JP2003035755A - Method for detecting stored power in battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately estimate the stored power in a secondary battery. SOLUTION: In the method for detecting the stored power in a battery for detecting the stored power in a secondary battery, the first stored power is calculated based on the charge/discharge current of the secondary battery, at the same time the second stored power is calculated based on the detection value of at least voltage and current in the secondary battery, weighted averaging is made for averaging by multiplying the first and second calculation values of stored power by a weighting coefficient, where the weighting coefficient is calculated based on at least one detected value out of the current, voltage, and temperature of the secondary battery.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a battery system, and more particularly to a system for managing the state of an assembled battery in which secondary batteries (hereinafter referred to as batteries) are assembled.

[0002]

2. Description of the Related Art Conventionally, there has been a method of detecting the amount of stored electricity in a battery by measuring the battery voltage, charge / discharge current and temperature to detect the state of charge of the battery. For example, it is disclosed in Japanese Patent Laid-Open No. 11-121048. In the conventional battery charge detection method, first, the battery voltage, current, and temperature are measured, and the change in the charge amount is calculated from the integrated value of the current, and the voltage, current, and temperature are compared with the battery characteristics to determine the charge amount. The method of determination was switched depending on the region of the amount of stored electricity.

[0003]

In the method of determining the charged amount of the battery from the integrated value of the current, the error contained in the integrated value of the current increases with the passage of time, and the error of the charged amount increases. In order to eliminate this error, there has been a problem that it is necessary to compare the battery voltage, the current, and the temperature with the battery characteristics to obtain the charged amount and to change the charged amount in order to calibrate the charged amount.

The present invention has been made in order to solve the above-mentioned problems, and an object thereof is to accurately estimate the charged amount even when the charged amount does not change.

[0005]

According to the invention of the present invention, a first charged amount is calculated based on a current during charging / discharging of a secondary battery,
A second charge amount is calculated based on a current and a voltage detected during charge / discharge of the secondary battery, and a weight is calculated based on at least one detected value of current, voltage, and temperature during charge / discharge of the secondary battery. It is characterized in that the coefficient is calculated, and the charged amount detection is performed by performing a weighted averaging process of averaging by multiplying the first and second calculated charged amounts by the weighting coefficient.

As a result, it is possible to accurately estimate the charged amount.

In addition to the above description, the present invention is characterized in that the weighting factor calculated based on at least one of the detected values of the current, voltage, and temperature is updated at predetermined time intervals.

As a result, it is possible to calculate the charged amount more accurately.

[0009]

FIG. 3 is a simplified equivalent circuit model of a battery. V + terminal 335 and V- terminal 336 are the positive and negative terminals of the battery, E is the electromotive voltage of the battery, R is the internal resistance, C is the parasitic capacitance, and Rc is the discharge resistance of the parasitic capacitance. Of these, E is the amount of electricity stored (hereinafter, remaining amount, SOC)
, R is one of the parameters for determining deterioration. V +
The battery voltage V between the terminals 335 to V-terminal 336, the current I flowing through the battery, and the temperature T outside the housing of the battery are directly measurable state quantities. Vc is the polarization voltage of C, IR is the voltage generated by the internal resistance R and the charging / discharging current I, and E,
R, C, Rc, Vc, etc. are state quantities that cannot be directly measured.

When the battery is charged and discharged with a current sufficiently smaller than the capacity of the battery, since Vc and IR are sufficiently small with respect to E, it can be approximated as V≈E. However, in the case of a large current, Vc and IR are large and V ≠ E.

Therefore, in order to obtain E and R, Vc is first estimated from the current history and V is corrected (V '= V-V).
c). Then, V '= IR + E is approximated, and the intercept and slope are obtained by a method such as regression analysis to estimate E and R.

FIG. 1 is a diagram showing a battery system which is an embodiment of the present invention. An assembled battery 10 in which a plurality of batteries are connected in series, and a current sensor 2 for detecting a current I flowing through the batteries
2. A voltage sensor 20 for detecting the battery voltage V for each predetermined number of series, a temperature sensor 24 for detecting the temperature T outside the battery casing, a relay 26, and a battery control device connected to each sensor and the relay and the host controller. It is composed of 30.

The battery control device 30 includes a battery voltage V of each of the current detection device 104 for measuring the current I and the assembled battery 10.
Voltage detecting device 102 for measuring temperature, temperature detecting device 100 for measuring temperature T, and integrated value ∫I of current flowing within a predetermined period
Integrated current detection device 106 for measuring dt, sampler 108 for determining the timing at which each detection device samples data, remaining amount estimation device 130, protection determination device 13
2, and peripheral device 134.

The remaining amount estimating device 130 is a remaining amount calculating device 11
0, a remaining amount correction device 116, a weighted averaging device 112, a storage device 114, and a clock 118.

The remaining amount calculation device 110 receives the temperature T, the battery voltage V, the current I, and the integrated value ∫Idt of the current from each detection device, and the temperature T, the battery voltage V, the current I, and the integrated value ∫I of the current.
A function of dt is calculated to calculate an error σa corresponding to an error between the remaining amount SOCa and the remaining amount SOCa for a predetermined number of batteries in a predetermined calculation cycle and output to the weighted averaging device 112. Details of the calculation will be described later.

The remaining amount correction device 116 receives the remaining amount SOC and σ output from the weighted averaging device 112 last time from the storage device 114 and the integrated value ∫Idt of the current from the integrated current detection device 106, and changes the remaining amount. And σ increase by the integrated value of current ∫
The remaining amount SOC is corrected by calculating with the function of Idt, and the present remaining amounts SOCb and σb are obtained and output to the weighted averaging device.
Details of the calculation will be described later.

The weighted averaging device 112 is the remaining amount calculating device 1.
10 and the remaining amount correction device 116 from the remaining amount SOCa,
The remaining SOCb and σa and σb are received from the clock,
The weight and σ after the weighted average calculation are calculated by the function of σ, and the remaining amount SOC is weighted and averaged according to the calculated weight to estimate the remaining amount SOC. Details of the calculation will be described later.
The calculated remaining amount SOC and σ are output to the storage device 114, the protection determination device 132, and the peripheral device 134.

The peripheral device 134 comprises a display device 120, a communication device 122, a cooling device 124, and a current interruption device 126.

The protection determining device 132 is the temperature detecting device 10.
0 to temperature T, voltage detection device 102 to battery voltage V
, The current I from the current detection device 104, and the remaining amount estimation device 1
The remaining amount, σ, and R are received from 30, and the battery voltage V, the current I, the temperature T, the sum of the remaining amount and σ, and R are determined to be within the use range, and the display device 120, the communication device 122, and the cooling device are used. A protection command is output to the device 124 and the current interruption device 126.

Further, the display device 120 displays not only the protection command but also the remaining amount, and the communication device 122 is the protection determination device 132.
And the remaining amount and the like, if necessary, are also output to a higher-level controller described later.

The cooling device 124 cools the battery based on a command from the protection determination device 132.

The current interrupt device 126 controls the relay 26 provided on the current path of the battery 10.

The operation of the battery controller 30 is as follows. First, when the operation is started, the battery voltage V and the current are detected by the sampler 108, the voltage detector 102, the current detector 104, the integrated current detector 106, and the temperature detector 100, for example, every one second. Measure I, integrated value of current ∫Idt, and temperature T.

Next, the remaining amount estimating device 130 reads the battery voltage V and the current I, the integrated value ∫Idt of the current, and the temperature T from each detecting device to estimate the remaining amount SOC and σ.

FIG. 4 is a diagram showing the relationship between E and the remaining amount of nickel-hydrogen batteries, nickel-cadmium batteries, graphite-based negative electrode Li-ion batteries, lead batteries, and the like. In these batteries, it is difficult to obtain the remaining amount in the region where E hardly changes with the change in the remaining amount. First, the remaining amount calculation device 1
In 10, C and Rc are defined in advance, the current detection result is input, Vc is calculated using the weighted product of the pulse response, the state transition equation, etc., and V is corrected. Next, the corrected data of the battery voltage V and the current I is subjected to regression analysis by the least square method or the like to calculate E and R. From the battery characteristics shown in FIG.
It is converted to Ca and output to the weighted averaging device 112. The calculation formula is as follows.

[0026]

[Equation 1] Here, the remaining amount SOC _table (E) is a value obtained by converting the voltage E into SOC by referring to the table. Further, the obtained R is output to the protection determination device 132. The calculation up to this point is also partially described in Japanese Patent Application No. 2000-034314 filed by the present applicant. Next, σa is obtained. S as described above
When the OC is obtained, the error factor is the voltage measuring device 1.
02 error, an error expected for Vc correction, and a deviation in measurement timing of current and voltage. Sum of those errors δ
The voltage obtained by adding E to E and the voltage obtained by subtraction are converted into the remaining amount SOC, and σa is calculated by the difference between the two remaining amount SOCs, and output to the weighted averaging device 112. The calculation formula is as follows.

[0027]

[Equation 2] In the case of the calculation result of E as shown in FIG.
As compared with the case of the calculation result of E as in (b), the remaining amount SOC
Since the sensitivity of E with respect to
Is big.

In this embodiment, the error of the voltage measuring device 102 is defined as a constant value and the error of Vc is defined as a ratio with respect to Vc, but the error of Vc may be a constant value. Also, C and Rc
Varies depending on the battery type and varies depending on the temperature T. In this embodiment, a table is prepared as a function of the temperature T, but it may be approximated by a formula. In addition, the variance of the current I that can be calculated simultaneously during the regression analysis and the difference between the maximum value and the minimum value of the current I
May be reflected in.

Here, a device for estimating deterioration from the internal resistance may be incorporated together with the remaining amount estimating device 130. Also,
Even if Vc is not corrected for a battery having a small internal polarization, a direct regression analysis of the battery voltage V is performed to obtain a sufficiently accurate E.
Can be asked. Further, E can be obtained from the battery voltage V, the current I, and the known R without performing regression analysis for the battery in which the change in R is small.

Further, the voltage E is compared with the remaining amount SOC by referring to the table.
When converting to, a plurality of tables may be prepared for the battery temperature and the table corresponding to the temperature detection result may be selected.

The calculation up to this point using "Equation 1" and "Equation 2" is an example of the method of calculating the second charged amount described in the claims, and E is based on the detected values of current and voltage. As a result, the second charged amount is also calculated based on the detected values of current and voltage.

In the remaining amount correction device 116, the storage device 114
From the previous SOC output by the weighted averaging device (t-
1) and σ (t-1) are read, the integrated value ∫Idt of the current read from the current accumulator is divided by the total capacity Q of the battery, and converted to the change in the remaining SOC to correct the remaining SOC. And outputs it to the weighted averaging device. The calculation formula is as follows.

[0033]

[Equation 3] In addition, the error (δ∫Idt) of the current accumulator is calculated as the remaining SOC.
Is converted to and added to σ, and σb is output to the weighted averaging device 112. The calculation formula is as follows.

[0034]

[Equation 4] Although the description about the charging efficiency of the battery is omitted, it is also effective to carry out the current integration on the charging side and the discharging side separately to correct the remaining amount in consideration of the charging efficiency.

The calculation up to this point using the equations 3 and 4 is an example of the method for calculating the first charged amount described in the claims.

FIG. 5 shows the relationship between σ and weight. In the weighted averaging device, based on σa and σb input from the remaining amount calculation device 110 and the remaining amount correction device 116, the σ-weighting coefficient relationship shown in FIG.
The SOC is weighted and averaged by adjusting the sum of the weighting factors to be 1. Here, in FIG. 5, the relationship between σ and the weighting coefficient is shown in the form of a graph, but in practice it may be held as a table or a formula. The calculation formula is as follows.

[0037]

[Equation 5] σ is calculated using the following calculation formula.

[0038]

[Equation 6] Here, Wa is a weighting coefficient of SOCa, and Wb is a weighting coefficient of SOCb. Wa and Wb are functions of σa, σa is a function of E, and E is a function of detected values of current, voltage, and temperature. As a result, Wa and Wb are calculated based on the detected values of current, voltage, and temperature. ing.

Next, the remaining SOC and σ obtained by the calculation are output to the storage device 114, the protection determination device 132, the display device 120, the communication device 122 and the like.

Here, in the case of a battery having an extremely long Vc time constant, when the current does not flow for a long time, the true Vc and the calculated Vc hardly change and the error does not change. Vc correction error occurs. If the estimation result of E includes an offset error, the error cannot be removed by any filtering process. In order to avoid such a problem, the variance of I and the difference between the maximum value and the minimum value of I, which are obtained at the same time when calculating the regression analysis, are compared with a reference value. By setting the coefficient to 0, it is possible to suppress the occurrence of offset error by extracting only when Vc is changing.

The above is the operation of the remaining amount estimation device 130 during operation. However, when the device is started, the remaining amount SOC held in the storage device 114 may have a large error due to self-discharge of the battery or the like. is there. In order to avoid this error, the operation at the time of start-up is different from that during operation.

In the remaining amount estimating device 130, the difference between the time at the time of the previous end and the time at the time of starting is calculated at the time of starting, and when the time more than the threshold has passed, the remaining amount calculating device 110 makes the first measurement. The battery voltage V is regarded as E, and the remaining SOCa and σ
Find a. Next, in the weighted averaging device 112, the remaining amount SO
The weight of Ca is set to 1 and the weight of the calculation result of the remaining amount correction device is set to 0. If the difference between the time at the end of the previous time and the time at the start is less than or equal to the threshold value, the same calculation as during driving is performed.

FIG. 6 shows σ, σa, and Wa in the case where the system is started after a lapse of time equal to or more than the above-mentioned threshold value from the time of the previous end.
It is a figure which shows the time change of. Although σ at the time of startup is equal to σa, σ is always smaller than σa after the second estimation of the remaining amount because of the characteristics of the arithmetic expression. If σa does not change after the start-up, σ decreases with the increase in the number of remaining amount calculations. When the remaining amount changes from the remaining amount region where the sensitivity of E with respect to the remaining amount shown in FIG. 4 (b) is low to the region where the sensitivity is high (FIG. 6), σa decreases, so Wa increases and σ Is decreasing. On the contrary, when the residual amount area with good sensitivity is changed to the insensitive area (FIG. 6), σa becomes large, so that the weight of the residual amount SOCa decreases, and the error included in the integrated value ∫Idt of the current is reduced. Therefore, σ increases. However, as σ increases, Wa increases, and the effect of error accumulation of the integrated value ∫Idt of the current and the effect of error reduction of the average value due to the increase in the number of measurements are balanced, and σ does not increase above the design value. Conventionally, in the remaining amount region where the sensitivity of E is poor, the remaining amount is calculated based only on the integrated value ∫Idt of the current,
Since there is an error accumulation in the integrated value ∫Idt of the current, the error of the remaining amount was inexhaustibly expanded with the passage of time. for that reason,
It was necessary to periodically calibrate the remaining amount by changing the remaining amount to a region where the E sensitivity is good. However, in this embodiment, E
Even if the battery is continuously used in the remaining amount area where the sensitivity is low, the error does not increase beyond the design value, so there is no need to change the remaining amount area.

FIG. 7 is a diagram showing the relationship between the remaining amount estimation accuracy and time. Generally, the error of the average value of the measurement results obtained by measuring a plurality of times is proportional to the −0.5th power of the number of measurements. The maximum error in this embodiment is the intersection of the curve a proportional to (measurement count × measurement period) ^−0.5 with the worst value of σa as the intercept, and the straight line b indicating the accumulation of the residual amount error due to current integration. Therefore, the design accuracy is satisfied by using current integration such as a straight line connecting the origin and the intersection of the straight line corresponding to the precision = design accuracy and the curve a.
Here, the smaller the slope of the straight line b, the higher the accuracy of current integration and the less error accumulation. Battery capacity 6.5Ah, σa
Assuming that the worst value of is 30%, the operation cycle is 1 minute (the time for which the data for regression analysis is gathered), and the design accuracy is 5%, the offset error allowed for the current integration is calculated to be 0.5A.

Conventionally, after the remaining amount is calibrated, the current integration is continued until the next calibration. Therefore, a straight line b'having the accuracy of the calibration as the intercept and the accuracy of the current integration as the slope is drawn, and the calibration is performed. The accuracy in the cycle is the maximum error. For example, when the calibration is performed every 500 km, assuming that the average speed is 25 km / h, the calibration cycle is 20 hours. Error during calibration is 1
If the allowable offset error is calculated under the other conditions similar to those described above, 0.013 A is obtained.

As described above, in order to realize the remaining amount accuracy equivalent to the conventional one, the present invention requires only 1/10 or less current integration accuracy. Therefore, the cost of the battery system can be reduced by using an inexpensive current sensor with lower accuracy.

Next, in the protection determination device, when the sum of the remaining amount and σ obtained by the weighted averaging device exceeds the set upper and lower limits, an overcharge / discharge abnormality is displayed, and the display device 120 or the communication device 122,
Alternatively, it is output to the current interruption device 126. If the variance of the remaining amount or the difference between the maximum value and the minimum value is calculated and the setting upper limit is exceeded, an equal charge request is issued to the display device 120 or the communication device 122.
Alternatively, it is output to the current interruption device 126. Equal charging is to continue charging with a small current even when the remaining amount is 100%. The fact that the charging efficiency of the battery decreases when the remaining amount increases and the remaining amount reaches the limit is utilized, and as a result, the battery with the lower remaining amount catches up with the battery with the higher remaining amount, and the variation in the remaining amount is reduced.

FIG. 8 is a diagram showing an example of the remaining amount calculation result using the present invention. Here, the current pattern in the period from 500 seconds to 5500 seconds was repeated five times to energize the battery to estimate the remaining amount SOC. Integrated value of current ∫Idt
The SOC obtained from the above does not eliminate the error of the initial value, and the remaining amount SOC obtained from E calculates a value with an error centered on the true value during energization. According to the present invention, the remaining amount SOC obtained by weighted averaging these changes in a manner similar to the true value, while eliminating the error contained in the initial value with the passage of time,
It approaches the true value. Here, when no current flows,
The error of the remaining amount SOC obtained from E becomes almost constant, and the remaining amount SOC estimation result does not approach the true value even by the present invention.
In such a case, when the measured current value is less than or equal to the threshold value, it is desirable to set the weight of the remaining amount SOC obtained from E to 0. Further, since the present invention is most effective when the current changes randomly, it is desirable to intentionally change the current after operating at a constant current for a certain period or more.

FIG. 2 shows a schematic diagram when the present invention is applied to a hybrid vehicle. 2, the same components as those in FIG. 1 are designated by the same reference numerals. As illustrated, the battery 10 is an assembled battery in which a plurality of batteries are connected in series, and is connected to a motor generator 60 via an inverter 40. Motor generator 60
Is connected to the engine 50 and the tire 70. Also,
The control CPU 32 includes a battery control device 30, an inverter 40,
It is connected to the engine 50, receives the state of the battery from the battery control device 30, and controls the motor generator 60 via the engine 50 and the inverter 40.

When a hybrid vehicle operates, energy is taken out from the engine or battery during acceleration, and kinetic energy is regenerated to the battery during deceleration. Therefore, it is preferable that the battery is always kept at a remaining amount of around 50% so that it can receive both charge and discharge.

As a characteristic of the battery, the usage pattern in which the remaining amount changes little tends to be less likely to deteriorate than the usage pattern in which the remaining amount changes greatly.

For this reason, it is desirable to control so as not to move largely from around 50% as much as possible, but conventionally it was necessary to periodically change the remaining amount in order to calibrate the remaining amount. However, with the method of the present invention, it is not necessary to change the remaining amount in order to perform the conventional remaining amount calibration,
The battery life can be extended and the running cost of the hybrid vehicle can be reduced.

Further, although the above embodiment is based on the battery storage amount detection method, the present invention is also applicable to a storage device using the battery storage amount detection method.

[0054]

According to the present invention, the amount of electricity stored in a battery can be accurately estimated.

[Brief description of drawings]

FIG. 1 is a diagram showing an outline of a battery system according to an embodiment of the present invention.

FIG. 2 is a diagram showing an outline of a hybrid vehicle according to the embodiment of the present invention.

FIG. 3 is a diagram showing an equivalent circuit of a battery according to the embodiment of the present invention.

FIG. 4 is a diagram illustrating a relationship between E and a remaining amount according to the embodiment of the present invention.

FIG. 5 is a diagram showing a relationship between σ and weight according to the embodiment of the present invention.

FIG. 6 is a diagram showing a calculation result of σ and a weight according to the embodiment of the present invention.

FIG. 7 is a diagram showing a relationship between remaining amount accuracy and time according to the embodiment of the present invention.

[Explanation of symbols]

10 ... Battery pack, 20 ... Voltage sensor, 22 ... Current sensor, 24 ... Temperature sensor, 30 ... Battery control device, 32 ...
Control CPU, 40 ... Inverter, 50 ... Engine, 60
... motor generator, 70 ... tire, 100 ... temperature detecting device, 102 ... voltage detecting device, 104 ... current detecting device, 106 ... integrated current detecting device, 108 ... sampler,
110 ... Remaining amount calculation device, 112 ... Weighted averaging device, 11
4 ... Storage device, 116 ... Remaining amount correction device, 118 ... Clock,
120 ... Display device, 122 ... Communication device, 124 ... Cooling device, 126 ... Current interruption device, 130 ... Remaining amount estimation device, 1
32 ... Protection determination device, 134 ... Peripheral device, 335 ... V +
Terminal, 336 ... V-terminal.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Akihiko Emori             7-1-1, Omika-cho, Hitachi-shi, Ibaraki Prefecture             Inside the Hitachi Research Laboratory, Hitachi Ltd. (72) Inventor Masato Isogai             Hitachima, 1-88, Torora, Ibaraki City, Osaka Prefecture             Within Kucsel Co., Ltd. F term (reference) 2G016 CA03 CB13 CB22 CC01 CC02                       CC04 CC06 CC07 CC24 CD02                       CF06                 5H030 AA03 AA04 AA06 AS08 FF21                       FF42 FF43 FF44

Claims (11)

[Claims] 1. A battery storage amount detection method for detecting a storage amount of a battery based on a current, a voltage, and a temperature detected during charging / discharging of a secondary battery, which is based on a current during charging / discharging of the secondary battery. Is calculated, and a second storage amount is calculated based on the current and voltage detected during charging / discharging of the secondary battery, and at least one of current, voltage, and temperature during charging / discharging of the secondary battery. A battery power storage characterized by calculating a weighting coefficient based on one detection value, and performing a weighted averaging process of averaging by multiplying the first and second calculated power storage values by the weighting coefficient to detect the power storage amount. Quantity detection method. 2. The battery storage amount detecting method according to claim 1, wherein the updating of the weighting factor calculated based on at least one detected value of the current, voltage, and temperature is performed at predetermined time intervals. A method for detecting the amount of stored electricity in a battery, comprising: 3. The battery storage amount detection method according to claim 1, wherein the weighting factor is calculated using at least one detection value of current, voltage and temperature. And the estimated error value of the second stored electricity amount calculation method. 4. The battery storage amount detection method according to any one of claims 1 to 3, wherein the second storage amount calculation method includes: a terminal voltage of the secondary battery; A method for detecting the amount of stored electricity in a battery, characterized in that an amount of stored electricity and an error in the amount of stored electricity are calculated based on the current flowing through the next battery. 5. The battery storage amount detection method according to claim 1 or 2, wherein the first storage amount calculation method is a storage amount detection value calculated by the weighted average in a time step one time before. Is set as an initial value, and the first storage amount is calculated by adding the storage amount change value calculated from the charging / discharging current integrated value of the secondary battery in the time step period to the initial value. Method for detecting the amount of stored electricity in a battery. 6. A power storage device for controlling a charging / discharging current of the secondary battery based on a power storage amount calculated by using at least one battery power storage amount detection method according to claim 1, wherein: The charging / discharging current control means for controlling the current supplied from the secondary battery to the load, the terminal voltage of the secondary battery, the current, and the detection means for detecting the temperature, respectively, the charging / discharging current control means is A power storage device, wherein a pulsed current component is superimposed on the current when the time change of the current supplied from the secondary battery to the load is less than or equal to a reference value. 7. A power storage device for controlling a charging / discharging current of the secondary battery based on a power storage amount calculated by using at least one battery power storage amount detection method according to claim 1, wherein: A power storage device, characterized in that when the current is equal to or more than a predetermined value, the first and second power storage amounts and the expected error value are calculated. 8. A power storage device for controlling a charging / discharging current of the secondary battery based on a power storage amount calculated by using at least one battery power storage amount detection method according to claim 1, wherein: Current detection means for detecting the current flowing through the secondary battery,
A battery for detecting the terminal voltage of the secondary battery, wherein when the current is equal to or higher than a predetermined value, the storage amount of the secondary battery and an estimated error value are calculated based on the current and the terminal voltage. A power storage device comprising an amount calculation means. 9. A power storage device for controlling a charging / discharging current of the secondary battery on the basis of a power storage amount calculated by using at least one battery power storage amount detecting method according to claim 1. A power storage device comprising: a startup detection unit that detects that a discharge current has flowed, and the storage amount of the secondary battery is calculated by the second storage amount calculation method according to the startup detection unit. 10. The power storage device according to claim 9, wherein the elapsed time after the storage amount of the secondary battery is calculated by the second storage amount calculation method according to the starting means is a predetermined value. A power storage device comprising a prohibition unit that prohibits calculation by the second storage amount calculation method when the time has not been reached. 11. A power storage device for controlling a charging / discharging current of the secondary battery based on a power storage amount calculated by using at least one battery power storage amount detection method according to claim 1. A power storage device, wherein the secondary battery is any one of a lead battery, a nickel hydrogen battery, a NiCd battery, and a lithium ion battery.