Model Predictive Voltage Control Cascaded Adaptive Droop Method for Three-Level Micro Power Inverter in Islanding Operation

The power distribution effect of traditional (power-voltage-current) three-loop droop control method is seriously affected by the resistance inductance ratio of the line, and the voltage-current double closed-loop PI control has many parameters adjustment. To solve the problems, a model predictive voltage control cascade adaptive droop method is proposed. Firstly, the proposed method realizes the model predictive voltage loop control through cost function design, simplifies the original double closed-loop control system structure. Simultaneously, it can realize the balance of midpoint potential through the constraint of cost function. Secondly, virtual impedance is introduced to change the equivalent output impedance of the micro power inverter so as to reduce the reactive power equipartition error. Thirdly, an adaptive droop control method is designed to realize the adaptive compensation of the system frequency and voltage, and solves the problem of extra output terminal voltage drop caused by virtual impedance. Finally, the effectiveness and feasibility of the improved control strategy are verified by the simulation results.