ABSTRACT

Inverters have made their significant place in the field of electrical engineering. They have been used in various applications ranging from low power applications to VFDs, STATCOM, (FACTS) devices, Naval Systems and Propulsion Systems. The output of inverter is considered to be the driving force to decide the possible applications where it can be used. The output of inverter has been the main interest for the researchers. The possible outputs can be square wave, quasi square wave and pure sine wave. However Total Harmonic Distortion (THD) puts constraints for square wave and quasi square wave inverters for high power applications. In this thesis, Cascaded H-Bridge Multilevel Inverters (CHB MLI) have be implemented with number of levels starting from five to eleven (5-level, 7-level, 9-level and 11- level). The models have been simulated on SIMULINKIMATLAB. In order to reduce the THD in output voltage and current waveforms, Multicarrier Sinusoidal Pulse Width Modulation (M-SPWM) controlling techniques have been implemented along with each inverter topology. Three techniques such as In Phase Disposition (IPD), Alternate Phase Opposition Disposition (APOD) and Phase Opposition Disposition (POD) have been compared taking THD considerations . From simulation results, it is confirmed that THD is decreased reasonably if higher inverter topologies are considered and POD-SPWM technique when implemented with 11-level CHB MLI, attains very less voltage THD of 10.62% and current THD of 3.7% when an
RL load is used.