Fixed Frequency Phase Shift Modulated LLC Resonant Converter Adapted to Ultra Wide Output Voltage Range

Abstract

Conventional frequency modulated LLC topology is unsuitable for ultra wide voltage range applications and suffers from poor voltage regulation performance at light load conditions. To cope with those issues, this paper proposes a novel two-phase dual LLC resonant converter. Both resonant tanks are driven by two fixed-frequency square waves, whose frequencies are always tuned at the optimal resonant frequency. A phase shift is introduced between those two square waves to regulate the output voltage. The proposed topology demonstrates good voltage regulation performance, which is weakly dependent on the load condition. Zero-voltage switching and zero-current switching are well realized on the power MOSFETs and diodes in a wide range. A 1 kW rated laboratory prototype is designed to convert 390 V input to 100-420 V output. The prototype demonstrates a 98.2% peak efficiency and good voltage regulation capability. The experimental results agree well with the theoretical analysis.