Single-phase AC-DC-AC multilevel converter based on H-bridges and three-leg converters connected in series

This paper investigates an ac-dc-ac multilevel power converter. The studied configuration is composed of two single-phase ac-dc-ac three-leg modules and series-connected H-bridges in the shared part of system. The converter is employed in applications with same input and output frequency, such as uninterrupted power supply (UPS) and unified power quality conditioner (UPQC) without isolation transformer. Such multilevel topology has lower dc-link voltage rating, consequently, presents low switch blocking voltages when compared to conventional topologies. System model, an overall control strategy to adjust the system variables, and a space-vector pulsewidth modulation (SV-PWM) strategy to symmetrical and asymmetrical dc-link voltages is presented. PWM and control strategies are developed to reduce the semiconductor total losses, harmonic distortion and switching stress. Two ac-dc-ac multilevel conventional structures are used to comparison criteria. Simulation and experimental results demonstrate the feasibility of the studied converter.