Sinusoidal Based Step Pulse PWM Method in Cascade Multilevel Inverters

Recently, an on-line step pulse PWM method has been introduced for cascade multilevel inverters. The simplicity of this method was derived from the principle control between two defined trajectories. For achieving good output performances, several exact angular sets are needed to be determined in advance by solving the trigonometric equations. If the number of step levels increases, then solving the transcendental equations for exact solutions may be quite difficult. This paper introduces a simple method to overcome the previously mentioned problem while number of step pulses is high. The principle control between two defined angular trajectories will again be used to obtain a linear control characteristics of fundamental voltages for the entire modulation index, including over modulation and the corresponding limit angular trajectories will be deduced appropriately from sinusoidal reference. The method will be mathematically formulated and validated. Some simulation results will be also presented.