Self-sustained oscillating resonant converters operating above the resonant frequency

This paper presents a new control technique for voltage fed load-resonant converters. Unlike conventional variable frequency controllers that externally impose the switching frequency, the proposed scheme is based on controlling the phase shift between one of the resonant circuit variables and the voltage at the output of the inverter. This approach ensures the operation above the resonant frequency and zero voltage switching in all operation conditions. The static characteristics, as well as the dynamic models of a series-parallel resonant converter with the proposed controller, are derived. Experimental results on a 1 kW prototype confirm the feasibility of the proposed technique.