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  • 1. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 3, May - June (2013), © IAEME63OPTIMAL PLACEMENT OF DSTATCOM IN AN INDIAN POWERSYSTEM FOR LOAD AND VOLTAGE BALANCINGD.K. Tanti1, M.K. Verma2, Brijesh Singh3, O.N. Mehrotra41,4Department of Electrical Engineering, B.I.T., Sindri (INDIA)2,3Department of Electrical Engineering, I.I.T.( BHU), Varanasi (INDIA)ABSTRACTThe present paper deals with the problem of unbalanced voltages arising due tounbalanced loads in an electrical power system network. In this paper, placement ofDistribution Static Compensator (DSTATCOM) in an Indian power system network has beenconsidered to balance load voltages and currents against switching of unbalanced loads.Impact of DSTATCOM has also been observed in balancing voltage at all other buses whichget affected due to connection of unbalanced load in the system. A feed forward neuralnetwork with back propagation algorithm has been trained with unbalanced bus voltages withtargets defined as balanced bus voltages prior to connection of unbalanced load in the system.The DSTATCOM has been placed at the bus having maximum squared deviation of threephase unbalanced bus voltage from its target value. Simulations have been carried out instandard MATLAB environment using SIMULINK and power system block-set toolboxes.Simulation results establish effectiveness of DSTATCOM placement in load and voltagebalancing in the Indian power system considered.Keywords: Power quality, Load balancing, Voltage balancing, DSTATCOM, Optimalplacement, ANN1. INTRODUCTIONPower quality is of increasing importance in worldwide distribution. The presentdistribution systems are facing severe power quality problems such as poor voltageregulation, high reactive power demand, harmonics in supply voltage and current, and loadunbalancing [1]. Therefore, maintenance of power quality is becoming of increasingINTERNATIONAL JOURNAL OF ELECTRICAL ENGINEERING& TECHNOLOGY (IJEET)ISSN 0976 – 6545(Print)ISSN 0976 – 6553(Online)Volume 4, Issue 3, May - June (2013), pp. 63-74© IAEME: www.iaeme.com/ijeet.aspJournal Impact Factor (2013): 5.5028 (Calculated by GISI)www.jifactor.comIJEET© I A E M E
  • 2. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 3, May - June (2013), © IAEME64importance in worldwide distribution systems. Industrial consumers with more automatedprocesses require high quality power supply else equipments such as microcontrollers,computers and motor drives may get damaged. High quality power delivery includesbalanced voltage supply to consumers. Connection of unbalanced load at a bus may causeunbalanced voltage and current drawn by other loads connected at that bus. Switching ofunbalanced load at a bus may also result in unbalanced voltage at some other buses.Unbalanced voltages contain negative and zero sequence components which may causeadditional losses in motors and generators, oscillating torques in Alternating Current (AC)machines, increased ripples in rectifiers, saturation of transformers, excessive neutral currentsand malfunctioning of several type of equipments. With the advancement in powerelectronics, new controllers known as Flexible AC Transmission System (FACTS) have beendeveloped [2]. These controllers have been proved to be quite effective in power flowcontrol, reactive power compensation and enhancement of stability margin in AC networks[3].Power electronics based controllers used in distribution systems are called custompower devices. Custom power devices have been proved to be quite effective in powerquality enhancement [1]. The custom power devices may be series, shunt, and series-shunt orseries-series type depending upon their connection in the circuit. Most prominent custompower devices include Distribution Static Compensator (DSTATCOM), Dynamic VoltageRestorer (DVR) and Unified Power Quality Conditioner (UPQC) [1]. There are severalpapers reported in literature on placement of custom power devices in balancing ofunbalanced load in radial distribution systems. Load voltage balancing using DVR againstunbalanced supply voltage in radial distribution system has been considered [4], [5].Placement of DSTATCOM in weak AC radial distribution system for load voltage andcurrent balancing has been considered in [6]. Balancing of source currents usingDSTATCOM in radial distribution system has been considered in [7]. In [7], unbalancing hasbeen caused by connection of unbalanced and non-linear load. Load compensation usingDSTATCOM against unbalancing caused by opening of one of the phase of the load in radialdistribution system has been considered in [8]. Balancing of supply across an unbalanced 4-phase load along with power factor improvement using DSTATCOM has been suggested in[9]. A Voltage Source Converter (VSC) based controller has been proposed in [10] to balanceterminal voltage of an isolated standalone asynchronous generator driven by constant speedprime mover. A non-linear and unbalanced load has been connected at the generatorterminals in [10] to create unbalance in supply voltages. The paper [11] uses three phase fourwire four leg VSC topology for a DSTATCOM application. The four leg inverter is operatedin a current controlled mode by a suitable control strategy to inject compensator currents inorder to achieve harmonic compensation, load balancing and power factor correction. Thecontrol of DSTATCOM for reactive power, harmonics and unbalanced load currentcompensation has been presented [12] for a diesel generator set for an isolated system. Thepaper [13] proposes a method to use SVCs (Static VAR Compensators) with four wire threephase loads for load balancing and reactive power compensation. A DVR/APF (Active PowerFilter) based on Proportional Resonant (PR) controller has been proposed in [14] to protectsensitive industrial loads at the point of common coupling, against voltage harmonics,imbalances and sags.Most of the work on placement of custom power devices in load balancing hasconcentrated on radial distribution systems. Very limited attempt seems to be made in loadbalancing in interconnected power systems using custom power devices. Unbalanced load
  • 3. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 3, May - June (2013), © IAEME65connected at a particular bus may cause voltage unbalances at several other buses in aninterconnected power system network. An Artificial Neural Network (ANN) based approachhas been applied for optimal placement of custom power devices in IEEE 14- bus systemconsidering it as an interconnected distribution system, for balancing bus voltages at all thebuses caused by unbalanced load connected at a particular bus [15]. However, IEEE 14-bussystem may be considered as a small and well behaved system. The methodology suitable foroptimal placement of custom power devices for this system may not be suitable for a largeand practical system. In this paper, Artificial Neural Network based approach suggested in[15] has been considered for optimal placement of DSTATCOM to balance unbalancedvoltages in a practical 75-bus Indian system representing earlier Uttar Pradesh andUttarakhand Power Corporation Network. The ANN has been trained with LevenbergMarquardth back-propagation algorithm (trainlm).2. DSTATCOM MODELIn the present work, DSTATCOM has been represented as three independentlycontrollable single phase current sources injecting reactive current in the three phases at thepoint of coupling. The proposed DSTATCOM model has been shown in Figure-1. Thecontrol scheme consists of three control switches which can be set on/off as per compensationrequirement.Figure-1. Proposed DSTATCOM model3. METHODOLOGYThe simulation model of the power system network under study is developed usingMATLAB/SIMULINK software [16]. The developed plant model was used to find threephase balanced bus voltages prior to switching of unbalanced load, unbalanced three phasevoltage and current at the bus where unbalanced load is switched on, and unbalanced three
  • 4. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 3, May - June (2013), © IAEME66phase voltages at other buses in the system. The voltage data base so prepared has been usedfor training of ANN for finding the optimal location of DSTATCOM. A feed forwardArtificial Neural Network with back propagation algorithm has been used. The neuralnetwork has been trained to give a desired pattern at the output, when the correspondinginput data set is applied. The training process is carried out with a large number of input andoutput target data. The system has been made unbalanced by connection of highly unbalancedload at different load buses. The three phase balanced per unit (p.u.) voltages of buses prior toconnection of unbalanced load, have been taken as output target data. The three phase p.u.voltages of buses under unbalanced loading conditions have been considered as input data totrain the neural network. Once the network is trained, some data are used to test the network.The testing results provide information about the optimal location for the placement ofDSTATCOM controller. Mean Square Error (MSE) has been computed for all the buses. Theload bus corresponding to highest mean Mean Square Error value has been selected as theoptimal bus for the placement of DSTATCOM controller.4. CASE STUDIESCase studies were performed on a practical 75-bus Indian system [17]. The 75 busIndian system is a reduced representation of earlier Uttar Pradesh and Uttarakhand PowerCorporation Network. It consists of 75 buses including 15 synchronous generators and 97transmission lines. There are 42 load buses in the system having a net real and reactive powerdemand of 6573.5 MW and 1002.37 MVAR, respectively. The single-line-diagram of thesystem has been shown in Figure-2. Simulation model of 75-bus system Indian system wasdeveloped using software package MATLAB/SIMULINK [16]. The simulation blockdiagram of the system has been shown in Figure-3. The developed plant model shown inFigure-3 was used to find three phase balanced bus voltages prior to switching of unbalancedload, unbalanced three phase voltage and current at the bus where unbalanced load isswitched on, and unbalanced three phase voltages at other buses in the system. In order tocreate unbalance loading condition, an additional Y- connected highly unbalanced load ;Phase A [P=1MW, Q=100MVAR] , Phase B [ P=25KW, Q=200KVAR] , Phase C [ P=1KW,Q=0.1KVAR] was connected at each bus considered at a time, with all other buses havingbalanced base case loadings. A feed forward neural network was trained with three phaseunbalanced bus voltages. The balanced three phase voltages of different buses prior toconnection of unbalanced load at a bus were considered as target data for the neural network.The Mean Square Errors (MSE) were calculated for all the load buses using training data andtarget data. The MSE of all the buses have been shown in Figure-4. It is observed fromFigure-4 that bus-47 has maximum MSE value. Therefore, bus-47 was selected as the optimallocation for the placement of DSTATCOM controller.Three phase voltage at all the buses and three phase current at the bus withunbalanced load were found with DSTATCOM placed at bus-47 for all the unbalancedloading cases. The variation of three phase voltage with respect to time for all the buses andvariation of three phase current with respect to time at the bus with unbalanced load wereplotted using MATLAB software [16]. Three phase voltage and current at bus-30 withunbalanced load connected at bus-30 have been shown in Figure-5. Three phase voltage atbuses 16, 49, 62 and 74 with unbalanced load connected at bus-30 have been shown inFigure-6. Three phase voltage and current at bus-39 with unbalanced load connected at bus-39 have been shown in Figure-7. Three phase voltage at buses 28, 57, 65 and 73 with
  • 5. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 3, May - June (2013), © IAEME67unbalanced load connected at bus-39 have been shown in Figure-8. Three phase voltage atbuses 20, 32, 52 and 69 with unbalanced load connected at bus-47 have been shown inFigure-9. Three phase voltage and current at bus-47 with unbalanced load connected at bus-47 have been shown in Figure-10. Three phase voltage and current at bus-50 with unbalancedload connected at bus-50 have been shown in Figure-11. Three phase voltage at buses 25, 34,53 and 64 with unbalanced load connected at bus-50 have been shown in Figure-12. Threephase voltage and current at bus-54 with unbalanced load connected at bus-54 have beenshown in Figure-13. Three phase voltage at buses 24, 42, 60 and 66 with unbalanced loadconnected at bus-54 have been shown in Figure-14. It is observed from figures 5, 7, 10, 11and 13 that placement of DSTATCOM at bus-47 results in considerable balancing of loadvoltage and current at the bus with unbalanced load. It is observed from figures 6, 8, 9, 12and 14 that placement of DSTATCOM at bus-47 is also able to produce considerable voltagebalancing at other buses.Figure-2. Single line diagram of the 75-bus Indian system
  • 6. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 3, May - June (2013), © IAEME68Figure-3. 75-bus Indian system (MATLAB/SIMULINK) modelFigure-4. Mean Square Error for different load buses (75-bus Indian System)
  • 7. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 3, May - June (2013), © IAEME69BusNo.Without DSTATCOM With DSTATCOM at Bus 473030Figure-5. Three phase voltage and current at bus-30 with unbalanced load connected at bus-30BusNo.Without DSTATCOM With DSTATCOM at Bus 4716496274Figure-6. Three phase voltage at buses 16, 49, 62 and 74 with unbalanced load connected at bus-30BusNo.Without DSTATCOM With DSTATCOM at Bus 473939Figure-7. Three phase voltage and current at bus-39 with unbalanced load connected at bus-39
  • 8. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 3, May - June (2013), © IAEME70BusNo.Without DSTATCOM With DSTATCOM at Bus 4728576573Figure-8. Three phase voltage at buses 28, 57, 65 and 73 with unbalanced load connectedat bus-39Busno.Without DSTATCOM With DSTATCOM at Bus 4720325269Figure-9. Three phase voltage at buses 20, 32, 52 and 69 with unbalanced load atconnected at bus-47
  • 9. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 3, May - June (2013), © IAEME71BusNo.Without DSTATCOM With DSTATCOM at Bus 474747Figure-10. Three phase voltage and current at bus-47 with unbalanced load connected atbus-47Busno.Without DSTATCOM With DSTATCOM at Bus 475050Figure-11. Three phase voltage and current at bus-50 with unbalanced load connected atbus-50Busno.Without DSTATCOM With DSTATCOM at Bus 4725345364Figure-12. Three phase voltage at buses 25, 34, 53 and 64 with unbalanced load atconnected at bus-50
  • 10. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 3, May - June (2013), © IAEME72Busno.Without DSTATCOM With DSTATCOM at Bus 475454Figure-13. Three phase voltage and current at bus-54 with unbalanced load connected atbus-54Busno.Without DSTATCOM With DSTATCOM at Bus 4724426066Figure-14. Three phase voltage at buses 24, 42, 60 and 66 with unbalanced load atconnected at bus-545. CONCLUSIONCustom power devices have shown to be quite effective in power qualityenhancement. However, due to high cost and for most effective utilization, these controllersare to be placed optimally in the system. In the present work, optimal placement ofDSTATCOM has been considered in a practical Indian power system based on ANNmethodology to balance voltages and currents caused by switching of unbalanced loads.Simulation results show that DSTATCOM is capable of enhancing not only voltage andcurrent unbalances at unbalanced load location, but also voltages at other locations.
  • 11. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 3, May - June (2013), © IAEME73REFERENCES[1] A. Ghosh and G. Ledwich, “Power quality enhancement using custom powerdevices”, Kluwer Academic Publishers (London) 2002.[2] N. G. Hingorani and L. Gyugyi, “Understanding FACTS: Concepts and technology ofFlexible AC Transmission System”, IEEE publication, 2000.[3] J. Dixon, Luis Moran, Jose Rodriguez, “Reactive power compensation technologies:State of art review”, Proceedings of the IEEE, Vol.93, No. 12, pp. 2144-2164,December 2005.[4] Arindam Ghosh and Gerald Ledwich, “Compensation of distribution system voltageusing DVR”, IEEE Transactions on Power Delivery, Vol. 17, No. 4, pp. 1030-1036,October 2002.[5] Pendro Roncero-Sanchez, Enrique Acha, Jose Enrique Ortega-Calderon, VicenteFeliu, and Aurelio Gareia-Cerrada, “A versatile control scheme for a DynamicVoltage Restorer for power quality improvement”, IEEE Transactions on PowerDelivery, Vol. 24, No. 1, pp. 277-284, January 2009.[6] Arindam Ghosh and Gerald Ledwich, “Load compensating DSTATCOM in weak ACsystems”, IEEE Transactions on Power Delivery, Vol. 18, No. 1, pp. 1302-1309,October 2003.[7] C. N. Bhende, Dr. M. K. Mishra, and Dr. H. M. Suryawanshi, “ A D-STATCOMmodeling, analysis and performance for unbalanced and non-linear loads”, Institutionsof Engineers(India) Journal – EL , Vol. 86, pp. 297-304, March 2006.[8] Wei-Neng Chang and Kuan-Dih Yeh, “Design and implementation of D-STATCOMfor fast load compensation of unbalanced loads, “Journal of Marine Science andTechnology” , Vol. 17, No. 4, pp. 257-263, 2009.[9] Zakir Husain, Ravinder Kumar Singh and Shri Niwas Tiwari, “ Balancing ofunbalanced load and power factor correction in multiphase ( 4 phase ) load circuitsusing D-STATCOM”, Proceedings of the World Congress on Engineering 2010, Vol.II WCE-2010, June 30-July 2, 2010, London (U.K).[10] Gaurav Kumar Kasal and Bhim Singh, “Harmonic elimination, voltage control andload balancing in an isolated power generation”, European Transactions onElectrical Power, Vol. 20, Issue 6, pp. 771-784, September 2010.[11] Srikanthan S, and Mahesh K. Mishra, “ Modeling of a four leg inverter basedDSTATCOM for load compensation” , pp. 1-6, 2010 International Conference onPower System Technology.[12] Bhim Singh and Jitendra Solanki, “ Load Compensation for Diesel Generator basedIsolated Generation System employing DSTATCOM” , IEEE Transaction on IndustryApplication, Vol. 47 No. 1, pp. 238-244 Jan./Feb. 2011.[13] F. R. Quintela, J. M. G. Arevalo, R. C. Redondo and N. R. Melchor, “ Four-WireThree-Phase Load Balancing with Static VARs Compensators” , pp. 562-568,Electrical Power & Enery Systems 33(2011).[14] Pablo Fernandez-Comesana, Francisco D. Freijedo, Jesus Doval-Gandoy, OscarLopez, Alejandro G. Yepes, Jano Malvar, “Mitigation of voltage sags, imbalances andharmonics in sensitive industrial loads by means of a series power line conditioners”,Electric Power Systems Research, Vol. 84, Issue 1, pp. 20-30, March 2012.
  • 12. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 3, May - June (2013), © IAEME74[15] D. K. Tanti, M.K.Verma, Brijesh Singh and O.N.Mehrotra, “Optimal Placement ofCustom Power Devices in Power System Network for Load and Voltage Balancing”, International Journal of Electrical Engineering and Technology (IJEET), Volume 3,Issue 3, pp. 187-199, October- December 2012, ISSN Print: 0976-6545,ISSN Online: 0976-6553.[16] MATLAB 7 User’s Guides for SIMPOWER SYSTEMS and Neural Network Tool-box.[17] S. N. Singh and S.C. Srivastava, “Corrective action planning to achieve optimalpower flow solution,” IEE Proceedings, Part C, Vol. 142, pp. 576-582, November1995.[18] D. Pattanayaka, M. Basub and R. N. Chakrabartic, “Multi-Objective DifferentialEvolution for Optimal Power Flow”, International Journal of Electrical Engineering &Technology (IJEET), Volume 3, Issue 1, 2012, pp. 31 - 43, ISSN Print : 0976-6545,ISSN Online: 0976-6553.[19] G.Kumar and P.S.Raju, “Study of DSTATCOM in Improved Custom Power Park forPower Quality Improvement”, International Journal of Electrical Engineering &Technology (IJEET), Volume 3, Issue 3, 2012, pp. 12 - 20, ISSN Print : 0976-6545,ISSN Online: 0976-6553.