ENHANCEMENT OF VOLTAGE QUALITY IN ISOLATED POWER SYSTEMS
By avinash&
akhilesh
INTRODUCTION
Despite the coverage of large areas one can still encounter situations in oil exploration areas and remote mining districts where loads are served by relatively small-capacity diesel generator-sets etc. and the main loads are smallgeneratoroften DC or AC drives which are connected through power converters In addition to the main drive loads there are some low-power sensitive lowloads such as computers or electronic controllers to ensure the proper functioning of the exploration/mining activities. These drive loads are non linear which produce harmonic currents resulting in distorted supply voltage These Sensitive loads are sensitive to distorted supply voltage and short duration disturbances which appear in the form of voltage-sags or voltagevoltagevoltageswells due to, the switching on/off of drive loads
OBJECTIVES
TO IMPROVE VOLTAGE QUALITY IN ISOLATED POWER SYSTEMS By
Mitigation of harmonics induced in the power system Mitigation of short duration voltage disturbances like voltage sag and voltage swell Protecting sensitive loads
SOURCES FOR VOLTAGE QUALITY PROBLEMS These are the main causes for voltage quality problems Voltage sag Voltage swell Harmonic distortions
SOLUTIONS OF VOLTAGE OR POWER QUALITY PROBLEMSHARMONIC MITIGATION
Active filters Passive filters MITIGATION OF VOLTAGE DIPS Energy storage systems MITIGATION OF BOTH VOLTAGE DIPS AND HARMONICS Series compensator
FILTERS ADD ITS PROPERTIES
PASSIVE FILTERSAdvantages Harmonic reduction Reactive power compensation Disadvantages Resonance with line impedance Heavy and bulky No mitigation of voltage dips
ACTIVE FILTERSAdvantages Cancel out harmonics Block resonance Disadvantages isadvantages Costly No mitigation of voltage dips
Energy storage systems doesn't mitigate harmonics but it mitigates tems voltage dips
SYSTEM MODEL FOR IMPROVEMENT OF VOLTAGE QUALITY IN ISOLATED SYSTEM USING SERIES COMPENSATION
DESCRIPTION In this it is discussed how a series compensator will effectively mitigate harmonic distortion and voltage dips(voltage sag, voltage swell) SERIES COMPENSATOR ESS(Energy storage system) VSI(Voltage source inverter) Filters ESS is A Energy Storage System which may be a battery , whose output is dc voltage VSI is a conventional inverter whose function is to convert dc input voltage to ac output voltage Filters may be active or passive filters used to eliminate harmonics generated in series compensator
EXPLANATION How harmonics are eliminated ? Series compensator generates an ac harmonic current which is equal and opposite to supply harmonic current as a result harmonics currents are minimized as a result voltage quality is improved Harmonic currents are generated through ESS and VSI AS series compensator is in the same branch as that of sensitive loads small harmonic currents generated in series compensator due to switching in VSI are eliminated using LC filters
SUPPLY VOLTAGE WITH FUNDAMENTAL AND HARMONIC COMPONENT
SUPPLY VOLTAGE WITH FUNDAMENTAL COMPONENT
Therefore only harmonic component is
Vsh
=
Vs1-VS2
i.e. output of series compensator should be
Vout = - Vsh
How voltage dips(sags,swells) are eliminated ? dips(sags,swells)ESS plays important role in elimination of voltage dips i.e ESS acts as a buffer The ESS would act as a buffer and provides the energy needed for load ridethrough during a voltage-sag voltage Conversely, during a voltage-swell, excess energy from the network voltagewould be stored in the SC so that VL can be controlled. VL thus voltage dips are eliminated
Continuous powerguiPI Curent Regulator 5 Sc ope 1 1 s 90 100
Id _ Refenc e
+ v -
a lp h a_ d eg AB BC CA p uls es
Vab+ v -
Vbc+ v -
0
B lo ck
Vc a
Sy nchroniz ed 6 -Puls e Generator
+ i -
Current MeasurementSc ope
Va
Vb
A Vabc Iabc B a b C c
g + A B C
+ - v
Vc Sy nchroniz ation Voltages
Three -Phase V-I Measurement
Thy ristor Converter
Vo
Sc ope 2
Three -Phase Parallel RLC Load
A B C
A
B
C
V ab c Ia b c a b c
Three -Phase V-I Measurement 2
WAVE FORM
SIMULATION WAVE FORM
CONCLUSION Power quality improvement in an isolated power system through series compensation has been investigated. A method to control the SC so that it can compensate for the harmonics under steady-state condition has been steadyproposed. The effectiveness of the proposed method has been verified through simulation.