Simultaneous voltage unbalance compensation and neutral-to-ground voltage minimization for an islanded mini-grid using model predictive control

This paper presents a model predictive control (MPC) and its application on a three-phase four-leg inverter in an islanded mini-grid to compensate for unbalanced load conditions while minimizing the neutral-to-ground voltage (NGV). The proposed approach uses the novel discrete-time model of the four-leg inverter and LC filter to predict the control variables. These predictions are evaluated by using a multiobjective cost function. The proposed method is based on the minimization of the cost function to select the best vector state of the power converter to be applied in the next sampling instance. The cost function in this study has two objectives: the adequately tracked low voltage reference and minimization of the NGV, simultaneously. The stability analysis is also defined to investigate the stable dynamics of the proposed MPC. The effectiveness of the suggested method is verified through simulations considering the single/three-phase and balanced/unbalanced loads. The distinguished results of the proposed work indicate that the proposed MPC algorithm provides high power quality under unbalanced and nonlinear load conditions with high stability. The robustness of the proposed controller is also studied with both inductive and capacitive filter parameter variations.