| Summary: | Recently, the demands of electrical supply by industries and domestics customers
have increased tremendously. This is due to the increase of large loads which are
sensitive in industries like semiconductor and the building of new housing estates.
These have caused power quality problems to both end users by the increasing
demand of electricity. The major power quality problems that always occur in power
systems are voltage sag, unbalanced voltage and unbalanced current. Various circuit
topologies and controls have been developed, aimed at mitigating these power
quality problems.
One of the solutions is by using the Custom Power devices. These Custom Power
devices respond to poor power quality problems such as voltage sag, unbalanced
voltage and unbalanced current by improve the quality of the system. Custom Power
family consists of Distribution Static Compensator (D-STATCOM), Dynamic
Voltage Restorer (DVR), Solid State Fault Current Limiter (SSFCL), Active Power
Filter (APF), and Solid State Transfer Switch (SSTC) are power electronic based
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devices. These Custom Power devices will solve power quality problems at the
distribution system by injecting voltage or current referring to the amount of
reference voltage or current from the distribution system.
In this thesis, D-STATCOM has been used as a device to solve voltage sags and
unbalanced fault conditions. From the studies, the conventional D-STATCOM
controller that uses Proportional Integration (PI) controller is capable of solving
voltage sag but not capable of solving the unbalanced conditions. This is because the
conventional PI controller cannot respond to the negative sequence components. The
negative sequence component is induced by unbalanced faults which happen in a
system. This negative sequence component will block the Gate Turn Off (GTO)
Thyristor from firing. From the studies, there are two types of techniques in solving
negative sequence components namely negative sequence controller or using DQ
transformation of the current.
This thesis explains the application of DQ transformation which changes the 3 phase
components to direct and quadrate components and the pole placement controller.
Both of these techniques have been consider for designing the new type of controller.
This new type of controller is capable of giving order to D-STATCOM to inject the
current to solve voltage sag and unbalanced conditions. The simulations of the D�STATCOM and the pole placement controller were implemented in Mathematical
Laboratory (MATLAB) program version 6.5 developed by MATHWORKS Inc. The
D-STATCOM has been connected to the llkV distribution system in shunt with
fault components. The results obtained from the simulations clearly showed that the
designed D-STATCOM with the new pole placement controller is capable of
mitigating voltage sag and unbalanced fault conditions. The developed simulation
model will be useful for future power quality studies in distribution systems.
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