New method of power control for series-parallel load-resonant converters maintaining zero-current switching and unity power factor operation

A power supply incorporating a series-parallel load-resonant converter capable of efficient operation over a wide range of output power is presented. The series-parallel resonant converter is shown to have three resonant frequencies. Operation of the circuit at each of these resonant frequencies maintains zero-current switching and high-frequency operation. The resonant circuit is designed to have different circuit resistances at each resonant frequency. The power delivered to the circuit, and hence the load, will therefore vary depending on which resonant frequency the circuit is excited at. This is the basis of a new method of power control for load-resonant converters disclosed in this paper. A welding power supply is designed and constructed which delivers pulsed output currents of 150 A while operating at 100 kHz and 60 A at 65 kHz. The power supply contains an active rectifier and draws near unity power factor.