Comparative Analysis of Modulating Technique in Three Level Cascaded H-Bridge Inverter

Abstract

The Core objective of electric system is to distribute constant voltage and frequency throughout the system, but due to harmonics it results into distorted voltage and current. Inverter is a device which converts AC into DC, but due to more distortion, less efficiency multilevel inverter came into consideration. Multilevel inverters are boon to the field of industries nowadays. It reduces harmonics contents in the system and produce output, such as a sine wave. Switching techniques which are required for multilevel inverter are high and fundamental switching frequency techniques. Selective harmonic elimination (SHE-PWM) is fundamental switching frequency modulating technique, which is responsible for elimination of lower order harmonics. SHE-PWM is implemented by solving nonlinear transcendental equations using iterative techniques. The switching angles found out using Newton Raphson (N-R) method. Sinusoidal pulse width modulation (SPWM) is high switching modulation technique, in this reference wave is compared with carrier wave and resultant will results into gate pulse. In this paper comparison of two modulating techniques are done on three phase three level inverter. Comparative analysis is done based on total harmonic distortion (THD) with the concept of eliminating same order of harmonics with both the techniques. FFT analysis and simulation results are presented with both the techniques so as to eliminate same order of harmonics.