A round robin algorithm for an embedded electronic battery equalizer

A special round robin (RR) algorithm has been developed to equalize nickel metal hydride (NiMH) battery packs using a new selective equalizer. This algorithm detects batteries either at a very low state of charge (SOC) or at an extremely high SOC. In this system, a set of electromechanical relays are connected in a matrix to route boost current to the weaker batteries. The relay switching is controlled by a 32-bit microcontroller, and the boost current is supplied by a boost charger. Once the RR algorithm detects a weak battery, it schedules the detected battery for a specific boost time. Test results show that the equalizer was able to re-balance an artificially unbalanced pack, and the capacity was increased by 27 % within six charge- discharge cycles. The number of cycles required to rebalance the pack was significantly reduced by using the RR algorithm.