State of charge method and apparatus

• US 20030076109A1
• Filed: 07/22/2002
• Published: 04/24/2003
• Est. Priority Date: 08/07/2001
• Status: Active Grant

• Current Assignee: GM Global Technology Operations LLC (General Motors Company)
• Original Assignee: General Motors Corporation (Motors Liquidation Co. GUC Trust)
• Inventors: Sarbacker, Shawn D., Koch, Brian James, Ying, Ramona Y., Verbrugge, Mark William, Tate, Edward Dean Jr., Frisch, Damon R.
• Granted Patent: US 6,639,385 B2
• Time in Patent Office: Days
• US Class Current: 324/427
• CPC Class Codes: G01R 31/3835 involving only voltage measurements
• CPC Class Codes: G01R 31/392 Determining battery ageing or deterioration, e.g. state of health

Abstract

A method for determining state of charge (SOC) of a battery system based upon an equivalent circuit of the battery system. A potential and resistance of the equivalent circuit are computed. The method uses a least squares regression means, and includes: providing a plurality of data points as a starting point based upon determinations including measurement or prior computation, wherein the determinations include a determination of a voltage of the battery system; weighting the plurality of data points; and computing values of the resistance and potential based upon weighted data points using recursive formulas, wherein only a state at a previous time is reflected respectively.

Claims

1. A method for determining a state of charge (SOC) of a battery system based upon an equivalent circuit of said battery system using least square regression comprising:

determining an open circuit potential and resistance of said equivalent circuit;

providing a plurality of data points based upon determinations including measurement or prior computation;

weighting said plurality of data points; and

computing values of said resistance and open-circuit potential based upon weighted data points using least square analysis expressed in recursive formulas to determine the SOC.

2. The method of claim 1 including determining a current-based state of charge measurement based on Coulomb integration if battery current is stable and a voltage based determination is inaccurate.

3. The method of claim 1 including using a skew test to determine whether said plurality of data points are skewed, said skew test incorporating an exponential forgetting factor or a charge-discharge weight factor.

4. The method of claim 3, wherein said skew test is performed using a fully recursive expression including a summation representing a state at the previous time step and a current data point.

5. The method of claim 1, wherein said weighting step includes using an exponential forgetting factor.

6. The method of claim 1 including computing a recursive power expression based on said data points, and a current data point.

7. A method for determining a state of charge (SOC) in a battery system based on determining values of a resistance R and an open circuit voltage V_oc, respectively, comprising:

creating at least two data points based upon measurement or prior computation;

establishing a linear relationship using said resistance R and said open circuit voltage V_oc;

applying least square analysis upon said linear relationship;

formulating a recursive relationship, wherein a first state at a backward time increment solely determines a current state after said backward time increment, said recursive relationship being the summation of said first state manifested in a recast summation derived from integrals, and a data point at current time.

8. The method of claim 7, including:

determining a first set of intermediate functions;

assigning initial values to said first set of intermediate functions;

establishing a recursive relationship of said set of intermediate functions; and

computing values of said resistance R and said open circuit voltage V_oc based upon said first set of intermediate functions.

9. The method of claim 7, wherein said first set of intermediate functions includes:

10. The method of claim 7, wherein said initial values include:

S_w|₁=Υ

₁

S_I|₁=Υ

₁I₁

S_II|₁=Υ

₁I₁²

S_V|₁=Υ

₁V₁

S_Iv|₁=Υ

₁I₁V₁

11. The method of claim 7, wherein said recursive relationship includes:

12. The method of claim 7, including applying a skewness test before said method is performed.

13. The method of claim 12, wherein said skewness test includes the steps of:

defining a second set of intermediate functions, wherein each of said second set of intermediate functions is expressed in a recursive form based on an immediate prior state in time;

assigning initial values to said second set of intermediate function;

applying said skewness test based upon said second set of intermediate functions; and

determining a result of said skewness test.

14. The method of claim 13, wherein said second set of intermediate functions includes:

15. The method of claim 7 including computing a recursive power expression based on said data points.

16. The method of claim 15, wherein said power expression is a max discharge and charge power of said battery system.

17. The method of claim 16, wherein said power expression is:

18. A vehicle powertrain control system, comprising:

a battery pack;

a power inverter coupled to said battery pack;

a controller controlling said power inverter, said controller monitoring a state of charge (SOC) of said battery pack; and

a program product for computing a resistance and an open circuit voltage both being functionally related to said SOC, said program product being associated to said controller.

19. The vehicle powertrain control system of claim 18, wherein said battery pack comprises lead acid batteries.

20. The vehicle powertrain control system of claim 18, wherein said battery pack comprises nickel/metal hydride (NiMH) batteries.

21. The vehicle powertrain control system of claim 18, wherein said battery pack comprises lithium ion batteries.