Carrier-based Closed-loop DC-link Voltage Balancing Algorithm for Four Level NPC Converters Based on Redundant Level Modulation

Four-level neutral-point-clamped (NPC) multilevel converter topologies have been proposed and actively studied for low/medium voltage applications. As an inherent issue with these topologies, the balancing of dc-link capacitors is challenging, especially when it operates as a single-end inverter/rectifier high power factors modulation indexes. This article proposes closed-loop algorithm that effective simple to implement regular level-shifted carriers four-level NPC converter, e.g., ?-type converter. approach based on redundant level (RLM), which utilizes one additional in switching cycle gain extra controllability capacitor voltages without distorting/undermining fundamental-frequency output voltage. An analytical expressions logical operations developed achieve dynamic RLM. The method over full span linear indexes (M = 0 ~ 1.15) factors. validated evaluated both simulations experiments.