Shunt Active Filters (SAF)

Transcription

1 EN-TH05-/004 Martt Tuomanen (9) Shunt Actve Flters (SAF) Operaton prncple of a Shunt Actve Flter. Non-lnear loads lke Varable Speed Drves, Unnterrupted Power Supples and all knd of rectfers draw a non-snusodal current from the network. Therefore they can be consdered to be harmonc current sources. Shunt Actve Flter works as a current source whch, when properly desgned and controlled, produces harmonc currents havng opposte phase than those harmonc currents produced by the non-lnear load. When such a Shunt Actve Flter s connected parallel wth a non-lnear load ts harmonc currents are compensated and the network s loaded wth almost fundamental current only. 3-phase 400V Hz or 60Hz -Σ h +Σ h Varable speed drve or some other harmonc source Actve flter Fgure. Non-lnear load wth shunt actve flter Nokan Capactors Ltd. P.O. Box 4 Tampere Fnland Tel: Fax:

2 EN-TH05-/004 Martt Tuomanen (9) Shunt Actve Flter and harmonc producng load Consderng harmonc current producng load lke a typcal voltage source Varable Speed Drve wth a 4% lne sde reactor n Fgure ts AC-sde current looks lke n Fgure 3. L L L3 4% AC-motor M 6-pulse dode rectfer nverter Fgure. Voltage Source Varable Speed Drve th harmonc 3.0% 7 th harmonc 9.5% th harmonc 6.4% 3 th harmonc 3.3% 7 th harmonc.4% 9 th harmonc.8% -.00 Fgure 3. AC sde current of a Voltage Source Varable Speed Drve and ts harmonc content n Fgure 4 there s the current produced by an actve flter to compensate harmonc currents shown n Fgure 3. Please note that n ths case actve flter s not producng fundamental reactve power and therefore there s no fundamental current but harmonc currents only. Nokan Capactors Ltd. P.O. Box 4 Tampere Fnland Tel: Fax:

3 EN-TH05-/004 Martt Tuomanen 3 (9) th harmonc 3.0% - 7 th harmonc 9.5% - th harmonc 6.4% -3 th harmonc 3.3% -7 th harmonc.4% -9 th harmonc.8% Fgure 4. Current of an actve flter and ts harmonc content Connectng ths actve flter parallel wth the load harmoncs are compensated and the network s loaded by almost fundamental current only lke shown n Fgure 5. 3-phase 400V Hz or 60Hz +Σ h -Σ h Varable speed drve or some other harmonc source Actve flter - 5 th harmonc 3.0% - 7 th harmonc 9.5% - th harmonc 6.4% -3 th harmonc 3.3% -7 th harmonc.4% -9 th harmonc.8% Fgure 5. The effect of the connecton of an actve flter parallel to the harmonc producng load. t should be noted that the output current of an actve flter has a contnuous spectrum of all harmoncs due to the accuracy of the control system. Therefore n the network current there are stll some harmonc currents. Nokan Capactors Ltd. P.O. Box 4 Tampere Fnland Tel: Fax:

4 EN-TH05-/004 Martt Tuomanen 4 (9) Connecton of Shunt Actve Flters n case of 3-phase 3-wre system current of the load s measured from two phases and the current of the thrd phase s derved from two others. Measured currents are used to control the output of the actve flter. n Fgure 6 there s the connecton of an actve flter n 3-phase 3-wre supply system. L L L 3 N PE CT L CT L Network currents PE L L L Actve flter Source of harmoncs Fgure 6. Connecton of the actve flter to 3-phase 3-wre supply system. n Fgure 7 there s the connecton of the actve flter to 3-phase 4-wre supply system. n ths case current s measured from each phase to allow also unsymmetrcal operaton of the actve flter. Ths verson of the actve flter can compensate zero sequence harmoncs too. L L L 3 N PE CT L CT L Network currents CT L 3 PE L L L N Actve flter Source of harmoncs Fgure 7. Connecton of the actve flter to 3-phase 4-wre supply system. Nokan Capactors Ltd. P.O. Box 4 Tampere Fnland Tel: Fax:

5 EN-TH05-/004 Martt Tuomanen 5 (9) Fgure 8 shows the block dagram of the actve flters wth ts man components. L L L 3 EMC flter Output reactor EMC GBT brdge Current Transducers GBT-Drvers nverter control Men machne nterface Source of harmoncs nverter + Fgure 8. Connecton of the actve flter to 3-phase 4-wre supply system. Experences wth shunt actve flter To demonstrate the operaton of shunt actve flter measurement was made at a DC-drve wthout and wth shunt actve flter Fgure 9. As can be seen the curve form of the supply current s almost fundamental current only when actve flter s on. t should also be noted that the fast changes of the supply current can be followed easly. Fgure 9. Network current of a DC-drve wthout actve flter (a) and wth shunt actve flter (b). Nokan Capactors Ltd. P.O. Box 4 Tampere Fnland Tel: Fax:

6 EN-TH05-/004 Martt Tuomanen 6 (9) Another example shows the hgh dynamcs of the shunt actve flter when compensatng fast changng harmonc producng loads. n Fgure 0 there s the current of a lft drve whle acceleratng wthout shunt actve flter wth the typcal 6-pulse rectfer current curve form. n Fgure there s the same current when actve flter s on. Comparson of the Fgures 0 and reveals that harmoncs are effectvely compensated and the system beng loaded wth fundamental current only. Fgure 0. Supply current of a lft drve whle acceleratng wthout actve flter. Fgure. Supply current of a lft drve whle acceleratng wth actve flter. Nokan Capactors Ltd. P.O. Box 4 Tampere Fnland Tel: Fax:

7 EN-TH05-/004 Martt Tuomanen 7 (9) Comparson of shunt actve and passve flters. When there s a need to compensate sgnfcant fundamental reactve power of relatvely stable harmonc producng loads the passve flters have turned out to be economcally justfed. Wth passve flters both reactve power compensaton and harmonc flterng can be made at the same tme. When there s a need to compensate fast changng harmonc currents and fundamental reactve power actve flters are the rght soluton. Very short response tme of the actve flters allows the better utlzaton of the supply system n respect of the voltage fluctuatons. The range of avalable shunt actve flters Current RMS : 3-phase 3-wre systems 400V, /60Hz 3-phase 4-wre systems 3x30V, /60Hz 5 A 3L/7 kva (40 A) 4L/7 kva (40 A) 30 A 3L/0 kva (45 A) 4L/0 kva (45 A) 35 A 3L/5 kva ( A) 4L/5 kva ( A) 40 A 3L/8 kva (60 A) 4L/8 kva (60 A) A 3L/35 kva (75 A) 4L/35 kva (75 A) 60 A 3L/4 kva (00 A) 4L/4 kva (00 A) 70 A 3L/ kva (0 A) 4L/ kva (0 A) 85 A 3L/60 kva (30 A) 4L/60 kva (30 A) 00 A 3L/70 kva ( A) 4L/70 kva ( A) 40 A 3L/00 kva (00 A) 4L/00 kva (00 A) 00 A 3L/40 kva (300 A) 4L/40 kva (300 A) 60 A 3L/80 kva (400 A) 4L/80 kva (400 A) Legend: 3L: for 3-phase 3-wre systems 4L: for 3-phase 4-wre systems wth zero sequence harmoncs and asymmetrcal loads n brackets: the peak value of the current to be compensated Please note that n case one actve flter s not bg enough t s possble to connect several actve flters parallel to reach requred rated current. The four wre actve flters are avalable n three dfferent varatons: Neutral current can be -tme, -tmes or 3-tmes lne current. Nokan Capactors Ltd. P.O. Box 4 Tampere Fnland Tel: Fax:

8 EN-TH05-/004 Martt Tuomanen 8 (9) Applcaton of shunt actve flters t should be noted that actve flters can be desgned to compensate both harmonc currents and fundamental reactve power. Addtonally to the system voltage U L the followng parameters of the current to be compensated have to be determned to be able to desgn the capacty of the shunt actve flter:. The root-mean-square of the current to be compensated RMS. The ampltude S d 3. The rate of rse of the current dt 4. The harmonc coeffcent k 5. For the 4-wre shunt actve flter: The geometrc sum of all harmoncs dvsble by 3. Rated output of the shunt actve flter for 3-wre and 4-wre applcaton for the compensaton of the harmonc currents: D 3 U L RMS k Rated output capacty of the shunt actve flter for sngle phase applcaton for the compensaton of the harmonc currents: D U RMS k Rated output of the shunt actve flter for 3-wre and 4-wre applcaton for the compensaton of the harmonc currents and reactve power: Q D + Q ( 3 U L RMS k ) + Q Rated output of the shunt actve flter for sngle phase applcaton for the compensaton of the harmonc currents and reactve power: Q D + Q ( U RMS k ) + Q Please note that the standard crest factor of the current of the shunt actve flter s. Nokan Capactors Ltd. P.O. Box 4 Tampere Fnland Tel: Fax:

9 EN-TH05-/004 Martt Tuomanen 9 (9) Defntons: Actve power P: P U cosϕ, where s fundamental current and ϕ s the angle between voltage and fundamental current Apparent power S : Fundamental apparent power S U Reactve power Q : Fundamental reactve power Q U snϕ Dsplacement factor cosϕ : cosϕ Total apparent power S: S U U P S 3 Total reactve power Q: Q Q S - P (U sn ϕ ) +U ( ) The reactve power conssts of fundamental reactve power Q and dstorton reactve power D. Dstorton reactve power D: D U U Σ oo h h> Content of the fundamental frequency g : g Harmonc coeffcent k : k k k g k + g P Power factor λ : λ g cosϕ S Current harmonc total dstorton THD : THD Σ n> n Nokan Capactors Ltd. P.O. Box 4 Tampere Fnland Tel: Fax: