Developed AC/DC/AC Converter Structure Based on Shunt Active Filter and Advanced Modulation Approach for Asymmetrical Cascade H-Bridge Multilevel Inverters

This article presents a free-harmonic ac/dc/ac converter structure using a novel modulation approach for asymmetrical cascade H-bridge multilevel inverter and, conventional rectifiers combined with a shunt active filter, for grid integration. The novel approach SMT-SHE combines two modulation techniques: the staircase modulation technique (SMT); and the selective harmonics elimination (SHE). SMT-SHE approach achieves a sinusoidal-like output stepping voltage with variable output voltage amplitude and free of wideband or/and specific harmonics to fulfill the sensitive loads’ specifications; by determining the appropriate SHE switching angles. The precalculated switching angles are optimized to minimize the number of H-bridge modules and lower the dc capacitor rating. Furthermore, a restriction on the switching angles is proposed to prevent the appearance of undesired harmonics (zeros, even) and, consequently, overcome the limitation of the SHE algorithm applicability. Finally, a real case study in the textile factory is conducted, using real measurements provided by power quality analyzer measuring devices, to validate the proposed ac/dc/ac converter supplying a sensitive load of 50 kVA, given by an asynchronous motor drive.