A novel isolated bidirectional DC-DC converter for ultra-capacitor application in hybrid and electric vehicles

This paper presents a new isolated bidirectional DC/DC converter for auxiliary power supplies in electric vehicles where high power density, bidirectional power flow and electric isolation are required. Compared to conventional bidirectional converters, this modified half-bridge circuit further minimizes components to 2 capacitors without any other change based on the existing highest power density circuit. With a novel PWM plus phase-shift (PPS) control strategy, it minimizes device current stresses over a wide input voltage range. Moreover, a natural zero-voltage switching method for the whole switches is achieved without additional device to reduce switching loss and device inrush voltage stresses. These advantages make the new converter promising for high power density applications, especially to overcome the high device current stresses problem caused by wide range ultra-capacitor voltage variation. In this paper, firstly, a complete design consideration and principle of the new topology is presented; secondly, an analysis of static state mode is provided; finally, a 15V/50W prototype is built up after a 60V/4kW modeling simulation on computer and it successfully proved this converter's device current stresses minimization and high power density characteristics.