Analysis of voltage output LCC resonant converters, including boost mode operation

A novel methodology for the high-speed analysis of LCC voltage output resonant power converters is presented. Termed rectifier transformed fundamental mode analysis, the procedure employs describing functions for determining equivalent passive circuit models for the combined rectifier, output filter and load circuitry. The resulting passive network is then used to predict voltages and currents throughout the converter. A refinement algorithm is also described that further enhances the accuracy of the analysis. Unlike previously published techniques, the proposed procedure is shown to accurately predict converter operation in the boost mode; a mode that normally requires the incorporation of an additional step-up transformer to realise output voltages that are higher than the input voltage in the converter topology under consideration. The accuracy of the procedure, and the enhancement that results from the refinement process, is demonstrated by comparing predictions of the maximum output voltage of LCC converters as a function of load, and the regulation at a fixed switching frequency as a function of the parallel rectifier capacitance with measurements from prototype converters, including operation in boost mode. The results confirm that the methodology is capable of correctly predicting the steady-state behaviour of voltage output LCC series resonant converters, particularly around the resonant frequency where previously published techniques can exhibit significant error.