An Isolated Identical Bipolar Buck-Boost AC-AC Converter With Step-Changed Frequency Operation and Reduced Active and Passive Components

This article introduces a novel buck-boost ac-ac converter with identical bipolar operation and high-frequency voltage isolation. The proposed converter offers several distinguishing features compared to existing isolated converters: First, it provides a significant reduction in the number of active and passive components. Second, it supplies continuous input and output currents with low harmonic contents. Third, it provides bipolar output with a two-winding transformer (instead of a three-winding transformer) with enhanced magnetic utilization and reduced cost and footprint. Finally, it can operate with different winding coefficients without compromising buck-boost functionality or limiting its magnitude coverage. Additionally, the converter facilitates buck-boost operation for all transformer winding ratio values, making it suitable for shallow and deep voltage sag/swell mitigation. The integration of a high-frequency transformer eliminates the need for a low-frequency coupling transformer. The proposed converter can provide a step control of output voltage frequency and performs normally under inductive and nonlinear loads. This article provides a detailed description of the proposed topology operation and its analysis, succeeded by experimental validations conducted on a laboratory-built converter, showcasing a peak efficiency of 93.3%. Extensive comparisons affirm that the proposed converter exhibits reduced input/output total harmonic distortion, broader voltage gain coverage, and superior efficiency compared to recently developed converters.