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ABSTRACT:A power electronic converters are becoming more and more popular for medium voltage & high power applications. To overcome the limitation of semiconductors current and voltage ratings in high power applications, multilevel inverter is often considered an effective solution. In addition, stepped waveform in the output of multilevel inverter has better harmonic spectrum than 2-level inverter in low switching frequencies. So, in recent years multilevel inverters have gained great interest in industry. Among the different solutions available for multilevel converters, the cascaded H-Bridge multilevel inverter are modular in nature and its asymmetric topologies allow to generate more voltage levels with less number of semiconductors and thus increase of output performance and system reliability. For these reasons, this kind of topology has attracted a lot of attention both from the customers and manufacturers view.This paper presents an asymmetrical cascaded H-Bridge multilevel inverter in three phase configuration using fixed frequency level shifted carrier based pulse width modulation technique feeding a three phase squirrel cage induction motor. This new control scheme is applied to 7, 9, 15 and 27 level asymmetrical cascaded H-Bridge multilevel inverter. Simulation using MATLAB/SIMULINK is done to verify the performance of all levels of an asymmetrical cascaded H-Bridge multilevel inverter. I.INTRODUCTIONMultilevel power conversion technology is a very rapidly growing area of power electronics with a good potential for further development [1]- [7]. The most attractive applications of this technology are in the medium voltage (2.3-13.8 KV)and high power range (0.2-40 MW), and include motor drives, power distribution, power quality and power conditioning applications [2]- [5]. Ordinary two level inverters cannot be used for high power and high voltage applications because of limitation in power handling capability and rating of the semiconductor devices [6]- [8]. To overcome the limited semiconductor voltage and current ratings, some kind of series and/or parallel connection will be necessary thereby allowing greater working voltages to be reached, which in turn increases the power they are able to handle [9]. Due to their ability to synthesize waveforms with a better harmonic spectrum and attain higher voltages, multi-level inverters are receiving increasing attention in the past few decades. The three most important topologies have been proposed for multilevel inverters [5]-[11]: diode-clamped (neutral-clamped); capacitor-clamped (flying capacitors) and cascaded H-Bridge Multilevel inverter with separate dc sources.Diode clamped requires more no of diodes and flying capacitor has capacitor balancing problem. In addition, several other topologies have been proposed in the literature [5], [7]. The cascaded H-bridge multilevel inverters having more no of advantages such as modular structure and less no of components required compare to other topologies. It is one of the topologies proposed for drive applic...

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