Analysis of THD for Multilevel Inverters with Novel Pulse Width Modulation Techniques

Abstract

Multilevel inverters are preferred to deliver necessary A.C voltages from D.C voltages. The required A.C voltage can be delivered by controlling the inverter with appropriate pulse width modulation technique. The major problems with inverters are total harmonic distortion and utilization of de-link voltage. Lot of research has been happening to improve the performance of inverters by using latest PWM techniques such as carrier based Sinusoidal PWM and Space Vector PWM. But the implementation of Space Vector PWM is very difficult for multilevel inverters. This paper gives the harmonic analysis of Cascaded H-bridge Multilevel Inverter (CMLI) and Diode Clamped Multilevel Inverter (DCMLI). By applying suitable Pulse Width Modulation Technique, the performance of these multilevel inverters can be improved. Different modulation strategies such as carrier-based Sinusoidal Pulse Width Modulation (SPWM) and a novel Third Harmonic Injected Pulse Width Modulation (THIPWM) are used. These modulation strategies include Phase Disposition, Phase Opposition Disposition, Alternate Phase Opposition Disposition and Phase Shifted Carrier. The triangular and trapezoidal triangular waves are considered as carrier waves. The THIPWM technique can be applied in overmodulation range also by changing the magnitude of sinusoidal wave. The simulations have been carried out for eleven-level CMLI and seven-level DCMLI using MATLAB/Simulink. The detailed performance analysis in terms of %THD and utilization of de-link voltage are presented.