AC-DC-AC Single-Phase Multilevel Converters Based on Three-Leg Modules Cascaded-Connected Through Transformers

This article investigates a family of single-phase ac-dc-ac multilevel converters that are capable of mitigating sags/swells and voltage harmonics in the grid supply, ensuring regulated load voltage (with fixed amplitude and frequency), and grid current with high power factor and low harmonic content. Thus, the converters are suitable to operate as a unified power quality compensator or uninterrupted power supply. The proposed topologies are composed of three-leg (3L) modules cascade-connected through transformers at the grid side. From the generalized model presented, topologies with two and three 3L modules are discussed. System equations, PWM strategies, and a control system are developed. Compared with the conventional one, the proposed topologies present better results in terms of harmonic distortions, semiconductor losses, and switching frequencies. Simulation and experimental results in different load conditions are provided to validate the feasibility of the system under grid disturbances and load transients.