الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
The main challenge of modern microgrids (MGs) is the capability to operate in either
grid-connected mode (GC) or islanding mode (IS) with DC-link voltage regulation for all
the utilized parallel-connected DC-AC converters in the MG during all operating modes
and, at the same time, is capable of transferring seamlessly between these two operating
modes. In each mode of operation MG DC-AC converters may be operated under current
source or voltage source control. In GC mode, MG inverters typically operate under a
current source control strategy, whereas in IS mode MG inverters operate under a voltage
source control approach.
This thesis presents a proposed control strategy that is capable of operating PV-based
MG systems in different operating modes. The proposed control approach is capable,
also, of transferring the PV-based MG system seamlessly between the different operating
modes. A PQ controller is utilized to realize the GC operation, whereas a V-f controller
is used for the IS operation. This seamless transition can be achieved by mitigating the
transient variations in the MG voltage, current, phase, and frequency at the point of
common coupling (PCC). In addition, the proposed strategy is capable to provide a
transient-free transition in the DC-link voltage of the utilized PV inverters. Thereby, the
proposed strategy has the capability to enhance the overall MG reliability. The
proposed control strategy is validated by software simulation using MATLAB/Simulink.
The simulation results indicate the effectiveness of the proposed strategy during MG
transitions.
In addition, the thesis suggests a novel control strategy that is capable of operating a
battery-based MG system in each of the GC and IS modes and, at the same time,
seamlessly transferring it between these two operating modes. As in the case of the PVbased
MG system, the GC operation is realized by using the PQ controller, whereas the
IS operation is realized by using the V-f controller. The smooth transfer between the two
modes is accomplished by minimizing the transient variations in the MG voltage, current,
frequency, and phase at the PCC. Additionally, the suggested strategy is qualified to
deliver a novel regulation and a transient-free transition for the DC-link voltage of the
used bi-directional DC-AC converter of the considered battery-based MG system.
Therefore, the suggested control strategy can potentially improve the reliability of the
battery-based MG system. The
proposed battery-based MG system is simulated and controlled by utilizing
MATLAB/Simulink. The simulation results demonstrate that the suggested control
strategy can effectively act during the operation of the considered battery-based MG
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system, either in the GC mode or the IS mode, and it can also effectively control the
transitions between the two operating modes.
Moreover, the hierarchical control framework of the proposed AC MG is designed to
manage the operation and coordination of all components included in the MG (e.g., PVbased
MG system, battery-based MG system, and AC loads) with the purpose of
enhancing the overall MG performance and reliability. The proposed AC MG is
simulated and controlled by utilizing MATLAB/Simulink. The simulation results, in each
case, indicate the effectiveness of the corresponding design control strategy during all
operating modes.