JP2007333447A - Charge state estimation device of secondary battery, charge state estimation method, and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve accuracy of an estimated SOC even when the range of an SOC permitted in controlling charge/discharge of a secondary battery is relatively wide. <P>SOLUTION: A battery ECU 20 calculates a no-load voltage of a secondary battery 30 based on at least a battery voltage and a charge/discharge current of the secondary battery 30, compensates the no-load voltage based on a compensation value representing a voltage drop portion by a memory effect caused by the discharging of the secondary battery 30, or a voltage rise portion by a memory effect caused by the charging of the secondary battery 30, in a range from a lower-limit threshold at which the state of charge of the secondary battery 30 is smaller than 50% to an upper-limit threshold value at which it is larger than 50%, and obtains electromotive force by subtracting a polarization voltage from the compensated no-load voltage. Then, the state of charge of the secondary battery 30 based on the compensated no-load voltage is estimated by referring to relationship information representing the relationship between the electromotive force and the state of charge. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a secondary battery such as a nickel metal hydride battery or a lithium ion battery, and more particularly to a technique for obtaining a charged state of the secondary battery.

  A technique for estimating the state of charge of a secondary battery such as a nickel metal hydride secondary battery or a lithium ion secondary battery (hereinafter referred to as SOC (State Of Charge)) and controlling the charge / discharge of the secondary battery based on the SOC It has been known.

  In general, when estimating the SOC, the integrated value of the current values input and output from the secondary battery is measured, or the relationship between the discharge voltage and the discharge current is calculated. In addition, a technique for correcting the SOC by predicting the amount of self-discharge discharged when the secondary battery is left to stand for accuracy from the standing temperature and the standing time is also known.

  In addition to self-discharge, there is a memory effect as a cause of lowering the estimated SOC accuracy. The memory effect is a phenomenon in which a voltage drop appears on the discharge side and a voltage rise appears on the charge side when partial charge and discharge are repeated in nickel-hydrogen secondary batteries and nickel cadmium secondary batteries that use nickel hydroxide as the positive electrode. is there. In recent years, it is said that a similar phenomenon occurs in a lithium ion secondary battery, though only slightly.

  Patent Document 1 discloses a technique for correcting the SOC obtained based on the discharge voltage, battery temperature, and discharge current of the secondary battery based on the number of times the secondary battery is charged / discharged or the amount of electricity. However, Patent Document 1 considers the influence of the memory effect during discharging, but does not consider the influence of the memory effect during charging.

  By the way, in the system that charges and discharges the secondary battery while maintaining the SOC at around 50%, for example, in a system in which the SOC usage range allowed when controlling the charging and discharging of the secondary battery is relatively narrow, the charging and discharging of the secondary battery is performed. When the discharge is repeated, as shown in FIG. 7, with the vicinity of 50% as a boundary, the SOC causes a voltage drop phenomenon due to the memory effect when the SOC is 50% or less, and the SOC causes the memory effect when the SOC is 50% or more. The phenomenon of voltage rise may appear.

  In Patent Document 2, the SOC range and the OCV range to which the correction value for the memory effect is applied are stored in the memory, the correction value is calculated based on the battery temperature and the charge / discharge current, and the correction value is calculated as follows: A technique is disclosed in which an OCV-SOC map is created by applying only in the SOC range and OCV range stored in a memory, and the SOC is estimated based on the OCV-SOC map. Patent Document 2 assumes a system in which the secondary battery is charged and discharged while maintaining the SOC at around 50%. The SOC is corrected with respect to the OCV-SOC map when the SOC is 50% or more. The discharge side correction is performed at 50% or less.

  However, for example, when the range of SOC allowed at the time of charging / discharging is widened, the memory effect may occur even if the SOC is 50% or less on the charge side and the SOC is 50% or more on the discharge side. For this reason, the technique described in Patent Document 2 cannot correct the influence of the memory effect, which may cause a decrease in the estimated SOC accuracy.

JP-A-9-129267 JP 2004-22322 A

  An object of the present invention is to improve the accuracy of estimated SOC even when the range of SOC allowed when controlling charge / discharge of a secondary battery is relatively wide.

  The secondary battery charge state estimation apparatus according to the present invention includes a no-load voltage calculation unit that calculates a no-load voltage of the secondary battery based on at least a battery voltage and a charge / discharge current of the secondary battery, and the secondary battery In a range from a lower threshold value that is lower than 50% to an upper threshold value that is higher than 50%, the voltage drop due to the memory effect accompanying the discharge of the secondary battery or the voltage due to the memory effect accompanying the charging of the secondary battery A no-load voltage correction unit that corrects the no-load voltage based on a correction value that represents an increase, an electromotive force calculation unit that calculates an electromotive force based on the no-load voltage calculated by the no-load voltage correction unit, A charging state estimation unit that estimates a charging state of the secondary battery based on the electromotive force with reference to relationship information indicating a relationship between the electromotive force and the charging state calculated by the electromotive force calculation unit. Features To.

  According to one aspect of the charging state estimation device according to the present invention, the no-load voltage correction unit is based on a memory effect associated with discharging of the secondary battery in a range where the charging state of the secondary battery is greater than 50%. The no-load voltage is corrected based on a correction value representing a voltage drop.

  According to one aspect of the state of charge estimation device according to the present invention, the no-load voltage correction unit has a memory effect associated with the state of charge of the secondary battery in a range where the state of charge of the secondary battery is less than 50%. The no-load voltage is corrected on the basis of a correction value representing a voltage increase due to.

  The secondary battery charge state estimation apparatus according to the present invention includes a no-load voltage calculation unit that calculates a no-load voltage of the secondary battery based on at least a battery voltage and a charge / discharge current of the secondary battery, and the secondary battery When the state of charge of the battery is greater than 50%, the no-load voltage is corrected based on a correction value representing a voltage drop due to the memory effect accompanying the discharge of the secondary battery, and the state of charge of the secondary battery is 50 Calculated by the no-load voltage correction unit and the no-load voltage correction unit for correcting the no-load voltage based on a correction value representing a voltage increase due to the memory effect associated with the charged state of the secondary battery in a range smaller than%. Based on the electromotive force with reference to the electromotive force calculation unit that calculates the electromotive force based on the no-load voltage that has been generated and the relationship information that indicates the relationship between the electromotive force and the state of charge calculated by the electromotive force calculation unit Of the secondary battery Characterized in that it comprises a state-of-charge estimation unit that estimates a conductive state.

  According to one aspect of the charging state estimation device according to the present invention, the charging state estimation device further includes an integrated charge / discharge electric quantity calculation unit that integrates the charge / discharge current over a predetermined period, and the no-load voltage correction unit Based on the ratio of the amount of discharged electricity and the amount of charged electricity of the secondary battery, if the ratio of the amount of discharged electricity is large, the correction of the no-load voltage is corrected using a correction value representing the voltage drop, and the amount of charged electricity When the ratio is large, the no-load voltage is corrected using a correction value representing the voltage increase.

  According to one aspect of the state-of-charge estimation device according to the present invention, the no-load voltage correction unit includes a physical quantity indicating a charge / discharge status of the secondary battery and a correction value indicating a voltage drop or a voltage increase due to a memory effect. And a correction value for a voltage drop or a voltage rise used for correcting the no-load voltage is determined.

  According to the present invention, it is possible to improve the accuracy of estimated SOC even when the range of SOC allowed when controlling charge / discharge of a secondary battery is relatively wide.

  A best mode for carrying out the present invention (hereinafter referred to as an embodiment) will be described with reference to the drawings, taking a hybrid electric vehicle as an example. In addition, although this embodiment demonstrates the hybrid electric vehicle which is one of the electric vehicles to an example, this embodiment is applicable also to the other electric vehicle provided with a motor (electric motor) as a drive source.

  FIG. 1 is a diagram illustrating a schematic configuration of a hybrid electric vehicle according to the present embodiment. In FIG. 1, a vehicle ECU 10 controls an inverter 50 and an engine electronic control unit (hereinafter referred to as engine ECU) 40. The engine ECU 40 controls the engine 60. The battery electronic control unit (hereinafter referred to as battery ECU) 20 also functions as a charge state estimation device, receives information such as the battery voltage V, charge / discharge current I, and battery temperature T from the secondary battery 30 and The SOC of the secondary battery 30 is estimated. Further, the battery ECU 20 transmits battery information such as the SOC and battery temperature of the secondary battery 30 to the vehicle ECU 10. The vehicle ECU 10 controls charging / discharging of the secondary battery 30 by controlling the engine ECU 40, the inverter 50, and the like based on various battery information.

  The secondary battery 30 supplies power to the motor 52. The inverter 50 converts the DC power supplied from the secondary battery 30 into AC power and supplies the AC power to the motor 52 when the secondary battery 30 is discharged.

  The engine 60 transmits power to the wheels via the power split mechanism 42, the speed reducer 44, and the drive shaft 46. The motor 52 transmits power to the wheels via the speed reducer 44 and the drive shaft 46. When the secondary battery 30 needs to be charged, a part of the power of the engine 60 is supplied to the generator 54 via the power split mechanism 42 and used for charging.

  The vehicle ECU 10 includes information on the operating state of the engine 60 from the engine ECU 40, operating information such as an accelerator pedal operation amount, a brake pedal operation amount, a shift range set by a shift lever, SOC from the battery ECU 20, and the like. Based on various battery information, a control command is output to engine ECU40 or inverter 50, and engine 60 and motor 52 are driven.

  As shown in FIG. 2, the secondary battery 30 is configured by connecting battery blocks B1 to B20 in series. Battery blocks B <b> 1 to B <b> 20 are accommodated in a battery case 32. Each of the battery blocks B1 to B20 is configured by electrically connecting two battery modules in series. Further, each battery module is configured by electrically connecting six unit cells in series. Has been. As each single battery, a nickel metal hydride battery, a lithium ion battery, or the like can be used. In this embodiment, a case where a nickel metal hydride battery is used will be described. In addition, the number of battery blocks, battery modules, and single cells is not particularly limited. The configuration of the secondary battery 30 is not limited to the above example.

  Further, a plurality of temperature sensors 34 are arranged in the battery case 32. The plurality of temperature sensors 34 are arranged so that a plurality of battery blocks having relatively close temperatures are grouped as one group, or one battery block having a relatively different temperature from any of the battery blocks is grouped as one group. This is done by arranging two temperature sensors 34. The grouping is performed by measuring the temperature of each battery block by a prior experiment or the like. In the present embodiment, M (M is an integer) number of temperature sensors 34 are provided, and the temperatures measured by the temperature sensors 34 are expressed as temperatures T (1) to T (M), respectively.

  In FIG. 2, the voltage measurement unit 22 measures the terminal voltage of the secondary battery 30. In the present embodiment, the voltage measurement unit 22 measures the terminal voltages Vb (1) to Vb (20) of the battery blocks B1 to B20. The voltage measuring unit 22 generates voltage data specifying the terminal voltages Vb (1) to Vb (20) and outputs them to the control unit 26. The output of the voltage data to the control unit 26 is performed at a preset period (for example, 100 ms), and the control unit 26 stores the voltage data in the storage unit 28. The control unit 26 calculates the battery voltage V by totaling the terminal voltages Vb (1) to Vb (20) indicated in the voltage data stored in the storage unit 28.

  The current measuring unit 23 measures the charge / discharge current I when the secondary battery 30 is charged / discharged. In the present embodiment, the current measuring unit 23 converts the analog signal output from the current sensor 35 into a digital signal, and based on this, the current input to the secondary battery 30 during charging, and the secondary battery 30 during discharging. Current data for specifying the output current is generated and output to the control unit 26. In addition, the current measurement unit 23 generates current data, for example, when charging is negative and when discharging is positive. Current data from the current measurement unit 23 to the control unit 26 is also performed at a preset period (for example, 100 ms), and the control unit 26 also stores the current data in the storage unit 28.

  The temperature measurement unit 24 measures the battery temperature of the secondary battery 30. In the present embodiment, the analog signal output from each temperature sensor 34 set for each group is converted into a digital signal, and based on this, temperature data for specifying the battery temperature for each group is generated, and this is used as the control unit 26. Output to. The output of the temperature data to the control unit 26 by the temperature measurement unit 24 is also performed at a preset period (for example, 100 ms), and the control unit 26 also stores the temperature data in the storage unit 28. For example, the control unit 26 obtains the battery temperature T by obtaining an average value of the temperatures T (1) to T (M) indicated in the temperature data stored in the storage unit 28.

  The control unit 26 estimates the state of charge of the secondary battery 30 (hereinafter referred to as SOC (State Of Charge)) based on the battery voltage V, the charge / discharge current I, the battery temperature T, etc. In the present embodiment, The SOC is estimated by the following method: That is, the no-load voltage calculation unit 261 obtains the pair data of the battery voltage V and the charge / discharge current I in the predetermined period D (for example, 60 [seconds]) from the storage unit 28. A plurality of data are obtained, and a first-order approximation line (voltage V-current I approximation line) is obtained from the pair data by regression analysis, and the V-intercept of the V-I approximation line is obtained as a reference voltage V0 (no load voltage). Next, the polarization voltage calculation unit 262 calculates the polarization voltage Vbus based on the amount of change in the accumulated capacity during a predetermined period (for example, 60 seconds), and the electromotive force calculation unit 263 calculates the polarization voltage Vbus from the reference voltage V0. Subtract Next, the battery state T is calculated from the plurality of electromotive force-SOC relationship information indicating the relationship between the electromotive force Vk and the SOC as shown in FIG. Corresponding relationship information is selected, and the SOC is estimated from the obtained electromotive force Vk with reference to the selected relationship information.

  By the way, when the secondary battery 20 is repeatedly charged and discharged, the so-called memory effect causes a voltage rise during charging and a voltage drop during discharging. For example, when the SOC is used in a relatively wide range and the SOC is charged / discharged while allowing the SOC to 20% to 80%, for example, as shown in FIG. Appears over a wide range of SOCs. Such a phenomenon is likely to occur when, for example, a hybrid electric vehicle continues to travel uphill or downhill for a long distance. Without considering the influence of the memory effect, the electromotive force Vk is calculated from the reference voltage V0 obtained as described above, and from the electromotive force Vk with reference to the electromotive force-SOC relationship information as shown in FIG. When the SOC is estimated, the accuracy of the estimated SOC may decrease.

  Therefore, in this embodiment, before the charge state estimation unit 264 estimates the SOC from the electromotive force Vk with reference to the electromotive force-SOC relationship information, the no-load voltage correction unit 265 uses the memory effect with respect to the reference voltage V0. Perform correction according to voltage drop or voltage rise. By performing such correction, the SOC usage range is relatively wide, and even when charging / discharging the secondary battery 30 while allowing the SOC to 20% to 80%, for example, the estimated accuracy of the SOC is reduced. Prevent inviting.

  Hereinafter, the procedure in which the battery ECU 20 estimates the SOC in the present embodiment will be described with reference to FIG.

  First, the battery ECU 20 calculates the reference voltage V0 based on a plurality of pair data of the battery voltage V and the charge / discharge current I measured in the predetermined period D as described above (S100). Next, the battery ECU 20 acquires the charging / discharging current I measured during the predetermined period D from the storage unit 28, and sums the acquired charging / discharging currents I in the integrated charging / discharging electric quantity calculation unit 266. A discharge electricity amount C is calculated. As described above, the storage unit 28 stores the charging / discharging current I with the charging time being negative and the discharging time being positive. Therefore, if the charge rate to the secondary battery 30 is large in the predetermined period D, the cumulative charge / discharge electricity amount C becomes negative, and conversely if the charge rate from the secondary battery 30 is large, the cumulative charge / discharge electricity amount. C becomes positive.

  Therefore, when the accumulated charge / discharge electricity amount C is greater than zero, the battery ECU 20 determines that the discharge rate is large (the determination result of step S104 is affirmative “Y”), and the memory is stored with respect to the reference voltage V0. Correction is performed to compensate for the voltage drop due to the effect (S106). More specifically, the battery ECU 20 uses the current data stored in the storage unit 28 to sum up the discharge currents that have been discharged by the secondary battery 30 so far, thereby calculating the total amount of electricity (hereinafter referred to as the total amount of discharged electricity). Calculated). Next, the battery ECU 20 determines a voltage correction amount (a value equal to or less than zero) corresponding to the total discharge electricity amount with reference to the discharge-side correction map as shown in FIG. The reference voltage V0 is corrected based on the voltage correction amount. Specifically, the voltage correction amount (a value less than or equal to zero) is subtracted from the reference voltage V0 of the discharge-side reference voltage line affected by the memory effect shown in FIG. In FIG. 6A, the total discharge electricity amount is used as a parameter for determining the voltage correction amount. However, it may be a physical amount representing the charge / discharge state of the secondary battery that changes corresponding to the voltage drop due to the memory effect. Other physical quantities may be used. Examples of other physical quantities include the total travel distance of the hybrid electric vehicle and the total charge / discharge period of the secondary battery 30. The correction map is created by obtaining the relationship between the voltage drop due to the memory effect and the total amount of discharge electricity by conducting an experiment or the like in advance. The same applies to the correction map on the charging side shown in FIG. 6B.

  On the other hand, the battery ECU 20 determines that the charging rate is high when the accumulated charge / discharge electricity amount C is equal to or less than zero (the determination result of step S104 is negative “N”), and the memory is stored with respect to the reference voltage V0. Correction is performed to compensate for the voltage increase due to the effect (S108). More specifically, the battery ECU 20 refers to a correction map on the charging side as shown in FIG. 6B stored in advance in the storage unit 28, and a voltage correction amount (a value equal to or greater than zero) corresponding to the total discharge electricity amount. And the reference voltage V0 is corrected based on the voltage correction amount. Specifically, the voltage correction amount (a value equal to or greater than zero) is subtracted from the reference voltage V0 of the charging-side reference voltage line affected by the memory effect shown in FIG.

  As described above, the battery ECU 20 determines the voltage correction amount with reference to the discharge-side correction map or the charge-side correction map in accordance with the charge / discharge status of the secondary battery 30 in the predetermined period D, and the voltage correction. The reference voltage V0 is corrected using the quantity. Next, the electromotive force Vk is obtained by subtracting the polarization voltage Vbus from the corrected reference voltage V0. Thereafter, the battery ECU 20 estimates the SOC corresponding to the electromotive force with reference to the electromotive force-SOC relation information as shown in FIG. Therefore, according to this embodiment, even when SOC is allowed to 20% to 80%, for example, and charging / discharging of the secondary battery 30 is performed, it is possible to prevent a decrease in estimated SOC accuracy. Further, according to the present embodiment, for example, even when the hybrid electric vehicle continues to travel uphill or downhill for a long distance, it is possible to prevent the estimated SOC from being degraded.

  In the above-described embodiment, a case has been described in which one discharge-side correction map and one charge-side correction map are prepared. However, the correction map referred to by the battery ECU 20 according to the battery temperature T and SOC is described. It may be changed.

  In the above description, the battery ECU 20 can be realized by installing a program for implementing various processes shown in FIG. 5 in the microcomputer and executing the program.

  That is, the microcomputer has various memories such as a CPU, ROM, RAM, and EEPROM, a communication bus, and an interface. The processing program stored in the ROM as firmware in advance is read out and sequentially executed by the CPU. The reference voltage-SOC relation information and the correction map are stored in the memory in advance, and the CPU inputs the reference voltage V0 based on the battery voltage V, the charge / discharge current I, etc. input from various sensors via the interface and stored in the memory. Further, referring to the correction map, the voltage correction amount for the reference voltage V0 is determined, the reference voltage V0 is corrected based on the voltage correction amount, and then the polarization voltage is subtracted from the reference voltage V0. Is calculated. Next, the state of charge of the secondary battery is estimated based on the electromotive force with reference to the electromotive force-SOC relationship information.

It is a figure which shows schematic structure of the hybrid electric vehicle which concerns on this embodiment. It is a figure which shows the functional block for demonstrating a secondary battery and battery ECU. It is a figure which shows an example of the electromotive force-SOC relationship information referred when battery ECU estimates the charge condition of a secondary battery. It is a figure which shows an example of the reference voltage-SOC relationship information for demonstrating the relationship between the voltage rise or voltage drop by a memory effect, and SOC. It is a flowchart which shows the procedure in which battery ECU estimates the charge condition of a secondary battery. It is a figure which shows an example of the correction map referred when battery ECU determines the voltage correction amount by the side of discharge. It is a figure which shows an example of the correction map referred when battery ECU determines the voltage correction amount by the side of charge. It is a figure which shows an example of the reference voltage-SOC relationship information for demonstrating the relationship between the voltage rise or voltage drop by a memory effect, and SOC.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Vehicle ECU, 20 Battery ECU, 30 Secondary battery, 40 Engine ECU, 42 Power split mechanism, 44 Reducer, 46 Drive shaft, 50 Inverter, 52 Motor, 54 Generator, 60 Engine

Claims (8)

A no-load voltage calculator that calculates a no-load voltage of the secondary battery based on at least the battery voltage and the charge / discharge current of the secondary battery;
A voltage drop due to a memory effect accompanying discharge of the secondary battery or a memory accompanying charging of the secondary battery in a range from a lower limit threshold value less than 50% to an upper limit threshold value greater than 50%. A no-load voltage correction unit that corrects the no-load voltage based on a correction value representing a voltage increase due to an effect;
An electromotive force calculation unit that calculates an electromotive force based on the no-load voltage calculated by the no-load voltage correction unit;
A charge state estimation unit that estimates a charge state of the secondary battery based on the electromotive force with reference to relationship information indicating a relationship between the electromotive force and the charge state calculated by the electromotive force calculation unit;
A charging state estimation device comprising: In the charging state estimation device according to claim 1,
The no-load voltage correction unit is
The state of charge of the secondary battery corrects the no-load voltage based on a correction value representing a voltage drop due to a memory effect accompanying discharge of the secondary battery in a range where the state of charge is greater than 50%. Estimating device. In the charging state estimation device according to claim 1,
The no-load voltage correction unit is
Charging wherein the no-load voltage is corrected based on a correction value representing a voltage increase due to a memory effect associated with the charging state of the secondary battery in a range where the charging state of the secondary battery is less than 50% State estimation device. A no-load voltage calculator that calculates a no-load voltage of the secondary battery based on at least the battery voltage and the charge / discharge current of the secondary battery;
In the range where the charge state of the secondary battery is greater than 50%, the no-load voltage is corrected based on a correction value representing a voltage drop due to the memory effect accompanying the discharge of the secondary battery, and the secondary battery is charged A no-load voltage correction unit that corrects the no-load voltage based on a correction value representing a voltage increase due to a memory effect associated with a charged state of the secondary battery in a range where the state is less than 50%;
An electromotive force calculation unit that calculates an electromotive force based on the no-load voltage calculated by the no-load voltage correction unit;
A charge state estimation unit that estimates a charge state of the secondary battery based on the electromotive force with reference to relationship information indicating a relationship between the electromotive force and the charge state calculated by the electromotive force calculation unit;
A charging state estimation device comprising: In the charging state estimation device according to any one of claims 1 to 4,
Furthermore, an integrated charge / discharge electricity amount calculation unit that integrates charge / discharge current over a predetermined period is provided,
The no-load voltage correction unit is
Based on the ratio between the amount of discharged electricity and the amount of charged electricity of the secondary battery in a predetermined period, when the ratio of the amount of discharged electricity is large, the no-load voltage is corrected using a correction value representing a voltage drop. When the ratio of the amount of charged electricity is large, the no-load voltage is corrected using a correction value representing the voltage increase.
The charge state estimation apparatus characterized by the above-mentioned. In the charging state estimation device according to any one of claims 1 to 5,
The no-load voltage correction unit is
Voltage drop used when correcting the no-load voltage with reference to a correction map showing a relationship between a physical quantity representing the charge / discharge status of the secondary battery and a correction value representing a voltage drop or voltage rise due to the memory effect Determine the correction value for the minute or voltage rise,
The charge state estimation apparatus characterized by the above-mentioned. A charging state estimation method for estimating a charging state of a secondary battery,
Calculating a no-load voltage of the secondary battery based on at least a battery voltage and a charge / discharge current of the secondary battery;
A voltage drop due to a memory effect accompanying discharge of the secondary battery or a memory accompanying charging of the secondary battery in a range from a lower limit threshold value less than 50% to an upper limit threshold value greater than 50%. A no-load voltage correction step for correcting the no-load voltage based on a correction value representing a voltage increase due to the effect;
An electromotive force calculation step of calculating an electromotive force based on the no-load voltage calculated in the no-load voltage correction step;
A step of estimating a charge state of the secondary battery based on the electromotive force with reference to relationship information indicating a relationship between the electromotive force and the charge state calculated in the electromotive force calculation step;
The charging state estimation method characterized by including. A program for causing a computer to execute a charging state estimation method for estimating a charging state of a secondary battery,
A voltage drop due to a memory effect accompanying discharge of the secondary battery or a memory accompanying charging of the secondary battery in a range from a lower limit threshold value less than 50% to an upper limit threshold value greater than 50%. A no-load voltage correction step for correcting the no-load voltage based on a correction value representing a voltage increase due to the effect;
An electromotive force calculation step for calculating an electromotive force based on the no-load voltage calculated in the no-load voltage correction step;
A charge state estimation step for estimating a charge state of the secondary battery based on the electromotive force with reference to relationship information indicating a relationship between the electromotive force and the charge state calculated in the electromotive force calculation step;
For causing the computer to execute.

Images