Finite Control Set Model Predictive-Sliding Mode Control Based Strategy for 4-L NNPC Converters

In this article, an improved finite control set (FCS)-model predictive control (MPC) strategy for four-level nested neutral point clamped (4L-NNPC) converters is proposed. Compared with two-level converters, multilevel converters reduce output harmonic distortion, switching stress, and power loss. However, in the application of the traditional FCS-MPC strategy in multilevel converters, the number of states increases exponentially with the number of levels, resulting in an increase in the computational burden of the controller. This article proposes a cost function based on the sliding mode theory, which simplifies the current prediction model and reduces the computational complexity of a single optimization. A level prescreening mechanism is designed to reduce the number of switch states to be evaluated from 216 to 64, thereby reducing the number of optimization iterations significantly. The simulation and experimental results show that compared with the traditional FCS-MPC, the proposed strategy significantly reduces the computational burden, while achieving better power quality, and can maintain the capacitance voltage balance.