Cascade-Free Fuzzy Finite-Control-Set Model Predictive Control for Nested Neutral Point-Clamped Converters With Low Switching Frequency

In this brief, a cascade-free fuzzy finite-control-set model predictive control (FCS-MPC) is proposed for nested neutral point-clamped converters with low switching frequency (SF). The main objective of the proposed method is to achieve a low SF operation. First, a new cost function is formulated to reduce the SF, and a fuzzy logic control (FLC) technique is employed to choose the weighting factors dynamically. As such, the FLC scheme has a good potential to avoid the constant of weighting factor for the conventional FCS-MPC strategy, especially in the presence of dynamic operation condition. Second, in order to enhance the dynamic response and improve the computationally efficient under low SF, a dynamic reference design with a simplified cascade-free strategy is embedded into the predictive controller. The novelty of this brief lies not only in combining the proposed cost function with the FLC technique for online determining the appropriate values of the weighting factors, but also in a compatible reference design that directly allows formulating the optimal control problem using a cascade-free structure. Finally, simulation results are presented for assessing the effectiveness of the proposed control strategy.