Selective Harmonic Elimination Notch Angle Calculation Using THD and ZHF Benchmarks for Cascaded Multilevel Inverters

This paper presents a detailed comparison of eliminated and non-eliminated harmonics for 3-level, 5-level and 13-level cascaded multilevel inverter. For this research, three different types of cascaded H-Bridge multilevel inverters are considered where each cascaded multilevel inverter generates a different output voltage, but the number of notch angles in all the three cases are kept identical. A unified approach is adopted to derive the mathematical model of each multilevel inverter output voltage waveform, RMS of output voltage, RMS of fundamental component, selective harmonic elimination system of equations for the low order harmonics elimination and output voltage total harmonic distortion. It is shown that since selective harmonic elimination system of equations can be expressed as a function of the notch angles, hence notch angles are determined while taking in account only those harmonics to be eliminated. The Newton-Raphson method is proposed to resolve the nonlinear transcendental equations of selective harmonic elimination for the three multilevel inverter cases. Consequently, once the notch angles are determined, all three multilevel inverters are analyzed by comparing Total Harmonic Distortion and Zero-Sequence Harmonics Factor. The elimination of triplen-harmonics by evaluating them in the non-linear transcendental system of equations is a significant contribution. The theoretical and simulated results are presented to verify the validity of the proposed work.