Series resonant converter control: stability and robustness induced by using standard regulators

The authors deal with the closed-loop behaviour of frequency controlled DC-DC series resonant power converters using standard regulators. A preliminary study, using a small signal modelling method, pointed out that the dynamic behaviour of this converter strongly depends on the operating point. This work revealed different behaviour areas, whose boundaries are a function of the ratio between the output filter and the resonant circuit capacitors. The authors propose to use these results to determine a control structure considering the type of specifications which implicitly precises the operation zone. A theoretical study allows one to predict the evolution of the closed-loop performances in the presence of a varying operating point. In particular, the apparition of instabilities is explained. Thus, the robustness and the limits of this linear control are evaluated, yielding general rules to select the adapted regulator in view of the desired closed-loop performances. These theoretical results are compared to experimental studies