A novel zero-voltage-switching (ZVS) push-pull forward converter with a parallel resonant network is presented in this paper. The novel topology can provide a releasing loop for the energy storage in a leakage inductor for the duration of the power switching by the resonant capacitors paralleled with the primary windings of the transformer. Then the transformer leakage inductor is utilized to be resonant with the parallel capacitor, and the ZVS operation is achieved. This converter exhibits many advantages such as lower duty-cycle losses, limited peak voltage across the rectifier diodes and a higher efficiency. Furthermore, the operating principles and key problems of the converter design are analyzed in detail, and the ZVS conditions are derived. A 500W experimental converter prototype has been built to verify the effectiveness of the proposed converter, and its maximum efficiency reaches 94.8%.

Individual difference of parallel batteries can cause battery overcharging or over-discharging. More seriously, single battery failure can result in system fault. An energy balancing strategy for battery stage of charge (SOC) balance and DC-DC converter output current sharing is proposed. In addition, the system is designed to cut off the module immediately once any cell fails. This strategy can extend batteries life effectively and enhance the system redundancy. Furthermore, two controllers are designed, one controller regulates the duty ratio of DC-DC converter to make the batteries SOC balanced when the SOC of cell is different, another controller is responsible for output current sharing after SOC balance. The simulation and experiment verification results show the effectiveness of the strategy.