Analysis of three phase cascaded H-bridge multilevel inverter for symmetrical & asymmetrical configuration

Abstract

The previous studies have shown the drawbacks of conventional inverters, specially for high power application. From the beginning of 21st century, drastic improvement in the harmonic profile and increased power rating of MLI made them highly popular for high power application. MLI's are widely utilized in industrial field employing motor drives, static VAR compensators and renewable energy systems, etc. Basically output voltage of a MLI has multiple levels as compare to conventional inverters. This increment in output voltage levels greatly affect the harmonic distortion due to which the output voltage is negligibly distorted and high quality of output waveform is obtained. Because of this features the MLI are highly preferred for high voltage and high power application. Up till now many topologies for MLI have been reported. Moreover, three major MLI structures are there, Cascaded H-bridge having isolated dc source, diode clamped and flying capacitor. Though there are various types of MLI are available, CHB MLI is one of the most productive topology among multilevel family. The CHB MLI is further divided in two configuration viz., symmetrical and asymmetrical CHB MLI. It depends on cascade connection of number of H-bridge inverter cells energies by the supplies which are in geometric progression (GP) with different ratios like 2,3 etc. This paper presents cascaded MLI approach for high voltage and high power output application, in which symmetrical and asymmetrical arrangements of seven level and nine level CHB MLI are investigated for structural and operational characteristics. Simulations are carried out in Matlab Simulink to analyzed the performance of Asymmetrical CHB MLI using SPWM technique. Simulation result for this proposed scheme are shown in this paper.