A polynomical model to calculate steady state set-point in the PRC-LCC topology with a capacitor as output filter

The behaviour of the series parallel resonant converter, PRC-LCC, with a capacitor as output filter is analyzed when operating on the optimum switching line. A polynomial is deduced to quickly compute what switching frequency and duty cycle are necessary at the control to obtain the desired output voltage and power in the converter. This polynomial is so simple that it is suitable for being implemented in low cost digital processors. It could provide, for instance, a start up strategy guiding the power supply to a known set point; or it could generate alarms if currents or voltages measured are larger than expected. In the paper, the steps to obtain such a model are described in detail. As an example, the coefficients of the polynomials are deduced when the series and the parallel capacitor are the same. The grade of accuracy of the model has been demonstrated through experimentation on a prototype.