Operaton of Shunt Acte Power Flter Under Unbalanced and Dstorted Load Condtons Metn Kesler 1, Engn Özdemr 1, Kocael Unersty, Techncal Educaton Faculty, Electrcal Educaton Department, 4138 Umuttepe, TURKEY 1 metnkesler@kocael.edu.tr, eozdemr@kocael.edu.tr Abstract In ths study, reduced current measurement control method s nestgated for operaton of 3-phase 4-wre shunt acte power flter (SAPF) under unbalanced and dstroted load condtons. The control method s based on Instantaneous Reacte Power theory (IRP) and requres only measurng the source currents to reduce the number of Current Sensors (CSs) needed n the conentonal control approach. The control technque has been tested under dfferent load condtons usng Matlab/Smulnk smulatons and aldated wth a 1kVA/38V expermental prototype based on TMS3F8335 Dgtal Sgnal Processor (DSP). Both smulaton and expermental test results demonstrate that the ablty of the reduced current measurement method, successful n meetng the IEEE 519-199 recommended harmonc standard lmts. 1. Introducton Harmonc current polluton of three-phase electrcal power systems s becomng a serous problem due to the wde use of nonlnear loads, such as dode or thyrstor rectfers and a ast arety of power electroncs based applances. Tradtonally, passe LC flters hae been used to elmnate the current harmoncs and to mproe the power factor. Howeer, passe LC flters are bulky, load dependent and nflexble. They can also cause resonance problems to the system. In order to sole these problems, APFs hae been reported [1-5] and consdered as a possble soluton for reducng current harmoncs and mprong the power factor. Fg. 1 shows the basc compensaton prncple of the three phase shunt APF. It s desgned to be connected n parallel wth the nonlnear load to detect ts harmonc and reacte current and to nject nto the system a compensatng current. In the conentonal p-q theory based control approach for the shunt APF, the compensaton current references are generated based on the measurement of load currents. Howeer, the current feedback from the SAPF output s also requred and therefore, mnmum sx CSs are desred n a unbalanced system. In addton, the reference current calculaton algorthm are smplfed and easly mplemented n the expermental prototype. In the reduced current measurement control algorthm, sensng only three-phase oltages, three source currents and a DC-lnk oltage s adequate to compute reference currents of the threephase SAPF. In ths way, the oerall system desgn becomes easer to accomplsh and the total mplementaton cost s reduced. S abc 3 Mans Sa c a La S abc R S L S = + C abc R C L abc L C R L L L L abc Non-lnear Load Shunt Acte Power Flter Fg.1. SAPF block dagram C DC Z load. Reference Current Sgnal Generaton for Shunt Acte Power Flter The shunt acte power flter control algorthm s shown n Fg.. Instantaneous reacte power (p-q) theory s used to control of shunt acte power flter n real tme. In ths theory, nstantaneous three-phase current and oltages are transformed to -- from a- b-c coordnates as shown n equaton (1) and (). Sa Sb Sc Sa Sb Sc p-q conerson - con. - con. o o + p p Ins. - LPF S Reacte Reference power p current S calc. calc. - S o * V DC V DC1 - p loss PI V DC + DC Reference current calc. - In. Trans. Sa Sb Hysteress Band Current control Fg.. Shunt acte power flter control block dagram. Sc GAH GAL GBH GBL GCH GCL I-9
1/ 1/ 1/ Sa 1-1/ -1/ Sb 3 (1) 3/ - 3/ Sc 1/ 1/ 1/ Sa 1-1/ -1/ Sb 3 () 3/ - 3/ Sc Load sde nstantaneous real and magnary power components are calculated by usng source currents and phase-neutral oltages as gen n equaton (3). p p q 3 - Instantaneous real and magnary powers nclude AC and DC components as shown n (4). DC components of p and q composed from poste sequence components ( p and q ) of load current. AC components ( ~ p and ~ q ) of p and q nclude harmonc and and negate sequence components of load currents [4,5]. In order to reduce neutral current, p was calculated by usng DC and AC components of magnary power and AC component of real power; as gen n (5) f both harmonc and reacte power compensaton s requred p ; p p ~ p ; q q ~ q (4). (3) reference currents and actual lne currents and usng hysteress band current control algorthm [6]. 3. Smulaton Results In ths study, reduced current measurement control method algorthm for SAPF s ealuated by usng smulaton results gen n Matlab/Smulnk software. The expermental and smulated SAPF system parameters are gen n Table I. In smulaton studes, the result are specfed before and after SAPF system s operated. In addton, when SAPF system s operated, load has changed and dynamc response of the system was tested. The reduced current measurement control method algorthm has consderably good smulaton results as compared the conentonal control algorthms. Table I. SAPF Expermental and Smulaton parameters. Parameters Value Source Voltage Sabc 38 V rms Frequency f 5 Hz 3-Phase AC Lne Inductance L Labc mh 1-Phase AC Lne Inductance L La1 1 mh Load 3-Phase DA Inductance L da3 1 mh 3-Phase DA Resstor R da3 3 1-Phase DA Resstor R da1 87,5 1-Phase DA Capactor C da1 4 F DC Voltage V DA 7 V Lnk Capactor1/ C 1 C 1 11 F AC Lne Inductance L Cabc 3.5 mh SAPF Flter Resstor R Cabc 5 Flter Capactor C Cabc 1 F Swtchng Frequency f pwm ~15 KHz S S 1 - p p p loss (5) * s and * s are reference currents of shunt acte power flter n - - coordnates. To compensate neutral current, * s=- These currents are transformed to three-phase system as shown below n equaton (6). * Sa * Sb * Sc 1/ 1/ 3 1/ 1-1/ -1/ * S 3/ * S (6) - 3/ * S The reference currents n three-phase system (* sa * sb e * sb ) are calculated n order to compensate neutral, harmonc and reacte currents n the load. The swtchng sgnals used n shunt acte power flter control algorthm are generated by comparng Fg. 3. The SAPF control algorthm block dagram. I-93
Load current compensaton smulaton results under non-lnear (unbalanced-dstorted) load current condtons are gen n Fg. 4. The neutral current compensaton results are gen n Fg. 5. Loadmans current and oltage waeforms n phase a are shown n Fg. 6. SAPF control algorthm has ablty to compensate both harmoncs and reacte power of the load and neutral current s also elmnated[4,5]. The reduced current measurement control method algorthm control technque has been ealuated and tested under dynamcal and steady-state load condtons Smulaton results for under load changng are shown n Fg. 7. Labc(A) Cabc(A) Sabc(A) La(V Sa(A) Sa(V) La(A) Ln(A) Cn(A) Sn(A) 4 - -4 Load Currents.5.3.35.4 - Flter Currents.5.3.35.4 - Source Currents.5.3 t(s).35.4 Fg. 4. Smulaton results for unbalanced and non-lnear load current condton. - Load Neutral Current.5.3.35.4 - Flter Neutral Current.5.3.35.4 - Source Neutral Current.5.3 t(s).35.4 - -.1 Fg. 5. Smulaton results for neutral current and reacte power compensaton. La Sa Sa La.15. t(s) Fg. 6. Smulaton results for reacte power compensaton. p(va) q(iva) Ya(V) Ka(A) Ca(A) Kn(A) Ya(V) Ka(A) 4 - -4 4 - -4 4 - -4 4 - -4 1 5 1 VDA(V) 5-5 - 8 Before SAPF After SAPF Operaton Load araton (Step Up) Load Currents (c) Source Currents (d) Flter Currents (e) Source Neutral Currents (f) Acte Power (g) Reacte Power (h) Reacte compensaton () 7 DC Lnk Voltage (k) 6.1.15. t(s).5.3 Fg. 7. Smulaton results for operaton performance of the SAPF system. 4. Expermental results The hardware mplementaton for the reduced current measurement control algorthm was ealuated by desgn and expermentaton of three-phase four-wre SAPF. A 3-phase dodebrdge rectfer wth the R-L load as the nonlnear load s connected to AC mans to demonstrate the effecteness of the SAPF wth the reduced current measurement control method. A 1- phase dode-brdge rectfer wth the R-C load s connected to AC mans to make unbalanced load. The am of the SAPF system s to compensate for the current harmoncs produced by a dode-brdge rectfer of 1 kva. The dc lnks of acte flters are connected to a common dc capactor of 11 mcrofarad and 7 V DC. The dode-brdge rectfer s consdered a harmonc producng load dentcal to a dc power supply that can found n any power electroncs based system. The control technque s mplemented on the TMS3F8335 DSP board. F8335 DSP has an nternal 68 kb RAM, kb OTP ROM, 51 kb flash, 18 channels pulse wdth modulaton (PWM), 1-bt 16 channels analog-to-dgtal (A/D) conerters, expanson nterfaces and parallel port JTAG nterface. It can perform parallel multply and arthmetc logc unt (ALU) on nteger or floatng pont data n a 6.67 ns sngle cycle nstructon tme wth a peak computaton rate of 15 mllon nstructon per second (MIPS). Fg. 8. Show the photograph of the SAPF expermental prototype system. The source oltage and current sgnals are measured LEM hall-effect sensor. Semkron SEMIX 11GD18Ds IGBT modules I-94
and the CONCEPT 6SD16EI sx-pack IGBT drer modules and Semkron SKHI61 IGBT drer are used for drng the IGBT swtches n power part of the SAPF system. IGBT drer module has short crcut and oer current protecton functons for eery IGBT and prodes electrcal solaton of all PWM sgnals appled to DSP. Fg. 9 shows expermental results for source current ( Sabc ) before and after flter operaton and current ( Sabc ) after flter operaton. Source current becomes snusodal and n phase wth the source oltage; hence, both harmoncs and reacte power are compensated smultaneously. Fg. 1 shows expermental results for source current ( Sa ) harmonc spectrum before and after flter operaton. Before harmonc compensaton the THD of the supply current was 9.13% and after the harmonc compensaton, t was reduced to 5.75% whch comples wth the IEEE 519 harmonc standards. Fg. 1. Expermental results for source current( Sa ) harmonc spectrum before and after flter operaton. Fg. 11. show expermental results for DC lnk oltage and source current( Sa ) before and after load araton (load step up), SAPF tested under dynamcal and steady-state load condtons under load changng. Fg.1. show expermental results for source currents ( Sabc ) and neutral current Sn Fg.13.show results for load neutral ( Ln ), flter neutral ( Cn ) and source neutral current Sn before and after flter operaton. Fg. 8. The photograph of the SAPF laboratory system. DC-lnk Voltage Sa Sa DC-lnk Voltage Fg. 9. Expermental results for source current( Sabc ) before and after flter operaton and current( Sabc ) after flter operaton. Fg.11. and Expermental results for DC lnk oltage and source current( Sa ) before and after load araton (load step up). These expermental results gen aboe shows that the harmoncs compensaton features of SAPF, by approprate control of shunt APF can be done effectely. SAPF wth reduced current measurement based control method can be compensatng neutral, harmonc and reacte currents effectely, n the unbalanced and dstorted load condtons. I-95
and effecteness of the control method under non-lnear and unbalanced load condtons. Fg.1. Expermental results for source current ( Sabc ) and neutral current Sn before and after flter operaton Ln Sn Cn Sabc Source Currents Fg.13. Expermental results for load neutral ( Ln ), flter neutral ( Cn ) and source neutral current Sn 5. Concluson Sn Source Neutral Current In ths paper, proposed control method based on reduced current measurement for shunt acte power flter wth only source current detecton s nestgated. Detecton of nether load lne current nor APF output current s not requred. Therefore, computatons and crcut mplementaton of the control system become qute smple compared to the conentonal load current detecton algorthms. In order to confrm the effecteness of ths control algorthm, the approach has been tested through the smulaton and expermental aldaton. Expermental test results usng a TMS3F8335 DSP are gen to demonstrate the performance of the reduced current measurement based control method for the shunt APF. Both smulatons and expermental results confrm that the reduced current measurement based control method for the shunt APF has some adantages smple and easy to mplement. The results obtaned hae clearly shown that, een usng only source current measurement, the APF performance s qute smlar to that of standard solutons. Moreoer, as the crcut needs only supply current feedback sgnals where the load CSs can be saed, the crcut desgn can be thus smplfed sgnfcantly. Expermental results obtaned from a laboratory model of 1 kva, along wth a theoretcal analyss, are shown to erfy the ablty 6. Acknowledgement Ths study s supported fnancally by Kocael Unersty Scentfc Research Fund. Ths work s also supported by Concept Inc. (Concept IGBT Drer), Semkron Inc. (IGBT and IGBT Drer), LEM Inc. (Voltage and Current sensor) and TI Inc. (F8335 ezdsp), whch s gratefully acknowledged. The authors gratefully acknowledge the contrbutons of Halm Özmen (from Semkron Turkey) and Robert Owen (from TI). 7. References [1] Le Roux, A.D., Du Tot, J.A., Ensln, J.H.R., Integrated acte rectfer and power qualty compensator wth reduced current measurement, Industral Electroncs, IEEE Transactons on, Volume 46, Issue 3, 54 511, (1999). [] Takeshta, T.; Matsu, N., Control of acte flters usng source current detecton, Industral Electroncs Socety, 3. IECON apos;3. The 9th Annual Conference of the IEEE, Volume, Issue, 1515-15 Vol., (3). [3] Chatterjee, K.; Fernandes, B.G.; Dubey, G.K., An nstantaneous reacte olt-ampere compensator and harmonc suppressor system, Power Electroncs, IEEE Transactons on, Volume 14, Issue, 381 39, (1999). [4] E. Ozdemr, M. Ucar, M. Kesler, M. Kale, "The Desgn and Implementaton of a Shunt Acte Power Flter based on Source Current Measurement", -, The IEEE Internatonal Electrc Machnes and Dres Conference, IEMDC 7, Antalya, Turkey, -, 68-613, (7) [5] E. Ozdemr, M. Ucar, M. Kesler, M. Kale, "A Smplfed Control Algorthm for Shunt Acte Power Flter Wthout Load and Flter Current Measurement", -, The 3nd Annual Conference of the IEEE Industral Electroncs Socety, IECON'6, Pars, France, -, 599-64, (6) [6] Peng, F. Z., OTT, G. W., Adams, D. J., Harmonc and Reacte Power Compensaton on the Generalzed Instantaneous Reacte Power Theory for Three-Phase Four-Wre Systems. IEEE Trans. on Power Elec., Vol. 13, No. 6, pp. 1174-1181, (1998). [7] Akag, H. and Fujta, H., A new power lne condtonal for harmonc compensaton n power systems, IEEE Trans. Power Del., ol. 1, no. 3, pp. 157 1575, Jul. 1995. [8] Akag, H., Kanazawa, Y., Nabae, A., Generaled Theory of Instatntenus Reactf Power and Ist Applcaton, Transacton off the IEE Japan, Part B,o 13, No.7, 483-49, n Japanese (1983.) [9] Akag, H., Ogasawara, S., Km, H., 1. The Theory of Instantaneous Power n Three-Phase Four-Wre Systems and Its Applcatons. Electrcal Engneerng n Japan, Vol. 135, No. 3, pp. 74-86. [1] H. Akag, E. H. Watanabe and M. Aredes, Instantaneous Power Theory and Applcatons to Power Condtonng. Wley-IEEE Press. Aprl 7. I-96