Single-phase Transformerless Unified Power Quality Conditioner Based on Three-Leg Converter

This paper proposes a single-phase transformerless unified power quality conditioner (UPQC) based on an AC-DC-AC converter with a shared leg. The topology is composed of three two-level legs such that the leg directly connected to the grid positive terminal is shared by shunt and series converters. The system provides a unity power factor at the grid side with high power quality and feeds the load with a sinusoidal waveform in both voltage swell and sag events. Furthermore, a new decoupling method of the series and shunt converters allows operating with high modulation index during rated conditions and voltage sag events. System model, dc-link voltage specifications, pulse-width modulation (PWM) techniques, and overall control strategies are presented. Additionally, simulation and experimental results are addressed to evaluate the feasibility of the proposed system.