Closed analytical model of a 20 kV output voltage, 800 W output power series-parallel-resonant converter with Walton Cockroft multiplier

A closed analytical model of an asymmetrically switched class D converter with series-parallel-resonant (LCC) tank and three-stage Walton Cockroft multiplier featuring output voltage adjustable from zero to 20 kV and a maximum output power of 800 W is presented. The converter circuit is briefly described. A model for the dynamic behaviour of the Walton Cockroft multiplier is developed via state space modelling in the discrete time domain, which then allows itself to be approximated as a low-pass filter with parameters that are a function of the converter operating point. The analytical model of the converter is based on the extended describing function and the generalised averaging technique. It is simulated using MATLAB and the results are compared to both simulation results using a switched model with SIMPLORER and measurements on the converter in operation. Agreements of simulated and experimental data support the models validity. The converter is controlled digitally with a Xilinx Spartan-3E FPGA.