STATE ESTIMATING DEVICE OF SECONDARY BATTERY

• US 20100153038A1
• Filed: 03/13/2008
• Published: 06/17/2010
• Est. Priority Date: 03/23/2007
• Status: Active Grant

• Current Assignee: Kabushiki Kaisha Toyota Chuo Kenkyusho (Toyota Motor Corporation), Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Original Assignee: Kabushiki Kaisha Toyota Chuo Kenkyusho (Toyota Motor Corporation), Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Inventors: Umeno, Takaji, Takemoto, Takeshi, Amano, Yasushi, Tomura, Shuji, Haga, Nobuyasu, Fuchimoto, Tetsuya, Nishi, Yuji
• Granted Patent: US 8,108,161 B2
• Time in Patent Office: Days
• US Class Current: 702/63
• CPC Class Codes: G01R 31/374 with means for correcting the measurement for temperature or ageing
• CPC Class Codes: G01R 31/3842 combining voltage and current measurements
• CPC Class Codes: G01R 31/389 Measuring internal impedance, internal conductance or related variables
• CPC Class Codes: G01R 31/392 Determining battery ageing or deterioration, e.g. state of health

Abstract

A battery state estimating unit (110) estimates an internal state of a secondary battery according to a battery model equation in every arithmetic cycle, and calculates an SOC based on a result of the estimation. A parameter characteristic map (120) stores a characteristic map based on a result of actual measurement performed in an initial state (in a new state) on a parameter diffusion coefficient (D_s) and a DC resistance (R_a) in the battery model equation. The parameter change rate estimating unit (130) estimates a DC resistance change rate (gr) represented by a ratio of a present DC resistance (R_c) with respect to a new-state parameter value (R_an) by parameter identification based on the battery model equation, using battery data (Tb, Vb and Ib) measured by sensors as well as the new-state parameter value (R_an) of the DC resistance corresponding to the p resent battery state and read from the parameter characteristic map (120).

Claims

1. A state estimating device of a secondary battery, comprising:

a detecting unit (20, 30, 40) for detecting a voltage, a current and a temperature of said secondary battery (10);

a battery state estimating unit (110) successively estimating a state quantity of said secondary battery according to a battery model equation based on at least one of the battery temperature (Tb) and the battery voltage (Vb), and the battery current (Ib) detected by said detecting unit;

a storing unit (120) prestoring data relating to change characteristics of an initial state parameter value (Ran, Dsn) of said secondary battery with respect to changes in battery state in connection with a predetermined parameter (Ra, Ds) of parameters used in said battery model equation; and

a change rate estimating unit (130, 200) estimating a parameter change rate (gr, gd) being a ratio of a present parameter value with respect to said initial state parameter value in connection with said predetermined parameter, wherein

said change rate estimating unit performs parameter identification based on said battery model equation using said battery temperature, said battery voltage and said battery current detected by said detecting unit as well as said initial state parameter value corresponding to the present battery state based on the data read from said storing unit, and thereby estimates said parameter change rate.

2. The state estimating device of the secondary battery according to claim 1, wherein

said battery state estimating unit (110) executes the estimation of the state quantity of said secondary battery (10) according to said battery model equation, for said predetermined parameter (Ra, Ds) in said battery model equation, using values obtained by multiplying said parameter change rate (gr#, gd#) estimated by said change rate estimating unit (130, 200) by said initial state parameter value (Ran, Dsn) corresponding to said battery state.

3. The state estimating device of the secondary battery according to claim 1, further comprising:

a deterioration degree estimating unit (150) estimating a degree of deterioration of said secondary battery (10) based on said parameter change rate (gr#, gd#) estimated by said change rate estimating unit (130, 200).

4. The state estimating device of the secondary battery according to claim 1, wherein

said predetermined parameter is a parameter (Ra) expressing a DC resistance of said secondary battery (10), and

said change rate estimating unit (130) successively estimates said parameter change rate (gr) by using, as its input/output, a state quantity (U(θ

−

V, Ran(θ

,T)×

I) obtained from said battery model equation and from said battery temperature (Tb), said battery current (Ib) and said battery voltage (Vb) detected by said detecting unit (20, 30, 40), and by employing a least-square method in a linear regression model equation using said parameter change rate (gr) as an estimation parameter.

5. The state estimating device of the secondary battery according to claim 4, wherein

said change rate estimating unit (130) estimates said parameter change rate (gr) by a recursive least-square method employing a forgetting coefficient for reducing a weight of past data relatively to that of present data.

6. The state estimating device of the secondary battery according to claim 4, wherein

said change rate estimating unit (130) stops the estimation of said parameter change rate (gr) when an absolute value of said battery current (Tb) detected by said detecting unit (20) is larger than a first reference value or when the absolute value of said battery current is smaller than a second reference value smaller than said first reference value.

7. The state estimating device of the secondary battery according to claim 4, wherein

the parameter (Ra) expressing said DC resistance is represented as a function of said battery temperature (Tb) and a local SOC (θ

) based on an estimated value of a reaction-participating material concentration at an interference of an active material (18) in an electrode (12, 15) of said secondary battery (10) estimated by said battery state estimating unit (110).

8. The state estimating device of the secondary battery according to claim 4, wherein

the parameter (Ra) expressing said DC resistance includes a charge-transfer resistance (Rr) and a pure electric resistance (Rd) inside said secondary battery (10), and

said change rate estimating unit (130) successively estimates said parameter change rates (gr1, gr2) of said charge-transfer resistance and said electric resistance independently of each other.

9. The state estimating device of the secondary battery according to claim 4, wherein

said battery model equation includes:

a voltage equation expressed by an open-circuit voltage (UP) being a function of a reaction-participating material concentration at a surface of an active material (18) inside said secondary battery and an overvoltage (Ra(0,T) x I) depending on the current, and

a diffusion equation defining a distribution of said reaction-participating material concentration inside said active material.

10. The state estimating device the secondary battery according to claim 9, wherein

said change rate estimating unit (110) stops the estimation of said parameter change rate (gr) when an absolute value of a difference between said reaction-participating material concentration at the surface of said active material (18) and an average value of the reaction-participating material concentration inside said active material is larger than a predetermined value, or before a predetermined time elapses after the absolute value of the concentration difference becomes smaller than said predetermined value.

11. The state estimating device of the secondary battery according to claim 1, wherein

said predetermined parameter includes a diffusion parameter (Ds) expressing a diffusion speed of a reaction-participating material in an active material (18) of said secondary battery (10);

said state estimating device further comprises;

an estimation data storing unit (160) for successively storing, as a time-series data array (DT(n)), said battery data of each of said battery voltage (Vb), said battery current (Ib) and said battery temperature (Tb) detected by said detecting unit (20, 30, 40) during a data storage period defined according to a predetermined condition; and

said change rate estimating unit (200) includes;

a battery model arithmetic unit (220) for obtaining a time-series estimated data string relating to predetermined battery data by performing arithmetic corresponding to said data storage period and according to said battery model equation handling said data array of the battery data as recursive inputs, and

an estimation processing unit (210, 230) estimating the parameter change rate (gd) of said diffusion parameter based on a comparison between said estimated data string obtained by said battery model arithmetic unit and the data string of said predetermined battery data stored in said estimation data storing unit.

12. The state estimating device of the secondary battery according to claim 11, wherein

said estimation data storing unit (160) starts said data storage period according to satisfaction of a predetermined storage start condition, and ends said data storage period according to satisfaction of a predetermined storage end condition;

said state estimating device further comprises an evaluation function arithmetic range determining unit (170) for determining an evaluation function arithmetic range (Tcl) representing a time range used for estimating said parameter change rate (gd);

said battery model arithmetic unit (220) executes arithmetic according to said battery model equation, for said diffusion parameter, using a value obtained by multiplying a candidate value of said parameter change rate (gd) by said initial state parameter value (Dsn) corresponding to the battery state at each point in time to be subjected to said arithmetic; and

said estimation processing unit (210, 230) includes;

an evaluation function arithmetic unit (230) calculating an evaluation function (I) corresponding to said evaluation function arithmetic range determined by said evaluation function arithmetic range determining unit, relating to said predetermined battery data, based on an error between an value of said estimated data string obtained by said battery model arithmetic unit and a value of said data string (DT(n)), and an estimation processing control unit (210) successively selecting a plurality of said candidate values, and estimating the parameter change rate (gd) of said diffusion parameter based on a comparison between the evaluation functions calculated with respect to said candidate values, respectively.

13. The state estimating device of the secondary battery according to claim 12, wherein

said battery model arithmetic unit (220) obtains said time-series estimated data string (Ite(n)) relating to said battery current (Ib) by performing arithmetic corresponding to said data storage period and according to said battery model equation using said data array of said battery voltage (Vb) and said battery temperature (Tb) as its recursive inputs, and

said evaluation function arithmetic unit (230) obtains said evaluation function (J) by integrating a square error between a value of the estimated data string and a value of said battery data array (Ib(n)) relating to said battery current, corresponding to said evaluation function arithmetic range.

14. The state estimating device of the secondary battery according to claim 12, wherein

said diffusion parameter (Ds) is represented as a function of said battery temperature (Tb).

15. The state estimating device of the secondary battery according to claim 12, wherein

said estimation data storing unit (160) determines that said storage start condition is satisfied, in response to a relaxation state of said secondary battery (10).

16. The state estimating device of the secondary battery according to claim 11, wherein

said battery model equation includes:

a voltage equation expressed by an open-circuit voltage (U(θ

)) being a function of a reaction-participating material concentration at a surface of an active material (18) inside said secondary battery (10) and an overvoltage (Ra(θ

,T)×

I) depending on the current, and

a diffusion equation defining a distribution of said reaction-participating material concentration inside said active material.

17. The state estimating device of the secondary battery according to claim 16, wherein

said estimation data storing unit (160) determines that said storage start condition is satisfied, when such a state continues for a predetermined time or more that an absolute value of said battery current (Ib) detected by said detecting unit (20) is smaller than a predetermined value, and a maximum concentration difference in a distribution of said reaction-participating material concentration inside said active material estimated by said battery state estimating unit (110) is smaller than a predetermined value.

18. The state estimating device of the secondary battery according to claim 16, wherein

said evaluation function arithmetic range determining unit (170) determines, as a start time, a point in time during said data storage period when said secondary battery (10) is in a charged state and a concentration difference of a predetermined value or more in absolute value occurs between said reaction-participating material concentration at the surface of said active material and an average value of the reaction-participating material concentration inside said active material in estimation by said battery state estimating unit (110), determines, as an end time, a point in time during said data storage period when said battery current (Ib) continuously takes an absolute value smaller than a predetermined value for a predetermined time or more thereafter, and determines a time range from said start time to said end time as said evaluation function arithmetic range (Tel) when a discharge current of a predetermined value or more has not occurred during the period from said start time to said end time.

19. The state estimating device of the secondary battery according to claim 18, wherein

said change rate estimating unit (200) inhibits setting of the new data storage period by said estimation data storing unit (160) during the estimation processing for said parameter change rate (gd), and allows setting of said new data storage period at the end of said data storage period without executing the estimation processing for said parameter change rate when said time range to be determined as said evaluation function arithmetic range is not present within said data storage period.

20. The state estimating device of the secondary battery according to claim 12, wherein

said estimation processing control unit (210) executes setting of said plurality of candidate values of said parameter change rate (gd) and fixing of the estimated value (gd#) of said parameter change rate, based on search according to a golden selection method.

21. The state estimating device of the secondary battery according to claim 11, wherein

said predetermined parameter further includes a resistance parameter (Ra) expressing a DC resistance of said secondary battery (10), and

said change rate estimating unit further includes a DC resistance change rate estimating unit (130) successively estimating a parameter change rate (gr) of said resistance parameter by using, as its input/output, a state quantity (U(θ

)−

V, Ran(θ

,T)×

I) obtained from said battery model equation and from said battery temperature (Tb), said battery current (Ib) and said battery voltage (Vb) detected by said detecting unit (20, 30, 40), and by employing a least-square method in a linear regression model equation using said parameter change rate (gr) as an estimation parameter.

22. The state estimating device of the secondary battery according to claim 21, wherein

said battery state estimating unit (110) executes the estimation of the state quantity of said secondary battery (10) according to said battery model equation, for each of said diffusion parameter (Ds) and said resistance parameter (Ra) in said battery model equation, using values obtained by multiplying said parameter change rate (gr#, gd#) successively estimated by said change rate estimating unit (130, 200) and said initial state parameter value (Ran, Dsn) corresponding to the present battery state based on the data read from said storing unit (120).

23. The state estimating device of the secondary battery according to claim 21, wherein

said change rate estimating unit (200) inhibits the use of said battery data array (DT(n)) during said data storage period for estimating the parameter change rate (gd) of said diffusion parameter when a change of a predetermined value or more occurs in said parameter change rate (gr) estimated by said DC resistance change rate estimating unit (130) or in the SOC of said secondary battery (10).

24. The state estimating device of the secondary battery according to claim 21, wherein

said battery model arithmetic unit (220) executes the arithmetic according to said battery model equation using, for said resistance parameter (Ra) in said battery model equation, said fixed parameter change rate (gr) and said initial state parameter value (Ran) corresponding to the battery state at each point in time to be subjected to said arithmetic.

25. The state estimating device of the secondary battery according to claim 21, wherein

said battery model arithmetic unit (220) executes the arithmetic according to said battery model equation using, for said resistance parameter (Ra) in said battery model equation, a value obtained by multiplying the average value of said parameter change rate (gr) successively estimated by said DC resistance change rate estimating unit during said data storage period by said initial state parameter value (Ran) corresponding to the battery state at each point in time to be subjected to said arithmetic.