Single-Phase AC-DC-AC Multilevel Converter Using High-Frequency Link to Improve Power Quality

Abstract

This paper investigates a single-phase ac-dc-ac multilevel converter formed by a three-leg module series-connected to an H-bridge at the load side of the system to achieve higher and multilevel output voltage. Asymmetrical operation is also analyses to improve voltage quality and efficiency. But the main issue with this operation condition is to balance the dc-link voltages when floating capacitors are used. A different approach to the studied topology by using a high-frequency link (HFL) is proposed in this paper. The proposed system is appropriated for applications such as uninterrupted power supply and a unified power quality conditioner. System equations, dc-link voltage specifications, power distribution analysis, and a space vector PWM are discussed. The proposed system control ensures suitable load voltage with constant amplitude and frequency, guarantees unity grid power factor, and maintains constant and controlled the dc-link voltages. Compared with the conventional topology that uses floating capacitors, the proposed topology has lower dc-link voltage rating, lower harmonic content, and lower switching power stresses and losses per leg. Experimental results validate the studies.