This paper describes the design of a 20 kW (10kV, 2A) DC power supply using two stage control which consists of the silicon controlled rectifier (SCR) for input voltage control and the series-parallel resonant converter (SPRC) for output voltage control. In order to overcome the general constraint of SPRC, the restricted controllable load range with softswitching, the additional stage for adjusting input voltage by controlling the triggering angle of SCR is proposed and it facilitates the wide load range operation of SPRC with maintaining high-efficiency not only light-load but also rated operation. From the analysis of the controllable load range of SPRC with soft-switching, the control methodology of both switching-frequency of resonant inverter and triggering angle of SCR is explained. Based on the proposed control concept, a detailed design of a 20 kW power supply is provided including the PSpice simulation, the high-voltage transformer and the high-voltage rectifier. Finally, the experimental results which were carried out with various kinds of load condition verify the high-performance of proposed two stage control method from the view point of high-efficiency, wide controllable load range, and reliability.
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