performance of 60-pulse vsc based statcom under power … · problems. among power system...

PERFORMANCE OF 60-PULSE VSCBASED STATCOM UNDER POWERQUALITY ISSUES USING WAVELET

ANALYSIS

M.NagaRaju1, V.V.K.Reddy2, M.Sushama3

1Associate Professor,2,3 ProfessorEEE department,

1Audisankara Institute of Technology,2NBKRIST, Andhrapradesh, India

3JNTUH College of engineering, Telangana, [email protected]

October 12, 2018

Abstract

Power quality is the main problem that the industry isfacing today. Power electronics and advanced control tech-nologies have made it possible to reduce the power qualityproblems. Among power system disturbances, voltage sags,swells and temporary faults are some of severe problems tothe power system loads. Flexible AC transmission system isone aspect of the power electronics revolution that is takingplace in all areas of electrical energy. The primary objec-tive of applying a static compensator in a power system is toincrease the power transmission capability from the gener-ators to loads. Power quality detection requires the featureextraction from the input disturbance signal. The proposedresearch work is carried to investigate the performance ofmodified configuration of Static synchronous Compensatorwithin the power system using wavelet multi resolution anal-ysis under various power quality problems. The system

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International Journal of Pure and Applied MathematicsVolume 120 No. 6 2018, 435-471ISSN: 1314-3395 (on-line version)url: http://www.acadpubl.eu/hub/Special Issue http://www.acadpubl.eu/hub/

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model comprising of 60-Pulse voltage source converter basedSTATCOM is constructed using MATLAB/Simulink. Thesimulation results showed that the proposed shunt compen-sator was efficient in mitigating the power quality problems.This approach is different from conventional methods andprovides effective solution to analyses the power system net-works under transients, faults and sudden load injections.

Key Words: Voltage source converter; STATCOM;Sage; Swell; Transients, faults; Power quality

1 INTRODUCTION

In the present scenario, most of the power systems in the developingcountries with large inter connected networks share the generationreserves to increase the reliability of the power system. However,the increasing complexities of large inter connected networks hadfluctuations in reliability of power supply, which resulted in systeminstability, difficult to control the power flow, existence of voltagesag, voltage swell, interruptions, harmonic distortions, transientsand security problems[1] that resulted large number blackouts indifferent parts of the world which are also called power qualityproblems. The reasons behind the above fault sequences may bedue to the systematically errors in planning and operation, weakinterconnection of the power system, lack of maintenance or due tooverload of the network. In order to overcome these consequencesand to provide the desired power flow along with system stabilityand reliability, installations of new transmission lines are required.However, installation of new transmission lines with the large in-terconnected power system are limited to some of the factors likeeconomic cost, environment related issues. These complexities ininstalling new transmission lines in a power system challenges thepower engineers to research on the ways to increase the power flowwith the existing transmission line without reduction in system sta-bility and security[2].Power Quality is the degree to which both the utilization and deliv-ery of electric power affects the performance of electric equipment.The power quality problem can be viewed from two different an-gles related to each side of the utility meter, namely the Utilityand Consumer. A perfect power supply would be one that is al-

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ways available within voltage and frequency tolerances and has apure noise-free sinusoidal wave shape. Power Quality means theability of utilities to provide electric power without interruption.Power Quality has become an important issue since many loadsat various distribution ends like adjustable speed drives, processindustries, printers, domestic utilities; computers, microprocessorbased equipments etc. have become intolerant to voltage fluctua-tions, harmonic content and interruptions. The FACTS devices canbe categories as shunt, series, series-series and combine shunt-seriescontrollers [3]. By the use of such controllable devices, line powerflows can be changed in such a way that thermal limits are not vio-lated, losses minimized, stability margin increased and contractualrequirement fulfilled without violating specified power dispatch [4-5]. Static Synchronous compensator (STATCOM) is one among thedifferent FACTS controllers introduced to improve the power flowcontrol with stability and reliability.A brief survey on the methods for power quality events classifica-tion is done in [6] New and powerful tools for analysis are currentlyavailable. Signal processing tools is used for the feature extractionof power signal. Wavelet analysis[ has been proven to be an effec-tive signal processing tool for the detection and analysis of powersignals but other signal processing tools such as Fourier transform,S-transform, time-time transform, higher-order statistics have alsobeen used to find out other salient features.In order to overcome the problems such mentioned above, the con-cept of custom power devices is introduced recently; custom poweris a strategy, which is designed primarily to meet the requirementsof industrial and commercial customer. The concept of custompower is to use power electronic or static controllers in the mediumvoltage distribution system aiming to supply reliable and high qual-ity power to sensitive users. The Static Synchronous Compensator(STATCOM) is a Voltage Source Converter (VSC) based FlexibleAC Transmission System (FACTS) controller for shunt compensa-tion among the transmission systems [7]. It can control bus voltageand power flows of sub-network. This paper presents the completedigital simulation of the improved configurations of STATCOMwithin the power system is performed in the MATLAB/Simulinkenvironment to handle the power quality issues. The paper pro-poses a full model comprising of voltage source converter based

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STATCOM is constructed for digital simulation to investigate theperformance of the controller on various power quality problemsand observed that considerable improvement is identified on 48 and60-pulse Voltage source converter.

2 Statcom and Control System Model

Fig.1 Single-line Diagram of a STATCOM

The Static Synchronous compensator (STATCOM) is a VoltageSource Converter (VSC) based Flexible AC Transmission System(FACTS) controller for shunt voltage sourced converters within thepower system. Single-line Diagram of a STATCOM and Its ControlSystem illustrated is shown in Fig.2. The 60-pulse voltage sourceconverter is composed of a series double bridge converter and anauxiliary circuit [8]. The converter is established to increase thenumber of output voltage pulses and decrease the harmonic distor-tion of output voltage and current. Without PWM or increasingthe number of bridges, the THD of the converter output voltagecan be theoretically reduced. The basic objective of a good VSCscheme is to produce a near sinusoidal ac voltage with minimalwave form distortion or excessive harmonics content.The 24 to 60 pulse converters are obtained by combining 12-pulsevoltage source Inverters, with the specified phase shift betweenconverters. For high-power applications with low distortion, thebest option is the 60-pulse converter, although using parallel fil-ters tuned to the 23th25th harmonics with a 24-pulse converter

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could also be adequately attentive in most applications, but the60-pulse converter scheme can ensure minimum power quality prob-lems and reduced harmonic resonance conditions on the intercon-nected grid network. The proposed configuration only needs oneinjection transformer, so that phenomenon does not exist. Also, de-creasing of transformer number is important for saving cost. Theconverter is operated under fundamental frequency for the mainbridges and six time fundamental frequency for the auxiliary cir-cuit, while much higher frequency is needed for PWM. By DC volt-age injection, the voltage across the main bridge valves, which arebeing turned on, is theoretically decreased to zero. Thus the con-verter switching loses and switching device dynamic voltage stressis reduced significantly. This characteristic is very important forhigh voltage application.

3 Wavelet Analysis

Concept of wavelet started to appear in early 1980s as a signalprocessing tool. Wavelet theory provided new method for decom-posing a function or signal into various frequency components, andthen study each component with a resolution match to its scale.A wavelet is a small wave, its energy is concentrated in time togive a tool for analysis of transients, non stationary, time varyingphenomenon which generally occurs in the power system network.Wavelet has ability to allow simultaneous time and frequency anal-ysis of a signal with a flexible mathematical foundation [9]. Inwavelet analysis, signal broken into a series of local basis func-tions called wavelets, which are scaled and shifted versions of theoriginal (or Mother) wavelet. Wavelet transform can be classifiedin three different ways known as the wavelet series, continuousWavelet Transform and discrete Wavelet Transform. The waveletcoefficients represent the information which is contained in variousfrequency bands of a signal. The peak magnitude, the mean value,square magnitude, the standard deviation, the entropy of these co-efficients at the different resolution levels are commonly used mag-nitudes proposed in the literature as characteristic features for thedetection and analysis of power quality events in power systems [10].Multiresolution analysis technique of wavelet is used in analysis of

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waveforms and images [11-12]. Wavelet functions and scaling func-tions are used as building blocks to decompose and reconstruct thesignal at different resolutions in Multi Resolution Analysis (MRA).

4 Proposed 60 Pulse Converter

Fig. 2 Proposed model with the 60-pulse STATCOM

The unified ac grid sample system with the Static synchronouscompensator for the shunt VSC and control scheme [13-14] is con-nected to four bus system. The single line diagram representingthe STATCOM and the host sample grid network as illustrated inFig2. The feeding network are at bus S1 where the voltage sourceis represented by a 25 kV with 100 MVA and 3MW injected loadconnected at B2 , at bus B3 with 5MW and 2Mvar injected load,and at bus B4 with 25KV,5Mvar. The STATCOM located at theleft end of the 10 km feeder from B2. It consists of three 100-MVA,three-level, 60-pulse GTO-based converters, connected as shunt atbus B2. The shunt converter can exchange power through a DCbus. The shunt converter operates as a STATCOM. It controlsthe bus B2 voltage by controlling the absorbed or generated reac-tive power while also allowing active power transfer to the shuntconverters through the DC bus. The reactive power variation isobtained by varying the DC bus voltage. The five three-level shuntconverters operate at a constant conduction angle (Sigma= 180-3.75= 176.25 degrees), thus generating a quasi-sinusoidal 60-step volt-age waveform. The first significant harmonics are the 59th and the

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61th. The digital simulation model comprises of five 12-pulse GTO-converters, phase-shifted by -3.75◦ from each other and model, canprovide the full 60-pulse converter operation. Using a symmetricalshift criterion, the 3.75◦ are provided in the following way: phase-shift winding with -3.75◦ on the two coupling transformers of one24-pulse converter and +3.75◦ on two transformers of the second 24-pulse converter and with -3.75◦ on two transformers of the other two24-pulse converter. The firing pulses need a phase-shift of, -3.75◦

respectively. The 60-pulseconverter model comprises five identical12-pulse GTO converters interlinked by five 12-pulse transformerswith phase-shifted windings. Fig. 4 depicts a schematic diagram ofthe 60-pulse GTO converters model for shunt VSC, where advancedfrom 60-pulse GTO as introduced in [8] and with the same methodcan be found for series VSC. The transformer connections and thenecessary firing-pulse logics to get this final 60-pulse operation aremodeled. The 60-pulse converter can be used in high-voltage high-power applications without the need for any ac filters due to itsvery low harmonic distortion content on the ac side. The outputvoltage have normal harmonics n = 60r ± 1, where r = 0, 1, 2,3i.e. 59th, 60th, 129th, 131th, 179yh, with typical magnitudes (1/59,1/61,1/129th, 1/131th, 1/179th ..), respectively, with respect to thefundamental; on the dc side, the lower circulating dc current har-monic content is the 60th.

Fig. 3 Digital simulation model of 60-pulse voltage sourceconverter

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5 Result Analysis

The variation of three phase currents and voltages are shown in Fig4 and Fig 5 under increased load in the transmission system.

Fig. 4 variation of 3ph currents under sudden load injected at BusB2.

Fig. 5 variation of 3ph voltages under sudden load injected at BusB2.

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Fig. 6 Analysis of wavelet detailed coefficients of current signal atsag

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Fig. 7 Analysis of wavelet detailed coefficients of voltage signal atsag

The analysis of wavelet detailed coefficients current and voltagesignals are illustrated under sudden load injection from bus 2 areillustrated in Fig 6 and Fig7.

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Fig 8. Variation of three phase currents at Bus B2 with 48-pulseVSC based STATCOM

Fig 9. Variation of three phase voltages at Bus B2 with 48-pulseVSC based STATCOM

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Fig 10. Analysis of wavelet detailed coefficients of current signalat Bus B2 of STATCOM with 48-pulse VSC

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Fig 11. Analysis of wavelet detailed coefficients of Voltage signalat B2 of STATCOM with 48-pulse VSC connected

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Fig 12. Sum of the detailed coefficients of current signal at BusB2 of STATCOM with 60-pulse VSC .

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Fig 13. Analysis of wavelet detailed coefficients of Voltage signalat Bus B2 of STATCOM with 60-pulse VSI

The variation of three phase signals of 48-Pulse VSC basedSTATCOM controller connected system current and voltages, waveletdetailed coefficients and sum of the detailed coefficients of currentand voltage signals are described in Fig [8-11]. The variation ofthree phase signals of 60-Pulse VSC based STATCOM controllerconnected system current and voltages, wavelet detailed coefficientsand sum of the detailed coefficients of current and voltage signalsare described in Fig [12-13] at sag due to under injecting suddenload.

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Fig 14. variation of 3ph currents under transient occur due tosudden injecting capacitor load from bus B2

Fig 15. variation of 3ph voltages under transient occur due tosudden injecting capacitor load from bus B2

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Fig 16. wavelet detailed coefficients of current signal at transientoccur due to sudden injecting capacitor load from bus B2

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Fig 17. Wavelet detailed coefficients of voltage signal at transientoccur due to sudden injecting capacitor load from bus B2

The variation of three phase currents and voltages are shown inFig 14, Fig 15 under transient condition due to sudden capacitivereactive load in the transmission system. The analysis of waveletdetailed coefficients current and voltage signals are illustrated undertransient condition due to sudden capacitive reactive load in thetransmission system from bus 2 are illustrated in Fig 16 and Fig17.

Fig 18. variation of three phase currents at Bus B2 with 48-pulseVST based STATCOM

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Fig 19. variation of three phase voltages at Bus B2 with 48-pulseVSC based STATCOM

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Fig 20. wavelet detailed coefficients of current signals at Bus B2with 48–pulse VSC based STATCOM

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Fig 21. wavelet detailed coefficients of voltage signals at Bus B2with 48-pulse VSC based STATCOM

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Fig 22. variation of three phase currents at Bus B2 with 60-pulseVSC based STATCOM

Fig 23. variation of three phase voltages at Bus B2 with 60-pulseVSC based STATCOM

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Fig 24. wavelet detailed coefficients of current signals at Bus B2with 60-pulse VST based STATCOM

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Fig 25. wavelet detailed coefficients of voltage signals at Bus B2with 60–pulse VST based STATCOM when sudden capacitive

load injected

The variation of three phase signals of 48-Pulse VSC basedSTATCOM controller connected system current and voltages, waveletdetailed coefficients and sum of the detailed coefficients of currentand voltage signals are described in Fig [18,19]. The variation ofthree phase signals of 60-Pulse VSC based STATCOM controllerconnected system current and voltages, Fig [18-25] under transientcondition due to sudden capacitive reactive load in the transmission

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system.

Fig 26. Variation of 3ph currents under AG Fault occur at 5Kmdistance from bus B2

Fig 27. Variation of 3ph voltages under AG Fault occur at 5Kmdistance from bus B2.

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Fig 28. wavelet detailed coefficients of current signals under AGFault occur at 5Km distance from bus B2

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Fig 29. wavelet detailed coefficients of voltage signals under AGFault occur at 5Km distance from bus B2.

The variation of three phase currents and voltages are shown inFig 26 and Fig 27 under AG Fault occur at 5Km distance from busB2. The analysis of wavelet detailed coefficients current and volt-age signals are illustrated under AG Fault occur at 5Km distancefrom bus B2 are illustrated in Fig 28 and Fig 29. The variationof three phase signals of 48-Pulse VSC based STATCOM controllerconnected system current and voltages, wavelet detailed coefficients

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and sum of the detailed coefficients of current and voltage signalsare described in Fig 30 and Fig 31.

Fig 30. variation of Three phase currents at Bus B2 with 48-pulseVST based STATCOM when AG Fault occurs

Fig 31. variation of Three phase voltages at Bus B2 with 48–pulseVST based STATCOM when AG Fault occur

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Fig 32. wavelet detailed coefficients of current signals at Bus B2with 48-pulse VST based STATCOM when AG Fault occurs

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Fig 33. wavelet detailed coefficients of voltage signals at Bus B2with 48-pulse VST based STATCOM when AG Fault occurs

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Fig 34. variation of Three phase currents at Bus B2 with 60-pulseVST based STATCOM when AG Fault occurs

Fig 35. variation of Three phase voltages at Bus B2 with 60-pulseVST based STATCOM when AG Fault occurs .

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Fig 36. wavelet detailed coefficients of current signals at Bus B2with 60-pulse VST based STATCOM when AG Fault occurs .

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Fig 37. wavelet detailed coefficients of voltage signals at Bus B2with 60-pulse VST based STATCOM when AG Fault occurs.

The variation of three phase signals of 60-Pulse VSC basedSTATCOM controller connected system current and voltages, waveletdetailed coefficients and sum of the detailed coefficients of currentand voltage signals are described in Fig [32-37] under AG Fault

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occur at 5Km distance from bus B2.

6 CONCLUSION

This paper presents comprehensive analysis on the developmentof technologies used to mitigate the power quality problem usingFlexible AC transmission controllers .Power electronics and ad-vanced control technologies have made it possible to reduce thepower quality problems. Among power system disturbances, volt-age sags, swells, transients and temporary faults are some of severeproblems to the power system loads are studied. The Static Syn-chronous Compensator (STATCOM) is a 60-pulse Voltage SourceConverter (VSC) based shunt compensation transmission systemsis developed using the MATLAB/Simulink. This paper presentsthe complete digital simulation of the improved configurations ofSTATCOM within the power system to handle power quality is-sues. The proposed system is tested under various power qualityproblems and found that increasing the number pulse in voltagesource converter based STATCOM can control power quality issueseffectively. For detecting and characterizing power system distur-bances wavelet based systems have been found to be more robustand effective. The proposed analysis on the development of tech-nologies used in power quality analysis, which is the major area ofresearch in the field of power system.

References

[1] Roger C. Dugan, Mark f. Mcgranaghan, Surya Santoso, H.Wayne Beaty, Electrical power systems quality ,Tata McGrawHills publications, 2002.

[2] Wang. T. X. and Choi S. S., Enhancement of Voltage Qual-ity in Isolated Power Systems, IEEE Transactions on powerdelivery, Vol. 22,No. 2, 1160 1168, 2007

[3] N. G. Hingorani and L. Gyugyi, Understanding FACTS Con-cepts and Technology of Flexible AC Transmission Systems,Pscataway, NJ: IEEE Press. 2000

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[4] Padiyar K. R., Facts Controllers in Power Transmission AndDistribution, New Age International (P) Limited, Publishers,2007.

[5] Edris, FACTS Technology Development: An Update, IEEEPower Engineering Review, Vol 20, No. 3, pp. 4-9, 2000.

[6] Blajszczak, G. Antos, P, Power Quality Park - Idea and feasi-bility study, Proc. Of Electric Power Quality and Supply Re-liability Conference (PQ), 16-18, pp 17 22, 2010.

[7] Ravi Kumar Goli , Abdul Gafoor Shaik, S.S Tulasi Ramc Atransient current based double line transmission system pro-tection using fuzzy-wavelet approach in the presence of UPFC,Elsevier, International journal on Electrical Power and EnergySystems, pp.9198, 2015

[8] W. Pan, Z. Xu, and J. Zhang, Novel configuration of 60-pulsevoltage source converter for STATCOM application, Interna-tional Journal of Emerging Electric Power Systems, Vol 8,2007.

[9] O. Rioul and M. Vetterli, Wavelets and signal processing, IEEESignal Processing Mag., pp. 14- 38, 1991.

[10] J. Barros, R.I. Diego, M.D. Apraiz, Applications of wavelets inelectric power quality: Voltage events, Electric Power SystemsResearch, vol. 88, pp. 130 136, 2012.

[11] C.K. Chui, An Introduction to Wavelets. New Yark: Academic,1992

[12] M. Misiti, Y. Misiti, G. Oppenheim, J.-M. Poggi, Wavelet tool-box for use with Matlab-Users guide, The MathWorks, 1997.

[13] H. Zhang, Z. Zha, M. Zhang, X. Zha, The Study on the Ap-plication of Repetitive Control in STATCOM, IEEE Inter-national Conference on Intelligent Computing and IntelligentSystems, Xiamen, China, Vol. 3, pp. 502-506, 2010.

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[14] M. S. El-Moursi, A. M. Sharaf, Novel Controllers for the 48-Pulse VSC StatCom and SSSC for Voltag Regulation and Re-active Power Compensation, IEEE Transactions on Power Sys-tems, Vol. 20, No. 4, pp. 1985-1997, 2005

[15] Anulekha Saha, Priyanath Das, and Ajoy Kumar Chakraborty,Performance analysis and comparison of various FACTS de-vices in power system, International Journal of Computer Ap-plications, Vol. 46, No. 15, pp.9-15, 2012.

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performance of 60-pulse vsc based statcom under power … · problems. among power system...

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