Small-signal equivalent circuit model of series resonant converter

A simple third-order equivalent circuit model of series resonant converter (SRC) is proposed in this paper. Up to now, the most successful equivalent circuit model of SRC is based on extended describing function concept, which is proposed by Dr. E. Yang [30]. However, the equivalent circuit is a complicated fifth-order circuit with the cross-coupling effect and no analytical solution is provided for transfer functions. This paper proposes a methodology to simplify the fifth-order equivalent circuit to a third-order equivalent circuit. The equivalent circuit model can predict the dynamic behavior very well when switching frequency is below, close to or above resonant frequency. Furthermore, for the first time, analytical expressions of transfer functions are provided to serve as a useful tool for feedback design. The equivalent circuit model is verified by Simplis simulation and experimental results.