Soft-switching Control For Onboard Full Bridge DC/DC Converter

The developed direct current to direct current(DC/DC)converter is an onboard equipment for electric energy conversion from the high voltage traction battery pack to the low voltage vehicular electrical network.As one of key apparatuses to keep the low voltage network steady and reliable,it is closely related in proper working of the electric vehicle.The soft-switching technology is usually used to get the DC/DC converter loss decreased and control period shortened.And it is significant in improving efficiency,stability and electro-magnetic compatibility(EMC)for the DC/DC converter.In this context,different topologies of the DC/DC converter are presented and analyzed.Satisfied with the wide-range load,the full bridge DC/DC converter is chosen with a lagging series diodes leg for the zero-current-switching(ZCS)mode.Its zeros-voltage-switching(ZVS)mode of the leading leg is easily developed.Furthermore,the pulse-width-modulation(PWM)modes for the four power semiconductors are stated in details.Based on the chosen full bridge converter topology,a 48 V/12 V onboard DC/DC converter model is designed,including the power circuit,the drive and control module,the feedback circuit,and the auxiliary power source.In the feedback control module,the average current feedback mode is developed with the single zero and single pole compensation network for the voltage loop and current loop.The small-signal equivalent circuit of the DC/DC converter is presented for parameters of the feedback compensation networks.Meanwhile,the Bode plots are used to verify stability of the feedback control module.Circuit simulation is conducted for variable loads and input voltage waves on the PSIM software.Results show that the DC/DC converter behaves steadily with good outputs and switching characteristics.Compared to the basic full bridge DC/DC converter,the purposed converter can run with soft-switching modes and improve efficiency and EMC.Finally,the DC/DC converter prototype is developed.Experimental results show that the designed scheme is feasible.Based on the comparison between test results and simulation results,some suggestions are provided for the next development.