Method for estimating a quantity of a state of a battery

• US 9,170,304 B2
• Filed: 04/09/2009
• Issued: 10/27/2015
• Est. Priority Date: 04/11/2008
• Status: Active Grant

• Current Assignee: Furukawa Electric Company Limited
• Original Assignee: Furukawa Electric Company Limited
• Inventors: Nukui, Katsuya
• Primary Examiner(s): Fantu, Yalkew
• Assistant Examiner(s): HERNANDEZ, MANUEL J
• Application Number:
  US12/420,945
• Publication Number:
  US 20090256524A1
• Time in Patent Office: 2,392 Days
• Field of Search: 320/132, 324/426, 324/427
• US Class Current: 1/1
• CPC Class Codes: G01R 31/3648 comprising digital calculation means, e.g. for performing an algorithm
• CPC Class Codes: G01R 31/382 Arrangements for monitoring battery or accumulator variables, e.g. SoC
• CPC Class Codes: G01R 31/3835 involving only voltage measurements
• CPC Class Codes: G01R 31/3842 combining voltage and current measurements
• CPC Class Codes: G01R 31/387 Determining ampere-hour charge capacity or SoC
• CPC Class Codes: G01R 31/388 involving voltage measurements
• CPC Class Codes: G01R 31/392 Determining battery ageing or deterioration, e.g. state of health

Abstract

There is provided a battery state detecting method that detects states by evaluating depletion caused by reaction processes whose speeds are different. Voltage V_mes, current I_mes and temperature T_mes of a battery are measured and inputted in Step S1 and it is judged whether or not an absolute value of the measured current Imes is smaller than a current threshold value Ithre in Step S2. OCV_{20 hr} is estimated from SOC^n-1 and SOH^n-1 after the previous discharge/charge based on a stable OCV estimating equation in Step S4 and a difference between the voltage measured value Vmes and the OCV_{20 hr} is calculated and stored in Step S5. A relaxation function Fⁿ(t) is updated corresponding to time t in processes in Steps S6 through S19. SOHⁿ is calculated by using the updated Fⁿ (t) in Step S17 and SOCⁿ is calculated in Step S19.

Claims

1. A battery state detecting method for estimating at least a quantity of a state of a battery, at least a state of charge (SOC) and a state of health (SOH),

wherein

the method comprises the steps of:

generating reference data associated with a reference relaxation function F^ref(t), wherein the reference relaxation function F^ref(t) approximates a variation of voltage Δ

V(t) obtained by measuring values of an open circuit voltage (OCV) of the battery in a standard state of the battery during a predetermined cycle, and wherein the predetermined cycle is associated with a period from a time of completion of discharge or charge of the battery to a time when a measured value of the OCV substantially becomes constant;

forming a relaxation function Fⁿ(t) that approximates the variation voltage Δ

V(t) based on a sum of at least a first relaxation function for a first reaction speed of the battery associated with an ion reaction and a second relaxation function for a second reaction speed of the battery associated with an electrolytic reaction; and

estimating the quantity of the state of the battery after the completion of the charge or the discharge based on the relaxation function Fⁿ (t) and the reference data associated with the reference relaxation function F^ref(t), wherein the first relaxation function and the second relaxation function are optimized by dividing the variation voltage Δ

V(t), which is approximated from the measured values of the OCV, into components corresponding to at least the first reaction speed and the second reaction speed, and SOC^ref and SOHi^ref are the SOC and an i-th SOH per reaction speed in the standard state of the battery, respectively, SOCⁿ and SOHiⁿ are the SOC and a different i-th SOH per reaction speed after the completion of an n-th charge or discharge, respectively, g(T) is a function associated with dependency on temperature T, fiⁿ (t) is an i-th relaxation function per reaction speed fi(t) included in the relaxation function Fⁿ(t), and fi^ref(t) is an i-th reference relaxation function per reaction speed fi(t) included in the reference relaxation function F^ref(t), and

wherein the relaxation function per reaction speed fiⁿ (t) after the completion of the n-th charge or discharge is expressed as;

fiⁿ(t)=f^ref(t)*(SOCⁿ/SOC^ref)*(SOHiⁿ/SOHi^ref)*g(T).

2. The battery state detecting method of claim 1,

wherein the relaxation function Fⁿ(t) is further formed as a function of a temperature of the battery that is measured after the completion of the charge or the discharge.

3. The battery state detecting method of claim 1,

wherein the relaxation function Fⁿ(t) is selected from a set of relaxation functions based on diffusion of an electrolytic solution within the battery and an elapsed time associated with an operation condition of a vehicle.

4. The battery state detecting method of claim 1,

wherein the estimating further comprises estimating the quantity of the state of the battery based on other reference data associated with an initial state of the battery.

5. The battery state detecting method of claim 1,

wherein

when the temperature T and the SOC are constant, the SOHiⁿ is expressed as:

SOHiⁿ={fiⁿ(t)/fi^ref(t)}*SOHi^ref.

6. The battery state detecting method of any of claim 3, 4 or 5, comprising:

measuring voltage and current of the battery;

calculating the variation of voltage Δ

V(t) at an elapsed time t after the completion of the charge or the discharge by using the measured values of the OCV measured during the predetermined cycle when the battery is determined to be stopping to charge or discharge on the basis of a predetermined charge or discharge stopping signal or the measured value of the current;

optimizing the first relaxation function associated with the first reaction speed and the second relaxation function associated with the second reaction speed based on respective time constants shorter than the elapsed time t to generate a modified first relaxation function and a modified second relaxation function; and

estimating the quantity of the state based on the modified first relaxation function, the modified second relaxation function, and a third relaxation function related to a third reaction speed associated with a time constant longer than the elapsed time t.

7. The battery state detecting method of claim 6,

wherein the battery is associated with a stopping state to discharge and charge in response to a determination that the current of the battery is less than a predetermined value of current.

8. The battery state detecting method of claim 1, comprising:

measuring voltage and current of the battery;

calculating the variation of voltage Δ

V(t) at an elapsed time t after the completion of the charge or discharge by using the measured values of the OCV measured during the predetermined cycle when the battery is determined to be stopping to charge or discharge on the basis of a predetermined charge or discharge stopping signal or the measured value of the current;

optimizing the first relaxation function associated with the first reaction speed and the second relaxation function associated with the second reaction speed based on respective time constants shorter than the elapsed time t to generate a modified first relaxation function and a modified second relaxation function; and

estimating the quantity of the state based on the modified first relaxation function, the modified second relaxation function, and a third relaxation function related to a third reaction speed associated with a time constant longer than the elapsed time t.

9. The battery state detecting method of claim 8,

wherein the battery is associated with a stopping state to discharge and charge in response to a determination that the current of the battery is less than a predetermined value of current.