CELL MONITORING AND BALANCING

• US 20090015206A1
• Filed: 07/10/2008
• Published: 01/15/2009
• Est. Priority Date: 07/13/2007
• Status: Active Grant

• Current Assignee: Black & Decker Incorporated (Stanley Black & Decker, Inc.)
• Original Assignee: Black & Decker Incorporated (Stanley Black & Decker, Inc.)
• Inventors: Trinh, Dahn, Carrier, David A., Brotto, Daniele C., White, Daniel J., Qin, Fugen, Seman, Andrew E. JR., Cruise, Nathan
• Granted Patent: US 8,274,261 B2
• Time in Patent Office: Days
• US Class Current: 320/134
• CPC Class Codes: G01R 31/3835 involving only voltage measurements
• CPC Class Codes: G01R 31/396 Acquisition or processing of data for testing or for monitoring individual cells or groups of cells within a battery
• CPC Class Codes: H01M 10/425 Structural combination with electronic components, e.g. electronic circuits integrated to the outside of the casing printed circuits H05K1/00
• CPC Class Codes: H01M 10/441 for several batteries or cells simultaneously or sequentially
• CPC Class Codes: H01M 10/482 for several batteries or cells simultaneously or sequentially
• CPC Class Codes: H01M 2010/4271 Battery management systems including electronic circuits, e.g. control of current or voltage to keep battery in healthy state, cell balancing
• CPC Class Codes: H01M 2220/30 Batteries in portable systems, e.g. mobile phone, laptop
• CPC Class Codes: H02J 7/0016 using shunting, discharge or bypass circuits
• CPC Class Codes: H02J 7/0019 using switched or multiplexed charge circuits
• CPC Class Codes: H02J 7/0031 using battery or load disconnect circuits H02J9/002 takes precedence
• CPC Class Codes: Y02E 60/10 Energy storage using batteries

Abstract

A method for monitoring the voltage of each of a plurality of cells of a battery pack is provided. The method may include monitoring a voltage potential for each of a plurality of cells in a battery pack utilizing a single channel of battery control unit within the battery pack. If, during discharge of the battery, e.g., the battery is being used to power a hand tool, the voltage potential of any cell is determined by the battery control unit to be below a predetermined minimum voltage, the battery control unit discontinues a current flow from battery pack to the tool. Additionally, during charging of the battery pack, if a voltage differential between any one of the cells and any other one of the cells is determined to be above a predetermined maximum differential, the battery control unit reduces the voltage potential stored in the cell having the higher voltage potential.

Claims

1. A method for monitoring the voltage of each of a plurality of cells of a battery pack, said method comprising:

monitoring a voltage potential for each of a plurality of cells in a battery pack utilizing a single channel of a battery control unit within the battery pack;

discontinuing current flow from battery pack when the voltage potential of any cell is determined by the battery control unit to be below a predetermined minimum voltage during discharge of the battery pack; and

reducing the voltage potential stored in any one or more of the cells when a voltage differential between the respective one or more cells and any other one of the cells having a lesser voltage potential is determined by the battery control unit to exceed a predetermined maximum differential during charging of the battery pack.

2. The method of claim 1 further comprising reducing the voltage potential stored in any one or more of the cells when the voltage potential of the respective one or more cells is determined by the battery control unit to be above a predetermined maximum voltage during charging of the battery pack.

3. The method of claim 2, wherein reducing the voltage potential comprises applying a shunt current to the respective one or more cells to discharge a desired amount of voltage from the respective one or more cells.

4. The method of claim 3, wherein reducing the voltage potential further comprises substantially simultaneously discharging the desired amount of voltage from the respective one or more cells.

5. The method of claim 1, wherein monitoring the voltage potential for each of the plurality of cells comprises sequentially sensing a node voltage at each of a plurality of nodes of a monitoring and balancing circuit, each node connecting one of the cells to a respective one of a plurality of monitoring and balancing (M&

B) sub-circuits of the monitoring and balancing circuit.

6. The method of claim 5, wherein monitoring the voltage potential for each of the plurality of cells further comprises calculating the voltage potential for each cell by sequentially subtracting from the node voltage of each respective cell from the node voltage of the previously sensed cell.

7. The method of claim 5, wherein monitoring the voltage potential for each of the plurality of cells utilizing a single channel of the battery control unit comprises receiving the node voltage signals from each of the M&

B sub-circuits at a measurement node common to each of the M&

B sub-circuits and coupling the common measurement node via a single analog to digital converter (ADC) to the battery control unit.

8. The method of claim 7 further comprises coupling at least one resistor, capacitor or combination thereof to the common measurement node.

9. The method of claim 5, wherein monitoring the voltage potential for each of the plurality of cells utilizing a single channel of the battery control unit comprises:

receiving the node voltage signals from each of the M&

B sub-circuits during a discharge mode, at a first sample rate, via a single discharge mode ADC coupled to a common measurement node, the discharge mode ADC interposed between the battery control unit and each of the M&

B sub-circuits; and

receiving the node voltage signals from each of the M&

B sub-circuits during a charge mode, at a second sample rate that is slower than the first sample rate, via a single charge mode analog to digital converter (ADC) coupled to a common measurement node, the charge mode ADC interposed between the battery control unit and each of the M&

B sub-circuits.

10. The method of claim 1, wherein reducing the voltage potential stored in any one or more of the cells comprises applying a shunt current to the one or more cells having the voltage differential with one of the cells having a lesser voltage potential that exceeds the maximum differential.

11. The method of claim 1, wherein reducing the voltage potential stored in any one or more of the cells comprises substantially simultaneously reducing the voltage potential in two or more cells.

12. The method of claim 1, wherein monitoring the voltage potential for each of the plurality of cells comprises varying a sample rate at which the voltage potentials of the cells are measured, based on a predetermined parameter of the cells during discharge of the battery pack.

13. The method of claim 12, wherein the predetermined parameter comprises one of measured cell voltages, current draw on the battery pack and temperature of the cells.

14. The method of claim 12, wherein varying the sample rate comprises determining which of an active discharge mode, a standby discharge mode and a hibernation discharge mode the battery pack is in.

15. The method of claim 14, wherein varying the sample rate comprises:

sampling the cell voltages at a constant sample rate when the battery pack is in the active discharge mode;

sampling the cell voltages at a varying rate, based on the predetermined parameter of the cells during discharge of the battery pack, when the battery pack is in the standby mode; and

ceasing to sample the cell voltages when the battery pack is in the hibernation mode.

16. The method of claim 15, wherein sampling the cell voltages at a varying rate comprises increasing the rate at which the cell voltages are sampled as the measured cell voltages decrease in value.

17. The method of claim 15, wherein sampling the cell voltages at a varying rate comprises:

measuring the cell voltage potentials and determining an average voltage potential of the cells;

executing a variable sample rate algorithm, using the average voltage potential as a variable of the algorithm, to determine a delay time before the cell voltages are measured again; and

subsequently measuring the cell voltages to determine a subsequent average voltage potential after the delay time has expired.

18. The method of claim 17, wherein executing the variable sample rate algorithm comprises at least one of:

accessing one or more look-up tables to determine the delay time based on the average voltage potential;

applying one or more conditional predetermined thresholds to determine the delay time based on the average voltage potential; and

implementing a mathematical equation to determine the delay time based on the average voltage potential.

19. The method of claim 14, wherein varying the sample rate further comprises:

sampling the cell voltages a constant first sample rate when the battery pack is determined to be in the active discharge mode;

sampling the cell voltages a constant second sample rate when the battery pack is determined to be in the standby discharge mode, the second sample rate being slower than the first sample rate; and

ceasing to sample the cell voltages when the battery pack is in the hibernation mode.

20. The method of claim 1, wherein monitoring the voltage potential for the plurality of cells comprises:

measuring a cumulative voltage potential across all of the cells as the battery pack is discharging;

measuring a cumulative voltage across a sub-set of the cells, the sub-set comprising N number of the cells where the number N is evenly dividable into the total number of cells;

dividing the cumulative voltage potential of all the cells by N to determine a calculated voltage across the sub-set of the cells; and

comparing the measured voltage across the sub-set of the cells with the calculated voltage across the sub-set of the cells to obtain a voltage differential.

21. The method of claim 20, further comprising terminating the discharging of the battery pack if the voltage differential is greater than a predetermined threshold.

22. A cell monitoring circuit for a battery pack having a plurality of battery cells contained therein, comprising:

a plurality of cell monitoring circuits, each cell monitoring circuit is configured to measure voltage across a different one of the battery cells and output a voltage measure to a measurement node common to the plurality of cell monitoring circuits;

a multiplexer controller coupled to each of the cell monitoring circuits and operable to select a voltage measure from at least one of the cell monitoring circuits to present at the measurement node; and

a battery control unit in data communication with the multiplexer controller and having an input coupled to the measurement node to receive a voltage measure therefrom.

23. The cell monitoring circuit of claim 22 wherein the battery control unit communicates with the multiplexer controller to sample a voltage across each battery cell when the battery pack is discharging and discontinue current flow from the battery pack when the sampled voltage is determined to be below a predetermined minimum voltage.

24. The cell monitoring circuit of claim 22 wherein the battery control unit communicates with the multiplexer controller to sample voltage stored in each battery cell when the battery pack is charging and reduce voltage stored in any one of the battery cells when a voltage differential between the respective battery cell and another one of the battery cells is determined by the battery control unit to exceed a predetermined differential.

25. The cell monitoring circuit of claim 22 wherein each of the cell monitoring circuits includes a switch that selectively controls when the voltage measure from cell monitoring circuit is present at the measurement node and the multiplexer controller having a control line coupled to the switch in each of the cell monitoring circuits.

26. The cell monitoring circuit of claim 22 further comprises an analog to digital converter coupled between the measurement node and the battery control unit.

27. The cell monitoring circuit of claim 22 further comprises at least one of resistor, capacitor or combination thereof coupled between the measurement node and ground.

28. The cell monitoring circuit of claim 22 further comprises a transistor coupled between the measurement node and ground with a gate controlled by the battery control unit.