Family of single-phase isolated highfrequency transformer integrated improved magnetically coupled Z-source ac ac converters

This study proposes single-phase improved coupled-inductor (CL) Z-source (ZS) ac ac converters with integratedhigh-frequency transformer (HFT) isolation. They can provide wide range of buck boost voltage with same/reversed phaseangle, similar to the existing ZS ac ac converters. Meanwhile, integrating a HFT with CL in proposed converters benefit in twofold: (i) the CL enhances the voltage gain, which in turn reduces the voltage stresses/ratings of active switches. Moreover, theturns ratio of CL add another degree of freedom to gain adjustment beside the duty ratio; (ii) the HFT (20 kHz) is integrated withCL by adding only one winding to the same magnetic core, which provides electrical isolation for applications such as dynamicvoltage restore, saving extra bulky line frequency (60 Hz) transformer. In addition, the proposed converters provide bothcontinuous input/output currents. The commutation strategy is also implemented to eliminate the switch voltage spikes. Aproposed HFT isolated improved three-winding δ-CL ZS (δ-ZS) ac ac converter is introduced at first, and its operation, circuitanalysis and component design/selection are discussed in detail along with comparisons with counterpart converters. Variousdifferent CL structures based proposed HFT isolated ZS ac ac converters are presented afterwards. Experimental results on200 W prototype converter are provided finally to verify their merits.