Battery management system and method

• US 20030139888A1
• Filed: 11/27/2002
• Published: 07/24/2003
• Est. Priority Date: 11/27/2001
• Status: Active Grant

• Current Assignee: Schneider Electric IT Corporation (Schneider Electric SE)
• Original Assignee: American Power Conversion Corporation (Schneider Electric SE)
• Inventors: Burns, Charles E.
• Granted Patent: US 6,983,212 B2
• Time in Patent Office: Days
• US Class Current: 702/63
• 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 battery management system for monitoring and recording a plurality of conditions in a battery having a string of units electrically connected in series, each of the units having positive and negative terminals, the system comprising:

a voltage detector circuit for measuring the voltage across the terminals of a unit of the battery;

a charge circuit for selectively supplying charge to the terminals of a individual unit of the battery;

a selector for selectively coupling the terminals of a unit to one of the voltage detector circuit and the charge circuit; and

a microprocessor for controlling the selector to couple the terminals of each of the units to one of the voltage detector and the charge circuit and for recording the state of the selector and an output of the voltage detector.

2. The battery management system according to claim 1, further comprising:

at least one sensor selectively connectable to the voltage detector for sensing a condition of operation of the battery; and

wherein the microprocessor records the output of the voltage detector from the at least one sensor.

3. The battery management system according to claim 2, wherein the at least one sensor includes at least one of an ambient temperature sensor, an pilot cell temperature sensor, and a discharge current sensor.

4. The battery management system according to claim 1, wherein the microprocessor includes a communication port for transferring recorded data to a remote location.

5. The battery management system according to claim 1, wherein the selector includes:

an interlock to allow a coupling between only one unit and one of the voltage detector and charge circuits.

6. The battery management system according to claim 5, wherein the selector includes:

a plurality of relays, each relay being associated with one of the units, each relay being movable between an open position in which current cannot flow to or from an associated unit through the relay and a closed position in which current can flow to or from the associated unit through the relay; and

wherein the interlock prevents movement of a relay from an open to a closed position if current is flowing through another relay.

7. The battery management system according to claim 1, wherein the microprocessor includes means for selectively connecting the selector to at least one unit and recording at least one data value in order to perform a desired test of the battery.

8. The battery management system according to claim 7, wherein the desired test includes at least one of a current response test and a bank discharge test.

9. The battery management system according to claim 1, wherein the microprocessor includes means for analyzing recorded data and detecting problems with any unit of the battery.

10. The battery management system according to claim 9, wherein the microprocessor further includes means for activating an alarm if a problem is detected.

11. The battery management system according to claim 9, wherein the microprocessor further includes means for recording detected problems.

12. The battery management system according to claim 1, wherein the microprocessor includes means for detecting a discharge knee characteristic of the battery.

13. The battery management system according to claim 12, wherein the means for detecting the discharge knee characteristic includes:

means for periodically sampling a voltage of each unit in the battery;

means for summing together the sampled voltages over a selected time interval;

means for storing a sum of sampled voltages for a selected time interval; and

means for comparing a current sum of sampled voltages to a stored sum of sampled voltages and indicating the knee discharge characteristic if the difference between the compared sums exceeds a threshold value.

14. 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:

selectively connecting a unit to a voltage detector circuit for measuring the voltage across the terminals of the unit;

selectively connecting a unit to a charge circuit for supplying charge to the terminals of a unit of the battery; and

recording an output of the voltage detector at selected time intervals.

15. The method for managing a battery according to claim 14, 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.

16. The method for managing a battery according to claim 14, 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.

17. The method for managing a battery according to claim 14, 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.

18. The method for managing a battery according to claim 14, further comprising the step of detecting a discharge knee characteristic of the battery.

19. The method for managing a battery according to claim 18, wherein step of detecting the discharge knee characteristic includes 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.