A Single-Phase Six-Switch AC-AC Converter With Highly-Efficient Bipolar Buck and Boost Operations

This paper proposes a highly-efficient bipolar buck boost AC-AC converter featuring a reduced number of active switches. By employing only six active switches, the proposed converter facilitates efficient symmetric-bipolar buck and boost operations, characterized by lower component voltage/current stress and ripples, features absent in existing AC-AC converters. Additionally, the converter offers the capability to adjust the output voltage frequency in discrete steps. Moreover, it employs only two inductors and filter capacitors, thereby providing second order input and output filters. Consequently, the converter ensures a continuous and low-ripple supply of input/output currents while eliminating the need for additional LC filters. Furthermore, due to the absence of bidirectional AC switches, the proposed converter mitigates device voltage or current overshoots during switching transitions, thus avoiding commutation issues without the necessity for lossy snubbers or safe-commutation algorithms. The paper explains the circuit operations of the proposed converter, based on developed PWM switch modulations, deriving various theoretical relations, and discussing component design. A comprehensive comparative evaluation against state-of-the-art bipolar AC-AC converters proves its superiority in terms of smaller voltage/current and power ratings of switching devices, reduced voltage/current ripples of passive components, minimized volume of passive components, and improved power conversion efficiency. Finally, experimental results from a laboratory-built prototype validate the theoretical analysis.