Harmonic-Free AC/DC/AC Structure with Innovative Modulation Technique for Asymmetrical Cascade H-Bridge Multi-Level Inverter

This paper presents an advanced solution for AC/DC/AC converter structure using a novel modulation approach for Asymmetrical Cascade H-Bridge Multi-Level Inverter (ACHB-MLI). This solution improves the structure performance and power quality of the output stepping voltage to fulfill the smart industrial grid requirements. Besides, a harmonic-free structure is employed to ensure integration with the grid, using conventional rectifiers combined with a shunt active filter.The novel approach presents a combination of two modulation techniques: Staircase Modulation Technique (SMT) and Selective Harmonics Elimination method (SHE). This combined approach (SMT-SHE) achieves an output stepping voltage closer to the sinusoidal waveform and free of predominant harmonics by determining the appropriate SHE switching angles.SMT-SHE approach will minimize the THD ratio, eliminate specific harmonic ranks, and allow an output voltage amplitude variation according to load specifications. Moreover, switching angles’ limitations are proposed to prevent the appearance of undesired harmonics (zeros, even), while minimum number of H bridge modules with a lower rating of the capacitors is proposed.Finally, the proposed AC/DC/AC converter is validated on an industrial network for supplying a specific load and tested within a MATLAB environment.