Highly-Efficient Three-Level AC-AC Converter with Identical In-Phase and Anti-Phase Buck-Boost Operations

In this paper, a new coupled-inductors based three-level bipolar buck-boost ac-ac converter is proposed. The proposed converter can produce highly efficient and symmetric in-phase and anti-phase buck and boost modes of operation with much lower component voltage and current stresses. This reduces the operation and design complexity, and helps to achieve a high-efficiency operation. The high-frequency modulating switches of proposed converter are implemented with coupled-inductor based dual-buck phase-leg, producing three-level input and output voltages, and providing inherent protection from voltage-source short-circuit issue during switch transitions. The other salient features of the proposed converter are no-commutation issue, no need of RC snubbers or dedicated safe-commutation algorithms, provision of high-quality and continuous input/output currents, and support for non-resistive loads. An in-depth circuit analysis of the proposed converter is provided based on proposed switch modulation strategies. The guidelines for component design/ selection are discussed, followed by the comparisons with state of the art three-level ac-ac converters. Finally, practical circuit verifications are performed on a laboratory assembled prototype.