Constant frequency, constant current load-resonant capacitor charging power supply

A capacitor charging power supply incorporating a series-parallel load-resonant converter, operating at resonance at a fixed frequency and providing a constant load current, is presented. A series-parallel load-resonant converter containing three resonant components is shown to have three resonant frequencies. It is shown that one of the resonant frequencies can be independent of the load value. Furthermore such a converter can be designed to supply constant current to a load. The circuit characteristics enable the power converter to efficiently charge a capacitor bank with minimum control circuitry. The resonant converter can be operated at a single frequency throughout the whole capacitor charging cycle from 0V to 640V. A power supply is constructed which delivers up to 2.6kW to a large capacitor bank, charging the bank from 0 to 640V at a constant switching frequency of 83kHz. The power supply draws 0.9 power factor with no power factor correction circuitry.