METHOD FOR CALCULATING POWER CAPABILITY OF BATTERY PACKS USING ADVANCED CELL MODEL PREDICTIVE TECHNIQUES

• US 20100174500A1
• Filed: 12/30/2009
• Published: 07/08/2010
• Est. Priority Date: 11/20/2003
• Status: Active Grant

• Current Assignee: LG Energy Solution Limited (LG Corporation)
• Original Assignee: LG Chem Limited (LG Corporation)
• Inventors: Plett, Gregory L.
• Granted Patent: US 7,969,120 B2
• Time in Patent Office: Days
• US Class Current: 702/63
• CPC Class Codes: G01R 31/3648 comprising digital calculation means, e.g. for performing an algorithm
• CPC Class Codes: G01R 31/367 Software therefor, e.g. for battery testing using modelling or look-up tables
• CPC Class Codes: G01R 31/374 with means for correcting the measurement for temperature or ageing
• CPC Class Codes: G01R 31/3828 using current integration

Abstract

The present invention relates to a method and an apparatus for estimating discharge and charge power of battery applications, including battery packs used in Hybrid Electric Vehicles (HEV) and Electric Vehicles (EV). One charge/discharge power estimating method incorporates voltage, state-of-charge (SOC), power, and current design constraints and works for a user-specified prediction time horizon Δt. At least two cell models are used in calculating maximum charge/discharge power based on voltage limits. The first is a simple cell model that uses a Taylor-series expansion to linearize the equation involved. The second is a more complex and accurate model that models cell dynamics in discrete-time state-space form. The cell model can incorporate a inputs such as temperature, resistance, capacity, etc. One advantage of using model-based approach is that the same model may be used in both Kalman-filtering to produce the SOC and the estimation of maximum charge/discharge current based on voltage limits.

Claims

1. A method for estimating a minimum charge power of a battery, comprising:

calculating a minimum charge current of the battery based on voltage limits of the battery; and

calculating the minimum charge power based on the maximum discharge current value.

2. The method of claim 1, further comprising:

calculating a minimum charge current of the battery based on state-of-charge limits of the battery;

calculating a minimum charge current of the battery based on current limits of the battery, wherein the minimum charge power is calculated from a maximum value of charge current chosen among the calculated minimum charge current based on voltage limits,

the calculated minimum charge current based on the state-of-charge limits, and the calculated minimum charge current based on the current limits.

3. The method of claim 2 wherein the estimating of minimum charge power takes into account a user-defined horizon of Δ

t.

4. The method of claim 2 wherein the step of calculating the minimum charge current of the battery based on state-of-charge limits obtains a state-of-charge by using a Kalman filtering method.

5. The method of claim 4 wherein an estimate of the uncertainty value yielded by the Kalman filtering method is used to find a confidence level of the calculated minimum charge current.

6. The method of claim 2 wherein the battery is a battery pack comprising n cells.

7. The method of claim 6 wherein the step of calculating the minimum charge current of the battery based on the state-of-charge limits calculates the current limits of each cell k in the battery pack using the equation

8. The method of claim 7 wherein minimum charge current of the battery pack based on state-of-charge limits is

9. The method of claim 1 wherein the step of calculating minimum charge current of the battery based on the voltage limits uses a cell model.

10. The method of claim 9 wherein the cell model is solved by a Taylor-series expansion.

11. The method of claim 9 wherein the cell model is solved by using a discrete time-state space model.

12. The method of claim 9 wherein the battery is a battery pack comprising n cells.

13. The method of claim 12 wherein the cell model is

v_k(t+Δ

t)=OCV(z_k(t+Δ

t))−

R×

i_k(t)

wherein v_k(t+Δ

t) denotes a cell voltage for cell k for the time period t units into the future, OCV(z_k(t+Δ

t)) denotes an open cell voltage as a function of the state of charge z_k for cell k for the time period t units into the future, R is a constant that denotes a cell'"'"'s internal resistance, and i_k(t) denotes a cell current.

14. The method of claim 13 wherein the minimum charge current based on the voltage limits is obtained by solving, through Taylor-series expansion

15. The method of claim 14 wherein the

16. The method of claim 13 wherein the cell model is solved by using a discrete time-state space model.

17. The method of claim 16 wherein the discrete time-state space model is

x_k[m+1]=f(x_k[m],u_k[m])

v_k[m]=g(x_k[m],u_k[m])

wherein m denotes a discrete time sample index, x_k[m] denotes a vector function of time and a state of the system, u_k[m] denotes an input to the system and includes cell current i_k[m] as a component, and f(•

) and g(•

) are functions chosen to model the cell dynamics.

18. The method of claim 17 wherein the u_k[m] inputs includes temperature.

19. The method of claim 17 wherein the u_k[m] inputs includes resistance.

20. The method of claim 17 wherein the u_k[m] inputs includes capacity.

21. The method of claim 17 wherein _min,k^chg,volt is found by looking for i_k that causes equality in

v_max=g(x_k[m+T],u_k[m+T])

wherein g(x_k[m+T],u_k[m+T]) finds a cell voltage Δ

t seconds into the future.

22. The method of claim 21 wherein the equality is found by a using bisection search algorithm.

23. The method of claim 17 wherein the equation

x_k[m+T]=Ax_k[m]+Bu_k[m] is linear, wherein A and B are constant matrices.

24. The method of claim 12 wherein the maximum value of charge current is chosen by using an equation

25. The method of claim 24 wherein the minimum charge power is calculated by solving

26. The method of claim 25 wherein P_min^chg is approximated to be

27. The method of claim 2 wherein any of the state-of-charge limits, the voltage limits, and the current limits can be eliminated from the calculations by using positive infinity or negative infinity to represent the eliminated limits in the calculations.

28. The method of claim 2 wherein any of the state-of-charge limits, the voltage limits, and the current limits is dependent on temperature.

29. The method of claim 2 wherein the calculated minimum charge power is checked to ensure that it falls within power limits of the battery.

30. A power estimating apparatus for estimating maximum discharge power of a battery comprising:

a voltage measurement means for measuring a voltage of the battery;

a temperature measurement means for measuring a temperature of the battery;

a current measurement means for measuring a current of the battery;

an estimator means for calculating the maximum discharge power of the battery, wherein the estimator means uses measurements from the voltage measurement means, the temperature measurement means, and current measurement means and performs calculations to estimate the maximum discharge power of the battery, the estimator means comprising;

means for calculating a maximum discharge current of the battery based on voltage limits of the battery;

means for calculating a maximum discharge current of the battery based on state-of-charge limits of the battery;

means for calculating a maximum discharge current of the battery based on current limits of the battery, wherein the maximum discharge power is calculated from a minimum value of discharge current chosen among the calculated maximum discharge current based on the voltage limits, the calculated maximum discharge current based on the state-of-charge limits, and the calculated maximum discharge current based on the current limits.

31. The power estimating apparatus of claim 30 wherein the estimator means takes into account a user-defined horizon of Δ

t.

32. The power estimating apparatus of claim 30 wherein the means for calculating maximum discharge current of the battery based on the state-of-charge limits obtains a state-of-charge by using a Kalman filtering method.

33. The power estimating apparatus of claim 32 wherein an estimate of the uncertainty value yielded by the Kalman filtering method is used to find a confidence level of the calculated maximum discharge current.

34. The power estimating apparatus of claim 32 wherein the battery is a battery pack comprising n cells.

35. The power estimating apparatus of claim 32 wherein the means for calculating maximum discharge current of the battery based on the voltage limits uses a cell model.

36. The power estimating apparatus of claim 35 wherein the cell model is solved by a Taylor-series expansion.

37. The power estimating apparatus of claim 35 wherein the cell model is solved by using a discrete time-state space model.

38. An power estimating apparatus for estimating minimum charge power of a battery comprising:

a voltage measurement means for measuring a voltage of the battery;

a temperature measurement means for measuring a temperature of the battery;

a current measurement means for measuring a current of the battery;

an estimator means for calculating the minimum charge power of the battery, wherein the estimator means uses measurements from the voltage measurement means, the temperature measurement means, and current measurement means and performs calculations to estimate the minimum charge power of the battery, the estimator means comprising;

means for calculating a minimum charge current of the battery based on voltage limits of the battery;

means for calculating a minimum charge current of the battery based on state-of-charge limits of the battery;

means for calculating a minimum charge current of the battery based on current limits of the battery, wherein the minimum charge current power is calculated from a maximum value of discharge current chosen among the calculated minimum charge current based on the voltage limits, the calculated minimum charge current based on the state-of-charge limits, and the calculated minimum charge current based on the current limits.

39. The power estimating apparatus of claim 38 wherein the estimator means takes into account a user-defined horizon of Δ

t.

40. The power estimating apparatus of claim 38 wherein the means for calculating minimum charge current of the battery based on the state-of-charge limits obtains a state-of-charge by using a Kalman filtering method.

41. The power estimating apparatus of claim 40 wherein an estimate of the uncertainty value yielded by the Kalman filtering method is used to find a confidence level of the calculated maximum discharge current.

42. The power estimating apparatus of claim 40 wherein the battery is a battery pack comprising n cells.

43. The power estimating apparatus of claim 40 wherein the means for calculating minimum current of the battery based on the voltage limits uses a cell model.

44. The power estimating apparatus of claim 43 wherein the cell model is solved by a Taylor-series expansion.

45. The power estimating apparatus of claim 43 wherein the cell model is solved by using a discrete time-state space model.