FCS-MPC with PNSC reference generation method for a 3L-NPC inverter under grid faults

Nowadays, grid faults consist anxious problem for grid inverters controller design. Conventional controllers are based on linear regulators such as PI and PR. This paper proposes a model predictive algorithm based on PNSC reference generation method to control the 3L-NPC inverter under grid voltage sags. The novel algorithm allows the easy inclusion of system nonlinearities, thus no additional fine tuning parameters are required. Moreover, no additional phase-locked loop synchronization technique is needed, reducing system complexity. A SOGI filter is added for voltage sequences extraction. The overall discrete model of the system is developed. Two-step horizon MPC algorithm is introduced for time delay compensation. Simulation results show the advantages of the proposed technique in terms of low harmonic line current content, low switching frequency operation, DC voltages balancing, good dynamic response and robustness to grid sags.