A robust fixed-frequency soft switching series resonant converter for transportation applications

Frequency modulation is often used in series resonant converters to gain output voltage regulation. Variable frequency however brings challenges for EMI filter and switch driver design and the desirable zero voltage switching cannot be maintained at light load conditions. This paper presents time-domain steady-state analysis of fixed-frequency series resonant converters with phase shift modulation. Three operation modes are identified and the mode boundaries are demonstrated. Based on this a passive robust auxiliary circuit is proposed to ensure the zero voltage switching of the converter in all three modes. The achievement of zero voltage switching is confirmed by experimental results.

I. Introduction

Series resonant converter (SRC) has been a well-established high-efficiency power converter topology for decades [1]. Recently, emerging technologies such as electric and hybrid vehicles demand high power density converters with improved efficiencies [2]–[4]. Also, the trend of introducing wireless power transfer for static and dynamic energy exchange with vehicles has revived the attention to resonant converters [5]–[8]. SRC has multiple advantages: intrinsic low switching losses (allowing high frequency operation and higher power density), taking advantage of inevitable parasitic inductances as a part of resonant tank, lower EMI levels, a single-capacitor output filer, flat efficiency versus load power, and intrinsic short circuit protection.