Design of Shunt Active Filter for Harmonic Compensation in a 3 Phase 3 Wire Distribution Network

Transcription

1 Internatonal Journal of Research n Electrcal & Electroncs Engneerng olume 1, Issue 1, July-September, 2013, pp , IASTER Onlne: , Prnt: Desgn of Shunt Actve Flter for Harmonc Compensaton n a 3 Phase 3 Wre Dstrbuton Network ABSTRACT Arun Shankar.K 1, Dr. N. Senthl Kumar 2 1 PG Scholar, 2 Assocate Professor School of Electrcal Engneerng, IT Unversty Chenna, Inda The thought of usng shunt actve flter (SAF) for load compensaton wth a control strategy of enhanced nstantaneous actve and reactve current component method s delberated n ths paper. As per IEEE-519 standard the performance evaluaton of the projected scheme s calculated n te of compensaton of reactve power, generaton of compensaton currents, and compensaton of harmonc n source currents. The projected control strategy s performance has been related wth nstantaneous reactve power theory (pq theory), and nstantaneous actve and reactve current component theory (dq theory) under balanced snusodal source voltage condtons. SAF has been comprehended by 3-phase voltage source converter (SC). SAF tracks control strateges and generates reference currents. Dssmlarty n magntude and harmonc content of source voltage has been detected for varous control strateges. Results have been obtaned for the projected theory under balanced snusodal source voltage condtons. Hgher performance s acheved by the mproved nstantaneous actve and reactve current component theory under all the varous source voltage condtons. For smulaton 3-phase, 3-wre dstrbuton system delverng power to non-lnear load s taken and studed. Keywords: Compensatng Harmoncs, Control Algorthms, Idq Theory, Non-Lnear Loads, Shunt Actve Flter (SAF), Supply oltage (Dstorted), Total Harmonc Dstorton. I. INTRODUCTION To ncrease the effectveness of the power system and controllablty there s an ncrease n the use of power electroncs based load. Ths causes the rse of harmonc dstorton levels n termnaton use servces and on complete power system [1]. IEEE-519 consstng of numerous standard rules and references ponts the power qualty strateges lke harmonc dstortons [2]. The harmonc dstortons from the non lnear loads are beng compensated by the use of the Actve Power Flter whch uses controlled power electronc swtches. At the pont of common couplng (PCC), Shunt Actve Power Flter produces current of equvalent and opposte n phase to the harmonc current draned by the non-lnear load and t s beng njected. Hence the currents were made to be pure snusodal n nature. To acqure preferred compensaton currents the choce of control strategy desgned for SAF shows a sgnfcant part. arous control algorthms have been exstng to assst ths purpose. They are based on the followng theores, synchronous reference frame theory (SRF), nstantaneous reactve power theory (pq), symmetrcal component theory (sc), unty power factor compensaton strategy, nstantaneous actve and reactve current component theory (dq theory), [3],[4],[5] and [6] respectvely. The sc theory, pq theory and dq theory are explaned completely wth necessary equatons n [3], [4] and [5] respectvely. The comparson of the sc theory, pq theory and the dq theory are beng portrayed n [7], under varous voltage condtons (balanced snusodal and dstorted). 85

2 Internatonal Journal of Research n Electrcal & Electroncs Engneerng olume-1, Issue-1, July-September, 2014, II. CONTROL ALGORITHMS To acqure the requred compensaton currents the choce of control strategy desgned for shunt actve flter s sgnfcant. 2.1 dq Theory, and pq Theory The non-lnear loads ncrease the % n the load current drawn by the non-lnear loads and reduce the power qualty of the entre system. The harmoncs that are ejected by the non-lnear loads, also affects the adjacent consumer. To mtgate the content and enhance the power qualty, the shunt actve power flters were came nto exstence. Among them the pq theory deals wth the trackng of the actve and reactve power from the load sde and processng that to attan the reduced %. Whereas the dq theory nvolves n quantfyng load currents n dq axes and compensatng the harmonc content accordng to that. The research dea deals wth a control strategy operatng at varous source voltages. pq theory and dq theory are explaned completely wth necessary equatons n [2] and [7], respectvely. 2.2 Projected Method In proposed topology the shunt actve flter s connected at the PCC and njects the correspondng compensatng currents at PCC to nullfy the harm. The shunt actve flter s understood by the 3 phase AC/DC rectfer. The operaton of SA F can be understood from the Fg. 1 Fg. 1. System confguraton wth practcal realzaton of SAF. The source voltages sa, sb, sc are measured from the power lnes and they are transformed nto alpha, beta quanttes by Clarke s transformaton. Then they are fltered by a low pass flter for the computaton of angle Ө, as shown n Fg. 2 and n equaton (2) and (3). The swtchng sgnals for the 3-phase SI s generated from the load currents by the followng transformatons as shown n the Fg. 3 and the equatons that govern ths process are (1), (4), (5), (14) and (15). 86

3 Internatonal Journal of Research n Electrcal & Electroncs Engneerng olume-1, Issue-1, July-September, 2014, Fg. 2. Block dagram for generaton of swtchng sgnals to SI. By relatng Clarke s transformaton, Load currents are obtaned n statonary (αβ) frame as gven by Eq. (1) 1 1 lα la = lb 0 - lβ 2 2 lc By relatng Clarke s transformaton, source voltages are obtaned n statonary (αβ) frame as gven by Eq. (2) 1 1 α sa = sb 0 - β 2 2 sc The transformaton angle Ө s calculated by Eq. (4), where af and bf are Source voltages n statonary reference frame after flterng. Butterworth low-pass flter s magntude response s gven by, H jω = A 2N 0.5 (3) 1+ Ω Ω C Where flter gan s gven by A, Cut-off frequency s gven by Ωc -1 βf θ=tan (4) αf 87

4 Internatonal Journal of Research n Electrcal & Electroncs Engneerng olume-1, Issue-1, July-September, 2014, Order of the flter s gven by N Now due to transformaton the drect and the quadrature components of currents are gven by as shown Eq. (5). ld 1 αf βf lα = (5) lq lβ αf + αf βf βf The Synchronous (dq) and statonary (αβ) reference frames showng current and voltage quanttes s shown n Eq (6),(7),(8)(9). The expressons for d and q are gven by the followng equatons as 2 2 d = dq = αβ = αf + βf (6) q =0 (7) The average and oscllatory quanttes found n ld and lq from Eq. (5) s dsntegrated as ld = ld + ld (8) = + (9) lq lq lq Where after the elmnaton of the average components found n the ld and lq, expressons for the compensaton currents become as gven under * cd = - ld (10) * cq = - lq (11) By relatng Inverse Park transformaton, Eq. (12) provdes the computaton of * cα and * cβ. * - cα 1 αf βf * = cd * (12) 2 2 * cβ + βf αf αf βf cq Eq. (13) provdes the nverse Clarke s transformaton to attan the values of * ca * cb and * cc from the expressons * cα and * cβ from Eq. (12). * ca * * cα cb = (13) * * 0 - cβ cc 2 2 III. ESTIMATION OF HARMONIC PURGING The performance of the Actve Power Flter on harmoncs eradcaton s estmated by smulatng the projected actve power flter under balanced source voltage condton (base case) on the non-lnear load. Thus the parameters for voltage sources, transmsson lnes, flters and the non-lnear load are provded n the appendx. 88

5 Internatonal Journal of Research n Electrcal & Electroncs Engneerng olume-1, Issue-1, July-September, 2014, Fg. 3. Smulaton crcut for Shunt Actve Power Flter. The dynamc stablty of the Actve Power Flter s projected by smulatng the projected actve power flter under dfferent load condtons. The load parameters are beng provded n the appendx. Frstly lnear balanced R-L load s connected to the source voltage, and then the nonlnear rectfer load s also connected nto the system. The two dfferent loads that are consdered n ths research are Balanced R-L load and nonlnear rectfer loads. Fg 4. Hysteress controller for generaton of gatng pulses The gatng sgnals for the SI are beng produced from the hysteress controller by comparng the reference compensaton current and the actual compensaton current flowng from the SI to the PCC. Thus the generaton of gatng sgnals s beng smulated as shown n Fg 4. The balanced source voltage s consdered as shown n fg 5. The values of the voltages are beng mentoned n the appendx and they are smulated wth and wthout the presence of actve power flter. The source voltage, values are beng tabulated and they are beng shown n table 1. The table 1 and table 2 show the and % for the source voltages and the load currents respectvely. The harmonc content found n the source current can also be found before flterng and that would be very hgh. The harmonc extenuaton s beng made by the proposed theory. Table 3 shows the and the % results for the source currents. 89

6 Iabc Iabc Iabc abc Internatonal Journal of Research n Electrcal & Electroncs Engneerng olume-1, Issue-1, July-September, 2014, SOURCE OLTAGE tme Fg. 5. Source voltage. 30 LOAD CURRENT tme Fg. 6. Load Current. 30 SOURCE CURRENT tme Fg. 7. Source Current. 8 COMPENSATION CURRENT tme Fg. 8. Compensaton Current. The compensaton current shown n fg8 compensates the harmoncs present n the load current (fg 5) and thus mantans the source current snusodal n nature as shown n fg 7. The source voltage s provded as balanced snusodal as shown n fg 5. 90

7 Internatonal Journal of Research n Electrcal & Electroncs Engneerng olume-1, Issue-1, July-September, 2014, Table 1 and values of Source oltage Source oltage sa sb sc () () () Table. 2 and values of Load current. Load current la lb lc Table. 3 and values of Source current after compensaton. Source Current sa sb sc In dq theory the balanced snusodal source currents are accomplshed. As per the IEEE-519 no dq theory s capable of restrctng and thus the elmnaton of the harmonc s beng effcently attaned. I. CONCLUSION Ths paper stresses worth of sutable control strategy for SAF n a 3-phase, 3-wre dstrbuton system wth non-lnear load to mprove power qualty under snusodal source voltage condtons. Contrast between three methods of control strateges s beng studed and outcomes have been obtaned for projected control strategy under balanced source voltage condtons. SAF shows a greater performance for an dq control strategy. The of the load current s beng reduced to the consderable quantty. As per IEEE-519 ethcs of harmonc current lmt, controllng the of the source current s accomplshed through dq theory.. ACKNOWLEDGMENT Arun Shankar.K. sncerely thanks hs parents and research supervsor Dr. N. Senthl Kumar, Assocate Professor, n School of Electrcal Engneerng (SELECT), IT Unversty Chenna Campus, Chenna , Taml Nadu, Inda. APPENDIX System desgn constrants: Supply voltage: ph = 230 ( value). 91

8 Internatonal Journal of Research n Electrcal & Electroncs Engneerng olume-1, Issue-1, July-September, 2014, Source mpedance: Rs = Ω. Ls = mh. Supply frequency: fs = 50 Hz. Compensator parameters: dc = 600. Cdc = 12 µf. Lf = 3.35 mh. Lnear load parameters: R = 45 Ω. L = 10 mh. Non-lnear load parameters: R = 65 Ω. L = 12 mh. C = 75 µf. REFERENCES [1] Mack GW, Santoso S. Understandng power system harmoncs. IEEE Power Eng. Rev 2001; 21(11):8 11. [2] IEEE Recommended Practces and Requrements for Harmonc Control n Electrcal Power Systems, IEEE Std ; [3] Akag H, Watanable E.H., Aredes M. Instantaneous power theory and applcatons to power condtonng. New Jersey, USA: John Wley & Sons; [4] Soares, erdelho P, Marques G. An nstantaneous actve and reactve current component method for actve flters. IEEE Trans Power Electron 2000; 15(4): [5] Ghosh A, Josh A. A new approach to load balancng and power factor correcton n power dstrbuton system. IEEE Trans Power Delvery 2000; 15(1): [6] Jan S, Agarwal P, Gupta H. Control algorthm for customer generated harmoncs and reactve power. IEEE Trans Power Delvery 2004; 19(1): [7] Namsh Zaver, Ajtsnh Chudasama, Control strateges for harmonc mtgaton and power factor correcton usng shunt actve flter under varous source voltage condtons, electrcal power and energy systems 42 (2012)