Development of 50-kV 100-kW Three-Phase Resonant Converter for 95-GHz Gyrotron

This paper describes the development of a 50-kV 100-kW cathode power supply (CPS) for the operation of a 30-kW 95-GHz gyrotron. For stable operation of the gyrotron, the requirements of CPS include low output voltage ripple and low arc energy less than 1% and 10 J, respectively. Depending on required specifications, a three-phase series-parallel resonant converter (SPRC) is proposed for designing CPS. In addition to high-efficiency performance of SPRC, three-phase operation provides the reduction of the output voltage ripple through a minimized output filter component that is closely related to the arc energy. For allowing symmetrical resonant current from three-phase resonant inverter, the high-voltage transformers are configured as star connection with floated neutral node. This facilitates balanced voltage on each secondary winding. In addition, distinctive design of the high-voltage rectifier is introduced, taking into consideration the effective series stacking of diodes by means of the parallel resonant capacitor. In particular, the implementation of the high-voltage part including transformer and rectifier is presented in detail. For providing high power density and high reliability, effective methods for winding the high-voltage transformer and stacking rectifier diodes are discussed. Finally, the developed CPS achieves 95.5% of maximum efficiency, 0.92 of maximum power factor, 500 W/liter of power density, 0.6% of output voltage ripple, with 8.3-J arc energy.