PUC Converter Based on AC-DC-AC Multilevel Topologies With a Shared Leg

In this paper, a single-phase ac-dc-ac multilevel configuration based on packed u-cell (PUC) is investigated. The system consists of a four-leg module with a u-cell connected to the shared part of the system and a low-frequency transformer at the grid side. The proposed converter allows one to compensate for grid voltage sags and swells, and to provide a high power factor at the grid side with low harmonic content. Besides, the proposed converter can operate with minimum dc-link voltage values in applications in which the grid and load frequency are the same, such as unified power quality conditioners (UPQC). The proposed configuration is compared to the conventional single-phase four-leg UPQC regarding the amount of power processed by the transformer, rating of semiconductor devices, harmonic distortion, ac-filter size, and semiconductor power losses. The system model, the operational constraints, the power distribution analysis, the overall control system strategy, and a space vector pulse-width modulation that exploits a simplified carrier-based approach are presented. Simulation and experimental results are provided to prove the viability of the system.