Abstract:
Power Electronics and Advanced Control technologies have made it possible to mitigate power quality problems
and maintain the operation of sensitive loads. Among power system disturbances, voltage sags, swells and
harmonics are some of the severe problems to the sensitive loads. The series compensation method is best
suited to protect such loads against those disturbances. The use of a series compensator (SC) to improve power
quality is an isolated power system is investigated. The role of the compensator is not only to mitigate the
effects of voltage sag, but also to reduce the harmonic distortion due to the presence of non linear loads in the
network. In this paper, a series compensator is proposed and a method of harmonic compensation is described
and a method to mitigate voltage sag is investigated. The proposed series compensator consists of Energy
Storage System (ESS) and Voltage Source Inverter (VSI), Injection Transformer. The ESS can be a capacitor of
suitable capacity. ESS would act as a buffer and generally provides the energy needed for load ride-through
during voltage sag. Injection Transformer is used to inject the voltage in transmission line in appropriate level.
In this way the terminal voltage of the protected sensitive load can be regulated to maintain a constant level. The
modeling and simulation of the proposed series compensator was implemented in Matlab Simulink work space.
Simulation results showed that the proposed series compensator was efficient in mitigating voltage sags and
harmonics and thus improve the power quality of the isolated power system. This approach is different from
conventional methods and provides effective solution. If this method is enhanced in future it could provide
much more improved power quality.
Keywords: Power Quality Problems; Series Compensator; ESS; VSI; Harmonics; Voltage Sag; MATLAB.
1. Introduction
Isolated power systems are commonly found in rural and remote areas of the world. Isolated power systems
are characterized by limiting generating capacity. The sensitive loads which are present in the isolated power
systems are much more affected by the power quality problems. Power Electronics and Advanced Control
technologies have made it possible to mitigate power quality problems and maintain the operation of sensitive
loads. Power quality problems encompass a wide range of disturbances such as voltage sags/swells, flickers,
harmonics distortion, impulse transient, and interruptions.
Among power system disturbances, voltage sags, swells and harmonics are some of the severe problems to
the sensitive loads, because (i) the occurrence of voltage sag in the system can cause devices/process down time,effect on product quality, failure/malfunction of equipments etc., (ii) the occurrence of harmonics in the system
can cause excessive losses and heating in motors, capacitors and transformers connected to the system. To avoid
those undesirable affects the proposed method mitigates the problems caused by voltage sag and harmonics.
This paper analyses the key issues in the power quality problems, In the proposed system Voltage sag occurs
due to the three phase fault in the transmission line and harmonics occurs due to the connection of controlled six
pulse converter (rectifier) to the main drive load(non linear load). All these factors affect the sensitive load
which is connected in parallel to the main drive load. So the proposed system protects the sensitive load by
mitigating the voltage sags and harmonics using series compensation technique.
2. Main Sources, Causes and Effects of Electrical Power Quality Problems:
Power Quality is “Any power problem manifested in voltage, current, or frequency deviations that results in
failure or misoperation of customer equipments”[1]. Power systems, ideally, should provide their customers
with an uninterrupted flow of energy at smooth sinusoidal voltage at the contracted magnitude level and
frequency. However, in practice, power systems, especially the isolated systems, some of the primary source of
distortion [2] can be identified as below.
 Non – Linear Loads
 Power Electronic Devices
 IT and Office Equipments
 Arcing Devices
 Load Switching
 Large Motor Starting
 Larger capacitor bank energies
 Embedded Generation
 Electromagnetic radiations and Cables
 Storm and Environment Related Causes
While power disturbances occur on all electrical systems, the sensitivity of today’s sophisticated electronic
devices makes them more susceptible to the quality of power supply. For some sensitive devices, a momentary
disturbance can cause scrambled data, interrupted communications, a frozen mouse, system crashes and
equipment failure etc. A power voltage spike can damage valuable components. Power quality encompass a
wide range of disturbances such as voltage sags/swells, flicker, harmonics distortion, impulse transient, and
interruptions

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