Apparatus and methods for estimating the state-of-charge of a power source

• US 7,405,537 B2
• Filed: 12/20/2004
• Issued: 07/29/2008
• Est. Priority Date: 12/20/2004
• Status: Expired due to Fees

• Current Assignee: GM Global Technology Operations LLC (General Motors Company)
• Original Assignee: GM Global Technology Operations Incorporated (Motors Liquidation Co. GUC Trust)
• Inventors: Rush, Scott A., Abeska, Edward J., Hoffman, Allan J.
• Primary Examiner(s): TSO, EDWARD H
• Application Number:
  US11/017,348
• Publication Number:
  US 20060132092A1
• Time in Patent Office: 1,317 Days
• Field of Search: 320/132, 320/134, 320/136, 320/149, 340/635, 340/636.1, 340/636.12
• US Class Current: 320/132
• 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

Abstract

Methods and apparatus are provided for estimating the remaining state-of-charge of a non-rechargeable power source, such as a back-up battery for an electronic module normally connected to a primary power source. A processor within the electronic module implements a prediction algorithm, in order to monitor the temperature of the back-up attery, and to calculate various current draws of the back-up battery. The processor adjusts the nominal self-discharge rate of the back-up battery in accordance with the measured temperatures, and calculates an adjusted self-discharge quantity. The processor also accumulates current draw data and reduces the initial state-of-charge value of the back-up battery by the temperature-adjusted self-discharge quantity and the cumulative current draw quantities to determine a remaining state-of-charge of the back-up battery. At a predetermined state-of-charge threshold level, an indicator can be activated to advise a user to replace the back-up battery.

Claims

1. A method of estimating the remaining state-of-charge of a non-rechargeable power source configured as a back-up power source for an electronic module normally powered by a primary power source, comprising the steps of:

a) calculating a self-discharge factor based on temperature;

b) combining a nominal self-discharge rate of the non-rechargeable power source with the self-discharge factor and an initial state of charge of the non-rechargeable power source to produce a temperature-adjusted self-discharge quantity;

c) calculating a quantity of parasitic leakage current draw from the non rechargeable power source;

d) calculating a quantity of voltage sampling current draw from the non-rechargeable power source;

e) calculating a quantity of transient current draw from the non-rechargeable power source;

f) subtracting the temperature-adjusted self-discharge quantity, the quantity of parasitic leakage current draw, the quantity of voltage sampling current draw, and the quantity of transient current draw from the initial state-of-charge of the non-rechargeable power source to generate an estimate of a remaining state-of-charge of the non-rechargeable power source; and

g) displaying the generated estimate to a user.

2. The method of claim 1 wherein the initial state-of-charge of the non-rechargeable power source is based on the ampere-hour rating of the non-rechargeable power source.

3. The method of claim 1 wherein the nominal self-discharge rate of the non-rechargeable power source is based on the self-discharge rating of the non-rechargeable power source.

4. The method of claim 1 wherein the self-discharge factor calculation is based on measured temperature values of the non-rechargeable power source.

5. The method of claim 1 wherein the self-discharge factor calculation is based on interpolated self-discharge factor values.

6. The method of claim 1 wherein the parasitic leakage quantity from the non-rechargeable power source is based on a predetermined value of the parasitic leakage current.

7. The method of claim 1 wherein the quantity of voltage sampling current draw from the non-rechargeable power source is based on a predetermined value of current drain during voltage sampling.

8. The method of claim 1 wherein the quantity of transient current draw from the non-rechargeable power source is based on a predetermined value of current drain during a low power operating mode of the electronic module.

9. The method of claim 8 wherein the transient current draw occurs when the non-rechargeable power source is used to power the electronic module at less than full power when the primary power source is removed.

10. A back-up power source for an electronic module connected to a primary power source, comprising:

a power source having an initial ampere-hour rating and a nominal self discharge rate;

a temperature measuring device configured to measure the temperature of the power source; and

a processor associated with the electronic module and coupled to the -temperature measuring device;

wherein the processor is configured to receive the temperature measurements of the power source from the temperature measuring device, and to calculate therefrom a temperature-adjusted self discharge quantity for the power source, and wherein the processor is further configured to calculate an estimated remaining state-of-charge of the power source, based on the reduction of the initial ampere-hour rating due to the temperature-adjusted self discharge quantity, and on the further reduction of the initial ampere-hour rating due to a cumulative parasitic leakage current draw, a cumulative voltage sampling check current draw, and a cumulative low power mode transient current draw.

11. The back-up power source of claim 10 wherein the temperature-measuring device is a thermistor.

12. The back-up power source of claim 10 wherein the parasitic leakage current draw accumulates during the time that the back-up power source is connected to the electronic module.

13. The back-up power source of claim 10 wherein the voltage sampling check current draw accumulates only when the back-up power source connection to the electronic module is checked.

14. The back-up power source of claim 10 wherein the transient current draw accumulates only when there is a loss of primary power and the electronic module is operating from the back-up power source in a low power mode.

15. A method for generating an estimate of the remaining state-of-charge of a power source, the method comprising the following algorithm, the method comprising the steps of:

performing the following algorithm to generate the estimate;

C(N)=C₀*{1−

SUM[R*E₁+R*E₂]}−

(I_L*T_L)−

(I_M*T_M)−

(I_C*T_C),

where C(N) is the remaining state-of-charge,

where C₀ is an initial state-of-charge of the non-rechargeable power source,

where R is a nominal self-discharge rate for the non-rechargeable power sources,

where E₁ is a temperature-adjusted discharge factors,

where E₂ is a temperature-averaged discharge factors,

where I_L is a parasitic leakage current,

where T_L is a first period of time,

where I_M is a back-up battery monitor current,

where T_M is a second period of time,

where I_C is a voltage check current,

where T_C is a third period of time,

where I_L*T_L is a cumulative parasitic leakage current draw,

where I_M*T_M is a cumulative monitor current draw, and

where I_C*T_C is a voltage check current draw; and

displaying the generated estimate to a user.