Efficiency Improvement of Step-Up Series Resonant DC-DC Converter in Buck Operating Mode

The paper focuses on the galvanically isolated series-resonant dc-dc converter (SRC) operating at low values of the quality factor of the resonant tank. The SRC topology is considered as a step-up front-end dc-dc converter with buck-boost functionality for integration of renewable energy sources in dc microgrids. The input voltage range could be expanded significantly by implementing different buck control methods at the constant switching frequency. Moreover, an additional control degree of freedom allowing optimization of the converter operation is topology reconfiguration between the full-bridge mode and the half-bridge mode. The paper describes the transition between these two modes of the input-side full-bridge inverter by applying hybrid phase shift modulation and asymmetrical pulsewidth modulation, respectively. Experimental results show the operation of the converter in a wide input voltage range and transition transients between the two modes.