An Improved Finite Control-Set Model Predictive Control for Nested Neutral Point Clamped Converter

Abstract

This paper presents an improved model predictive control with a finite control set (IFCS-MPC) for a four-level nested neutral point clamped (4L-NNPC) inverter. Controlling flying capacitors (FCs) voltages of 4L-NNPC, especially at low output frequency, is a challenging issue. In the proposed method, the control objectives of 4L-NNPC (current, FCs voltages, and switching losses of power devices) are formulated in terms of FCS-MPC. Furthermore, a computational burden reduction technique is introduced that reduces the search space from 216 to 96 switching states for a three-phase system. In addition to the current control, the proposed control method has the ability to control FCs voltages in the entire operating frequency range and also decreases the switching losses of the converter in comparison to the alternative methods. Also, it offers a lower computational burden than conventional FCS-MPC, which is of importance in implementation of MPC. The performance of the suggested method is verified on a 4L-NNPC in MATLAB/SIMULINK. Also, the experimental results are carried out based on a scaled-down hardware prototype validating the theoretical claims.