Battery management system and method

• US 7,728,552 B2
• Filed: 09/15/2005
• Issued: 06/01/2010
• Est. Priority Date: 11/27/2001
• Status: Expired due to Fees

• Current Assignee: American Power Conversion Corporation (Schneider Electric SE)
• Original Assignee: American Power Conversion Corporation (Schneider Electric SE)
• Inventors: Burns, Charles E.
• Primary Examiner(s): Tso; Edward
• Assistant Examiner(s): Fantu; Yalkew
• Application Number:
  US11/227,853
• Publication Number:
  US 20060012341A1
• Time in Patent Office: 1,720 Days
• Field of Search: 320/116, 320/126, 320/118, 320/122, 364/550
• US Class Current: 320/116
• CPC Class Codes: H02J 7/0014 Circuits for equalisation of charge between batteries
• CPC Class Codes: H02J 7/0019 using switched or multiplexed charge circuits
• CPC Class Codes: H02J 7/0048 Detection of remaining charge capacity or state of charge [SOC]
• CPC Class Codes: H02J 7/005 Detection of state of health [SOH]

Abstract

A battery management system is disclosed for control of individual cells in a battery string. The battery management system includes a charger, a voltmeter, a selection circuit and a microprocessor. Under control of the microprocessor, the selection circuit connects each cell of the battery string to the charger and voltmeter. Information relating to battery performance is recorded and analyzed. The analysis depends upon the conditions under which the battery is operating. By monitoring the battery performance under different conditions, problems with individual cells can be determined and corrected.

Claims

1. A method for managing a battery having a string of units electrically connected in series, each of the units having positive and negative terminals, the method comprising the steps of:

supplying charge selectively to a selected single unit of the string of units electrically connected in series with a charging circuit;

measuring the voltage across the terminals of the selected unit of the battery with a single voltage detector circuit;

recording an output of the voltage detector; and

detecting a discharge knee characteristic of the battery based on the output from the voltage detector for the unit, detecting the discharge knee including the steps of;

periodically sampling a voltage of the selected unit;

comparing a sum of sampled voltages for a first selected time interval to a sum of sampled voltages for a second selected time interval; and

determining a knee discharge characteristic if a difference between the compared sums exceeds a threshold value.

2. The method of claim 1 further comprising selectively connecting a unit to a charge circuit for supplying charge to the terminals of a unit of the battery.

3. The method for managing a battery according to claim 1, further comprising the steps of:

determining a condition of operation of the battery, wherein the condition of operation includes one of an ambient temperature, a pilot cell temperature and a discharge current; and

recording the determined condition.

4. The method for managing a battery according to claim 1, further comprising the steps of:

determining a problematic condition for at least one unit of the battery based upon recorded data; and

activating an alarm when a problematic condition is detected.

6. The method for managing a battery according to claim 2, further comprising the step of:

determining a current flowing through the charge circuit when connected to a unit of the battery;

determining a voltage level for the unit connected to the charge circuit based upon the detected current; and

recording the voltage level.

7. The method of claim 2 further comprising automatically controlling the coupling of a unit of the battery to one of the voltage detector circuit and the charge circuit based on a condition of the unit of the battery.

8. The method of claim 7 further comprising supplying charge to the terminals of the unit of the battery and measuring a current value of the charge.

9. The method of claim 8 further comprising comparing the current value to a benchmark current value for the unit and determining whether a threshold value of current to the unit has been exceeded.

5. A method for managing a battery having a string of units electrically connected in series, each of the units having positive and negative terminals, the method comprising the steps of:

supplying charge to a selected unit of the battery with a charging circuit;

measuring the voltage across the terminals of the selected unit of the battery with a single voltage detector circuit;

recording an output of the voltage detector;

detecting a discharge knee characteristic of the battery based on the output from the voltage detector for the unit, detecting the discharge knee including the steps of;

periodically sampling a voltage of each unit in the battery;

summing together the sampled voltages over selected time intervals;

comparing a sum of sampled voltages for a first selected time interval to a sum of sampled voltages for a second selected time interval; and

determining a knee discharge characteristic if the difference between the compared sums exceeds a threshold value.

10. A method for detecting a discharge knee of a battery using an apparatus including storage and a processor coupled to the storage, the method comprising the steps of:

periodically sampling, by the processor, a voltage in the battery;

comparing, by the processor, a sum of sampled voltages for a first selected time interval to a sum of sampled voltages for a second selected time interval; and

determining, by the processor, a knee discharge characteristic if a difference between the compared sums exceeds a threshold value.

11. The method for detecting the discharge knee according to claim 10, further comprising:

storing, in the storage, the sum of sampled voltages for the first selected time interval; and

storing, in the storage, the sum of sampled voltages for the second selected time interval.

12. The method for detecting the discharge knee according to claim 10, further comprising:

summing, by the processor, the sampled voltages for the first selected time interval; and

summing, by the processor, the sampled voltages for the second selected time interval.

13. The method for detecting the discharge knee according to claim 10, further comprising storing, in the storage, an indication of the knee discharge characteristic.