Fixed Frequency Model Predictive Control for Three-Phase VSR Under Unbalanced Grid Condition

Under the three-phase unbalanced grid condition, the commonly used controller design methods of three-phase voltage source rectifiers (VSR) are based on the instantaneous power model and the current and voltage double-closed loop control structure. The inner current loop proportional integral (PI) controllers are designed for the positive- and negative sequence current components, separately, therefore, there are eight mutual influenced control parameters need to be tuned, which is very complicated. In this paper, a current loop fixed frequency model predictive control (MPC) method is proposed for the three-phase VSR under the unbalanced voltage input condition. As compared to the traditional double-closed loop PI control structure based on the conventional instantaneous power model, the proposed method uses less control parameters with easy tuning rule, and simple control structure. The proposed current loop MPC control strategy can effectively restrain the active power oscillation and the current harmonics in both balanced and unbalanced grid input condition, which is proved by both simulation and experiment results.