Studying the Total harmonic distortion (THD)for multilevel DC/AC Inverter

Abstract

This paper presents the generation of sinewave AC voltage from DC battery using Cascaded multilevel inverters connected in series . The concept of multilevel voltage source inverters and their topologies are described. The (Optimising stepped sinewave) technique for a cascaded multilevel inverter is presented to get an ac voltage from a dc power supply in order to decrease the total harmonic distortion in the output voltage of the multilevel inverter by applying two techniques: zero crossing and nonzero crossing for different steps . The optimised harmonic stepped-waveform technique is applied to the multilevel inverter using cascaded-inverters with separated dc sources for 3,5,and 7 nonzero crossing stepped sine wave by using Matlab software . The effect of number of steps on the generated voltage has been analyzed .Total harmonic distortion is decreased by 23.29% for zero crossing stepped and by 22.29% for non-zero crossing stepped. Key words : Inverter, Zero crossing, non zero crossing, OHSW technique, Low switching frequency, AC and DC voltage, THD.