JPH0980131A - Battery capacity estimation method - Google Patents

Abstract

(57) [Abstract] An object of the present invention is to estimate a storage battery capacity in a relatively short time and with high accuracy, to continue power supply even if a power failure occurs during measurement, and to further degrade a specific battery cell. The purpose of the present invention is to provide a method for estimating the storage battery capacity that does not accelerate the battery life. According to the present invention, in a method of discharging a storage battery for a short time, measuring a terminal voltage at that time, and estimating the capacity of the storage battery using the terminal voltage, a reference formula created in advance and the terminal voltage are used. The function conversion related to time is performed so as to be compared and coincident with each other, and the storage battery capacity is estimated with high accuracy.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a storage battery capacity estimation method for measuring a storage battery capacity in use in an uninterruptible power supply system composed of a power converter that inputs AC or DC and a backup storage battery. It is a thing.

[0002]

2. Description of the Related Art A conventional capacity test method is shown in FIG. In FIG. 12, 1 is an AC or DC power supply, 2 is a power converter, 3 is a storage battery, 4 is a load device, 5 is a changeover switch,
6 is a constant current load for discharge. In this method, normally, the storage battery 3 that is connected in parallel to the output terminal of the power conversion device 2 is disconnected and connected to the discharging constant current load 6 to discharge at a predetermined current, and the terminal voltage of the storage battery 3 is discharged. The time required to reach the cutoff voltage is measured, and the product It (Ah) of the discharge current value I and the discharge time t is obtained. For simplicity, the discharging constant-current load 6 may use a simple resistor.
Although this method can accurately grasp the capacity of the storage battery 3, it takes a long measurement time and the storage battery 3 is disconnected from the power feeding system during the measurement. Therefore, if a power failure occurs at this time, the load device 4
There is a drawback that power cannot be continuously supplied to. If the load device 4 is a communication device such as an exchange or a transmission device, the effect of this power failure is extremely large.

In order to solve the drawback that the storage battery is disconnected from the power supply system during measurement, the method shown in FIG. 13 has been conventionally performed. 13, 1 to 4 are the same as those in FIG. 12, 7 is a battery cell having the lowest voltage, 8 is a changeover switch,
Reference numeral 9 is a constant current load for discharging, 10 is a charger for recharging discharged battery cells, and 11 is an AC or DC power supply. FIG.
In the method No. 3, all the cell voltages of the storage battery 3 are measured in advance, and the discharge test as described above is performed on the cell having the lowest voltage among them, and the product I of the discharge current I and the discharge time t is obtained.
Was seeking t (Ah). According to this method, since only one cell of the storage battery 3 composed of a plurality of cells is discharged, even if a power failure occurs during the test, the voltage of the battery 3 is reduced by one cell at the maximum. The power supply to the load device 4 can be continued. So this method
The discharge is only a single cell, and the measurement is simple. However, the measurement time only needs to be the value obtained by dividing the battery capacity,
There was a problem that it was still long and required a lot of operations.

Further, conventionally, in order to shorten the measuring time, from the discharge characteristics by the shallow discharge as shown in FIG.
A method of estimating the discharge characteristics up to the rated capacity has been considered, but the accuracy is poor and it has not been put to practical use. In FIG. 14, the discharge characteristic was estimated from the discharge amount of 0 to 30% by using a linear function to quintic function approximation, and as shown in the figure, the accuracy was poor and it could not be put to practical use. FIG.
4, it seems that the fourth-order approximation is relatively correct, but the discharge voltage targeted for capacity estimation is 1.9V to 1.8V.
V, not fitted.

[0005]

The conventional battery capacity test cannot be put to practical use because the capacity accuracy is poor when trying to shorten the measurement time. Further, when the measurement time is lengthened, the capacity accuracy is improved, but the measurement time is long and many operations are required. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a storage battery capacity estimation method that can be measured in a relatively short time and has relatively good accuracy.

[0006]

In order to achieve the above object, the storage battery capacity estimating method according to the present invention creates a highly accurate discharge characteristic reference formula for a new battery of the same kind as the storage battery in advance, and In the discharge state, measure the terminal voltage and discharge time. Furthermore, by comparing the discharge characteristic reference formula, which was acquired in advance, with the discharge characteristic reference formula and using a modified reference formula modified to match the measured terminal voltage and discharge time, Estimate time to reach or battery capacity. Therefore, the present invention is characterized in that a discharge characteristic reference formula is created in advance, a modified reference formula is created by modifying the discharge characteristic reference formula so as to match the measured value, and a new method of creating the modified reference formula is provided. There is.

That is, according to the present invention, a battery pack or a single battery is discharged for a short time, and the storage battery capacity or the discharge voltage characteristic with respect to the discharge time and the previously obtained long-time discharge characteristic of the same kind of battery are used. The main feature is to obtain long-term discharge characteristics. The conventional technology is different in that the long-term discharge characteristic or the storage battery capacity is estimated only from the discharge voltage-time characteristic of the battery.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 shows an example of an embodiment corresponding to the claims of the present invention, and shows a calculation procedure of a discharge characteristic reference formula necessary for calculating a storage battery capacity. The procedure 1 discharges a storage battery to a predetermined discharge end voltage at the same discharge rate. In addition, the battery to be used is the same kind of battery (for example, lead storage battery, Ni-
It is desirable that the same manufacturer, the same product type, and the same capacity are used for the Cd battery or the like, but even if they are different, there is not much difference as long as they have the same discharge rate, so there is not much problem and the present invention can be applied. The procedure 2 measures the terminal voltage and the discharge time for each discharge time in the discharge test. In the procedure 3, the discharge characteristic reference equation is calculated by using the ordinary least square method using the plurality of terminal voltages up to the discharge end voltage and the plurality of discharge times obtained in the calculation of the discharge characteristic reference equation. The formula to calculate is
Any functional expression such as a linear expression, a quadratic expression, an n-order expression, an exponential function, an elliptic function, etc. may be used. Here, the case where the calculation is performed by the quadratic equation that can obtain a relatively accurate result will be described, but it goes without saying that the calculation can be applied to other functions as well. In step 4, the reference equation and the capacity ratio of the battery to be measured are calculated. If so, the conversion to the rated capacity is performed in step 3. In step 5, a discharge test is performed on a storage battery of the same type, and a plurality of terminal voltages of the battery and discharge time are measured. In step 6, the data acquired in step 5 is compared with the reference expression, and the reference expression is adjusted to the acquired data. In step 7, the reduction rate can be calculated by combining the measured value and the reference formula. In procedure 8, the discharge characteristic equation of the battery measured in procedure 5 can be calculated by substituting the reduction rate into the reference equation. In step 9, the discharge characteristic formula is used to calculate the discharge time up to a predetermined discharge end voltage. Step 10 is step 9
The battery capacity is calculated by multiplying the discharge time calculated in step 3 by the discharge current.

A detailed description will be given below for each procedure with reference to specific drawings. FIG. 2 shows 200A performed in steps 1 and 2.
It is a 0.1C discharge characteristic measurement result of h seal lead acid battery.
Here, 0.1 C discharge means discharging a battery having a nominal capacity of 200 Ah at 20 A, for example. In this example, the characteristics of the sealed lead-acid battery up to the final discharge voltage of 1.8 V are measured. Where A is the discharge characteristic of a new battery, and B is
Is a capacity of a new battery same as A, which is deteriorated by temperature acceleration 8
0% discharge characteristic of the battery, C is the same discharge characteristic of the same battery as A and has a capacity of 60%, and D is the same discharge discharge characteristic of the same battery as A, which has a capacity of 45% It is a characteristic. FIG. 2 shows the discharge characteristics of the accelerated deterioration battery in order to verify the present invention. However, in actual application, only the discharge characteristics of a new battery are necessary. As shown in FIG. 2, the discharge characteristics of the battery are that the initial discharge voltage a, b,
c and d do not change much, and in the case of a sealed lead-acid battery, the capacity is 30 mA at most from the new battery to the capacity of 45%.
And about 1.5% of the initial discharge voltage of the battery. However, the change in discharge time is 45% for a battery
Compared to a new battery, it is reduced to 45% and reaches 55% of the discharge time. Therefore, if it is possible to calculate a discharge characteristic that considers only the change of the discharge time in the deterioration, it is possible to accurately approximate the discharge characteristic including the deterioration characteristic. Next, the discharge characteristic reference formula calculated in step 3 will be described. FIG. 3 shows a case where the discharge characteristics of the sealed lead-acid battery are approximated by a high-order equation. Here, A is a measured value, B is a linear approximation formula, C is a quadratic approximation formula, D is a cubic approximation formula, E is a quaternary approximation formula, and F is a quintic approximation formula. Also, in FIG.
The correlation coefficient of the approximate expressions of B to F is shown. As shown in FIG. 4, the correlation coefficient approaches 1 when the order increases, but if it is a quadratic equation, the correlation coefficient is 0.98 or more, and even if the order is increased, the improvement of the correlation coefficient is 0. It is only about 0.005. Therefore, the discharge characteristics of the sealed lead-acid battery can be calculated with a certain degree of accuracy by using the quadratic approximation formula, and the calculation time for comparing the actual measurement value with the reference formula can be shortened, and the calculation algorithm can be made economical. Therefore, the discharge characteristic reference equation V of the sealed lead-acid battery is defined as the following equation.

V = At ² + Bt + C (1) When approximated by the equation (1), the initial discharge voltages a, b, c and d change by only a few percent even if they deteriorate as shown in FIG. This means that in the equation (1), the C of the 0th order term does not change even if the capacity deteriorates, and the coefficient A of the other 2nd order term and the coefficient B of the 1st order term
It shows that only the change greatly. The 0th-order term C is expressed by the following equation from the electromotive force E, the internal resistance R, and the discharge current I, from the viewpoint of the electrochemical reaction of the battery.

C = E-RI (2) The electromotive force E is mainly determined by the electrolytic solution specific gravity, and even if it deteriorates, it does not change at the time of full charge at the initial stage of discharge unless the specific gravity changes significantly. Further, the internal resistance R becomes about twice as large as the capacity deterioration of 70%. However, originally, the internal resistance of a new battery is 0.
It is as small as 3 mΩ and the discharge current is 0.1 C (200
In the case of Ah battery, the voltage drop due to internal resistance is as small as 20 A), so the voltage drop due to internal resistance is very small compared to the electromotive force E = 2.1 V, so ignore the voltage drop due to internal resistance immediately after discharge at 0.1 C discharge. Does not matter much. On the other hand, the quadratic term coefficient A and the quadratic term coefficient B change because the specific gravity of the electrolytic solution gradually decreases depending on the amount of discharge when discharging, so that the electromotive force E and the internal resistance R change. But,
It is considered that the specific gravity of the electrolytic solution in the battery is the same, which is greatly related to the electromotive force and the internal resistance at the same discharge voltage but different discharge times. Therefore, in the discharge characteristic, only the discharge time t at which the discharge voltage is reached differs depending on the degree of deterioration. Considering this mathematically, it indicates that the ratio of only the function of the time t should be converted according to the degree of deterioration. That is, assuming that the discharge characteristic of the deteriorated battery is the equation (1) and the deterioration rate for changing the discharge time is D, the discharge characteristic of the equation (1) is expressed by the following equation.

V = A't ² + B't + C = A (t ² / D ² ) + B (t / D) + C = A [t ² / D ² ] + B [t / D] + C = At ' ² + Bt' + C (3) where A'and B'are the discharge characteristic approximation coefficients of the deteriorated battery or the battery to be measured, and D = deterioration rate t '= t / D is the discharge characteristic of the new battery. It is a conversion formula for converting into the discharge characteristic of. FIG. 5 shows an actual discharge characteristic of a deteriorated battery and an approximate expression when the function conversion shown in Expression (3) is performed. As shown in the figure, the measured value and the approximate expression agree very well, which shows that the above concept is correct. Therefore, in Procedure 3, the discharge characteristics of the reference battery can be approximated as shown in equation (3) to calculate A ′, B ′, and C. Step 4
Then, the conversion to the discharge characteristic reference formula of the battery with the rated capacity is performed. Generally, a new battery has a capacity higher than the rated capacity. Therefore, it is necessary to convert the battery discharge characteristic reference equation into a discharge reference equation that estimates the rated capacity. As the conversion method, function conversion at time t is performed in the same manner as the conversion method from Expression (1) to Expression (3). Therefore, the discharge reference formula is as follows.

V = A ′ [1 / E] ² t ² + B ′ [1 / E] t + C = (A ′ / E ² ) t ² + (B ′ / E) t + C = αt ² + βt + C where E is the rating Conversion coefficient to capacity, α = A ′ / E ² β = B ′ / E (4)

Α, β, and C are coefficients of discharge characteristics of a battery having the rated capacity of a new battery, which is uniquely determined when the discharge current is determined. Therefore, FIG. 6 shows an example of the discharge reference formula converted into the rated capacity. The discharge reference formula calculated here is used to estimate the discharge characteristic of an arbitrary storage battery. As described with reference to FIG. 5, the discharge characteristic expression of an arbitrary storage battery is expressed by the following expression obtained by converting the expression (4) into a function with respect to t.

V = (α / D ² ) t ² + (β / D) t + C (5) D in the equation (5) is a desired capacity reduction rate. Therefore, in step 5, a battery whose arbitrary capacity is to be measured is discharged with a discharge current substantially equal to the capacity reference formula, and the discharge time t ₁ and the discharge voltage V ₁ at a predetermined discharge amount (Ah) are measured, Substituting into the equation (5) gives the following equation.

V ₁ = (α / D ² ) t ₁ ² + (β / D) t ₁ + C (6) From the equation (6), (C−V ₁ ) D ² + βDt ₁ + αt ₁ ² = 0 (7 ) Becomes, and the capacity decrease amount D required for the procedure 7 is calculated by the following equation.

[0017]

[Equation 1] Although the solution of D has two numbers, the number of D> 0 is set as the value of D.
It is better to increase the discharge time t _{1 as} much as possible in order to reduce the error, but if t ₁ is made too long, it becomes the same as the conventional capacity test by discharge, so t ₁ is the product of the discharge current and 100% of the rating. Compared with the above, the measurement time is shorter and the operation does not take much if it is set to about 10 to 30%. (8)
When D is found from the equation, the measured discharge characteristic equation of the battery required in step 8 can be calculated as the following equation.

V = (α / D ² ) t ² + (β / D) t + C (9) In FIG. 7, the product of t ₁ and the discharge current is 10 to 30% of the rated capacity.
The error with the actual discharge characteristics is shown. The error is -1
It is about 6.15 to 6.17%. Further, the discharge time t _x required for the storage battery to reach _a predetermined voltage V _a in step 9 is expressed by the following equation when V = V _a is substituted into the equation (5) and solved for t _x .

[0019]

[Equation 2] Therefore, the battery capacity Q in the procedure 10 can be calculated from the discharge current and the discharge time of the formula (10) as the following formula.

Q = t _x × I (11) FIG. 8 shows another embodiment of the present invention. Here, the comparison with the reference formula in step 6 is performed with the inclination. Here, measured values of discharge characteristics Q is explained in two points of V _1, V _2, but 2
The same applies for points and above. In the figure, the discharge voltage in the discharge time t ₁ in discharge characteristics Q V _1, put a discharge voltage in the discharge time t ₂ and V _2, the calculation method of the present invention, the 2
The capacity decrease rate is adjusted so that the slope ΔV ₁₂ between the discharge voltage and the discharge time at the point, ΔV _AB between V _A , t _A and V _B , t _B shown in the reference formula (5) is adjusted to ΔV _12. Calculate D. That is, the formula represented by the formula (5) having C and the gradient ΔV ₁₂ is calculated. In equation (5), V ₁ , t
Substituting ₁ and V ₂ and t ₂ respectively gives the following equation.

V ₁ = (α / D ² ) t ₁ ² + (β / D) t ₁ + C (12) V ₂ = (α / D ² ) t ₂ ² + (β / D) t ₂ + C (13) ) Subtracting both equations gives ΔV ₁₂ . D is calculated so that ΔV _AB is equal to ΔV ₁₂ . That is, ΔV ₁₂ = (V ₁ −V ₂ ) = (α / D) (t ₁ ² −t ₂ ² ) + (β / D) (t ₁ −t ₂ ) (14) From formula (14), ₁₋ V ₂ ) D ² −β (t ₁ −t ₂ ) D−α (t ₁ ² −t ₂ ² ) = 0 (15), and the capacity decrease rate D is given by the following equation.

[0022]

(Equation 3) Moreover, the discharge time t _a at any discharge voltage V _a can be calculated from the following equation.

[0023]

(Equation 4) The actual discharge times t ₁ and t ₂ should be made as large as possible in order to reduce the error. However, if t ₁ and t ₂ are made too long, they become the same as the conventional capacity test by discharge, maintenance operation, If a power failure occurs during the test immediately after the test, the storage battery will be immediately discharged and the system will be shut down. Therefore, if t ₁ and t ₂ have a product of discharge current of about 10 to 30% compared to the rated capacity, the measurement time will be shorter, the operation will not take much, and the system will be adversely affected. Absent.

FIG. 9 shows the difference between this calculation method and the actual measurement value.
Here, the error (1) is an error when the discharge voltage data of the discharge amounts 10% and 20% is used, and the error (2) is the discharge amount 20% and 3
The error when using the discharge voltage data of 0%, the error (3) is the error when using the discharge voltage data of 10% and 30% of the discharge amount, and the error of this calculation method is 20 to 30%. is there.

FIG. 10 shows another embodiment of the present invention. Here, it is a method in which the comparison with the reference expression of the procedure 6 is performed with an inclination, and the contact point C with the Y axis is corrected with an actually measured value. In addition, here, the actual measurement value of the discharge characteristic Q will be described with respect to two points of V ₁ and V ₂ , but the same applies to the case of two or more points. In the figure, the discharge characteristic Q
In the calculation method of the present invention, the discharge voltage V _{1 at} the discharge time t _{1 and} the discharge voltage at the discharge time t ₂ are defined as V ₂ and the gradient ΔV ₁₂ between the discharge voltage and the discharge time at these two points. The capacity decrease rate D is calculated so that the slope ΔV _AB between V _A , t _A and V _B , t _B shown in 2) is matched with ΔV ₁₂ . Substituting V ₁ , t ₁ , and V ₂ , t ₂ into the equation (5) gives the following equation.

V ₁ = (α / D ² ) t ₁ ² + (β / D) t ₁ + C (18) V ₂ = (α / D ² ) t ₂ ² + (β / D) t ₂ + C (19) ) Subtracting both equations gives ΔV ₁₂ . D is calculated so that ΔV _AB is equal to ΔV ₁₂ . That is, ΔV ₁₂ = (V ₁ −V ₂ ) = (α / D) (t ₁ ² −t ₂ ² ) + (β / D) (t ₁ −t ₂ ) (20) ₁₋ V ₂ ) D ² −B (t ₁ −t ₂ ) D−A (t ₁ ² −t ₂ ² ) = 0 (21), and the capacity decrease rate D is as follows.

[0027]

(Equation 5) When the discharge characteristic is calculated by the reference equation such as the following equation using D calculated by the equation (22), the characteristic shown by R in FIG. 10 is obtained.

V = (α / D ² ) t ² + (β / D) t + C (23) Here, A, B, and C are known from the discharge reference formula A. In addition, the discharge initial voltage V ₀ (discharge voltage V
_If the voltage obtained by extrapolating from ₁ , V ₂ to discharge time 0) is the same as the discharge reference formula P, that is, C in formula (18), V ₀
= C, the discharge characteristics R overlap at V ₁ and V ₂ , and the error is small. However, in an actual battery, after a number of years of installation, it changes slightly (several tens of mV) due to changes in internal resistance and electrolyte specific gravity. Therefore, the discharge characteristic R and the actual discharge characteristic Q are different, and as shown in FIG.
discharge time t _a in _a results an error as t _E.
Therefore, in the present invention, C _A is calculated from the discharge initial voltage of the reference formula by the following formula, and C is corrected. That is, C
_A becomes the following expression from the expression (23).

C _A = V− (α / D ² ) t ² − (β / D) (24) In the equation (24), V = V ₁ (when t = t ₁ ) or V = V ₂ (When t = t ₂ ) is substituted to calculate C _A. Therefore, the discharge estimation formula is as follows.

[0030] V = (α / D ²⁾ with ^{t 2 + (β / D)} t + C A (25) Equation (25), the discharge time t _a at any discharge time V _a can be calculated from the following equation.

[0031]

(Equation 6)

FIG. 11 shows the error between this calculation method and the measured value.
Here, the error (4) is an error when the discharge voltage data of the discharge amounts 10% and 20% is used, and the error (5) is the discharge amount 20% and 3
The error when the discharge voltage data of 0% is used, the error (6) is the error when the discharge voltage data of 10% and 30% is used, and the error of this calculation method is 10 to 15%. According to another embodiment of the present invention, the error can be improved by about 10 to 15% as compared with the method of adjusting only the inclination. The actual discharge times t ₁ and t ₂ should be increased as much as possible in order to reduce the error, but if t ₁ and t ₂ are made too long, the capacity test will be the same as the conventional capacity test by leaving it alone, and maintenance operation, When a power failure occurs during the test or immediately after the test, the storage battery is immediately discharged and the system goes down. Then, t
_1, t ₂ is 10 to the product of the discharge current compared to the rated capacity
If it is set to about 30%, the measurement time is short and the operation is not so much so that the system is not adversely affected.

[0033]

As described above, according to the present invention, it is possible to estimate the capacity of a storage battery in a relatively short time and with a relatively high accuracy without discharging the storage battery to the discharge end voltage as in the conventional example. it can. Furthermore, the present invention does not accelerate the deterioration of a specific battery cell and the complexity of previously measuring the voltage of each battery cell as shown in another conventional example. Therefore, according to the present invention, a highly reliable power supply system can be economically configured in a short time without spending a lot of maintenance work.

[Brief description of drawings]

FIG. 1 is a procedure diagram for calculating a discharge characteristic reference expression according to an exemplary embodiment of the present invention.

FIG. 2 is a characteristic diagram illustrating the operation of the storage battery.

FIG. 3 is a characteristic diagram for explaining the matching between the approximate expression of the present invention and an actual measurement value.

FIG. 4 is a characteristic diagram showing a quadratic correlation coefficient used in the description of the embodiment of the present invention.

FIG. 5 is a characteristic diagram showing discharge characteristics estimated in the embodiment of the present invention and actual discharge characteristics.

FIG. 6 is a characteristic diagram illustrating a discharge reference formula according to an exemplary embodiment of the present invention.

FIG. 7 is a characteristic diagram illustrating an error in the embodiment of the present invention.

FIG. 8 is a characteristic diagram illustrating an operation of the exemplary embodiment of the present invention.

FIG. 9 is a characteristic diagram illustrating an error in the embodiment of the present invention.

FIG. 10 is a characteristic diagram illustrating an operation of the exemplary embodiment of the present invention.

FIG. 11 is a characteristic diagram illustrating an error in the embodiment of the present invention.

FIG. 12 is a configuration explanatory view showing an example of a conventional capacity test method.

FIG. 13 is a configuration explanatory view showing another example of the conventional capacity test method.

FIG. 14 is a discharge characteristic diagram according to a conventional estimation method.

[Explanation of symbols]

1 ... AC or DC power supply, 2 ... Power conversion device, 3 ... Storage battery, 4 ... Load device, 5 ... Changeover switch, 6 ... Discharge constant current load, 7 ... Lowest voltage battery cell, 8 ... Changeover switch,
9 ... Constant current load for discharging, 10 ... Charger for recharging discharged battery cells, 11 ... AC or DC power supply.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Ryo Tanaka 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation

Claims (5)

[Claims] 1. A method of discharging a storage battery for a short time, measuring the terminal voltage of the storage battery, and estimating the capacity or discharge time of the storage battery using the terminal voltage, wherein the storage battery discharge characteristics of the storage battery and the same kind of battery are used. A storage battery capacity estimation method characterized by comparing a discharge reference formula created in advance with the terminal voltage, changing the time axis of the discharge reference formula to match the terminal voltage, and estimating the discharge time or the discharge capacity. . 2. A comparison between a discharge reference equation and the terminal voltage
The storage battery capacity estimation method according to claim 1, wherein the absolute value of the terminal voltage is used, and the time axis of the discharge reference formula is changed so that the absolute values match. 3. Comparing the discharge reference expression and the terminal voltage,
The storage battery capacity estimating method according to claim 1, wherein the time axis of the discharge reference formula is changed so that the slopes are the same among a plurality of the terminal voltages and the slopes match. 4. The intercept with respect to the Y axis of the discharge reference equation is replaced with the intercept with the Y axis obtained by substituting the terminal voltage and the discharge time into the discharge reference equation with the time axis changed. The method of estimating the storage battery capacity according to claim 1, wherein the discharge time or the discharge capacity is estimated. 5. The storage battery capacity estimating method according to claim 1, wherein the discharge reference equation is a quadratic equation.