Analysis and design of a series resonant converter with wide operating range and minimized transformer ratings

This paper is introducing a new method of operation for a series resonant converter, with intended application in megawatt high voltage DC wind turbines. Compared to a frequency-controlled series resonant converter operated in sub-resonant mode, the new method (entitled pulse removal technique) allows the transformer design to be determined by peak load and maximum switching frequency, while still avoiding over-excitation at reduced load and reduced excitation frequency. This promises transformer size reduction of more than 50%, while losses are kept below 1% from zero to nominal power. A step by step design procedure is proposed and circuit component ratings and efficiency are compared for two variants.