A new phase-controlled parallel resonant converter

A new phase-controlled resonant inverter is obtained by paralleling the ac loads of two identical parallel resonant inverters. A phase shift between the drive signals of the two inverters controls the amplitude of the output voltage of the new inverter. A voltage-driven rectifier is used as an ac load of the inverter which results in a phase-controlled parallel resonant dc-dc converter. A frequency-domain analysis is performed for the steady-state operation of the inverter and two types of voltage-driven rectifiers and design equations are derived. The converter can be operated at a constant switching frequency which reduces EM1 problems. It is found that for switching frequencies higher than the resonant frequency by a factor of 1.07, the load of each switching leg is inductive which allows for the use of power MOSFETs as switches. The converter is capable of regulating the output voltage in the range of load resistance from full load to no load. An experimental prototype of the phase-controlled parallel resonant converter with a center-taped rectifier was built and extensively tested at an output power of 50 W and a switching frequency of 116 kHz.