An Expandable Buck-Boost AC–AC Converter With Few Components, Wide Step-Down Conversion Ratio, Continuous Input Current and Common-Ground

Abstract

This paper proposes a new non-isolated single-phase buck-boost AC–AC converter with a reduced number of active and passive components and an improved buck-boost conversion ratio. The extension of the proposed circuit is also presented, which can generate a symmetric-bipolar buck-boost voltage. The converter achieves a wide step-down operating area due to the appropriate use of a coupled inductor, where small duty ratios are needed to obtain low step-down conversion ratios. This not only improves the efficiency but is also ideal for mitigating deep voltage sag/swell in applications such as a dynamic voltage restorer (DVR). Two out of four power switches used operate at high frequency in each input voltage half-cycle, while the other switches ensure safe commutation, which significantly reduces the switching losses compared to similar circuits. In addition, the topology has better total switch voltage stress (TSV) and switching device power (SDP) indexes than its competitors. The total volume of magnetic elements has also been improved. The converter ensures input current continuity using an input inductor and eliminates the need for additional harmonic filters. Due to its common-ground feature, a bulky line-frequency transformer can be eliminated when used in series with loads in applications such as a DVR. This article explains the operating principle of the proposed topology and evaluates its performance using a hardware prototype. Results verify the converter's operation and its superior features.