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IJEEE, Vol. 3, Issue 5 (October, 2016) e-ISSN: 1694-2310 | p-ISSN: 1694-2426

POWER QUALITY IMPROVEMENT INDISTRIBUTION SYSTEM USING DSTATCOM

WITH FUZZY LOGIC CONTROLPoornima S1 , Jois K George2

PG Student [PEPS], Dept. of EEE, KITS Engineering College, Kottayam, Kerala, India1

Assistant Professor, Dept. of EEE, KITS Engineering College, Kottayam, Kerala, India2

spoornima11@gmail.com

Abstract-A Distribution Static Synchronous Compensator(DSTATCOM) is used here to compensate power qualityproblems. In this paper, the performance of DSTATCOM tomitigate the voltage sag is analyzed and fuzzy logic controlleris developed. A 6 pulse Voltage Source Inverter basedDSTATCOM is developed using MATLAB simulationprogram. The model is simulated, with and withoutDSTATCOM. The results are analyzed and shows theeffectiveness of DSTATCOM

Index Terms- Distribution System, DSTATCOM, FuzzyController, Power Quality, VSI.

I. INTRODUCTIONThe quality of electric power available to the end user is

very important in today’s scenario. Proliferation of widevariety of electronic device in to the electric power systemhas caused the issue of power quality Power quality meansdifferent thing to different people. It actually refers to thefaithfulness of system to supply and maintain load voltageas pure sinusoidal waveform at rated voltage and frequency.The possible causes of power quality issues may bebecause of voltage sag, voltage swell, under voltage, overvoltage, interruption, harmonic distortion, noise. Voltagesag is fundamental decrease in supply for a short duration.The duration of voltage sag varies between 0.5 cycles tominute .Voltage sag problems mainly occur due to the useof process control equipments, adjustable speed drives,computers etc. A DSTATCOM can be used as a solutionfor the power quality problems such as voltage sag, voltageswell, voltage flicker and harmonics.

II. BASIC THEORY OF DSTATCOMThe DSTATCOM is a shunt connected reactive

power compensator that is capable of generating orabsorbing reactive power. Here IGBT based VSI isused that is connected in shunt with thedistribution system. A coupling transformer is placed inbetween distribution system and DSTATCOM forisolation purpose .The device should be placed near theload side for maximum compensation. The schematicview of DSTATCOM is shown in Fig.1.TheDSTATCOM consists of DC voltage source invertersusing six IGBT’s, DC capacitor and a coupling

transformer. A DSTATCOM can improve the powersystem performance in the following areas Dynamic voltage control in transmission and

distribution system Power factor correction Control of reactive power and voltage flicker

The capacitor in the DSTATCOM maintains dc voltage tothe inverter. The amplitude of the inverter voltage isproportional to the dc voltage of the capacitor, which isproportional to the amount of energy stored in capacitor.If there is any difference in phase shift, active power flows

through the inverter, charging or discharging the capacitor.The charging or discharging of the capacitor affect the dcvoltage level and alters the amplitude of the inverter acvoltage.

Working PrincipleThe working principle of DSTATCOM depends upon thereactive current generation. In this method the anglebetween the ac system and DSTATCOM voltages controlsthe active power flow and the reactive power flow iscontrolled by the difference between the magnitudes ofthese voltages.

III. FUZZY LOGIC CONTROLLER

Fuzzy logic was invented by Lotfi Zadeh in 1965 based onfuzzy sets theory. Fuzzification converts crisp inputvariables into fuzzy variables. Fuzzy inference systeminvolves membership functions, fuzzy logic operators andif-then rules. Rule base represents the controlling system.Defuzzification converts the fuzzy output variables backto crisp variables

Fig.1.Basic circuit diagram of DSTATCOM

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Fig 2. Fuzzy Logic Controller

Fig.2 represents Fuzzy Logic Controller. Fuzzy logicToolbox consists of two types Fuzzy Inference Systems.They are Mamdani type and Sugeno type.

Design of fuzzy Logic ControllerHere the Fuzzy Logic Controller consists of two inputs.They are error and change in error. The seven linguisticvariables selected are NL, NM, NS, ZO, PS, PM and PL.Membership function for both the input and output aretriangular shaped A rule base with forty nine rules iscreated using these seven linguistic variablesThe error iscalculated as the difference between supply voltage andreference voltage. Error rate is the rate of change of errorFuzzy logic Rule base is shown in the table below

Fig. 3 .Fuzzy logic controller scheme

e\∆e NL NM NS ZO PS PM PL

PL ZO PS PM PL PL PL PL

PM NS ZO PS PM PL PL PL

PS NM NS ZO PS PM PL PL

ZO NL NM NS ZO PS PM PL

NS NL NL NM NS ZO PS PM

NM NL NL NL NM NS ZO PS

NL NL NL NL NL NM NS ZO

Fig.4. Fuzzy Logic Rule base

Fig 3.shows a fuzzy logic controller scheme having twoinputs:

error change in error,

There is only one output for fuzzy controllerInput and output using Fuzzy Logic Controller is shown inthe following figures

Fig.5. Input and Output

IV. SYSTEM IMPLEMENTATIONThree phase source is connected to three phase twowinding transformer through three phase series RLCbranch Output terminals of two winding transformer isconnected to load through a breaker; DSTATCOM isconnected to the system for compensation purpose.Fig.6.shows the MATLAB/SIMULINK model

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Fig.6. Simulation diagram

Fig.7. Modeling of DSTATCOM

V. SIMULATION RESULTSThe system is simulated using Matlab Simulink SimPowerSystems. During simulation in the first case noDSTATCOM is placed for compensation of voltage sag. Inthe second case Fuzzy controlled DSTATCOM is operatedfor compensation. During the occurrence of a fault in thesystem without DSTATCOM voltage sag occurs. WhenFuzzy controlled DSTATCOM is introduced in to thesystem it provides much improvement for voltage sagmitigation

Fig.8. Input Voltage

Fig.9. Input Current

Fig.10.Output voltage and current without DSTATCOM

Fig.11.Output voltage and current with DSTATCOM

VI. CONCLUSIONThe capability of DSTATCOM to mitigate power qualityproblems is validated using MATLAB. The system isoperated with and without using DSTATCOM. Therespective results obtained in both the cases are analyzedand compared. For validation of its working in real life, itneeds to be implemented for actual working environment

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