Optimum trajectory switching control for series parallel resonant converter

The series parallel resonant converter (SPRC) is known to have combined merits of the series resonant converter (SRC) and parallel resonant converter (PRC). However, the presence of a three-element LCC structure makes the SPRC´s transient dynamics complex and its quick control difficult. This paper provides an analysis and a solution for this problem. It firstly presents the SPRC dynamics using the state-plane analysis technique and then provides a method to derive the optimal trajectory during transients for the SPRC. The method minimizes the transient response of the SPRC to within one switching cycle by deriving two optimal switching instances. The derivation of the optimal state trajectory during transients for the SPRC is described. Simulation results validate the method and show significant improvement in transient response compared to that of a step change in frequency control.