Simplified Finite-Set Model Predictive Control for Full-Frequency Operation of Five-Level Nested Neutral-Point-Clamped Inverters

This paper proposes a simplified finite-set model predictive control (FS-MPC) algorithm for full-frequency operation of five-level nested neutral-point-clamped (5L-NNPC) inverters. Compared to the existing FS-MPC of 5L-NNPC inverters, the proposed algorithm substantially reduces the computational burden and simplifies the tuning of the weighting factor while ensuring low current harmonics and full-frequency capacitor voltage balance. The full-frequency operating conditions that the candidate set should satisfy are first acquired considering the periodic characteristics of the capacitor voltages. On this basis, a computationally efficient varying candidate set selection method is proposed for high-frequency operation, while a simple compensation set is introduced for low-frequency operation. Besides, an online approach is proposed to calculate available switching states for different candidate sets, eliminating tedious offline pre-processing. Furthermore, a staged cost function evaluation method is presented to further simplify the computation. Experimental results validate the proposed algorithm.