Performance improvement of PWM control methods for voltage step-down in series resonant DC-DC converters

Abstract

The paper is focused on galvanically isolated series resonant DC-DC converters (SRCs) with a low quality factor of the resonant tank. These converters provide input voltage regulation at fixed switching frequency and good power density. Different modulation methods at the fixed switching frequency enable the implementation of the voltage buck functionality in these converters. The SRC under study is considered as a step-up front-end DC-DC converter for the integration of renewable energy sources in DC microgrids. The paper evaluates the voltage buck performance of the SRC achieved by using different pulse-width modulation (PWM) methods including conventional PWM and shifted PWM. Moreover, the new PWM methods, i.e., the hybrid shifted PWM (HSPWM), improved shifted PWM (ISPWM), and hybrid PWM (HPWM), are proposed to overcome the disadvantages of the existing methods. They improve the power conversion efficiency in the buck mode by reducing the power losses in the semiconductor switches and the isolating transformer of the SRC. The proposed and the existing methods are benchmarked in terms of the components stresses and power conversion efficiency. The presented findings have been experimentally validated by the help of a 200W prototype, which demonstrated the lowest power loss in the case of the HPWM.