Multi-Phase Series Resonant DC-to-DC Converters: Transient Investigations

This paper investigates multi-phase series resonant DC-to-DC converters during transient operation. The topology is presented and its principle working during transient conditions is described for switching frequencies equal to the resonant frequency. It is demonstrated that load step changes may cause voltage and current oscillations, which may damage converter components. These oscillations can be damped by proper design of the output capacitor. The state space averaging technique is used to obtain a simple equivalent DC circuit, which describes the voltage and current waveforms very precisely. A simplification of the model enables the analytical calculation of the design rules for the output capacitor. Based on these design rules, a 5 kW/100 kHz laboratory prototype of a three-phase topology has been built. The prototype is used to verify the analysis experimentally