A Single-Phase Four-Switch Symmetric Bipolar Buck–Boost AC–AC Converter With Continuous Input Current and Simple Commutation Process

Single-phase bipolar ac–ac converters are increasingly popular owing to their applications in series voltage regulation and step-controlled frequency systems. However, existing asymmetric bipolar ac–ac converters suffer from limited operational ranges with uneven component stresses, complex design, and control. While symmetric bipolar ac–ac converters can relieve these issues, they typically demand a significant number (≥5) of controlled switches. This article introduces a new symmetric bipolar buck–boost ac–ac converter with a smaller switch count. The proposed topology employs only four controlled switches, along with a smaller energy-storing component count, and provides an identical bipolar output with a symmetric buck–boost voltage gain of ±D/(1 − D). The developed converter maintains continuous input current with a smaller harmonic profile, eliminating the need for an additional input LC filter. It features a straightforward commutation process, saving the demand for snubber circuits or complex commutation methods, thereby simplifying circuit design and control while enhancing robustness. The detailed circuit operation of the developed converter is explained with the proposed switch modulation schemes, and various theoretical findings are presented. Thorough comparisons, including the average and peak switching device powers ($\mathbf{S}\mathbf{D}\mathbf{P}_{\mathbf{a}\mathbf{v}\mathbf{g}}~ \mathbf{and}~ \mathbf{SDP}_{\mathbf{pk}}$), confirmed the superior semiconductor device performance of the proposed converter with reduced power rating, cost, losses, and thermal requirements. The theoretical findings are finally validated on a 400-W prototype circuit.