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1. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –INTERNATIONAL JOURNAL OF ELECTRICAL ENGINEERING 6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME & TECHNOLOGY (IJEET)ISSN 0976 – 6545(Print)ISSN 0976 – 6553(Online) IJEETVolume 4, Issue 2, March – April (2013), pp. 136-154© IAEME: www.iaeme.com/ijeet.aspJournal Impact Factor (2013): 5.5028 (Calculated by GISI) ©IAEMEwww.jifactor.com COMPARISION OF Pi, FUZZY & NEURO-FUZZY CONTROLLER BASED MULTI CONVERTER UNIFIED POWER QUALITY CONDITIONER B.RAJANI1, Dr.P.SANGAMESWARA RAJU2 1 Phd.Research Scholar,S.V.University.College of Engineering, Dept.of Electrical Engg Tirupathi, A.P INDIA 2 Professor, SV University, Tirupathi, Andhra Pradesh, INDIA ABSTRACT Multi converter -Unified power quality conditioner (MC-UPQC) is one of the new power electronics devices that are used for enhancing the PQ. This paper presents a new unified power-quality conditioning system (MC-UPQC), capable of simultaneous compensation for voltage and current in multibus/multifeeder systems. In this configuration, one shunt voltage-source converter (shunt VSC) and two or more series VSCs exist. The system can be applied to adjacent feeders to compensate for supply-voltage and load current imperfections on the main feeder and full compensation of supply voltage imperfections on the other feeders. In the proposed configuration, all converters are connected back to back on the dc side and share a common dc-link capacitor. sharing with one DC link capacitor. The discharging time of DC link capacitor is very high, and so it is the main problem in MC- UPQC device. To eliminate this problem, an enhanced Neuro-fuzzy controller (NFC) based MC-UPQC is proposed in this paper. NFC is the combination of neural network (NN) based controller and fuzzy logic controller (FLC). Initially, the error voltage and change of error voltage of a nonlinear load is determined. Then the voltage variation is applied separately to FLC and NN-based controller. In order to regulate the dc-link capacitor voltage, Conventionally, a proportional controller (PI) is used to maintain the dc-link voltage at the reference value. The transient response of the PI dc-link voltage controller is slow. So, a fast acting dc-link voltage controller based on the energy of a dc-link capacitor is proposed. The transient response of this controller is very fast when compared to that of the conventional dc-link voltage controller. By using fuzzy logic controller instead of the PI controller the transient response is improved. The DC capacitor charging output voltage is increased and 136
International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEMEthe response is fast when compared with fuzzy by using the Neuro –Fuzzy logic controllerand hence, the PQ of the system is enhanced. The proposed controller is tested and the resultsof tested system and their performances are evaluated & the Voltage and current harmonics(THD’s) of MC-UPQC with different intelligence techniques are calculated and listedTherefore, power can be transferred from one feeder to adjacent feeders to compensate forsag/swell and interruption. The performance of the proposed configuration has been verifiedthrough simulation studies using MATLAB/SIMULATION on a two-bus/two-feeder systemshow the effectiveness of the proposed configuration.KEYWORDS: power quality (PQ), matlab/simulation multi converter unified power-qualityconditioner (MC-UPQC), (VSC), fuzzy logic controller (FLC), neural network (NN) basedcontroller, neuro-fuzzy controller (NFC), harmonics.1. INTRODUCTION Power quality is the combination of voltage quality and current quality. Voltagequality is concerned with the deviation of actual voltage from ideal voltage. Current quality isthe equivalent definition for the current. Any deviation of voltage or current from the ideal isa power quality disturbance. Any change in the current gives a change in the voltage and theother way around. Voltage disturbance originate in the power network and potentially affectthe customers, where as current disturbance originate with customer and potentially affect thenetwork . As commercial and industrial customers become more and more reliant on highquality and high-reliability electric power, utilities have considered approaches that wouldprovide different options or levels of premium power for those customers who requiresomething more than what the bulk power system can provide insufficient power quality canbe caused by failures and switching operations in the network, which mainly result in voltagedips, interruptions, and transients and network disturbances from loads that mainly result inflicker (fast voltage variations), harmonics, and phase imbalance. Momentary voltage sagsand interruptions are by far the most common disturbances that adversely impact electriccustomer process operations in large distribution systems. In fact, an event lasting less thanone-sixtieth of a second (one cycle) can cause a multimillion-dollar process disruption for asingle industrial customer. Several compensation  devices are available to mitigate theimpacts of momentary voltage sags and interruptions. When PQ problems are arising fromnonlinear customer loads, such as arc furnaces, welding operations, voltage flicker andharmonic problems can affect the entire distribution feeder . Several devices have beendesigned to minimize or reduce the impact of these variations. The primary concept is toprovide dynamic capacitance and reactance to stabilize the power system. This is typicallyaccomplished by using static switching devices to control the capacitance and reactance, orby using an injection transformer to supply the reactive power to the system. Now a days,voltage based converter improving the power quality (PQ) of power distribution systems. AUnified Power Quality Conditioner (UPQC) can perform the functions of both D-STATCOM and DVR. The UPQC consists of two voltage source converters (VSCs) that areconnected to a common dc bus. One of the VSCs is connected in series with a distributionfeeder, while the other one is connected in shunt with the same feeder. The dc-links of bothVSCs are supplied through a common dc capacitor. It is also possible to connect two VSCs totwo different feeders in a distribution system is called Interline Unified Power QualityConditioner (IUPQC) This paper presents a new Unified Power Quality Conditioning systemcalled Multi Converter Unified Power Quality Conditioner (MC-UPQC) . 137
International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEMECIRCUIT CONFIGURATION As shown in this Fig.1 two feeders connected to two different substations supply theloads L1 and L2. The MC-UPQC is connected to two buses BUS1 and BUS2 with voltagesof ut1 and ut2, respectively. The shunt part of the MC-UPQC is also connected to load L1with a current of il1. Supply voltages are denoted by us1 and us2 while load voltages are ul1and ul2. Finally, feeder currents are denoted by is1 and is2 and load currents are il1 and il2.Bus voltages ut1 and ut2 are distorted and may be subjected to sag/swell. The load L1 is anonlinear/sensitive load which needs a pure sinusoidal voltage for proper operation while itscurrent is non-sinusoidal and contains harmonics. The load L2 is a sensitive/critical loadwhich needs a purely sinusoidal voltage and must be fully protected against distortion,sag/swell and interruption. These types of loads primarily include production industries andcritical service providers, such as medical centers, airports, or broadcasting centers wherevoltage interruption can result in severe economical losses or human damages Figure- 1. Single - line diagram of MC-UPQC connected distribution system2. MC–UPQC STRUCTURE The internal structure of the MC–UPQC is shown in Figure-2. It consists of threeVSCs (VSC1, VSC2, and VSC3) which are connected back to back through a common dc-link capacitor. In the proposed configuration, VSC1 is connected in series with BUS1 andVSC2 is connected in parallel with load L1 at the end of Feeder1. VSC3 is connected inseries with BUS2 at the Feeder2 end. Figure- 2 Typical MC-UPQC used in a distribution system. 138
International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEMEReactor and high-pass output filter as shown in Figure-3. The commutation reactor (Lf) andhigh- pass output filter (R f, C f) are connected to prevent the flow of switching harmonicsinto the power supply. Each of the three VSCs in Figure-2 is realized by a three-phaseconverter with a commutation Figure-3. Schematic structure of a VSC As shown in Figure-2. all converters are supplied from a common dc-link capacitorand connected to the distribution system through a transformer. Secondary (distribution) sidesof the series-connected transformers are directly connected in series with BUS1 and BUS2,and the secondary (distribution) side of the shunt-connected transformer is connected inparallel with load L1. The aims of the MCUPQC are: 1) To regulate the load voltage (ul1)against sag/swell, interruption, and disturbances in the system to protect the Non-Linear/sensitive load L1. 2) To regulate the load voltage (ul2) against sag/swell, interruption,and disturbances in the system to protect the sensitive/critical load L2. 3) To compensate forthe reactive and harmonic components of nonlinear load current (il1) In order to achieve thesegoals, series VSCs (i.e., VSC1 and VSC3) operate as voltage controllers while the shunt VSC(i.e., VSC2) operates as a current controller.3. CONTROL STRATEGY As shown in Figure-2, the MC-UPQC consists of two series VSCs and one shunt VSC- which are controlled independently. The switching control strategy for series VSCsand the shunt VSC are selected to be sinusoidal pulse width-modulation (SPWM) voltagecontrol and hysteresis current control, respectively. Details of the control algorithm, whichare based on the d-q method , will be discussed later. Shunt-VSC: Functions of the shunt-VSC are: 1) To compensate for the reactivecomponent of load L1 current; 2) To compensate for the harmonic components of load L1current; 3) To regulate the voltage of the common dc-link capacitor. Figure-4. Control block diagram of the shunt VSC. 139
International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEMEFigure-4. shows the control block diagram for the shunt VSC. The measured load current (il- dqoabc) is transformed into the synchronous reference frame by usingWhere the transformation matrix is shown in (2),By this transform, the fundamental positive-sequence component, which is transformed intodc quantities in the axes, can be easily extracted by low-pass filters (LPFs). Also, allharmonic components are transformed into ac quantities with a fundamental frequency shiftWhere il-d and il-q are d-q components of load current, il_d and il_q are dc components, and il˜dand il˜q are the ac components of il-d, and il-q.If is is the feeder current and ip f is the shunt VSC current and knowing is =il - ipf , then d–qcomponents of the shunt VSC reference current are defined as followsConsequently, the d–q components of the feeder current areThis means that there are no harmonic and reactive components in the feeder current.Switching losses cause the dc-link capacitor voltage to decrease. Other disturbances, such asthe sudden variation of load, can also affect the dc link. In order to regulate the dc-linkcapacitor voltage, a proportional–integral (PI) controller is used as shown in Fig. 4. The inputof the PI controller is the error between the actual capacitor voltage (udc) and its referencevalue (udc ref). The output of the PI controller (i.e., delta idc) is added to the component of theshunt-VSC reference current to form a new reference current as follows: 140
International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEMEAs shown in Fig. 4, the reference current in (6.11) is then transformed back into the abcreference frame. By using PWM hysteresis current control, the output-compensating currentsin each phase are obtained.Series-VSC: Functions of the series VSCs in each feeder are:1 To mitigate voltage sag and swell;2 To compensate for voltage distortions, such as harmonics;3 To compensate for interruptions (in Feeder2 only). Figure-5. Control block diagram of the series VSC.The control block diagram of series VSC is shown in Figure.5.The bus voltage (ut-abc) isdetected and then transformed into the synchronous dq0 reference frame usingut1p, ut1n and ut10 are fundamental frequency positive-, negative-, and zero-sequencecomponents, respectively, and uth is the harmonic component of the bus voltage. Accordingto control objectives of the MC-UPQC, the load voltage should be kept sinusoidal withconstant amplitude even if the bus voltage is disturbed. Therefore, the expected load voltagein the synchronous dqo reference frame (u l-dqoexp) only has one value 141
International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEMEWhere the load voltage in the abc reference frame (u l-abcexp) isThe compensating reference voltage in the synchronous dqo reference frame (ul-dqoexp) isdefined asThis means ut1p-d in (12) should be maintained at Um while all other unwanted componentsmust be eliminated. The compensating reference voltage in (15) is then transformed back intothe abc reference frame. By using an improved SPWM voltage control technique (sine PWMcontrol with minor loop feedback), the output compensation voltage of the series VSC canbe obtained4. NEURO-FUZZY CONTROLLER (NFC): A neuro-fuzzy system is a fuzzy system that uses a learning algorithm derived from orinspired by neural network theory to determine its parameters (fuzzy sets and fuzzy rules) byprocessing data samples.NFC is the combination of Fuzzy Inference System (FIS)and NN.The fuzzy logic is operated based on fuzzy rule and NN is operated based on training dataset.The neural network training dataset are generated from the fuzzy rules. The function of NFCis explained in the below section.4.1 FUZZY LOGIC CONTROLLER Fuzzy control system is a control system based on fuzzy logic –a mathematicalsystem that analyzes along input values in terms of logical variables that take on continuousvalues between 0 and 1. Controllers based on fuzzy logic give the linguistic strategies controlconversion from expert knowledge in automatic control strategies. Professor Lotfia Zadehat University of California first proposed in 1965 as a way to process imprecise data itsusefulness was not seen until more powerful computers and controllers were available . Inthe fuzzy control scheme, the operation of controller is mainly based on fuzzy rules, whichare generated using fuzzy set theory. Fuzzy controller plays an important role in thecompensation of PQ problem the steps involved in fuzzy controller are fuzzification, decisionmaking, and defuzzification. Fuzzification is the process of changing the crisp value intofuzzy value. The fuzzification process has no fixed set of procedure and it is achieved bydifferent types of fuzzifiers. The shapes of fuzzy sets are triangular, trapezoidale and more.Here, a triangular fuzzy set is used. The fuzzified output is applied to the decision makingprocess, which contains a set of rules. Using the fuzzy rules, the input for bias voltagegenerator is selected from FIS. Then, the defuzzification process is applied and the fuzzifiedcalculated voltage (Vdc )is determined. The structure of designed FLC is illustrated asfollows. 142
International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME 6553(Online Figure-6. Block diagram of a fuzzy logic controllerand the steps for designing FLC are pointed below . • Fuzzification strategy • Data base building • Rule base elaboration • Interface machine elaboration • Defuzziffication strategy In addition, design of fuzzy logic controller can provide desirable both small signaland large signal dynamic performance at same time, which is not possible with linear controltechnique. The development of fuzzy logic approach here is limited to the des design andstructure of the controller. .The inputs of FLC are defined as the voltage error, and change oferror.Fuzzy sets are defined for each input and out put variable. There are seven fuzzy levels(NB-negative big, NM-negative medium, NS-negative small Z-zero, PS-positive small, PM- negative NS positive PMpositive medium, PB-positive big) the membership functions for input and output variables positiveare triangular. The min-max method interface engine is used. The fuzzy method used in this maxFLC is center of area. The complete set of control rules is shown in Table.1. Each of the 49 controlcontrol rules represents the desired controller response to a particular situation. Figure.6shows the block diagram of a fuzzy logic controller .The block diagram presented in Figure- .The7..shows a FLC controller in the MATLAB simulation. The simulation parameters are shownin Table1. The performance of degree of member ship functions are shown in Fig Figure-8. Figure-7. The block diagram presented in Figure above shows a FLC controller in the MATLAB simulation 143
International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME Figure-8. Performance of Membership Function (i) Error Voltage, (ii) Change of Error Voltage and (iii)Output Voltage. Table 1. Fuzzy rule table Change in Error Error NB NM NS Z PS PM PB NB NB NB NB NB NM NS Z NM NB NB NB NM NS Z PS NS NB NB NM NS Z PS PM Z NB NM NS Z PS PM PB PS NM NS Z PS PM PB PB PM NS Z PS PM PB PB PB PB Z PS PM PB PB PB PB 144
International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME4.2 DESIGNING & TRAINING OF ANN An artificial neural network (ANN), often just called a "neural network" (NN), is amathematical model or computational model based on biological neural networks. It consistsof an interconnected group of artificial neurons and processes information using aconnectionist approach to computation. In most cases an ANN is an adaptive system thatchanges its structure based on external or internal information that flows through the networkduring the learning phase. In more practical terms neural networks are non-linear statisticaldata modeling tools. They can be used to model complex relationships between inputs andoutputs or to find patterns in data. NN is an artificial intelligence technique that is used forgenerating training data set and testing the applied input data . A feed forward type NN isused for the proposed method. Normally, the NN consist of three layers: input layer, hiddenlayer and output layer. Here, the error, change of error, and the regulated output voltage aredenoted as Ve ,V∆e,VDCNN respectively. The structure of the NN is described as follows. Figure-9.. Structure of the NN for Capacitor Voltage Regulation. In Figure-9., the input layer, hidden layer and output layer of the network are (H11,H12), (H21 ,H22…..H2N), and H31 respectively. The weight of the input layer to hiddenlayer is denoted asw11, w 12,w1N ,w21, w22 ,and w2N . The weight of the hidden layer to outputlayer is denoted as w 211,w221 ,w2N1 . Here, the Back Propagation (BP) training algorithm isused for training the network. Figure-10. Shows the Proposed System NN Structure. Figure-11.shows the NN Performance Plots (i) Regression Analysis, (ii) Network Validationperformance and (iii)Training State. Figure-10. Proposed System NN Structure. 145
International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME Figure-11. NN Performance Plots (i) Regression Analysis, (ii) Network Validation performance and (iii)Training State.5. SIMULATION STUDIES The performance of the simulation model of MC-UPQC in a two-feeder distributionsystem as in figure.1 is analyzed by using MATLAB/SIMULATION The supply voltages ofthe two feeders consists of two three-phase three-wire 380(v) (RMS, L-L), 50-Hz utilities.The BUS1 voltage (ut1) contains the seventh-order harmonic with a value of 22%, and theBUS2 voltage (ut2) contains the fifth order harmonic feeder1 load is a combination of athree-phase R-L load (R = 10 Ohms, L =30µ H) and a three-phase diode bridge rectifierfollowed by R-L load on dc side (R = 10 Ohms, L = 100 mH) which draws harmonic current.Similarly to introduce distortion in supply voltages of feeder2 , 7th and 5th harmonic voltagesources, which are 22 % and 35% of fundamental input supply voltages are connected inseries with the supply voltages VSC1 and VSC3 respectively. In order to demonstrate theperformance of the proposed model of MC-UPQC simulation case studies are carried out.The simulink model for distribution system with MC-UPQC is shown in Figure 12. 146
International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME Figure-12. Simulink model of distribution system with MC-UPQC5.1 COMPENSATION OF CURRENT AND VOLTAGE HARMONICS Simulation is carried out in this case study under distorted conditions of current infeeder1 and supply voltages in feeder1. Figure-13. represents three-phase load, compensationand source currents and capacitor voltage of feeder1 before and after compensation with PIcontroller in figure.13 and with Fuzzy in figure 14. It is to be noted that the shuntcompensator injects compensation current at 0.1s as in Fig13. The Effectiveness of MC-UPQC is evident from Fig. 13. as the source current becomes sinusoidal and balanced from0.5 s. The Total Harmonic Distortion (THD) of load and source currents is identical beforecompensation and is observed to be 28.5%. After compensation the source current THD isobserved to be less than 5 %. The THD values of sourcevoltage and current are listed in table-2 , the dc voltage regulation loop has functioned properly under all disturbances, such assag/swell in both feeders. Thus a significant improvement in the frequency spectrum andTHD after compensation is clearly Table.2 Voltage and current harmonics (THD’s) of MC- UPQCOrder of WITHOUT WITHOUT MCUPQC MCUPQC MCUPQC MCUPQC MCUPQC MCUPQCharmonics MCUPQC MCUPQC with PI with PI with with with with utility side utility side controller controller FUZZY FUZZY NEURO- NEURO- voltage current utility side utility side controller controller FUZZY FUZZY voltage current utility side Utility controller controller voltage side utility side Utility current voltage side current5th & 7th 0.92 1.276 0.7201 0.42 0.5401 0.2573 0.22 0.0409 147
International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME Figure-13.Simulation Result for Nonlinear load current, compensating current, Feeder1 current, and capacitor voltage with PIcontroller Figure-14.Simulation Result for Nonlinear load current, compensating current, Feeder1 current, and capacitor voltage with FUZZYcontroller Figure-15.Simulation Result for Nonlinear load current, compensating current, Feeder1 current, and capacitor voltage with NEURO-FUZZY 148
International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME Figure-16. Simulation Result for BUS1 voltage, series compensating voltage, and load voltage in Feeder1 Figure-17. Simulation Result for BUS2 voltage, series compensating voltage, and load voltage in Feeder2 From the simulation results as shown in the above figure.11 and figuer.12 distortedvoltages of BUS1 and BUS2 are satisfactorily compensated for across the loads L1 and L2with very good dynamic response .5.2 COMPENSATION OF VOLTAGE HARMONICS, VOLTAGE SAG/SWELL The BUS1 voltage(ut1) contains seventh-order harmonics with a value of 22%, TheBUS1 voltage contains 25% voltage sag from 0.1s to 0.2s and 20% voltage swell from 0.2s to0.3s. and the BUS2 voltage (ut2) contains the fifth order harmonic with a value of 35%. TheBUS2 voltage contains 35% sag from 0.15s to 0.25s and 30% swell from 0.25s to 0.3s Thenonlinear/sensitive load L1 is a three-phase rectifier load which supplies an RL load of 10and 30µH. The MC–UPQC is switched on at t=0.02s. The BUS1 and BUS2 voltages, thecorresponding compensation voltages injected by VSC1,and VSC3 and finally load L1 andL2 voltages are shown in figure.15 figure.16 and figure. 17 respectively. 149
International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME5.3 UPSTREAM FAULT ON FEEDER2 When a fault occurs in Feeder2 in any form of L-G, L-L-G, and L-L-L-G faults, thevoltage across the sensitive/critical load L2 is involved in sag/swell or interruption. Thisvoltage imperfection can be compensated for by VSC2. In this case, the power required byload L2 is supplied through VSC2 and VSC3. This implies that the power semiconductorswitches of VSC2 and VSC3 must be rated such that total power transfer is possible. Theperformance of the MC-UPQC under a fault condition on Feeder2 is tested by applying athree- phase fault to ground on Feeder2 from 0.3s to 0.4 s. Simulation results are shown infigure.18Figure-18. simulation results for an upstream fault on Feeder2, BUS2 voltage, compensating voltage, and loads L1 and L2 voltages.5.4. SUDDEN LOAD CHANGE To evaluate the system behavior during a load change, the nonlinear load L1 isdoubled by reducing its resistance to half at 0.5 s. The other load, however, is keptunchanged. In this case load current and source currents are suddenly increased to double andproduce distorted load voltages (Ul1 and Ul2) the performance of the MC-UPQC is testedwhen sudden load change occurs in feeder-1 at nonlinear/sensitive load with PI ,Fuzzy andwith neuro-Fuzzy controller as shown in figure.19 ,figure .20 and figure-21.respectively Figure-19.Simulation results for load change: nonlinear load current, Feeder1 current, load L1 voltage, load L2 voltage, and dc-link capacitor voltage with PI controller 150
International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME Figure-20.Simulation results for load change: nonlinear load current, Feeder1 current, load L1 voltage, load L2 voltage, and dc-link capacitor voltage with FUZZY Figure-21.Simulation results for load change: nonlinear load current, Feeder1 current, load L1 voltage, load L2 voltage, and dc-link capacitor voltage with NEURO-FUZZY5.5. UNBALANCED SOURCE VOLTAGE IN FEEDER-1. The MC-UPQC performance is tested when unbalance source voltage occurs infeeder-1 at nonlinear/sensitive load without and with MC-UPQC. The control strategies forshunt and series VSCs, Which are introduced and they are capable of compensating for theunbalanced source voltage and unbalanced load current. To evaluate the control systemcapability for unbalanced voltage compensation, a new simulation is performed. In this newsimulation, the BUS2 voltage and the harmonic components of BUS1 voltage are similar.However, the fundamental component of the BUS1 voltage (Ut1fundamental) is anunbalanced three-phase voltage with an unbalance factor (U- /U+) of 40%.The simulationresults show that the harmonic components and unbalance of BUS1 voltage are compensatedfor by injecting the proper series voltage. In this figure, the load voltage is a three-phasesinusoidal balance voltage with regulated amplitude. The simulation results for the three-phase BUS1 voltage series compensation voltage, and load voltage in feeder-1 are shown inFigure.22. 151
International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME Fig 22.BUS1 voltage, series compensating voltage, and load voltage in Feeder1 under unbalanced source voltage.6. CONCLUSION A new custom power device named as MC-UPQC, to mitigate current and voltageharmonics, compensate reactive power and to improve voltage regulation. The compensationperformance of shunt and a novel series compensator are established by the simulation resultson a two-feeder, multibus distribution system. The proposed MC-UPQC can accomplishvarious compensation functions by increasing the number of VSCs. This paper illustratescompensating ac unbalanced loads and a dc load supplied by the dc-link of the compensatoris presented. The transient response of the MC-UPQC is very important while compensatingfast varying loads. When there is any change in the load it will directly effects the dc-linkvoltage .The transient response of the conventional dc-link voltage controller is very slow.So, an energy based dc-link voltage controller is taken for the fast transient response. Theconventional Neuro-fuzzy logic controller gives the better transient response and also DCcapacitor Voltage magnitude increased as shows in the results than that of the conventional PIand fuzzy controller. which are discussed above. The efficacy of the proposed controller isestablished through a digital simulation. It is observed from the above studies the proposedneuro-fuzzy logic controller gives the fast transient response for fast varying loads whencompared with PI and FUZZY logic controllers. the response of Neuro-Fuzzy controller isfaster and the THD is minimum for the both the voltage and current which is evident from theplots and comparison Table .2 Proposed model for the MC-UPQC is to compensate inputvoltage harmonics and current harmonics caused by non-linear load. The performance of theMC-UPQC is evaluated under various disturbance conditions like the supply voltage and loadcurrent imperfections such as sags, swells, interruptions, voltage imbalance, flicker, andcurrent unbalance. Voltage and current harmonics (THD’s) of MC- UPQC with differentintelligence techniques have been verified and among them Neuro-Fuzzy controller showsbetter result when compared with Pi and Fuzzy .The MC-UPQC is expected to be anattractive custom power device for power quality improvement of multibus/multi-feederdistribution systems in near future. 152
International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEMEREFERENCES Hamid Reza Mohammadi, Ali Yazdian Varjani, and Hossein Mokhtari,“Multiconverter Unified Power-Quality Conditioning System: MC- UPQC” IEEETRANSACTIONS ON POWER DELIVERY, VOL. 24, NO. 3, JULY 2009. R.Rezaeipour and A.Kazemi, “Review of Novel control strategies for UPQC”,Internal Journal of Electric and power Engineering 2(4) 241-247, 2008. S. Ravi Kumar and S.Siva Nagaraju“ Simulation of DSTATCOM and DVR in powersystems” Vol. 2, No. 3, June 2007 ISSN 1819-6608 ARPN Journal of Engineering andApplied Sciences. M.V.Kasuni Perera” Control of a Dynamic Voltage Restorer to compensate singlephase voltage sags” Master of Science Thesis Stockholm, Sweden 2007. M. Basu, S. P. Das, and G. K. Dubey, “Comparative evaluation of two models ofUPQC for suitable interface to enhance power quality,” Elect.Power Syst. Res., pp. 821–830, 2007. A. K. Jindal, A. Ghosh, and A. Joshi, “Interline unified power quality conditioner,”IEEE Trans. Power Del. vol. 22, no. 1, pp. 364–372, Jan. 2007. P.Hoang, K.Tomosovic, “Design and an analysis an adaptive fuzzy power systemstabilizer”, Vol. 11, No. 2.June 1996. Momoh, X. W. Ma, “Overview and Literature survey of Fuzzy set theory in powersystems”,IEEE Trans.on Power Systems, Vol. 10, No.3, Aug. 1995. pp. 1676-1690. RVD Rama Rao,.Subhrans Sekhar Dash,” Power Quality Enhancement by UnifiedPower Quality Conditioner Using ANN with Hysteresis Control” International Journal ofComputer Applications,Vol.6, No.1, pp.9-15, September 2010. Othmane Abdelkhalek, Chellali benachaiba, Brahim gasbaoui and Abdelfattahnasri, "Using of ANFIS and FIS methods to improve the UPQC performance”,International Journal of Engineering Science and Technology, Vol. 2, No.12, pp.6889-6901, 2010. P. Jeno Paul and T. Ruban Deva Prakash, "Neuro-Fuzzy Based Constant Frequency-Unified Power Quality Conditioner", International Journal of System Signal Control andEngineering Application, Vol.4, No.1, pp.10-17, 2011. 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 2, Issue 2, 2011, pp. 12 - 20, ISSN Print : 0976-6545, ISSNOnline: 0976-6553. Preethi Thekkath and Dr. G. Gurusamy,, “Effect of Power Quality on Stand ByPower Systems”, International Journal of Electrical Engineering & Technology (IJEET),Volume 1, Issue 1, 2010, pp. 118 - 126, ISSN Print : 0976-6545, ISSN Online: 0976-6553. A.Padmaja, V.S.Vakula, T.Padmavathi and S.V.Padmavathi, “Small Signal StabilityAnalysis Using Fuzzy Controller and Artificial Neural Network Stabilizer”, InternationalJournal of Electrical Engineering & Technology (IJEET), Volume 1, Issue 1, 2010,pp. 47 - 70, ISSN Print : 0976-6545, ISSN Online: 0976-6553. 153
International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEMEAUTHORS BIOGRAPHY B.Rajani received B.Tech degree in Electrical & Electronics Engineering from S.I.S.T.A.M college of Engineering, Srikakulam 2002 and M.E degree in Power Systems and Automation from Andhra university,Visakhapatnam in the year 2008.she presently is working towards her Ph.D degree in S.V.University, Tirupathi. Her areas of interest are in power systems operation &control and stability. Dr. P.Sangameswarararaju received Ph.D from Sri Venkateswara Univerisity, Tirupathi, Andhra Pradesh. Presently he is working as professor in the department of Electrical & Electronics Engineering, S.V. University. Tirupati, Andhra Pradesh. He has about 50 publications in National and International Journals and conferences to his credit .His areas of interest are in power system operation &control and stability. 154