LAUSR

This study proposes single-phase improved coupled-inductor (CL) Z-source (ZS) ac–ac converters with integrated high-frequency transformer (HFT) isolation. They can provide wide range of buck–boost voltage with same/reversed phase angle, similar to the existing ZS ac–ac converters. Meanwhile, integrating a HFT with CL in proposed converters benefit in two-fold: (i) the CL enhances the voltage gain, which in turn reduces the voltage stresses/ratings of active switches. Moreover, the turns ratio of CL add another degree of freedom to gain adjustment beside the duty ratio; (ii) the HFT (20 kHz) is integrated with CL by adding only one winding to the same magnetic core, which provides electrical isolation for applications such as dynamic voltage restore, saving extra bulky line frequency (60 Hz) transformer. In addition, the proposed converters provide both continuous input/output currents. The commutation strategy is also implemented to eliminate the switch voltage spikes. A proposed HFT isolated improved three-winding Δ-CL ZS (Δ-ZS) ac–ac converter is introduced at first, and its operation, circuit analysis and component design/selection are discussed in detail along with comparisons with counterpart converters. Various different CL structures based proposed HFT isolated ZS ac–ac converters are presented afterwards. Experimental results on 200 W prototype converter are provided finally to verify their merits.