JP2020177813A - Power storage system - Google Patents

Abstract

To monitor the state of a power storage device with high accuracy, on the basis of voltage and current of the power storage device.SOLUTION: A power storage system 1 includes a voltage sensor 20 for detecting voltage of a battery 10 repeatedly, a current sensor 30 for detecting current inputted to the battery 10 and outputted therefrom repeatedly, and a battery ECU 40 for calculating the internal resistance of the battery 10. When the first current detection time by the current sensor 30, the voltage detection time by the voltage sensor 20 and the second current detection time by the current sensor 30 are in this order, the battery ECU 40 calculates the internal resistance on the basis of voltage VB1 at the voltage detection time and current IB1 at the first current detection time, if a time difference TA between the voltage detection time and the first current detection time is shorter than a time difference TB between the second current detection time and the voltage detection time, and calculates the internal resistance on the basis of the voltage VB1 at the voltage detection time and current IB2 at the second current detection time if the time difference TA is longer than the time difference TB.SELECTED DRAWING: Figure 6

Description

The present disclosure relates to a power storage system, and more specifically to a power storage system including a voltage sensor and a current sensor.

In recent years, vehicles such as hybrid vehicles have become widespread. These vehicles are provided with a sensor for detecting the voltage of the power storage device and a voltage sensor for detecting the current input / output to the power storage device. The vehicle control device calculates the internal resistance or SOC (State Of Charge) of the power storage device based on the signals from the voltage sensor and the current sensor. As a result, the control device monitors the state of the power storage device.

The battery monitoring system disclosed in Japanese Patent Application Laid-Open No. 2014-200125 (Patent Document 1) includes a current / voltage measuring unit and a plurality of voltage measuring units. The current / voltage measuring unit measures the current of the plurality of batteries connected in series and the voltage of the first battery among the plurality of batteries according to the measurement instruction. The plurality of voltage measuring units measure the voltage of the second battery other than the first battery among the plurality of batteries according to the measurement instruction.

Japanese Unexamined Patent Publication No. 2014-200125

In the following, as an example of the parameters representing the state of the power storage device, the internal resistance of the power storage device will be described. The internal resistance of the power storage device is calculated by dividing the voltage value detected by the voltage sensor by the current value detected by the current sensor. Since the voltage value and the current value can change with time, it is desirable to use the voltage value and the current value detected at the same timing in order to calculate the internal resistance of the power storage device with high accuracy. For example, in the battery monitoring system disclosed in Patent Document 1, the detection timing of the voltage value and the detection timing of the current value can be matched by appropriately setting the output timing of the measurement instruction.

However, depending on the configuration of the power storage system, it is not always possible to match the detection timing of the voltage value with the detection timing of the current value. For example, it may be difficult to match the two detection timings depending on the method / operation of the voltage sensor and the current sensor. Then, due to the time difference (synchronization deviation) of the detection timing, the calculation accuracy of the internal resistance of the power storage device may decrease, in other words, the state of the power storage device may not be monitored with high accuracy.

The present disclosure has been made to solve such a problem, and an object of the present disclosure is to enable highly accurate monitoring of the state of the power storage device based on the voltage and current of the power storage device.

A power storage system according to a certain aspect of the present disclosure repeatedly detects a power storage device, a voltage sensor that repeatedly detects the voltage of the power storage device and outputs a signal indicating the detection result, and repeatedly detects the current input / output to the power storage device. It includes a current sensor that outputs a signal indicating a detection result, and a calculation device that calculates a parameter indicating the state of the power storage device based on a signal from the voltage sensor and a signal from the current sensor. In the arithmetic unit, when the first current detection time by the current sensor, the voltage detection time by the voltage sensor, and the second current detection time by the current sensor are arranged in this order, the voltage detection time and the first current detection time When the time difference between and is shorter than the time difference between the second current detection time and the voltage detection time, the parameter is calculated based on the voltage value at the voltage detection time and the current value at the first current detection time. On the other hand, when the time difference between the voltage detection time and the first current detection time is longer than the time difference between the second current detection time and the voltage detection time, the voltage value at the voltage detection time and the second The parameter is calculated based on the current value at the current detection time.

According to the above configuration, the arithmetic unit calculates the time difference between the first current detection time and the subsequent voltage detection time, and also between the voltage detection time and the second current detection time. Calculate the time difference. Then, the arithmetic unit calculates a parameter (internal resistance, SOC, etc.) by combining the voltage and the current having a relatively small time difference. Since it is highly possible that the smaller the time difference is, the smaller the amount of change in the current during that time is, the parameter calculation error caused by the time difference can be reduced and the parameter calculation accuracy can be improved. Therefore, the state of the power storage device can be monitored with high accuracy.

According to the present disclosure, the state of the power storage device can be monitored with high accuracy based on the voltage and current of the power storage device.

It is a figure which shows schematic the whole structure of the vehicle in this embodiment. It is a functional block diagram which shows the structural example of the power storage system. It is a timing chart for demonstrating the signal processing in the comparative example. It is a timing chart for demonstrating the first synchronization rule in this embodiment. It is a timing chart for demonstrating the second synchronization rule in this embodiment. It is a flowchart for demonstrating the internal resistance calculation process in this embodiment.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The same or corresponding parts in the drawings are designated by the same reference numerals, and the description thereof will not be repeated.

In the embodiment described below, an example in which the power storage system is mounted on a vehicle will be described in the present disclosure. However, the application of the power storage system according to the present disclosure is not limited to that for vehicles.

[Embodiment]
<Vehicle configuration>
FIG. 1 is a diagram schematically showing an overall configuration of a vehicle according to the present embodiment. FIG. 1 shows a hybrid vehicle as an example. The vehicle 100 includes a power storage system 1. The power storage system 1 includes a battery 10, a voltage sensor 20, a current sensor 30, and an electronic control unit (battery ECU: Electronic Control Unit) 40 for a battery. In addition to the power storage system 1, the vehicle 100 includes a system main relay (SMR) 51, a smoothing capacitor C1, a converter 52, a smoothing capacitor C2, inverters 61 and 62, and motor generators 71 and 72. , The engine 81, the power dividing device 82, the drive wheels 83, and the hybrid electronic control unit (HV-ECU) 90 are further provided.

The battery 10 is an assembled battery including a plurality of cells. Each cell is, for example, a nickel metal hydride battery or a lithium ion secondary battery. The battery 10 is discharged to supply electric power to the traveling motor generator 72. Further, the battery 10 is charged by receiving the electric power output from the converter 52 to the positive electrode line PL1. The battery 10 corresponds to the "power storage device" according to the present disclosure. As the "storage device" according to the present disclosure, a capacitor such as an electric double layer capacitor may be adopted instead of the battery 10.

The voltage sensor 20 is electrically connected between the positive electrode line PL1 and the negative electrode line NL. The voltage sensor 20 detects the voltage VB of the battery 10 and outputs a signal indicating the detection result to the battery ECU 40. The voltage sensor 20 may be provided inside the battery 10 (so-called inside the battery pack).

The current sensor 30 is electrically connected on the positive electrode line PL1 between the battery 10 and the SMR 51. The current sensor 30 detects the current IB input / output to / from the battery 10 and outputs a signal indicating the detection result to the battery ECU 40. The configurations of the voltage sensor 20 and the current sensor 30 will be described in more detail with reference to FIG.

The battery ECU 40 includes an input / output port 43, a CPU (Central Processing Unit) 42, and a memory 42 (see FIG. 2). The battery ECU 40 monitors the state of the battery 10 based on the information stored in the memory 42 and the signals from the voltage sensor 20 and the current sensor 30. The battery ECU 40 outputs the monitoring result to the HV-ECU 90. The configuration of the battery ECU 40 will also be described in detail with reference to FIG.

The SMR 51 is electrically connected to the positive electrode line PL1 and the negative electrode line NL. The closing / opening of the SMR 51 is controlled according to a control signal from the HV-ECU 90. When the SMR 51 is closed, power can be transferred and received between the battery 10 and the converter 52.

The smoothing capacitor C1 smoothes the AC component of the voltage fluctuation between the positive electrode line PL1 and the negative electrode line NL.

The converter 52 is, for example, a boost chopper circuit, and is electrically connected between the battery 10 and the inverters 61 and 62. The converter 52 boosts or lowers the voltage between the positive electrode line PL1 and the positive electrode line PL2 according to the control signal from the HV-ECU 90.

The smoothing capacitor C2 smoothes the AC component of the voltage fluctuation between the positive electrode line PL2 and the negative electrode line NL.

Each of the inverters 61 and 62 is a general three-phase inverter, and is electrically connected to the positive electrode line PL2 and the negative electrode line NL. The inverters 61 and 62 are provided corresponding to the motor generators 71 and 72, respectively. Based on the signal from the HV-ECU 90, the inverter 61 converts the AC power generated by the motor generator 71 into DC power using the output of the engine 81, and outputs the DC power to the positive electrode line PL2. Based on the signal from the HV-ECU 90, the inverter 62 converts the DC power received from the positive electrode line PL2 into AC power, and outputs the AC power to the motor generator 72.

Each of the motor generators 71 and 72 is an AC motor, for example, a permanent magnet type AC synchronous motor in which a permanent magnet is embedded in a rotor. The motor generator 71 generates AC power by using the power of the engine 81 received via the power dividing device 82, and outputs the AC power to the inverter 61. The motor generator 72 generates torque for driving the drive wheels 83 by the AC power received from the inverter 62.

The engine 81 is an internal combustion engine such as a gasoline engine or a diesel engine. The power splitting device 82 is configured by, for example, a planetary gear mechanism (not shown) and is connected to the drive shafts of the engine 81, the motor generator 71, and the drive wheels 83. The power generated by the engine 81 is divided into two paths by the power dividing device 82. One is a path transmitted to the drive shaft of the drive wheel 83, and the other is a path transmitted to the motor generator 71.

Like the battery ECU 40, the HV-ECU 90 includes a CPU, a memory, and input / output ports (none of which are shown). The HV-ECU 90 controls the SMR 51, the converter 52, the inverters 61 and 62, and the engine 81. This control is realized by software processing that executes a pre-stored program in the CPU and / or hardware processing by an electronic circuit. An ECU (engine ECU) for controlling the engine 81 may be separately provided.

<Power storage system configuration>
FIG. 2 is a functional block diagram showing a configuration example of the power storage system 1. With reference to FIG. 2, as described above, the power storage system 1 includes a battery 10, a voltage sensor 20, a current sensor 30, and a battery ECU 40.

The voltage sensor 20 is a digital output voltage sensor and includes an A / D converter 21 and a filter 22. The / D converter 21 converts an analog signal detected by a detection mechanism (for example, a Hall element) (not shown) into a digital signal and outputs the analog signal to the filter 22. The filter 22 filters the digital signal from the A / D converter 21 by software processing and / or hardware processing and outputs it to the battery ECU 40. This signal is output from the voltage sensor 20 when the voltage sensor 20 responds to the output command CMD from the battery ECU 40.

The current sensor 30 is a digital output current sensor and includes an A / D converter 31, a filter 32, and a driver 33. Similar to the A / D converter 21, the A / D converter 31 converts an analog signal detected by a detection mechanism (not shown) into a digital signal and outputs the analog signal to the filter 32. The filter 32 filters the digital signal from the A / D converter 31 by software processing and / or hardware processing and outputs it to the driver 33. The driver 33 stabilizes the output of the digital signal filtered by the filter 32 to the battery ECU 40. The signal from the driver 33 is output to the battery ECU 40 without receiving an output command from the battery ECU 40.

The battery ECU 40 includes a CPU 41, a memory 42, and an input / output port 43. The input / output port 43 includes an input port IN1 that receives a signal from the voltage sensor 20, an output port OUT1 that outputs an output command CMD to the voltage sensor 20, and an input port IN2 that receives a signal from the current sensor 30. .. The input / output port 43 does not include an output port that outputs an output command to the current sensor 30.

The CPU 41 outputs an output command CMD to the voltage sensor 20. Further, the CPU 41 calculates the internal resistance of the battery 10 based on the signal from the voltage sensor 20 and the signal from the current sensor 30. The CPU 41 outputs the calculation result of the internal resistance of the battery 10 to the HV-ECU 90. The CPU 41 may include a soft filter 411 that filters the signal by software.

<Voltage / current detection timing>
The power storage system 1 configured as described above is characterized in signal processing by the battery ECU 40. In order to facilitate understanding of this feature, the following description will be made in comparison with the signal processing in the comparative example. Since the configurations of the voltage sensor and the current sensor in the power storage system according to the comparative example are the same as the configurations of the voltage sensor 20 and the current sensor 30 in the power storage system 1 according to the present embodiment, the description will not be repeated. In the following, when the components (CPU 41, input / output port 43, etc.) included in the battery ECU 40 are not particularly distinguished, they are simply referred to as the battery ECU 40. The battery ECU 40 corresponds to the "arithmetic unit" according to the present disclosure.

FIG. 3 is a timing chart for explaining signal processing in the comparative example. With reference to FIG. 3, the battery ECU 40 outputs an output command CMD to the voltage sensor 20 at regular intervals, for example. The voltage sensor 20 transmits (outputs) a signal indicating the detection result of the voltage of the battery 10 in response to the output command CMD. In the example shown in FIG. 3, the first detection of the voltage value (voltage VB1) of the battery 10 is completed at time t13. In other words, the battery ECU 40 acquires the voltage value of the battery 10 at time t13 as the voltage VB1. Similarly, the second detection of the voltage VB2 is completed at time t16, and the third detection of the voltage VB3 is completed at time t18. In this way, the battery ECU 40 acquires the voltage value of the battery 10 based on the control of the battery ECU 40 itself.

On the other hand, the battery ECU 40 does not output an output command to the current sensor 30. The current sensor 30 autonomously detects the input / output current of the battery 10 and transmits a signal indicating the detection result. In the example shown in FIG. 3, the first detection of the current value (current IB1) of the battery 10 is completed at time t11. After that, the first filtering process of the current IB1 is executed, the filtering process is completed at time t12, and data transmission (output of the detection result) from the current sensor 30 to the battery ECU 40 is started. At the following time t14, the second detection of the current value (current IB2) of the battery 10 is completed. Then, at time t15, the second filtering process of the current IB1 is completed, and data transmission from the current sensor 30 is started. The description is not repeated, but the same applies to the third series of processes.

In this case, the battery ECU 40 calculates the first internal resistance using the voltage VB1 detected at time t13 and the current IB1 detected at time t11. However, there is a time difference of Δt1 between the time t11 and the time t13. This means that the detection timing of the voltage VB1 and the detection timing of the current IB1 are not completely synchronized, and a time lag occurs. Therefore, in the following, this deviation is also referred to as “synchronization deviation Δt1”.

Similarly, the battery ECU 40 calculates the second internal resistance using the voltage VB2 detected at time t16 and the current IB2 detected at time t14. There is a synchronization shift Δt2 between the time t14 and the time t16. Further, the battery ECU 40 calculates the third internal resistance using the voltage VB3 detected at time t18 and the current IB3 detected at time t19. There is a synchronization shift Δt3 between the time t18 and the time t19.

Since the battery ECU 40 does not control the current detection timing, the three synchronization shifts Δt1 to Δt3 may differ from each other. In the example shown in FIG. 3, the synchronization deviation Δt1 is the longest, the synchronization deviation Δt2 is the next longest, and the synchronization deviation Δt3 is the shortest. The longer the synchronization shift, the worse the correspondence between the voltage VB and the current IB. That is, there is a possibility that the voltage VB (or the current IB) changes within the synchronization time, or the amount of the change in the voltage VB (or the current IB) becomes large. Then, the calculation accuracy of the internal resistance of the battery 10 may decrease.

Therefore, in the present embodiment, as described below, a configuration is adopted in which the combination of the voltage VB and the current IB used for calculating the internal resistance is determined according to the magnitude of the synchronization deviation Δt1 to Δt3. More specifically, in the present embodiment, which of the two rules is used to calculate the internal resistance is determined according to the magnitude of the synchronization deviation Δt1 to Δt3. The above two rules are referred to as a "first synchronization rule" and a "second synchronization rule". Each rule will be described below.

FIG. 4 is a timing chart for explaining the first synchronization rule in the present embodiment. FIG. 5 is a timing chart for explaining the second synchronization rule in the present embodiment.

With reference to FIG. 4, in the present embodiment, the battery ECU 40 calculates the “time difference TA” (corresponding to the synchronization deviation Δt1 in the comparative example) between the detection time t21 of the current IB1 and the detection time t23 of the voltage VB1. To do. Further, the battery ECU 40 calculates the “time difference TB” between the detection time t23 of the voltage VB1 and the detection time t24 of the current IB2. Then, the battery ECU 40 compares the time difference TA and the time difference TB. When the time difference TA is shorter than the time difference TB, the battery ECU 40 adopts the first synchronization rule. In the first synchronization rule, the battery ECU 40 calculates the internal resistance of the battery 10 based on the first voltage VB1 and the first current IB1. On the other hand, as shown in FIG. 5, when the time difference TB is shorter than the time difference TA, the battery ECU 40 adopts the second synchronization rule and is based on the first voltage VB1 and the second current IB2. The internal resistance of the battery 10 is calculated.

As described above, in the present embodiment, the battery ECU 40 calculates the time difference TA between the detection timing of a certain current IB and the detection timing of the subsequent voltage VB, and also calculates the detection timing of the voltage VB and the detection timing thereof. The time difference TB with the detection timing of the subsequent current IB is calculated. Then, the battery ECU 40 calculates the internal resistance by combining the voltage VB and the current IB, which have a relatively small time difference. The smaller the time difference, the smaller the amount of change in the current IB during that period is likely to be. Therefore, it is possible to reduce the error of the internal resistance caused by the time difference (synchronization deviation) and improve the calculation accuracy of the internal resistance.

However, in the example shown in this embodiment, since the detection of the current IB is an internal process of the current sensor 30, the battery ECU 40 cannot accurately acquire the detection time (t21, t31, etc.) of the current IB. That is, it is difficult for the battery ECU 40 to directly calculate the time difference TA and TB. On the other hand, the battery ECU 40 can accurately acquire the reception start time (t22, t32, etc.) of the signal indicating the current IB. Then, the magnitude relationship between the time difference TA and the time difference TB can be determined based on the time difference α between the reception start time of the signal indicating the current IB and the detection time (t33, t33, etc.) of the voltage VB. More specifically, the threshold value TH is set in advance based on the specifications of the current sensor 30 (time required for internal processing, etc.). Then, when the time difference α is equal to or less than the threshold value TH, the time difference TA becomes less than or equal to the time difference TB. On the contrary, when the time difference α is longer than the threshold value TH, the time difference TB is shorter than the time difference TA.

The method for setting the time difference α is not limited to the above method. For example, the time difference between the detection time of the voltage VB (t23, t33, etc.) and the reception end time of the signal indicating the current IB immediately after that may be α.

<Internal resistance calculation flow>
FIG. 6 is a flowchart for explaining the internal resistance calculation process in the present embodiment. In FIG. 6, the process executed by the current sensor 30 is shown on the left side of the figure, the process executed by the battery ECU 40 is shown in the center, and the process executed by the voltage sensor 20 is shown on the right side. The central process is read from the main routine by the battery ECU 40 and repeatedly executed every time a predetermined control cycle elapses or a predetermined condition is satisfied. Each step (hereinafter abbreviated as S) executed by the battery ECU 40 is basically realized by software processing by the battery ECU 40, but dedicated hardware (not shown) manufactured in the battery ECU 40 is used. ) May be realized.

In S11, the current sensor 30 detects the current IB flowing through the battery 10. After that, the current sensor 30 performs a predetermined internal process (filtering process, etc.) on the detected current IB (S12), and transmits the process result to the battery ECU 40 (S13). This series of processes does not depend on the command from the battery ECU 40, and is executed independently by the current sensor 30.

On the other hand, in S21, the battery ECU 40 transmits a command (output command) CMD that serves as a trigger for detecting and outputting the voltage VB of the battery 10 to the voltage sensor 20. The voltage sensor 20 detects the voltage VB of the battery 10 in response to the output command CMD from the battery ECU 40 (S31). Further, the voltage sensor 20 performs a predetermined internal process (filtering process, etc.) on the detected voltage VB (S32), and transmits the process result to the battery ECU 40 (S33).

After transmitting the output command CMD, the battery ECU 40 receives the current IB transmitted from the current sensor 30 (S22). Further, the battery ECU 40 receives the voltage VB transmitted from the voltage sensor 20 (S23). The battery ECU 40 temporarily stores the received voltage VB and current IB values in the memory 42.

In S24, the battery ECU 40 calculates the time difference α between the reception start time of the current IB (processing start time of S22) and the reception time of the voltage VB (processing end time of S23). Then, the battery ECU 40 compares the calculated time difference α with the predetermined threshold value TH (S25). As described above, the threshold value α is set so that TA ≦ TB when the time difference α is equal to or less than the threshold value TH, and TB <TA when the time difference α is longer than the threshold value TH.

When the time difference α is equal to or less than the threshold value TH (YES in S25), the battery ECU 40 combines the voltage VB (n) received in the current calculation cycle with the current IB (n) received in the current calculation cycle. The internal resistance R (n) of the battery 10 in the current calculation cycle is calculated according to the synchronization rule (see FIG. 4) (S26). Note that n is a natural number indicating the number of the calculation cycle.
R (n) = VB (n) / IB (n) ... (1)

On the other hand, when the time difference α is longer than the threshold value TH (NO in S25), the battery ECU 40 receives the voltage VB (n) in the current calculation cycle and the current IB (n-1) received in the previous calculation cycle. ), The internal resistance R (n) of the battery 10 in the current calculation cycle is calculated according to the second synchronization rule (see FIG. 5) (S27).
R (n) = VB (n) / IB (n-1) ... (2)

Then, in S28, the battery ECU 40 uses the internal resistance R (n) calculated by the processing of S26 or S27 for monitoring the battery 10 or outputs the internal resistance R (n) to the HV-ECU 90 for charge / discharge control of the battery 10. ..

As described above, in the present embodiment, the voltage is such that the synchronization deviation (Δt1 to t3, etc.) becomes relatively small based on the time difference (TA, TB, etc.) between the current detection time and the voltage detection time. Combine VB and current IB. The smaller the time difference is, the more likely it is that the current IB has not changed during that time, or that the amount of change is small even if the current IB has changed. Therefore, by determining the combination of the voltage VB and the current IB, which have a small time difference in two consecutive calculation cycles for each calculation cycle, the error of the internal resistance due to the synchronization deviation is reduced and the internal resistance The calculation accuracy can be improved.

In the present embodiment, the configuration in which the internal resistance is calculated from the voltage VB and the current IB of the battery 10 has been described as an example, but other parameters that require the simultaneousness of the voltage VB and the current IB are calculated. May be good. Specifically, when the SOC of the battery 10 is performed by referring to the SOC (State Of Charge) -OCV (Open Circuit Voltage) curve obtained in advance, the battery voltage VB (CCV: Closed Circuit Voltage) is used as an ohm. OCV is calculated by subtracting the loss (= IB × internal resistance R) (OCV = VB-IB × R). In this case, if the time difference between the detection time of the voltage VB and the detection time of the current IB is large, the accuracy of OCV calculation will decrease. Therefore, the accuracy of OCV calculation can be improved by the same processing as in the above example.

The embodiments disclosed this time should be considered as exemplary in all respects and not restrictive. The scope of the present disclosure is indicated by the scope of claims rather than the description of the embodiment described above, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

100 vehicles, 1 power storage system, 10 batteries, 20 voltage sensors, 30 current sensors, 21,31 A / D converters, 22, 32 filters, 33 drivers, 40 battery ECUs, 41 CPUs, 411 soft filters, 42 memories, 43 inputs Output port, IN1, IN2 input port, OUT1 output port, 52 converter, 61,62 inverter, 71,72 motor generator, 81 engine, 82 power divider, 83 drive wheel, C1, C2 smoothing capacitor, PL1, PL2 positive electrode line , NL negative electrode wire.

Claims (1)

Power storage device and
A voltage sensor that repeatedly detects the voltage of the power storage device and outputs a signal indicating the detection result,
A current sensor that repeatedly detects the current input / output to and from the power storage device and outputs a signal indicating the detection result.
A computing device for calculating a parameter representing the state of the power storage device based on the signal from the voltage sensor and the signal from the current sensor is provided.
In the arithmetic unit, when the first current detection time by the current sensor, the voltage detection time by the voltage sensor, and the second current detection time by the current sensor are arranged in this order,
When the time difference between the voltage detection time and the first current detection time is shorter than the time difference between the second current detection time and the voltage detection time, the voltage value at the voltage detection time and the said While calculating the parameter based on the current value at the first current detection time,
When the time difference between the voltage detection time and the first current detection time is longer than the time difference between the second current detection time and the voltage detection time, the voltage value at the voltage detection time and the said A power storage system that calculates the parameters based on the current value at the second current detection time.

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