JP2008096328A - Charging rate estimation method, charging rate estimating device, and secondary battery power supply system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a charging rate estimation method, a charging rate estimation device, and a secondary battery power supply system, capable of stably determining the optimum values of adjustment parameters of an approximate expression that allows determination of high-accuracy approximation for the open-circuit voltage of a secondary battery, in a short time, and for the estimation of the charging rate. <P>SOLUTION: In step S104, a voltage drop amount ΔV in data acquisition period is calculated. In step S105, coefficient β is calculated from the ΔV, calculated in step S104 and Ci input from a storage part 140. In step S106, initial value Ai0 of an adjustment parameter Ai is calculated by using the coefficient β calculated in the step S105, and initial value Vc0 of an adjustment parameter Vc is calculated. By using the initial values Ai0, Vc0 of the adjustment parameters thus determined and Bi0 read from the storage part 140, advance is made to next step S107, where the adjustment parameters are optimized by the method of least squares. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a technical field of a charging rate estimation method and a charging rate estimation device that estimate a charging rate of a secondary battery that supplies power to a load.

  2. Description of the Related Art Conventionally, it is required to accurately know the remaining charge rate for secondary batteries such as lead storage batteries mounted on automobiles and the like. Generally, in a secondary battery, since there is a correlation between the charging rate and the open circuit voltage, the charging rate can be estimated by obtaining the open circuit voltage.

  However, the open circuit voltage of the secondary battery needs to be performed in a state where charging or discharging is not performed, and it takes a long time for the open circuit voltage to become stable after completion of charging or discharging. Therefore, the open circuit voltage of the secondary battery is measured within a short time under a predetermined condition, and a function that approximates the time characteristic of the open circuit voltage is determined using the measured voltage value, and the open circuit voltage is opened based on the determined function. Various methods for obtaining the convergence value of the circuit voltage have been proposed (for example, Patent Documents 1 to 3).

  When the convergence value of the open circuit voltage of the secondary battery is obtained by the conventional method, the accuracy depends on the accuracy of the function used for the approximate calculation. For example, a general method is to calculate the convergence value of the open circuit voltage based on a function having time characteristics such as a polynomial function or a logarithmic function. However, it is difficult for these functions to approximate the time characteristic of the open circuit voltage of the secondary battery with high accuracy, and an error in the convergence value of the obtained open circuit voltage becomes large.

On the other hand, in Patent Document 4, an exponential decay function of the fourth order or higher is used for the approximate calculation of the open circuit voltage of the secondary battery, so that the open circuit voltage can be approximated with high accuracy, and the charging rate is highly accurate. Can be estimated.
JP-A-7-98367 JP 2002-234408 A JP 2003-75518 A JP 2005-43339 A

  However, the conventional secondary battery charging rate estimation method has the following problems. The approximate expression used for the approximate calculation of the open circuit voltage has an adjustment parameter to improve the accuracy of the estimated value of the open circuit voltage, and is obtained by measuring the open circuit voltage of the secondary battery under a predetermined condition. This tuning parameter was optimally determined using voltage measurements.

  However, when a complex nonlinear function such as a fourth or higher order exponential decay function is used for the approximate calculation of the open circuit voltage of the secondary battery, the least square method is used when optimizing the adjustment parameter using the voltage measurement value. It is necessary to solve the sequential solution such as Gauss-Newton method or Levenberg-Marquardt method or the filtering operation such as Kalman-filter operation. Depending on the initial value, there is a possibility that calculation may diverge and the optimum solution value of the adjustment parameter may not be obtained, and even if it is obtained, it takes a very long time.

  Therefore, the present invention has been made to solve these problems, and the optimum value of the adjustment parameter of the approximate expression that can approximate the open circuit voltage of the secondary battery with high accuracy is determined in a short time and stably. It is an object of the present invention to provide a charging rate estimation method, a charging rate estimation device, and a secondary battery power supply system that can estimate a charging rate.

  According to a first aspect of the charging rate estimation method of the present invention, the time variation of the open circuit voltage (OCV) of the secondary battery after the end of charge / discharge is approximated by a voltage characteristic equation having an adjustment parameter, A charging rate estimation method for calculating an open circuit voltage when the secondary battery is stable from a voltage characteristic equation to estimate a charging rate of the secondary battery, and obtaining predetermined data after completion of charging and discharging of the secondary battery In the period, a plurality of voltage measurement values of the secondary battery are acquired, and the adjustment parameter is calculated using a predetermined relational expression that depends on a change amount of the voltage measurement value in the data acquisition period and a predetermined calculation method set in advance. The adjustment parameter is optimal when the error between the open circuit voltage calculated by the voltage characteristic equation and the voltage measurement value is minimized while the adjustment parameter is gradually corrected from the initial value. Estimate It is characterized in.

In another aspect of the charging rate estimation method of the present invention, when the adjustment parameters are Ai (i = 1 to n), Bi (i = 1 to n) and Vc, and n is an integer of 4 or more, the voltage The specific formula is
[Equation 9]
V (t) = A1 · exp (B1 · t)) + A2 · exp (B2 · t) +.
+ An · exp (Bn · t) + Vc
And the constants α and Ci set in advance (i = 1 to n), where Va is the voltage measurement value at the beginning of the data acquisition period, and Vb is the voltage measurement value immediately before the end of the data acquisition period. Using
[Equation 10]
(C1 + C2 +... + Cn) · β = (Va−Vb) · α
Parameter β to satisfy
[Equation 11]
Ai0 = Ci · β (i = 1 to n)
Ai0 calculated in step S is used as the initial value of the adjustment parameter Ai,
[Equation 12]
Vc0 = Va− (Va−Vb) · α
Vc0 calculated by the above is used as the initial value of the adjustment parameter Vc.

  Another aspect of the charging rate estimation method of the present invention is characterized in that an initial value of the adjustment parameter Bi (i = 1 to n) is a constant set in advance.

  In another aspect of the charging rate estimation method of the present invention, a temperature function for calculating an initial value of the adjustment parameter Bi (i = 1 to n) from a temperature of the secondary battery is set in advance, and the data acquisition period A temperature measurement value is obtained by measuring the temperature, and the initial value of the adjustment parameter Bi (i = 1 to n) is determined by substituting the temperature measurement value into the temperature function.

  Another aspect of the charging rate estimation method of the present invention is characterized in that at least one of the Va and the Vb is an average value calculated by averaging two or more voltage measurement values.

  Another aspect of the charging rate estimation method of the present invention is characterized in that the open circuit voltage when the secondary battery is stable is given by Vc when the optimum value of the adjustment parameter is determined.

  According to another aspect of the charging rate estimation method of the present invention, the open circuit voltage when the secondary battery is stable is calculated by substituting a predetermined time for a function equation that determines the optimum value of the adjustment parameter. It is characterized by that.

  A first aspect of the charging rate estimation device according to the present invention is a charging rate estimation device that estimates a charging rate of a secondary battery, a voltage sensor that measures the voltage of the secondary battery, and a voltage characteristic having an adjustment parameter. A control unit that executes and controls calculation for estimating the charging rate using an equation; a storage unit that stores a voltage measurement value measured by the voltage sensor; and data used for the calculation by the control unit; The control unit acquires a plurality of voltage measurement values of the secondary battery from the voltage sensor in a predetermined data acquisition period after the end of charging and discharging of the secondary battery, and the control unit in the data acquisition period An initial value of the adjustment parameter is set by a predetermined relational expression that depends on a change amount of the voltage measurement value and a predetermined calculation method set in advance, and the voltage characteristic is gradually corrected from the initial value. Estimating the optimum value of the adjustment parameter when the error between the open circuit voltage calculated in step 1 and the voltage measurement value is minimum, and stabilizing the secondary battery from the voltage characteristic equation using the optimum value of the adjustment parameter The open circuit voltage at the time is calculated to estimate the charging rate.

According to a second aspect of the charging rate estimation device of the present invention, when the control unit sets the adjustment parameters to Ai, Bi (i = 1 to n) and Vc, and n is an integer of 4 or more,
[Equation 13]
V (t) = A1 · exp (B1 · t)) + A2 · exp (B2 · t) +.
+ An · exp (Bn · t) + Vc
Is used as the voltage specifying formula, Va is the voltage measurement value at the initial stage of the data acquisition period, and Vb is the voltage measurement value immediately before the end of the data acquisition period. 1-n)
[Equation 14]
(C1 + C2 +... + Cn) · β = (Va−Vb) · α
Parameter β to satisfy
[Equation 15]
Ai0 = Ci · β (i = 1 to n)
Ai0 calculated in step S is used as the initial value of the adjustment parameter Ai,
[Equation 16]
Vc0 = Va− (Va−Vb) · α
Is used as the initial value of the adjustment parameter Vc.

  The 1st aspect of the secondary battery power supply system of this invention is provided with the charging rate estimation apparatus as described in a 1st aspect or a 2nd aspect.

  According to the present invention, the time variation of the open circuit voltage of the secondary battery is approximated by the voltage characteristic equation having the adjustment parameter, and the initial value of the adjustment parameter is suitably set, so that the adjustment parameter The optimum value can be determined stably in a short time. Then, the open circuit voltage when the secondary battery is stable can be estimated with high accuracy using the optimized adjustment parameter, and thereby the charge rate estimation method, the charge rate estimation device, and the charge rate can be estimated with high accuracy. A secondary battery power supply system can be provided.

  Configurations of a charging rate estimation method, a charging rate estimation device, and a secondary battery power supply system according to a preferred embodiment of the present invention will be described in detail with reference to the drawings. In addition, about each structural part which has the same function, the same code | symbol is attached | subjected and shown for simplification of illustration and description. Below, the case where this invention is applied with respect to the secondary battery mounted in vehicles, such as a motor vehicle, is demonstrated.

  A secondary battery power supply system according to an embodiment of the present invention will be described with reference to FIG. FIG. 2 is a block diagram showing a schematic configuration of the secondary battery power supply system 100 according to the present embodiment. The secondary battery power supply system 100 includes a secondary battery 110, a voltage sensor 120 that measures the voltage of the secondary battery 110, and a control unit that controls the secondary battery 110 by inputting a voltage measurement value from the voltage sensor 120. 130, a storage unit 140 that stores data used for control performed by the control unit 130, and a charging circuit 150 for charging the secondary battery 110 based on a control command from the control unit 130. .

  The secondary battery power supply system 100 configured as described above is connected to a load 10 such as a motor, and power is supplied from the secondary battery 110 to the load 10. In the case of a vehicle such as an automobile, for example, a lead storage battery is used as the secondary battery 110.

  The control unit 130 is configured by a CPU or the like that performs arithmetic processing, controls the overall operation of the secondary battery power supply system 100, and executes arithmetic processing for charging rate estimation described later at a predetermined timing. Yes. The storage 140 connected to the control unit 130 includes a ROM for storing various programs such as a control program in advance, a RAM for storing various data used for processing of the control unit 130, and the like. .

  The charging rate estimation apparatus according to the present invention can be configured with at least a control unit that executes arithmetic processing for charging rate estimation described later, a storage unit 140, and a voltage sensor 120. In the embodiment shown in FIG. 2, a control unit that performs calculation processing for charging rate estimation is included in the control unit 130 that controls the overall operation of the secondary battery power supply system 100.

  Next, a charging rate estimation method for the secondary battery 110 used in the secondary battery power supply system 100 according to the present embodiment will be described. In general, the charging rate of the secondary battery has a strong correlation with the open circuit voltage when the secondary battery is stable, so when the open circuit voltage at the stable time is obtained, the charging rate of the secondary battery is estimated from this It becomes possible to do.

  However, particularly in a secondary battery mounted on a vehicle, since charging and discharging are frequently repeated, it is normal that the voltage is not stable. When charging / discharging is performed, polarization occurs inside the secondary battery, and this is gradually eliminated after completion of charging / discharging. It usually takes an extremely long time of several tens of hours to several days until the polarization is eliminated and the secondary battery is stabilized. Therefore, the secondary battery is often charged and discharged again before it becomes sufficiently stable, and it is extremely difficult to measure the open circuit voltage when the secondary battery is stable.

In the present embodiment, the control unit 130 uses a voltage characteristic equation that can approximate the temporal variation of the open circuit voltage with high accuracy, so that the open circuit voltage when the secondary battery 110 is stable can be estimated with high accuracy. ing. By using an approximate expression including a fourth-order or higher exponential decay function as the voltage characteristic expression, it is possible to estimate the time fluctuation of the open circuit voltage with high accuracy. In this embodiment, an approximate expression including the following fourth-order exponential decay function is used as an example.
[Equation 17]
V (t) = A1 · exp (B1 · t)) + A2 · exp (B2 · t) +
A3 * exp (B3 * t)) + A4 * exp (B4 * t) + Vc (Formula 1)

  In the above (Formula 1), A1 to A4, B1 to B4 (hereinafter referred to as Ai and Bi) and Vc are adjustments for adjusting V (t) so that the open circuit voltage can be estimated with high accuracy. It is a parameter (fitting parameter). These adjustment parameters are adjusted so that the error between the voltage measurement value at a predetermined time t and V (t) is minimized.

  FIG. 3 shows an example of measuring the time fluctuation of the open circuit voltage over 60 minutes after charging the secondary battery 110 as an example of the time fluctuation of the open circuit voltage after the end of charging and discharging of the secondary battery 110. In the figure, the voltage measurement values for 10 minutes after the end of charging are indicated by ● and the voltage measurement values thereafter are indicated by ○.

Fig. 2 shows the results of fitting the voltage measurement value (● mark) for 10 minutes after the end of charging with the voltage characteristic equation having the fourth-order exponential decay function shown in (Equation 1) and fitting using the logarithmic function. 3 is also shown. The results of optimal fitting of each are as follows.
[Equation 18]
V (t) = 1.80933exp (-t / 4.65331) + 0.2895exp (-t / 0.41691)
-0.90055exp (-t / 4.65129) + 0.9exp (-t / 0.004) +13.35703 (Formula 2)
V (t) =-0.2517ln (t) +14.072 (Formula 3)

  As is obvious from comparing the above fitting equation with the measured voltage value (marked with ○) after 10 minutes from the end of charging, the error is increased with the passage of time in the case of fitting using the logarithmic function (Equation 3). On the other hand, in the case of fitting with a voltage characteristic equation having a fourth-order exponential decay function (Equation 2), even after 10 minutes from the end of charging, it shows a very good agreement with the measured voltage value. It can be seen that the time variation of the voltage can be estimated with high accuracy.

  As described above, in order to be able to estimate the open circuit voltage of the secondary battery 110 with high accuracy using the voltage characteristic equation having the fourth-order exponential decay function shown in (Equation 1), It is necessary to measure the open circuit voltage of the secondary battery 110 for a predetermined data acquisition period and optimally fit (Equation 1) using this voltage measurement value. In addition, the fitting needs to be performed in a short time so that the calculation does not diverge so that the controller 130 can estimate the charging rate and immediately use it for control or the like.

  In order to fit the voltage characteristic equation of (Equation 1) to the voltage measurement value with high accuracy in a short time, it is important to appropriately select and use the initial values of the adjustment parameters used in (Equation 1). is there. Among them, the adjustment parameters A1 to A4 and Vc change depending on the state of charge of the secondary battery 110, the degree of deterioration, and the like. Therefore, appropriately setting the initial values of the adjustment parameters A1 to A4 and Vc speeds up the fitting. In addition, the effect is large in performing stably. Hereinafter, a method of suitably setting the initial value of the adjustment parameter in the charging rate estimation method used in the present embodiment will be described with reference to FIG.

FIG. 4 is a diagram illustrating an example of a change in the open circuit voltage of the secondary battery 110 for explaining a method of setting the initial value of the adjustment parameter of (Equation 1). In the figure, a circle indicates a voltage measurement value 21 acquired from the voltage sensor 120, which is acquired during a data acquisition period after the end of charging / discharging of the secondary battery 110. When the voltage at the beginning of the data acquisition period is Va, the voltage immediately before the end of the data acquisition period is Vb, and the voltage change during that period is ΔV, ΔV is expressed as the following equation.
[Equation 19]
ΔV = Va−Vb (Formula 4)

  Va may be an average of a plurality of voltage measurement values at the beginning of the data acquisition period. For example, Va may be obtained by averaging the voltage measurement values of 21a shown in FIG. Similarly, Vb may be an average of a plurality of voltage measurement values immediately before the end of the data acquisition period. For example, the voltage measurement value of 21b shown in FIG.

Using the above ΔV, the initial value (constant Vc0) of the constant term Vc in (Expression 1) is set using the following expression.
[Equation 20]
Vc0 = Va−α · ΔV (Formula 5)
Here, α is a constant set through experiments and the like in advance. The open circuit voltage when the secondary battery 110 is in a stable state coincides with Vc when the exponential decay function depending on the time t becomes 0 in (Equation 1). Therefore, (Expression 5) is an expression for setting an initial value of the open circuit voltage at the time of stabilization.

In addition, for the adjustment parameters A1 to A4, values serving as references for the initial values (hereinafter referred to as reference values) are determined in advance and stored in the storage unit 140. That is, when the initial value of Ai (i = 1 to n) is Ai0 and the reference value is Ci,
[Equation 21]
Ai0 = Ci · β (Formula 6)
Thus, the initial value Ai0 of Ai is determined. The reference value Ci is an initial value of the adjustment parameter Ai and its proportional relationship is determined in advance.

Hereinafter, a method of determining the coefficient β in (Expression 6) will be described. In (Expression 1), the following expression is established when time t = 0.
[Equation 22]
V (0) = A1 + A2 + A3 + A4 + Vc (Formula 7)
Here, V (o) is an open circuit voltage at the start of data acquisition.
[Equation 23]
V (0) = Va (Formula 8)
It becomes.

In (Expression 7), by using respective initial values as Ai and Vc, and further using (Expression 5) and (Expression 8),
[Equation 24]
Va = A10 + A20 + A30 + A40 + Vc0
= A10 + A20 + A30 + A40 + (Va-α · ΔV) (Formula 9)
It becomes. From the above formula,
[Equation 25]
A10 + A20 + A30 + A40 = α · ΔV (Formula 10)
Holds.

Furthermore, from (Equation 6) and (Equation 10)
[Equation 26]
(C1 + C2 + C3 + C4) · β = α · ΔV (Formula 11)
From this, the coefficient β is determined by the following equation.
[Equation 27]
β = α · ΔV / (C1 + C2 + C3 + C4) (Formula 12)
In (Expression 12), ΔV is calculated from the voltage measurement value, and α and Ci are data determined in advance and stored in the storage unit 140. Therefore, β is determined from (Expression 12), and the initial value Ai0 of Ai is set from (Expression 6).

The initial value Ai0 of the adjustment parameter Ai and the initial value Vc0 of Vc are determined as described above, whereas Bi (i = 1 to n), which is another adjustment parameter, determines the initial value in advance. The data can be stored in the storage unit 140 and read and used.

  Next, the process flow estimation method of the secondary battery 110 executed in the control unit 130 of the present embodiment will be described with reference to the flowchart shown in FIG. The calculation process shown in FIG. 1 is a process that is mainly executed by the control unit 130 based on a control program held in the storage unit 140, and has a predetermined value after the secondary battery 110 is charged and discharged in the secondary battery power supply system 100. Execution starts at the timing.

  When the control unit 130 requests charging rate estimation processing at a predetermined timing after completion of charging / discharging, first, in step S101, parameters necessary for calculation processing are set. As parameters necessary for the arithmetic processing, the sampling interval ΔTs when acquiring the voltage measurement value from the voltage sensor 120, the number Ns of sample acquisitions, and the initial value of the adjustment parameter of the voltage characteristic equation of (Equation 1) are set. There are initialization parameters. As the sampling interval ΔTs and the sample acquisition number Ns, values determined in advance may be used. For example, values such as ΔTs = 10 (seconds) and Ns = 60 (pieces) may be used.

  The initialization parameters include the parameter α used in (Expression 5), the reference value Ci used in (Expression 6), and the initial value Bi0 of the adjustment parameter Bi. As the parameter α, an optimum value can be determined in advance by experiments or the like. As for the reference value Ci, the optimum proportional relationship between the adjustment parameters A1 to A4 can be evaluated in advance, and a value corresponding to this proportional relationship can be set as Ci. Similarly, a suitable value can be determined in advance for the initial value Bi0 of the adjustment parameter Bi. These are stored in the storage unit 140 in advance.

  In step S102, voltage measurement values are acquired from the voltage sensor 120 until the number of sample acquisitions Ns is reached at the sampling interval ΔTs. Here, the acquired voltage measurement value is Vm (j) (j = 1 to Ns), and this is sequentially stored in the storage unit 140.

  In step S103, the voltage measurement value Va at the beginning of data acquisition in step S102 and the voltage measurement value Vb immediately before the end of data acquisition are calculated. The first voltage measurement value Vm (1) after the start of acquisition can be set as Va. Alternatively, Va may be an average value of a plurality of voltage measurement values Vm (j) (j = 1, Ma) at the beginning of acquisition. Similarly, Vm (Ns) can be set as Vb. Alternatively, an average value of a plurality of voltage measurement values immediately before the end of acquisition may be Vb.

  In step S104, the voltage drop amount ΔV in the data acquisition period is calculated based on (Equation 4). In step S105, the coefficient β is calculated based on (Equation 12) from ΔV calculated in step S104 and Ci input from the storage unit 140.

  In step S106, the initial value Ai0 of the adjustment parameter Ai is calculated based on (Equation 6) and the initial value Vc0 of the adjustment parameter Vc is calculated based on (Equation 5) using the coefficient β calculated in step S105. . Using the adjustment parameter initial values Ai0 and VC0 determined as described above and Bi0 read from the storage unit 140, the process proceeds to optimization parameter adjustment in the next step S107. Although the present embodiment is described on the premise of optimization by the least square method, there is no problem even if Kalman-filter operation or the like is used.

In step S107, the adjustment parameter is set to step S106 so that the error variance of the following expression expressed by the voltage characteristic expression of (Expression 1) and the voltage measurement value Vm (j) acquired from the voltage sensor 120 in step S102 is minimized. Update sequentially from the initial value obtained in step 1.
[Equation 28]
S = Σ [V (j) −Vm (j)] ² (Formula 13)

  In step S108, the optimum values of the adjustment parameters obtained by the least square method in step S107 are Ai, Bi, and Vc, which are stored in the storage unit 140, and this is used when the voltage characteristic equation (Equation 1) is calculated later. Use.

In the last step S109, the charging rate of the secondary battery 110 is estimated using the optimized adjustment parameter Vc. When calculating the stable open circuit voltage Vo using the voltage characteristic equation (Equation 1), if t is increased in (Equation 1), the exponential decay term converges to 0. Therefore, the stable open circuit voltage Vo is It becomes equal to the constant term Vc of (Formula 1). Thus, when (Formula 1) is used as the voltage characteristic expression of the secondary battery 110, the open circuit voltage Vo at the time of stability can be immediately known from the constant term Vc of (Formula 1).
As another method, the stable open circuit voltage Vo can be obtained by substituting a predetermined required time for stabilization of a predetermined battery voltage into the voltage characteristic equation (Equation 1) into which the optimized adjustment parameter is substituted. it can.

  As described above, since the voltage characteristic equation (Equation 1) can accurately estimate the change in the open circuit voltage of the secondary battery 110, the reliability of the charging rate estimated above is high. It can be used for alarm output and load control.

  FIG. 5 shows a schematic configuration of a secondary battery power supply system according to another embodiment of the present invention. In the secondary battery power supply system 200 of this embodiment shown in FIG. 5, a temperature sensor 210 for measuring the temperature of the secondary battery 110 is added, and the battery temperature measured by the temperature sensor 210 is taken into the control unit 130. It is configured as follows.

  As the initial value of the adjustment parameter Bi (i = 1 to n), the initial value stored in the storage unit 140 as a fixed value is used in the first embodiment. However, by changing the adjustment parameter Bi according to the temperature of the secondary battery 110, the open circuit voltage can be estimated with higher accuracy. Therefore, by determining the initial value of the adjustment parameter Bi depending on the temperature of the secondary battery 110, the optimization of the adjustment parameter by the least square method can be further accelerated. .

  In the present embodiment, a temperature function for calculating the initial value Bi0 of the adjustment parameter Bi from the temperature of the secondary battery 110 is determined in advance and stored in the storage unit 140. Then, based on the measured temperature acquired from the temperature sensor 210, the initial value Bi0 of the adjustment parameter Bi is calculated from the above temperature function.

  In the present embodiment, when the initial value Bi0 of the adjustment parameter Bi is calculated from the temperature of the secondary battery 110, the flow of processing in the control unit 130 shown in FIG. 1 is changed as follows. First, in step S101, the above temperature function is input from the storage unit 140 in place of the initial value Bi0.

  In step S102, in addition to obtaining the voltage measurement value, the temperature measurement value of the secondary battery 110 is obtained from the temperature sensor 210. Further, in step S106, in addition to calculating Ai0 and Vc0, the initial value Bi0 is calculated by substituting the temperature measurement value acquired in step S102 into the above temperature function. As temperature measurement values to be substituted into the above temperature function, all temperature measurement values acquired from the temperature sensor 210 may be averaged and used, or any one of them may be selected and used.

  As described above, in the present embodiment, the initial value of the adjustment parameter Bi is calculated from the temperature measurement value of the secondary battery 110 and used, so that the voltage characteristic equation (formula 1) using the adjustment parameter of the initial value is used. ) Calculates an open circuit voltage closer to the voltage measurement. Therefore, by using the initial value of the present embodiment, it is possible to converge the least square method at a higher speed and determine the optimum value of the adjustment parameter.

  In the above-described embodiment, the voltage characteristic formula (Formula 1) has been described using an example including four terms of the exponential decay function. However, the present invention is not limited to four terms and may include exponential decay functions of more terms. In addition, the number of voltage measurement values obtained after the completion of charging / discharging of the secondary battery, the sampling interval, and the like can be changed as appropriate according to the characteristics and the degree of deterioration of the secondary battery. Furthermore, α and Ci, which are constants set in advance, may be selected or calculated according to the type, temperature, deterioration degree, and the like of the secondary battery.

  In addition, although this embodiment demonstrated the secondary battery power supply system provided with the structure which estimates the charging rate of the secondary battery for vehicles mounted in a vehicle, this invention is limited to the secondary battery for vehicles use. The present invention can be widely applied to various devices equipped with a general secondary battery.

3 is a flowchart for explaining a charging rate estimation method for a secondary battery according to the present invention. It is a block diagram which shows schematic structure of the secondary battery power supply system which concerns on 1 embodiment of this invention. It is a figure which shows the example which measured the time fluctuation of the open circuit voltage over 60 minutes after charge of a secondary battery. It is a figure which shows the example of the change of the open circuit voltage of a secondary battery for demonstrating the method to set the initial value of an adjustment parameter. It is a block diagram which shows schematic structure of the secondary battery power supply system which concerns on another embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Load 100, 200 ... Secondary battery power supply system 110 ... Secondary battery 120 ... Voltage sensor 130 ... Control part 140 ... Memory | storage part 150 ... Charging circuit 210 ...・ Temperature sensor

Claims (10)

The time variation of the open circuit voltage (OCV) of the secondary battery after the end of charging / discharging is approximated by a voltage characteristic equation having an adjustment parameter, and the open circuit voltage when the secondary battery is stable from the voltage characteristic equation. Is a charging rate estimation method for estimating the charging rate of the secondary battery,
In a predetermined data acquisition period after the end of charging / discharging of the secondary battery, a plurality of voltage measurement values of the secondary battery are acquired,
Setting an initial value of the adjustment parameter with a predetermined relational expression depending on a change amount of the voltage measurement value in the data acquisition period and a predetermined calculation method set in advance;
Estimating an optimum value of the adjustment parameter when an error between the open circuit voltage calculated by the voltage characteristic equation and the voltage measurement value is minimized while gradually adjusting the adjustment parameter from the initial value. How to estimate the charging rate. When the adjustment parameter is Ai (i = 1 to n), Bi (i = 1 to n), and Vc, and n is an integer of 4 or more, the voltage specifying expression is time t.
[Equation 1]
V (t) = A1 · exp (B1 · t)) + A2 · exp (B2 · t) +.
+ An · exp (Bn · t) + Vc
Represented by
When the voltage measurement value at the initial stage of the data acquisition period is Va and the voltage measurement value immediately before the end of the data acquisition period is Vb, constants α and Ci (i = 1 to n) set in advance are used.
[Equation 2]
(C1 + C2 +... + Cn) · β = (Va−Vb) · α
Parameter β to satisfy
[Equation 3]
Ai0 = Ci · β (i = 1 to n)
Ai0 calculated in step S is used as the initial value of the adjustment parameter Ai,
[Equation 4]
Vc0 = Va− (Va−Vb) · α
The charging rate estimation method according to claim 1, wherein Vc0 calculated in step 1 is used as the initial value of the adjustment parameter Vc. The charging rate estimation method according to claim 2, wherein an initial value of the adjustment parameter Bi (i = 1 to n) is a constant set in advance. A temperature function for calculating an initial value of the adjustment parameter Bi (i = 1 to n) from the temperature of the secondary battery is set in advance,
Measuring the temperature during the data acquisition period to obtain a temperature measurement value;
The charging rate estimation method according to claim 2, wherein an initial value of the adjustment parameter Bi (i = 1 to n) is determined by substituting the temperature measurement value into the temperature function. The charging rate estimation method according to claim 2, wherein at least one of the Va and the Vb is an average value calculated by averaging two or more voltage measurement values. The charging rate estimation method according to claim 2, wherein the open circuit voltage when the secondary battery is stable is given by Vc when the optimum value of the adjustment parameter is determined. 3. The charging rate according to claim 2, wherein the open circuit voltage when the secondary battery is stable is calculated by substituting a predetermined time for a function formula that determines the optimum value of the adjustment parameter. Estimation method. A charging rate estimation device for estimating a charging rate of a secondary battery,
A voltage sensor for measuring a voltage of the secondary battery;
A control unit that executes and controls calculation for estimating the charging rate using a voltage characteristic equation having an adjustment parameter;
A storage unit for storing a voltage measurement value measured by the voltage sensor and data used for the calculation by the control unit;
The control unit acquires a plurality of voltage measurement values of the secondary battery from the voltage sensor during a predetermined data acquisition period after the end of charging and discharging of the secondary battery, and sets the voltage measurement value in the data acquisition period. The initial value of the adjustment parameter is set by a predetermined relational expression that depends on the amount of change and a predetermined calculation method set in advance, and the adjustment parameter is calculated from the initial value and the voltage characteristic formula is used to calculate the initial value. The optimum value of the adjustment parameter when the error between the open circuit voltage and the measured voltage value is minimized is estimated, and the A charging rate estimation apparatus characterized by calculating a circuit voltage and estimating the charging rate. When the control parameter is Ai, Bi (i = 1 to n) and Vc, and n is an integer of 4 or more,
[Equation 5]
V (t) = A1 · exp (B1 · t)) + A2 · exp (B2 · t) +.
+ An · exp (Bn · t) + Vc
Is used as the voltage specifying formula, Va is the voltage measurement value at the initial stage of the data acquisition period, and Vb is the voltage measurement value immediately before the end of the data acquisition period. 1-n)
[Equation 6]
(C1 + C2 +... + Cn) · β = (Va−Vb) · α
Parameter β to satisfy
[Equation 7]
Ai0 = Ci · β (i = 1 to n)
Ai0 calculated in step S is used as the initial value of the adjustment parameter Ai,
[Equation 8]
Vc0 = Va− (Va−Vb) · α
The charging rate estimation apparatus according to claim 7, wherein Vc0 calculated in step (b) is used as the initial value of the adjustment parameter Vc. A secondary battery power supply system comprising the charge rate estimation device according to claim 7 or 8.

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