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  1. 1. S.Md.Ishaq, W.V.Jahnavi, T.Devaraju / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 Vol. 2, Issue4, July-August 2012, pp.1796-1805 Unified Power Quality Conditioner in a Grid Connected Photo- voltaic SystemS.MD.ISHAQ, M.Tech, W.V.JAHNAVI, M.Tech, T.DEVARAJU, M.E, Ph.D,Student, Asst.Professor (S.L), Professor, HOD,Electrical Power Systems, E.E.E.Department, E.E.E.Department,Sree Vidyanikethan Engineering Sree Vidyanikethan Engineering Sree Vidyanikethan EngineeringCollege. College. College.ABSTRACT In this paper the design of combined op- voltage is not pure sinusoidal. As these devices areeration of UPQC and PV-ARRAY is proposed. the most important cause of harmonics, inter harmon-The proposed system is composed of series and ics, notches and neutral currents, the power qualityshunt inverters connected back to back by a dc- should be improved. The solution to PQ problem canlink to which pv-array is connected. This system is be achieved by adding auxiliary individual deviceable to compensate voltage and current related with energy storage at its dc-link by PV-array.problems both in inter-connected mode and This auxiliary equipment has the generalislanding mode by injecting active power to grid. name of power conditioners and are mainly charac-The fundamental aspect is that the power elec- terised by the amount of stored energy or stand alonetronic devices (PE) and sensitive equipments (SE) supply time. That auxiliary equipment having bothare normally designed to work in non-polluted “shunt” and “series” inverter connected back to backpower system, so they would suffer from mal- by a dc-link is called the “unified power quality con-functions when supply voltage is not pure sinusoi- ditioner” (UPQC).dal. Thus this proposed operating strategy with UPQC with PV-ARRAY is greatly studiedflexible operation mode improves the power qual- by several researchers as a basic device to control theity of the grid system combining photovoltaic ar- power quality. The duty of UPQC is reducing pertur-ray with a control of UNIFIED POWER bations which affect on the operation of sensitiveQUALITY CONDITIONER. loads. UPQC is able to compensate voltage sag, swell, voltage and current harmonics using shunt andNOMENCLATURE series inverters.IL load current In spite of this issue, UPQC is able to com-VL load voltage pensate voltage interruption and active power injec-CF filter capacitance tion to grid because in its dc-link there is energy stor- IF filter current age known as distributed generating (D.G) source.VDC Dc voltage The attention to distributed generating (DG)IS source current sources is increasing day by day. The reason is theirVS source voltage important roll they will likely play in the future ofVf filter voltage power systems (Blaabjerg et al, 2004), (Barker andCs source capacitance deMello, 2000).Recently, several studies are accom-Ls source inductance plished in the field of connecting DGs to grid usingIabc 3-phase instantaneous load current power electronic converters. Here, grids interfaceVlabc 3-phase instantaneous load voltages shunt inverters are considered more where the reasonVsabc 3-phase source voltages is low sensitiveness of DGs to grids parameters andIldq Two axis currents DG power transferring facility using this approach.∆idc dc link capacitor voltage Although DG needs more controls to reduce theIc compensating current problems like grid power quality and reliability, PVPLL phase locked loop energy is one of the distributed generation sourcesLPF low pass filter which provides a part of human required energyPI proportional plus integral controller nowadays and will provide in the future. The greatestPWM pulse width modulation share of applying this kind of energy in the futureMPPT maximum power point tracking will be its usage in interconnected systems. Nowa- days, European countries, has caused interconnectedI.INTRODUCTION systems development in their countries by choosing One of the important aspects is that, power supporting policies. In this paper, UPQC and PVelectronic devices and sensitive equipments are de- combined system has been presented. UPQC intro-signed to work in non-polluted power systems. So, duced in has the ability to compensate voltage sagthey would suffer from malfunctions when the supply and swell, harmonics and reactive power. 1796 | P a g e
  2. 2. S.Md.Ishaq, W.V.Jahnavi, T.Devaraju / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 Vol. 2, Issue4, July-August 2012, pp.1796-1805 A. Shunt inverter control In fig. 1 the general structure of grid con- B. Series inverter controlnected PV systems is shown. The advantage of pro- C. DC/DC converterposed combined system is voltage interruption com- Controlling strategy is designed and appliedpensation and active power injection to grid in addi- for two interconnected and islanding modes. In inter-tion to the mentioned abilities. Also, this proposed connected mode, source and PV provide the loadsystem has higher efficiency and functioning ability power together while in islanding mode; PV transfersin compare with other common PVs and causes re- the power to the load lonely. By removing voltageduction in systems total cost. Simulation results, us- interruption, system returns to interconnected “MATLAB” software show that this proposedsystem operates correctly. A. Shunt inverter control: In this paper, shunt inverter undertakes twoII.SYSTEM DESCRIPTION main duties. First is compensating both current har- UPQC has two shunt and series voltage monics generated by nonlinear load and reactivesource inverters which are as 3-phase 3-wire or 3- power, second is injecting active power generated byphase 4-wire. Shunt inverter is connected to point of PV system. The shunt inverter controlling systemcommon coupling (PCC) by shunt transformer and should be designed in a way that it would provide theseries inverter stands between source and coupling ability of undertaking two above duties.point by series transformer. Shunt inverter operates Shunt inverter control calculates the com-as current source and series inverter operates as volt- pensation current for current harmonics and reactiveage source. Power when PV is out of the grid. Fig.2: shunt inverter control block The power loss caused by inverter operationFig. 1: Configuration of proposed UPQC with PV should be considered in this calculation. It has the ability of stabilizing DC-link voltage during shunt UPQC is able to compensate currents har- inverter operation to compensate voltage distortions.monics, to compensate reactive power, voltage dis- The stabilization is maintained by DC-link capacitortortions and can compensate voltage interruption be- voltage controlling loop in which P.I. controller iscause of having PV-array as a source. Common inter- applied.connected PV systems structure is as fig. 1 which is Shunt inverter control consists of the controlcomposed of PV array, DC/DC and DC/AC convert- circuit as shown in figure below:ers. In this paper a new structure is proposed forUPQC, where PV is connected to DC link in UPQCas energy source. In this case, UPQC finds the ability of in-jecting power using PV to sensitive load duringsource voltage interruption. Fig. 1 shows the configu-ration of proposed system. In this proposed system,two Operational modes are studied as follow:A. Interconnected mode: where PV transfers powerto load and source.B. Islanding mode: where the source voltage is in-terrupted and PV provides a part of load power sepa- Fig.3: control block diagram of shunt inverterrately.SYSTEM DESIGN: A.1. Shunt inverter control in Interconnected The controlling design of proposed system is mode:composed of three following parts: 1797 | P a g e
  3. 3. S.Md.Ishaq, W.V.Jahnavi, T.Devaraju / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 Vol. 2, Issue4, July-August 2012, pp.1796-1805 Mode-1 of fig.3 shows UPQC shunt voltagesource inverter controlling block diagram to whichSynchronous reference frame theory then is applied Harmonic currents can be eliminated by lowby extracting the sensitive load currents as ILA, ILB, pass filter. In this case injected byILC. shunt inverter. When unbalance condition occurs in each The compensation reference currents arephase the stationary values are changed as +ve, − ve& „0‟ sequences. So exact analysis is difficult to considered as:achieve. So the measured load currents applying syn- As it is shown in fig. 3, the reference cur-chronous reference frame conversion method (dq0) rents will transfer to ABC frame by reverse convert-or parks transformation are transferred to dq0 frame ing the Synchronous reference frame. Resulted refer-using sinusoidal functions, i.e., frequency and phase ence currents will be compared with shunt inverterangle of the converted load currents are determined. Output currents (Ifa, Ifb, Ifc) in a PWM current con- troller (hysteresis type) and required controlling This function is obtained by PLL by taking pulses are generated. Applying these signals to shuntsource side voltages VSA, VSB, VSC as reference, inverter power switches gate, required compensationwhich provides to maintain the synchronism with current is generated by voltage and current. NOTE: In machine analysis, for the development ofABC-DQ0 transformation: electric torque Te, requires the interaction between two axis currents which must be in quadrature. Hence, in this transformation it is important to con- sider this condition. A.2. shunt inverter control in islanding mode: In addition to previous duties, shunt inverterFig.3 (a): abc-dq phasor Fig.3 (b): abc-dq block control should inject active power of PV system to This transformation can be thought of in control when PV is operating. If the voltage interrup-geometric terms: As the projection of the three phase tion occurs at load, that exceeds a threshold value, theseparate sinusoidal phase quantities on two axes, inverter operation will switch from interconnectedcalled the direct (d) and quadrature (q) axis. mode to islanding mode. PV system provides re- The direct & quadrature axis currents are: quired active power to stabilize load voltage. (1) General form of transformation is replacingold variables by a new set of variables:[New variables] = [transformation matrix] [old Vari-ables]Where, (2) (3) (4) Fig.4: shunt-inverter in islanding mode In this case, shunt inverter controls output (5) voltage and current in order to inject to load using PI controller as shown below: 2π 2π cos θ cos(θ − ) cos(θ + ) 3 3 Ia 2 2π 2π = sin θ sin(θ − ) sin(θ + ) Ib 3 3 3 1 1 1 Ic 2 2 2 (6)The d-axis and q-axis currents are con-stant and instantaneous values considered as: (7) 1798 | P a g e
  4. 4. S.Md.Ishaq, W.V.Jahnavi, T.Devaraju / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 Vol. 2, Issue4, July-August 2012, pp.1796-1805 Fig. 4(a): Controlling block diagram of shunt inverter distortions and helps the voltage of load voltage stay in islanding mode (balanced sinusoidal 3-phase).This reduces steady state error and maintains constantpower. In voltage control current is considered asleading (capacitive load) and corresponding d-q cur-rents are obtained as output as shown below: (8) (9) Are inputs to current controller.In this control considering current lagging (inductiveload), the corresponding DQ-voltages are obtained asoutput as shown below: Fig.5 (a): control block diagram of series inverter In order to reach this aim synchronous refer- (10) ence frame theory is applied. In this method only d- axis component is being controlled i.e., active power (11) component. By compensating the active power com- ponent, reactive power component will be compen- Double times the calculation is performed to sated automatically.maintain„s‟ constant(S = P+JQ), from this maximumdistortions are removed and compensating output In this method the desired value of loadvalue is obtained. From the figure.4 these voltages phase voltage is replaced in d and q-axis. The loadare again transformed to A-B-C sequence and com- voltage should be kept sinusoidal with constant am-pared with angular waveform in PWM control, and plitude even if the voltage on system side is dis-corresponding control pulses are generated. Applying turbed.these signals to shunt inverter switch, the correspond- At interruption mode the system voltagesing voltage is given to load. are detected and then transformed toB.Series inverter controlling: dq0 reference frame and this set of relations in be- tween the 3- variables and dq variables is known The duty of the series inverter is to compen- as park‟s transformation as shown below:sate the voltage disturbance in the source side, grid Park’s:which is due to the fault in the distribution line. Se-ries inverter control calculates the voltage referencevalues which are injected to grid by series inverter. Inorder to control series inverter of UPQC, load sinu-soidal voltage controlling strategy is proposed asshown in figure below: Fig.6: phasor of abc-dq (11) (12) Fig.5: series inverter block diagram (13) This means d-axis of load reference voltageIn this condition UPQC, series inverter would be equals “VM”, while q-axis and zero axis of load refer-controlled in a way that it compensates the whole ence voltage equals zero. Where Vm is desired peak 1799 | P a g e
  5. 5. S.Md.Ishaq, W.V.Jahnavi, T.Devaraju / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 Vol. 2, Issue4, July-August 2012, pp.1796-1805value of load voltage and (θ) is voltage phase anglewhich is calculated by phase locked loop (PLL). Bysubtracting the desired value of d-axis phase voltage SOLAR-ARRAY:(V*Ld) from VSd, all distortions VLd in d-axis are ob- The circuit of PV-Array is shown below:tained. Also, the desired value of load phase voltagein q-axis is zero. In other words, VSq represents totalq-axis distortions. So series compensation referencevoltage is resulted by relation (14): (14) The above equation of compensation refer-ence voltage is then inversely transformed into a-b-creference frame as: V*Fabc 𝐚𝐛𝐜 𝐕 ∗ 𝐅𝐚𝐛𝐜 = [𝐓 𝐝𝐪𝟎 ]−𝟏 [𝐕 𝐝𝐪𝟎 ] (14.1) 𝟏 Fig.7: circuit of pv-array 𝐜𝐨𝐬 𝛉 𝐬𝐢𝐧 𝛉 𝐕𝐚 𝟑 𝐕𝐝 A solar cell basically is a p-n semi- 𝟐𝛑 𝟐𝛑 𝟏 𝐕𝐛 = 𝐜𝐨𝐬( 𝛉 − 𝟑 ) 𝐬𝐢𝐧( 𝛉 − 𝟑 ) 𝟑 × 𝐕𝐪 conductor junction which is made of several poly- 𝐕𝐜 𝟐𝛑 𝟐𝛑 𝟏 𝐕𝟎 crystalline silicon cells. At junction electrons from 𝐜𝐨𝐬( 𝛉 + ) 𝐬𝐢𝐧( 𝛉 + ) the sides mix and form a barrier, making it hard for 𝟑 𝟑 𝟑 (14.2) electrons on the N-side to cross to the P-side. Even- These voltages are compared with an angu- tually equilibrium is reached, and an electric fieldlar waveform in PWM controller and required con- separates the sides.trolling pulses (g1... g6) are generated to be applied When photon (sun light) hits a solar cell, itsto series voltage source inverter switches. This cor- energy frees electron-hole pairs. The electric fieldrected method is programmable with a low cost. The will send the free electron to the N-side and hole toother advantage is that the controlling System‟s cal- the P-side. This cause further disruption of electricalculation time is shortened and so controlling systems neutrality, and if an external current path is provided.response is faster. Note: electrons will flow through the path to theirNote: In order to improve series inverter operation, original side (p-side) to unite with holes that the elec-SPWM method is used where the resulted value of tric field sent here, doing work for us along the way.subtracting V*Fabc from VFabc is multiplied to a con- The electron flow provides the current, andstant coefficient and the obtained value is added to cell electric field causes a voltage.V*Fabc . Applying this method distinctively improvesoperation of series inverter. Equivalent circuit of PV-array:C. DC-DC Converter controlling to obtain theMaximum Point Of PV-Array: At, present Pv systems are not very efficientwith only about 12-20% efficiency in their ability toconvert sunlight to electrical power. The efficiency can drop further due to other Fig.7 (a): equivalent pv circuitfactors such as: An equivalent circuit used together with the (i) Solar panel temperature. following set of circuit equations to express a typical (ii) Load conditions. current – voltage (I-V) characteristic of pv modules and arrays as shown below: In order to maintain the power derived fromthe solar panel it is important to operate the panel atits optimal power point. An important considerationin achieving high efficiency in PV power system is to (15)match “ PV source and load impedance properly forany weather conditions, thus obtaining maximumpower generation”. (16) So in order to increase the efficiency, asmuch power as possible should be extracted from thearray. The possible technique for this is known as (17)“Maximum Power Point Tracking” (MPPT). 1800 | P a g e
  6. 6. S.Md.Ishaq, W.V.Jahnavi, T.Devaraju / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 Vol. 2, Issue4, July-August 2012, pp.1796-1805 The algorithm reads the value of current and voltage from pv-array module. Power is calculated from the measured voltage and current. (18) The slope of the power can be calcu- lated by consecutive output voltages and output cur- rents and can be expressed as: (19)S → solar insolation (w/m2)Tref → reference temperature (298 k)T → cell temperature →(21)Eg → band gap enargy of the cell semi conductorK → boltzman constantRS → series resistanceRsh → shutn resistanceN →diode emission factorIDO → diode reversal currentISho → short circuit current at reference stateJO → temperature coefficientFrom equation (18), Eg and IDO are not independentof each other. Fig.5: The operating region on the curveThus, Eg is calculated using: So through this maximising the cyclic proc- ess, correspondingly i/p and o/p pulses are generated (20) by the control circuit and given to switch „s‟, this m→ no cells in series switch provides the required voltage and also if there The method to obtain optimum power point is any ripples they are eliminated and pure DC isat solar array is algorithm of perturbation and obser- given to dc link.vation (P & O) in Mppt. Hence at every instant of PV-array we are determining MPP and correspondingly capacitor-DCPERTURBATION AND OBSERVATION: link‟s voltage is charged. This method is used to achieve the maxi-mum power point. According to the structure of The advantage of P&O method is its simpleMPPT, the required parameters are only voltage (v) application and its disadvantage is its capability toand current (I) of pv-modules. determine the correct MPP during sudden and fast variation in environmental conditions. Of course, the probability of sudden variations in environmental conditions is very low. As it is seen in fig. 8, the duty cycle of converter switch is determined by measuring voltage and arrays current values in specific periods of time and applying maximum power tracking algo- rithm. Finally, by applying this type of control with PV-array generation the power quality of the System is improved or will be made more reliable. RESULTS AND DISCUSSION In simulation part, power system is mod- elled as a 3-wired 3-phase system by an RC load with uncontrolled diode rectifier. The PV model applied in Fig.7(b): MPPT algorithm flow chart simulation is as fig. 6 whose parameters are regulated for normal condition (25°c temp & sun radiation) Circuit parameters used in simulation are located in 1801 | P a g e
  7. 7. S.Md.Ishaq, W.V.Jahnavi, T.Devaraju / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 Vol. 2, Issue4, July-August 2012, pp.1796-1805table 1. The maximum simulation time is regulatedon 600msec. Shunt inverter starts to operate at100msec and series inverter starts at 200msec. Table 1: Grid parametersSource phase voltage (r m s) 220v/50HzDc link voltageShunt inverter ratingSeries inverter rating Fig. 10: Current of shunt inverter injected to gridShunt inverter inductance(Lf)Shunt inverter capacitance(Cf)Switching frequency 20KHzSeries inverter inductance(Ls)Series inverter capacitance(Cs)Series inverter Resistance(Rs) 12 Fig.11: source currentPV Array RatingNonlinear loads current is illustrated in fig. 8. Fig. 12: source current and voltage Fig. 11 shows the source current and fig. 12 presents the source voltage. At 0.45sec when PV out- Fig. 8: Nonlinear loads current ages, source current returns to sinusoidal mode after passing he transient state. With respect to fig. 12 it Active and reactive powers consumed by can understood that, before PV outages, voltage hasload are shown in fig. 9. Simulated load consumes 180° phase difference with its current and PV injects17kW active power and 8kVAr reactive power. In this current to source in addition to providing load. Afterpart of simulation, it is assumed that the PV array is PV outages, it is seen that, voltage and current are ininterconnected to grid and outages after 0.45s of op- same phase and UPQC compensates current harmon-eration. The current, injected by shunt inverter is ics and power factor. Fig. 13 shows the total har-shown in fig. 10. As it is shown in fig. 10 at the pres- monic distortions (THD) of source and load currents.ence of PV, shunt branch injects a high current to Shunt inverter has been able to make currents wavegrid, a part of which is consumed to feed the load and form sinusoidal and reduce the THD of load currentelse is injected to grid. When PV outages, the shunt from 22% to 3%.branch undertakes the duty of compensating currentharmonics and currents reactive power. Fig.13 : Load and source current THDFig. 9: Active and reactive power consumed by Nonlinear load 1802 | P a g e
  8. 8. S.Md.Ishaq, W.V.Jahnavi, T.Devaraju / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 Vol. 2, Issue4, July-August 2012, pp.1796-1805 In fig. 14 active and reactive powers injected sag compensation increases and a part of activeby shunt inverter are shown. When PV outages, in- power injected by series inverter decreases.jective reactive power doesnt vary distinctively,while injective active power decreases to a negativevalue from 37.5kW. In other words, shunt inverter isnot able to inject active power after PV outages andrequired active power of series inverter is providedthrough shunt inverter from the grid. Fig. 16: voltage sag in source voltage Fig. 14: Active and reactive power injected by shunt inverter Fig. 17: load voltage and source current DC link voltage is shown in fig.15 for theabove cases. When PV outages, the voltage of DClink decreases and returns to its desired value by cor-rect operation of DC controlling loop. In this part ofsimulation, by applying voltage sag to the grid side,series inverter‟s operation is studied to improve volt-age sag and it is investigated that how series andshunt inverters inject power to the grid at the pres-ence of PV. Fig.16 source side voltage in which volt-age sag has occurred during 0.25 to 0.35 seconds isshown. Fig. 18: voltage injection by series inverter Fig. 15: DC link voltage Fig. 19: Active power injected by series and shunt inverters In the third part of simulation, voltage interruption isFig. 17 shows the load side voltage and source cur- applied in the source and the operation of PV systemrent. Load voltage is completely compensated and in providing the power which is required by load iscurrent has 180° phase difference with load voltage. studied. In order to do this, a voltage interruptionThis issue shows the complete compensation of loads occurs at 0.5 seconds and immediately the powerreactive power too. The voltage injected by series switches parallel with series transformer are closedinverter to compensate the voltage sag is shown in and so other switches allocated between shunt andfig. 18. The active power injected by series and shunt series inverters are opened and so isolate shunt in-inverters during voltage sag occurrence is shown in verter from the grid. Controlling algorithm of parallelfig. 19. When voltage sag occurred, share of series inverter, switches from interconnected mode toinverter in PVs active power transferring and voltage islanding mode. In fig. 20 the source side voltage is shown during voltage interruption occurrence. Fig. 21 shows load current. When interruption occurs, 1803 | P a g e
  9. 9. S.Md.Ishaq, W.V.Jahnavi, T.Devaraju / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 Vol. 2, Issue4, July-August 2012, pp.1796-1805load current is provided by shunt inverter and PV. method is used to achieve the maximum power pointThe active power injected by shunt inverter to load is of PV array. This proposed systems operation is ana-shown in fig. 22. As it is seen, during interruption lyzed using (MATLAB) software and simulationoccurrence, the power injected by PV is the function results confirm that the proposed system operatesof the loads required power in PV power range off correctly.course. REFERENCES 1. M. Siahi,“Design and simulation of UPQC to improve Power Quality and Transfer Power of photovoltaic array to grid”. IEEE transaction on basic and applied sciences, 5(3): 662-673, 2011. 2. K. R. Padiyar, “facts controllers in power transmission and distribution”, New age in- ternational (P) LIMITED, PUBLISHERS,2007. Fig. 20: voltage interruption in source voltage 3. Basu, M., Shyama P. Das, Gopal K. Dubey, 2007. “Comparative evaluation of two mod- els of UPQC for Suitable interface to en- hance power quality”. J. Electric Power Sys- tems Research, 77: 821-830. Digital Object Identifier(DOI): 10.1016/j.epsr.2006.07.008. 4. Watanable, H., T. Shimizu, G. Kimura, “A novel utility interactive photovoltaic inverter with Generation control circuit”. IEEE In- dustrial Electronics Society, 1998. 5. Akagi, H., Y. Kanazawa and A. Nabae, Fig. 21: load current during voltage interruption oc 2007. “Instantaneous reactive power com- currence pensator comprising switching devices without energy storage components”. IEEE Trans. Ind.Appl., 20: 625-630. Digital Ob- ject Identfier(DOI):10.1109/TPWRD.2005. 6. Akagi, H. and H. Fujita, 1995. “A new power line conditional for harmonic com- pensation in Power systems”. IEEE Transac- tion on Power Delivery, 10(3): 1570-1575. Digital Object Idetifier (DOI): 10.1109/61.400941. 7. Aredes, M. and E.H. Watanabe, 1995. “New control algorithms for series and shunt three- Fig. 22: active power injected by shunt inverter to Phase four-wire active power Filters”. IEEE load Transaction on Power Delivery, 10: 1649-Conclusion 1656. In this paper, the results of analyzing com-bined operation of UPQC and PV is explained. The 8. Barker, P.P. and R.W. de Mello, 2000. “De-proposed system is composed of series and shunt termining the impact of distributed genera-inverters, PV array and DC/DC converter which can tion on power systems: Part1-Radial distri-compensate the voltage sag, swell, interruption and bution systems”. Proceeding of IEEE Powerreactive power and harmonics in both islanding and Engineering Society Summer Meetinginterconnected modes. The advantages of proposed 1645-1656.system is reducing the expense of PV interface in-verter connection to grid because of applying UPQC 9. Basu, M., Shyama P. Das, Gopal K. Dubey,shunt inverter and also is the ability of compensating 2007. “Comparative evaluation of two mod-the voltage interruption using UPQC because of con- els of UPQC for suitable interface to en-necting PV to DC link. In this proposed system, P&O 1804 | P a g e
  10. 10. S.Md.Ishaq, W.V.Jahnavi, T.Devaraju / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 Vol. 2, Issue4, July-August 2012, pp.1796-1805 hance power quality”. J. Electric Power Sys- tems Research, 77: 821-830. Digital Object Identifier(DOI): 10.1016/j.epsr.2006.07.008.10. Blaabjerg, F., Z. Chen, S.B. Kjaer, 2004. “Power electronics as efficient interface in dispersed power generation systems”. IEEE Transaction on Power Electronics. 19(5): 1184-1194. Digital Object Identifier (DOI):10.1109/TPEL.2004.833453.11. Chen, Y., X. Zha, and J. Wang, 2000. “Uni- fied power quality conditioner (UPQC): The theory, modelling and application. Proceed- ing of Power System Technology Confer- ence”, 3: 1329-1333. Digital Object Identi- fier (DOI): 10.1109/ICPST.2000.12. Fujita, H. and H. Akagi, 1998. “The unified power quality conditioner: The integration of series and Shunt active filters”. IEEE Transaction on Power Electronics, 13(2): 315-322.Digital Object Identifier (DOI):10.1109/63.662847.13. Ghosh, A. and G. Ledwich, 2001. “A unified power quality conditioner (UPQC) for si- multaneous Voltage and current compensa- tion”. Electric Power Systems Research, 59: 55-63. Digital Object Identifier (DOI): 10.1016/ S0378-7796(01)00141-9.14. Han, B., B. Bae, H. Kim, S. Baek, 2006. “Combined Operation of Unified Power Quality Conditioner With Distributed Gen- eration”. IEEE Transaction on Power Deliv- ery, 21: 330-338. Digital Object Identifier (DOI): 10.1109/ TPWRD. 2005.852843. 1805 | P a g e