A comparison and optimum design of reluctance-controlled classical load-resonant converters

Fundamental frequency analysis is used to obtain the steady-state operation of the three most popular load resonant converters, when operated with limited frequency range due to a variable inductance. The power throughput is regulated by electronically varying the reluctance of the resonant inductor. The developed design equations indicate that the converters operate efficiently in the region of maximum control gain, with a phase around 35 degrees. The validity of the proposed design equations and the identified optimum operating conditions are confirmed through time-domain simulations and measurements from a 200 W, 500 kHz prototype of a series-parallel resonant converter.