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Study of Wavelet based DG for power qualityimprovement

J.Pardha saradhi1 Dr.R.Srinivasarao2 Dr.V.Ganesh3

1 Department of EEE, Bapatla Engineering college,bapatla ,Andhrapradesh

2Department of EEE, JNTU kakinada ,Andhrapradesh3 Department of EEE, JNTU Anantapur,pulivendula ,Andhrapradesh

[email protected]@gmail.com

[email protected]

AbstractThis paper proposes a comprehensive approachto the planning of distribution networks and the control of

dispersed generator (DG). Firstly, a distribution system

without dispersed generator is analyzed. The system

parameters are also analyzed when dg is connected to

load. If sudden drop out of source occurs, seriousproblems across the load arises .i.e. it leads to voltage dip.

Since the optimal solution contains Distributed Generators

(DGs) to maximize reliability, the DG must be able to

operate in islanded mode. This paper describes the load

characteristics with and without dg during normal load

conditions. The second part of the paper reviews the

charactestics of dg without load connection. A battery

consumes energy during either condition i.e. with and

without load. A rectifier circuit is developed for

conversion purpose. Sequence analyzer is also included to

get the characteristics of dg in either of the conditions.

Wavelet analysis is used to analyze the dg

characterstics.db4 is used to analyze the signal. Thestudies are performed based on well known software

package MATLAB simulink. The work shows that

Reliable, Effective and Efficient operation of DG source in

coordination with main utility network

Keywordsdistribution system, DG, MATLAB simulink,wavelet analysis, battery.

I. INTRODUCTIONNow a days dispersed generator (DG) plays a major role indistribution system. Developing countries like India mainlyfacing the severe power quality problems mainly during peakload conditions. So, at that conditions DG[1] can be switchedon so that we can ensure quality of power at consumer

premises. DGs are small (usually under 10 MW), modularelectric generation and storage technologies that provideelectric capacity and/or energy when and where needed. Theyare owned by a customer, utility or another entity, andconnected to the grid at a distribution voltage level. TheDiscos/ end-users particularly in India can install DG units withintheir service area. Due to the availability of such a flexibleoption at the distribution[2] voltage level, the distributionnetwork is now being transformed from passive network to anactive network. The use of distributed generation (DG) indistribution system is expected to increase in the near future

due to its positive impacts such as voltage support, improvedreliability, small size and losses reduction.

In this paper the performance of wavelet basedSynchronous Generator which acts as a Dispersed Generatoranalyzed during different conditions.

The performance of DG is evaluated ,when the load issuddenly drop out from the source ,at the particular instant oftime DG ill inject power, so that the consumer will notaffected by any power cut. The response of load during anycondition i.e. load drop out from the source is analyzed. Thewavelet response of dg also obtained. In this paper dg alsofeeds to battery to feed dc loads and in either of the conditionsdg charges battery. Rectifier circuit is developed by usingIGBT.and it is given to battery. The output characteristics ofrectifier and battery also obtained .the characteristics arestudied. Phase sequence analyzer[3] is used to analyze dgcharactersics.The load characteristics are obtained by usingwavelets.

Harmonics and discontinuities generated in powersystem can have a wide frequency bandwidth, from high-frequency transients and edges to slowly varying harmoniccomponents. Hence, analysis only in the frequency or timedomain alone is not sufficient to capture features that arespread within a wide bandwidth. Wavelet transform providesa local representation (in both time and frequency) of a signal.Therefore it is suitable for analyzing a signal where time andfrequency resolution is needed, unlike FFTwhich gives aglobal presentation of the signal. This paper studies thecharacteristics of DG and load with the help of Wavelettransform (WT). This study provides us with an efficient wayto classify different load characterstics, and coordinate

between different protective devices in the distributionsystem.

II .WAVELET THEORYThe Wavelet transform (WT)[7] is a mathematical tool, likethe Fourier transform for signal analysis. A wavelet is anoscillatory waveform of effectively limited duration that hasan average value of zero. Fourier analysis consists of breakingup a signal into sine waves of various frequencies. Similarly,wavelet analysis is the breaking up of a signal into shifted andscaled versions of the original (or mother) wavelet.
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Fourier analysis does not provide good results for the non-stationary signals, i.e., where the signal parameters changeover the time unlike the stationary signal, because intransforming the complete signal to the frequency domain, thetime information gets lost in Fourier analysis. This deficiencyin the Fourier analysis can be overcome to some extent byanalysing a small section of the signal at a time - a techniquecalled windowing the signal, first proposed by Dennis Gabor.This leads to an analysis technique called Short-Time FourierTransform (STFT). But the drawback in STFT is that the sizeof the time-window is same for all frequencies. Waveletanalysis overcomes this deficiency by allowing a windowingtechnique with variable-sized regions, i.e., wavelet analysisallows the use of long time intervals where we want moreprecise low-frequency information, and shorter regions wherewe want high-frequency information.

A. Continuous Wavelet Transform

The continuous wavelet transform (CWT) is defined as thesum over all time of the signal multiplied by scaled andshifted versions of the wavelet function . The CWT of a

signal x(t) is defined as

CWT(a, b)x(t)a*,b(t)dt, (1)

where

a,b(t) | a |1 / 2 ((tb) / a). (2)

(t) is the mother wavelet, the asterisk in (1) denotes acomplex conjugate, and a, bR, a 0, (R is a real continuousnumber system) are the scaling and shifting parametersrespectively. | a |1/ 2 is the normalization value of a,b (t) sothat if (t) has a unit length, then its scaled version a,b (t)also has a unit length.

B. Discrete Wavelet Transform

Discrete Wavelet Transform is found to be useful inanalysing transient phenomenon such as that associated withfaults on the transmission lines. Multi-Resolution Analysis(MRA)[8] is one of the tools of Discrete Wavelet Transform(DWT), which decomposes original, typically non-stationarysignal into low frequency signals called approximations andhigh frequency signals called details, with different levels orscales of resolution. It uses a prototype function called motherwavelet for this. At each level, approximation signal isobtained by convolving signal with low pass filter followed bydyadic decimation, whereas detail signal is obtained byconvolving signal with high pass filter followed by dyadic

decimation. The decomposition tree [11]is shown in Fig. 1.

c j+1(k)

cj(k)

d j+1(k)dj(k)

Fig. 1 Decomposition Tree

The DWT maps the one dimensional time domain signal f(t)into two dimensional signal as:

f(t) =cj (k) (tk) +d j (k)( 2- jt - k) ( 3 )k k j

Where cj, dj are approximate and detail coefficientrespectively; (t) and (t) are scaling and wavelet functions

respectively and j is the decomposition level.III. POWER SYSTEM MODEL

The single line diagram of the power system under study isshown in Fig.2. Simulink is used for detailed modelling ofpower system network and different conditions. A 132 KV,100 Km circuit Transmission line is selected for simulation.The transmission line is simulated using distributed parametermodel. The non linear load is taken in distribution level

operated at 415 volts as shown in fig.

Fig2.one line diagram of a test system

The load characteristics are obtained during threeconditions.

Case i) During source and load both are in operation.Case ii) During source is in operationCase iii) During DG in operationWavelet based load characteristics are studied during three

conditions. Sequence analyser also used to obtain itssequence. The analysis also made on source side variationswith respect to starting of alternator.


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IV.RESULTS

Fig. 3 shows the load voltage and current variation fornormal network variation. Fig. 6 shows the load voltage andoperational conditions of the DG.Fig. 7shows variation of loadvoltage, current for only source is connected to theload.Fig.6shows High capacity battery charging to serve dcloads and phase analyzer and wavelets (db4) also consideredto study the characteristics of load during all the conditions.

A. Case i) During source and load both are in operation

Fig3.rectifier output voltage

Fig4.Alternator output voltage at starting

Fig5.load voltage

B.Case ii) During source is in operation

Fig6.load voltage

Fig7.Battey charging

C.Case iii) During DG in operation

Fig8.source variation with respect to alternator starting


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Fig9.battery output

Fig10.load voltage

Fig11.Rectifier output voltage

V.CONCLUSION

Now a days DG pays a major role in distribution system,DGs may be adapted mainly for the countries which arefacing peak load problems. The main view of this paper is tofeed the loads during the peak loads, and rest of the times DGfeeds to dc loads .So that we can effectively use the DG with100% reliability. In this paper, firstly, distribution systems

without dispersed generator are discussed. The systemparameters are also discussed when dg is connected to load. Ifsudden drop out of source occurs, serious problems across theload arises .i.e. it leads to voltage dip. Since the optimalsolution contains Distributed Generators (DGs) to maximizereliability, the DG must be able to operate in islanded [1]mode. This paper describes the load characteristics with andwithout dg during normal load conditions. The second part ofthe paper reviews the charactestics of dg without loadconnection. A battery [10] consumes energy during eithercondition i.e. with and without load. A rectifier circuit isdeveloped for conversion purpose. Sequence analyzer is usedto get the characteristics of dg in either of the conditions.

Wavelet analysis is used to analyze the dg characterstics.db4[9] is used to analyze the signal.

REFERENCES[1]A. Borbely, and J. Kreider (2001). Distributed Generation: The PowerParadigm for the New Millennium,CRC-Press, USA.[2]S. Jang, and K. Ho Kim, An Islanding Detection Method for DistributedGenerations Using Voltage

[3 Suresh K. Gawre, N.P.Patidar and R. K. Nema,Application of waveletTransform in power Quality: A ReviewInternational Journal of ComputerApplications (0975 8887) Volume 39 No.18, February 2012

[4]M. Marei, T. Abdel-Galil, E. El-Saadany, and M. Salama, HilbertTransform Based Control Algorithm of the DG Interface for Voltage FlickerMitigation, IEEE Transactions on Power Delivery, Vol. 20, No. 2,April2005.[5]Sachin K. Jain, Student Member, IEEE, D. Saxena, S. N. Singh, SeniorMember, IEEEAdaptive Wavelet Neural Network Based HarmonicEstimation of Single-Phase Systems India2006.[6N.M. Pindoriya, S.N. Singh, and S.K. Singh, "An adaptive waveletneural network-based energy price forecasting in electricity markets,"IEEE Trans. Power Syst., vol. 23, no. 3, pp. 1423-1432, 2008.[7] G. Panda, P.K. Dash, A.K. Pradhan, S.K. Meher, Data compression ofpower quality events using the slantlet transform, IEEE Trans. Power Deliv.17 (2002) 662667.[8] E.Y. Hamid, Z.I. Kawasaki,Wavelet-based data compression of powersystem disturbances using the minimum description length criterion, IEEETrans. Power Deliv. 17 (2002) 460466.[9] O .N. Gerek, D.G. Ece, 2D analysis and compression of power qualityeventdata, IEEE Trans. Power Deliv. 19 (2004) 791798.

[10]p.s.bimbhraPowewrElectronics"[11] Abhisek Ukil, nonmember, Rastko ivanovi,Member, IEEEAbrupt Change Detection in Power System Fault Analysis using

Wavelet Transform

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