High frequency resonant inverter for contactless energy transmission over large air gap

The paper investigates the influence of geometrical and electrical parameters on energy transmission through air gaps of several hundred millimetres. The transferable electric power and the efficiency of magnetic assemblies with large air gaps can be considerably improved by using higher transmission frequencies in the range of several hundred kilohertz. Contactless energy transmission systems operate at resonance. With a proper choice of the resonance capacitors on the primary and secondary side, the contactless system represents an ohmic load for the primary inverter. Therefore switching events take place at zero current (ZCS) without auxiliary commutation elements, which is an important precondition for reaching higher transmission frequencies. For this application a special inverter was developed. The phase-shifted controlled bridge at the primary side is equipped with IGBT and freewheeling SiC Schottky diodes. Because of their ultra low reverse recovery charge, the operation behaviour is much better compared to fast Si diodes. The different switching events of the inverter with freewheeling SiC Schottky diodes are investigated in detail. An experimental arrangement transfers an electric power of 1 kW through an air gap of 300 mm. At a 100 kHz transmission frequency the overall efficiency, including magnetic and power electronic components, is greater than 80%.