Sendyne, a maker of battery measurement systems and modeling tools, has been awarded a patent for a novel active cell balancing topology.
Active cell balancing is the process of transferring energy to and from individual cells in a battery pack so that all cells will operate at the same State of Charge (SOC). Because individual cells have slightly different capacities, if energy were not redistributed, discharging would end when the cell with the lowest capacity was empty.
There are several current approaches to cell balancing, and all have drawbacks. Some require bulky and costly switches, inductors, or capacitors; some suffer substantial energy losses during the balancing process; some require an external energy input, but cannot redistribute charge between cells in a string; some only serve to discharge particular cells, thus wasting energy.
According to Sendyne, its new topology achieves active balancing with fewer and smaller components than other methods, and many of the parts are readily available at low cost. It permits any cell in a pack to charge any other cell with maximum efficiency and minimal operational losses. It requires one MOSFET switch for each cell, one low-cost transformer for each set of four to eight cells in series, and one shared parallel energy bus for the entire battery system.