Battery voltage sensorless charge equalizer using the multi-winding transformer

A simple and easy magnetic coupling equalizer for a series-connected lithium-ion battery string is presented. The equalizer applies identical duty cycle to all active power switches without using the voltage sensing circuits and the secondary side components of multi-winding transformer. During the turn-on switching interval, the equalizer automatically transfers energy from the high-voltage battery cells to the low-voltage battery cells. The proposed equalizer can effectively reduce size, cost, and design complexity of the equalizer system.