A direct multi-cells-to-multi-cells equalizer based on LC matrix converter for series-connected battery strings

Abstract

Due to the low switching loss, the LC series resonant conversion (LCSRC) as an energy carrier is promising in the battery equalizers. However, when LCSRC is applied to multi-cells series-connected batteries, the balancing speed and efficiency will be seriously low. Therefore, a direct multi-cells-to-multi-cells (MC2MC) equalizer based on LC matrix converter (LCMC) is proposed, which can transfer energy directly from the consecutive higher-voltage cell group to the consecutive lower-voltage cell group, achieving a high balancing speed and efficiency. Moreover, the switching loss for balancing is reduced by operating the LCMC at the zero-current switching (ZCS) condition. An experimental cell balancing circuit for an eight-cell lithium-ion battery string shows that it is possible to realize faster balancing with higher efficiency. The measured balancing efficiencies are 99.2% and 75.9% at the powers of 0.17 W and 0.45 W, respectively.