Systems and methods for cell balancing
A cell balancing circuit comprises a first cell having a first voltage, a second cell in series with the first cell and having a second voltage that is greater than the first voltage, and a bypass path in parallel with the second cell for enabling a bypass current for the second cell if a difference between the first voltage and the second voltage is greater than a predetermined threshold. The bypass current is enabled for a balancing time period that is proportional to the difference between the first voltage and the second voltage.
1. A cell balancing circuit for balancing a plurality of cells, comprising:
a logic core operable for detecting if any cell is in balancing phase, reading a full charge capacity (FCC) recorded in a previous cycle for each cell when no cell is in said balancing phase, checking a timer coupled to a cell if said cell is in said balancing phase, balancing said cell while said timer is counting, and terminating said balancing phase when said timer expires, for calculating a state-of-charge (SOC) for each of said cells, for searching a minimum SOC and a maximum SOC of said cells, for detecting an unbalanced condition if a difference between said maximum SOC and said minimum SOC is greater than a predetermined threshold, and for determining a balancing time period that is proportional to said difference if said unbalanced condition occurs,
wherein said cell balancing circuit enables a bypass current for a cell having said maximum SOC for said balancing time period if said unbalanced condition occurs.
2. The cell balancing circuit as claimed in claim 1 , wherein said SOC for each of said cells is determined by a ratio of a cell capacity of each of said cells to said full charge capacity of each of said cells.
3. A method for balancing a plurality of cells, comprising:
detecting if any cell is in balancing phase;
reading a full charge capacity (FCC) recorded in a previous cycle for each cell when no cell is in said balancing phase;
checking a timer coupled to a cell if said cell is in said balancing phase;
balancing said cell while said timer is counting;
terminating said balancing phase when said timer expires;
calculating a state-of-charge (SOC) for each of said cells;
searching a minimum SOC and a maximum SOC of said cells;
detecting an unbalanced condition if a difference between said maximum SOC and said minimum SOC is greater than a predetermined threshold;
determining a balancing time period that is proportional to said difference if said unbalanced condition occurs; and
enabling a bypass current for a cell having said maximum SOC for said balancing time period if said unbalanced condition occurs.
4. The method as claimed in claim 3 , wherein said SOC for each of said cells is determined by a ratio of a cell capacity of each of said cells to said full charge capacity of each of said cells.