An Isolated SEPIC-Based AC-AC Converter for Voltage Sag/Swell Mitigation

Abstract

This paper proposes a high-frequency isolated buck-boost AC-AC converter based on the single-ended-primary-inductance-converter (SEPIC) topology and its extension circuit with bipolar output. The proposed converters can achieve a wide range of voltage step-down and step-up operations with both same- and reversed-phase outputs. All configurations ensure low harmonic input current and are fully compatible with non-unity power factor loads. Comparisons with counterpart converters demonstrate that this topology outperforms in terms of inductor volume metrics, total switch voltage, and power switch utilisation factor. Unlike most counterparts, only one of the four power switches in the proposed topology operates at a high frequency in each voltage half-cycle, minimising switching losses and enhancing efficiency. Additionally, snubber circuits are eliminated, ensuring spike-free operation for power switches. The proposed bipolar output converter can be easily connected in series with the load as a dynamic voltage restorer without a line-frequency transformer. The topology benefits from continuous input current and regular operation with inductive loads. In this article, theoretical analysis is presented and supported by laboratory hardware verification. A 250W prototype has been built and tested as a dynamic voltage restorer (DVR). Results confirm the operation of the converter and demonstrate its capability to mitigate deep voltage sags/swells (≥ 50%) due to high-gain operation.