Model Predictive Control With Reduced Common-Mode Voltage Based on Optimal Switching Sequences for Nested Neutral Point Clamped Inverter

This article proposes a new model predictive control strategy with reduced common-mode voltage (CMV) based on optimal switching sequences (OSS-MPC) for a three-phase (3PH) four-level nested neutral point clamped (4L-NNPC) inverter. The proposed method controls load current, mitigates the voltage fluctuations of flying capacitors (FCs) in the entire operating frequency range, and provides a constant inverter switching frequency. In this work, the switching sequences (SSs) are configured so that the peak CMV is limited to $V_{dc}/6$. By involving time in the optimization process, the balance of FCs voltages is realized in the entire operating frequency, especially in low-frequency operating mode. Also, the voltage fluctuations of FCs are further mitigated through a mathematical-logic technique. To implement the proposed method on the digital signal processor, the deadbeat control technique is also used to reduce the search space, and thus, the computation burden. The performance of the proposed method is verified in MATLAB/SIMULINK. The experimental results are carried out based on a scaled-down hardware prototype validating the theoretical claims.