الفهرس 
Modeling and stability assessment of inverter-based AC microgrids
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Abstract
This thesis proposes a hybrid microgrid control strategy to ensure seamless transfer from grid-connected mode to island mode and resilient operation under the occurrence of other large signal disturbances by assessing the dynamic performance of the complete system with time domain simulations. The microgrid under investigation involves two configurations: the first one uses an aggregate of inverter-based and synchronous machine-based distributed generators (DG{u2019}s) while the second configuration is 100% inverter-based. Some of the employed voltage source converters (VSC{u2019}s) are used to interface renewable energy sources (RES{u2019}s) while other inverter-based DG{u2019}s are fed from energy storage systems (ESS{u2019}s) to simulate a diverse and typical microgrid. The structure of each DG type, modes of operation, and corresponding control systems are described in details to demonstrate the applicability of the used model. Matlab simulink is used to model the study microgrid and to assess its stability subsequent to large load connection disconnection, renewable energy source loss, temporary faults, and faults provoking islanding. The voltage at the Point of common coupling (PCC) and microgrid frequency are measured in each case to evaluate the microgrid stability. The volatility of renewable energy sources and their impact on the microgrid frequency are investigated in both configurations. Eventually, the critical islanding time (CIT) is determined in both cases for different depths of fault followed by microgrid mode switching