A multi-winding transformer-based active cell equalizer with self-driven switches for series-connected lithium-ion batteries and super-capacitors

This work introduces a new multi-winding transformer-based cell equalizer with self-driven switches seriesconnected energy storage cells. With the equalizer, all series-connected cells can be equalized in both charging and discharging manners, towards the same balance voltage. In order to reduce the conduction loss in balancing process, all switching devices in the new equalizer are implemented by MOSFETs. By introducing a center tap, each secondary winding can be divided into two sub-windings, one of which is used to control the MOSFET switches while another one is used to supply the balancing voltage of cells. Therefore, the proposed cell equalizer can achieve the equalization automatically without any switch driving circuits, voltage sensors and complex control strategies. It greatly simplifies the complexity of the balance circuit and reduces the system cost. The circuit structure can be extended by adding more balancing units to meet the requirements of high voltage. Circuit configuration, operation principle, modeling and design considerations are analyzed in detail. Finally, simulation and experimental results are provided to verify the feasibility of the proposed cell equalizer.