Dynamical modeling for series-parallel resonant converter under optimized modulation

The series-parallel resonant converter is one of the most popular topologies among resonant converters. In order to achieve a further reduction of transistor switching losses, an optimized modulation strategy was proposed and implemented full digitally. This yields zero-current switching on one full bridge leg and zero-voltage switching on the other leg. Costs of the optimized modulation are the increased complexities in modeling and controller design, because the state-of-the-art extended describing function method is not suitable anymore. In this contribution a novel dynamical modeling for series-parallel resonant converters under optimized modulation is presented, which is based on the sampled-data method. The dynamic interaction between power circuit and the digital optimized modulation control unit is considered properly. Duty-ratio-to-output-voltage small-signal behaviors predicted by the proposed model are verified by circuit simulation and experimental results.