A Single-Phase Reduced-Switch Bipolar Buck–Boost AC–AC Converter With Continuous Input/Output Currents and No Commutation Issue

This article develops a new single-phase bipolar buck-boost ac-ac converter with only five switches. The proposed topology can offer symmetric in-phase and antiphase buck-boost voltage operations, along with discrete frequency control achieved through stepwise increments or decrements of the output voltage frequency. It utilizes an input-side switch for voltage boosting, and four output-side switches configured as an H-bridge module provide both voltage buck and polarity shaping functions. In the proposed operations, four output switches of the converter form two parallel paths during high-current stress intervals, relieving switch current stresses, reducing switch conduction loss, and easing thermal management. In addition, it can provide both continuous supply and load currents, ensuring high-quality input and output powers without requiring additional LC filters. The proposed converter naturally achieves safe commutation, as it does not use the bidirectional ac switches of conventional ac-ac converters. Therefore, it is more robust without the need for RC snubbers or a safe commutation algorithm. The proposed converter with bipolar buck-boost outputs can be utilized as a dynamic voltage restorer (DVR), while its step-variable frequency operation is applicable in high-gain rectification and traction systems. This article analyzes the circuit operation in all modes, provides component design guidelines, and offers extensive comparisons. At last, experiments on a 400-W circuit were performed to validate the theoretical claims.