Generalized solutions for THD investigation in cascaded multicell multilevel converters modulated with selective harmonic elimination PWM switching method

This paper presents the generalized solutions for nonlinear equations of pulse-width-modulation (PWM) switching technique in the cascaded multicell multilevel converters which are modulated under the selective harmonic elimination (SHE) method. The provided solutions are used to explore the total harmonic distortion (THD) of line-to-line voltages in three-phase cascaded multilevel converters. First, PWM nonlinear equations for eliminating an specific harmonics from line-to-line voltages of three-phase cascaded multilevel converters are solved numerically using Newton iterative method. This solution provides an specific switching angle set for a cascaded multicell multilevel converter utilized at a definite modulation index. Afterwards, modulation index is changed to get a new (updated) nonlinear equation with a new possible solution set. This results in all feasible generalized solutions for switching angles. Next, numerically derived feasible solutions are used to explore the THD of the line-to-line voltages in the cascaded multilevel converters having different harmonic contents. In some cases, simulation results are presented to verify the derived switching angles for eliminating specific harmonics.