State Based Full and Empty Control for Rechargeable Batteries

• US 20150247902A1
• Filed: 05/18/2015
• Published: 09/03/2015
• Est. Priority Date: 12/07/2010
• Status: Active Grant

• Current Assignee: Maxim Integrated Products, Inc. (Analog Devices, Inc.)
• Original Assignee: Maxim Integrated Products, Inc. (Analog Devices, Inc.)
• Inventors: Wortham, Jason Allen
• Granted Patent: US 9,791,517 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G01R 31/367 Software therefor, e.g. for battery testing using modelling or look-up tables
• CPC Class Codes: G01R 31/3835 involving only voltage measurements
• CPC Class Codes: H01M 10/44 Methods for charging or discharging circuits for charging H02J7/00
• CPC Class Codes: H01M 10/48 Accumulators combined with arrangements for measuring, testing or indicating the condition of cells, e.g. the level or density of the electrolyte constructional details of current conducting connections for detecting conditions inside cells or batteries, e.g. details of voltage sensing terminals, H01M50/569
• CPC Class Codes: H02J 7/00 Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
• CPC Class Codes: H02J 7/0048 Detection of remaining charge capacity or state of charge [SOC]
• CPC Class Codes: H02J 7/00714 in response to battery charging or discharging current
• CPC Class Codes: Y02E 60/10 Energy storage using batteries

Abstract

State based full and empty control for rechargeable batteries that will assure a uniform battery empty condition, even in the presence of a load on the battery. A fuel gauge provides a prediction of the open circuit voltage of the battery, and when the predicted open circuit voltage of the battery reaches the predetermined open circuit voltage of an empty battery, the load is terminated, after which the battery will relax back to the predetermined open circuit voltage of an empty battery. A similar technique is disclosed for battery charging, allowing faster battery charging without overcharging. Preferably an RC battery model is used as the fuel gauge to provide the prediction, but as an alternative, a coulomb counter may be used to provide the prediction, with error correction between successive charge discharge cycles.

Claims

1. A method of determining an empty state of a battery comprising:

monitoring the battery with a fuel gauge to predict an open circuit voltage of the battery, even in the presence of a variable load on the battery;

determining the empty state of the battery when the OCV prediction crosses a threshold.

2. The method of claim 1 wherein the fuel gauge is a simulated battery model.

3. The method of claim 2 wherein the battery model is a resistor capacitor battery model.

4. The method of claim 2 wherein the battery is a rechargeable battery.

5. The method of claim 4 further comprising determining a full state of the battery by;

charging the battery to a voltage in excess of a predetermined open circuit voltage representing a battery full state;

terminating the charging when the battery model predicts the open circuit voltage of the battery to be a predetermined full open circuit battery voltage to allow the open circuit battery voltage to relax to the predetermined full open circuit voltage.

6. The method of claim 1 wherein the fuel gauge is a coulomb counter and the battery is a rechargeable battery.

7. The method of claim 6 wherein the coulomb count of the coulomb counter from full to empty is adjusted based on the open circuit voltage of the empty battery after relaxation and the intended open circuit voltage of the empty battery.

8. A method of determining an empty state of a battery comprising:

monitoring the battery using an RC battery model fuel gauge to predict an open circuit voltage of the battery, even in the presence of a load on the battery, the battery being a rechargeable battery;

determining the empty state of the battery when the OCV prediction crosses a threshold;

also determining a full state of the battery by;

charging the battery to a voltage in excess of a predetermined open circuit voltage representing a battery full state;

terminating the charging when the battery model predicts the open circuit voltage of the battery to be a predetermined full open circuit battery voltage to allow the open circuit battery voltage to relax to the predetermined full open circuit voltage.

9. A method of determining an empty state of a battery comprising:

providing a fuel gauge that predicts the open circuit voltage of a battery responsive to at least one of a terminal voltage of the battery and current out of the battery, even when the battery is under a load;

monitoring at least one terminal voltage of the battery and the current out of the battery;

determining when the predicted open circuit voltage is equal to a predetermined empty state battery voltage.

10. The method of claim 9 wherein the fuel gauge is a voltage model fuel gauge, and the at least one of the terminal voltage of the battery and current out of the battery is the terminal voltage of the battery.

11. The method of claim 10 wherein the fuel gauge includes a coulomb counter, and the at least one of the terminal voltage of the battery and current out of the battery is both the terminal voltage of the battery and the current out of the battery.

12. The method of claim 9 wherein the fuel gauge is a coulomb counter, the at least one of the terminal voltage of the battery and current out of the battery is the current out of the battery, and the coulomb count from full to empty is adjusted up or down for the next charge discharge cycle based on the error between the open circuit voltage of the battery after relaxation and the intended open circuit voltage of the battery representing empty.

13. A method of determining a full state of a battery comprising:

providing a fuel gauge that predicts the open circuit voltage of a battery responsive to at least one of a terminal voltage of the battery and current out of the battery, even when the battery is under a load;

monitoring the at least one of the terminal voltage of the battery and the current out of the battery;

determining when the predicted open circuit voltage is equal to a predetermined full state battery voltage.

14. The method of claim 13 wherein the fuel gauge is a voltage model fuel gauge, and the at least one of the terminal voltage of the battery and current out of the battery is the terminal voltage of the battery.

15. The method of claim 14 wherein the fuel gauge includes a coulomb counter, and at least one terminal voltage of the battery and current out of the battery is both the terminal voltage of the battery and the current out of the battery.

16. The method of claim 13 wherein the fuel gauge is a coulomb counter, at least one terminal voltage of the battery and current out of the battery, and the coulomb count from empty to full is adjusted up or down for the next charge discharge cycle based on the error between the open circuit voltage of the battery after relaxation and the intended open circuit voltage of the battery representing full.