Enhanced EPS-PSM Hybrid Control of CLLC Resonant Converter with Improved Light-Load Efficiency

Pulse frequency modulation (PFM) is the traditional method to drive CLLC resonant converters. However, PFM suffers the problems of unsatisfactory voltage regulation and low efficiency under light-load conditions under light-load conditions. Phase-shift modulation techniques, such as inner phase shift (IPS) modulation, can overcome this challenge. However, more improvements are demanded due to high circulating currents and difficulties in achieving zerovoltage switching (ZVS) in phase-shift modulations. Therefore, this article proposes an optimization for extended phase-shift (EPS) control to improve the light-load efficiency. In order to study the relations between phase-shifts of EPS control and converter efficiency, a detailed circuit model is established to solve time-domain expressions of circuit variables, the voltage gain and root mean square (RMS) values of resonant currents. Finally, based on these analyses, a proper selection of phase-shift values of EPS is determined to achieve higher efficiency of the CLLC converter at light-load conditions. The validity of the proposed optimized EPS control is verified on a 200V/30.,60 V, 300 W Si-based CLLC resonant converter prototype.