Noel ontrol Method for Unfed Power Qualty ondtoner (UPQ Under NonIdeal Mans Voltage and Unbalanced Load ondtons Metn Kesler Kocael Unersty Techncal Educaton Faculty, 4138 Umuttepe Kocael Turkey metnkesler@kocael.edu.tr bstractths paper presents a new control method to compensate the power qualty problems through a threephase unfed power qualty condtoner (UPQ under nondeal mans oltage and unbalanced load condtons. The performance of proposed control system was analyzed usng smulatons wth Matlab/Smulnk program, and expermental results wth the hardware prototype. The proposed UPQ system can mproe the power qualty at the pont of common couplng (P on power dstrbuton system under nondeal mans oltage and unbalanced load condtons. I. INTRODUTION Unfed power qualty control was wdely studed by many researchers as an eentual method to mproe power qualty of electrcal dstrbuton system [13]. The functon of unfed power qualty condtoner s to compensate supply oltage flcker/mbalance, reacte power, negatesequence current, and harmoncs. In other words, the UPQ has the capablty of mprong power qualty at the pont of nstallaton on power dstrbuton systems or ndustral power systems. Therefore, the UPQ s expected to be one of the most powerful solutons to large capacty loads senste to supply oltage flcker/mbalance []. The UPQ consstng of the combnaton of a seres acte power flter ( and shunt can also compensate the oltage nterrupton f t has some energy storage or battery n the dc lnk [3]. The shunt s usually connected across the loads to compensate for all currentrelated problems such as the reacte power compensaton, power factor mproement, current harmonc compensaton, and load unbalance compensaton [1], whereas the seres s connected n a seres wth the lne through seres transformers. It acts as controlled oltage source and can compensate all oltagerelated problems, such as oltage harmoncs, oltage sag, oltage swell, flcker, etc. In ths paper a new control algorthm for the UPQ system s optmzed wthout measurng transformer oltage, load and flter current, so that system performance s mproed. The proposed control technque has been ealuated and tested under nondeal mans oltage and unbalanced load condtons usng Matlab/Smulnk software. The proposed method s also aldated through expermental study. Engn Ozdemr Kocael Unersty Techncal Educaton Faculty, 4138 Umuttepe Kocael Turkey eozdemr@kocael.edu.tr II. UPQ ONTROL LGORITHM The UPQ conssts of two oltage source nerters connected back to back wth each other sharng a common dc lnk. One nerter s controlled as a arable oltage source n the seres, and the other as a arable current source n the shunt. Fg. 1 shows a basc system confguraton of a general UPQ consstng of the combnaton of a seres and shunt. The man am of the seres s harmonc solaton between load and supply; t has the capablty of oltage flcker/ mbalance compensaton as well as oltage regulaton and harmonc compensaton at the utltyconsumer P. The shunt s used to absorb current harmoncs, compensate for reacte power and negatesequence current, and regulate the dclnk oltage between both s. The proposed UPQ control algorthm block dagram n Matlab/Smulnk smulaton software s shown n Fg.. Sa Ta La Sa a La 3 Sabc Mans Voltage = = RS Tabc Sabc L S RT LT Seres Tabc D Shunt P RL R L abc Labc LL Labc Nonlnear Load Fg. 1. Unfed power qualty condtoner confguraton.. Reference Voltage Sgnal Generaton for Seres The functon of the seres s to compensate the oltage dsturbance n the source sde, whch s due to the fault n the dstrbuton lne at the P. The seres control algorthm calculates the reference alue to be njected by the seres transformers, comparng the postesequence component wth the load sde lne oltages. The proposed seres reference oltage sgnal generaton algorthm s shown n Fg. 3. In equaton (1, supply oltages Sabc are transformed to dq coordnates. Zload 978144447831/1/$5. 1 IEEE 374
Sabc a Labc a Labc a Pulse g Ldc3 N h5 b c b c b c Rdc3 3Phase Source Sn Dscrete, Ts = 5e6 s. Sn Sabc a 1 b 1 c 1 1Phase Sees Transformers Tabc Tabc Ln abc Ln a b c LLabc LLa1 3Phase NonLnear Load dc1 Rdc1 pow ergu RTabc LTabc 1 VD Labc Rabc 1Phase NonLnear Load Tabc g g abc (Seres cte Power Flter (Shunt cte Power Flter Sabc abc sn_cos dq Sabc PLL em dq abc sn_cos Sabc Sabc D Vabc Iabc p Valf a Ebeta Vo Io p Valf a Vbeta Vo Io Vdc I'Salf a I'Sbeta I' Labc 'Tabc Tabc Sabc 'Sabc Sabc 'Sabc I' 'Sbeta 'Salf a Fg.. The proposed UPQ control algorthm block dagram n MTL Smulnk. S Sd Sq 1 = sn(wt 3 cos(wt 1 sn(wt cos(wt π 3 π 3 1 Sa π sn(wt Sb 3 π Sc cos(wt 3 The oltage n d axes ( Sd gen n ( conssts of aerage and oscllatng components of source oltages ( Sd and ~ Sd. The aerage oltage Sd s calculated by usng second order LPF (low pass flter. = ( Sd ~ Sd Sd The load sde reference oltages Labc are calculated as gen n equaton (3. The swtchng sgnals are assessed by comparng reference oltages ( Labc and the load oltages ( Labc and a snusodal controller. La sn(wt cos(wt 1 π π Sd Lb = sn(wt cos(wt 1 3 3 3 π π Lc sn(wt cos(wt 1 3 3 These produced threephase load reference oltages are compared wth load lne oltages and errors are then processed by snusodal controller to generate the requred swtchng sgnals for seres IGT swtches. (1 (3. Reference urrent Sgnal Generaton for Shunt The shunt descrbed n ths paper used to compensate the current harmoncs and reacte power generated by the nonlnear load. The shunt reference current sgnal generaton block dagram s shown n Fg. 3. The nstantaneous reacte power (pq theory s used to control of shunt n real tme. In ths theory, the nstantaneous threephase currents and oltages are transformed to α coordnates as shown n equaton (4 and (5. La Lb Lc Sa Sb Sc Sa Sb Sc α con. α con. PLL o α o α S dq transform. Sd Sq p p Instantaneous LPF Power calculate q q p 1 p * V D VD1 Σ PI VD LPF α Reference current calc. D p loss S Lα dq Sd In. Lb transfor m Lc Sq Sα S α In. Trans. Sa Sb Sc Seres Snusodal Shunt Hysteress and Fg. 3. Seres reference oltage and shunt reference current sgnal generaton block dagram. S GH GL GH GL GH GL GH GL GH GL GH GL 375
α α 1/ 1/ 1/ Sa = 1 1/ 1/ Sb (4 3 3/ 3/ Sc 1/ 1/ 1/ Sa = 1 1/ 1/ Sb (5 3 3/ 3/ Sc The source sde nstantaneous real and magnary power components are calculated by usng source currents and phaseneutral oltages as gen n (6. The nstantaneous real and magnary powers nclude both oscllatng and aerage components as shown n (7. erage components of p and q consst of poste sequence components ( p and q of source current. The oscllatng components ( ~ p and ~ q of p and q nclude harmonc and negate sequence components of source currents [4]. In order to reduce neutral current, p s calculated by usng aerage and oscllatng components of magnary power and oscllatng component of the real power; as gen n (8 f both harmonc and reacte power * compensaton s requred. sα, * s and * s are the reference currents of shunt n α coordnates. These currents are transformed to threephase system as shown n (9. p q p = α α α = ; p = p ~ p (7 Sα 1 α p p = S α α * Sa * Sb = * Sc 1/ 1/ 3 1/ 1 1/ 1/ p loss (6 (8 * S 3/ * S α (9 3/ * S The reference currents are calculated n order to compensate neutral, harmonc and reacte currents n the load. These reference source current sgnals are then compared wth sensed threephase source currents, and the errors are processed by hysteress band controller to generate the requred swtchng sgnals for the shunt swtches [6]. III. SIMULTOIN RESULTS In ths study, a new control algorthm for the UPQ s ealuated by usng smulaton results gen n Matlab/Smulnk software under nondeal mans oltage and unbalanced load current condtons. The smulated UPQ system parameters are gen n Table I. In smulaton studes, the results are specfed before and after UPQ system are operated. In addton, when the UPQ system s operated, the load has changed and dynamc response of the system s tested. The proposed control method has been examned under nondeal mans oltage and unbalanced load current condtons. efore harmonc compensaton, the THD of the supply current s 6.3%. The obtaned results show that the proposed control technque allows the 3.4% mtgaton of all harmonc components. Source Load dclnk Shunt Seres TLE I. UPQ SYSTEM PRMETERS Parameters Value Voltage Sabc 38 V rms Frequency f 5 Hz 3Phase ac Lne Inductance L Labc mh 1Phase ac Lne Inductance L La1 1 mhω 3Phase dc Inductance L dc3 1 mh 3Phase dc Resstor R dc3 3 Ω 1Phase dc Resstor R dc1 87,5 Ω 1Phase dc apactor dc1 4 μf Voltage V D 7 V apactor 1/ 1 μf ac Lne Inductance L abc 3.5 mh Flter Resstor R abc 5 Ω Flter apactor abc 1 μf Swtchng Frequency f pwm ~15 khz ac Lne Inductance L Tabc 1.5 mh Flter Resstor R Tabc 5 Ω Flter apactor Tabc μf Swtchng Frequency f pwm 1 khz Smulaton results for the load and source oltages under unbalanceddstorted mans oltage condtons are shown n Fg. 4. Load current compensaton smulaton results under nondeal (unbalanceddstorted mans oltage condtons are gen n Fg. 5. Sabc(V Tabc(V Labc(V Source Voltages.15..5.3 Flter Voltages.15..5.3 t(s Load Voltages.15..5.3 Fg. 4. Smulaton results for unbalanced and dstorted mans oltage condton. The neutral current compensaton results are gen n Fg. 6. The proposed UPQ control algorthm has ablty to compensate both harmoncs and reacte power of the load 376
and neutral current s also elmnated. The proposed control technque has been ealuated and tested under dynamcal and steadystate load condtons. Smulaton results for under load changng are shown n Fg. 7. Labc( abc( Sabc( 4 4 Load urrents.5.3.35.4 Flter urrents.5.3.35.4 t(s Source urrents.5.3.35.4 harmoncs produced by a dodebrdge rectfer of 1 kv, but also to elmnate the oltage harmoncs contaned n the receng termnal oltage of the load. The UPQ conssts of two back to back connected oltage source nerters and three DSP processors for controllng shunt and seres s and computer communcaton for all system control functons. The dc lnk of both s s connected to a common dc capactor of 11 mcrofarad and 7 V dc. ll of the crcut parameters and expermental condtons are set up exactly the same as the smulaton condtons. lthough the proposed control scheme cannot be studed expermentally for unbalanced mans oltage condtons, an optmal control can be desgned to elmnate ths problem, whch wll hae been dscussed as a future work. Fg. 5. Smulaton results for unbalanced and nonlnear load current condton. Ln( Load Neutral urrent.5.3.35.4 n( Sn( Flter Neutral urrent.5.3.35.4 Source Neutral urrent.5.3.35.4 Fg. 6. Smulaton results for neutral current compensaton. Fg. 8. The photograph of the proposed UPQ system. Labc(V Labc(V Sabc( Sn( VD(V efore UPQ fter UPQ Operaton Load Varaton (Stepup Load Voltages.1.15..5.3 4 4 Load urrents.1.15..5.3 4 4 Source urrents.1.15..5.3 4 4 Source Neutral urrent.1.15..5.3 8 7 6 t(s D Lnk Voltage.1.15..5.3 Fg. 7. Smulaton results for operatonal performance of the UPQ system. IV. EXPERIMENTL TEST RESULTS Fg. 8 shows an expermental system confguraton photograph of the proposed UPQ system. The am of the UPQ system s not only to compensate for the current The source and load oltages are sensed usng LEM LV 5P oltage sensors, whereas, all the currents are sensed usng LEM L55P HallEffect current sensors. The seres and shunt nerters are bult usng SEMIX 11GD18Ds sxpack IGT swtches from Semkron. ONEPT 6SD16EI and Semkron SKHI 61 IGT drers are used for seres and shunt respectely. The IGT drer modules hae short crcut and oer current protecton functons for eery IGT and prodes electrcal solaton for all sgnals appled to the dgtal sgnal processor (DSP. The proposed expermental control system conssts of three DSP cards from TI (TMS3F8335. Three DSP cards are desgned to control shunt and seres and one of them s responsble for all system operaton and power qualty analyss. oth nerters use the arable frequency hysteress band controller. Fg. 9 shows source oltage and current waeforms before flterng. fter compensaton, source current becomes snusodal and n phase wth the source oltage; hence, both harmoncs and reacte power are compensated smultaneously. efore harmonc compensaton, the THD of the supply current s 9.13% and after the harmonc compensaton, t s reduced to 5.3% whch comples wth the IEEE 519 harmonc standards. Fg. 1 and Fg. 11 show expermental results for source oltage ( Sa, flter current ( a and source current ( Sa after flter operaton respectely. 377
Sa Sa harmonc spectrum Sa Sa Fg. 9. Expermental results for source oltage ( Sa and source current ( Sa before flter operaton. Dlnk Voltage a harmonc spectrum Sa a Fg.13. Expermental results for dc lnk oltage and source current ( Sa before and after load araton (load stepup. Fg. 1. Expermental results for source oltage ( Sa and flter current ( a after flter operaton. Sabc Source urrents Sa Sa Sn Source Neutral urrent Sa harmonc spectrum Fg.14. Expermental results for source current ( Sabc and neutral current Sn before and after flter operaton Fg. 11. Expermental results for source oltage ( Sa and source current ( Sa after flter operaton. Fg. 1 shows expermental results for threephase source currents ( Sabc before and after flter operaton. Fg. 13 shows expermental results for the dc lnk oltage and the source current ( Sa before and after load araton (load stepup, the shunt tested under dynamcal and steadystate load condtons under load changng. Fg. 14 shows the expermental results for source currents ( Sabc and neutral current ( Sn before and after flter operaton. Fg. 15 shows results for load neutral ( Ln, flter neutral ( n and source neutral current ( Sn before and after flter operaton. Ln Sn n Fg.15. Expermental results for load neutral ( Ln, flter neutral ( n and source neutral current ( Sn. Sabc Source urrents Fg. 1. Expermental results for source current ( Sabc before and after flter operaton. These expermental results gen aboe shows that the harmonc compensaton features of the UPQ, by approprate control of the shunt can be done effectely. The shunt wth reduced current measurement based control method can be compensatng neutral, harmonc and reacte currents effectely, n the unbalanced and dstorted load condtons. The seres expermental results for mans and load oltages before flter operaton s shown n Fg. 16. Fg. 17 shows the expermental results for the load oltages n threephase form before and after flter operaton. 378
Fg. 16. Expermental results for mans and load oltages before flter operaton. Labc Load oltages La Load oltage Sa Source oltage Fg. 17. Expermental results for load oltages n threephase form before and after flter operaton. V. ONLUSION Ths paper descrbes a new control strategy used n the UPQ system, whch manly compensate reacte power and oltage and current harmoncs n the load under nondeal mans oltage and unbalanced load current condtons. The proposed control strategy use only loads and mans oltage measurements for seres based on the synchronous reference frame theory. The nstantaneous reacte power theory s used for shunt control algorthm by measurng mans oltage and currents. The conentonal methods requre measurements of the load, source and flter oltages and currents. The smulaton results show that, when unbalanced and nonlnear load current or unbalanced and dstorted mans oltage condtons, the aboe control algorthms elmnate the mpact of dstorton and unbalance of load current on the power lne, makng the power factor unty. Meanwhle, the seres solates the loads oltages and source oltage, the shunt prodes threephase balanced and rated currents for the loads. The expermental results obtaned from a laboratory model of 1 kv, along wth a theoretcal analyss, are shown to erfy the ablty and effecteness of the proposed UPQ control method. KNOWLEDGEMENT Ths study s supported fnancally by TUITK research fund number 18E83 and Kocael Unersty Scentfc Research Fund. Ths work s also supported by oncept Inc. (oncept IGT drer, Semkron Inc. (IGT and IGT drer, LEM Inc. (oltage and current sensor and TI Inc. (F8335 ezdsp, whch s gratefully acknowledged. The authors gratefully acknowledge the contrbutons of Halm Ozmen (from Semkron Turkey and Robert Owen (from TI. REFERENES [1] H. kag, and H. Fujta, new power lne condtonal for harmonc compensaton n power systems, IEEE Trans. Power Del., ol. 1, no. 3, pp. 157 1575, Jul. 1995. [] H. Fujta, and H. kag, The unfed power qualty condtoner: The ntegraton of seres and shuntacte flters, IEEE Trans. Power Electron., ol. 13, no., pp. 315 3, Mar. 1998. [3] H. kag, E. H. Watanabe and M. redes, Instantaneous Power Theory and pplcatons to Power ondtonng. WleyIEEE Press. prl 7. [4] D. Graoac,. Katc, and. Rufer, Power Qualty Problems ompensaton wth Unersal Power Qualty ondtonng System, IEEE Transacton on Power Delery, ol., no., 7. [5]. Han,. ae, H. Km, and S. aek, ombned Operaton of Unfed PowerQualty ondtoner wth Dstrbuted Generaton, IEEE Transacton on Power Delery, ol. 1, no. 1, pp. 33338, 6. [6] M. redes, combned seres and shunt acte power flter, n Proc. IEEE/KTH Stockholm Power Tech onf., Stockholm, Sweden, pp. 18, June 1995. [7] Y. hen, X. Zha, and J. Wang, Unfed power qualty condtoner (UPQ: The theory, modelng and applcaton, Proc. Power System Technology Power on Int. onf., ol. 3, pp. 139 1333,. [8] F. Z. Peng, J.W. McKeeer, and D. J. dams, power lne condtoner usng cascade multleel nerters for dstrbuton systems, IEEE Trans.Ind. ppl., ol. 34, no. 6, pp. 193 198, No./Dec. 1998. [9] G. M. Lee, D.. Lee and J. K. Seok, ontrol of seres acte power flter compensatng for source oltage unbalance and current harmoncs, IEEE Transacton on Industral Electroncs, ol. 51, no. 1, pp. l3 139, Feb. 4. [1] V. Khadkkar,. handra, New ontrol Phlosophy for a Unfed Power Qualty ondtoner (UPQ to oordnate LoadReacte Power Demand etween Shunt and Seres Inerters, IEEE Trans. on Power Delery, ol.3, no.4, pp. 5534, 8. [11] M. redes, H. kag, E.H. Watanabe, E. V. Salgado, L. F. Encarnacao, omparsons etween the pq and pqr Theores n ThreePhase FourWre Systems, IEEE Transactons on Power Electroncs, ol. 4, no. 4, pp. 94933, prl, 9. [1]. Esfandar, M. Parnan,. Emad, H. Mokhtar, pplcaton of the Unfed Power Qualty ondtoner for Mtgatng Electrc rc Furnace Dsturbances, Internatonal Journal of Power and Energy Systems, ol. 8, no. 4, pp. 363371, 8. 379