الفهرس 
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Abstract
Photovoltaic (PV) systems are currently getting more attention due to the declining prices of PV modules. This price declination makes grid connected PV systems one of the strong participants in the electricity generation mix of several countries around the globe.
Grid connected PV systems have several topologies with regards to their interface with the electric network. These include centralized, string, multi-string, master-slave and micro-converter topologies. These topologies differ from each other from the view point of cost and control.
The aim of this thesis is to perform a comparative study on the reliability of different topologies of grid connected photovoltaic (PV) systems. The reliability of each topology is investigated by considering the components of the system and their connection. Moreover, the impact of different environmental conditions, including irradiance and temperature, is considered in the analysis.
To perform the required analysis, suitable reliability indices that are based on calculating the probability of the different operating states are used. These states are evaluated using two different methods: first, the state enumeration method (SE) which is based on computing the availability of each component, and second, the Markov model (MM) which is based on computing failure rate and repair rate of each component.
The study of this thesis is carried out on a 58.5 KWp grid connected photovoltaic system. The PV array is modeled in the Simulink/MATLAB environment to estimate the maximum output power from the irradiance and temperature at a certain location. The irradiance and temperature are obtained over a period of three years with one hour time resolution and the obtained power is then clustered to ten different levels. This data is then input to an algorithm implemented in the MATLAB environment to estimate the reliability of different topologies using the SE and MM approaches. A useful comparison between the performance of different topologies has been made showing the advantages and disadvantages of each.