A single-phase isolated high step-down ac-ac converter with no commutation problem using switching cell and coupled inductor

In this paper, a high-frequency isolated buck ac-ac converter is proposed using switching cell structure and coupled inductor, which is immune to damaging of switching devices because of open or short circuit problem. The proposed converter does not require any lossy RC snubber or sensing the input voltage polarity for implementation of dedicated soft commutation strategy, to solve the commutation problem. Although the proposed converter adds two coupled inductors to solve the commutation problem, however, the size of the transformer and output inductor can be reduced significantly. Moreover, all the passive components experience twice the switching frequency, and the use of external fast recovery diodes allow to further increase the switching frequency, which can significantly reduce the passive component sizes. The proposed converter has no dead time needed in switching signals and therefore, can produce high quality output waveforms. Analysis of the proposed converter and its operation are explained followed by the experimental results.