Soft switching techniques to improve efficiency of a non-resonant HF link DC-AC converter

This paper presents some new ideas on high frequency (HF) link DC-DC or DC-AC converters. Simulation and experimental results will be presented in the case of the design of a DC-AC converter for driving wheel motors for an electric vehicle. The purpose of such an application is to boost energy stored in low-voltage batteries (or other energy storage system like fuel cells) to high-AC voltage output to feed permanent magnet brushless DC motors. In this direct conversion structure, transistors (IGBTs and MOSFETs) operate under soft switching conditions that is to say that this converter will present very low losses. Another advantage will be discussed with the HF link bus that permits the adaptation of voltage levels thanks to new planar technology for transformers. For the experimental test bench an 18kW DC-AC HF (20kHz) link converter has been designed to feed 400V brushless wheel motor with a low voltage simulated battery source of about 67V.