A novel robust control method for series parallel resonant converter (SPRC)

In this paper, a novel robust control method for the Series Parallel Resonant Converter (SPRC) is presented. Using a novel analytical tool that combines the state plane analysis and the theorem of superposition with added constraint due to the diode commutation condition for this third order non-linear system, the exact gain and frequency expression for the SPRC under the load-independent operation point can be obtained. Moreover, this method of analysis gives additional insight to the system dynamics and based on it, it is found that the diode commutation point (DCP) and transistor switching point (TSP) coincides when the SPRC operate at the load independent operation point. A control method that synchronizes the DCP and TSP is therefore proposed. Further analysis reveals that this simple control method is robust to the resonant parameters with the SPRC self-oscillating naturally at a fixed switching frequency determined by the values of the resonant parameters. To show the convergence of the SPRC under such control method, a stability analysis using the method of perturbation is presented. Finally, simulations results are presented to demonstrate the stability and robustness of the SPRC to the resonant parameters.