AC-DC Single-Phase Multilevel Converters with Floating DC-Link and Reduced Controlled Switches

This paper presents the DC-link voltage balancing for two single-phase unidirectional cascaded multilevel rectifiers. They are composed of a cascaded connection of two power cells (H-bridges), whose the higher voltage one has a reduced number of controlled switches while the lower voltage cell is a floating bridge. An asymmetrical voltage ratio was employed in presented topologies, allowing to increase the number of voltage levels, and consequently, the power quality provided. Each leg is either a Neutral-Point Clamped (NPC) leg, which generates 3 voltage levels, or a 2-level leg. The Pulse-Width Modulation (PWM) strategy based on level-shifted carriers is presented. The double-band hysteresis technique and a PI controller with a Phase-Locked Loop (PLL) system are integrated into the PWM strategy to control DC-link voltages. Simulation and experimental results are presented to show the performance of the balance scheme.