Five-Leg Single-Phase Transformerless Unified Power Quality Conditioner

This paper proposes a transformerless single-phase unified power quality conditioner (UPQC) consisting of a three-leg converter and a hybrid shunt converter. The proposed system provides grid voltage compensation for both sags and swells while simultaneously maintaining a high grid-side power factor with low harmonic content. The system operates with a high modulation index during rated conditions and grid voltage sags. Compared to the conventional single-phase three-leg UPQC, the proposed configuration offers advantages regarding required semiconductor device ratings, harmonic distortion, and power losses. The paper presents the system model, a simplified carrier-based space vector pulse-width modulation scheme, operational constraints, and overall control strategies. Simulation and experimental results are addressed to validate the feasibility of the proposed system.