Three-Phase Four-Wire Transformerless Unified Power Quality Conditioner Based on Single-phase and Three-Phase Cells

This paper proposes a three-phase four-wire transformerless unified power quality conditioner (UPQC). Comprising three single-phase cells and a three-phase cell, this configuration enables power exchange across different converter phases and, consequently, allows the balancing control of the dc-link voltages in unbalanced scenarios. Compared with conventional transformerless solutions, the proposed converter offers some advantages. It can operate with power unbalances in the load, does not require open-ended connections, and can compensate voltage sags without requiring dc sources. The converter model, pulse-width modulation (PWM), and control strategy are presented, as well as simulation results and experimental results to validate the feasibility of the system.