Rapid push pull resonant charger for high power, high voltage applications using low input voltage

This paper presents a novel approach to rapid, high power, high voltage capacitor charger that is fed from low voltage input source and achieves high efficiency in small dimensions. The charger is based on parallel resonant push-pull topology. Output current of the proposed charger is shown to be approximately constant regardless of the rising output voltage. The charged capacitor is fed by a linearly rising power profile. The behavior differs from series resonant and flyback charger topologies where output capacitor is fed by linearly decaying and constant power, respectively. The parallel resonant topology enables charging from a low voltage source using a relatively low transformer winding ratio, in one stage. The proposed charger is controlled by the digital controller dsPIC33FJ16GS502 (Microchip USA). Zero current soft switching is performed using a varying switching frequency based on continuous controller calculations during charging. Feasibility of the proposed charger and its control were tested experimentally on a prototype charger, which was operated at 0.7kW from a low input voltage source of 28V. The charger was loaded by an output capacitor of 250nF, which was charged at the rate of 600 charging cycles per second to 3kV. Good agreement was found between the proposed analytical model and experimental results.