A High Voltage Variable Inductor LCC Resonant Converter with High Power Factor over Wide Load Range

High voltage power supplies (HVPS) are widely used to supply vacuum tubes. Regarding to their high efficiency, resonant converters are a choice of HVPS structure. In this application, HVPS is faced with wide variation of the load power. On the other hand, output voltage regulation over wide load range is essential. However, there are several problems dealing with resonant converters such as output voltage regulation and low-efficient performance in a light load. In this paper, a control scheme for a series-parallel resonant converter is presented. This scheme regulates the output voltage of the converter over load variation range. A variable inductor placed as the series inductor in the resonant tank achieves constant maximum power factor. Output voltage is regulated by phase-shift method and the switching frequency is constant. Experimental results are presented to confirm the proposed method.