voltage sensor for detecting the battery voltage, and a control device for estimating the battery's state of charge (SOC). When the control device detects that the battery has been replaced, it uses the voltage detected by the voltage sensor to estimate the SOC based on the battery's SOC-OCV characteristics. Furthermore, when the control device detects that the battery has been replaced, if a relay connecting the battery to a load is connected, it corrects the SOC estimated based on the SOC-OCV characteristics based on the current discharged or charged via the relay.

[0008] In this configuration, when a battery is replaced, the control device estimates the State of Charge (SOC) based on the SOC-OCV characteristics using the voltage detected by the voltage sensor. When the device detects that a battery has been replaced, if a relay connecting the battery to the load is connected, it is possible that the replaced battery is discharging or charging. When the device detects that a battery has been replaced, if a relay connecting the battery to the load is connected, the SOC can be estimated more accurately by correcting the SOC based on the discharge or charge current via the relay.

[0009] Furthermore, the battery system of this disclosure comprises a battery, a voltage sensor for detecting the battery's voltage, and a control device for estimating the battery's State of Charge (SOC). The control device is configured to, when the battery is replaced, use the voltage detected by the voltage sensor to estimate the SOC based on the battery's SOC-OCV characteristics, and to correct the SOC using the fully charged capacity in the SOC-OCV characteristics and the fully charged capacity when the battery has deteriorated, which is the fully charged capacity when the battery has deteriorated. The fully charged capacity when the battery has deteriorated is set in advance.

[0010] When replacing batteries, used or refurbished batteries may be used as replacements. In this configuration, when a battery is replaced, the control device uses the voltage detected by the voltage sensor to estimate the State of Charge (SOC) based on the battery's SOC-OCV characteristics. Then, it corrects the SOC using the full charge capacity in the SOC-OCV characteristics and a preset full charge capacity at a degraded state. This allows for a more accurate estimation of the SOC even when replacing a battery that has degraded and whose full charge capacity has decreased. [Effects of the Invention]

[0011] According to this disclosure, the State of Charge (SOC) of a battery can be estimated when the battery is replaced. [Brief explanation of the drawing]

[0012] [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 illustrates the SOC-OCV characteristics of the single cell (LFP battery) of this embodiment. [Figure 3] This flowchart shows an example of the SOC estimation process performed by the battery ECU during battery replacement in this embodiment. [Figure 4] This flowchart shows an example of input / output current integration processing performed by the battery ECU. [Figure 5] This figure shows a portion of the flowchart for the SOC estimation process performed by the battery ECU during battery replacement in Embodiment 2. [Figure 6] This diagram illustrates the SOC-OCV characteristics after battery replacement. [Modes for carrying out the invention]

[0013] The embodiments of this disclosure will be described in detail below with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and their descriptions will not be repeated.

[0014] [Embodiment 1] FIG. 1 is an overall configuration diagram of an electric vehicle 1 equipped with a battery system S according to the present embodiment. In the present embodiment, the electric vehicle 1 is, for example, an electric vehicle. The electric vehicle 1 includes a motor generator (MG: Motor Generator) 10 that is a rotating electric machine, a power transmission gear 20, drive wheels 30, a power control unit (PCU: Power Control Unit) 40, a system main relay (SMR: System Main Relay) 50, a battery 100, a monitoring unit 200, a battery ECU (Electronic Control Unit) 300 that is an example of a control device, and a control ECU 500.

[0015] 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. The output torque of the MG 10 is transmitted to the drive wheels 30 via the power transmission gear 20 configured to include a reduction gear, a differential gear, and the like.

[0016] During braking of the electric vehicle 1, the MG 10 is driven by the drive wheels 30, and the MG 10 operates as a generator. Accordingly, the MG 10 also functions as a braking device that performs regenerative braking that converts kinetic energy of the electric vehicle 1 into electric power. Regenerative electric power generated by the regenerative braking force of the MG 10 is stored in the battery 100.

[0017] The PCU 40 is a power conversion device that bidirectionally converts power between the MG 10 and the battery 100. The PCU 40 includes, for example, an inverter and a converter that operate based on a control signal from the control ECU 500.

[0018] When the battery 100 is discharged, the converter boosts a voltage supplied from the battery 100 and supplies the boosted voltage to the inverter. The inverter converts DC power supplied from the converter into AC power to drive the MG 10.

[0019] When charging the battery 100, the inverter converts the AC power generated by the MG 10 into DC power and supplies the DC power to the converter. The converter steps down the voltage supplied from the inverter to a voltage suitable for charging the battery 100 and supplies the stepped-down voltage to the battery 100.

[0020] The SMR 50 is electrically connected to a power line connecting the battery 100 and the PCU 40. When the SMR 50 is closed (turned ON) in accordance with a control signal from the control ECU 500 (that is, in a connected state), power can be transferred between the battery 100 and the PCU 40. On the other hand, when the SMR 50 is opened (turned OFF) in accordance with a control signal from the control ECU 500 (that is, in a disconnected state), the electrical connection between the battery 100 and the PCU 40 is cut off.

[0021] The battery 100 stores electric power for driving the MG 10. The battery 100 is a rechargeable DC power supply (secondary battery), and is an assembled battery in which a plurality of unit cells (battery cells) 100a are electrically connected in series. The battery 10 and the unit cell 100a correspond to the "battery" in the present disclosure. The unit cell 100a may be configured of, for example, a lithium ion battery. In the present embodiment, a lithium iron phosphate battery (LFP battery) using phosphorus (P), iron (Fe), and lithium (Li) as a positive electrode material is employed as the unit cell 100a.

[0022] The monitoring unit 200 includes a voltage sensor 210, a current sensor 220, and a temperature sensor 230. The voltage sensor 210 detects the voltage VB of the unit cell 100a (the voltage VB between the respective terminals of the unit cell 100a). The current sensor 220 detects the current IB input / output to / from the battery 100 (unit cell 100a). Note that, when the battery 100 is discharged, the current IB becomes a negative (-) value, and when the battery 100 is charged, the current IB becomes a positive (+) value. The temperature sensor 230 detects the temperature TB of each of the unit cells 100a. Each sensor outputs its detection result to the battery ECU 300.

[0023] The electric vehicle 1 is equipped with an inlet 60, and the battery 100 can be externally charged using an electric vehicle supply equipment (EVSE) 400. The inlet 60 is configured to be connectable to a connector 420 provided at the end of the charging cable 410 of the EVSE 400. The inlet 60 is electrically connected to a power line connected to the battery 100 via a charging circuit 70. In this embodiment, when the SMR 50 is closed, the inlet 60 and the battery 100 are connected, enabling external charging. The charging circuit 70 may include a charging relay. Alternatively, the inlet 60 (charging circuit 70) may be connected to the power line between the battery 100 and the SMR 50 via a charging relay, and the battery 100 may be configured to be externally charged when the charging relay is closed. The SMR 50 or the charging relay corresponds to the "relay" in this disclosure.

[0024] The battery ECU 300 includes a CPU 301 and a memory 302. The memory 302 includes non-volatile memory (for example, flash memory). The battery ECU 300 estimates the State of Charge (SOC) of the battery 100 using signals received from the monitoring unit 200 and outputs it to the control ECU 500. The battery system S consists of the battery 100 (single cell 100a), the monitoring unit 200, the battery ECU 300, etc.

[0025] The control ECU 500 includes a CPU 501 and a memory 502. The memory 502 includes non-volatile memory (for example, flash memory). Based on signals received from the battery ECU 300, 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 502, the control ECU 500 controls each device so that the electric vehicle 1 reaches a desired state.

[0026] Figure 2 illustrates the SOC-OCV characteristics of the single cell (LFP battery) 100a of this embodiment. In Figure 2, the vertical axis represents the OCV [V] of the single cell 100a, and the horizontal axis represents the SOC [%] of the single cell 100a. As shown in Figure 2, the relationship between SOC and OCV (hereinafter referred to as the "SOC-OCV characteristic" or "OCV curve") shows that the change in OCV is small in relation to the change in SOC, and there is a wide region where the change in the OCV curve is minute (voltage flat region). For this reason, when estimating the SOC of battery 100 (single cell 100a) based on the SOC-OCV characteristics using the voltage VB detected by the voltage sensor 210, the accuracy of SOC estimation deteriorates in the voltage flat region. For this reason, it is desirable to estimate SOC using the current integration method (Coulomb count method).

[0027] In the battery system S, the battery 100 may be replaced. When replacing the battery 100, it is desirable to estimate the State of Charge (SOC) of the replaced battery 100. If the SOC is estimated using the current integration method when replacing the battery 100, it takes a lot of time to complete the SOC estimation. For this reason, it is conceivable to detect the voltage VB when replacing the battery 100 and estimate the SOC based on the SOC-OCV characteristic using the detected voltage VB. In this case, it is preferable to estimate the SOC using the voltage VB detected after the battery 100 is replaced but before the battery 100 is connected to the load. This is because the voltage VB before the battery 100 is connected to the load corresponds to the OCV.

[0028] The replacement of battery 100 is determined (detected) after the battery ECU 300 is started, for example, by the presence or absence of a battery replacement signal input from a service tool. Therefore, when the replacement of battery 100 is detected, the SMR50 may already be connected and battery 100 may be connected to a load. In this case, even if the State of Charge (SOC) is estimated using the voltage VB detected by the voltage sensor 210 when the replacement of battery 100 is detected, there is a concern that the estimation error of the SOC will be large.

[0029] In this embodiment, when it is detected that the battery 100 has been replaced, if the SMR50 (or charging relay) connecting the battery 100 to the load is connected, the SOC estimated based on the SOC-OCV characteristics is corrected based on the discharge or charge current via the SMR50 (or charging relay) to reduce the SOC estimation error.

[0030] Figure 3 is a flowchart showing an example of the SOC estimation process at the time of battery replacement performed by the battery ECU 300 in this embodiment. This flowchart is executed when the IG switch (power switch) 250 is turned ON and the battery ECU 300 is started up. In step 10 (hereinafter, steps are abbreviated as "S"), the voltage VB detected by the voltage sensor 210 is stored in the memory 302 as the starting voltage VBs.

[0031] In the following S11, it is determined whether or not a battery replacement has occurred. For example, if the control ECU 500 receives a replacement signal from the service tool ST used by the battery replacement worker, it may be determined that a battery replacement has occurred. Also, if the identification number (ID) of the battery 100 stored in the non-volatile memory of memory 302 or memory 502 is different from the identification number of the battery 100, it may be determined that a battery replacement has occurred. If no battery replacement has occurred, the process proceeds to S12; if a battery replacement has occurred, the process proceeds to S13.

[0032] In S12, it is determined whether the IG switch 250 has been switched from ON to OFF. If the IG switch 250 has been switched OFF, the routine ends. If the IG switch 250 is ON, the process returns to S11 to determine whether the battery has been replaced.

[0033] In S13, it is determined whether the SMR50 (or charging relay) is connected (whether it is in the ON state or not). If the SMR50 is not connected (in the OFF state), proceed to S14. If the SMR50 is connected, proceed to S15.

[0034] In S14, the SOC of each cell 100a is calculated using the starting voltage VBs and based on the SOC-OCV characteristics (Figure 2). The SOC of all cells 100a contained in battery 100 is calculated from the starting voltage VBs of each cell 100a, and this routine is completed.

[0035] In S15, the SOC of a single 100a cell is calculated using the starting voltage VBs and based on the SOC-OCV characteristics (Figure 2). This SOC is then corrected by the integrated current value ΣQ, and this corrected value is calculated as the SOC. Once the SOC of all single 100a cells has been corrected by the integrated current value ΣQ and the SOC has been calculated, this routine terminates.

[0036] Figure 4 is a flowchart showing an example of input / output current integration processing performed by the battery ECU 300. This flowchart is repeated at predetermined intervals when the battery ECU 300 is running. In S20, it is determined whether the SMR50 is in the ON state or not. If the SMR50 is connected and in the ON state, proceed to S21; if the SMR50 is disconnected and in the OFF state, proceed to S22.

[0037] In S21, the current IB detected by the current sensor 220 is integrated to calculate the integrated current value ΣQ[Ah], and then the routine ends. When battery 100 is discharged, the current IB is a negative (-) value, and when battery 100 is charged, the current IB is a positive (+) value. Therefore, the integrated current value ΣQ decreases during discharge and increases during charging. In S22, the integrated current value ΣQ is set to 0 (zero), and then the routine ends.

[0038] Referring to Figure 3, in S15, the SOC calculated based on the SOC-OCV characteristics is corrected using the current integration value ΣQ. When the SOC calculated from the SOC-OCV characteristics is called "SOC1", then "SOC = SOC 1+(The calculation is performed as ΣQ / X). X[Ah] is the capacity (fully charged capacity) of a single cell 100A when the SOC is 100[%] in the SOC-OCV characteristics shown in Figure 2, and is a preset value. After estimating the SOC in S14 and S15, the SOC may be calculated (updated as needed) using the current integration method with the current IB detected by the current sensor 220.

[0039] According to this embodiment, when it is detected that the battery 100 has been replaced, if the SMR50 (or charging relay) connecting the battery 100 to the load is connected, the SOC (SOC1) estimated from the SOC-OCV characteristics using the starting voltage VBs is corrected based on the current (integrated current value ΣQ) discharged or charged via the SMR50 (or charging relay). As a result, after the battery 100 is replaced, the SOC is estimated from the SOC-OCV characteristics using the voltage VB (starting voltage VBs) detected before the battery 100 is connected to the load, and this SOC is corrected based on the integrated current value ΣQ charged or discharged via the SMR50 (or charging relay), thereby reducing the SOC estimation error.

[0040] [Embodiment 2] In some cases, used or rebuilt batteries are used as replacement batteries. In this case, if the State of Charge (SOC) is estimated based on the OCV curve (SOC-OCV characteristics) of a new battery, the estimated SOC may be smaller than the actual SOC, raising concerns that the replacement battery may be overcharged. Therefore, when a battery replacement is detected, the OCV curve used to calculate the SOC may be switched, and the SOC may be calculated using the OCV curve after battery degradation. The OCV curve after degradation may be set according to a predetermined degradation state; for example, when a battery replacement is detected, the SOC may be calculated using an OCV curve corresponding to a capacity retention rate of 75%.

[0041] Even when switching to the OCV curve after degradation, the degradation state of the replaced battery may differ from the degradation state that was previously assumed. For this reason, it is desirable to accurately determine the degree of degradation (capacity retention rate) of the replaced battery. When determining the degree of battery degradation, it is preferable to first completely discharge the battery (SOC=0[%]), and then charge it to full charge to determine the full charge capacity.

[0042] In some cases, the degradation state of a replaced battery may be better than expected, and the full charge capacity of the replaced battery may be greater than the full charge capacity of the degraded OCV curve. In this case, the State of Charge (SOC) calculated from the degraded OCV curve will be smaller than the actual SCO. Therefore, if the battery charging and discharging is controlled using the calculated SOC, even if the battery is discharged until the SOC reaches 0% to completely discharge it, the actual SOC may not reach 0%, and the full charge capacity of the replaced battery may not be calculated accurately.

[0043] In Embodiment 2, the State of Charge (SOC) at the time of battery replacement can be estimated so that the replaced battery can be discharged until the SOC reaches 0%. Figure 5 shows a part of the flowchart of the SOC estimation process at the time of replacement performed by the battery ECU 300 in Embodiment 2. In Embodiment 2, S14 in the flowchart shown in Figure 3 is replaced with S141 and S142 shown in Figure 5, and the SOC used in S15 (Figure 3) is replaced with the SOC calculated in S142.

[0044] In S141, similar to S14 (Figure 3), the SOC of each cell 100a is calculated using the starting voltage VBs and based on the SOC-OCV characteristics (Figure 2). Once the SOC of all cells 100a contained in battery 100 has been calculated from the starting voltage VBs of each cell 100a, the process proceeds to S142.

[0045] In S142, the SOC calculated in S141 is corrected using the full charge capacity X [Ah] in the SOC-OCV characteristics (OCV curve) in Figure 2 and the full charge capacity Y [Ah] in the SOC-OCV characteristics (OCV curve) used for charge / discharge control after battery replacement. Figure 6 is a diagram illustrating the SOC-OCV characteristics after battery replacement. In Figure 6, the vertical axis is the OCV [V] of single cell 100a, and the horizontal axis is the SOC [%] of single cell 100a. In Figure 6, the solid OCV curve is the same as the OCV curve in Figure 2, for example, the OCV curve of a new battery 100. In Figure 6, the dashed OCV curve is the SOC-OCV characteristics for performing charge / discharge control of battery 100 after battery replacement. In LPF batteries with a flat voltage region, even if degradation occurs, there is almost no change in the OCV curve in the low SOC region, and the solid SOC curve and the dashed OCV curve overlap in the low SOC region.

[0046] In Figure 6, X[Ah] is the capacity at SOC=100[%] on the solid OCV curve, and is the full charge capacity of the solid OCV curve. The full charge capacity X corresponds to the "full charge capacity in the SOC-OCV characteristics" in this disclosure. Y[Ah] is the capacity at SOC=100[%] on the dashed OCV curve, and is the full charge capacity of the dashed OCV curve. The full charge capacity Y corresponds to the "full charge capacity at degradation" in this disclosure. The dashed OCV curve is pre-set to control the charging and discharging of battery 100 after battery replacement, and may, for example, correspond to a capacity retention rate of 75[%] on the solid OCV curve. In this case, "X / Y=1.33".

[0047] In S142, the SOC calculated in S141 is corrected by multiplying it by "X / Y" (SOC ← SOC × (X / Y)). Once the SOC of all single cells 100a contained in battery 100 has been corrected, this routine is terminated.

[0048] In this second embodiment, the SOC used in S15 (Figure 3) is replaced with the SOC calculated in S142, and this SOC is corrected by the current integration value ΣQ to obtain the correct SOC. Once the SOC of all single cells 100a has been corrected by the current integration value ΣQ, the routine is terminated.

[0049] In this second embodiment, when the battery is replaced, the SOC is estimated based on the SOC-OCV characteristics using the initial voltage VBs detected by the voltage sensor 210. Then, the SOC is corrected using the full charge capacity X and the full charge capacity Y. For example, as shown in Figure 6, when the initial voltage VBs is Va, the SOC estimated based on the SOC-OCV characteristics (solid line) is 45%, and the capacity retention rate of the OCV curve (dashed line) pre-set for charge / discharge control of battery 100 after battery replacement is 75%, then "X / Y = 1.33", so the SOC becomes 60% (= 45 × 1.33). Therefore, by discharging from SOC = 60% to complete discharge (SOC = 0%) using the OCV curve (dashed line), the actual SOC can be discharged to 0%. As a result, by charging to full charge after complete discharge, the full charge capacity of the replaced battery 100 can be accurately calculated. After calculating the full charge capacity of the replaced battery 100, the State of Charge (SOC) is estimated using a new OCV curve based on this full charge capacity. Alternatively, the SOC may be estimated using the current integration method in combination.

[0050] Replacement batteries are generally distributed with a low State of Charge (SOC) to suppress degradation. When estimating SOC using a pre-set OCV curve after degradation, if the OCV curve in the low SOC region changes depending on the battery's degradation state, a large error will occur in the estimated SOC if the replacement battery differs from the degradation state of the pre-set OCV curve. Therefore, it is not possible to discharge the actual SOC to 0%. In LPF batteries with a flat voltage region, even if degradation occurs, there is almost no change in the OCV curve in the low SOC region. Therefore, even if the full charge capacity of the replacement battery differs from the pre-set full charge capacity Y (full charge capacity after degradation), the actual SOC can be discharged to 0% by correcting the SOC using the full charge capacity X and full charge capacity Y.

[0051] In this second embodiment, steps S13 and S15 of the flowchart shown in Figure 3 may be omitted, and steps S141 and S142 may be processed when a positive result is obtained in S11.

[0052] The following configurations can be given as embodiments of the present disclosure. 1) A battery system comprising a battery, a voltage sensor for detecting the battery voltage, and a control device for estimating the battery's State of Charge (SOC), wherein the SOC-OCV characteristics of the battery have a voltage flat region where the change in OCV with respect to SOC is small, and the control device is configured to, when the battery is replaced, estimate the SOC based on the SOC-OCV characteristics using the voltage detected by the voltage sensor, correct the SOC using the full charge capacity X in the SOC-OCV characteristics and the full charge capacity Y in the SOC-OCV characteristics when the battery has deteriorated, and discharge the battery so that it is completely discharged using the corrected SOC and the SOC-OCV characteristics when the battery has deteriorated.

[0053] 2) In the battery system described in 1, the control device is configured to calculate the full charge capacity of the battery after replacement by charging the battery to full charge after it has been completely discharged.

[0054] In the above embodiment, a lithium iron phosphate battery (LFP battery) was used as the single cell 100a. However, the single cell 100a 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).

[0055] 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.

[0056] 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]

[0057] 1 Electric vehicle, 10 Motor generator (MG), 20 Drive transmission gear, 30 Drive wheels, 40 PCU, 50 SMR, 60 Inlet, 70 Charging circuit, 100 Battery, 100A single cell, 200 Monitoring unit, 210 Voltage sensor, 220 Current sensor, 230 Temperature sensor, 300 Battery ECU, 301 CPU, 302 Memory, 400 EVSE, 420 Connector, 500 Control ECU, 501 CPU, 502 Memory, S Battery system.

Claims

1. Batteries and A voltage sensor for detecting the voltage of the aforementioned battery, The system comprises a control device for estimating the state of charge (SOC) of the battery, When the control device detects that the battery has been replaced, Using the voltage detected by the voltage sensor, the SOC is estimated based on the SOC-OCV characteristics of the battery, A battery system configured to correct the State of Control (SOC), estimated based on the SOC-OCV characteristics, based on the current discharged or charged via the relay, when a relay connecting the battery and the load is connected.

2. The fully charged capacity at the time of degradation, which is the fully charged capacity of the battery when it has degraded, is predetermined. The control device is The battery system according to claim 1, wherein the SOC estimated based on the SOC-OCV characteristics is corrected using the full charge capacity in the SOC-OCV characteristics and the full charge capacity during degradation.

3. Batteries and A voltage sensor for detecting the voltage of the aforementioned battery, The system comprises a control device for estimating the state of charge (SOC) of the battery, When the battery is replaced, the control device will... Using the voltage detected by the voltage sensor, the SOC is estimated based on the SOC-OCV characteristics of the battery, The system is configured to correct the SOC using the full charge capacity in the SOC-OCV characteristics and the full charge capacity when the battery has deteriorated. The aforementioned fully charged capacity at the time of degradation is a preset value for the battery system.

4. The battery system according to claim 1 or claim 3, wherein the SOC-OCV characteristics of the battery have a voltage flat region in which the change in OCV is small relative to the SOC.

5. The battery system according to claim 1 or 3, wherein a signal indicating that the battery has been replaced is input from a service tool.

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