Modeling and Verification of the State Space Equation for an Isolated Series Resonant Converter

Resonant converter due to implementation of zero voltage switching (ZVS) or zero current switching (ZCS), are very interested. Although using these techniques, increases the efficiency and also decreases the generated EMI noise, obtaining the small-signal model of these converters is very complicated. The state-space variables mostly change as a sinusoid curve, so the average of these variables is equal to zero. Therefore the traditional method such as state-space averaging is not applicable in order to obtaining the state space equation of the converter. In this article, the state space equation is obtained by using the extended describing functions. To verify the obtained equation, the Middlebrook method is suggested. By means of this method, the bode-plot of the open-loop transfer function could be obtained based on the existing hardware. So an isolated series resonant converter is implemented and the required signals are measured in order to draw the bode-plot of the open-loop transfer function based on Middlebrook method. Verification is performed by comparing the experimental results with simulation results.