Method and apparatus for reducing battery charge time and energy consumption, as in a nickel metal hydride battery pack

• US 6,215,281 B1
• Filed: 03/16/2000
• Issued: 04/10/2001
• Est. Priority Date: 03/16/2000
• Status: Expired due to Term

• Current Assignee: GM Global Technology Operations LLC (General Motors Company)
• Original Assignee: General Motors Corporation (Motors Liquidation Co. GUC Trust)
• Inventors: Koch, Brian J.
• Primary Examiner(s): Wong, Peter S.
• Assistant Examiner(s): LUK, LAWRENCE W
• Application Number:
  US09/526,361
• Time in Patent Office: 390 Days
• Field of Search: 320/150, 320/152, 320/117, 320/118, 320/119, 320/137, 320/160
• US Class Current: 320/150
• CPC Class Codes: H02J 7/0014 Circuits for equalisation of charge between batteries
• CPC Class Codes: H02J 7/007194 of the battery
• CPC Class Codes: H02J 7/14 for charging batteries from dynamo-electric generators driven at varying speed, e.g. on vehicle
• CPC Class Codes: Y02T 10/70 Energy storage systems for electromobility, e.g. batteries

Abstract

The present invention in one form provides for an improved battery charging apparatus and method comprising a controller and battery balancing system including an algorithm which monitors temperature of the battery pack and state of charge. These are factored for a charge efficiency through comparison to a pre-determined table of charge efficiency values, and then compared against a threshold charge efficiency below which charging is considered not optimal. The charging operation is discontinued in the event charge efficiency is below the threshold value.

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 optimizing the charging of the battery pack, comprising the steps of:

establishing pre-selected charge efficiency values as a function of battery pack temperature and state of charge (SOC), including a threshold value CE below which charging is considered to be not optimal;

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

measuring overall pack temperature;

performing a full charging event if the measured pack temperature is below T_hi or if the thermal system is not in a cooling mode;

if the pack temperature is above T_hi, measuring SOC of the battery pack;

(i) then determining the then-existing charge efficiency (CE_t);

(ii) comparing CE_t against the threshold value CE;

completing any charge cycle underway if CE_t is below the threshold value CE, and then proceeding to a support mode without equalization;

if CE_t is above the threshold value CE, continuing charging with periodic repetition of steps (i) and (ii) until full charging is completed or until CE_t falls below the threshold value CE, in which event any charge cycle underway is completed and the support mode is entered.

2. The battery charging method of claim 1 wherein the pack cooling system has a cooling medium, and T_hi is measured at a point in the cooling system through which said cooling medium flows before heat transfer from the pack.

3. The battery charging system of claim 1 including the further step of establishing a state of charge threshold value below which charge efficiency is not considered to be a factor (SOC_CE), and comparing SOC against SOC_CE, and continuing any charge cycle regardless of whether CE_t is below CE if SOC is below SOC_CE.

4. The battery charging system of claim 3 wherein CE is about 75% and SOC_CE is about 80%.

5. 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 optimizing the charging of the battery pack, comprising the steps of:

establishing pre-selected charge efficiency values as a function of battery pack temperature and state of charge (SOC), including a threshold value CE below which charging is considered to be not optimal;

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

establishing a threshold SOC_CE below which CE is not considered as a charge completion criterion;

measuring overall pack temperature;

performing a full charging event if the measured pack temperature is below T_hi or if the thermal system is not in a cooling mode;

if the pack temperature is above T_hi, measuring SOC of the battery pack;

(i) then determining the then-existing charge efficiency (CE_t);

(ii) comparing SOC against SOC_CE;

(iii) comparing CE_t against the threshold value CE;

completing any charge cycle underway if CE_t is below the threshold value CE, and SOC is greater than SOC_CE, and then proceeding to a support mode without equalization;

if CE_t is above the threshold value CE or SOC is less than SOC_CE, continuing charging with periodic repetition of steps (i), (ii) and (iii) until full charging is completed or until CE_t falls below the threshold value CE and SOC is greater than SOC_CE, in which event any charge cycle underway is completed and the support mode is entered.

6. An apparatus for improved battery charging 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 pre-selected charge efficiency data values as a function of battery pack temperature and state of charge (SOC), including a threshold value CE below which charging is considered to be not optimal, and being programmed with a pre-selected cooling medium temperature criterion (T_hi) above which cooling by the pack cooling system is considered reduced in effectiveness;

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 and measuring a current which is used to calculate state of charge, said current sensor generating a current signal;

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

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

said controller having a charging program for optimum charging which measures overall pack temperature and cooling medium temperature, and performs a full charging event if the measured cooling medium temperature is below T_hi or if the thermal system is not in a cooling mode, and if the cooling medium temperature is above T_hi, measuring SOC of the battery pack,

(i) then determining the then-existing charge efficiency (CE_t),

(ii) comparing CE_t against the threshold value CE, and

completing any charge cycle underway if CE_t is below the threshold value CE, thereafter proceeding to a support mode without equalization, and

if CE_t is above the threshold value CE, continuing charging including equalization with periodic repetition of steps (i) and (ii) until full charging is completed or until CE_t falls below the threshold value CE, in which event any charge cycle underway is completed and the support mode is entered.

7. The battery charging apparatus of claim 6 including establishing in the controller a state of charge threshold value below which charge efficiency is not considered to be a factor (SOC_CE), with said controller comparing SOC against SOC_CE, and continuing any charge cycle regardless of whether CE_t is below CE if SOC is below SOC_CE.

8. The battery charging apparatus claim 7 wherein CE is about 75% and SOC_CE is about 80%.

9. An apparatus for improved battery charging 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 pre-selected charge efficiency data values as a function of battery pack temperature and state of charge (SOC), including a threshold value CE below which charging is considered to be not optimal, and being programmed with a pre-selected cooling medium inlet temperature criterion (T_hi) above which pack cooling by the pack cooling system is considered reduced in effectiveness;

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

a current sensing means communicating with the battery pack for calculation of SOC and generating a current signal;

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

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

said controller means having a charging program means for optimum charging which measures overall pack temperature and cooling medium temperature, and performs a full charging event if the measured cooling medium temperature is below T_hi or if the thermal system is not in a cooling mode, and if the cooling medium temperature is above T_hi, measuring SOC of the battery pack,

(i) then determining the then-existing charge efficiency (CE_t),

(ii) comparing CE_t against the threshold value CE, and

completing any charge cycle underway if CE_t is below the threshold value CE, thereafter proceeding to a support mode without equalization, and

if CE_t is above the threshold value CE, continuing any charge cycle including equalization with periodic repetition of steps (i) and (ii) until full charging is completed or until CE_t falls below the threshold value CE, in which event charging is terminated and the support mode is entered.

10. The battery charging apparatus of claim 9 including establishing in the controller a state of charge threshold value below which charge efficiency is not considered to be a factor (SOC_CE), with said controller comparing SOC against SOC_CE, and continuing any charge cycle regardless of whether CE_t is below CE if SOC is below SOC_CE.

11. The battery charging apparatus of claim 10 wherein CE is about 75% and SOC_CE is about 80%.