الفهرس 
Introduction & Literature ReviewOnly 14 pages are availabe for public view
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Abstract
The accelerating penetration of distributed energy resources (DERs) in the Low
Voltage (LV) networks has revealed their adverse impact on voltage profiles, power
quality and protections along these networks. Consequently, the presence of these DERs
requires providing more ancillary services. On the other hand, these DERs are
essentially interfaced with the network through power electronic converters, for
instance, Photovoltaic (PV) systems, Fuel cells, Batteries are usually connected through
(DC/AC) inverting stage to deliver power to the grid. Also, wind turbines are connected
through (AC/DC/AC) converting stages. The main aim of these converters is to connect
them to the grid. Fortunately, these converters have a very good potential to use them
in enhancing power quality in these networks. Traditionally, Central power plants were
used to provide ancillary services besides their main function of delivering electric
power. Since, DERs are now replacing central power plants, they must provide ancillary
services. Hence, Directing the control of these DERs converters to solve power quality
issues is gaining high importance.
Voltage regulation, unbalance and harmonics mitigation are some examples of
the functions that can be implemented through the DERs converters. This thesis presents
a wind energy conversion system (WECS) with a back-to-back converter performing its
main function of maximizing wind turbine output power and regulating its output active
and reactive power. Added to these basic functions, ancillary services are provided to a
local load and Medium Voltage (MV) grid. A tertiary winding transformer is used as
the point of common coupling between the WECS, the MV grid, and the local load. The
tertiary winding transformer makes up for the need of two transformers: one for stepping
up the WECS voltage to the MV grid and the other for stepping down the WECS voltage
to the LV load.
Extraction of load unbalance is investigated through different algorithms.
Adaptive Notch Filter (ANF) has demonstrated a leading response over the conventional
methods for calculating the symmetrical components under different unbalance
conditions. Unbalance in the grid currents is then effectively compensated and the
currents from/to the MV grid are ensured to be balanced. A new method is also
presented making use of the digital filters initially used in enhancing communication
signals, radars, sonars and in other bio-medical applications. The new method is
implemented using Infinite Impulse Response (IIR) adaptive notch filter based on
simplified lattice algorithm (SLA). The proposed approach based on SLA outperforms the ANF in terms of steady-state accuracy and the required sampling rate of the input
signal, thus it would be the preferred choice for real time processing.
In this thesis, the proposed WECS with the tertiary winding transformer has
successfully satisfied its additional control actions for power quality mitigation. Voltage
regulation of the load voltage at different loading conditions is achieved. In addition,
unbalance compensation under different unbalance cases was achieved. Various
unbalance detection methods are compared according to their accurate extraction of
symmetrical components and the speed of their extraction. The system is simulated
using PSCAD/EMTDC and results are presented to confirm validity of the presented
methods.