Research on FCS-MPC Strategy with Peak Current Limitation for Fault-Tolerant NPC Three-Level PV Grid-Connected Inverter Under Unbalanced Grid Voltages

For the problems of power fluctuation and over-current in grid-connected inverters under unbalanced grid voltage, a fault ride through control strategy based on finite control set-model predictive control (FCS-MPC) with peak current limitation is proposed for fault-tolerant NPC three-level photovoltaic grid-connected inverter. Firstly, the current reference value is calculated with the goal of balancing the current, eliminating active and reactive power oscillations. Then, the quantitative relationship between the power reference set value and the peak output current value is deduced to guide the power reference value setting under unbalanced grid voltage. In addition, the grid-connected model predictive current control strategy based on the reference voltage cost function method is used to realize the accurate tracking of the reference current. Simulation results show that the proposed method can realize the control objectives of output current balance, active power constant, and reactive power constant under unbalanced grid voltage, and the current peak is limited effectively under the three control objectives.