Passivity-Based Cascade-Free Finite-Set Model Predictive Control for Nested Neutral Point-Clamped Converters

This paper focuses on a novel passivity-based cascade-free finite-control-set model predictive control scheme (CFFCS-MPC) for nested neutral point-clamped converters (NNPCs). It can be realized by combining an FCS-MPC and a passivity-based dynamic reference design point of view, which is responsible for controlling the multi-objective optimization control problem based on a cascade-free structure without weighting factors. However, it is of importance to highlight that, due to the existence of a large number of switching combinations and redundancies, the online computational effort will be increased by employing the proposed CFFCS-MPC approach, especially for higher-level power converter topologies. To solve this issue, a simplified computational scheme is presented by introducing the passivity-based dynamic reference concept into the design of sector distribution method. Alternatively, a simplified cost function based on the reference output voltage-vector tracking error is embedded into the proposed design. The merits of the proposed solution summarized as follows: 1) Enhanced system robustness; 2) no weighting factors; 3) high dynamics; and 4) low computational complexity. Finally, the proposed methodology is verified analytically and confirmed by comprehensive results that prove the theoretical investigations.