BATTERY STATE-OF-CHARGE ESTIMATION METHOD AND BATTERY MANAGEMENT SYSTEM

• US 20130138370A1
• Filed: 11/30/2012
• Published: 05/30/2013
• Est. Priority Date: 11/30/2011
• Status: Active Grant

• Current Assignee: Silicon Works Co., Ltd.
• Original Assignee: Silicon Works Co., Ltd.
• Inventors: KIM, Yong Goo, OH, Hyung Seog, HONG, Ju Pyo, CHUNG, Chun Sik, KIM, Jae Wan, KIM, Chol Ho, KIM, Moon Young, KIM, Jun Ho, PARK, Jin Sik
• Granted Patent: US 10,295,604 B2
• Time in Patent Office: Days
• US Class Current: 702/63
• CPC Class Codes: G01R 31/367 Software therefor, e.g. for battery testing using modelling or look-up tables
• CPC Class Codes: G01R 31/3828 using current integration
• CPC Class Codes: G01R 31/3842 combining voltage and current measurements
• CPC Class Codes: G05B 11/01 electric

Abstract

Provided are a battery state-of-charge (SOC) estimation method and a battery management system which are capable of estimating an SOC using an inexpensive processor and a small-capacity memory. The SOC estimation method includes an SOC table creation step, an SOC calculation step, an SOC comparison step, and a processing step. The battery management system includes a battery, a sensing resistor, a control switch unit, and a processor.

Claims

1. A battery state-of-charge (SOC) estimation method comprising:

an SOC table creation step of dividing the entire area of a two-dimensional coordinate system representing a relation between battery open-circuit voltages and battery SOCs into a plurality of steps at a plurality of different temperatures at a time point when a battery is charged or discharged, and storing function information representative of the relation between battery open-circuit voltages and battery SOCs for each step in an SOC table;

an SOC calculation step of applying an initial SOC extracted by using the function information stored in the SOC table, parameters of elements used in a battery equivalent model, an open-circuit voltage of the battery, and an amount of current inputted to or outputted from the battery to a current integral equation, and calculating an SOC of the battery;

an SOC comparison step of extracting an SOC corresponding to the open-circuit voltage applied at the SOC calculation step using the function information stored in the SOC table, and comparing the extracted SOC and the calculated SOC; and

a processing step of displaying the calculated SOC when a difference between the extracted SOC and the calculated SOC is smaller than a critical value.

2. The battery SOC estimation method of claim 1, wherein the SOC table creation step comprises:

measuring battery SOCs based on change of the battery open-circuit voltage at the plurality of different temperatures;

representing the battery SOCs based on the change of the battery open-circuit voltage, measured at the plurality of different temperatures, on a two-dimensional coordinate system and connecting the battery SOCs through a line;

distinguishing steps in which increase tendencies or decrease tendencies of the data represented on the two-dimensional coordinate system are different from each other; and

acquiring function information representative of each step, and storing the acquired function information in the SOC table.

3. The battery SOC estimation method of claim 2, wherein the function information indicates a gradient and an intercept of a linear function, and

the gradient a and the intercept b satisfy the following equations:

4. The battery SOC estimation method of claim 1, wherein the current integral equation at the SOC calculation step is expressed as follows:

5. The battery SOC estimation method of claim 1, further comprising a model parameter estimation step of measuring an open-circuit voltage of the battery and a current inputted to or outputted from the battery, and calculating resistance of a resistor applied to the battery equivalent model and capacitance of a capacitor applied to the battery equivalent model.

6. The battery SOC estimation method of claim 5, wherein in the model parameter estimation step,

when the current is inputted to the battery, a charge control switch installed between the battery and a current source is turned on and off by a charge control signal having a predetermined frequency such that the current inputted to the battery has a pulse form with a predetermined frequency, during a predetermined time period of the entire time period in which the current is inputted to the battery, and

when the current is outputted from the battery, a discharge control switch installed between the battery and a load receiving the current from the battery is turned on and off by a discharge control signal having a predetermined frequency such that the current outputted from the battery also has a pulse form with a predetermined frequency, during a predetermined time period of the entire time period in which the current is outputted from the battery.

7. The battery SOC estimation method of claim 6, wherein the model parameter estimation step comprises calculating the resistance value of the resistor applied to the battery equivalent model and the capacitance of the capacitor applied to the battery equivalent model, using a battery current and a battery open-circuit voltage in a period including a period in which the pulse-type current transits and a period in which the pulse-type open-circuit voltage transits in correspondence to the pulse-type current.

8. The battery SOC estimation method of claim 1, wherein the processing step comprises:

displaying the calculated SOC and the fact that the difference between the extracted SOC and the calculated SOC is larger than the critical value, when the difference between the extracted SOC and the calculated SOC is larger than the critical value; and

displaying only the calculated SOC when the difference between the extracted SOC and the calculated SOC is smaller than the critical value.

9. The battery SOC estimation method of claim 8, wherein the processing step comprises displaying the number of errors in which the fact that the difference between the extracted SOC and the calculated SOC is larger than the critical value is detected.

10. The battery SOC estimation method of claim 9, wherein the processing step comprises updating the SOC table creation step when the number of errors exceeds a predetermined reference number.

11. A battery management system comprising:

a sensing resistor connected to one end of a battery;

a control switch unit configured to transmit a current supplied from a current source to the battery or transmit a current outputted from the battery to a load, in response to a control signal; and

a processor configured to generate the control signal, calculate parameters of elements applied to an equivalent model of the battery using a measured temperature of the battery, a current of the battery, and an open-circuit voltage of the battery, and create and store an SOC table using the temperature and the open-circuit voltage of the battery.

12. The battery management system of claim 11, wherein the control signal comprises a charge control signal and a discharge control signal, and

the control switch unit comprises:

a charge control switch configured to switch the current supplied from the current source to the battery in response to the charge control signal; and

a discharge control switch configured to switch the current outputted from the battery to the load in response to the discharge control signal.

13. The battery management system of claim 12, wherein the processor represents a relation between battery SOCs and battery open-circuit voltages on a two-dimensional coordinate system at a plurality of different temperatures at a time point when a battery is charged or discharged, distinguishes steps in which increase tendencies or decrease tendencies of the data represented on the two-dimensional coordinate system are different from each other, and stores function information representative of the relation between battery open-circuit voltages and battery SOCs for each step in the SOC table.

14. The battery management system of claim 13, further comprising a user interface device configured to divide the entire region of the two-dimensional coordinate system representing the relation between battery open-circuit voltages and battery SOCs in a plurality of steps at the plurality of different temperatures at a time point when a battery is charged or discharged, calculate a gradient and intercept of a linear function representative of the relation between battery open-circuit voltages and battery SOCs for each step, and transmit the calculated gradient and intercept to the processor.

15. The battery management system of claim 13, wherein the function information indicates a gradient and an intercept of a linear function, and

the gradient a and the intercept b satisfy the following equations:

16. The battery management system of claim 15, wherein the processor calculates a current SOC of the battery using the temperature of the battery, the open-circuit voltage of the battery, and the gradient and intercept of the linear function stored in the SOC table, and extracts an SOC based on the open-circuit voltage of the battery when the SOC of the battery was calculated, by referring to the SOC table,

when the difference between the calculated SOC and the extracted SOC is larger than a predetermined critical value, the processor issues a command to display the calculated SOC and the fact that the difference between the calculated SOC and the extracted SOC is larger than the critical value, and

when the difference between the calculated SOC and the extracted SOC is smaller than the predetermined critical value, the processor issues a command to display the calculated SOC.

17. The battery management system of claim 16, wherein the processor issues a command to store the number of errors in which the fact that the difference between the calculated SOC and the extracted SOC is larger than the critical value is detected, when the difference between the calculated SOC and the extracted SOC is larger than the predetermined critical value, and to update the data stored in the SOC table when the number of errors is larger than a predetermined reference number.

18. The battery management system of claim 12, wherein the processor controls the charge control signal such that the current supplied to the battery has a pulse form with a predetermined frequency during some periods of the period in which the battery is charged, and controls the discharge control signal such that the current supplied to the load from the battery has a pulse form with a predetermined frequency during some periods of the period in which the battery is discharged, in order to calculate parameters of elements applied to the battery equivalent model.