Battery capacity estimation device and battery capacity estimation method

Abstract

This battery capacity estimation device comprises: a battery voltage estimation unit 11 that measures or estimates the battery voltage of a secondary battery 1; a charge / discharge control unit 12 that controls charging and discharging of the secondary battery 1; a state-of-charge estimation unit 13 that estimates the state of charge (SOC) of the secondary battery 1; and a battery capacity estimation unit 14 that estimates the battery capacity. The charge / discharge control unit 11 controls charging and discharging of the secondary battery up to a start point by charging or discharging the secondary battery at a constant first current for a first time or longer, and after passing the start point, controls charging and discharging of the secondary battery by charging or discharging at a second current so that the SOC changes from the start point by a prescribed change margin or more, and controls charging or discharging of the secondary battery up to an end point by charging or discharging the secondary battery at the constant first current for a second time or longer. The state-of-charge estimation unit 13 acquires a start-point SOC indicating the SOC at the start point and uses the start-point SOC, the battery voltage at the start point, and the battery voltage at the end point as a basis for estimating an end-point SOC indicating the SOC at the end point. The battery capacity estimation unit 14 estimates the battery capacity on the basis of the SOC difference between the start-point SOC and the end-point SOC and a quantity of electric charge obtained by integrating the current from the start point to the end point.

Description

Battery capacity estimation device and battery capacity estimation method

[0001] The present invention relates to a battery capacity estimation device and a battery capacity estimation method.

[0002] For example, a method for estimating a full charge capacity of a battery described in Patent Document 1 includes the steps of: estimating a first full charge capacity based on a charge / discharge current amount of the battery and an SOC before and after charge / discharge; estimating a first resistance that is the internal resistance of the battery at the time the first full charge capacity is estimated and a second resistance that is the internal resistance of the battery at a time after the time the first full charge capacity is estimated; calculating a first corrected resistance by correcting the first resistance using a first coefficient based on at least one of the temperature and the SOC of the battery at the time the first resistance is estimated; and calculating a second corrected resistance by correcting the second resistance using a second coefficient based on at least one of the temperature and the SOC of the battery at the time the second resistance is estimated; and estimating a second full charge capacity that is the full charge capacity of the battery at the time the second resistance is estimated based on the first full charge capacity and a resistance ratio between the first corrected resistance and the second corrected resistance.

[0003] JP 2011-215125 A

[0004] The charge capacity estimation method described in Patent Document 1 estimates the full charge capacity of a battery based on the correlation between the full charge capacity and the cell internal resistance. However, if the actual full charge capacity of the battery deviates from the correlation between the full charge capacity and the cell internal resistance due to battery degradation, there is a problem in that the accuracy of estimating the full charge capacity decreases.

[0005] The problem to be solved by the present invention is to provide a battery capacity estimation device and a battery capacity estimation method that can estimate battery capacity with high accuracy.

[0006] The present invention solves the above problem by controlling the charging and discharging of the secondary battery up to a starting point by charging or discharging the secondary battery at a constant first current for a predetermined first hour or more, controlling the charging and discharging of the secondary battery after passing the starting point by charging or discharging at a second current so that the charge state changes from the starting point by a predetermined change width or more, controlling the charging and discharging of the secondary battery up to an end point by charging or discharging the secondary battery at a constant first current for a predetermined second hour or more, obtaining the starting point SOC, estimating the end point SOC based on the starting point SOC, the battery voltage at the starting point, and the battery voltage at the end point, and estimating the battery capacity of the secondary battery based on the SOC difference between the starting point SOC and the end point SOC and the amount of charge obtained by integrating the current from the starting point to the end point.

[0007] According to the present invention, the battery capacity can be estimated with high accuracy.

[0008] FIG. 1 is a block diagram showing a battery capacity estimation system according to this embodiment. FIG. 2 is a graph showing current / voltage characteristics when charging in a charge / discharge sequence in the battery capacity estimation system according to this embodiment. FIG. 3 is a flowchart showing the steps of a battery capacity estimation method using the battery capacity estimation system according to this embodiment. FIG. 4 is a graph showing current / voltage characteristics when charging in a charge / discharge sequence in a battery capacity estimation system according to a modification of this embodiment. FIG. 5A is a flowchart showing the steps of a battery capacity estimation method using the battery capacity estimation system according to a modification of this embodiment. FIG. 5B is a flowchart showing the steps of a battery capacity estimation method using the battery capacity estimation system according to a modification of this embodiment.

[0009] A battery capacity estimation system according to this embodiment will be described with reference to the drawings. Fig. 1 is a block diagram showing the battery capacity estimation system according to this embodiment. The battery capacity estimation system is a system that estimates the current battery capacity of a secondary battery 1 in order to estimate the state of health (SOH) of the secondary battery 1 with high accuracy in a short period of time.

[0010] As shown in FIG. 1 , the battery capacity estimation system includes a secondary battery 1, a DC-DC converter 2, a voltage sensor 3, a current sensor 4, and a controller 10. The secondary battery 1 includes a battery group in which a plurality of batteries are connected. The secondary battery 1 is, for example, a lithium-ion secondary battery. Examples of this lithium-ion secondary battery include, but are not limited to, a battery that uses silicon or a silicon-containing active material as the negative electrode active material, or a battery that uses a sulfur-containing active material as the positive electrode active material. Furthermore, the secondary battery 1 may be a liquid electrolyte lithium-ion secondary battery or an all-solid-state lithium-ion secondary battery.

[0011] Although not shown, the positive electrodes of the batteries included in the secondary battery 1 are electrically connected to the negative electrodes of the other batteries via bus bars. In other words, the multiple batteries included in the secondary battery 1 are modularized by being connected via bus bars.

[0012] The DCDC converter 2 is a power conversion device that converts the voltage input from the secondary battery 1 to a predetermined voltage and outputs power to a load such as a motor. The DCDC converter 2 is also a power conversion device that converts the voltage input from a load such as a motor or a charging device to a predetermined voltage and outputs power to the secondary battery 21. The DCDC converter 2 is controlled by a controller 10. The secondary battery 1 is connected to the input side of the DCDC converter 2, and a load is connected to the output side of the DCDC converter 2. The load is a charging device or the like, and the secondary battery 1 is electrically connected to the charging device.

[0013] The voltage sensor 3 is a sensor for detecting the voltage between the terminals of the secondary battery 1. The voltage sensor 3 is connected between the wiring connected to the positive and negative electrodes of the secondary battery 1. The current sensor 4 is a sensor for detecting the input / output current of the secondary battery 1. The current sensor 4 is connected to the wiring connected to the positive or negative electrode of the secondary battery 1. The voltage sensor 3 and current sensor 4 detect the battery state and output the detected values ​​to the controller 10.

[0014] The controller 10 is a battery control unit (BCU). The controller 10 controls the charging and discharging of the secondary battery 1 and estimates the battery capacity of the secondary battery 1 based on the detected voltage detected by the voltage sensor 3 and / or the detected current detected by the current sensor 4. The controller 10 is composed of a memory such as a ROM or a RAM, a processor such as a CPU, etc. The controller 10 also has a battery voltage estimation unit 11, a charge / discharge control unit 12, an SOC estimation unit 13, and a battery capacity estimation unit 14 as functional blocks for controlling the charging and discharging of the secondary battery 1 and estimating the battery capacity.

[0015] The battery voltage estimation unit 11 measures or estimates the battery voltage of the secondary battery 1. For example, the battery voltage estimation unit 11 measures the battery voltage by acquiring a detected value from the voltage sensor 3. Alternatively, the battery voltage estimation unit 11 may estimate the battery voltage by performing a predetermined calculation process or correction process on the detected value from the voltage sensor 3.

[0016] The charge / discharge control unit 12 controls the charging and discharging of the secondary battery 1. In this embodiment, as will be described later, the secondary battery 1 is charged and / or discharged in order to estimate the battery capacity of the secondary battery 1. A charge / discharge current for estimating the battery capacity is set, and the charge / discharge control unit 12 outputs a control command to the DC / DC converter so that the charge / discharge current of the secondary battery 1 becomes the set current value. In the following description, the charge / discharge current is a general term for the charge current and the discharge current, and refers to at least one of the charge current and the discharge current.

[0017] The state of charge (SOC) estimation unit 13 estimates the state of charge (SOC) of the secondary battery 1. The SOC estimation unit 13 estimates the SOC by integrating charge and discharge currents (current integration). The SOC estimation unit 13 also estimates the SOC based on the correlation (SOC-OCV characteristics) between the SOC and the open circuit voltage (OCV) of the secondary battery 1. The SOC-OCV characteristics are determined depending on the materials and structure used in the secondary battery 1 and can be identified from experimental data. The controller 10 may store a table indicating the SOC-OCV characteristics in memory, and the SOC estimation unit 13 may estimate the SOC by referring to the table. Note that the SOC-OCV characteristics change depending on the deterioration state of the secondary battery 1, so the SOC estimation unit 13 may correct the SOC-OCV characteristics depending on the deterioration state of the secondary battery 1.

[0018] The battery capacity estimation unit 14 estimates the battery capacity of the secondary battery 1. The battery capacity estimation unit 14 may estimate the battery capacity of the secondary battery 1 while the secondary battery 1 is being charged or discharged. When estimating the battery capacity, the battery capacity estimation unit 14 outputs a control command to the charge / discharge control unit 12 so that the secondary battery 1 is charged or discharged in a charge / discharge sequence. Incidentally, the battery capacity (C Ｎ The calculation formula for (1) is given by the following formula: ΔAh indicates the current integrated value accumulated over a predetermined time period, and ΔSOC indicates the difference (amount of change) in SOC over the predetermined time period.

[0019] The current integration (ΔAh) can be calculated by integrating the charge / discharge current of the secondary battery 1, and therefore can be calculated even while the secondary battery 1 is being charged or discharged. Meanwhile, with regard to the calculation of ΔSOC, although the SOC is determined from the SOC-OCV characteristics, it is difficult to calculate the OCV while the secondary battery 1 is being charged or discharged. Furthermore, although it is possible to calculate the OCV by stopping the charge / discharge of the secondary battery 1, there is a time period (hereinafter also referred to as the relaxation wait time) until the battery voltage relaxes after the charge / discharge of the secondary battery 1 is stopped. Therefore, the OCV cannot be calculated while the battery voltage is relaxing, and a relaxation wait time is required to calculate ΔSOC. In other words, there is a problem in that it takes a long time to estimate the battery capacity. In other words, to estimate the battery capacity using equation (1), the method for calculating ΔSOC during the charge / discharge current of the secondary battery 1 is important.

[0020] In this embodiment, ΔSOC is calculated by focusing on the fact that the battery voltage characteristics when the secondary battery 1 is charged and discharged at a constant current are similar to the SOC-OCV characteristics. For example, when the secondary battery 1 is charged at a constant current, the battery voltage (cell voltage) of the secondary battery 1 increases over charging time, and the SOC gradually increases. At this time, the battery voltage of the secondary battery 1 is the sum of the voltage corresponding to the resistance loss due to the internal resistance of the secondary battery 1 and the OCV. During charging of the secondary battery 1, voltage changes due to changes in internal resistance are limited compared to OCV changes. In other words, as the constant current charging of the secondary battery 1 progresses and the battery voltage increases, the voltage corresponding to the resistance loss does not change significantly between low and high SOC, and the battery voltage increases as the OCV increases. As a result, the battery voltage characteristics during constant current charging are similar to the SOC-OCV characteristics. Furthermore, because the voltage corresponding to the resistance loss varies depending on the magnitude of the charging current, reducing the charging current can suppress the voltage change corresponding to the resistance loss. In other words, by charging and discharging the secondary battery 1 at a constant current and treating the voltage change in the battery voltage as equivalent to a change in SOC, it is possible to calculate ΔSOC even while the secondary battery 1 is charging and discharging current, and the battery capacity of the secondary battery 1 can be estimated with high accuracy in a short period of time.

[0021] In this embodiment, a charge / discharge sequence for estimating battery capacity is determined in advance to estimate the battery capacity while approximating the battery voltage characteristics and SOC-OCV characteristics when the secondary battery 1 is charged / discharged. The charge / discharge control unit 12 charges the secondary battery 1 using the following charge / discharge sequence in response to a control command from the battery capacity estimation unit 14. First, the charge / discharge control unit 12 controls the charge / discharge of the secondary battery 1 from an unloaded state of the secondary battery 1 to a start point by charging or discharging the secondary battery 1 at a constant first current for at least a first time. The start point is the timing for calculating the SOC required to estimate the battery capacity. Next, after passing the start point, the charge / discharge control unit 12 controls the charge / discharge of the secondary battery 1 by charging or discharging at a second current so that the SOC of the secondary battery 1 changes by at least a predetermined variation width. Then, the charge / discharge control unit 12 controls the charge / discharge of the secondary battery 1 to an end point by charging or discharging the secondary battery 1 at the first current for at least a second time. The end point is the timing for calculating the SOC required to estimate the battery capacity.

[0022] The SOC estimation unit 13 acquires the start-point SOC indicating the SOC at the start point, and estimates the end-point SOC indicating the SOC at the end point based on the start-point SOC, the battery voltage at the start point, and the battery voltage at the end point. The battery capacity estimation unit 14 estimates the battery capacity based on the SOC difference between the start-point SOC and the end-point SOC, and the amount of charge (accumulated current value) obtained by integrating the current from the start point to the end point.

[0023] The charge / discharge sequence and the method for estimating battery capacity will be described below. Fig. 2 is a graph showing the current / voltage characteristics when charging according to the above charge / discharge sequence. Fig. 3 is a flowchart showing the steps of the battery capacity estimation method performed by the battery capacity estimation system according to this embodiment. The flowchart shown in Fig. 3 is repeatedly executed at a predetermined interval.

[0024] The controller 10 manages an estimated state variable (S) as a value indicating a control state for estimating battery capacity, and sets the estimated state variable (S) in accordance with the progress of the charge / discharge sequence. The initial value of the estimated state variable (S) is zero, increases as the sequence progresses, and is reset when the estimation of battery capacity is completed. In step S1, the controller 10 determines whether the estimated state variable (S) is zero. If the estimated state variable (S) is zero, in step S2, the battery capacity estimation unit 14 determines whether the zero current state has continued for a certain period (t ａ It is determined whether a certain period (t ａ The time required for the battery voltage to reach a constant voltage after the charge / discharge current is reduced to zero is preferably set to, for example, a relaxation waiting time or longer. ａ ) may be experimentally set. In the case where the secondary battery 1 has not been charged or discharged for a long period of time, such as when it is stored in a warehouse, the ａ ) waiting time is not required.

[0025] For a certain period of time (t ａ ) has not passed, the controller 10 temporarily ends the flow shown in FIG. 3 and restarts the control flow from step S1.

[0026] For a certain period of time (t ａ) has passed, the controller 10 performs the following control process in step S3. The battery voltage estimation unit 11 estimates the battery voltage (V ｏ The SOC estimation unit 13 estimates the battery voltage (V ｏ ) SOC corresponding to ０ That is, the SOC estimation unit 13 calculates the SOC based on the battery voltage when the charging / discharging current is zero. ０ The charge / discharge control unit 12 determines the charging current of the secondary battery 1 as a constant current (I １ The battery capacity estimation unit 14 sets the current integration (ΔAh ０ The current integration is calculated using the formula (ΔAh ０ +I １ ×ΔT ｐ ) and the period (ΔT ｐ ) is calculated. The controller 10 sets the estimated state variable (S) to "1." As shown in FIG. ０ At time t, the controller 10 executes the flow of step S3. ０ Thereafter, the secondary battery 1 is charged with a charging current (I １ ) and the battery voltage is V ｏ gradually rises from

[0027] After setting the estimated state variable (S) to "1", the control flow is executed again repeatedly, the determination flow of step S1 proceeds to "No", and in step S4, the controller 10 determines whether the estimated state variable (S) is "1". If the estimated state variable (S) is "1", in step S5, the battery capacity estimation unit 14 determines whether the estimated state variable (S) is "1" for a certain period (t ｂ It is determined whether a certain period (t ｂ ) is the time required for the state of charge of the electric double layer capacitance and the SOC distribution in the battery to settle after the current is applied, and should be set to be equal to or longer than the waiting time required to wait for the transient state of the secondary battery 1 to ease. ｂ ) may be set experimentally.

[0028] For a certain period of time (t ｂ If the predetermined period (t) has not elapsed, the controller 10 temporarily ends the flow shown in FIG. 3 and restarts the control flow from step S1.ｂ ) is passed, the control flow of steps S1, S4, and S5 is executed in a loop, and the current (I １ ) is continuously charged at a constant current.

[0029] For a certain period of time (t ｂ ) has passed, the controller 10 performs the following control process in step S6. The battery voltage estimation unit 11 estimates the battery voltage (V １ ) is estimated. １ ) is the voltage at the starting point. The battery capacity estimation unit 14 calculates the current integration (ΔAh ０ The SOC estimation unit 13 calculates the SOC at the start point using the following equation (2). １ Calculate SOC １ indicates the starting SOC of the secondary battery 1 (starting SOC). In addition, Ah ｂａｓｅ is the estimated value of the previous battery capacity, and in the case of the first time, it is the capacity of the new battery.

[0030] The battery capacity estimation unit 14 calculates the SOC from the SOC-OCV characteristics. １ OCV corresponding to １ The charge / discharge control unit 12 calculates the charging current of the secondary battery 1 as I ２ The battery capacity estimation unit 14 starts calculating the current integration (ΔAh). The current integration is calculated using the formula (ΔAh+I ２ ×ΔT ｐ ) and the period (ΔT ｐ The controller 10 sets the estimated state variable (S) to "2". The charging current (I ２ ) is the charging current (I １ ) or more, and in order to obtain a certain range of ΔSOC in a short time, the charging current (I １ ) is set to a value greater than the charging current (I ２ ) charging, the SOC will be SOC １ will increase from

[0031] As shown in FIG. １ At time t, the controller 10 executes the flow of step S6. １ Thereafter, the secondary battery 1 is charged with a charging current (I ２) and the battery voltage is V １ The battery capacity calculation starts from time t １ The period for waiting for the transient state to relax (t ｂ ) indicates that the battery voltage is not estimated and is not used to estimate the battery capacity.

[0032] After setting the estimated state variable (S) to "2", the control flow is executed again repeatedly, and the determination flow of steps S1 and S4 proceeds to "No". In step S7, the controller 10 determines whether the estimated state variable (S) is "2". If the estimated state variable (S) is "2", in step S8, the battery capacity estimation unit 14 determines whether the estimated state variable (S) is "2" for a certain period (t ｃ It is determined whether a certain period (t ｃ ) is the time during which the SOC difference between the start point and the end point is maintained so that the accuracy of the battery capacity estimation can be ensured. ｃ ) may be set by experimentally examining the relationship between the estimation accuracy and the SOC difference.

[0033] For a certain period of time (t ｃ If the predetermined period (t) has not elapsed, the controller 10 temporarily ends the flow shown in FIG. 3 and restarts the control flow from step S1. ｃ ) is passed, the control flow of steps S1, S4, S7, and S8 is executed in a loop, and the current (I ２ ) constant current charging continues.

[0034] For a certain period of time (t ｃ ) has elapsed, in step S9, the charge / discharge control unit 12 reduces the charging current of the secondary battery 1 to I ３ Set the charging current (I ３ ) is the charging current (I １ ) is the same size as (I ３ =I １ ) The controller 10 also sets the estimated state variable (S) to "3".

[0035] As shown in FIG. ２ At time t, the controller 10 executes the flow of step S9. ２ Thereafter, the secondary battery 1 is charged with a charging current (I ３) and the battery voltage gradually increases.

[0036] After setting the estimated state variable (S) to "3", the control flow is executed again repeatedly, and the judgment flow of steps S1, S4 and S7 proceeds to "No". In step S10, the controller 10 judges whether the estimated state variable (S) is "3". If the estimated state variable (S) is "3", in step S11, the battery capacity estimation unit 14 judges whether the estimated state variable (S) is "3". ｂ It is determined whether a certain period (t ｂ ) at time t ０ From time t １ For a certain period (t ｂ ) is the same length as

[0037] For a certain period of time (t ｂ If the predetermined period (t) has not elapsed, the controller 10 temporarily ends the flow shown in FIG. 3 and restarts the control flow from step S1. ｂ ) is passed, the control flow of steps S1, S4, S7, S10, and S11 is executed in a loop, and the current (I ３ ) constant current charging continues.

[0038] For a certain period of time (t ｂ ) has passed, the controller 10 performs the following control process in step S12. ２ ) is estimated. ２ ) is the voltage at the end point. The SOC estimation unit 13 estimates the battery voltage (V １ ) and battery voltage (V ２ ) and calculate the voltage difference (ΔV) １ By adding the voltage difference (ΔV) to ２ ) is calculated. ２ indicates the SOC at the end of the secondary battery 1 (end SOC). The SOC estimation unit 13 calculates the OCV from the SOC-OCV characteristics. ２ SOC corresponding to ２ The battery capacity estimation unit 14 calculates the SOC １ and SOC ２The battery capacity estimation unit 14 then calculates the SOC difference (ΔSOC) between the current accumulated value (ΔAh) and the current accumulated value (ΔAh). The battery capacity estimation unit 14 estimates the current battery capacity (Ah) of the secondary battery 1 using the following equation (3):

[0039] After estimating the current battery capacity (Ah) of the secondary battery 1, the controller 10 ends the control flow.

[0040] As shown in FIG. ３ At time t, the controller 10 executes the flow of step S12. ２ Thereafter, the secondary battery 1 is charged with a charging current (I ３ ) and the battery voltage gradually rises to V ２ The end point of the battery capacity calculation is set at time t ３ The period for waiting for the transient state to relax (t ｂ ) indicates that the battery voltage is not estimated and is not used to estimate the battery capacity.

[0041] Next, we will explain how the above-mentioned battery capacity estimation method can estimate the battery capacity with high accuracy in a short time. First, the controller 10 flows the same current at least at the start and end points of ΔSOC in order to consider the voltage fluctuation of the secondary battery 1 as a change in OCV. That is, during the first fixed period (t ｂ ) charging current (I １ ) and the second fixed period (t ｂ ) charging current (I ３ ) are set to the same magnitude. If the charging current is too large, the resistance will fluctuate due to temperature changes inside the secondary battery 1, the SOC distribution will increase, and the resistance loss will increase, which will deteriorate the estimation accuracy. １ , I ３ ) to a low current. For example, １ , I ３ ) should be set small within the allowable range determined by the measurement accuracy of the current sensor 4. This allows the battery capacity to be estimated with high accuracy in a short time. １ , I ３If the charging current (I) is too small, it takes a long time to estimate the battery capacity, so the current may be set within a range where deterioration in estimation accuracy is acceptable. １ , I ３ If ) is too small, the characteristics of the charge / discharge current become nonlinear, reducing the accuracy of estimating the resistance, so the current may be set to a value that does not cause nonlinearity.

[0042] Also, SOC １ and SOC ２ If the SOC difference (ΔSOC) between the charging current (I) and the charging current (I) is too small, the proportion of the resistance loss in ΔV becomes large, and the voltage fluctuation of the secondary battery 1 cannot be regarded as an OCV change due to the influence of the resistance loss fluctuation. ２ ) to the charging current (I １ , I ３ ) is set to be larger than the charging current (I ２ The upper limit of the charging current (I) is set according to the maximum power supplied by the charging device, or may be an upper limit current that can prevent the electrodeposition of lithium contained in the secondary battery 1. ２ ) to the charging current (I １ , I ３ ) and lengthen the period between the start and end points. This allows for highly accurate estimation of the battery capacity.

[0043] In the flowchart of the battery capacity estimation method, if the deterioration state of the secondary battery 1 is unknown at the time of the initial calculation of the battery capacity, the battery capacity (Ah ｂａｓｅ The battery capacity estimation unit 14 may then use the calculated battery capacity (Ah) to re-estimate the battery capacity. １ The battery capacity (Ah ｂａｓｅ) is replaced with the calculation result (Ah), and all SOC-OCV characteristics used in the calculation are switched to SOC-OCV characteristics corresponding to the calculation result Ah, and then the battery capacity can be calculated in the same manner as above. Also, although the above describes a method for estimating the battery capacity when the secondary battery 1 is being charged, the same method can also be applied to estimate the battery capacity when the secondary battery 1 is being discharged. That is, in the flowchart shown in FIG. 3, the charging current (I １ , I ２ , I ３ ) can be set to the same magnitude of discharge current.

[0044] As described above, the battery capacity estimation device or the battery capacity estimation method according to this embodiment measures or estimates the battery voltage of the secondary battery 1 and supplies a constant current I １ (corresponding to the "first current" of the present invention) for a certain period (t ｂ ) (corresponding to the "first time" of the present invention) or more, the charge and discharge of the secondary battery 1 is controlled up to the starting point, and after passing the starting point, the current I ２ By charging or discharging the secondary battery 1 at a constant current I (corresponding to the "second current" of the present invention), the charge and discharge of the secondary battery 1 is controlled so that the SOC of the secondary battery 1 changes by a predetermined change width or more from the starting point. １ (=I ３ ) for a certain period (t ｂ ) (corresponding to the "second time" of the present invention) or more, the controller 10 controls the charging and discharging of the secondary battery 1 until the end point. １ ) and obtain the starting SOC (SOC １ ), the starting battery voltage (V １ ), and the end point battery voltage (V ２ ) based on the end point SOC (SOC ２ ) and estimates the battery capacity (Ah) of the secondary battery 1 based on the SOC difference (ΔSOC) between the start point SOC and the end point SOC and the charge amount obtained by integrating the current from the start point to the end point (current integration: ΔAh). １ and I ３The same constant current is passed through the secondary battery 1, the SOC difference is calculated from the difference in battery voltage between the start point and the end point, and the battery capacity is calculated using the current integrated value (ΔAh) between the start point and the end point (ΔAh / ΔSOC). This eliminates the need to wait for the battery voltage to relax, and high-speed current control or measurement is not required. Furthermore, the battery capacity can be estimated without using a correlation between alternative indicators such as resistance and battery capacity. As a result, battery capacity can be estimated quickly, at low cost, and with high accuracy.

[0045] In this embodiment, the charge / discharge control unit 12 controls the charge current I １ (I ３ ) is reduced within the tolerance determined by the measurement accuracy of the current sensor. This reduces the effect of voltage fluctuations due to resistance loss and improves the accuracy of estimating battery capacity.

[0046] In this embodiment, the charge / discharge control unit 12 controls the charge current I ２ Charging current I １ (I ３ This makes it possible to quickly determine the difference between the SOC at the start point and the SOC at the end point, thereby enabling the battery capacity to be estimated in a short time.

[0047] In this embodiment, the charge / discharge control unit 12 controls the charging current I ２ Charging current I １ (I ３ For example, if charging is interrupted for some reason before reaching the end point in the charging sequence of FIG. 2, the battery voltage at the end point (V ２ ) cannot be obtained, so the battery capacity cannot be estimated. ２ Charging current I １ (I ３ ), even if charging is interrupted, the battery voltage at the end point (V ２ ) can be obtained and the battery capacity can be estimated.

[0048] As a first modification of this embodiment, a plurality of start points and end points may be provided as the timing for calculating the SOC required to estimate the battery capacity. Also, periods for flowing a charge current and a discharge current may be provided to obtain the battery voltage at a plurality of start points, respectively. Periods for flowing a charge current and a discharge current may be provided to obtain the battery voltage at a plurality of end points, respectively. The start points include a charge start point, which is the start point of the charge side, and a discharge start point, which is the start point of the discharge side, respectively. The end points include a charge end point, which is the start point of the charge side, and a discharge end point, which is the end point of the discharge side. The controller 10 calculates the SOC at each of the start point and end point of the charge side. １ and SOC ２ and estimate the SOC at the start and end of the discharge ３ and SOC ４ Then, the controller 10 estimates the SOC １ and SOC ２ SOC difference and SOC ３ and SOC ４ Alternatively, the battery capacity may be calculated for each SOC difference, and the final battery capacity may be estimated from the calculation results.

[0049] In the first modification, the charge / discharge control unit 12 charges the secondary battery 1 to a charge start point with a constant charge current, charges the secondary battery 1 to a discharge start point with a constant discharge current, and after the SOC has changed from the start point by a predetermined change width or more, charges the secondary battery 1 to a charge end point with the constant charge current and discharges the secondary battery 1 to a discharge end point with the constant discharge current. The SOC estimation unit 13 then acquires a charge start point SOC indicating the SOC at the charge start point, acquires a discharge start point SOC indicating the SOC at the discharge start point, estimates a charge end point SOC indicating the SOC at the charge end point based on the charge start point SOC, the battery voltage at the charge start point, and the battery voltage at the charge end point, and estimates a discharge end point SOC indicating the SOC at the discharge end point based on the discharge start point SOC, the battery voltage at the discharge start point, and the battery voltage at the discharge end point. Then, the battery capacity estimation unit 14 estimates the battery capacity based on the SOC difference between the charging start point SOC and the charging end point SOC, the charge amount obtained by integrating the current from the charging start point to the charging end point, the SOC difference between the discharging start point SOC and the discharging end point SOC, and the charge amount obtained by integrating the current from the discharging start point to the discharging end point.

[0050] The charge / discharge sequence and the method for estimating battery capacity in Modification 1 will be described below. Fig. 4 is a graph showing current / voltage characteristics when charging using the charge / discharge sequence in Modification 1. Figs. 5A and 5B are flowcharts showing the steps of the battery capacity estimation method performed by the battery capacity estimation system according to this embodiment. In the following description, the same content as the control flow shown in Fig. 3 among the control flows in Figs. 5A and 5B will be omitted, and the description of the same control flow will be appropriately cited from the above embodiment.

[0051] The control flow of steps S21 and S22 is the same as the control flow of steps S1 and S2. ａ ) has passed, the control flow proceeds to "Yes" in step S22, and the controller 10 executes the control flow of step S23. Of the control flow of step S23, the parts that are common to the control flow of step S3 will not be explained, and the differences will be explained below. The battery capacity estimation unit 14 calculates the current integration (ΔAh ０ａ , ΔAh ０ｂ ) calculation is started. ０ａ , ΔAh ０ｂ ) is the calculation formula (ΔAh ０ａ +I １ ×ΔT ｐ , ΔAh ０ｂ +I １ ×ΔT ｐ ) and the period (ΔT ｐ ) is calculated every time. ０ａ ) indicates the current integration up to the start of charging, and the current integration (ΔAh ０ｂ ) indicates the current integration up to the discharge start point. ０ At time t, the controller 10 executes the flow of step S3. ０ Thereafter, the secondary battery 1 is charged with a charging current (I １ ) is charged.

[0052] The control flow of step S24 is the same as the control flow of step S4. If the estimated state variable (S) is "1", the control flow proceeds to "Yes" in step S24, and in step S25, the battery capacity estimation unit 14 performs a predetermined period (t ｂ１It is determined whether a certain period (t ｂ１ ) is the time required for the state of charge of the electric double layer capacitance and the SOC distribution in the battery to settle after the current is applied, and should be set to be equal to or longer than the waiting time required to wait for the transient state of the secondary battery 1 to ease. ｂ１ ) may be set experimentally.

[0053] For a certain period of time (t ｂ１ ) has passed, the controller 10 performs the following control process in step S26. １ａ ) is estimated. １ ) is the voltage at the start of charging. The battery capacity estimation unit 14 calculates the current integration (ΔAh ０ａ The SOC estimation unit 13 calculates the SOC at the start of charging using the following equation (4): １ａ Calculate SOC １ａ indicates the SOC of the secondary battery 1 at the start of charging (start of charging SOC). In addition, Ah ｂａｓｅ is the estimated value of the previous battery capacity, and in the case of the first time, it is the capacity of the new battery.

[0054] The battery capacity estimation unit 14 calculates the SOC from the SOC-OCV characteristics. １ａ OCV corresponding to １ａ The charge / discharge control unit 12 calculates the current of the secondary battery 1 as the discharge current I １ Discharge current (I １ ) is the charging current (I １ ) and the direction of current flow is opposite. ａ The current integration is calculated using the formula (ΔAh ａ +I １ ×ΔT ｐ ) and the period (ΔT ｐ The controller 10 sets the estimated state variable (S) to "2".

[0055] As shown in FIG. １ａ At time t, the controller 10 executes the flow of step S26. １ａ At time t, the charge state changes to the discharge state.１ａ Thereafter, the secondary battery 1 discharges a current (I １ ) is discharged.

[0056] In step S27, the controller 10 determines whether the estimated state variable (S) is "2". If the estimated state variable (S) is "2", in step S28, the battery capacity estimation unit 14 ｂ２ It is determined whether a certain period (t ｂ２ ) is the time required for the state of charge of the electric double layer capacitance and the SOC distribution in the battery to settle after switching from charging to discharging, and should be set to be equal to or longer than the waiting time for waiting for the transient state of the secondary battery 1 to ease. ｂ２ ) may be set experimentally.

[0057] For a certain period of time (t ｂ２ ) has passed, the controller 10 performs the following control process in step S29. １ｂ ) is estimated. １ｂ ) is the voltage at the start of discharge. ０ｂ The SOC estimation unit 13 calculates the SOC at the start of discharge using the following equation (5): １ｂ Calculate SOC １ｂ indicates the SOC at the start of discharge of the secondary battery 1 (start of discharge SOC). In addition, Ah ｂａｓｅ is the estimated value of the previous battery capacity, and in the case of the first time, it is the capacity of the new battery.

[0058] The battery capacity estimation unit 14 calculates the SOC from the SOC-OCV characteristics. １ｂ OCV corresponding to １ｂ The charge / discharge control unit 12 calculates the current of the secondary battery 1 as the charging current I ２ The battery capacity estimation unit 14 sets the current integration (ΔAh ａ The current integration is calculated using the formula (ΔAh ａ +I ２ ×ΔT ｐ ) and the period (ΔT ｐ The controller 10 sets the estimated state variable (S) to "3".

[0059] As shown in FIG. １ｂ At time t, the controller 10 executes the flow of step S29. １ｂ At time t, the discharge changes to the charge. １ｂ Thereafter, the secondary battery 1 is charged with a charging current (I ２ ) is charged.

[0060] In step S30, the controller 10 determines whether the estimated state variable (S) is "3". If the estimated state variable (S) is "3", in step S31, the battery capacity estimation unit 14 ｃ It is determined whether a certain period (t ｃ ) is the time during which the SOC difference between the start point and the end point is maintained so that the accuracy of the battery capacity estimation can be ensured. ｃ ) may be set by experimentally examining the relationship between the estimation accuracy and the SOC difference.

[0061] For a certain period of time (t ｃ ) has elapsed, in step S32, the charge / discharge control unit 12 reduces the charging current of the secondary battery 1 to I ３ Set the charging current (I ３ ) is the charging current (I １ ) is the same size as (I ３ =I １ ) The controller 10 also sets the estimated state variable (S) to "4".

[0062] As shown in FIG. ２ａ At time t, the controller 10 executes the flow of step S32. ２ａ At this point, the charging current is I ２ From I ３ At time t ２ａ Thereafter, the secondary battery 1 is charged with a charging current (I ３ ) is charged.

[0063] In step S33, the controller 10 determines whether the estimated state variable (S) is "4". If the estimated state variable (S) is "4", in step S34, the battery capacity estimation unit 14 ｂ１ ) has elapsed.

[0064] For a certain period of time (t ｂ１ ) has passed, the controller 10 performs the following control process in step S35. The battery voltage estimation unit 11 estimates the battery voltage (V ２ａ ) is estimated. ２ａ ) is the voltage at the end point. １ａ ) and battery voltage (V ２ａ ) and the voltage difference (ΔV ａ ) and calculate the OCV １ａ voltage difference (ΔV ａ ) at the end point, the open circuit voltage (OCV ２ａ ) is calculated. ２ａ indicates the OCV at the end of charge of the secondary battery 1 (end of charge OCV). The SOC estimation unit 13 calculates the OCV from the SOC-OCV characteristics. ２ａ SOC corresponding to ２ａ The battery capacity estimation unit 14 calculates the SOC １ａ and SOC ２ａ SOC difference (ΔSOC ａ The battery capacity estimation unit 14 calculates the current integration (ΔAh ａ The battery capacity estimation unit 14 calculates the current battery capacity (Ah) of the secondary battery 1 using the following equation (6). ａ ) is estimated.

[0065] The charge / discharge control unit 12 controls the current of the secondary battery 1 to a discharge current I ３ Discharge current (I ３ ) is the charging current (I ３ ) and the direction of the current flow is opposite. The controller 10 sets the estimated state variable (S) to "5".

[0066] As shown in FIG. ２ｂ At time t, the controller 10 executes the flow of step S26. ２ｂ At time t, the charge state changes to the discharge state. ２ｂ Thereafter, the secondary battery 1 discharges a current (I ３ ) is discharged.

[0067] In step S36, the controller 10 determines whether the estimated state variable (S) is "5". If the estimated state variable (S) is "5", in step S37, the battery capacity estimation unit 14 ｂ２ ) has elapsed.

[0068] For a certain period of time (t ｂ２ ) has passed, the controller 10 performs the following control process in step S38. The battery voltage estimation unit 11 estimates the battery voltage (V ２ｂ ) is estimated. ２ｂ ) is the voltage at the end point. １ｂ ) and battery voltage (V ２ｂ ) and the voltage difference (ΔV ｂ ) and calculate the OCV １ｂ voltage difference (ΔV ｂ ) at the end point, the open circuit voltage (OCV ２ｂ ) is calculated. ２ｂ indicates the OCV at the end of discharge of the secondary battery 1 (end of discharge OCV). The SOC estimation unit 13 calculates the OCV from the SOC-OCV characteristics. ２ｂ SOC corresponding to ２ｂ The battery capacity estimation unit 14 calculates the SOC １ｂ and SOC ２ｂ SOC difference (ΔSOC ｂ The battery capacity estimation unit 14 calculates the current integration (ΔAh ｂ The battery capacity estimation unit 14 calculates the current battery capacity (Ah) of the secondary battery 1 using the following calculation formula (7). ｂ ) is estimated.

[0069] Then, the battery capacity estimation unit 14 calculates the battery capacity (Ah ａ ) and battery capacity (Ah ｂ ) and calculate the average of the battery capacity (Ah). The method of calculating the battery capacity (Ah) is not limited to averaging. For example, the battery capacity (Ah ａ ) and battery capacity (Ah ｂ) by a predetermined coefficient (weighting) and then add them up. In this way, the battery capacity estimation unit 14 estimates the battery capacity (Ah) based on the battery data from the start point to the end point on the charging side and the battery data from the start point to the end point on the discharging side.

[0070] In the battery capacity estimation device according to the first modification, the SOC estimation unit 13 acquires the charge start point SOC and the discharge start point SOC, estimates the charge end point SOC based on the charge start point SOC, the battery voltage at the charge start point, and the battery voltage at the charge end point, and estimates the discharge end point SOC based on the discharge start point SOC, the battery voltage at the discharge start point, and the battery voltage at the discharge end point. The battery capacity estimation unit 14 estimates the battery capacity based on the SOC difference between the charge start point SOC and the charge end point SOC, the charge amount obtained by integrating the current from the charge start point to the charge end point, the SOC difference between the discharge start point SOC and the discharge end point SOC, and the charge amount obtained by integrating the current from the discharge start point to the discharge end point. This allows the battery capacity to be estimated by acquiring the battery voltages at the start and end points both during charging and discharging, thereby suppressing deterioration in accuracy due to resistance loss.

[0071] In the charge / discharge sequence of Modification 1, charging is performed first, but discharging may be performed first and then charging, or charging may be performed first at the start point and discharging first at the end point. Furthermore, for example, if the battery capacity estimation system is installed in a vehicle, it is advisable to ensure a method of consuming the power generated by the battery, such as by having the drive motor consume ineffective power (zero driving force) during discharging.

[0072] In the charge / discharge sequence of Modification 1, charging and discharging are performed in the order of starting point charging, starting point discharging, terminal point charging, and terminal point discharging. However, charging and discharging may also be performed in the order of starting point charging, terminal point charging, starting point discharging, and terminal point discharging. In this case, it is preferable to provide a period of high current charging between the starting point charging and terminal point charging, and a period of high current discharging between the starting point discharging and terminal point discharging. This allows the charge capacity of the secondary battery after the terminal point discharging to be adjusted to the state before the starting point, making it suitable for storing the secondary battery 1.

[0073] In the first modification, the current at the starting point (I １ ) and the end point current (I ３) is the same magnitude, the discharge current (I １ , I ３ ) and charging current (I １ , I ３ The size of the terminal 1 may be different between the charging side and the non-charging side.

[0074] As a second modification of the present embodiment, the SOC estimation unit 13 may acquire a plurality of start-point SOCs and estimate a plurality of end-point SOCs, and the battery capacity estimation unit 14 may estimate the battery capacity based on the plurality of start-point SOCs and the plurality of end-point SOCs. ｂ ) is a long time, and then for a certain period (t ｂ ) at time (t １ During the period close to the start point, the battery voltage estimation unit 11 estimates the battery voltage (V １ For example, the battery voltage estimation unit 11 estimates the battery voltage (V １＿１ ~V １＿５ Then, the SOC estimation unit 13 estimates the battery voltage (V １＿１ ~V １＿５ ) for the starting SOC １＿１ ~Starting point SOC １＿５ The following is calculated. １＿１ ~SOC １＿５ The calculation method is the same as that in step S6, and current integration is also performed in the same way.

[0075] For example, in the charging sequence shown in FIG. ｂ ) is a long time, and then for a certain period (t ｂ ) at time (t ３ During the period close to the end point, the battery voltage estimation unit 11 estimates the battery voltage (V ２ ) is estimated multiple times. The number of times is the same at the start point and the end point. For example, the battery voltage estimation unit 11 estimates the battery voltage (V ２＿１ ~V ２＿５ Then, the SOC estimation unit 13 estimates the battery voltage (V ２＿１ ~V ２＿５ ) for the end point SOC ２＿１ ~End point SOC ２＿５ The following is calculated.２＿１ ~SOC ２＿５ The calculation method is the same as that in step S12, and current integration is also performed in the same way.

[0076] The battery capacity estimation unit 14 calculates the starting SOC １＿１ ~Starting point SOC １＿５ and the end point SOC ２＿１ ~End point SOC ２＿５ After matching the number of times, the SOC difference (ΔSOC １ ~ΔSOC ５ The battery capacity estimation unit 14 calculates the SOC difference (ΔSOC １ ~ΔSOC ５ ) to battery capacity (Ah １ ~Ah ５ ) are calculated respectively. １ ~Ah ５ The calculation method for the battery capacity (Ah) is the same as that in step S12. １ ~Ah ５ The final battery capacity (Ah) is estimated by taking the average or median of the battery capacity (Ah). １ ~Ah ５ Alternatively, a calculation method may be used in which the battery capacity estimation accuracy is increased by multiplying each of the battery capacity estimation accuracy values ​​(values) by a predetermined coefficient (weighting) and then adding the results. This allows for estimation of multiple battery capacities based on data from multiple start and end points, thereby enabling highly accurate estimation of battery capacities. Furthermore, even if there is a condition in which the accuracy of battery capacity estimation is likely to deteriorate due to the SOC sensitivity of resistance loss, SOC-OCV characteristics, etc., deterioration of accuracy can be suppressed.

[0077] In a third variation of this embodiment, the charge / discharge control unit 12 may control charging of the secondary battery 1 mounted on the vehicle in a normal charging mode, and the battery capacity estimation unit 14 may estimate the battery capacity from battery data of the secondary battery charged in the normal charging mode. As described above, the battery capacity estimation method of this embodiment assumes a charging sequence in which the secondary battery 1 is charged and discharged at a constant current. Therefore, if a battery capacity estimation system is mounted on a vehicle, a constant current cannot be generated while the vehicle is running because the current cannot be freely controlled. Furthermore, when the vehicle is stopped, the SOC may decrease, potentially interfering with driving. Furthermore, during rapid charging, although charging would normally be possible in a short time, estimating the battery capacity takes time. Therefore, by performing the battery capacity estimation method of this embodiment during normal charging, the battery capacity can be estimated without compromising user convenience.

[0078] Although the embodiments of the present invention have been described above, these embodiments are described to facilitate understanding of the present invention and are not described to limit the present invention. Therefore, each element disclosed in the above embodiments is intended to include all design modifications and equivalents that fall within the technical scope of the present invention.

[0079] REFERENCE SIGNS LIST 1 secondary battery 2 DC-DC converter 3 voltage sensor 4 current sensor 10 controller 11 battery voltage estimation unit 12 charge / discharge control unit 13 SOC estimation unit 14 battery capacity estimation unit

Claims

A battery capacity estimation device for estimating the battery capacity of a secondary battery, comprising: a battery voltage estimation unit that measures or estimates the battery voltage of the secondary battery; a charge and discharge control unit that controls the charge and discharge of the secondary battery; a state of charge (SOC) estimation unit that estimates the state of charge of the secondary battery; a battery capacity estimation unit that estimates the battery capacity; The charge and discharge control unit controls the charge and discharge of the secondary battery up to a starting point by charging or discharging the secondary battery with a constant first current for a first time or longer; after passing the starting point, controls the charge and discharge of the secondary battery by charging or discharging with a second current so that the SOC changes by a predetermined change width or more from the starting point; controls the charge and discharge of the secondary battery up to an end point by charging or discharging the secondary battery with the constant first current for a second time or longer; The state of charge estimation unit acquires a starting point SOC indicating the SOC at the starting point; estimates an end point SOC indicating the SOC at the end point based on the starting point SOC, the battery voltage at the starting point, and the battery voltage at the end point; The battery capacity estimation unit is a battery capacity estimation device that estimates the battery capacity based on the SOC difference between the starting point SOC and the end point SOC, and the charge amount obtained by integrating the current from the starting point to the end point. 　 The battery capacity estimation device according to claim 1, wherein the charge and discharge control unit is a battery capacity estimation device that reduces the first current within an allowable range determined by the measurement accuracy of a current sensor. 　 The battery capacity estimation device according to claim 1 or 2, wherein the charge and discharge control unit is a battery capacity estimation device that makes the second current larger than the first current. 　 The battery capacity estimation device according to claim 1 or 2, wherein the charge and discharge control unit is a battery capacity estimation device that makes the second current the same size as the first current. 　 The battery capacity estimation device according to any one of claims 1 to 4, wherein the starting point includes a charging starting point that is a starting point on the charging side and a discharging starting point that is a starting point on the discharging side; the end point includes a charging end point that is a starting point on the charging side and a discharging end point that is an end point on the discharging side; the charge and discharge control unit charges the secondary battery with a constant charging current up to the charging starting point; charges the secondary battery with a constant discharging current up to the discharging starting point; after the SOC changes by a predetermined change width or more from the starting point, charges the secondary battery with the constant charging current up to the charging end point and discharges the secondary battery with the constant discharging current up to the discharging end point; The state of charge estimation unit acquires a charging starting point SOC indicating the SOC at the charging starting point; Obtain a discharge start SOC indicating the SOC of the discharge start point, Based on the charge start SOC, the battery voltage at the charge start point, and the battery voltage at the charge end point, estimate a charge end SOC indicating the SOC at the charge end point, Based on the discharge start SOC, the battery voltage at the discharge start point, and the battery voltage at the discharge end point, estimate a discharge end SOC indicating the SOC at the discharge end point, The battery capacity estimation unit, A battery capacity estimation device that estimates the battery capacity based on the SOC difference between the charge start SOC and the charge end SOC, the charge amount obtained by integrating the current from the charge start point to the charge end point, the SOC difference between the discharge start SOC and the discharge end SOC, and the charge amount obtained by integrating the current from the discharge start point to the discharge end point. 　 The battery capacity estimation device according to any one of claims 1 to 4, The state of charge estimation unit, Obtain a plurality of the start SOCs, Estimate a plurality of the end SOCs, A battery capacity estimation device in which the battery capacity estimation unit estimates the battery capacity based on the plurality of start SOCs and the plurality of end SOCs. 　 The battery capacity estimation device according to any one of claims 1 to 5, The charge and discharge control unit, Controls charging of the secondary battery mounted on the vehicle in a normal charging mode, The battery capacity estimation unit, A battery capacity estimation device that estimates the battery capacity from battery data of the secondary battery charged in the normal charging mode. 　 A battery capacity estimation method executed by a processor for estimating the battery capacity of a secondary battery, The processor, Measures or estimates the battery voltage of the secondary battery, Controls charging and discharging of the secondary battery up to a start point by charging or discharging the secondary battery with a constant first current for a predetermined first time or more, After passing the start point, controls charging and discharging of the secondary battery by charging or discharging with a second current so that the state of charge (SOC) of the secondary battery changes by a predetermined change width or more from the start point, Controls charging and discharging of the secondary battery up to an end point by charging or discharging the secondary battery with the constant first current for a predetermined second time or more, Obtain a start SOC indicating the SOC of the start point, Based on the start SOC, the battery voltage at the start point, and the battery voltage at the end point, estimate an end SOC indicating the SOC at the end point, A battery capacity estimation method for estimating the battery capacity of the secondary battery based on the SOC difference between the start SOC and the end SOC and the charge amount obtained by integrating the current from the start point to the end point.

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