A Comparative Study of Total Harmonic Distortion in Multi-Level Voltage Source Inverter

Reduction the harmonic contents in the output voltage waveform of the Voltage Source Inverter (VSI) is of primary concern. Different control strategies were developed to reduce the harmonic contents of voltage waveform. In this context, pulse width modulation (PWM) control strategy is well known. Unfortunately, its output controllability is limited since the modulation index and the chopping-to-supply frequency ratio, which are the only control parameters, have fixed values. In this paper, a multi-level voltage source inverter with improved harmonic elimination capability is presented. The output voltage waveform is developed through a multi-stage dc link. The performance and the total harmonic distortion of the proposed design are compared for different number of output voltage levels. Moreover, a comparison is also made with a sinusoidal-pulse-width-modulation (SPWM) inverter. Results show that the inverter presented, when compared to conventional multi-level counterparts and to that using SPWM technique, provides lower value of the THD factor. In addition, increasing the number of the voltage levels of the proposed inverter circuit reduces further the THD factor of the output voltage waveform.