Battery system and method for estimating full charge capacity

Abstract

To accurately estimate a capacity (full charge capacity) of a battery.SOLUTION: A threshold cumulative value calculation unit 310 calculates a threshold cumulative value Qs. A current cumulating unit 320 cumulates a charging current. When a first current cumulative value ΣQ1, which is a cumulative value from a start of charging, becomes equal to or larger than the threshold cumulative value Qs, a maximum value detection unit 340 starts detection of a maximum value of an amount of change in a voltage VB. A full charge capacity calculation unit 360 calculates a full charge capacity X by adding a first current cumulative value ΣQ2, which is a current cumulative value from when the maximum value is detected to when a full charge is detected, to a reference capacity when the maximum value is detected.SELECTED DRAWING: Figure 6

Description

Technical Field

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[0001] The present disclosure relates to a battery system and a method for estimating a full charge capacity.

Background Art

[0002] Japanese Patent Application Laid-Open No. 2014-167457 (Patent Document 1) describes detecting a singular point that is a maximum value of a 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, when there are a plurality of singular points in a secondary battery, the singular point on the higher voltage side is selected and the capacity of the secondary battery is estimated. Specifically, detection of singular points is performed from the start of charging, and based on the voltage, SOC (State of Charge), etc. at the start of charging, it is determined whether it is the first singular point to appear or the next singular point to appear, and the singular point on the higher voltage side is specified to estimate the capacity of the secondary battery. However, at the start of charging, due to the influence of polarization etc., there may be cases where singular points (maximum values of voltage change amounts) cannot be accurately detected. Therefore, there is a concern that an accurate capacity cannot be estimated.

[0005] An object of the present disclosure is to accurately estimate the capacity (full charge capacity) of a battery.

Means for Solving the Problems

[0006] The charging system of this disclosure comprises a battery, a voltage sensor for detecting the battery voltage, a current sensor for detecting the battery charging current, and a control device. The control device includes a current integration unit for calculating a charging current integration value, which is the cumulative value of the battery charging current, and a maximum value detection unit for detecting the maximum value of the voltage change during battery charging based on the battery voltage. The control device detects a maximum value after a first current integration value, which is the cumulative value of the charging current from the start of battery charging, reaches or exceeds a predetermined value. The control device estimates the full charge capacity of the battery based on a second current integration value, which is the cumulative value of the charging current from the time the maximum value is detected until the battery is fully charged.

[0007] In this configuration, the battery system's control unit calculates a first current integration value, which is the integrated value of the charging current from the start of battery charging, in its current integration unit. The control unit detects a maximum value of the voltage change in its maximum value detection unit after the first current integration value exceeds a predetermined value. The current integration unit calculates a second current integration value, which is the integrated value of the charging current from the time the maximum value is detected until the battery is fully charged. Based on the second current integration value, the control unit estimates the full charge capacity of the battery.

[0008] The maximum value of the voltage change during charging is detected after the first integrated current value exceeds a predetermined value. Detection of the maximum value of the voltage change is not performed until the first integrated current value exceeds a predetermined value. Therefore, the maximum value on the high-voltage side of the battery can be detected without being affected by polarization at the start of charging, and the full charge capacity of the battery can be accurately estimated.

[0009] Preferably, the predetermined value may be set based on the time from the end of the previous charge / discharge of the battery to the start of the current charge, the voltage at the start of the charge, and the temperature of the battery at the start of the charge.

[0010] With this configuration, the polarization state can be determined by the time elapsed between the end of the previous charge / discharge cycle and the start of the current charge cycle, and the remaining capacity (or state of charge) of the battery can be determined by the voltage at the start of charging and the battery temperature at the start of charging. By setting predetermined values ​​using these parameters, it is possible to reliably ensure that a maximum value occurs on the low-voltage side of the battery between the start of charging and the first integrated current value exceeding a predetermined value. This allows for reliable detection of a maximum value on the high-voltage side.

[0011] Preferably, the full charge capacity is calculated by adding a second integrated current value to a preset reference capacity.

[0012] The high-voltage maximum occurs when the battery's remaining capacity is approximately the same, regardless of the battery's degradation state. The remaining capacity at the time of the high-voltage maximum is set as the reference capacity. By adding the second integrated current value to this reference capacity, the full charge capacity can be estimated.

[0013] Preferably, the control device may further include an offset learning unit that stops charging the battery when it is being charged and calculates an offset value of the current sensor. The control device calculates the offset value using the offset learning unit, provided that a maximum value has been detected.

[0014] In this configuration, the offset learning unit calculates the offset value only when a local maximum is detected. Since charging is not stopped by offset learning until a local maximum is detected, local maximum detection can be performed effectively.

[0015] The method for estimating the full charge capacity of a battery according to this disclosure includes: determining whether a first integrated current value, which is the cumulative value of the charging current from the start of charging of the battery, is greater than or equal to a predetermined value; detecting a maximum value of the voltage change of the battery if the first integrated current value is greater than or equal to the predetermined value; calculating a second integrated current value by integrating the charging current from the time the maximum value is detected until the battery is fully charged; and estimating the full charge capacity of the battery by adding the second integrated current value to a preset reference capacity.

[0016] According to this method, when the first integrated current value is greater than or equal to a predetermined value, the maximum value of the battery's voltage change is detected, and the charging current from the time the maximum value is detected until the battery is fully charged is integrated to calculate the second integrated current value. Then, the second integrated current value is added to a preset reference capacity to estimate the battery's full charge capacity. Detection of the maximum value of the voltage change is not performed until the first integrated current value is greater than or equal to a predetermined value. Therefore, the maximum value on the high-voltage side of the battery can be detected without being affected by polarization at the start of charging, and the battery's full charge capacity can be accurately estimated. [Effects of the Invention]

[0017] According to this disclosure, the battery capacity (full charge capacity) can be accurately estimated. [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] Figures (A) and (B) show the relationship between OCV and remaining capacity in the single cell (LFP battery) of this embodiment. [Figure 3] This flowchart shows an example of the full charge capacity estimation process performed by the ECU. [Figure 4] This flowchart shows an example of the charging current integration process performed by the ECU. [Figure 5] This flowchart shows the offset learning process performed by the ECU. [Figure 6]This is a diagram showing an example of functional blocks configured in an ECU in the present embodiment.

Embodiment for Carrying Out the Invention

[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 denoted by the same reference numerals and their description 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 the present embodiment. In the present 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 as 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, a differential device, and the like.

[0022] During braking of the electric vehicle 1, MG10 is driven by the drive wheels 30 and MG10 operates as a generator. Thereby, MG10 also functions 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 in MG10 is stored in the battery 100.

[0023] PCU40 is a power conversion device that converts power bidirectionally between MG10 and the battery 100. PCU40 includes, for example, an inverter and a converter that operate based on a control signal from 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 composed of multiple single cells 100a stacked and electrically connected in series, for example. Battery 100 and single cells 100a correspond to the "battery" in this disclosure. Single cells 100a may be composed of lithium-ion batteries, for example. In this embodiment, a lithium iron phosphate battery (LFP battery) is used as the single cell 100a, using lithium iron phosphate as the positive electrode active material.

[0028] 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 single cell 100a (the voltage VB between each terminal of the single cell 100a). The current sensor 220 detects the current IB that is input to and output from the battery 100 (single cell 100a). The temperature sensor 230 detects the temperature TB of each single cell 100a. 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 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 full charge capacity estimation processing and offset learning processing, which will be described later. The battery system S consists of a battery 100 (single cell 100a), monitoring unit 200, ECU 300, etc.

[0032] Figure 2 shows the relationship between OCV (Open Circuit Voltage) and remaining capacity in the single cell 100a (LFP battery) of this embodiment. In Figure 2(A), the vertical axis is the OCV [V] of the single cell 100a, and the horizontal axis is the remaining capacity (charge capacity) [Ah] of the single cell 100a. As shown in Figure 2(A), the relationship between OCV and remaining capacity (hereinafter, this relationship will also be 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 100a of this embodiment, there are two steps P1 and P2.

[0033] The first step P1 (where the OCV is on the low-voltage side) occurs when the SOC of a new 100a cell is around 30%. The second step P2 (where the OCV is on the high-voltage side) occurs when the SOC of a new 100a cell is around 60%. As shown by the dashed lines in Figure 2(A), the position of these steps does not change even when the 100a cell deteriorates and its full charge capacity decreases (when the capacity retention rate of the 100a cell decreases). Even if the 100a cell deteriorates, the value of the remaining capacity at which the steps appear does not change.

[0034] Figure 2(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 2(B), the voltage change ΔVB reaches a maximum value of M1 at the remaining capacity corresponding to step P1, and a maximum value of M2 at the remaining capacity corresponding to step P2. Therefore, the remaining capacity at which the voltage change ΔVB reaches a maximum value of M1 is stored as the reference capacity C1, and the charging current from when the voltage change ΔVB reaches a maximum value of M1 until full charge is calculated, and by adding this calculated value to the reference capacity C1, the full charge capacity of battery 100 (single cell 100a) can be estimated. Furthermore, the remaining capacity at which the voltage change ΔVB reaches its maximum value M2 is stored as the reference capacity C2. By integrating the charging current from the time the voltage change ΔVB reaches its maximum value M2 until it is fully charged, and adding this integrated value to the reference capacity C2, the full charge capacity of battery 100 (single cell 100a) can be estimated.

[0035] The accuracy of the integrated charging current deteriorates as the integration time increases (as the integrated amount increases), because detection errors of the current sensor 220 and other factors are also integrated. In this embodiment, in order to improve the accuracy of estimating the full charge capacity, a maximum value M2 corresponding to the step P2 of the second stage (where the OCV is on the high-voltage side) is detected, and the charging current from the time the maximum value M2 is reached until full charge is achieved is integrated to estimate the full charge capacity.

[0036] Figure 3 is a flowchart showing an example of the full charge capacity estimation process performed by the ECU 300. This flowchart is executed when external charging of the battery 100 begins and is performed for each individual cell 100a. 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 acquires various parameters in step (hereinafter, step is abbreviated as "S") 10. In this embodiment, the ECU 300 acquires the IGOFF time Toff, voltage VB, and temperature TB. The IGOFF time is the time from the end of the previous charge / discharge cycle until the start of the current charge (external charge). For example, the IGOFF time may be acquired by measuring the time from when the IG switch (power switch) 250 is turned off until the start of charging using a timer (not shown). Voltage VB is the voltage of each individual cell 100a detected by the voltage sensor 210. Temperature TB is the temperature of each individual cell 100a detected by the temperature sensor 230.

[0037] In the subsequent S11, the threshold integrated value Qs is calculated. The threshold integrated value Qs is calculated, for example, using a three-dimensional map (not shown) with IGOFF time, voltage VB, and temperature TB as parameters. In this embodiment, the lowest value of the temperature TB of each cell 100a, which is the minimum temperature TBmin, is adopted as the temperature TB, and the threshold integrated value Qs is calculated from the three-dimensional map with IGOFF time, voltage VB, and minimum temperature TBmin as parameters. The threshold integrated value Qs corresponds to the "predetermined value" in this disclosure.

[0038] In S12, it is determined whether the first current integration value ΣQ1 exceeds the threshold integration value Qs. The first current integration value ΣQ1 is the integrated value of the charging current from the start of external charging of the battery 100 (single cell 100a) to the present. Figure 4 is a flowchart of an example of the charging current integration process performed by the ECU 300. This flowchart is executed when external charging of the battery 100 begins. First, in S20, it is determined whether the flag F is 1. Flag F is a flag that is set to 1 in S14 (Figure 3), which will be described later, and is set to 0 at the start of external charging and in S16 (Figure 3), which will be described later. At the start of external charging, flag F is 0, so the process proceeds to S21, where the charging current is integrated and the first current integration value ΣQ1 is calculated. The charging current may be the input current to the battery 100 detected by the current sensor 220. The first current integration value ΣQ1 is calculated until flag F is set to 1.

[0039] Returning to Figure 3, in S12, if the first integrated current value ΣQ1 is less than or equal to the threshold integrated value Qs, the process in S12 is repeated until the first integrated current value ΣQ1 exceeds the threshold integrated value Qs. When the first integrated current value ΣQ1 becomes greater than the threshold integrated value Qs, the process proceeds to S13, where the maximum value of the voltage fluctuation amount ΔVB is detected.

[0040] The threshold integrated value Qs is predetermined through experiments, etc., so that when the first current integrated value ΣQ1, which is accumulated from the start of external charging, becomes equal to or greater than the threshold integrated value Qs, the remaining capacity of the single cell 100a becomes greater than the remaining capacity at step P1 (maximum value M1). For example, the threshold integrated value Qs is set to a larger value the shorter the IGOFF time, the lower the voltage VB, and the lower the minimum temperature TBmin. As a result, the greater the degree of polarization at the start of charging, and the lower the state of charge (the lower the remaining capacity) at the start of charging, the larger the threshold integrated value Qs will be set. For example, the threshold integrated value Qs is set so that when the remaining capacity of the single cell 100a exceeds S, which is greater than the remaining capacity at step P1 (maximum value M1), as shown in Figure 2(A), a positive judgment is made in S12. In other words, in the shaded areas of Figures 2(A) and (B), the detection of the maximum value of the voltage change ΔVB is masked (the detection of the maximum value is not performed).

[0041] In S13, the maximum value of the voltage change ΔVB is detected. The voltage change ΔVB may be the change in voltage VB with respect to the remaining capacity (charging capacity) [V / Ah], or the change in voltage VB with respect to time (charging time) [V / s]. The maximum value may be detected when the current voltage change ΔVB is small compared to the previous voltage change ΔVB, and the maximum value M2 is detected. Alternatively, the maximum value may be detected when the sign of the derivative of the voltage change ΔVB changes from positive to negative. If the maximum value of the voltage change ΔVB is detected in S13, the process proceeds to S14. The maximum value detected in S13 is the maximum value M2 (see Figure 2(B)).

[0042] In S14, the flag F is set to 1, and then the process proceeds to S15. In S15, it is determined whether or not battery 100 is fully charged. For example, if battery 100 is being charged using CCCV (Constant Current-Constant Voltage), it may be determined that it is fully charged when the charging current falls below a set value. Alternatively, it may be determined that battery 100 is fully charged when the voltage VB of any single cell 100a reaches the charging termination voltage. When battery 100 is fully charged, the process proceeds to S16, where the full charge capacity X of the single cell 100a is calculated, and the flag F is set to 0. Note that when battery 100 is fully charged, external charging is stopped (ended).

[0043] Referring to Figure 4, when flag F becomes 1, the process proceeds to S22, where the charging current is integrated and the second integrated current value ΣQ2 is calculated. In the following S23, it is determined whether or not battery 100 is fully charged. If it is fully charged, the routine ends; otherwise, the calculation of the second integrated current value ΣQ2 continues. The second integrated current value ΣQ2 is the integrated value of the charging current from when a maximum value is detected in S13 (see Figure 3) (when flag F is set to 1) until it is fully charged.

[0044] Returning to Figure 3, in S16, the fully charged capacity X of the single cell 100a is calculated by adding the second integrated current ΣQ2 to the reference capacity C2 (X = C2 + ΣQ2). The reference capacity C2 is the remaining capacity (charge capacity) of the single cell 100a at the maximum value M (step P2), as shown in Figures 2(A) and (B), and is set in advance through experiments or other means.

[0045] The first integrated current value ΣQ1 and the second integrated current value ΣQ2 are calculated by integrating the values ​​detected by the current sensor 220. If the detection error of the current sensor 220 is large, the calculation accuracy of the first integrated current value ΣQ1 and the second integrated current value ΣQ2 deteriorates. In particular, in the case of normal charging using an AC power supply, the charging current is small compared to rapid charging, and the effect of the detection error of the current sensor 220 becomes larger. For this reason, it is desirable to perform offset learning (zero point correction of the current sensor 220) to correct the offset error of the current sensor 220.

[0046] When performing offset learning for the current sensor 220, charging and discharging of the battery 100 are stopped, and no charging or discharging current flows. In S13 (see Figure 3), if charging is stopped to perform offset learning while a maximum value of the voltage change amount ΔVB is detected, there is a concern that the voltage VB will fluctuate, leading to a false detection of the maximum value or failure to detect the maximum value at all. In this embodiment, offset learning is performed on the condition that a maximum value of the voltage change amount ΔVB has been detected.

[0047] Figure 5 is a flowchart of the offset learning process performed by the ECU 300. This flowchart is executed when external charging of the battery 100 begins. In S30, it is determined whether or not a maximum value of the voltage change amount ΔVB has been detected in all of the individual cells 100a that make up the battery 100. If all of the individual cells 100a are determined to be positive in S13 (see Figure 3), then S30 is also determined to be positive, and the process proceeds to S32. If no maximum value has been detected in any of the individual cells 100a, then it is determined to be negative, and the process proceeds to S31.

[0048] In S31, offset learning of the current sensor 220 is disabled, and then the process returns to S30. In this case, external charging of the battery 100 is not stopped for the purpose of offset learning. In S32, offset learning is enabled, and then the current routine is terminated.

[0049] When offset learning is permitted, the ECU 300 performs offset learning using a learning routine (not shown). Offset learning pauses charging, so that no charge or discharge current flows to the battery 100. Then, using the detection signal from the current sensor 220 when the charge or discharge current is 0, an offset value (correction value) is determined, and the zero point of the current sensor 220 is corrected. The pause in charging may be performed at predetermined intervals (for example, every 15 minutes).

[0050] Figure 6 shows an example of a functional block configured in the ECU300 in this embodiment. Threshold Sum Calculation Department Unit 310 calculates a threshold integrated value Qs using the IGOFF time Toff, voltage VB, and temperature TB. The current integration unit 320 calculates a first current integrated value ΣQ1 and a second current integrated value ΣQ2 by integrating the current IB during external charging. The comparison unit 330 compares the first current integrated value Q1 with the threshold integrated value Qs and determines whether the first current integrated value ΣQ1 exceeds the threshold integrated value Qs. The maximum value detection unit 340 detects a maximum value of the voltage change amount ΔVB based on the voltage VB if the first current integrated value ΣQ1 exceeds the threshold integrated value Qs. The full charge determination unit 350 determines that the battery 100 is fully charged based on the voltage VB or current IB. The full charge capacity calculation unit 360 calculates the full charge capacity X by adding the second current integrated value ΣQ2 to the reference capacity C2. When a maximum value is detected in all single cells 100a, the offset learning unit 370 performs offset learning of the current sensor 220.

[0051] According to this embodiment, a first integrated current value ΣQ1, which is the integrated value of the charging current from the start of charging of the battery 100, is calculated. After the first integrated current value ΣQ1 becomes equal to or greater than a threshold integrated value Qs, the maximum value of the voltage change amount ΔVB is detected. Then, a second integrated current value ΣQ2, which is the integrated value of the charging current from the time the maximum value of the voltage change amount ΔVB is detected until the battery 100 is fully charged, is calculated. The full charge capacity X is calculated by adding the second integrated current value ΣQ2 to the reference capacity C1. Detection of the maximum value of the voltage change amount ΔVB is not performed until the first integrated current value ΣQ1 becomes equal to or greater than a threshold integrated value Qs. Therefore, the maximum value M2 corresponding to the step P2 on the high-voltage side of the OCV can be detected well without being affected by polarization at the start of charging, and the full charge capacity X can be accurately estimated.

[0052] According to this embodiment, the threshold integrated value Qs is set based on the IGOFF time Toff, the voltage VB at the start of charging, and the temperature TB at the start of charging. The polarization state can be determined by the time from the end of the previous charge / discharge of the battery 100 to the start of the current charge (IGOFF time Toff), and the remaining capacity (or state of charge) of the battery 100 (single cell 100a) can be determined by the voltage VB at the start of charging and the temperature TB at the start of charging. By setting the threshold integrated value Qs using these parameters, it can be reliably ensured that the OCV reaches a maximum value M1 corresponding to the step P1 on the low-voltage side between the start of charging and the first current integrated value ΣQ1 becoming equal to or greater than the threshold integrated value Qs. This allows for the reliable detection of the OCV's maximum value M2 corresponding to the step P2 on the high-voltage side.

[0053] According to this embodiment, the full charge capacity is estimated using the second current integration value ΣQ2, which is calculated from the point where the maximum value M2 corresponding to the step difference P2 of the second stage (where the OCV is on the high-voltage side) is reached until the battery is fully charged. This reduces the integration error of the charging current and improves the accuracy of estimating the full charge capacity X.

[0054] According to this embodiment, offset learning of the current sensor 220 is performed after a maximum value M2 is detected in all single cells 100a. As a result, charging is not stopped when a maximum value of the voltage change amount ΔVB is detected for offset learning, thus suppressing false detection of maximum values ​​caused by fluctuations in voltage VB, etc.

[0055] 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) and the maximum value of the voltage change ΔVB can be detected.

[0056] 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.

[0057] 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]

[0058] 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, 100a single cell, 200 Monitoring unit, 210 Voltage sensor, 220 Current sensor, 230 Temperature sensor, 300 ECU, 310 Threshold integrated value calculation unit, 320 Current integrated unit, 330 Comparison unit, 340 Maximum value detection unit, 350 Full charge determination unit, 360 Full charge capacity calculation unit, 370 Offset learning unit, 400 DC power supply, 420 Connector, 500 AC power supply, 520 Connector, S Battery system.

Claims

1. A battery system comprising a battery, a voltage sensor for detecting the voltage of the battery, a current sensor for detecting the charging current of the battery, and a control device, The aforementioned battery has, in relation to the closed-circuit voltage of the battery and the remaining capacity of the battery, a step where the voltage increases from a flat voltage region and then returns to a flat voltage region, and the closed-circuit voltage has a first step on the low-voltage side and a second step on the high-voltage side. The control device is A current integration unit calculates the integrated charging current value, which is the integrated value of the charging current of the aforementioned battery, A maximum value detection unit that detects the maximum value of the voltage change during charging of the battery based on the voltage, A threshold integral value calculation unit calculates a predetermined value based on the time from the end of the previous charge / discharge of the battery to the start of the current charge, the voltage at the start of charging, and the temperature of the battery at the start of charging. An offset learning unit that stops charging the battery during charging and calculates the offset value of the current sensor, The unit includes a full charge capacity calculation unit that calculates the full charge capacity of the battery, The predetermined value is calculated such that when the first integrated current value, which is the integrated value of the charging current from the start of charging of the battery, becomes greater than or equal to the predetermined value, the remaining capacity becomes greater than the remaining capacity at the first step difference. The maximum value detection unit detects the maximum value after the first current integrated value exceeds a predetermined value. The full charge capacity calculation unit calculates the full charge capacity of the battery by adding a second integrated current value, which is the integrated value of the charging current from when the maximum value is detected until the battery is fully charged, to a reference capacity corresponding to the remaining capacity at the second step difference. The offset learning unit calculates the offset value on the condition that the maximum value has been detected, in a battery system.

2. A method for estimating the full charge capacity of a battery, The aforementioned battery has, in relation to the closed-circuit voltage of the battery and the remaining capacity of the battery, a step where the voltage increases from a flat voltage region and then returns to a flat voltage region, and the closed-circuit voltage has a first step on the low-voltage side and a second step on the high-voltage side. The first integrated current value, which is the cumulative value of the charging current from the start of charging of the battery, is determined to be equal to or greater than a predetermined value. When the first integrated current value is equal to or greater than the predetermined value, the maximum value of the voltage change during charging of the battery is detected, The charging current from the time the aforementioned maximum value is detected until the battery is fully charged is accumulated to calculate the second integrated current value, The fully charged capacity of the battery is estimated by adding the second integrated current value to a preset reference capacity, The process includes, on the condition that the aforementioned maximum value is detected, stopping the charging and calculating the offset value of the current sensor that detects the charging current, The predetermined value is calculated based on the time from the end of the previous charge / discharge of the battery to the start of the current charge, the voltage at the start of charging, and the temperature of the battery at the start of charging, and is the value at which the remaining capacity becomes greater than the remaining capacity at the first step when the first integrated current value becomes greater than or equal to the predetermined value. A method for estimating the full charge capacity, wherein the reference capacity is the capacity corresponding to the remaining capacity at the second step.

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