METHOD AND SYSTEM FOR CELL EQUALIZATION WITH CHARGING SOURCES AND SHUNT REGULATORS

• US 20090267565A1
• Filed: 07/02/2009
• Published: 10/29/2009
• Est. Priority Date: 11/10/2004
• Status: Active Grant

• Current Assignee: Eaglepicher Technologies LLC (Eaglepicher Corporation)
• Original Assignee: Eaglepicher Technologies LLC (Eaglepicher Corporation)
• Inventors: Miller, Greg, Shimp, Phillip, Pennock, Tim, Coatney, Eric, Studyvin, William B.
• Granted Patent: US 7,825,629 B2
• Time in Patent Office: Days
• US Class Current: 320/116
• CPC Class Codes: H02J 7/0016 using shunting, discharge or bypass circuits

Abstract

A system and method for charging a rechargeable, or secondary, battery including a series string of cells, includes a topology of charging sources that selectively provides charging current to cells that need to be charged, but avoids overcharging cells that are already charged above a predetermined voltage threshold. Based on individual cell voltage measurements, the charging current is controlled in a manner to direct charging current to the battery cell(s) needing charge until these cells are fully charged, and by-passes battery cells that are fully charged or become fully charged.

Claims

1. A system for charging a secondary battery, comprising:

a plurality of battery cells connected in a series string, wherein said series string comprises;

a first battery cell at a load end and an nth battery cell at a ground end, and

a cell junction located between each respective pair of battery cells;

a plurality of charging sources, wherein;

a first charging source electrically coupled to said load end,

a second charging source electrically coupled to a first cell junction between said

first battery cell and a second battery cell located adjacent to said first battery cell, and

an additional charging source electrically coupled to each cell junction occurring

every two cells thereafter; and

a plurality of shunt regulators, wherein a respective shunt regulator is connected in parallel across each of said second battery cell to said nth battery cell, wherein each of said plurality of shunt regulators is configured to operate in a first state and a second state, and wherein each of said plurality of shunt regulators repeatedly cycles between said first state and said second state, and wherein different levels of current are provided to each cell to achieve cell equalization.

2. The system of claim 1, wherein said plurality of shunt regulators comprises:

(n−

1) shunt regulators.

3. The system of claim 1, wherein said plurality of charging sources comprises:

(n+2)/2 charging sources when n is an even number;

and (n+1)/2 charging sources when n is an odd number.

4. The system of claim 1, further comprising:

a charging source electrically coupled to each of said plurality of charging sources, wherein said charging source provides charging current to each of said plurality of battery cells.

5. The system of claim 1, further comprising:

a plurality of controllers, wherein a controller is coupled to a respective charging source of said plurality of charging sources, and each of said controllers includes circuitry to at least one of switch on and switch off each of said plurality of charging sources.

6. The system of claim 5, wherein said circuitry is configured to allow only one charging source to be switched on at a time.

7. The system of claim 1, further comprising:

a shunt controller coupled to each of said plurality of shunt regulators, wherein each shunt controller is configured to cycle each of said plurality of shunt regulators between said first state and said second state.

8. The system of claim 7, wherein said shunt controller is configured to cycle each of said plurality of shunt regulators to said first state if a battery cell with which said shunt regulator is coupled across in parallel is fully charged, and cycle each of said plurality of shunt regulators to said second state if said battery cell is not fully charged.

9. A charging system for charging a rechargeable battery comprised of n cells connected in a serial string from a first cell at one end to an nth cell at another end with a respective cell junction being located between each adjacent cell, the system comprising:

a plurality of switched charging sources, selectively coupled with a respective one of the cell junctions, wherein a number of the switched charging sources is less than (n); and

a plurality of shunt regulators, wherein a respective shunt regulator is connected in parallel across each of the second cell through the nth cell, such that a number of the shunt regulators is (n−

1), wherein each of said plurality of shunt regulators is configured to operate in a first state and a second state, wherein each of said plurality of shunt regulators repeatedly cycles between said first state and said second state, and wherein different levels of current are provided to each cell to achieve cell equalization.

10. The charging system of claim 9, further comprising:

a charging source electrically coupled with each of the switched charging sources such that the switched charging sources may be configured to provide charging current to one or more of the n cells.

11. The charging system of claim 9, further comprising:

a respective cell monitoring circuit configured to measure a voltage of an associated cell; and

a controller coupled to each of the cell monitoring circuits, the shunt regulators, and the switched charging sources;

wherein the shunt regulators and the switched charging sources are operated by the controller to provide charging current to each cell having a voltage below a predetermined threshold and to avoid providing charging current to each cell having a voltage at or above a predetermined threshold.

12. The charging system of claim 11, wherein the controller operates only one of the switched charging sources in the first state at any given time.

13. A method for equalizing voltage of a secondary battery being charged, the battery comprised of n cells connected in a serial string from a first cell at a load end to an nth cell at a ground end with a respective cell junction being located between each adjacent cell, the method comprising the steps of:

coupling a plurality of switched charging sources to the serial string, wherein a first switched charging source is electrically coupled to the one end of the serial string, and second switched charging source is electrically coupled at the cell junction between the first cell and an adjacent second cell; and

a respective switched charging source is electrically coupled at the cell junctions occurring every two cells thereafter;

coupling a plurality of shunt regulators to the serial string, wherein a respective shunt regulator is connected in parallel across each of the second cells through the nth cell, wherein each of said plurality of shunt regulators is configured to operate in a first state and a second state, and wherein each of said plurality of shunt regulators repeatedly cycles between said first state and said second state , and wherein different levels of current are provided to each cell to achieve cell equalization; and

operating the switched charging sources and the shunt regulators to selectively provide charging current to one or more of the n cells.

14. The method of claim 13, wherein said step of connecting a plurality of shunt regulators to the serial string comprises the step of:

connecting (n−

1) shunt regulators to the serial string.

15. The method of claim 13, wherein said step of connecting the plurality of switched charging sources to the serial string comprises the step of:

connecting ((n+2)/2) switched charging sources to the serial string when n is an even number.

16. The method of claim 13, wherein said step of connecting the plurality of switched charging sources to the serial string comprises the step of:

connecting ((n+1)/2) switched charging sources to the serial string when n is an odd number.

17. The method of claim 13, further comprising the steps of:

operating each of the switched charging sources in one of a first state and a second state, wherein when a switched charging source is in the first state, the source provides a charging current to the respective cell junction where that switched charging source is electrically coupled; and

when the switched charging source is in the second state, the source does not provide a charging current to the respective cell junction where that switched charging source is electrically coupled; and

operating each of the shunt regulators in said first state to bypass charging current around the respective cell across which it is connected and operate as a high-impedance electrical path in said second state.

18. The method of claim 13, further comprising the step of:

operating the shunt regulators and the switched charging sources to provide charging current to each cell having a voltage below a predetermined threshold and to avoid providing charging current to each cell having a voltage at or above a predetermined threshold.

19. The method of claim 18, further comprising the steps of:

monitoring a respective voltage level of each of the n cells; and

determining which of the n cells is at or above a predetermined voltage threshold.

20. A method for equalizing voltage of a secondary battery comprising the steps of:

a) monitoring an amount of charge contained within a plurality of battery cells utilizing at least one cell monitor to determine if at least one battery needs charging;

b) transmitting a signal to begin charging operations from said at least one cell monitor, to a controller, when at least one of said plurality of battery cells needs charging;

c) determining, by said controller, which charging source, of a plurality of charging sources, to utilize to charge said at least one of said plurality of battery cells needing charging;

d) switching on, by said controller, an appropriate charging source of said plurality of charging sources to charge said at least one of said plurality of battery cells needing charging, wherein said appropriate charging source is determined by its location with respect to at least one battery cell needing charge;

e) switching on at least one shunt regulator coupled in parallel to at least one of said plurality of battery cells, wherein said at least one shunt regulator is a shunt regulator coupled in parallel across a battery cell including a charge amount greater than a threshold amount; and

f) configuring said at least one shunt regulator to operate in one of a first state and a second state, wherein said at least one shunt regulator set repeatedly cycles between said first state and said second state, and wherein different levels of current are provided to each cell to achieve cell equalization.

21. The method of claim 20, wherein said step of switching on at least one shunt regulator occurs prior to said step of switching on an appropriate charging source.

22. The method of claim 20, further comprising the steps of:

g) continuing to monitor, by said cell monitor, said plurality of battery cells until at least one battery cell receiving charging current is charged to a threshold amount of charge; and

h) cycling to said first state, by said controller, a shunt regulator coupled in parallel to said battery cell receiving charging current when said battery cell receiving charging current contains said threshold amount of charge.

23. The method of claim 22, further comprising:

i) repeating steps g) and h) until each of said plurality of battery cells contains said threshold amount of charge.

24. The method of claim 23, further comprising the steps of:

i) switching off, by said controller, said charging source when each of said plurality of battery cells contains said threshold amount of charge; and

j) cycling any shunt regulator to said second state, by said controller, any shunt regulator cycled to said first state by said controller.