الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
To restore the load voltage, Dynamic Voltage Restorer (DVR) which is installed
between the supply and a critical load should inject voltage and active power to the
distribution system during voltage sag. Due to the energy storage capacity limitation
of the dynamic voltage restorer DC link, a new device which is named Inter-line
Dynamic Voltage Restorer (JDVR) is introduced and discussed. The IDVR consists of
several voltage source inverters connected to different independent distribution
feeders with common DC bus. When one of the inverters compensates for voltage sag
that appears in its feeder (voltage controller), the other inverters control the voltage of
DC link capacitor via pumping the required power into the DC bus (power controller).
Each inverter will have both voltage and power controllers. Only one controller is in
use during the system abnormal conditions according to its feeder state. The voltage
controller uses one of the dynamic voltage restoration techniques (in-phase injection
or pre-sag supply voltage injection or energy saving injection). In this thesis, the in-
phase injection technique is applied and two types of loads are considered (constant
impedance and three phase induction motor). Since the voltage restoration process
may need real power injection into the distribution system, the power controller
injects this power via injecting suitable voltage into the sending feeder. In this work
the voltage injection in power controller is simulated by voltage DROP across series
virtual impedance. A new scheme is proposed to select the impedance value (virtual
impedance injection scheme). The impedance value is selected such that the power
consumed by this impedance represents the required power to be transferred without
perturbing voltage of the load connected to that feeder. The proposed control strategy
have been modeled and simulated by MATLAB/SIMUUNK. The simulation and
experimental results verify the effectiveness of IDVR and the suggested control
method. The performance of this system is also studied during voltage swell,
unbalanced supply and other different conditions and showed to be very satisfactory.
For multi-feeder IDVR system the power controllers participate in injecting
the required power. A proposed scheme is introduced to determine the reference
power of each power controller in multi-feeder IDVR.
This thesis is also concerned with how to transfer power between the feeders
during normal voltages level in two-line lDVR system through the common DC link
(load sharing mode). In this case, the two feeders are under power control and the
injected voltage is selected to achieve the concept of power exchange between the
feeders without perturbing the load voltage magnitude of each feeder. The
Experimental and simulation results substantiate the proposed concept.
IDVR is shown to be a promising candidate to solve voltage regulation
problems. It can be used in conjunction with renewable energy sources. These
additional sources may be coupled in parallel with the system DC link to share in
supplying the required active power. This can be done if the injected power from
neighbor feeder is not sufficient to mitigate the voltage decrease in the other feeder or
the feeders are experiencing the same type of voltage decrease at the same time.