A New Topology for Power Quality Improvement using 3-Phase 4-Wire UPQC with Reduced DC-Link Voltage Rating

Transcription

1 IJMTST Volue: 2 Issue: 03 March 2016 ISSN: New Topoloy for Power Quality Iproveent usin 3-Phase 4-Wire UPQ with Reduced D-Link Voltae Ratin D. Tatarao 1 K. Lakshi 2 1ssociate Professor, Departent of lectrical and lectronics nineerin, ditya ollee of nineerin, Surapale,.P, India. 2Senior ssistant Professor, Departent of lectrical and lectronics nineerin, ditya ollee of nineerin, Surapale,.P, India. STRT Paper Setup ust be in 4 size with Marin: Top 1.1 inch, otto 1 inch, Left 0.5 inch, Riht 0.5 inch, This paper introduces a new concept of optial utilization of a Unified power quality conditioner (UPQ). The series inverter of UPQ is controlled to perfor siultaneous Methods: voltae sa/swell copensation and load reactive power sharin with the shunt inverter. The active power control approach is used to copensate voltae sa/swell and is interated with theory of power anle control (P) of UPQ to coordinate the load reactive power between the two inverters. MTL/SIMULINK-based siulation results are discussed to support the developed concept. Finally, the proposed UPQ concept is validated. KYWORDS: Power anle control, UPQ, MTL/SIMULINK opyriht 2015 International Journal for Modern Trends in Science and Technoloy ll rihts reserved. I. INTRODUTION onventionally, passive L filters and fixed copensatin devices with soe deree of variation like thyristor switched capacitors, thyristor switched reactors were eployed to iprove the power factor of ac loads. Such devices have the deerits of fixed copensation, lare size, aein and resonance. Nowadays equipents usin power seiconductor devices, enerally known as active power filters (PF's), ctive Power Line onditioners (PL's) etc. are used for the power quality issues due to their dynaic and adjustable solutions. Flexible Transission Systes (FTS) and usto Power products like STTOM (Static synchronous opensator), DVR (Dynaic Voltae Restorer), etc. deal with the issues related to power quality usin siilar control strateies and concepts. asically, they are different only in the location in a power syste where they are deployed and the objectives for which they are deployed. ctive Power Filters can be classified, based on converter type, topoloy and the nuber of phases. onverter types are urrent Source Inverter (SI) with inductive enery storae or Voltae Source Inverter (VSI) with capacitive enery storae. The topoloy can be shunt, series or cobination of both. The third classification is based on the nuber of phases, such as sinle phase systes, three phase systes or three phase four wire systes. In this paper, various extraction aloriths for eneratin reference sinals and various odulation techniques for eneratin pulses already developed and published are discussed. riterion for selection of dc link capacitor and interfacin filter desin are also discussed. The Objective of this thesis, one such PL known as Unified Power Quality onditioner (UPQ), which can be used at the P for iprovin power quality, is desined, siulated usin proposed control stratey and the perforance is evaluated for various nonlinear loads (steel plant loads). II. LITRTUR SURVY More recently, new PWM based converters for otor control are able to provide alost unity power factor operations. This situation leads to two observations: on one hand, there is electronic equipent which enerates haronics and, on the other hand, there is unity power factor otor drive 57 International Journal for Modern Trends in Science and Technoloy

2 New Topoloy for Power Quality Iproveent usin 3-Phase 4-Wire UPQ with Reduced D-Link Voltae Ratin syste which doesn't need power factor correction capacitor. lso, we cannot depend on this capacitor to filter out those haronics. This is one of the reasons that the research is bein done in the area of PF and less pollutant drives. Loads, such as, diode bride rectifier or a thyristor bride feedin a hihly inductive load, presentin theselves as current source at point of coon couplin (P), can be effectively copensated by connectin an PF in shunt with the load. On the other hand, there are loads, such as Diode ride havin a hih dc link capacitive filter. These types of loads are ainin ore and ore iportance ainly in fors of to D power supplies and front end to D converters for otor drives. For these types of loads PF has to be connected in series with the load. The voltae injected in series with the load by series PF is ade to follow a control law such that the su of this injected voltae and the input voltae is sinusoidal. Thus, if utility voltaes are non-sinusoidal or unbalanced, due to the presence of other clients on the sae rid, proper selection of anitude and phase for the injected voltaes will ake the voltaes at load end to be balanced and sinusoidal. The shunt PF acts as a current source and inject a copensatin haronic current in order to have sinusoidal, in-phase input current and the series PF acts as a voltae source and inject a copensatin voltae in order to have sinusoidal load voltae. The developents in the diital electronics, counications and in process control syste have increased the nuber of sensitive loads that require ideal sinusoidal supply voltae for their proper operation. In order to eet liits proposed by standards it is necessary to include soe sort of copensation. In the last few years, solutions based on cobination of series active and shunt active filter have appeared. Its ain purpose is to copensate for supply voltae and load current iperfections, such as sas, swells, interruptions, ibalance, flicker, voltae ibalance, haronics, reactive currents, and current unbalance. This cobination of series and shunt PF is called as Unified Power Quality onditioner (UPQ). In ost of the articles control techniques suested are coplex requirin different kinds of transforations. The control technique presented here is very siple and does not require any transforation. III. TOPOLOGY SD LSSIFITION F s can be classified based on the topoloy used as series or shunt filters, and unified power quality conditioners use a cobination of both. obinations of active series and passive shunt filterin are known as hybrid filters. Fi.3 is an exaple of an active shunt filter, which is ost widely used to eliinate current haronics, reactive power copensation (also known as STTOM), and balancin unbalanced currents. It is ainly used at the load end, because current haronics are injected by nonlinear loads. It injects equal copensatin currents, opposite in phase, to cancel haronics and/or reactive coponents of the nonlinear load current at the point of connection. It can also be used as a static VR enerator (STTOM) in the power syste network for stabilizin and iprovin the voltae profile. Fi.1 urrent fed type F Fi.2 Voltae fed type F Fi.4 shows the basic block of a stand-alone active series filter. It is connected before the load in series with the ains, usin a atchin transforer, to eliinate voltae haronics, and to balance and reulate the terinal voltae of the load or line. It has been used to reduce neative-sequence voltae and reulate the voltae on three-phase systes. It can be installed by electric utilities to copensate voltae haronics and to dap out haronic propaation caused by 58 International Journal for Modern Trends in Science and Technoloy

3 IJMTST Volue: 2 Issue: 03 March 2016 ISSN: resonance with line ipedances and passive shunt copensators. Fi.5 shows the hybrid filter, which is a cobination of an active series filter and passive shunt filter. It is quite popular because the solid-state devices used in the active series part can be of reduced size and cost (about 5% of the load size) and a ajor part of the hybrid filter is ade of the passive shunt L filter used to eliinate lower order haronics. It has the capability of reducin voltae and current haronics at a reasonable cost. Fi.3 Shunt-type F Fi.4 Series-type F Fi.5 Hybrid filter Fi.6 Unified Power Quality onditioner Fi.6 shows a unified power quality conditioner (also known as a universal F), which is a cobination of active shunt and active series filters. The dc-link storae eleent (either inductor or dc-bus capacitor) is shared between two current-source or voltae-source brides operatin as active series and active shunt copensators. It is used in sinle-phase as well as three-phase confiurations. It is considered an ideal F, which eliinates voltae and current haronics and is capable of ivin clean power to critical and haronic-prone loads, such as coputers, edical equipent, etc. It can balance and reulate terinal voltae and eliinate neative-sequence currents. Its ain drawbacks are its lare cost and control coplexity because of the lare nuber of solid-state devices involved.. Supply-Syste-ased lassification This classification of F s is based on the supply and/or the load syste havin sinle-phase (two wire) and three-phase (three wire or four wire) systes. There are any nonlinear loads, such as doestic appliances, connected to sinle-phase supply systes. Soe three-phase nonlinear loads are without neutral, such as SD s, fed fro three-wire supply systes. There are any nonlinear sinle-phase loads distributed on four-wire three-phase supply systes, such as coputers, coercial lihtin, etc. Hence, F s ay also be classified accordinly as two-wire, three-wire, and four-wire types. 1. Two-Wire F s: Two-wire (sinle phase) F s are used in all three odes as active series, active shunt, and a cobination of both as unified line conditioners. oth converter confiurations, current-source PWM bride with inductive enery storae eleent and voltae-source PWM bride with capacitive dc-bus enery storae eleents, are used to for two-wire F circuits. In soe cases, active filterin 59 International Journal for Modern Trends in Science and Technoloy

4 New Topoloy for Power Quality Iproveent usin 3-Phase 4-Wire UPQ with Reduced D-Link Voltae Ratin is included in the power conversion stae to iprove input characteristics at the supply end. 2. Three-Wire F s: Three-phase three-wire nonlinear loads, such as SD s, are ajor applications of solid-state power converters and, lately, any SD s, etc., incorporate F s in their front-end desin. lare nuber of publications have appeared on three-wire F s with different confiurations. ll the confiurations shown in Fis1 Fi6. are developed, in three-wire F s, with three wires on the ac side and two wires on the dc side. ctive shunt F s are developed in the current-fed type (Fi.1) or voltae-fed type with sinle-stae (Fi.2) or ulti-step/ultilevel and ulti-series confiurations. ctive shunt F s are also desined with three sinle-phase F s with isolation transforers for proper voltae atchin, independent phase control, and reliable copensation with unbalanced systes. ctive series filters are developed for stand-alone ode (Fi.4) or hybrid ode with passive shunt filters (Fi.5). The latter (hybrid) has becoe quite popular to reduce the size of power devices and cost of the overall syste. cobination of active series and active shunt is used for unified power quality conditioners (Fi.6) and universal filters. 3. Four-Wire F s: lare nuber of sinle-phase loads ay be supplied fro three-phase ains with neutral conductor. They cause excessive neutral current, haronic and reactive power burden, and unbalance. To reduce these probles, four-wire F s have been attepted. They have been developed as: 1) active shunt ode with current feed and voltae feed; 2) active series ode; and 3) hybrid for with active series and passive shunt ode.. Operation of Three Phase ctive Power Filters The basic confiuration of a three-phase three-wire active power filter is shown in Fi.7. The diode bride rectifier is used as an ideal haronic enerator to study the perforance of the ctive filter. The current-controlled voltae-source inverter (VSI) is shown connected at the load end. This PWM inverter consists of six switches with anti parallels diode across each switch. The capacitor is desined in order to provide D voltae with acceptable ripples. In order to assure the filter current at any instant, the D voltae V dc ust be at least equal to 3/2 of the peak value of the line ains voltae. Fi.7 onfiuration of the three phase, three wire ctive filterin syste. Three aspects have to be considered in the desin of PF. 1. The paraeters of the inverter such as inverter switches and the values of the link inductances. 2. Modulation ethod used 3. The control ethod used to enerate the haronic reference teplate. IV. PROPOSD UNIFID POWR QULITY ONDITIONR (UPQ) The Unified Power Quality onditioner (UPQ) is a ore coplete solution for the power quality proble. The basic structure of this equipent is shown in shown in Fi.4. In this fiure, the UPQ is an association of a series and shunt active filter based on two converters with coon dc link. The series converter has the function to copensate for the haronic coponents (Includin unbalances) 60 International Journal for Modern Trends in Science and Technoloy

5 IJMTST Volue: 2 Issue: 03 March 2016 ISSN: present in the source voltaes in such a way that the voltae on the load is sinusoidal and balanced. (connected to a D capacitor). There are two possible ways of connectin the unit to the terinal voltae (V t)at P 1. Riht-shunt UPQ (Fi. 9a), where the shunt copensator (I ) is placed at the riht side of the series copensator (V ). 2. Left-shunt UPQ (Fi. 9b), where the shunt copensator (I ) is placed at the left side of the series copensator (V ). Fi.8 asic lock Diara of UPQ The shunt active filter has the function of eliinatin the haronic coponents of nonlinear loads in such a way that the source current is sinusoidal and balanced. This equipent is a ood solution for the case when the voltae source presents distortion and a haronic sensitive load is close to a nonlinear load asshown in Fi8.To provide a balance, distortion-free, and constant anitude power to sensitive load and, at the sae tie, to restrict the haronic, unbalance, and reactive power deanded by the load and hence to ake the overall power distribution syste ore healthy, the unified power quality conditioner (UPQ) is one of the best solutions. unified power quality conditioner (UPQ) is a device that is siilar in construction to a unified power flow conditioner (UPF). The UPQ, like a UPF, eploys two voltae source inverters (VSIs) that are connected to a coon dc enery storae capacitor. One of these two VSIs is connected in series with the ac line while the other is connected in the shunt with the sae line. UPF is eployed in a power transission syste to perfor shunt and series copensation at the sae tie. Siilarly a UPQ can also perfor both the tasks in a power distribution syste. power distribution syste, on the other hand, ay contain unbalance, distortion and even dc coponents. Therefore a UPQ ust operate under this environent while providin shunt or series copensation.. UPQ onfiurations Unified power quality conditioners are viable copensation devices that are used to ensure that delivered power eets all required standards and specifications at the point of installation. The ideal UPQ can be represented as the cobination of avoltae-source converter (injectin series voltae V ), a current-source converter (injectin shunt current I ), and a coon D link These two structures have siilar features; however, the overall characteristics of the riht shunt UPQ are superior (e.., operation at zero power injection/absorption ode, achievin unity power factor at load terinals, and full reactive power copensation). In this chapter, a riht-shunt UPQ confiuration is assued and analyzed. Fi. 9 Ideal UPQ Structure (a) the Riht-Shunt UPQ (b) The Left-Shunt UPQ V. THR PHS FOUR WIR (3P4W) UPQ STRUTUR Generally, a 3P4W distribution syste is realized by providin a neutral conductor alon with three power conductors fro eneration station or by utilizin a three-phase -Y transforer at distribution level. Fi.10 shows a 3P4W network in which the neutral conductor is provided fro the eneratin station itself, where Fi. 11 shows a 3P4W distribution network considerin, a -Y transforer. ssue a plant site where three-phase three-wire UPQ is already installed to protect a sensitive load and to restrict any entry of distortion fro load side toward utility, as shown in Fi. 12. If we want to uprade the syste now fro 3P3W to 3P4W due to installation of soe sinle-phase loads and if the distribution transforer is close to the plant under consideration, utility would provide the neutral conductor fro this transforer without ajor cost involveent. In certain cases, this ay be a costly solution because the distribution transforer ay not be situated in close vicinity. 61 International Journal for Modern Trends in Science and Technoloy

6 New Topoloy for Power Quality Iproveent usin 3-Phase 4-Wire UPQ with Reduced D-Link Voltae Ratin Fi. 10 3P4W distribution syste: neutral provided fro eneration station transforer in order to connect one of the inverters in the series with the line to function as a controlled voltae source. If we could use the neutral of three-phase series transforer to connect a neutral wire to realize the 3P4W syste, then 3P4W syste can easily be achieved fro a 3P3W syste (Fi. 13). The neutral current, present if any, would flow throuh this fourth wire toward transforer neutral point. Thefour-le VSI topoloy is considered to copensate the neutral current flowin toward the transforer neutral point. fourth le is added on the existin 3P3W UPQ, such that the transforer neutral point will be at neutral point will be at virtual zero potential. Fi. 11 3P4W distribution syste: neutral provided fro Δ-Y transforer Recently, the utility service providers are puttin ore and ore restrictions on current total haronic distortion (THD) liits, drawn by nonlinear loads, to control the power distribution systes haronic pollution. t the sae tie, the use of sophisticated equipent/load has increased sinificantly, and it needs clean power for its operation. Therefore, in future distribution systes and plant/load centers, application of UPQ would be coon. The 3P4W topoloy that can be realized fro 3P3W syste is shown in the Fi. 12. This syste has all the advantaes of eneral UPQ, in addition to easy expansion of 3P3W syste to 3P4W syste. Thus, this topoloy ay play an iportant role in the future 3P4W distribution syste for ore advanced UPQ-based plant/load center installation, where utilities would be havin an additional option to realize a 3P4W syste just by providin a 3P3W supply. Fi. 12 3P3W UPQ structure s shown in Fi. 12, the UPQ should necessarily consist of three-phase series Fi. 13 3P4W UPQ structure This neutral current can be copensated by usin a split capacitor topoloy or a four-le voltae-source inverter (VSI) topoloy for a shunt inverter. The four-le VSI topoloy requires one additional le as copared to the split capacitor because the split capacitor topoloy essentially needs two capacitors and an extra control loop to aintain a zero voltae error difference between both the capacitor voltaes, resultin in a ore coplex control loop to aintain the dc bus voltae at constant level. VI. SIMULTION RSULTS In this section UPQ, shunt VS controller, series VS controller, loads and series transforer blocks are ipleented in MTL/SIMULINK and also explained in detail.. Ipleentation of UPQ Unified power quality conditionin syste (UPQ) consists of three VSs in which two VSs are connected in series to the two feeders and one VS is connected in parallel to load end of the first feeder. These three VSs connected back to back throuh a coon dc-link capacitor. ach of the VSs in Fi. 14 realized by a three-phase converter with a coutation reactor and hih-pass output filter. The coutation reactor and hih-pass 62 International Journal for Modern Trends in Science and Technoloy

7 a b c a b c co co IJMTST Volue: 2 Issue: 03 March 2016 ISSN: output filter are connected to prevent the flow of switchin haronics into the power supply. a a N b Three-Phase Proraable Voltae Source t1 c b c t3 N LOD Isrn s21 Goto2 Tier1 Three-Phase reaker1 s11 s13 s15 s23 s25 Tier Three-Phase reaker t5 a SRIS SHUNT a b Vdc s12 v + - s24 s26 s22 b c c t4 s14 s16 Vdc1 v + - Discrete, Ts = 5e-005 s powerui Measureents1 Fi14. Siulink block diara of UPQ The purpose of UPQ is to reulate the load voltaes aainst voltae sas, voltae swells and disturbances in the in the syste and to copensate the reactive and haronic coponents of nonlinear load currents.. Ipleentation of VSs The structure of VS is shown in the Fi. 15 Fi. 16Siulink diara of three-phase series transforer D. Ipleentation of Shunt and Series ontrollers The Siulink block diara of shunt controller is shown in the Fi. 17. Fi. 15 Siulink block diara of VSs In the internal structure of UPQ three VSs are present. Out of three VSs, two VSs are operatin as voltae controllers and one VS is operatin as current controller. ach VS consists of six switches (IGTs) are present.. Ipleentation of Series Transforer The UPQ should necessarily consist of two three-phase series transforer in order to connect of the two VSs in series with the lines to function as a controlled voltae sources. Fi. 17Siulink block diara of shunt controller transfored into the synchronous dq0 frae. low pass filter is used to extract the haronics. The PI contoller is used to reulate the dc-link capacitor voltae. The Siulink block diara of series controller is shown in the Fi International Journal for Modern Trends in Science and Technoloy

8 New Topoloy for Power Quality Iproveent usin 3-Phase 4-Wire UPQ with Reduced D-Link Voltae Ratin Fi. 18 Siulink block diara of series controller. Siulation Results: The siulation results with the odified topoloy are shown in Fis.In this topoloy, the value of the capacitor(f ) in the shunt active filter branch is chosen to be 65 μf,and total dc bus voltae is aintained at 560 V. The voltae across the series capacitor in phase-a (vcfa) and the phase-aload voltae (vla) are shown in Fi. Fro this fiure, itis clear that the voltae across the capacitor is in phase opposition to the terinal voltae. ccordin to (16), the voltae across the capacitor adds to the dc-link voltae and injects the required copensation currents into the P. Fi 21: Siulation results usin conventional topoloy. D capacitor voltae VII. ONLUSION odified UPQ topoloy for three-phase four-wire syste has been proposed in this paper, which has the capability to copensate the load at a lower dc-link voltae under non stiff source. Desin of the filter paraeters for the series and shunt active filters is explained in detail. The proposed ethod is validated throuh siulation and experiental studies in at three-phase distribution syste with neutral-claped UPQ topoloy (conventional). The proposed odified topoloy ives the advantaes of both the conventional neutral-claped topoloy and the four-le topoloy. Detailed coparative studies are ade for the conventional and odified topoloies. Fro the study, it is found that the odified topoloy has less averae switchin frequency, less THDs in the source currents, and load voltaes with reduced dc-link voltae as copared to the conventional UPQ topoloy Fi 19: Siulation results usin conventional topoloy. Terinal voltaes with sa, DVR-injected voltaes, and load voltaes after copensation. Fi 20: Siulation results usin conventional topoloy. Shunt active filter currents RFRNS [1]. W. Gunther and H. Mehta, survey of distribution syste power quality-preliinary results, I Trans. Power Del., vol. 10, no. 1,pp , Jan [2] M. F. McGranahan, D. R. Mueller, and M. J. Saotyi, Voltae sas in industrial syste, I Trans. Ind. ppl., vol. 29, no. 2, pp , Mar./pr [3] H. kai, Trends in active filters line conditioner, I Trans. Power lectron., vol. 9, no. 3, pp , May [4] H.kai, Newtrendsinactivefilters for power conditionin, I Trans. Ind. ppl., vol. 32, no. 6, pp , Nov./Dec [5] H. Fujita and H. kai, The unified power quality conditioner: The interation of series active filters and shunt active filter, I Trans.Power. lectron., vol. 13, no. 2, pp , Mar [6] M. H. H. hen, Modelin and controllin of unified power quality conditioners, in Proc. onf. Rec., Hon Kon, hina, pp [7]. Sepúlveda, J. spinoza, L. Moran, and R. Ortea, nalysis and desin of a linear control stratey for 64 International Journal for Modern Trends in Science and Technoloy

9 IJMTST Volue: 2 Issue: 03 March 2016 ISSN: three-phase UPQs, in Proc.onf. Rec., Nov. 2004, vol. 3, pp [8] L. Landaeta,. Sepúlveda, J. spinoza, and. aier, ixed LQRI/PI based control for three-phase UPQs, in Proc. onf.ion, Nov. 2006, pp [9] P. Kenneth, urrent-source converter for otor drives, I Trans. Ind. ppl., vol. I-8, no. 6, pp , Nov [10] P.nkineedu Prasad, N.Venkateswarlu. V.Raesh, L.V.NarasihaRao Modified Three-Phase Four-Wire UPQ Topoloy with Reduced D-Link Voltae Ratin - International lectrical nineerin Journal (IJ) Vol. 6 (2015) No.2, pp ISSN [11] D. Graovac, V. Kati,. Rufer, and J. Kne, Unified power quality conditioner based on current source converter topoloy, presented at the onf. Rec. lect. Power n., Graz, ustria, u [12] K. Vadirajacharya, P. arwal, and H. Gupta, siple control stratey for unified power quality conditioner usin current source inverter, in Proc. onf. Rec. IP, May 2008, pp [13] P. Melin, J. spinoza, N. Zarari, M. Sanchez, and J. Guzan, Modelin issues in three-phase current source rectifiers that use dapin resistors, [14] N. Zarari, G. Joos, and P. Zioas, Input filter desin for PWM current-source rectifiers, I Trans. Ind. ppl., vol. 30, no. 6, pp , Nov./Dec [15] J. spinoza and G. Joos, State variable decouplin and power flow control in PWM current-source rectifier, I Trans. Ind. lectron., vol. 45, no. 1, pp , Feb [16] P. Melín, J. spinoza, J. Muñoz,. aier, and. spinosa, Decoupled control of a unified power conditioner based on current source topoloy for fast ains disturbance copensation, in Proc. onf. Rec. IIT, Mar. 2010, pp International Journal for Modern Trends in Science and Technoloy