Stackable bi-directional multicell battery balancer

1. A battery balancing system comprising:

at least one sub-stack, each sub-stack comprising a plurality of cells connected in series;

a balancing module for each sub-stack, the balancing module comprising an independent bidirectional balancer for each cell in the sub-stack;

a monitor module configured to sense a SOC of each cell in each sub-stack;

a microprocessor configured to determine an average SOC of the cells for each sub-stack; and

a daisy chained stackable serial port configured to transmit information to each balancing module, wherein each balancing module is configured to:

provide an additional charge to any weak cell from its sub-stack during a discharging of the battery, and remove additional charge from any weak cell and provide it to its sub-stack during a charging of the battery; and

remove an additional charge from any strong cell and provide it to its sub-stack during the discharging of the battery, and provide an additional charge from the sub-stack to any strong cell during the charging of the battery.

2. The battery balancing system of claim 1 , wherein any number of sub-stacks can be stacked in series and controlled using a common stackable serial control.

3. The battery balancing system of claim 1 , wherein each sub-stack comprises six series connected cells.

4. The battery balancing system of claim 1 , wherein every strong or weak cell in a sub-stack is balanced simultaneously.

5. The battery balancing system of claim 4 , wherein every strong or weak sub-stack is balanced simultaneously.

6. The battery balancing system of claim 1 , wherein any number of sub-stacks are balanced simultaneously.

7. The battery balancing system of claim 1 , further comprising:

at least one transformer having a primary side and a secondary side, wherein each transformer comprises a separate coil for each cell on the primary side and a single coil corresponding to a plurality of adjacent sub-stacks on the secondary side;

each coil including a first terminal and a second terminal,

wherein each coil on the primary side has a transistor and a resistor in series with the second terminal;

wherein each coil on the secondary side has a transistor and a resistor in series with a second terminal;

wherein the first terminal of each coil on the primary side of each transformer is connected to a cell;

wherein the first terminal of the coil on the secondary side of each transformer is connected to a first terminal of a secondary side of a transformer of an adjacent independent bidirectional balancer; and

wherein the resistor in series with a second terminal of the secondary side of each transistor is connected to the lowest voltage of its sub-stack.

8. The battery balancing system of claim 7 , wherein:

each transformer is configured to transfer charge between its sub-stack and an adjacent sub-stack;

the primary side of each transformer is connected to its respective cell in its sub-stack and the secondary side to its sub-stack and an adjacent sub-stack; and

the connection of each transformer to its respective adjacent sub-stack is interleaved.

9. The battery balancing system of claim 7 , wherein a maximum voltage across the secondary side of each coil is limited by a breakdown voltage of its respective series transistor.

10. The battery balancing system of claim 1 , wherein the balancing module is configured to allow each cell within a sub-stack to achieve a same voltage at a first predetermined point in a charge cycle and a second predetermined point in a discharge cycle.

11. The battery balancing system of claim 10 , wherein:

the first predetermined point is at 70% capacity of the cells within the sub-stack; and

the second predetermined point is at 30% capacity of the cells within the sub-stack.

12. A method of balancing a battery comprising:

sensing an SOC of each cell in every sub-stack;

calculating an average SOC for every sub-stack;

determining a strength of each cell in every sub-stack in relation to the average SOC in every sub-stack;

simultaneously providing an additional charge to weak cells from their respective sub-stack during a discharging of the battery;

simultaneously removing an additional charge from weak cells to their respective sub-stack during a charging of the battery;

simultaneously removing an additional charge from strong cells to their respective sub-stack during a discharging of the battery; and

simultaneously providing an additional charge to strong cells from their respective sub-stack during a charging of the battery.

13. The method of claim 12 further comprising:

transferring charge between one sub-stack to another sub-stack of the battery through at least one intermediary sub-stack in an interleaved manner.

14. The method of claim 12 further comprising allowing each cell within a sub-stack to achieve a same voltage at a first predetermined point in a charge cycle and a second predetermined point in a discharge cycle.

15. The method of claim 14 , wherein:

the first predetermined point is at 70% capacity of the cells within the sub-stack; and

the second predetermined point is at 30% capacity of the cells within the sub-stack.