Reduced Order Small Signal Modeling of Parallel Resonant Converter based on State-plane Analysis

Parallel resonant DC-DC converter operating in continuous conduction mode with variable frequency modulation is considered in this work. Existing techniques to arrive at the plant model of the converter relies on extended describing functions based approach which ignores the effect of harmonics and considers only the fundamental component. The proposed small signal modeling approach is based on the state plane analysis of the resonant converter which is exact and considers all the operating modes of the converter. In conjunction with basic averaging techniques used in Discontinuous Conduction Mode (DCM) of PWM converters, closed form expressions for the open loop control to output transfer function of the converter is derived. The closed form expressions are shown to be accurate upto (1/20)th of the switching frequency. Simulation and experimental data on a 5 kW prototype is presented to validate the analysis.