A Proposed Technique for Harmonic Reduction of Three Phase Cascade Multilevel Inverter (CMLI)

Abstract

Inverters are widely used in many applications & the object of using the inverter is produce ac voltage with controllable magnitude & frequency. But the inverters where found in both the industrial motor drive industry & in the emerging distributed power generation industry, since these were essentially the only source of three phase inverters in the power range of interest. There are many types of multilevel inverters (MLI), but the cascaded multilevel inverter (CMLI) is most the favorite one for industrial applications. The three phase (CMLI) is used with optimization technique to suppress specific low-order harmonics or minimize total harmonic content & then improvement system efficiency .This technique of pulse width modulation (PWM) based on Walsh function harmonic elimination method. In this technique the harmonic amplitude of the inverter output voltage can be expressed as functions of switching angles. Thus, the switching angles are optimized by solving linear algebraic equations instead of solving nonlinear transcendental equations. This technique is suitable for higher level of three phase cascade multilevel inverter (CMLI) where other existing methods fail to compute the switching angles due to more computational burden. For the number of output voltage levels where multiple solutions exist, the solutions where produce least total harmonic distortion (THD) in the output voltage is chosen. As compared with previous work, the decrease in the THD can be reduced to (3%) in case of the proposed technique. In this paper, significant decrease in THD is obtained by solving linear algebraic equations for switching angles....