With the increasing unbalanced loads connect to the three-phase four-wire power system, three-phase unbalance caused by these loads will reduce the service life of electrical equipment and increase line loss. To solve these problems by reducing the three-phase unbalance, a three-level neutral point clamped compensator based on model predictive control strategy is proposed. Considering distorted point voltage of common coupling affects the performance of the compensator, fundamental positive-sequence voltage extraction is applied to eliminate the influence. Based on model predictive control strategy, a new method to track and compensate zero-sequence current is also proposed. Assumed zero-sequence output voltage of the inverter is used to predict the next period current. Compared with the values of the cost function generated by the 27 switching states, the optimal switching pattern that minimizes the cost function is selected for the next period control. The simulation results show the validity and accuracy of the strategy algorithm.

MODEL PREDICTIVE CONTROL,three-phase four-wire,network unbalance,neutral-point voltage balance,neutral point clamped