الفهرس 
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Abstract
Recently, microgrid applications are become widely utilized because of its
features, where it is a local interconnection between distributed generators (DGs) and
loads. Distributed generators can be renewable energy sources (RES), conventional
sources, or both types. Microgrid can offer many benefits such as losses reduction during
energy transfer from generation unit to load, reduction in the amount of harmful gases, and
enhancement the system reliability. However, microgrids with dominant renewable
resources face many challenges such as deteriorating the power quality in terms of
voltage and frequency. In the thesis, frequency variation will be studied in detail, where
it occurs because of sudden changes in load or climatic changes that cause a temporary
mismatch between generation and load. The change in frequency depends on the microgrid
grid inertia. A low inertia operation leads to increase rate-of-change-of-frequency
(ROCOF), and low frequency nadir in a very short time. Such situations can lead to tripping
of frequency relays (causing under-frequency load shedding) and, in the worst case, may
lead to cascaded outages.
In the first microgrid, a proposed technique is applied to a microgrid containing
a wind turbine and thermal power plant to overcome the decoupling problem. The
inherent inertia of the wind turbine that is in the rotating masses is used to store/release
energy from/into the system during transient periods through speed control.
In the second microgrid, a microgrid consists of a PV plant and a thermal power
plant, there is no inertia in the PV plant because of the absence of the rotating mass. In
the thesis, the super-capacitor is integrated with the DC bus of the grid interface inverter
of the PV system, and voltage control based on frequency deviation to imitate the
synchronous generator inertia is applied.
In the third microgrid, a microgrid has a wind turbine, a PV plant, and a thermal
power plant, a control scheme is proposed which boosts the cooperation of wind and
PV generation systems to support the microgrid frequency response concurrently.
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