Series resonant converter for pulsating power operating at fixed frequency

This paper presents a Series Resonant Converter (SRC) isolated power supply to regulate several outputs, delivering 70kW average power pulsating from no load to several hundred kW. The design is for magnetic resonance imaging (MRI) system application. The full-bridge power stage is controlled at fixed frequency with phase-shift between the two legs. The power supply has been designed to operate on discontinuous conduction mode, keeping soft switching over the whole power range, and tolerant to inductance and capacitance spread. The control has a feedback loop for output voltage regulation and a faster loop regulating the power through the resonant tank. The design has been implemented in a protype and the paper shows test results with the pulsating power load of the system. The proposed approach provides the high performance needed for MRI. All the outputs are tightly regulated even with the large power transients and the soft switching ensures low losses for improved footprint.