الفهرس 
CHAPTER (1): INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Multilevel inverters (MLI) have been increasing attention in recent years because they have many attractive features. Such as, low total harmonic distortion in the output waveform, the dv/dt of switches is low and lower switching frequency. The family of multilevel inverters has emerged as the solution for medium and high power applications. Increasing the number of levels reduces harmonics, so it is logical to investigate higher-order multilevel inverters. Maximizing the levels for different multilevel inverter topologies is accomplished by increasing number of switches required. So Much effort has been focused on decreasing the number of switches used in MLI with increasing the number of output levels. This thesis presents a simplified design of multilevel inverter with a few number of semiconductor switches and increasing number of output levels. One stage of the proposed inverter leads to get seven levels in the output voltage, while, forty-nine levels can be obtained when using two stages. Only six semiconductor switches are required for each stage. Standard DC sources are used, so, DC-DC converter is not required to get the desired output AC standard voltage. Total harmonic distortion in the output waveform of the two stage inverter is within IEEE standard limits, so, using filter to improve output waveform is unnecessary. Description and analyses of the power circuit are included for the proposed multilevel inverter. Mathematical relations and switching sequence of the proposed topology are presented. Modes of operation for the switching states are described. Modulation strategy and design of the switching pulse system are explained with analysis in details. Computer simulations are carried out for the proposed topology by Matlab Simulink software. The prototypes of one-stage and two-stage multilevel inverters were built and tested in the laboratory by a DSP 1104 evaluation board in order to verify the theoretical analysis. The experimental setup and hardware implementation are described. Several of experimental results for the proposed topology are included and discussed. The simulation and experimental results allow the investigation of output voltage and load current of the proposed MLI. Also, harmonic spectrum of output
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voltage and current are studied. Variable frequency output voltage and transient voltage during switching on the system are also investigated. The results show that the proposed MLI can achieve sinusoidal output voltage waveform with reduced number of power electronic components. Total harmonic distortion (THD) is minimized. The proposed modulation strategy has a better performance with lower switching frequency for switches. The simulation results are proved the good agreement when compared with the relevant experimental results.