Method of computing AC impedance of an energy system

• US 6,765,389 B1
• Filed: 06/12/2003
• Issued: 07/20/2004
• Est. Priority Date: 06/12/2003
• Status: Expired due to Fees

• Current Assignee: EnerDel, Inc. (Ener1, Inc.)
• Original Assignee: Delphi Technologies, Inc. (BorgWarner Incorporated)
• Inventors: Moore, Stephen W.
• Primary Examiner(s): TIBBITS, PIA FLORENCE
• Application Number:
  US10/460,383
• Time in Patent Office: 404 Days
• Field of Search: 324/430, 324/426, 324/429, 324/460, 324/433, 320/134, 320/132, 702/63, 702/64, 702/65, 703/13, 716/4
• US Class Current: 324/430
• CPC Class Codes: G01R 31/389 Measuring internal impedance, internal conductance or related variables

Abstract

An energy system is formed of a plurality of battery cells, and has an application associated therewith that draws power from the energy system. As the application is being used, voltage and current measurements are taken at a predetermined rate, and stored in a history table to create a series of time-based measurements. The measurements stored in the history table are then processed to compute an impedance parameter value corresponding to the AC impedance of the energy system This impedance parameter value is then stored in a memory buffer where it can be used to carry out various diagnotic and control functions.

Claims

1. A method for computing the AC impedance of an energy system, comprising the steps of:

providing and activating an application coupled to the energy system;

measuring electrical characteristics associated with the energy system as power is drawn by the application from the energy system as a function of time by sampling the electrical characteristics at a predetermined rate to produce and define a series of time-based measurements;

storing the series of time-based measurements in a history table;

processing the series of time-based measurements to determine an impedance parameter value indicative of an AC impedance of the energy system; and

storing the determined impedance parameter value.

2. The method of claim 1 wherein said measuring step includes the substeps of:

selecting the electrical characteristics sampled in said sampling step from the group comprising a voltage level and a current level; and

sampling the voltage and current levels.

3. The method of claim 1 wherein the measuring step further includes the substeps of:

establishing said history table to have a first-in value entry and a last-in value entry, with a predetermined number of value entries inbetween; and

displacing the first-in value entry with each subsequent measurement.

4. The method of claim 1 wherein the processing step further includes the substeps of:

determining a deviation between the most recent time-based measurement and the series of stored time-based measurements; and

calculating the impedance and open circuit voltage of the energy system when the deviation meets a predetermined acceptable level.

5. The method of claim 4 wherein the calculating step further includes calculating the impedance and open circuit voltage by computing the slope and intercept of the series of time based measurements.

6. The method of claim 5 wherein the calculating step further includes computing the slope and by applying a least squares algorithm to said series of time based measurements.

7. A method for computing the AC impedance of an energy system, comprising the steps of:

forming the energy system so as to include a battery comprising a plurality of cells made up of lithium chemistry salts;

providing and activating an application coupled to the energy system;

measuring electrical characteristics associated with the energy system as power is drawn by the application from the energy system as a function of time to define a series of time-based measurements;

processing the series of time-based measurements to determine an impedance parameter value indicative of an AC impedance of the energy system; and

storing the determined impedance parameter value.

8. The method of claim 7, wherein the measuring step further includes the substep of determining the electrical characteristics of each of the plurality of cells.

9. A method for computing the AC impedance of an energy system, comprising the steps of:

providing a dynamoelectric machine coupled to the energy system;

operating the dynamoelectric machine whereby power is drawn from the energy system;

measuring the voltage and current drawn by the dynamoelectric machine from the energy system as a function of time;

sampling the voltage and current drawn from the energy system at a predetermined rate to produce a series of time-based measurements;

storing the measurements in a history table within the energy system;

determining a deviation between the most recent measurement and the series of time-based measurements stored in the history table;

calculating the impedance and open circuit voltage of the energy system when the deviation meets a predetermined acceptable level to determine an impedance parameter value indicative of the AC impedance of the energy system; and

storing the determined impedance parameter and open circuit voltage values.

10. The method of claim 9 wherein the step of providing an energy system further includes the step of forming an energy system so as to include a battery comprising a plurality of cells.

11. The method of claim 10 wherein the forming step is performed by the substep of producing the plurality of cells so as to employ lithium chemistry salts.

12. The method of claim 9 wherein the measuring step further includes the step of determining the voltage and current of each of the plurality of cells.

13. The method of claim 9 wherein the processing step further includes the substeps of:

establishing said history table to have a first-in value entry and a last-in value entry, with a predetermined number of value entries inbetween;

displacing the first-in value entry with each subsequent measurement.

14. The method of claim 9 wherein the calculating step further includes calculating the impedance and open circuit voltage by calculating a slope and intercept of the series of time based measurements.

15. The method of claim 14 wherein the calculating step further includes the calculating of said slope and intercept by applying the least squares method as known in the art.