Sliding-mode current control design for a grid-connected three-level NPC inverter

Three-level neutral point clamped (NPC) inverter topologies are becoming more and more the interest of studies, especially in grid connected systems, due to their advantages compared to other multilevel inverters. Synchronization with an AC source remains a challenge ring current injection to the grid. In order to enhance the performance and the immunity of such grid connected inverters, a sliding mode current controller based on Gao´s reaching law has been designed in this paper, and then applied to a three-wire three-level NPC inverter to have a unity power factor system. A PI regulator has been also employed to deal with the split DC-capacitors voltage unbalance problem. Robustness towards external disturbances was verified through simulations using MATLAB.