الفهرس 
2 Indirect AC-AC converterOnly 14 pages are availabe for public view
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Abstract
In recent years, AC–AC converters have become increasingly popular in a variety of industrial applications. However, recent research on the AC–AC converter technology mainly focuses on load requirements. The AC–AC converters are required not only for the lowvoltage
but also for the high-voltage and high power applications. In high voltage and high power applications, cascaded AC–AC converters are commonly used. Cascaded converters have many merits which attract the researchers to work with, the most highlighted strengths of using these converters can be summarized as; first,
can easily work at medium and high voltages; second, can be used to obtained high-gain output voltages using low-voltage rating switching devices; third, they can operate at high switching frequencies; and finally, can produce AC output voltages with higher power quality
waveforms. Due to these features, the cascaded converters have been recognized as attractive topology solid-state transformers (SSTs), a micro-grid, wind-farm (WF) system and photovoltaic (PV) systems etc. The thesis proposes configuration topologies with boosting capability for power quality issues. The first suggested architecture was built using modified configuration boost AC-AC
converter that provides high voltage gain. The second configuration of the cascaded boost AC-AC converter has the same features as the first converter without the commutation problem. As a result of cascaded connection, these two topologies have the capability to continue working under short- and open-circuit failure conditions without damaging the
switches. The control system is developed so that the systems can operate at the desired voltage gain even if one of the cascaded units fails. The third configuration is a new double step AC–AC boost converter with high voltage gain. The performance of the proposed topology is improved compared to conventional boost converter. This configuration provides high voltage gain up to 5-time, less voltage stress across switches, small size, low cost, and nearly sinusoidal output voltage. The suggested topologies have nearly unity power factor at the input side, high a steady-state performance, and fast dynamic response. Moreover, the merits of all configurations are low operating duty-cycle, low voltage stress across switches, small size and low cost. The operation modes and mathematical model for the topologies are presented. The effectiveness of the proposed technique is demonstrated via computer simulation using MATLAB/Simulink. Simulation results for the system under consideration show that the proposed system has low total harmonic distortion (THD), nearly unity power factor (PF), lower number of units and better performance. The simulation results for static load are studied in both
transient, stop working unite (SWU) and steady-state operations. The control strategy of the converters could be implemented by using a digital signal processor (DSP) or microprocessor to achieve pulse gates. The models of cascaded AC – AC converter for static load controlled by a DSP-1104 evaluation board was built and tested in the laboratory. The experimental results show that the proposed cascaded AC – AC boost converter control method can achieve nearly sinusoidal input current waveform for both transient and steady-state operations. When comparing the relevant experimental results with the simulation results, it’s
showed a good agreement.