Apparatus for calculating open circuit voltage of secondary battery and power storage system

Abstract

To provide a device for calculating an open-circuit voltage of a secondary battery that can calculate the open-circuit voltage of a secondary battery with high accuracy while operating a power storage system without any trouble.SOLUTION: A device includes a current superposition circuit 30 for superimposing a pulse current on at least one of a charging current supplied from a charger 60 to a secondary battery 10 and a discharging current supplied from the secondary battery 10 to a load, and an OCV analysis unit 21 for calculating the internal resistance of the secondary battery 10 based on an amount of increase or decrease corresponding to the period of the pulse current of a current value superimposed with a pulse current by a current superimposing circuit 30, and an amount of increase or decrease corresponding to the period of the pulse current of a terminal voltage of the secondary battery 10, and, calculating the open-circuit voltage of the secondary battery 10 based on the calculated internal resistance and the terminal voltage and current value of the secondary battery 10.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a calculation device for an open circuit voltage of a secondary battery, and Energy storage system To Regarding. [Background technology]

[0002] There is known a device that inputs detected values ​​of the charge / discharge current and the terminal voltage of a secondary battery, and calculates the open circuit voltage of the secondary battery based on internal resistance information of the secondary battery (see, for example, Patent Document 1). This device calculates the open circuit voltage of the secondary battery by subtracting from the terminal voltage the voltage drop caused by the charge / discharge current flowing through the internal resistance of the secondary battery, and adding to the terminal voltage a correction amount calculated based on the temperature and charge / discharge current of the secondary battery. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2013-126258 A Summary of the Invention [Problem to be solved by the invention]

[0004] The internal resistance of a secondary battery changes due to various factors such as battery temperature, charging rate (SOC: State of Charge), deterioration rate (SOH: State of Health), etc. It is difficult to track such changes in internal resistance and calculate the internal resistance with high accuracy, which may result in errors in the calculation of the open circuit voltage of the secondary battery.

[0005] A method is conceivable in which the open circuit voltage for each charging rate of the secondary battery is obtained by changing the charging rate and measuring the terminal voltage of the secondary battery in an unloaded state for each charging rate. However, with this method, in order to obtain the open circuit voltage of the secondary battery with high accuracy, it is necessary to divide the charging rate into smaller parts and increase the number of measurements in an unloaded state, which increases the number of times the operation of the power storage system is stopped and put into an unloaded state, which creates a problem of interfering with the operation of the power storage system.

[0006] In view of the above circumstances, the present invention provides a secondary battery open circuit voltage calculation device capable of calculating the open circuit voltage of a secondary battery with high accuracy while operating a power storage system without any problems; and Energy storage system M The purpose is to provide. [Means for solving the problem]

[0007] The apparatus for calculating the open circuit voltage of a secondary battery according to the present invention comprises: When the electric vehicle decelerates, From the charging section The electric vehicle Charging power supplied to the secondary battery In the flow a current superposition circuit for superposing a pulse current; and The charging current An increase or decrease in the current value according to the period of the pulse current; When the pulse current is superimposed on the charging current by the current superimposition circuit, The amount of increase or decrease in the terminal voltage of the secondary battery according to the period of the pulse current is used as the basis for determining whether the secondary battery is in a low-voltage state or not. When charging Calculate the internal resistance, When the pulse current is superimposed on the charging current by the current superimposition circuit, The terminal voltage and When the pulse current is superimposed on the charging current by the current superimposition circuit, The current value and 、 Calculated When the secondary battery is charged a calculation unit that calculates an open circuit voltage of the secondary battery based on the internal resistance. The calculation unit calculates the internal resistance of the secondary battery during charging for each period of the pulse current based on the following formula (I), and calculates the open circuit voltage of the secondary battery for each period of the pulse current using the calculated internal resistance of the secondary battery during charging: do. r(t)=(V 2C (t)-V 1C (t)) / (I 2C (t)-I 1C (t))…(I) where r(t) is the internal resistance of the secondary battery during charging, and I 2C (t) is the maximum current value for each period of the pulse current when the pulse current is superimposed on the charging current by the current superimposition circuit, and I 1C (t) is the minimum current value for each period of the pulse current when the pulse current is superimposed on the charging current by the current superimposition circuit, and V2C (t) is the maximum value of the terminal voltage for each period of the pulse current when the pulse current is superimposed on the charging current by the current superimposition circuit, and V 1C (t) is the minimum value of the terminal voltage for each period of the pulse current when the pulse current is superimposed on the charging current by the current superimposition circuit. Further, a calculation device for an open circuit voltage of a secondary battery of the present invention includes a current superposition circuit that superimposes a pulse current on a discharge current supplied from a secondary battery of an electric vehicle to a load of the electric vehicle when the electric vehicle is accelerating, and calculates an internal resistance of the secondary battery during discharge based on an increase / decrease in a current value of the discharge current on which the pulse current is superimposed by the current superposition circuit, the increase / decrease being in accordance with a period of the pulse current, and an increase / decrease in a terminal voltage of the secondary battery when the pulse current is superimposed on the discharge current by the current superposition circuit, the increase / decrease being in accordance with the period of the pulse current, and a calculation unit that calculates an open-circuit voltage of the secondary battery based on the terminal voltage when the pulse current is superimposed on the discharge current by the current superposition circuit, the current value when the pulse current is superimposed on the discharge current by the current superposition circuit, and the calculated internal resistance of the secondary battery during discharge, wherein the calculation unit calculates the internal resistance of the secondary battery during discharge for each period of the pulse current based on the following formula (II), and calculates the open-circuit voltage of the secondary battery for each period of the pulse current using the calculated internal resistance of the secondary battery during discharge. r(t)=-(V 2C (t)-V 1C (t)) / (I 2C (t)-I 1C (t))…(II) where r(t) is the internal resistance of the secondary battery during discharge, and I 2C (t) is the maximum current value for each period of the pulse current when the pulse current is superimposed on the discharge current by the current superimposition circuit, and I 1C (t) is the minimum current value for each period of the pulse current when the pulse current is superimposed on the discharge current by the current superimposition circuit, and V 2C (t) is the maximum value of the terminal voltage for each period of the pulse current when the pulse current is superimposed on the discharge current by the current superimposition circuit, and V 1C (t) is the minimum value of the terminal voltage for each period of the pulse current when the pulse current is superimposed on the discharge current by the current superimposition circuit.

[0008] The power storage system of the present invention comprises: Electric vehicle Charging current is supplied from the charging section, The electric vehicle Supplying discharge current to the load The electric vehicle A secondary battery; When the electric vehicle is decelerating, the power supply from the charging unit to the secondary battery is The charging In the flow a current superposition circuit for superposing a pulse current; and The charging current A current sensor for detecting a current value; When the pulse current is superimposed on the charging current by the current superimposition circuit, a voltage sensor for detecting a terminal voltage of the secondary battery; When the pulse current is superimposed on the charging current by the current superimposition circuit, an increase or decrease in the current value detected by the current sensor according to a period of the pulse current; When the pulse current is superimposed on the charging current by the current superimposition circuit, Based on the amount of increase or decrease of the terminal voltage detected by the voltage sensor according to the period of the pulse current, When charging Calculate the internal resistance, When the pulse current is superimposed on the charging current by the current superimposition circuit, The terminal voltage and When the pulse current is superimposed on the charging current by the current superimposition circuit, The current value and 、 Calculated When the secondary battery is charged a calculation unit that calculates an open circuit voltage of the secondary battery based on the internal resistance. The calculation unit calculates the internal resistance of the secondary battery during charging for each period of the pulse current based on the following formula (I), and calculates the open circuit voltage of the secondary battery for each period of the pulse current using the calculated internal resistance of the secondary battery during charging: do. r(t)=(V 2C (t)-V 1C (t)) / (I 2C (t)-I 1C (t))…(I) where r(t) is the internal resistance of the secondary battery during charging, and I 2C (t) is the maximum current value for each period of the pulse current when the pulse current is superimposed on the charging current by the current superimposition circuit, and I 1C (t) is the minimum current value for each period of the pulse current when the pulse current is superimposed on the charging current by the current superimposition circuit, and V 2C (t) is the maximum value of the terminal voltage for each period of the pulse current when the pulse current is superimposed on the charging current by the current superimposition circuit, and V 1C (t) is the minimum value of the terminal voltage for each period of the pulse current when the pulse current is superimposed on the charging current by the current superimposition circuit. Further, the power storage system of the present invention includes a secondary battery of the electric vehicle that is supplied with a charging current from a charging unit of the electric vehicle and that supplies a discharge current to a load of the electric vehicle, a current superposition circuit that superimposes a pulse current on the discharge current that is supplied from the secondary battery to the load when the electric vehicle is accelerating, a current sensor that detects a current value of the discharge current on which the pulse current is superimposed by the current superposition circuit, a voltage sensor that detects a terminal voltage of the secondary battery, an increase / decrease amount of the current value detected by the current sensor when the pulse current is superimposed on the discharge current by the current superposition circuit in accordance with a period of the pulse current, and a voltage sensor that detects a terminal voltage of the secondary battery when the pulse current is superimposed on the discharge current by the current superposition circuit. a calculation unit that calculates an internal resistance of the secondary battery during discharge based on an amount of increase or decrease in the terminal voltage detected by the current superposition circuit according to the period of the pulse current, and calculates an open-circuit voltage of the secondary battery based on the terminal voltage when the pulse current is superimposed on the discharge current by the current superposition circuit, the current value when the pulse current is superimposed on the discharge current by the current superposition circuit, and the calculated internal resistance of the secondary battery during discharge, wherein the calculation unit calculates the internal resistance of the secondary battery during discharge for each period of the pulse current based on the following formula (II), and calculates the open-circuit voltage of the secondary battery for each period of the pulse current using the calculated internal resistance of the secondary battery during discharge. r(t)=-(V 2C (t)-V 1C (t)) / (I 2C (t)-I 1C (t))…(II) where r(t) is the internal resistance of the secondary battery during discharge, and I 2C (t) is the maximum current value for each period of the pulse current when the pulse current is superimposed on the discharge current by the current superimposition circuit, and I 1C (t) is the minimum current value for each period of the pulse current when the pulse current is superimposed on the discharge current by the current superimposition circuit, and V 2C (t) is the maximum value of the terminal voltage for each period of the pulse current when the pulse current is superimposed on the discharge current by the current superimposition circuit, and V 1C (t) is the minimum value of the terminal voltage for each period of the pulse current when the pulse current is superimposed on the discharge current by the current superimposition circuit. Effect of the Invention

[0010] According to the present invention, it is possible to calculate the open circuit voltage of a secondary battery with high accuracy while operating the power storage system without any problems. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram showing an outline of the configuration of a power storage system according to one embodiment of the present invention during charging. [Diagram 2] FIG. 2 is a diagram showing an outline of the configuration of the electricity storage system according to one embodiment of the present invention during discharging. [Diagram 3] FIG. 3 is a diagram showing changes in charging current and terminal voltage when the secondary battery is being charged. [Figure 4] FIG. 4 is a diagram showing changes in discharge current and terminal voltage when the secondary battery is discharged. [Diagram 5] FIG. 5 is a diagram showing changes in charge / discharge current and terminal voltage of a secondary battery in an electric vehicle during travel. [Figure 6] FIG. 6 is a graph showing the results of a test carried out to confirm the effect of the method for calculating the open circuit voltage of a secondary battery according to one embodiment of the present invention. [Figure 7] FIG. 7 is a histogram showing the normal distribution of open-circuit voltages obtained as continuous data in the test. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The present invention will be described below along with preferred embodiments. Note that the present invention is not limited to the embodiments shown below, and can be modified as appropriate within the scope of the present invention. In addition, in the embodiments shown below, some configurations are omitted from illustration and description, but for the details of the omitted technologies, publicly known or well-known technologies are applied as appropriate within the scope of no contradiction with the contents described below.

[0013] Fig. 1 is a diagram showing an outline of the configuration of a power storage system 1 according to one embodiment of the present invention during charging, and Fig. 2 is a diagram showing an outline of the configuration of the power storage system 1 according to one embodiment of the present invention during discharging. As shown in these figures, the power storage system 1 of this embodiment includes a secondary battery 10, an MCU (Micro Control Unit) 20, a current superposition circuit 30, a voltage sensor 40, and a current sensor 50. As shown in Fig. 1, the secondary battery 10 is charged by a charging current supplied from a charger 60 during charging. On the other hand, as shown in Fig. 2, the secondary battery 10 supplies a discharging current to a load 70 during discharging.

[0014] The secondary battery 10 is a secondary battery such as a lithium ion battery, and is, for example, a secondary battery for in-vehicle use, stationary use, or smart devices. When the secondary battery 10 is for in-vehicle use, examples of the load 70 include a drive motor, an air conditioner, and various in-vehicle electrical components. When the secondary battery 10 is for stationary use, examples of the load 70 include household electrical appliances and commercial power systems. When the secondary battery 10 is for smart devices, examples of the load 70 include a liquid crystal display unit and a communication module.

[0015] Furthermore, when the secondary battery 10 is for an electric vehicle, the drive motor generates power in response to the vehicle's running during the running, causing the secondary battery 10 to enter a discharging state. On the other hand, when the electric vehicle decelerates, the drive motor becomes a generator to generate regenerative power, causing the secondary battery 10 to enter a charging state. That is, when the secondary battery 10 is for an electric vehicle, the drive motor can be exemplified as the charger 60. On the other hand, when the secondary battery 10 is for a stationary vehicle, the charger 60 can be exemplified as a commercial power supply system, a power generation system utilizing solar power, or the like.

[0016] The MCU 20 includes an OCV analysis unit 21 that analyzes the outputs of various sensors such as the voltage sensor 40 and the current sensor 50 to estimate the characteristics of the open circuit voltage (OCV) of the secondary battery 10.

[0017] As shown in Fig. 1, the current superposition circuit 30 superimposes a pulse current on a charging current supplied from a charger 60 to a secondary battery 10 when the secondary battery 10 is being charged. Also, as shown in Fig. 2, the current superposition circuit 30 superimposes a pulse current on a discharging current supplied from the secondary battery 10 to a load 70 when the secondary battery 10 is being discharged.

[0018] The voltage sensor 40 measures the terminal voltage of the secondary battery 10 and outputs it to the MCU 20. Also, as shown in Fig. 1, the current sensor 50 measures the current obtained by superimposing the above-mentioned pulse current on the charging current supplied from the charger 60 to the secondary battery 10 during charging, and outputs it to the MCU 20. Furthermore, as shown in Fig. 2, the current sensor 50 measures the current obtained by superimposing the above-mentioned pulse current on the discharging current supplied from the secondary battery 10 to the load 70 during discharging, and outputs it to the MCU 20.

[0019] The OCV analysis unit 21 of the MCU 20, the current superposition circuit 30, the voltage sensor 40, and the current sensor 50 constitute a calculation device 100 for the open circuit voltage of the secondary battery 10. When charging the secondary battery 10, the calculation device 100 superimposes a pulse current on the charging current using the current superposition circuit 30 to alternately change the C rate of the charging current between 1C and 2C, thereby fluctuating the terminal voltage of the secondary battery 10 detected by the voltage sensor 40. When discharging the secondary battery 10, the calculation device 100 superimposes a pulse current on the discharging current using the current superposition circuit 30 to alternately change the C rate of the discharging current between 1C and 2C, thereby fluctuating the terminal voltage of the secondary battery 10 detected by the voltage sensor 40.

[0020] The fluctuation of the terminal voltage during charging and discharging of the secondary battery 10 occurs according to the period of the pulse current. The OCV analysis unit 21 calculates the internal resistance of the secondary battery 10 based on the amount of increase or decrease in the terminal voltage detected by the voltage sensor 40 according to the period of the pulse current, and the amount of increase or decrease in the charge / discharge current detected by the current sensor 50 according to the period of the pulse current. Then, the OCV analysis unit 21 calculates the open circuit voltage of the secondary battery 10 using the calculated internal resistance.

[0021] 3 is a diagram showing changes in charging current and terminal voltage when charging the secondary battery 10. This diagram shows how the current superimposing circuit 30 superimposes a pulse current on the charging current to alternately change the C rate of the charging current between 1C and 2C. This diagram also shows how the terminal voltage changes in response to the charging current whose C rate alternates between 1C and 2C. Note that alternating the C rate between 1C and 2C is just one example, and other rates may be used.

[0022] I in the figure 1C (t) is the charging current when the C rate drops to 1C, and is defined by the following equation (1). I 1C (t)=I V (t)+I V '(t) …(1) However, I V (t) is the current value output from the charger 60 at time t, and IV '(t) is the current value output from the current superposition circuit 30 at time t.

[0023] I in the figure 2C (t) is the charging current when the C rate increases to 2C, and is defined by the following equation (2). I 2C (t)=I V (t+1)+I V '(t+1) …(2) However, I V (t+1) is the current value output from the charger 60 at time t+1, and I V '(t+1) is the current value output from the current superposition circuit 30 at time t+1.

[0024] V in the figure 1C (t) is the terminal voltage when the charging current C rate drops to 1C, and is defined by the following equation (3). V 1C (t) = V(t) … (3) where V(t) is the voltage at time t.

[0025] V in the figure 2C (t) is the terminal voltage when the C rate of the charging current increases to 2C, and is defined by the following equation (4). V 2C (t) = V(t + 1) … (4) where V(t+1) is the voltage at time t+1.

[0026] Here, the terminal voltage is V 1C (t) and V 2C The main factor that causes the voltage to fluctuate between time (t) and the internal resistance r(t) of the secondary battery 10 is the voltage drop due to the internal resistance r(t) of the secondary battery 10. The internal resistance r(t) of the secondary battery 10 at time t is defined by the following equation (5). r(t)=(V 2C (t)-V 1C (t)) / (I 2C (t)-I 1C (t)) …(5)

[0027] By determining the internal resistance r(t) of the secondary battery 10 at time t, the open circuit voltage V OC (t) can be calculated using any of the following formulas (6) to (8). V OC (t)=V 1C (t)-r(t)×I 1C (t) …(6) V OC (t)=V 2C (t)-r(t)×I 2C (t) …(7) V OC (t)=((V 1C (t)-r(t)×I 1C (t))+(V 2C (t)-r(t)×I 2C (t))) / 2 …(8)

[0028] During charging of the secondary battery 10, the OCV analysis unit 21 of the MCU 20 calculates the internal resistance r(t) of the secondary battery 10 based on the above formula (5), and uses the calculated internal resistance r(t) to calculate the open circuit voltage V OC Calculate (t).

[0029] 4 is a diagram showing changes in the discharge current and terminal voltage during discharge of the secondary battery 10. This diagram shows how the C rate of the discharge current is alternately changed between 1C and 2C by superimposing a pulse current on the discharge current by the current superimposing circuit 30. This diagram also shows how the terminal voltage changes in response to the discharge current whose C rate alternates between 1C and 2C.

[0030] I in the figure 1C (t) is the discharge current when the C rate drops to 1C, and is defined by the above formula (1). V (t) is interpreted as the current output from the secondary battery 10 at time t.

[0031] I in the figure 2C (t) is the discharge current when the C rate increases to 2C, and is defined by the above formula (2). However, IV (t+1) is interpreted as the current output from the secondary battery 10 at time t+1.

[0032] V in the figure 1C (t) is the terminal voltage when the C rate of the discharge current drops to 1C, and is defined by the above formula (3). Also, V 2C (t) is the terminal voltage when the C rate of the discharge current increases to 2C, and is defined by the above equation (4).

[0033] Here, the terminal voltage is V 1C (t) and V 2C The main factor that varies between time (t) and time (t) is the voltage drop due to the internal resistance r(t) of the secondary battery 10. The internal resistance r(t) of the secondary battery 10 at time t is defined by the following equation (9). r(t)=-(V 2C (t)-V 1C (t)) / (I 2C (t)-I 1C (t)) …(9)

[0034] By determining the internal resistance r(t) of the secondary battery 10 at time t, the open circuit voltage V OC (t) can be calculated using any of the following formulas (10) to (12). V OC (t)=V 1C (t)-r(t)×I 1C (t) …(10) V OC (t)=V 2C (t)-r(t)×I 2C (t) …(11) V OC (t)=((V 1C (t)-r(t)×I 1C (t))+(V 2C (t)-r(t)×I 2C (t))) / 2 …(12)

[0035] The OCV analysis unit 21 of the MCU 20 calculates the internal resistance r(t) of the secondary battery 10 based on the above formula (9) when the secondary battery 10 is discharged, and uses the calculated internal resistance r(t) to calculate the open circuit voltage V OC Calculate (t).

[0036] FIG. 5 is a diagram showing changes in the charge / discharge current and terminal voltage of the secondary battery 10 in a running electric vehicle. As shown in this diagram, the charge / discharge current and terminal voltage of the secondary battery 10 change when the electric vehicle equipped with the secondary battery 10 accelerates or decelerates. Specifically, when the electric vehicle accelerates, the current value changes in the positive direction and the terminal voltage gradually decreases. Here, the negative current in the diagram is the discharge current. On the other hand, when the electric vehicle decelerates, the current value changes in the positive direction and the terminal voltage gradually increases. Here, the positive current in the diagram is the charge current.

[0037] When the electric vehicle is decelerating, the MCU 20 superimposes a pulse current on the charging current by the current superimposition circuit 30, and the OCV analysis unit 21 calculates the terminal voltage V of the secondary battery 10 detected by the voltage sensor 40. 1C (t), V 2C (t) and the charging current I detected by the current sensor 50 1C (t),I 2C The internal resistance r(t) of the secondary battery 10 is calculated based on the internal resistance r(t), and the open circuit voltage V of the secondary battery 10 is calculated based on the calculated internal resistance r(t). OC Calculate (t).

[0038] On the other hand, when the electric vehicle accelerates, the MCU 20 superimposes a pulse current on the discharge current by the current superimposition circuit 30, and the OCV analysis unit 21 calculates the terminal voltage V 1C (t), V 2C (t) and the discharge current I detected by the current sensor 50 1C (t),I 2C The internal resistance r(t) of the secondary battery 10 is calculated based on the internal resistance r(t), and the open circuit voltage V of the secondary battery 10 is calculated based on the calculated internal resistance r(t). OC Calculate (t).

[0039] By the way, the open circuit voltage V of the secondary battery 10 calculated by the above formulas (1) to (12) OC Since (t) is time series data, many open circuit voltages V OC (t) is obtained as continuous data. For example, if sampling is performed at 10 ms / time, 10,000 open circuit voltages V are obtained in 100 seconds. OC Data (t) is obtained.

[0040] Here, the open circuit voltage of a secondary battery does not change significantly in a short period of time, so in a short period of time, the calculated open circuit voltage V OC The data in (t) is only affected by the noise of the current sensor and voltage sensor, and the calculated open circuit voltage V OC The median of the normal distribution of (t) is a highly reliable value. Therefore, in this embodiment, the OCV analysis unit 21 calculates the open circuit voltage V OC (t) is normalized, and the median of the normal distribution is taken as the open circuit voltage V OC It is calculated as follows.

[0041] FIG. 6 shows the open circuit voltage V OC 1 is a graph showing the results of a test carried out to verify the effectiveness of the calculation method of the internal resistance r(t) of the secondary battery cell. In this test, a pulse current of 0 A and 1 A was superimposed by the current superimposing circuit 30 on the discharge current discharged from the test secondary battery cell to a specified load, thereby changing the discharge current and acquiring the internal resistance r(t). The acquired internal resistance r(t) was used to calculate the open circuit voltage V of the secondary battery cell. OC In this test, sampling was performed at 10 ms per time. The calculated open circuit voltage V OC The time from 50,000 to 60,000 cycles shown on the horizontal axis in Figure 6 corresponds to 100 seconds.

[0042] Figure 7 shows the open circuit voltage V OC This is a histogram showing the normal distribution of the open circuit voltage V OCThe center of the normal distribution of the data in (t) is around 3.788V. Therefore, this 3.788V is the open circuit voltage V OC By extracting the open circuit voltage V OC The calculation result is obtained.

[0043] As described above, in the energy storage system 1 of this embodiment, the current superimposing circuit 30 superimposes a pulse current on the charging current supplied from the charger 60 to the secondary battery 10 and the discharging current supplied from the secondary battery 10 to the load 70. The OCV analysis unit 21 of the MCU 20 calculates the current value I 1C (t),I 2C The increase or decrease in the pulse current (t) according to the period and the terminal voltage V of the secondary battery 10 1C (t), V 2C Based on the amount of increase or decrease according to the period of the pulse current (t), the internal resistance r(t) of the secondary battery 10 is calculated, and the terminal voltage V of the secondary battery 10 is calculated. 1C (t), V 2C (t) and the current value I 1C (t),I 2C Based on the calculated internal resistance r(t) and the calculated internal resistance r(t), the open circuit voltage V OC (t), V OC In this way, the internal resistance r(t) of the secondary battery 10 is calculated without requiring a no-load state, while continuing charging and discharging the secondary battery 10, i.e., without stopping the operation of the power storage system 1, and the open circuit voltage V of the secondary battery 10 is calculated using the calculated internal resistance r(t). OC (t), V OC can be calculated.

[0044] In addition, the current value I 1C (t),I 2C (t) and the terminal voltage V of the secondary battery 10 1C (t), V 2C (t), and the internal resistance r(t) and open circuit voltage V OC (t), V OCBy repeatedly calculating the current I in response to the charge state of the secondary battery 10 and the running state of the vehicle, the OCV characteristic corresponding to the charge rate and the running state can be obtained as continuous data. The OCV characteristic thus obtained is a current value I 1C (t),I 2C (t), terminal voltage V 1C (t), V 2C The OCV characteristic is calculated based on the internal resistance r(t) calculated using ...

[0045] In the energy storage system 1 of this embodiment, the internal resistance r(t) of the secondary battery 10 during charging is calculated for each period of the pulse current based on the above formula (5), and the open circuit voltage V OC In the power storage system 1 of the present embodiment, the internal resistance r(t) of the secondary battery 10 during discharge is calculated for each period of the pulse current based on the above formula (9), and the open circuit voltage V OC (t) is calculated for each period of the pulse current. As a result, the internal resistance r(t) and open circuit voltage V OC The calculation of (t) can be repeatedly performed according to the state of charge of the secondary battery 10 and the running state of the vehicle, and the OCV characteristics according to the state of charge and the running state can be obtained as continuous data.

[0046] Furthermore, in the energy storage system 1 of this embodiment, the open circuit voltage V OC (t) is normalized, and the median of the normal distribution is calculated as the open circuit voltage of the secondary battery 10. Here, since the open circuit voltage of the secondary battery 10 does not fluctuate significantly in a short time, it is possible to obtain OCV characteristics with higher accuracy.

[0047] The present invention has been described above based on an embodiment, but the present invention is not limited to the above embodiment, and modifications may be made without departing from the spirit of the present invention, and publicly known or well-known technologies may be combined as appropriate.

[0048] For example, in the above embodiment, the open circuit voltage V OC The median of the normal distribution of (t) was calculated as the open circuit voltage of the secondary battery 10, but the open circuit voltage V OC The average value of (t) may be calculated as the open circuit voltage of the secondary battery 10. Moreover, it is not essential to obtain both the open circuit voltage during charging of the secondary battery 10 and the open circuit voltage during discharging of the secondary battery 10, and it is sufficient to obtain at least one of them. [Explanation of symbols]

[0049] 1: Energy storage system 10: Secondary battery 20: MCU (calculation unit) 21: OCV analysis section (calculation section) 30: Current superposition circuit 40: Voltage sensor 50: Current sensor 60: Charger (charging part) 70: Load 100: Calculation device (calculation device for open circuit voltage of secondary battery) r(t): Internal resistance I 1C (t) : Current value (charge / discharge current) I 2C (t) : Current value (charge / discharge current) V 1C (t) : Terminal voltage V 2C (t) : Terminal voltage V OC : Open circuit voltage V OC (t) : Open circuit voltage

Claims

1. A current superposition circuit that superposes a pulse current on a charging current supplied from a charging unit of an electric vehicle to a secondary battery of the electric vehicle when the electric vehicle is decelerating; a calculation unit that calculates an internal resistance of the secondary battery during charging based on an amount of increase or decrease in the current value of the charging current on which the pulse current is superimposed by the current superimposition circuit, depending on the period of the pulse current, and an amount of increase or decrease in a terminal voltage of the secondary battery when the pulse current is superimposed on the charging current by the current superimposition circuit, depending on the period of the pulse current, and calculates an open circuit voltage of the secondary battery based on the terminal voltage when the pulse current is superimposed on the charging current by the current superimposition circuit, the current value when the pulse current is superimposed on the charging current by the current superimposition circuit, and the calculated internal resistance of the secondary battery during charging; Equipped with The calculation unit calculates the internal resistance of the secondary battery during charging for each period of the pulse current based on the following formula (I), and calculates the open-circuit voltage of the secondary battery for each period of the pulse current using the calculated internal resistance of the secondary battery during charging. r(t)=(V 2C (t)-V 1C (t)) / (I 2C (t)-I 1C (t))...(I) where r(t) is the internal resistance of the secondary battery during charging, I2C(t) is the maximum current value for each period of the pulse current when the pulse current is superimposed on the charging current by the current superimposition circuit, I1C(t) is the minimum current value for each period of the pulse current when the pulse current is superimposed on the charging current by the current superimposition circuit, V2C(t) is the maximum terminal voltage for each period of the pulse current when the pulse current is superimposed on the charging current by the current superimposition circuit, and V1C(t) is the minimum terminal voltage for each period of the pulse current when the pulse current is superimposed on the charging current by the current superimposition circuit.

2. A current superposition circuit that superposes a pulse current on a discharge current supplied from a secondary battery of the electric vehicle to a load of the electric vehicle when the electric vehicle is accelerating; a calculation unit that calculates an internal resistance of the secondary battery during discharge based on an increase / decrease amount of the current value of the discharge current on which the pulse current is superimposed by the current superimposition circuit, in accordance with the period of the pulse current, and an increase / decrease amount of a terminal voltage of the secondary battery when the pulse current is superimposed on the discharge current by the current superimposition circuit, in accordance with the period of the pulse current, and calculates an open circuit voltage of the secondary battery based on the terminal voltage when the pulse current is superimposed on the discharge current by the current superimposition circuit, the current value when the pulse current is superimposed on the discharge current by the current superimposition circuit, and the calculated internal resistance of the secondary battery during discharge; Equipped with The calculation unit calculates the internal resistance of the secondary battery during discharge for each period of the pulse current based on the following formula (II), and calculates the open-circuit voltage of the secondary battery for each period of the pulse current using the calculated internal resistance of the secondary battery during discharge. r(t)=-(V 2C (t)-V 1C (t)) / (I 2C (t)-I 1C (t))...(II) where r(t) is the internal resistance of the secondary battery during discharge, I2C(t) is the maximum current value for each period of the pulse current when the pulse current is superimposed on the discharge current by the current superimposition circuit, I1C(t) is the minimum current value for each period of the pulse current when the pulse current is superimposed on the discharge current by the current superimposition circuit, V2C(t) is the maximum terminal voltage for each period of the pulse current when the pulse current is superimposed on the discharge current by the current superimposition circuit, and V1C(t) is the minimum terminal voltage for each period of the pulse current when the pulse current is superimposed on the discharge current by the current superimposition circuit.

3. 3 . The device for calculating an open circuit voltage of a secondary battery according to claim 1 , wherein the calculation unit normalizes the open circuit voltage calculated for each period of the pulse current, and calculates a median of the normal distribution as the open circuit voltage.

4. A secondary battery of an electric vehicle that is supplied with a charging current from a charging unit of the electric vehicle and supplies a discharging current to a load of the electric vehicle; a current superposition circuit that superposes a pulse current on the charging current supplied from the charging unit to the secondary battery when the electric vehicle is decelerating; a current sensor that detects a current value of the charging current on which the pulse current is superimposed by the current superimposition circuit; a voltage sensor that detects a terminal voltage of the secondary battery when the pulse current is superimposed on the charging current by the current superimposition circuit; a calculation unit that calculates an internal resistance of the secondary battery during charging based on an amount of increase or decrease in the current value detected by the current sensor when the pulse current is superimposed on the charging current by the current superposition circuit, the amount of increase or decrease in the terminal voltage detected by the voltage sensor when the pulse current is superimposed on the charging current by the current superposition circuit, the amount of increase or decrease in the terminal voltage detected by the voltage sensor when the pulse current is superimposed on the charging current by the current superposition circuit, the amount of increase or decrease in the terminal voltage or the current value when the pulse current is superimposed on the charging current by the current superposition circuit, the amount of increase or decrease in the terminal voltage or the current value when the pulse current is superimposed on the charging current by the current superposition circuit, the amount of increase or decrease in the terminal voltage or the current value when the pulse current is superimposed on the charging current by the current superposition circuit, and the calculated internal resistance of the secondary battery during charging; Equipped with The calculation unit calculates the internal resistance of the secondary battery during charging for each period of the pulse current based on the following formula (I), and calculates the open-circuit voltage of the secondary battery for each period of the pulse current using the calculated internal resistance of the secondary battery during charging. r(t)=(V 2C (t)-V 1C (t)) / (I 2C (t)-I 1C (t))...(I) where r(t) is the internal resistance of the secondary battery during charging, I2C(t) is the maximum current value for each period of the pulse current when the pulse current is superimposed on the charging current by the current superimposition circuit, I1C(t) is the minimum current value for each period of the pulse current when the pulse current is superimposed on the charging current by the current superimposition circuit, V2C(t) is the maximum terminal voltage for each period of the pulse current when the pulse current is superimposed on the charging current by the current superimposition circuit, and V1C(t) is the minimum terminal voltage for each period of the pulse current when the pulse current is superimposed on the charging current by the current superimposition circuit.

5. A secondary battery of an electric vehicle that is supplied with a charging current from a charging unit of the electric vehicle and supplies a discharging current to a load of the electric vehicle; a current superposition circuit that superposes a pulse current on the discharge current supplied from the secondary battery to the load when the electric vehicle is accelerating; a current sensor for detecting a current value of the discharge current on which the pulse current is superimposed by the current superimposition circuit; a voltage sensor for detecting a terminal voltage of the secondary battery; a calculation unit that calculates an internal resistance of the secondary battery during discharge based on an increase / decrease amount of the current value detected by the current sensor when the pulse current is superimposed on the discharge current by the current superposition circuit, the increase / decrease amount being in accordance with the period of the pulse current, and an increase / decrease amount of the terminal voltage detected by the voltage sensor when the pulse current is superimposed on the discharge current by the current superposition circuit, the increase / decrease amount being in accordance with the period of the pulse current, and calculates an open circuit voltage of the secondary battery based on the terminal voltage when the pulse current is superimposed on the discharge current by the current superposition circuit, the current value when the pulse current is superimposed on the discharge current by the current superposition circuit, and the calculated internal resistance of the secondary battery during discharge; Equipped with The calculation unit calculates the internal resistance of the secondary battery during discharge for each period of the pulse current based on the following formula (II), and calculates the open-circuit voltage of the secondary battery for each period of the pulse current using the calculated internal resistance of the secondary battery during discharge. r(t)=-(V 2C (t)-V 1C (t)) / (I 2C (t)-I 1C (t))...(II) where r(t) is the internal resistance of the secondary battery during discharge, I2C(t) is the maximum current value for each period of the pulse current when the pulse current is superimposed on the discharge current by the current superimposition circuit, I1C(t) is the minimum current value for each period of the pulse current when the pulse current is superimposed on the discharge current by the current superimposition circuit, V2C(t) is the maximum terminal voltage for each period of the pulse current when the pulse current is superimposed on the discharge current by the current superimposition circuit, and V1C(t) is the minimum terminal voltage for each period of the pulse current when the pulse current is superimposed on the discharge current by the current superimposition circuit.

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