A single-phase quasi-Z-source AC-AC converter with high-frequency transformer isolation

Abstract

AC-AC converters based on Z-source networks have some unique advantages such as; provision of a wide range output voltage with both step-up and step-down capability, reversing or maintaining phase-angle, reducing the inrush and harmonic currents, and enhanced reliability. However, these existing Z-source ac-ac converters are non-isolated, and therefore, they need external bulky line frequency transformer for electrical isolation and safety for applications such as dynamic voltage restorers (DVRs) etc. This line frequency transformer has some demerits such as high cost, large size, relatively high losses, saturation and start up inrush current. To overcome these drawbacks, new type of quasi-Z-source ac-ac converter is proposed with high-frequency transformer for electrical isolation and safety. The proposed high-frequency transformer (HFT) isolated qZ-source ac-ac converter sustain all the aforementioned benefits of its existing non-isolated counterparts, and additionally, the HFT eliminates the need for bulky line frequency transformer which enhances the power density and efficiency, and reduces the cost of the system. Circuit topology and analysis of the proposed qZ-source ac-ac converter with HFT isolation is given, followed by the experimental results.