Dual-Mode Operation of 3-Level 4-Leg AT-NPC Inverter for Microgrids

This study presents dual-mode operation and seamless transfer of 3-level 4-leg Advanced T-type Neutral Point Clamped (AT-NPC) inverter for low voltage microgrids. The proposed control technique is designed with Proportional Resonant (PR) based current controlled in grid-connected operation and with Proportional Multi Resonant (PMR) based voltage controlled in islanded operation. In order to ensure smooth transition between these operating modes, combined seamless transfer method is proposed. The proposed 3-phase 4-leg inverter system can supply both 1-phase and unbalanced 3-phase load groups in islanded mode. A laboratory prototype is installed for the experimental testing of the 3-phase 4-leg AT-NPC 3-level inverter system. The proposed system is simulated via PSIM software and the model-based embedded codes are generated with PSIM/SimCoder software. Real-time control algorithm of the inverter system is carried out with TMS320F28335 digital signal controller board. Finally, the operation performance of the inverter system is investigated both in the islanded/grid-connected mode and the seamless transfer process between these two operating modes.