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.