Modeling and digital control of a phase-controlled series-parallel resonant converter

A nonlinear model for a phase-controlled series-parallel resonant converter is developed using the extended describing function method and d-q decomposition. The model is linearized and reduced using the balanced model reduction technique. Based on the reduced model and taking into account the zero-order hold delay and the computation delay in the sampled-data system, a digital controller for the converter is designed. The controller is implemented with a digital signal processor (DSP). The closed-loop converter with the DSP controller is built and tested experimentally. Recorded transient waveforms show that the closed-loop converter is capable of not only responding to the reference input change as required by the design specifications, but also stabilizing the output effectively under disturbances from both the output and the input.