Battery resistance estimation device and battery resistance estimation method

Abstract

To provide a battery resistance estimation device that can estimate a battery resistance with high accuracy.SOLUTION: A battery resistance estimation device comprises: a battery voltage estimation part 11 that measures or estimates the battery voltage of a secondary battery 1; a charge and discharge control unit 12 that controls the charging and discharging of the secondary battery 1; a charge state estimation part 13 that estimates the charge state (SOC) of the secondary battery 1; and a battery resistance estimation part 14 that estimates the battery resistance. The charge state estimation part 13 acquires an initial SOC, and estimates a terminal SOC based on the initial SOC, an initial battery voltage, and a terminal battery voltage. The battery resistance estimation part 14 calculates an initial OCV or a terminal OCV using the SOC-OCV characteristic relationship from the initial SOC or terminal SOC, calculates an estimated OCV, and estimates a resistance based on an initial or terminal battery voltage, an initial or terminal SOC, an estimated battery voltage, and the estimated OCV.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] Conventionally, an estimation method for estimating a polarization electromotive voltage has been known. For example, the estimation method described in Patent Document 1 estimates a polarization value fdyn based on the current battery state quantity, and corrects the polarization value fdyn by multiplying it by a polarization value correction rate kf. Further, the sequentially estimated polarization values are attenuated according to a predetermined time constant and then time-integrated to estimate a polarization electromotive voltage Vdyn that reflects the charge and discharge history of the battery.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the estimation method described in Patent Document 1 above, when the battery deteriorates, the estimation accuracy of the polarization electromotive force decreases, and thus there is a problem that the battery resistance cannot be accurately estimated from the polarization electromotive voltage estimated by the above method.

[0005] The problem to be solved by the present invention is to provide a battery resistance estimation device and a battery resistance estimation method capable of accurately estimating the battery resistance with high precision.

Means for Solving the Problems

[0006] The present invention controls the charge and discharge of a secondary battery up to a starting point by charging or discharging the secondary battery at a constant current for 1 hour or more, and controls the charge and discharge of the secondary battery so that the state of charge (SOC) changes by a predetermined change width or more from the starting point by charging or discharging after passing the starting point. The charge and discharge of the secondary battery are controlled by charging or discharging the secondary battery at a constant current for 2 hours or more up to an end point, an estimated current larger than the constant current is passed through the secondary battery, the starting point SOC is obtained, and the end point SOC is estimated based on the starting point SOC, the battery voltage at the starting point, and the battery voltage at the end point. The starting point OCV or the end point OCV is calculated from the starting point SOC or the end point SOC using the relationship of the SOC-OCV characteristics, the estimated OCV is calculated, and the resistance is estimated based on the battery voltage at the starting point or the end point, the starting point SOC or the end point SOC, the estimated battery voltage, and the estimated OCV, thereby solving the above problems.

Advantages of the Invention

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

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

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

[0010] As shown in FIG. 1, the battery control system includes a secondary battery 1, a DCDC converter 2, a voltage sensor 3, a current sensor 4, and a controller 10. The secondary battery 1 includes a battery pack in which a plurality of batteries are connected. The secondary battery 1 is, for example, a lithium-ion secondary battery. As this lithium-ion secondary battery, for example, although not particularly limited, examples include those using silicon or an active material containing silicon as the negative electrode active material, or those using an active material containing sulfur as the positive electrode active material. Further, as the secondary battery 1, an electrolytic solution lithium-ion secondary battery may be used, or a all-solid-state lithium-ion secondary battery may also be used.

[0011] Although not particularly shown, the positive electrode of the battery included in the secondary battery 1 is electrically connected to the negative electrode of another battery via a bus bar. That is, the plurality of batteries included in the secondary battery 1 are modularized by being connected via a bus bar.

[0012] The DCDC converter 2 is a power conversion device that converts the voltage input from the secondary battery 1 into 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 into a predetermined voltage and outputs power to the secondary battery 21. This DCDC converter 2 is controlled by the 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 wirings connected to the positive electrode and the negative electrode 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 electrode or the negative electrode of the secondary battery 1. The voltage sensor 3 and the current sensor 4 detect the state of the battery and output the detected values to the controller 10.

[0014] The controller 10 is a battery control unit (BCU). 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 controls the charge and discharge of the secondary battery 1 and estimates the battery resistance of the secondary battery 1. The controller 10 is composed of a memory such as a ROM or a RAM, and a processor such as a CPU. The controller 10 also has a battery voltage estimation unit 11, a charge / discharge control unit 12, a SOC estimation unit 13, and a battery resistance estimation unit 14 as functional blocks for controlling the charge and discharge 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 the detected value from the voltage sensor 3. The battery voltage estimation unit 11 may also estimate the battery voltage by performing a predetermined arithmetic process or correction process on the detected value of the voltage sensor 3.

[0016] The charge / discharge control unit 12 controls the charge and discharge of the secondary battery 1. In the present embodiment, as will be described later, the charge and / or discharge of the secondary battery 1 is performed to estimate the battery resistance of the secondary battery 1. A charge / discharge current for estimating the battery resistance 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 is 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 the charge and discharge current (current integration). The SOC estimation unit 13 also estimates the SOC based on the correlation between the SOC and the open-circuit voltage (OCV) of the secondary battery 1 (SOC-OCV characteristic). The SOC-OCV characteristic is a characteristic determined according to the materials, structure, etc. used in the secondary battery 1 and can be specified from experimental data. The controller 10 may store a table indicating the SOC-OCV characteristic in the memory, and the SOC estimation unit 13 may estimate the SOC by referring to the table. Note that since the SOC-OCV characteristic changes according to the degradation state of the secondary battery 1, the SOC estimation unit 13 may correct the SOC-OCV characteristic according to the degradation state of the secondary battery 1.

[0018] The battery resistance estimation unit 14 estimates the battery resistance of the secondary battery 1. The battery resistance estimation unit 14 may estimate the battery resistance of the secondary battery 1 during charge and discharge of the secondary battery 1. When estimating the battery capacity, the battery resistance estimation unit 14 outputs a control command to the charge and discharge control unit 12 so that the secondary battery 1 is charged and discharged in a charge and discharge sequence.

[0019] Incidentally, as a method for calculating the battery resistance of the secondary battery 1, there is the following method. First, the SOC of the secondary battery 1 is charged to, for example, 50 percent, and voltage relaxation is waited until the battery voltage of the secondary battery 1 becomes the OCV, and then discharged for a predetermined time. Such measurements are repeated while changing the current, and the voltage change (ΔV) from the OCV according to the magnitude of the current is measured. Then, the measured current and the voltage change are plotted to obtain a regression line, and the battery resistance (DCR) can be calculated from the slope of the regression line. However, in such a method, since there is a waiting time until the battery voltage becomes the OCV, it takes time to calculate the battery resistance.

[0020] The OCV can generally be obtained from the relationship of the SOC-OCV characteristic. During charge and discharge of the secondary battery 1, it is difficult to accurately grasp the OCV, and even if charging or discharging is performed to obtain a desired SOC, it is difficult to obtain the OCV in a short time.

[0021] Therefore, in the present embodiment, attention is paid to the fact that the battery voltage characteristics when the secondary battery 1 is charged and discharged with a constant current become characteristics similar to the SOC-OCV characteristics, and the OCV is obtained. For example, when the secondary battery 1 is charged with a constant current, the battery voltage (cell voltage) of the secondary battery 1 increases as the charging time elapses, and the SOC gradually increases. At this time, the battery voltage of the secondary battery 1 is a voltage obtained by adding the voltage corresponding to the resistive loss caused by the internal resistance of the secondary battery 1 and the OCV. During the charging of the secondary battery 1, the voltage change caused by the change in the internal resistance is limited compared to the OCV change. That is, when the constant current charging of the secondary battery 1 progresses and the battery voltage increases, the voltage corresponding to the resistive loss does not change so much at low SOC and high SOC, and as the OCV increases, the battery voltage increases, and the battery voltage characteristics in constant current charging are similar to the SOC-OCV characteristics. In addition, since the voltage corresponding to the resistive loss changes depending on the magnitude of the charging current, by reducing the charging current, the voltage change corresponding to the resistive loss can be suppressed. That is, by charging and discharging the secondary battery 1 with a constant current and treating the voltage change of the battery voltage equivalently to the OCV change, the OCV can be calculated even during the charge and discharge current of the secondary battery 1, and the battery resistance of the secondary battery 1 can be estimated with high accuracy in a short time.

[0022] In this embodiment, in order to estimate the battery resistance while making the battery voltage characteristics and the SOC-OCV characteristics similar when charging and discharging the secondary battery 1, a charge and discharge sequence for estimating the battery resistance is predetermined. The charge and discharge control unit 12 charges the secondary battery 1 in the following charge and discharge sequence according to a control command from the battery resistance estimation unit 14. First, the charge and discharge control unit 12 controls the charge and discharge of the secondary battery 1 from the no-load state of the secondary battery 1 to the starting point by charging or discharging the secondary battery 1 with a constant first current (constant current) for a first time or longer. The starting point is the operation timing of the SOC required for estimating the battery resistance. Next, after passing the starting point, the charge and discharge control unit 12 controls the charge and discharge of the secondary battery 1 so that the SOC of the secondary battery 1 changes by a predetermined change width or more by charging or discharging. Then, the charge and discharge control unit 12 controls the charge and discharge of the secondary battery to the end point by charging or discharging the secondary battery 1 with a constant first current (constant current) for a second time or longer. The end point is the operation timing of the SOC required for estimating the battery resistance. Also, in the charge and discharge sequence for estimating the battery resistance, the charge and discharge control unit 12 passes an estimation current larger than the current. The estimation current may be passed between the starting point and the end point. For example, after passing the starting point, the current when charging or discharging the secondary battery 1 so that the SOC of the secondary battery 1 changes by a predetermined change width or more may be used as the estimation current. Also, the current when charging or discharging the secondary battery 1 with a constant first current (constant current) for a second time or longer may be used as the estimation current.

[0023] Then, the SOC estimation unit 13 acquires the starting point SOC indicating the SOC of the starting point, and estimates the end point SOC indicating the SOC of the end point based on the starting point SOC, the battery voltage at the starting point, and the battery voltage before the end point. The battery resistance estimation unit 14 calculates the starting point OCV indicating the open circuit voltage (OCV) of the starting point or the end point OCV indicating the OCV of the end point from the starting point SOC or the end point SOC using the relationship of the SOC-OCV characteristics, and calculates the estimation OCV indicating the OCV when the estimation current is passed through the secondary battery 1. Also, the battery resistance estimation unit 14 estimates the battery resistance based on the battery voltage at the starting point or the end point, the starting point SOC or the end point SOC, the estimation battery voltage indicating the battery voltage when the estimation current is passed through the secondary battery 1, and the estimation OCV.

[0024] The charge-discharge sequence and the method for estimating the battery resistance will be described below. FIG. 2 is a graph showing the current / voltage characteristics when charging with the above charge-discharge sequence. FIG. 3 is a flowchart showing the procedure of the battery resistance estimation method by the battery resistance estimation system according to the present embodiment. Note that the flowchart shown in FIG. 3 is repeatedly executed at a predetermined cycle.

[0025] The controller 10 manages an estimated state variable (S) as a value indicating a control state for estimating the battery resistance, and sets the estimated state variable (S) in accordance with the transition 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 the battery resistance ends. In step S1, the controller 10 determines whether the estimated state variable (S) is zero. If the estimated state variable (S) is zero, then in step S2, the battery resistance estimation unit 14 determines whether a state of zero current has elapsed for a certain period (t а ). The certain period (t а ) is the time required for the battery voltage to reach a constant voltage after setting the charge-discharge current to zero, and may be set to, for example, be equal to or longer than the relaxation waiting time. The certain period (t а ) may be set experimentally. Note that when the secondary battery 1 has been stored in a warehouse or the like and a state of not being charged or discharged for a long time continues, the waiting time of the certain period (t а ) is not necessary.

[0026] If the certain period (t а ) has not elapsed, the controller 10 temporarily ends the flow shown in FIG. 3 and resumes the control flow from step S1.

[0027] If the certain period (t а ) has elapsed, then in step S3, the controller 10 performs the following control process. The battery voltage estimation unit 11 estimates the battery voltage (V o ) of the secondary battery 1. The SOC estimation unit 13 estimates the battery voltage (V oCalculate the SOC0 corresponding to (0). That is, the SOC estimation unit 13 obtains SOC0 based on the battery voltage when the charge and discharge current is zero. The charge and discharge control unit 12 sets the charge current of the secondary battery 1 to a constant current (I1). The battery resistance estimation unit 14 starts the calculation of the current integration (ΔAh0). The current integration is calculated by the arithmetic formula (ΔAh0 + I1×ΔT p ) at each period (ΔT p ). The controller 10 sets the estimated state variable (S) to "1". As shown in FIG. 2, at time t0, the controller 10 performs the flow of step S3. After time t0, the secondary battery 1 is charged with the charging current (I1), and the battery voltage gradually rises from V o .

[0028] After setting the estimated state variable (S) to "1", the control flow is repeatedly executed again. 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 resistance estimation unit 14 determines whether a certain period (t b ) has elapsed. The certain period (t b ) is the time required for the charge state of the electric double layer capacitor and the SOC distribution in the battery to settle after flowing the current, and it may be set to be longer than the waiting time for relaxing the transient state of the secondary battery 1. The certain period (t b ) may be set experimentally.

[0029] If the certain period (t b ) has not elapsed, the controller 10 temporarily ends the flow shown in FIG. 3 and resumes the control flow from step S1. Until the certain period (t b ) elapses, the control flows of steps S1, S4, and S5 are looped and executed, and the constant current charging of the current (I1) continues.

[0030] If the certain period (t b) When the above has elapsed, in step S6, the controller 10 performs the following control process. The battery voltage estimation unit 11 estimates the battery voltage (V1) of the secondary battery 1. The battery voltage (V1) is the starting voltage. The battery resistance estimation unit 14 finishes the calculation of the current integration (ΔAh0). The SOC estimation unit 13 calculates the SOC1 at the starting point from the following arithmetic expression (1). SOC1 indicates the SOC (starting SOC) at the starting point of the secondary battery 1.

Number

[0031] The battery resistance estimation unit 14 calculates the OCV1 corresponding to SOC1 from the SOC-OCV characteristics. The charge and discharge control unit 12 sets the charging current of the secondary battery 1 to I2. The battery resistance estimation unit 14 starts the calculation of the current integration (ΔAh). The current integration is calculated by the arithmetic expression (ΔAh + I2×ΔT p ) and is calculated every period (ΔT p ). The controller 10 sets the estimated state variable (S) to "2". The charging current (I2) is equal to or greater than the charging current (I1), and in order to obtain a certain width of ΔSOC in a short time, it may be set to a value larger than the charging current (I1). Due to the charging of the charging current (I2), the SOC will change by more than a predetermined change width (ΔSOC) from the starting point.

[0032] As shown in FIG. 2 at time t1, the controller 10 executes the flow of step S6. After time t1, the secondary battery 1 is charged with the charging current (I2), and the battery voltage gradually rises from V1. Also, the starting point of the battery capacity calculation is set as time t1, and within the period (t b ) for waiting for the relaxation of the transient state, the battery voltage is not estimated and the battery voltage is not used for the estimation of the battery resistance.

[0033] After setting the estimated state variable (S) to "2", the control flow is executed repeatedly again. The determination flows of steps S1 and S4 proceed to "No", and at step S7, the controller 10 determines whether the estimated state variable (S) is "2". If the estimated state variable (S) is "2", then at step S8, the battery resistance estimation unit 14 determines whether a certain period (t c ) has elapsed. The certain period (t c ) is a time during which a difference in SOC can be created between the starting point and the ending point so as to ensure the accuracy of the battery capacity estimation. The certain period (t c ) may be set by experimentally examining the relationship between the estimation accuracy and the SOC difference.

[0034] If the certain period (t c ) has not elapsed, the controller 10 temporarily ends the flow shown in FIG. 3 and resumes the control flow from step S1. Until the certain period (t c ) elapses, the control flows of steps S1, S4, S7, and S8 are looped and executed, and the constant current charging of the current (I2) continues.

[0035] If the certain period (t c ) has elapsed, then at step S9, the charge and discharge control unit 12 sets the charging current of the secondary battery 1 to I3. The charging current (I3) has the same magnitude as the charging current (I1) (I3 = I1). Also, the controller 10 sets the estimated state variable (S) to "3".

[0036] As shown in FIG. 2, at the time point of time t3, the controller 10 executes the flow of step S9. After time t3, the secondary battery 1 is charged with the charging current (I3), and the battery voltage gradually increases.

[0037] After setting the estimated state variable (S) to "3", the control flow is executed repeatedly again. The determination flows of steps S1, S4, and S7 proceed to "No", and at step S10, the controller 10 determines whether the estimated state variable (S) is "3". If the estimated state variable (S) is "3", then at step S11, the battery resistance estimation unit 14 determines whether a certain period (t bDetermine whether it has passed through (). For a certain period (t b ) is a certain period (t) from time t0 to time t1 b ) is the same length as.

[0038] If a certain period (t b ) has not passed, the controller 10 temporarily ends the flow shown in FIG. 3 and resumes the control flow from step S1. Until a certain period (t b ) has passed, the control flows of steps S1, S4, S7, S10, and S11 are looped and executed, and the constant current charging of the current (I3) continues.

[0039] When a certain period (t b ) has passed, in step S12, the controller 10 performs the following control process. The battery voltage estimation unit 11 estimates the battery voltage (V2) of the secondary battery 1. The battery voltage (V2) is the voltage at the end point. The SOC estimation unit 13 calculates the voltage difference (ΔV) between the battery voltage (V1) and the battery voltage (V2), and adds the voltage difference (ΔV) to OCV1 to calculate the open circuit voltage (OCV2) at the end point. SOC2 indicates the SOC at the end point (end point SOC) of the secondary battery 1. The SOC estimation unit 13 calculates SOC2 corresponding to OCV2 from the SOC-OCV characteristics. The battery resistance estimation unit 14 calculates the SOC difference (ΔSOC) between SOC1 and SOC2. The battery resistance estimation unit 14 finishes calculating the current integration (ΔAh). The controller 10 estimates the current battery capacity (Ah) of the secondary battery 1 from the following arithmetic formula (2).

Equation

[0040] As shown in FIG. 2, at time t2, the controller 10 executes the flow of step S12. After time t3, the secondary battery 1 is charged with the charging current (I3), and the battery voltage gradually rises to reach V2. Also, the end point of the calculation of the battery capacity is set as time t2, and within the period (t b ) for waiting for the relaxation of the transient state, the battery voltage is not estimated and the battery voltage is not used for the estimation of the battery resistance.

[0041] In step S13, the controller 10 performs the following control process. The battery voltage estimation unit 11 estimates the battery voltage (V3) of the secondary battery 1. The battery voltage (V3) is the voltage at time t3 and corresponds to the intermediate voltage between the start point and the end point. The battery resistance estimation unit 14 calculates the current integration (ΔAh1) by multiplying the charging current (I3) during a certain period (t b ) until the end point. The current integration (ΔAh1) corresponds to the integrated value of the current (I3) flowing during a certain period (t b ). The SOC estimation unit 13 estimates SOC3 from the following arithmetic expression (3).

Equation

[0042] The battery resistance estimation unit 14 calculates the estimated OCV (OCV3) corresponding to SOC3 from the SOC-OCV characteristics. The estimated OCV corresponds to the calculated value of the OCV when the estimated current is flowing through the secondary battery 1. In other words, the estimated OCV corresponds to the OCV in that state by flowing a current with a magnitude different from that of the constant current (I1) for estimating the battery resistance. The battery resistance estimation unit 14 calculates the voltage difference (ΔV L ) by subtracting OCV2 from the battery voltage (V2). Note that the battery resistance estimation unit 14 may calculate the voltage difference (ΔV L ) by subtracting OCV1 from the battery voltage (V1). The battery resistance estimation unit 14 calculates the voltage difference (ΔV H ) by subtracting OCV3 from the battery voltage (V3). The battery resistance estimation unit 14 plots the current (I1 or I3 and I2) and the voltage changes (ΔV L , ΔV H ) to obtain a regression line, and estimates the current battery resistance from the slope of the regression line. After estimating the current battery resistance of the secondary battery 1, the controller 10 ends the control flow.

[0043] Next, the point that a highly accurate battery resistance can be estimated in a short time by the above battery resistance estimation method will be described. First, in order for the controller 10 to regard the voltage fluctuation of the secondary battery 1 as almost an OCV change, the same current is passed at least at the start point and the end point of ΔSOC. That is, among the charge and discharge sequences, the charging current (I1) passed during the first fixed period (t b ) and the charging current (I3) passed during the second fixed period (t b ) are made the same magnitude. Also, if the charging current is too large, the resistance fluctuation due to the temperature change inside the secondary battery 1 and the SOC distribution become large, and the estimation accuracy deteriorates due to the large resistance loss. Therefore, the charging currents (I1, I3) are set to low currents. For example, the charging currents (I1, I3) may be made small within the allowable range determined from the measurement accuracy of the current sensor 4. Thereby, the battery resistance can be estimated with high accuracy and in a short time. Note that if the charging currents (I1, I3) are too small, it takes time to estimate the battery capacity, so the current magnitude may be set within the range where the deterioration of the estimation accuracy is acceptable. Also, if the charging currents (I1, I3) are too small, the characteristics of the charge and discharge current become non-linear and the estimation accuracy of the resistance decreases, so the current magnitude may be set so as not to become non-linear.

[0044] Also, if the SOC difference (ΔSOC) between SOC1 and SOC2 is too small, the ratio of the resistance loss in ΔV becomes large and it is affected by the fluctuation of the resistance loss, and the voltage fluctuation of the secondary battery 1 cannot be regarded as an OCV change. Therefore, ΔSOC is set to a certain width (magnitude) or more. Preferably, the charging current (I2) is made larger than the charging currents (I1, I3). Thereby, the battery capacity can be estimated with high accuracy and in a short time. Note that the upper limit of the charging current (I2) may be set according to the maximum supply power of the charging device, or may be the upper limit current that can avoid the electrodeposition of lithium contained in the secondary battery 1. To increase the SOC difference (ΔSOC), the charging current (I2) may be made the same magnitude as the charging currents (I1, I3) and the period between the start point and the end point may be lengthened. Thereby, the battery resistance can be estimated with high accuracy.

[0045] Also, in the above battery resistance estimation method, at least two types of currents with different magnitudes are passed through the secondary battery 1 in the charge-discharge sequence. And since the time for measuring the start point and the end point is short, the cumulative error of the SOC calculation by current integration at that time can be ignored.

[0046] In the battery resistance estimation method flowchart, when the degradation state of the secondary battery 1 is unknown at the first calculation of the battery resistance, once the battery capacity (Ah base ) at the time of new product is used to calculate the battery capacity (Ah). And the battery resistance estimation unit 14 may estimate the battery capacity again using the calculation result (Ah) of the battery capacity. At this time, replace the battery capacity (Ah base ) used for the calculation of SOC1 at the start point with the calculation result (Ah), and further switch all the SOC-OCV characteristics used in the calculation to the SOC-OCV characteristics corresponding to the calculation result Ah, and then calculate the battery capacity in the same manner as above. Also, in the above, the battery resistance estimation method when charging the secondary battery 1 was described, but the same method can be applied to estimate the battery capacity and the battery resistance also during the discharge of the secondary battery 1. That is, in the flowchart shown in FIG. 3, the charging currents (I1, I2, I3) may be set to discharge currents of the same magnitude.

[0047] As described above, the battery resistance estimation device or the battery resistance estimation method according to the present embodiment measures or estimates the battery voltage of the secondary battery 1, and charges or discharges the secondary battery at a constant current I1 (constant current) for a certain period (t b )(corresponding to the "first time" of the present invention) or more to control the charge and discharge of the secondary battery 1 up to the start point, and after passing the start point, by charging or discharging, the charge and discharge of the secondary battery 1 are controlled so that the SOC of the secondary battery 1 changes by a predetermined change width or more from the start point, and the secondary battery 1 is charged or discharged at a constant current I1 for a certain period (t b)(Corresponding to the "second hour" of the present invention), by charging or discharging for a time longer than this, the charge and discharge of the secondary battery 1 are controlled until the end point. Further, the controller 10 passes an estimated current (I2) larger than the constant currents (I1, I3) through the secondary battery 1. The controller 10 acquires the starting point SOC (SOC1), and estimates the end point SOC (SOC2) based on the starting point SOC (SOC1), the battery voltage (V1) at the starting point, and the battery voltage (V2) at the end point. The controller 10 calculates the starting point OCV or the end point OCV using the relationship of the SOC-OCV characteristics from the starting point SOC or the end point SOC, and calculates the estimated OCV. The controller 10 estimates the battery resistance based on the battery voltage at the starting point or the end point, the starting point SOC or the end point SOC, the intermediate voltage (corresponding to the "estimated battery voltage" of the present invention) indicating the battery voltage when the estimated current is passed through the secondary battery 1, and the estimated OCV. As a result, since there is no need to wait until the battery voltage becomes the OCV, the battery resistance can be estimated in a short time and with high accuracy.

[0048] Also, in the present embodiment, the charge and discharge control unit 12 reduces the charging current I1 (I3) within an allowable range determined by the measurement accuracy of the current sensor. Thereby, the influence of the voltage fluctuation due to the resistive loss component can be reduced, and the estimation accuracy of the battery resistance can be improved.

[0049] In the present embodiment, a certain period (t b ) until the end may be made longer than a certain period (t b ) until the starting point. That is, in FIG. 2, the period from time t3 to time t2 may be made longer than the period from time t0 to time t1. Since measurement is performed after changing from a state of zero current to a low current (I1) at the starting point, the amount of change in current is small, but at the end point, measurement is performed after changing from a large current (I2) flowing to achieve the desired SOC to a constant current (I3), so the amount of change in current becomes larger than at the starting point. Therefore, a certain period (t b ) until the end is made longer than a certain period (t b ) until the starting point. Thereby, while suppressing the influence of the transient change after the current change, the time required for the total resistance estimation can be shortened.

[0050] In this embodiment, during the switching from the estimated current (I2) to the constant current (I3), the charge / discharge control unit 12 may cause a current in the direction opposite to the constant current (I3) to flow through the secondary battery 1. That is, in FIG. 2, after time t3, a discharge current is caused to flow for a short period of time, and then the constant current (I3) is caused to flow to charge the secondary battery 1. That is, instead of just waiting for the transient state of the secondary battery 1 to relax, a current in the reverse direction is caused to flow. As a result, the transient state can be relaxed in a short time, and the time required for estimating the battery resistance can be shortened. When the switching from the estimated current (I2) to the constant current (I3) is a switching of the discharge current, a charging current may be caused to flow during the switching from the estimated current (I2) to the constant current (I3).

[0051] As a first modification example of this embodiment, after changing the SOC by a predetermined change width or more from the starting point, the charge / discharge control unit 12 may make the charge / discharge current from the starting point to the ending point multi-stage. FIG. 4 is a graph showing the current / voltage characteristics when charging in the charge / discharge sequence in the first modification example. The charging sequence until time t3 is the same as that in the above embodiment, and the control flow and control content by the controller 10 are also the same. When a certain period (t c ) has elapsed, the charge / discharge control unit 12 sets the charging current of the secondary battery 1 to I4. The charging current (I4) is larger than the charging currents (I1, I3) and smaller than the charging current (I2). The charge / discharge control unit 12 causes the charging current (I4) to flow through the secondary battery 1 for a certain period (t b1 ). Then, when a certain period (t b1 ) has elapsed, the charge / discharge control unit 12 sets the charging current of the secondary battery 1 to I3. The charge / discharge control unit 12 causes the charging current (I3) to flow through the secondary battery 1 for a certain period (t b2 ).

[0052] As shown in FIG. 4, the charging current decreases from I2 to I4 at the time (t3) when a certain period (t c ) has elapsed, and decreases from I4 to I3 at the time (t4) when a certain period (t b1 ) has elapsed. At the time t2, the controller 10 estimates the battery voltage (V2) at the time (t2) and estimates the end point SOC. The method for estimating the end point SOC is the same as that in step S12.

[0053] The controller 10 estimates the battery voltage (V4) at time (t4) and estimates the SOC for estimation (SOC4). First, the battery resistance estimation unit 14 multiplies the charging current (I3) by a certain period (t b2 ) to calculate the current integration (ΔAh2). The current integration (ΔAh2) corresponds to the integrated value of the current (I3) flowing during a certain period (t b2 ). The SOC estimation unit 13 estimates SOC4 from the following arithmetic expression (4).

Equation

[0054] The controller 10 estimates the battery voltage (V3) and SOC3 at time (t3). First, the battery resistance estimation unit 14 multiplies the charging current (I4) by a certain period (t b1 ) to calculate the current integration (ΔAh x ). The current integration (ΔAh x ) corresponds to the integrated value of the current (I4) flowing during a certain period (t b1 ). The SOC estimation unit 13 estimates SOC3 from the following arithmetic expression (5).

Equation

[0055] The battery resistance estimation unit 14 calculates the voltage difference (ΔV L ) and the voltage difference (ΔV HPerform the calculation. The calculation method is the same as that in step S13. The battery resistance estimation unit 14 calculates OCV4 corresponding to SOC4 from the SOC-OCV characteristics. The battery resistance estimation unit 14 subtracts OCV4 from the battery voltage (V4) to calculate the voltage difference (ΔV M ) is calculated. The battery resistance estimation unit 14 uses the current (I1 or I3, I2, and I4) and the voltage change (ΔV L , ΔV M , ΔV H ) to plot a regression line and estimates the current battery resistance from the slope of the regression line.

[0056] As described above, in Modification 1 of the present embodiment, the charge and discharge control unit 12 passes three or more different currents including the constant currents (I1, I3) and the estimation currents (I2, I4) through the secondary battery 1. The battery resistance estimation unit 14 estimates the battery resistance based on the battery voltage and OCV when three or more currents are passed through the secondary battery. Thereby, the battery resistance can be estimated in a short time and with high accuracy.

[0057] Also, in Modification 1, the charge and discharge control unit 12 passes three or more currents (I1 or I3, I2, and I4) through the secondary battery 1 in descending order. Thereby, since the waiting time (t b1 or t b2 corresponding) for the transient state due to the current change to settle can be shortened when the change width of the current is smaller, the total time required for resistance estimation can be shortened.

[0058] In the modification, when plotting the current (I1 or I3, I2, and I4) and the voltage change (ΔV L , ΔV M , ΔV H ) to obtain a regression line, if the plot position deviates from the regression line and linearity cannot be ensured, the battery resistance may be estimated after excluding the estimation results with non-linearity. Thereby, it is possible to estimate the battery resistance after confirming whether linearity is ensured, and the estimation accuracy is improved.

[0059] In Modification 1, the battery resistance estimation unit 14 may estimate the battery resistance based on the battery voltage and the OCV when the larger current among three or more types of currents is passed through the secondary battery 1. In the example of FIG. 4, the battery resistance estimation unit 14 does not use the data of the current (I1 or I3) and the voltage change (ΔV L ), but plots the currents (I2, I4) and the voltage changes (ΔV M , ΔV H ) to obtain a regression line, and estimates the current battery resistance from the slope of the regression line. Thereby, the battery resistance can be estimated using data that is easy to maintain linearity, and the estimation accuracy is improved.

[0060] As a second modification of the present embodiment, the charge and discharge control unit 12 controls the charging of the secondary battery 1 mounted on the vehicle in the normal charging mode, and the battery resistance estimation unit 14 may estimate the battery resistance from the battery data of the secondary battery charged in the normal charging mode. As described above, the battery resistance estimation method in the present embodiment assumes a charging sequence in which the secondary battery 1 is charged and discharged with a constant current. Therefore, when the battery resistance estimation system is mounted on a vehicle, during driving, the current cannot be freely manipulated, so a constant current cannot be created. Also, when the vehicle is stopped, the SOC may decrease, which may interfere with driving. Also, during rapid charging, although it can be charged in a short time originally, it takes time for the estimation of the battery capacity. Therefore, by performing the battery resistance estimation method in the present embodiment during normal charging, the battery resistance can be estimated without impairing the convenience for the user.

[0061] Although the embodiments of the present invention have been described above, these embodiments are described for facilitating the understanding of the present invention, and are not described for limiting the present invention. Therefore, each element disclosed in the above embodiments is intended to include all design changes and equivalents belonging to the technical scope of the present invention.

Explanation of Reference Numerals

[0062] 1... Secondary battery 2... DCDC converter 3... Voltage sensor 4... Current sensor 10…Controller 11…Battery voltage estimation unit 12…Charge and discharge control unit 13…SOC estimation unit 14…Battery resistance estimation unit

Claims

1. A battery resistance estimation device for estimating the battery resistance of a secondary battery, comprising: a battery voltage estimation unit that measures or estimates the battery voltage of the secondary battery; a charge / 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 resistance estimation unit that estimates the battery resistance, wherein the charge / discharge control unit controls the charge and discharge of the secondary battery up to a starting point by charging or discharging the secondary battery at a constant 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 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 at the constant current for a second time or longer; flows an estimation current larger than the constant current through the secondary battery; wherein 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; wherein the resistance estimation unit calculates a starting point OCV indicating the open circuit voltage (OCV) at the starting point or an end point OCV indicating the OCV at the end point from the starting point SOC or the end point SOC using the relationship of the SOC-OCV characteristics; calculates an estimation OCV indicating the OCV when the estimation current is flowed through the secondary battery; A battery resistance estimation device that estimates the battery resistance based on the battery voltage at the starting point or the end point, the starting point SOC or the end point SOC, the estimation battery voltage indicating the battery voltage when the estimation current is flowed through the secondary battery, and the estimation OCV.

2. The battery resistance estimation device according to claim 1, wherein the charge / discharge control unit reduces the constant current within an allowable range determined by the measurement accuracy of the current sensor.

3. The battery resistance estimation device according to claim 1 or 2, wherein the second time is longer than the first time.

4. The battery resistance estimation device according to claim 1 or 2, wherein the charge / discharge control unit flows a current in the opposite direction to the constant current through the secondary battery while switching from the estimation current to the constant current.

5. The battery resistance estimation device according to claim 1 or 2, wherein the charge / discharge control unit flows three or more different currents including the constant current and the estimation current through the secondary battery, wherein the battery resistance estimation unit A battery resistance estimation device that estimates the battery resistance based on the battery voltage and the OCV when the above three or more types of currents are passed through the secondary battery.

6. The battery resistance estimation device according to claim 5, wherein the charge and discharge control unit is a battery resistance estimation device that passes the three or more types of currents through the secondary battery in descending order.

7. The battery resistance estimation device according to claim 1 or 2, wherein the charge and discharge control unit passes three or more different magnitudes of currents including the constant current and the estimation current through the secondary battery, and the battery resistance estimation unit, is a battery resistance estimation device that estimates the battery resistance based on the battery voltage and the OCV when the larger of the three or more types of currents is passed through the secondary battery.

8. The battery resistance estimation device according to any one of claims 1 or 2, wherein the charge and discharge control unit, controls the charging of the secondary battery mounted on the vehicle in a normal charging mode, and the battery resistance estimation unit, is a battery resistance estimation device that estimates the battery capacity of the secondary battery from the battery data of the secondary battery charged in the normal charging mode.

9. A battery resistance estimation method executed by a processor for estimating the battery resistance of a secondary battery, wherein the processor, measures or estimates the battery voltage of the secondary battery, controls the charge and discharge of the secondary battery up to a starting point by charging or discharging the secondary battery at a constant current for a first time or more, after passing the starting point, controls the charge and discharge of the secondary battery so that the state of charge (SOC) of the secondary battery changes by a predetermined change width or more from the starting point by charging or discharging, controls the charge and discharge of the secondary battery up to an end point by charging or discharging the secondary battery at the constant current for a second time or more, passes an estimation current larger than the constant current through the secondary battery, acquires a starting point SOC indicating the SOC of the starting point, estimates an end point SOC indicating the SOC of the end point based on the starting point SOC, the battery voltage of the starting point, and the battery voltage of the end point, calculates a starting point OCV indicating the open circuit voltage (OCV) of the starting point or an end point OCV indicating the OCV of the end point from the starting point SOC or the end point SOC using the relationship of the SOC-OCV characteristics, calculates an estimation OCV indicating the OCV when the estimation current is passed through the secondary battery. A battery resistance estimation method for estimating the battery resistance based on the battery voltage at the start point or the end point, the start point SOC or the end point SOC, an estimated battery voltage indicating the battery voltage when the estimation current is passed through the secondary battery, and the estimated OCV.

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