Method and system for determining the SOC of a rechargeable battery

• US 7,888,911 B2
• Filed: 02/16/2007
• Issued: 02/15/2011
• Est. Priority Date: 08/18/2004
• Status: Expired due to Fees

• Current Assignee: GP Batteries International Limited (Gold Peak Industries Limited)
• Original Assignee: GP Batteries International Limited (Gold Peak Industries Limited)
• Inventors: Wong, Kin Pun, Yeo, Che Wee, Ng, Sung On Andrew
• Primary Examiner(s): Tso; Edward
• Assistant Examiner(s): Muralidar; Richard V
• Application Number:
  US11/675,910
• Publication Number:
  US 20080231238A1
• Time in Patent Office: 1,460 Days
• Field of Search: 320/132, 320/159, 320/164
• US Class Current: 320/132
• CPC Class Codes: B60L 15/209 for overtaking
• CPC Class Codes: B60L 2240/80 Time limits
• CPC Class Codes: B60L 50/66 Arrangements of batteries
• CPC Class Codes: B60L 53/11 DC charging controlled by the charging station, e.g. mode 4
• CPC Class Codes: B60L 58/24 for controlling the temperature of batteries
• CPC Class Codes: B60W 10/26 for electrical energy, e.g. batteries or capacitors
• CPC Class Codes: B60W 20/00 Control systems specially adapted for hybrid vehicles hybrid vehicle design, B60K6/00; electric vehicles B60L
• CPC Class Codes: B60W 20/13 in order to stay within battery power input or output limits; in order to prevent overcharging or battery depletion
• CPC Class Codes: B60W 2510/244 Charge state
• CPC Class Codes: B60W 2510/246 Temperature
• CPC Class Codes: G01R 31/3648 comprising digital calculation means, e.g. for performing an algorithm
• CPC Class Codes: G01R 31/374 with means for correcting the measurement for temperature or ageing
• CPC Class Codes: G01R 31/3832 without measurement of battery voltage
• CPC Class Codes: H01M 10/052 Li-accumulators
• CPC Class Codes: H01M 10/30 Nickel accumulators H01M10/34 takes precedence
• CPC Class Codes: H01M 10/345 Gastight metal hydride accumulators
• CPC Class Codes: H01M 10/4207 for several batteries or cells simultaneously or sequentially
• CPC Class Codes: H01M 10/443 in response to temperature
• CPC Class Codes: H01M 10/446 Initial charging measures
• CPC Class Codes: H01M 10/486 for measuring temperature
• CPC Class Codes: Y02E 60/10 : Energy storage using batteries
• CPC Class Codes: Y02T 10/64 : Electric machine technologies in electromobility
• CPC Class Codes: Y02T 10/70 : Energy storage systems for electromobility, e.g. batteries
• CPC Class Codes: Y02T 10/7072 : Electromobility specific charging systems or methods for batteries, ultracapacitors, supercapacitors or double-layer capacitors
• CPC Class Codes: Y02T 10/72 : Electric energy management in electromobility
• CPC Class Codes: Y02T 90/12 : Electric charging stations
• CPC Class Codes: Y02T 90/14 : Plug-in electric vehicles

Abstract

A method of determining the state of charge (SOC) of a rechargeable battery, the method comprising charging the battery using a substantially constant charge current; measuring the battery temperature; and conducting a first measurement of the battery voltage at a time interval, t₁, from the start of the charging, and a second measurement of the battery voltage at a time interval, t₂, from the first measurement.

Claims

1. A method of determining the state of charge (SOC) of a rechargeable battery, the method comprising

charging the battery using a substantially constant charge current, wherein the battery has an unknown SOC at the commencement of the charging;

measuring a battery temperature;

conducting a first measurement of the battery voltage at a time interval, t₁, from the start of the charging, and a second measurement of the battery voltage at a time interval, t₂, from the first measurement, and

determining the SOC of the battery based on the charge current, the battery temperature and the first and second measurements.

2. The method as claimed in claim 1, wherein t₁ is chosen such that a substantially stable behavior in a charging characteristic of the battery at the charge current is reached before the first voltage measurement.

3. The method as claimed in claim 1, wherein t₁ and t₂ are chosen such that the second voltage measurement is prior to reaching a substantially unstable behavior in the charging characteristic before a maximum charging voltage is reached.

4. The method as claimed in claim 1, wherein t₁ and t₂ are calculated from different percentages of C/I, wherein C is a nominal capacity of the battery and I is the charge current.

5. The method as claimed in claim 4, wherein t₁ is about 2% of C/I, and t₂ may be about 10% of C/I.

6. The method as claimed in claim 1, wherein the battery comprises a Nickel Metal Hydride Battery, a Nickel Cadmium Battery, a Lead Acid Battery, a Nickel Zinc Battery, or a Lithium Rechargeable Battery.

7. The method as claimed in claim 1, wherein the method further comprises calibrating an on-vehicle SOC integrator circuit of a hybrid EV or pure EV based on the determined SOC.

8. The method as claimed in claim 1, wherein the method comprises determining a first SOC value based on a voltage increase measured between the first and second voltage measurements, determining a second SOC value based on the voltage measured at the second voltage measurement, and applying a weighted averaging processing to obtain the SOC from the first and second SOC values.

9. The method as claimed in claim 1, wherein the measuring of the battery voltage and the battery temperature comprises utilizing on-vehicle gauges of a hybrid EV or pure EV and/or external gauges.

10. The method as claimed in claim 1, wherein the charging of the battery comprises utilizing an external current source and/or an on-vehicle current source for provision of the substantially constant charge current.

11. The method as claimed in claim 1, wherein the battery temperature is measured at the time of the first voltage measurement and/or at the time of the second voltage measurement.

12. A system for determining the state of charge (SOC) of a rechargeable battery, the system comprising

a source for charging the battery using a substantially constant charge current, wherein the battery has an unknown SOC at the commencement of the charging;

a measurement unit for measuring the battery temperature and for conducting a first measurement of the battery voltage at a time interval, t₁, from the start of the charging, and a second measurement of the battery voltage at a time interval, t₂, from the first measurement; and

a processor unit for determining the SOC of the battery based on the charge current, the battery temperature and the first and second measurements.

13. The system as claimed in claim 12, wherein t₁ is chosen such a substantially stable behavior in a charging characteristic of the battery at the charge current is reached before the first voltage measurement.

14. The system as claimed in claim 12, wherein t₁ and t₂ are chosen such that the second voltage measurement is prior to reaching a substantially unstable behavior in the charging characteristic before a maximum charging voltage is reached.

15. The system as claimed in claim 12, wherein t₁ and t₂ are calculated from different percentages of C/I, wherein C is a nominal capacity of the battery and I is the charge current.

16. The system as claimed in claim 15, wherein t₁ is about 2% of C/I, and t₂ is about 10% of C/I.

17. The system as claimed in claim 12, wherein the battery comprises a Nickel Metal Hydride Battery, a Nickel Cadmium Battery, a Lead Acid Battery, a Nickel Zinc Battery, or a Lithium Rechargeable Battery.

18. The system as claimed in claim 12, wherein the processor unit determines a first SOC value based on a voltage increase measured between the first and second voltage measurements, determines a second SOC value based on the voltage measured at the second voltage measurement, and applies a weighted averaging processing to obtain the SOC from the first and second SOC values.

19. The system as claimed in claim 12, wherein the measurement unit comprises on-vehicle gauges of a hybrid EV or pure EV and/or external gauges.

20. The system as claimed in claim 12, wherein the source comprises a current source external to a hybrid EV or pure EV.

21. The system as claimed in claim 12, wherein the source comprises an on-vehicle current source.

22. The system as claimed in claim 12, wherein the measurement unit measures the battery temperature at the time of the first voltage measurement and/or at the time of the second voltage measurement.