Selective Harmonic Mitigation Model Predictive Control for Grid-Connected Converters Working With a Very Low Apparent Switching Frequency

This article proposes a Selective Harmonic Mitigation Model Predictive Control (SHM-MPC) strategy for grid-connected converters working with a very low apparent switching frequency. A three-level SHM pattern in accordance with grid-code standards, a variable sampling-period hardware implementation, and an improved problem formulation are realized, which respectively comply with the IEEE 519-2022 standard limits, adapt to grid-frequency variations, and minimize real-time processing requirements. The proposed solution is experimentally validated on a scaled-down grid-connected three-level Cascaded H-Bridge (3L-CHB) converter working at 350 Hz and compared against a standard problem formulation. The results indicate that the proposed solution is feasible, the algorithm can be solved in real time, and it can be implemented on a Digital Signal Processor (DSP), while emphasizing the impact of grid frequency variability. These results are further illustrated in a supplementary video containing all the experimental tests, demonstrating that operating with a very low apparent switching frequency, combined with a distorted and variable grid, imposes hardware design restrictions that must be considered in the problem formulation to enable implementation without degrading either the current harmonic spectrum or the THD.