Battery charge maintenance through opportunity equalization

• US 6,225,780 B1
• Filed: 02/24/2000
• Issued: 05/01/2001
• Est. Priority Date: 02/24/2000
• Status: Expired due to Term

• Current Assignee: GM Global Technology Operations LLC (General Motors Company)
• Original Assignee: General Motors Corporation (General Motors Company)
• Inventors: Koch, Brian James
• Primary Examiner(s): Wong, Peter S.
• Assistant Examiner(s): LUK, LAWRENCE W
• Application Number:
  US09/512,011
• Time in Patent Office: 432 Days
• Field of Search: 320/118, 320/117, 320/119, 320/150, 320/152, 320/160, 320/137
• US Class Current: 320/118
• CPC Class Codes: H02J 7/0013 acting upon several batteries simultaneously or sequentially H02J7/1423 takes precedence
• CPC Class Codes: Y02T 10/70 Energy storage systems for electromobility, e.g. batteries

Abstract

In one aspect of the invention as applied to vehicles, such as electric automotive systems, battery equalization is optimized through performance simultaneously with other routine vehicle functions in the way of maintenance during periods when the temperature of the battery pack is in a lower temperature regime. An equalization current is chosen as a function of the ambient conditions and effectiveness of the thermal system detected by the battery pack control module, so that heat can be minimized as well as then more easily removed from the battery pack, thereby also reducing the length of the process. Opportunity equalization therefore is performed more frequently than is typical at more convenient times and in a manner to optimize the process in view of existing conditions.

Claims

1. In a rechargeable electrochemical battery system having a series arrangement of multiple batteries in a pack, and a pack cooling system having a cooling mode, a method of equalizing a state of charge among the multiple batteries, comprising the steps of:

establishing a pre-selected state of charge criterion (SOC_min) below which equalization will not occur;

establishing a first pre-selected pack temperature criterion (T_opp) above which equalization will not occur;

measuring overall pack temperature;

calculating state of charge; and

initiating equalization of charge in the pack at a first current if the state of charge is above said SOC_min and said overall pack temperature is below T_opp.

2. The equalization method of claim 1 further including the steps of:

establishing a second pre-selected cooling medium temperature criterion (T_hi) above which pack cooling by the pack cooling system is considered reduced in effectiveness, and

initiating equalization of charge in the pack at a second current which is lower than said first current if the second pre-selected temperature is above said T_hi, said second current being applied rather than said first current.

3. The equalization method of claim 2 wherein the pack cooling system has a cooling medium, and T_hi is measured at a point in the pack cooling system through which said cooling medium flows before heat transfer from the pack.

6. The equalization method of claim 2 wherein said second current is varied as a function of temperature.

7. The equalization method of claim 2 wherein equalization continues until the pack cooling mode has been completed or a pre-established amp-hour input has been reached.

4. A method of equalizing a state of charge among multiple batteries in a rechargeable electrochemical battery system having a series arrangement of the batteries in a pack, and a pack cooling system having a cooling mode using a cooling medium, comprising the steps of:

determining if the pack cooling system is in the cooling mode and engaged in pack cooling;

establishing a pre-selected state of charge criterion (SOC_min) below which equalization will not occur;

establishing a first pre-selected pack temperature criterion (T_opp) above which equalization will not occur;

establishing a second pre-selected temperature criterion (T_hi) based upon a cooling medium temperature above which pack cooling by the pack cooling system is considered reduced in effectiveness,

measuring overall pack temperature;

calculating state of charge; and

if the cooling system is in the cooling mode, initiating equalization of charge in the pack at a first current if the state of charge is above said SOC_min and said overall pack temperature is below T_opp, and said cooling medium temperature is less than T_hi, or initiating equalization of charge in the pack at a second current which is lower than said first current if the state of charge is above said SOC_min and the pack temperature is below said T_opp but said cooling medium temperature is above said T_hi.

5. The equalization method of claim 4 wherein T_hi is measured to determine the cooling medium temperature as applied to the pack.

8. The equalization method of claim 4 wherein said second current is varied as a function of temperature.

9. The equalization method of claim 4 wherein equalization continues until the pack cooling mode has been completed or a pre-established amp-hour input has been reached.

10. In a rechargeable nickel metal hydride battery pack, a method of equalizing a state of charge among multiple batteries the battery pack having a series arrangement of the batteries in the pack, and a pack cooling system having a cooling medium and a cooling mode, comprising the steps of:

determining if the pack cooling system is in the cooling mode and engaged in pack cooling;

establishing a pre-selected state of charge criterion (SOC_min) below which equalization will not occur;

establishing a first pre-selected pack temperature criterion (T_opp) above which equalization will not occur;

establishing a second pre-selected cooling medium temperature criterion (T_hi) above which pack cooling by the pack cooling system is considered reduced in effectiveness,

measuring overall pack temperature, with T_hi being measured at a point in the pack cooling system through which said cooling medium flows before heat transfer from the pack to establish the temperature of the cooling medium as applied to the pack;

measuring state of charge; and

if the cooling system is in the cooling mode, initiating equalization of charge in the pack at a first current if the state of charge is above said SOC_min and said overall pack temperature is below T_opp, and the cooling medium temperature is less than T_hi, or initiating equalization of charge in the pack at a second current which is lower than said first current, said second current being varied as a function of temperature, if the state of charge is above said SOC_min and the pack temperature is below said T_opp but the cooling medium temperature is above said T_hi, with equalization continuing until the pack cooling mode has been completed or a pre-established amp-hour input has been reached.

11. An apparatus for improved equalization of state of charge in a rechargeable electrochemical battery system having a series arrangement of multiple batteries in a pack, and a pack cooling system having a cooling mode, comprising:

a battery pack controller having comparator circuitry, said controller being programmed with a pre-selected state of charge criterion (SOC_min) below which equalization will not occur, and a first pre-selected pack temperature criterion (T_opp) above which equalization will not occur;

a temperature sensor communicating with a pack temperature sensing point, said temperature sensor generating a temperature signal;

a current sensor communicating with the battery pack to calculate state of charge;

signal circuitry communicating said temperature signal and said current signal to said controller;

equalization charge circuitry connecting a source of current to each said battery; and

said controller having an equalization program which initiates an equalization charge from said source of current at a first current when the state of charge is above said SOC_min and said pack temperature is below T_opp.

12. The equalization apparatus of claim 11 wherein said controller is further programmed with a second pre-selected cooling medium temperature criterion (T_hi) above which pack cooling by the pack cooling system is considered reduced in effectiveness, and said program initiates equalization of charge in the pack at a second current which is lower than said first current if the state of charge is above said SOC_min, and the pack temperature is below said T_opp but said cooling medium temperature is above said T_hi.

13. The equalization apparatus of claim 12 wherein said program varies said second current as a function of temperature.

14. The equalization apparatus of claim 13 wherein said program continues equalization until the pack cooling mode has been completed or a pre-established amp-hour input has been reached.

15. An apparatus for improved equalization of state of charge in a rechargeable electrochemical battery system having a series arrangement of multiple batteries in a pack, and a pack cooling system having a cooling mode, comprising:

battery pack controller means having comparator circuitry, said controller means being programmed with a pre-selected state of charge criterion (SOC_min) below which equalization will not occur, and a first pre-selected pack temperature criterion (T_opp) above which equalization will not occur;

temperature sensing means communicating with a pack temperature sensing point, said temperature sensor means generating a temperature signal;

state of charge sensor means communicating with said battery pack for measuring state of charge, said state of charge sensor means generating a charge signal;

signal circuitry means communicating said temperature signal and said charge signal to said controller means;

equalization charge circuitry means for connecting a source of current to each said battery; and

said controller means further having equalization program means for initiating an equalization charge from said source of current at a first current when the state of charge is above said SOC_min and said pack temperature is below T_opp.

16. The equalization apparatus of claim 15 wherein said controller means is further programmed with a second pre-selected pack temperature criterion (T_hi) relating to cooling medium temperature above which pack cooling by the pack cooling system is considered reduced in effectiveness, and said program means initiates equalization of charge in the pack at a second current which is higher than said first current if the state of charge is above said SOC_min, the pack temperature is below said T_opp and the cooling medium temperature is above said T_hi.