JP7620466B2 - Apparatus for calculating open circuit voltage of secondary battery and power storage system - Google Patents

Description

The present invention relates to a calculation device for an open circuit voltage of a secondary battery, and a power storage system.

There is a known device that uses the detected values of the charge/discharge current and the terminal voltage of a secondary battery as inputs, and calculates the open circuit voltage of the secondary battery based on the internal resistance value 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.

JP 2013-126258 A

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

One possible method is to obtain the open-circuit voltage for each charging rate of the secondary battery 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 energy storage system needs to be stopped and put into an unloaded state, creating a problem in that it interferes with the operation of the energy storage system.

In view of the above circumstances, an object of the present invention is to provide a device for calculating the open circuit voltage of a secondary battery, which can calculate the open circuit voltage of a secondary battery with high accuracy while operating the energy storage system without any problems, and a power storage system .

The device for calculating the open circuit voltage of a secondary battery of the present invention calculates an internal resistance of the secondary battery during charging based on a current superposition circuit that superimposes a pulse current on a charging current supplied to the secondary battery of the electric vehicle from a charging unit of the electric vehicle when the electric vehicle is decelerating, an increase/decrease in the current value of the charging current on which the pulse current is superimposed by the current superposition circuit, the increase/decrease in the current value corresponding to the period of the pulse current, and an increase/decrease in the terminal voltage of the secondary battery when the pulse current is superimposed on the charging current by the current superposition circuit , the increase/decrease in the terminal voltage corresponding to the period of the pulse current. 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 charging current, 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 , wherein 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.
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, 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.

The power storage system of the present invention includes a secondary battery of an electric vehicle that is supplied with a charging current from a charging unit of the electric vehicle and that supplies a discharging current to a load of the electric vehicle , a current superposition circuit that superimposes a pulse current on the charging current that is supplied from the charging unit to the secondary battery when the electric vehicle decelerates, a current sensor that detects a current value of the charging 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 when the pulse current is superimposed on the charging current by the current superposition circuit, an increase/decrease amount of the current value detected by the current sensor when the pulse current is superimposed on the charging current by the current superposition circuit in accordance with a period of the pulse current, and a calculation unit that calculates an internal resistance of the secondary battery during charging based on an 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 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 , wherein 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.
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, 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.

According to the present invention, the open circuit voltage of the secondary battery can be calculated with high accuracy while operating the energy storage system without any problems.

FIG. 1 is a diagram showing an outline of the configuration of a power storage system according to an embodiment of the present invention during charging. FIG. 2 is a diagram showing an outline of the configuration of the power storage system according to one embodiment of the present invention during discharging. FIG. 3 is a diagram showing changes in charging current and terminal voltage when the secondary battery is being charged. FIG. 4 is a diagram showing changes in discharge current and terminal voltage when the secondary battery is discharged. FIG. 5 is a diagram showing changes in charge/discharge current and terminal voltage of a secondary battery in an electric vehicle while it is running. 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. FIG. 7 is a histogram showing the normal distribution of open circuit voltages obtained as continuous data in the test.

The present invention will be described below in accordance with a preferred embodiment. Note that the present invention is not limited to the embodiment described below, and can be modified as appropriate without departing from the spirit of the present invention. In addition, in the embodiment described below, some configurations are omitted from illustration and description, but for the details of the omitted technology, publicly known or well-known technology is applied as appropriate within the scope of not causing any inconsistencies with the contents described below.

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 a 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 discharge current to a load 70 during discharging.

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, various in-vehicle electrical equipment, etc. When the secondary battery 10 is for stationary use, examples of the load 70 include household electrical equipment, commercial power systems, etc. When the secondary battery 10 is for smart devices, examples of the load 70 include a liquid crystal display unit, a communication module, etc.

When the secondary battery 10 is for an electric vehicle, the drive motor generates power in response to the vehicle's running, causing the secondary battery 10 to enter a discharged state. On the other hand, when the electric vehicle decelerates, the drive motor becomes a generator and generates regenerative power, causing the secondary battery 10 to enter a charged state. In other words, 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 that utilizes solar power, etc.

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

As shown in FIG. 1, the current superposition circuit 30 superimposes a pulse current on the charging current supplied from the charger 60 to the 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 the discharging current supplied from the secondary battery 10 to the load 70 when the secondary battery 10 is being discharged.

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. Also, 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.

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.

Fluctuations in the terminal voltage during charging and discharging of the secondary battery 10 occur 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. The OCV analysis unit 21 then calculates the open circuit voltage of the secondary battery 10 using the calculated internal resistance.

Figure 3 shows the changes in charging current and terminal voltage when charging the secondary battery 10. This figure shows how the current superimposition circuit 30 superimposes a pulse current on the charging current, causing the C rate of the charging current to alternate between 1C and 2C. This figure also shows how the terminal voltage changes in response to the charging current whose C rate alternates between 1C and 2C. Note that alternating between 1C and 2C C rates is just one example, and other rates may be used.

In the figure, I _1C (t) is the charging current when the C rate drops to 1C, and is defined by the following formula (1).
I _1C (t) = I _V (t) + I _V '(t)...(1)
Here, I _V (t) is the current value output from the charger 60 at time t, and I _V '(t) is the current value output from the current superposition circuit 30 at time t.

In the figure, I _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)
Here, 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.

In the figure, V _1C (t) is the terminal voltage when the C rate of the charging current 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.

In the figure, V _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).
_V2C (t)=V(t+1)...(4)
where V(t+1) is the voltage at time t+1.

Here, the main factor that causes the terminal voltage to fluctuate between V _1C (t) and V _2C (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 (5).
r(t)=(V _2C (t)-V _1C (t))/(I _2C (t)-I _1C (t))...(5)

By determining the internal resistance r(t) of the secondary battery 10 at time t, the open circuit voltage V _OC (t) of the secondary battery 10 can be calculated by any one of the following equations (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)

When charging 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 equation (5), and uses the calculated internal resistance r(t) to calculate the open-circuit voltage V _OC (t) of the secondary battery 10 based on any of the above equations (6) to (8).

Figure 4 shows the change in discharge current and terminal voltage when the secondary battery 10 is discharged. This figure shows how the current superposition circuit 30 superimposes a pulse current on the discharge current, causing the C rate of the discharge current to alternate between 1C and 2C. This figure also shows how the terminal voltage changes in response to the discharge current whose C rate alternates between 1C and 2C.

In the figure, I _1C (t) is the discharge current when the C rate drops to 1 C, and is defined by the above formula (1). However, _IV (t) in the above formula (1) should be read as the current output from the secondary battery 10 at time t.

In the figure, _I2C (t) is the discharge current when the C rate increases to 2C, and is defined by the above formula (2). However, _IV (t+1) in the above formula (2) should be interpreted as the current output from the secondary battery 10 at time t+1.

V _1C (t) in the figure 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) in the figure is the terminal voltage when the C rate of the discharge current rises to 2C and is defined by the above formula (4).

Here, the main factor that causes the terminal voltage to fluctuate between V _1C (t) and V _2C (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)

By determining the internal resistance r(t) of the secondary battery 10 at time t, the open circuit voltage V _OC (t) of the secondary battery 10 can be calculated by any one of the following equations (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)

When the secondary battery 10 is discharged, the OCV analysis unit 21 of the MCU 20 calculates the internal resistance r(t) of the secondary battery 10 based on the above equation (9), and uses the calculated internal resistance r(t) to calculate the open-circuit voltage V _OC (t) of the secondary battery 10 based on any of the above equations (10) to (12).

Figure 5 is a diagram showing the changes in the charge/discharge current and terminal voltage of the secondary battery 10 in a traveling electric vehicle. As shown in this figure, 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 figure 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 figure is the charge current.

When the electric vehicle decelerates, the MCU 20 superimposes a pulse current on the charging current using the current superposition circuit 30, and the OCV analysis unit 21 calculates the internal resistance r(t) of the secondary battery 10 based on the terminal voltages V _1C (t), V _2C (t) of the secondary battery 10 detected by the voltage sensor 40 and the charging currents I _1C (t), I _2C (t) detected by the current sensor 50, and calculates the open-circuit voltage V _OC (t) of the secondary battery 10 based on the calculated internal resistance r(t).

On the other hand, when the electric vehicle accelerates, the MCU 20 superimposes a pulse current on the discharge current using the current superposition circuit 30, and the OCV analysis unit 21 calculates the internal resistance r(t) of the secondary battery 10 based on the terminal voltages V _1C (t), V _2C (t) of the secondary battery 10 detected by the voltage sensor 40 and the discharge currents I _1C (t), I _2C (t) detected by the current sensor 50, and calculates the open-circuit voltage V _OC (t) of the secondary battery 10 based on the calculated internal resistance r(t).

Incidentally, since the open circuit voltage V _OC (t) of the secondary battery 10 calculated by the above formulas (1) to (12) is time series data, a large number of open circuit voltages V _OC (t) are obtained as continuous data over time t. For example, when sampling is performed about once every 10 ms, 10,000 pieces of open circuit voltage V _OC (t) data are obtained in 100 seconds.

Here, since the open circuit voltage of a secondary battery has a characteristic that it does not change significantly in a short period of time, in a short period of time, the data of the calculated open circuit voltage _VOC (t) is only affected by the variation due to the noise of the current sensor and the voltage sensor, and the median of the normal distribution of the calculated open circuit voltage _VOC (t) is a highly reliable value. Therefore, in this embodiment, the OCV analysis unit 21 converts the open circuit voltage _VOC (t) obtained as continuous data (e.g., 10,000) into a normal distribution for each predetermined period of time (e.g., 100 seconds), and calculates the median of the normal distribution as the open circuit voltage _VOC of the secondary battery 10.

FIG. 6 is a graph showing the results of a test carried out to confirm the effect of the calculation method of the open circuit voltage V _OC of the secondary battery 10 of this embodiment. In this test, the current superposition circuit 30 superimposed pulse currents of 0 A and 1 A on the discharge current discharged from the test secondary battery cell to a predetermined load to change the discharge current, thereby acquiring the internal resistance r(t), and using the acquired internal resistance r(t), the open circuit voltage V _OC (t) of the secondary battery cell was calculated. In this test, sampling was carried out at 10 ms/time. Then, the calculated open circuit voltage V _OC (t) was compared with the true value of the open circuit voltage. The time from 50,000 times to 60,000 times shown on the horizontal axis of FIG. 6 corresponds to 100 seconds.

7 is a histogram showing the normal distribution of the open-circuit voltage V _OC (t) obtained as continuous data in this test. As shown in this histogram, the center of the normal distribution of the open-circuit voltage V _OC (t) data is near 3.788 V. Therefore, by extracting this 3.788 V as the open-circuit voltage V _OC , a highly accurate calculation result of the open-circuit voltage V _OC can be obtained.

As described above, in the energy storage system 1 of this embodiment, the current superposition 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 internal resistance r(t) of the secondary battery 10 based on the amount of increase/decrease in the current values _I1C (t) and _I2C (t) on which the pulse current is superimposed by the current superimposition circuit 30, which corresponds to the period of the pulse current, and the amount of increase/decrease in the terminal voltages _V1C (t) and _V2C (t) of the secondary battery 10, which correspond to the period of the pulse current, and calculates the open-circuit voltages _VOC (t) and VOC of the secondary battery 10 based on the terminal voltages _V1C (t) and _V2C (t ₎ of the secondary battery 10, the current values I1C(t) and _I2C ( _t ) on which the pulse current is superimposed, and the calculated internal resistance r(t). This makes it possible to calculate the internal resistance r(t) of the secondary battery 10 without requiring a no-load state, while continuing to charge and discharge the secondary battery 10, i.e., without stopping the operation of the energy storage system 1, and to calculate the open-circuit voltages _VOC (t) and _VOC of the secondary battery 10 using the calculated internal resistance r(t).

In addition, by repeatedly measuring the current values _I1C (t), _I2C (t) and the terminal voltages _V1C (t), _V2C (t) of the secondary battery 10 and calculating the internal resistance r(t) and open circuit voltages _VOC (t), _VOC of the secondary battery 10 according to the charging state of the secondary battery 10 and the running state of the vehicle, the OCV characteristic according to the charging rate and running state can be obtained as continuous data. The OCV characteristic thus obtained is calculated based on the internal resistance r(t) calculated using the current values _I1C (t), _I2C (t) and the terminal voltages _V1C (t), _V2C (t) measured in real time. Therefore, the OCV characteristic obtained in this embodiment is highly accurate, taking into account fluctuations due to various error factors such as the battery temperature, charging rate, and deterioration rate of the secondary battery 10.

In the power storage system 1 of the present 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 (t) of the secondary battery 10 during charging is calculated for each period of the pulse current using the calculated internal resistance r(t). In addition, in the power storage system 1 of the present embodiment, the internal resistance r(t) of the secondary battery 10 during discharging is calculated for each period of the pulse current based on the above formula (9), and the open circuit voltage V _OC (t) of the secondary battery 10 during discharging is calculated for each period of the pulse current using the calculated internal resistance r(t). This makes it possible to repeatedly calculate the internal resistance r(t) and open circuit voltage V _OC (t) of the secondary battery 10 according to the charging state of the secondary battery 10 and the running state of the vehicle, and to obtain the OCV characteristics according to the charging rate and running state as continuous data.

Furthermore, in the energy storage system 1 of this embodiment, the open circuit voltage V _OC (t) acquired as continuous data 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 acquire OCV characteristics with higher accuracy.

The present invention has been described above based on the embodiments, but the present invention is not limited to the above embodiments, and modifications may be made without departing from the spirit of the present invention, and publicly known or well-known technologies may be appropriately combined.

For example, in the above embodiment, the median of the normal distribution of the open-circuit voltage V _OC (t) acquired as continuous data is calculated as the open-circuit voltage of the secondary battery 10, but the average value of the open-circuit voltage V _OC (t) acquired as continuous data may be calculated as the open-circuit voltage of the secondary battery 10. Also, it is not essential to acquire 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 acquire at least one of them.

1: Power storage system 10: Secondary battery 20: MCU (calculation unit)
21: OCV analysis unit (calculation unit)
30: Current superposition circuit 40: Voltage sensor 50: Current sensor 60: Charger (charging unit)
70: Load 100: Calculation device (calculation device for calculating open circuit voltage of secondary battery)
r(t): Internal resistance I _1C (t) : Current value (charge/discharge current)
_I2C (t) : Current value (charge/discharge current)
_V1C (t) ：Terminal voltage _V2C (t) : Terminal voltage V _OC : Open circuit voltage V _OC (t) : Open circuit voltage

Claims (5)

a current superposition circuit that superposes a pulse current on a charging current supplied from a charging unit of the 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 a current value of the charging current on which the pulse current is superimposed by the current superimposition circuit, the amount of increase or decrease corresponding to a 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, the amount of increase or decrease corresponding 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 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 ,
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. 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 amount of increase or decrease in a current value of the discharge current on which the pulse current is superimposed by the current superimposition circuit, the amount of increase or decrease corresponding to a 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 discharge current by the current superimposition circuit, the amount of increase or decrease corresponding 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 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 ,
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 . 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. a secondary battery of the 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 ... and the calculated internal resistance of the secondary battery during charging ,
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. a secondary battery of the 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 amount of increase or decrease in the current value detected by the current sensor when the pulse current is superimposed on the discharge 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 discharge 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 discharge 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 discharge 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 discharge current by the current superposition circuit, and the calculated internal resistance of the secondary battery during discharge ,
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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