CA2122129A1 - Active filter for reducing non-fundamental currents and voltages - Google Patents
Active filter for reducing non-fundamental currents and voltagesInfo
- Publication number
- CA2122129A1 CA2122129A1 CA002122129A CA2122129A CA2122129A1 CA 2122129 A1 CA2122129 A1 CA 2122129A1 CA 002122129 A CA002122129 A CA 002122129A CA 2122129 A CA2122129 A CA 2122129A CA 2122129 A1 CA2122129 A1 CA 2122129A1
- Authority
- CA
- Canada
- Prior art keywords
- current
- power line
- voltage
- power
- fundamental frequency
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Classifications
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/01—Arrangements for reducing harmonics or ripples
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
- Y02E40/40—Arrangements for reducing harmonics
Abstract
ABSTRACT OF THE DISCLOSURE
An AC power line is monitored for currents and voltages at non-fundamental frequencies (including harmonics). A
controlled active filter injects compensating current into the AC power line. The injected compensating current is responsive to both the sensed non-fundamental frequency current and to the sensed non-fundamental frequency voltage residing on the poewr line. In one embodiment, the controlled active filter comprises a transconductance amplifier which obtains its operating power from a controlled flow of power from the AC power line being monitored.
An AC power line is monitored for currents and voltages at non-fundamental frequencies (including harmonics). A
controlled active filter injects compensating current into the AC power line. The injected compensating current is responsive to both the sensed non-fundamental frequency current and to the sensed non-fundamental frequency voltage residing on the poewr line. In one embodiment, the controlled active filter comprises a transconductance amplifier which obtains its operating power from a controlled flow of power from the AC power line being monitored.
Description
-~o 94/05067 2 1 2 2 1 2 9 P~rtUS93/07985 '~
i . ^ .. , ACITVE ~ILTER FOR REDUClNG
NQN-~UNDAMENTAL CUR~15 AND VOLTAGES
. .
.,, lhis invendon relates gen~y to imp~ovcmcnts in power dis~ibu~on s~stems ant, m~ par~cularly, to clee~rical current inj~on for more effccd /ely r~duang non-fundam0tal cu~rents and voltages in a powe~ distribu~on sys~m.
Ihe wide usc of nonlillear loads, suc~ as ~ose presented by dcc~mic S power conv~rs for co~nputers and other decu~nic eq~ment, has incre~ed the ha~c content of ~e vol~e ~nd current wa~efomls in alt~na~ng c~ (AC) power di~ribudon s3~ems. ~e probl~n has become espciaDy acute in largc of ~e buildin~s wl~ ~e AUmbe~ of such de~ic og ~pment are oq~adng t~ causing a corre~onding incrcase in po~Ycr line ~momcs. In some of ~ése b~3dings, ~e cu~t disbordon levels may reach 80~
Such harmo~c cmrents h conjun~tion with ~cir assoctated source in~prDduced~donofthelincvolt~gcsand ~esedis-oned lineYoltages ca~ cause eq~dpm~nt to Alalfi~l~ The eloc~pletic fields a~sociatod with tbe basmonic c~ents can int~rfere with tel~hone and o~er communication sy~ems, and ~e h~nonic cum~ts can dso result in averheated conduc~rs in conduits and panel bax~s ~nd in ove~ud Ls~ibution t~ansform~s. Under ~ loa&g, neu~al conduc~rs ~ three phasc pow dis~ibu~on ~gstems, : which normally carry inslgdficant CU~lt3 for linear loads. are now car~ying currents up to approximately 73X g~ r than the ac~ual line cu~ents.
Pnor systems for cont~olling or limidng the hannonic currents and the distor~on Yohages they p~duce havc included; (1) plac~ng limits on the arnount of harmonic cu~ent tha~ loads are ~ed to draw by ~etter load design; (2) .
~O 94/0s~67 2 1 2 2 1 2 9 Pcr/US93/079B5 - - using passive filters; (3) adding power line conditioners which effcc~cly isolate Ioads ~rotn the power sys~em; (4) runn~ng the genera~ing or dis~ibution system b~low~d capacity lo reduco lbe sou~ impedance and also reduce ~osses; (S) Ising zl~-zag and phase-shifdng tJansr~ormers: and (63 using aaive ~l~g S techniques.
s The technohgy exist~ f~r substan~ally reduc~ng the harmonic cunents drawn by most offentin~ loads through bcttet load design. Howcve~ e requisite additional power components ant contro1 circuhy atd to manuf~c~ring costs. and the costs of retro-fitdng ~ng oquipm~t, such as the la~e inmlled 10 base of personal compu~s, can be prohibidve. Therefore, this ap~oach is not -~ likdy to bc implcmcnt~d in thc near future.
In~ c ant shunt passi~e filters can be designed and inscallod to remove I~monics tbat occur at ~ic f~quencics. Passiv~ fil~e~ usc capacitoq~ and inductors to shunt unwanted hannonic currents. 'rnc usc of ~eact;vc compo~s IS can p¢ovidc cffec~vs filtcdng if p~pe ly designed and~nt~ into the po~
~m. Howevcr. passhre fltcrs gcn~all~ ap~te in a ~row f~quency band ant ba~ omc severe disadvan1ages wl~`i~h ohen outweigh ~c sdvant~ges. Sucll disad~t~ges inclùdc catastrophic fi~ilure of f~ta componems ~vhen une~d harmonic cu~nts are ~, dc~da~on of filt x pcrformancc wh~n load 20 ot powor souroe cha~ d~ange, and deg~adadon of the dectri~
di~ibudon system due to harmordc reson~noes created ~y the passive filter i~self.
Power line oondi~onen which ~lize A~-~DC and DC~AC tandem power conve~sion s~ages iso1ate load l~nonlc cunents *om the input AC li~e.
To be effec~ve in reducing Iw3ide harmonics, howev~, the input AC~ DC
25 comc~sion circuit must use low ~ic con~ ion t~chnology. Because tbls ype of power condi~ feeds all ~e load power ~rough ~vo power conve~on stagcs, ~e power loss is substandal on a rdad~ basls. The power line condidone~ is a Ye~ expensi~e so1u~on if the sole funcdon is tho reducdon of hannonic cu~cnts.
~ WO 94/05067 2 1 2 2 1 2 9 P~r/US93/07985 Running the system below rated capacity is also an undesi~able app~ach.
The system then would not be used tO the full extent of i~ abilities, thus lost `. ca~ity reSults witb thc associa~d loss of e~ficiency and increasc in cos~
zag connec~ons on the socondasy windirl~s of sh~ee-phase distribLtion 5 ~ansformcrs havc been used in an a~empl to rcduce thc flow of ~ird hannon~
(and othcr ~iplc) cutrents through thc ~ansform ineo d~e "u~s~casn~ pnmaly ~ts. This method of controlling harmonic cur~ents does not rcmoYe no~-tdpae l~rA~ and is less cff~cdve when the third hannonic cu~rents are not balancod 3 between the phascs. Exccssive powe~ loss in the soconda~ windings duc to 10 hannoniccurr~nts ~acon~deration. AddiQonally, zig-zagphase-shif~
transfonne~s cannot be usct for singl~pbasc c~ts.
A p~.shif~ng ~ansfiorma which ouq)uts two th~ phase volta~c scts ha~ing ~ s of p~ Shif~ bc~n than can p~ovide c~on of Sf~h and sG~nth harmor~c a-rrents ~ the ups~cam pow a~cuit. Best result~ occur 1~ when loads ha~ g ~imilar fif~ and scvcnth hannonic cu~eats can be eguallsr di~ded bdw~en tb~ ~wo th~ee phase ou~uts. ~he addidon of pl~shi~ng ~o~s u~ ~B pow t~ ins~atioas C?~ be an ~e ha~c cu~ent ~olu~on. In adti~on lo the co~ of ins~lling thc t~ansform~s, load circuits must be dividod and connec~ uough se~ate di~t~ibll~on circuits, . 20 ~fl ~sfonoer~ also c~nnot be u~od for sul~e phase cirwits.
Ihe use of acthre cusrent i~jecdon ~or thc oompeAsa~on of lurmon~c a~ts ~as pmposod ln thc arlg 1970'8. In the hannonic ausent ~oc~on filt, an inJo~don power sou~e i~ connested ac~oss the AC power liAC at a point ~t ~ the power s~rce and the load and provides a con~rolled output 25 curJent. C~ent to thc load is set~ and analyz d, and the harmonic componantS arc input to thc injection power source. Il~ ection pow souroe p~duces thc appropriate input-dgnal-tooutput~ent ~atio to supply the ha~ ~ic cu~ents trawn by tho load, and the~cfore thc harmonic cuurent~ drawn ~y ~e load from the AC power sourc~ arc ideally reduced to zero.
~o 94/05067 Pcl/US93/0798s . ~
The conventional current injecion filter pr~duc~s an undesi-able response, howev, in the Glse where distortion in the AC volta~c source is par~i?~ly res~s~1e~for the existence of dis~orted cu~ents tO the load. Due to the habili~
of pnor cuIrent injec~on filters to de~mine ~he sourcc of thc distortcd load 5 cu~q~s, such traditional cum!nt injection filters ~11 supply the load wi~ ~c ssune harmonic cu~ents that ~e voltage source was supplying ~ereby ~mlo~ing~
the distDned AC voltagc source for the harmonic vol~ages. ll~e distorted voltagesource may now produce increasct harmonic volugcs. Similarly, t~ansient dlsmrbances dlat a~e no~mally tamped by the laad can becomc undarnpct by ~bc 10 ~c~on of thc uadi~ional cu~ent injecuon filter if it is made ~ wnsive to ~ient . currents.
Hence, those concemed unth tcducing she non-fundamental wn~ent in power distnbudon systems ha~c r~ri~d a neot for a more effective ~lter sy~em; one ~hlch can ~educe cu~rent di~orion causod by ~e load without idng voltage tis~ion produc~d by thc voltage sourcc. ~ddit`ionally, thr~
a~an~dfor~ding ~uch aflltersy~m withoutuntuee~andwithout dls~bing d~ in~ed ba5e of a~i~dng load equipmcnt. T~e present f~fills ~ neods.
Bridly ant h ~netal te ms, dle present invcndon employs cu~t cu~en~ fl~g ~o thc load and thc other controi signal is propordonal to Ihe line vollagc. Ea~h contrcl signal is fll~red to ren~e she fiJ_tal f~equcnC3~; e-8-2S 60 Hz, ~ is a~pL;ed to tll~e cunent gen~adng mea~s. In one embotimcnt, thocon1rol s~gnals are conlbinod and a single ~wit~ng-modc ~ansoondu~nce an~lificr r#iponsive to ~e control signal comUna~on is usct as ~e cu~t gene~adng means.
The cumn~ gencratillg means is controlled by the con~aol signals to irUoct 30 into the power lln~ a cu~ent component prapordonal to the ha~monic and ot~
:~ `
~0 ~4/05~67 PCr/US93/0~985 -s- :
- non-fundamental frcq~ency currents flowing toward the load and a cu~rent com~onent propor~onal t~ the non-fundamcntal frequtc~ line Yoltages but oppo~ite~in phase. Because thc second componcnt of the inje~cd current is propor~onal t~ ~he non-iundamental ~equency linc voltages on lhc power line but ~ ;
S is out of phase witll them, the cu~ent generadng ~ acts as a ~sis~ve load ~ thesc vollages and powcr will flow into thc cunent 8en~a~ng means at these non-fundamen~ equency voltag~s thcr~by loading thcm and reducing thar amplitudes.
ln one ~nent. thc powa flowing into the c~em generadng mcans -! lo as a result of the loadin~ of ~e non-fundamcntal frequen~y voltages coun~a~s c int~nal losses of the o~nt gale~ng means and, if the power fhwing in excoods ~ose losscs, the excess powcr is conYcrted to power at the filndamental fr~qua7c~ and supplied baclc ~ the AC power line.
Other aspec~ and advaD~ges of ~e invention will becomc ~ppa~ent fir~m thcfollowing ddailcd dcscs~on, and ~caooornpanyi~g draw~gs, mt~g by way of a~npk the fca~s of the mven~on.
BRI~: ~SCR.~ON OF 7~11~k~
FIG. I is a bloclc diag~am of an acive f~ter in acoordance wi~ Ihe p~ ples of the inven~ion;
PIG. 2 is an ova~l blaclc dia~n illustrating one embodlnxnt of ~e p~ent inventdon;
FIG. 3 iS a nwrc de~ilet ~chemadc diag~n illustrating ~e ci~cUit of ~a.
2;
FIG. 4 is a ~chemadc dis~am illust~ting one embodimcnt of a ::
25 t~nductance amplirler using a voltage-modc, switching-mode amplifier and intcn~al cun~nt feedbaclt control and PI~S. 5A tbrough SC p~scnt examploe of cu~rent wavofonns.
~ED DES~ON
Ref~ing now tO tbe d-awings with more par~icularit~r, wherein lilce ~ ~
30 refer~ce numelals are used to indicate li10e or co~esponting elemcnts among the ~ :
, ' '"" `' , ~ vo 94/0s067 2 1 2 2 1 2 9 PCr/US93/0798s seve a~ YieWS, in FIG. 1, an AC power source 10 provides voltage V5 through in~nal impedance Z~ ~o AC power line 12. The voltage Vs has a fundamcntal - f~u~ component o and may includc non-fundamental frequency componeDts suclr as harmonics of the fun~arnen~al frcquency or t~nsient voltages. Ihe '. 5 voltage V1 on the AC power line 1~ is applicd to load 14 which may produce nonlinear loading reprcsented by non-fiJndamcntal *~u~ncy load uurent sourcc ~, IN- ThC ;mPOdanCC ZL of thc laat is shown in paralld with the load cu~e~t SOU~Ce IN- l~pically, POWer SOUrCe 10 alSO hCdS Other IOadS 15 Wh;Ch ~Y alSo 'j produce nonlin~ar h6ding r~p~sented by non-fimdamental *~quency load cusrcnt source IN' and impedance ZL'-,. In ~he embodiment of ~G. 1, an acuYe ~lter 16 has ~vo conne~ions with dlc AC power linc 12. The fi~ connoction comprises a point 19 where ~c wltage Vl sf thc AC pow~ linc 12 is s0~d and wh~e thc mjecdon curren~ I1 ~s provitod to thc AC pow line 12. The ~ocond connestion ¢omprises a a~
~ ~anstucer 20 which is conn~ed to the ~C power line 12 be~wee~ the load 14 and the point of connec~on 19 for the injec~on currcnt.
Refcrring now ts E~l¢. 2, thc cu~ent ~ng t~ansducu 20 p~ovides a voltage V~ which is pr~ o~l to thc load cu~ent IL on the AC line 12 dr~wn by ~c 1aad 14. A first vol~ge sa~ng arcuut 22 ps~id~s a volt~ge V3 whlcl~
i~ p~oporti~ to thc vol~e Vl on the AC pcwer l~nc 12 serlsed at a point 19 but with a phase inve~ion. ln ~ embodiment, the ac~e filter 16 complisa a bi~di~ficnal trans~ntuc~nce amplifia 18 and thc first vol~ge ~g ci~dt 22 connects to the oulput of the transconduc~nce amplificr 18. Voltages V2 a~
~3 arc combincd in a j~ ion 24 so that thc output voltagc V4 oquals a linear combilladon of voltages Y2 and V3. Voltage V4 is filte~et by a notch filter 26 to r~novc thc fund~mcntal f~uon~y coJs ponent ~O. ~e ou~ut voltage VS of ~he nott h fil~er 26 i~ combincd vnth an input powe~ cont~ol signal V10 (descdbed bdow) in a junc~on 28 to providc an output voltage V6 which is a l~r comb~ation of volta~es VS and V10. Thc tlansconductance amplifier 18 30 p~tuces an output ~njection cunent I1 whiCh is propor~onal to this analo~ input 94~5067 2 1 2 2 1 2 9 Pcr/US93/07985 vol~age signal V6. As us~d herein, a transconductance ampli~cr is an amplifier whic~ produces a cu~ent ou~ur in responsc to a ~ input. ~n this ~nibodi*lent, the ~nsconduc~nce amplifier 18 is bi~donal; i.e., power efficien~y flows in either direc~on between its output and its en~gy stolage bus.
In the ~t shown in FICi. 2, the voltage ~f2 is a current sensc con~o1 signal and thc vol~gc ~f3 is a vo1tage se~sc contro1 si~al. These control sig~
are filtered by no~ fil~ 26 ~o remove the fi~ menlal f~quenc~ oomponcnt fO ~d src spplied lo a cUSl~lt SOU~CC 18 tO con~l that cll~lt SOI~Ce tO illjeCt a cumcnt into thc AC power L~ne. Although in FIG. 2, the control sig~als V2 and V3 havc been oombined, ~is has bcen donc in this cmbodimcnt to incn~ase effi~. Only onc notch filter a~d one cu~eAt source arc neodod. Ir~ er ~dimeJ~ hc oon~ol signals mar be sepasately ~'il~d ant may be ~ded to sepa3a~ cu~ent souroes. Ea:h curr~t souroo wo~ inject ~ cun~ to th¢ AC pow~ linc ~ponsive to its respe~vc control sig~ owcv tbc lS embodiment of FIG. 2 uscs ody a sin~c filt~ and a singlc cu~nt source thus low~n~ the number of parts ~n tl sctive ~ t~is embo~nent, thc transco~uc~nce a~aifier 18 does not tequirc ~
Ir~nt pow sollrcc ot se~c connec~on to the AC powe~ line 12.
~4bead, it draws sny nooted power from the AC power linc 12 through ~ts ou~ut 2t) pott U i8 dibod in morc de~l bolow.
~ seoond volta~e sensing clradt 30 provides a re~res~ta~e volt;~ge Y7 whi~ is ~b~o p~por~oùal to thc ~aJ~ge ~ c AC power line 12.
R~scn~vc ~ age V~ isap~ied to the inputpo~ Q~ of a gain con~ 32, ~vhich in this cmbotimcnt is an el~onlc gain con~ller implenunted by an 25 a~og multipli~. A sen~ng ampliffer 34 conne~s to th~ DC bus 36 of the t~Dsconduc5~ancc 5~nplifi 18 to ps~fide a s~roltage V8 which is ~or~ond to tho DC parame~ at rela~es to the DC ene~r sborago d~vice in the t~conduc~ am~lifier 18. When the tr~nsconduct~ncc 5~nplifier 18 u~lizc~
a ~tage-snotc switchin~ ~Implifi fior cxatnple, thc voltage V8 is made 30 p~l to the DC voltage on the an~lificr's DC voltage bus capa~tor. On - .. ~, .,. . .... ,., . :,.. ~. . .. . .... .
vo s4/0so~7 2 1 2 2 1 2 9 PCr/uS93~07s#s the other hand, when the ~nsconduclance amplifier 18 u~lizes a current-mode swit:hing amplifier, thc voltagc V8 is m~de propor~onal lo d~e DC C~Ent in the ain'plifie~'s DC current bus inductor.
The voltage V8 is compa~d to a refc~enoe voltage V"~ at a comparing S ~fier 38 to produce a I)C eIror vd~c W. 'rhe enor voltage V9 is a~plied to thc controll ~nput (Y) of the gain controller 32 eo control the ~ol~ge at ~eoutput po~t ~ of thc gau~ controllcr 32. The output (Z) of ~he ga~n contro31er 32 is flltetod by a band pass fllter 39 to rcmovc non-fundamaltal *~queocy co~onents and dlc filtacd ~igaal, designatçd as ~oltage V10, is ~pliod to ~e junction 28 to control the t~ansconductance amplifi 18. The voltage V~" is se~ected so d~at suffia~t power is dsawn *~m dl¢ AC pow~ linc 12 bo n~air~i~
thc desi~ C bus ~roltagc or cu~t to run ~e l~an~onductancc ~nplifier 18.
Ttlc output current 11 ôf thc tQ~nsoonduclance a~ er 18 is ~refo~e a :
combina~on of thrcc cu~t components. Ihc first cumilt component of Il a a~ ordonal to the non-~ntd *equa~r ameAt5 inc~
load cur~nt IL flow~g tow~d the laad 14. lhc salsit~r ~ ~e rent t~ansdu~r 2~ and the vollage-t~ent gain of thc tra~sconduc~oc ampl~i 18 are chos~ to malce t~is curr~t component oqual to thc non-f~mdan~t~
*oquenc~ cutrcnt~ of IL flOWjng tOWard the ~ 4.
Z4 Tl~ sooond cu~rcnt component of Ii is a a~ent propa~donal to the non-1imdament~1 froqucnc3~ volt~Bc on d~e AC power llne 12 but a~ositc in ph~se.
Ibc ~vity of the fi~st ~ age ~g cu~ uit 22 i~chosen to provide a des~ot rstio oî cu rent to voltagc, so that the output of ~e ~soonduaance ~ier 18 funaions as a r~sdve load on non-fimdam~l ~reque~ vollage oo~nts on thc AC power Une 12. Power ~ flow into tbe t~sn~ool~duc~nce ampl~fier 18 for those volt~ge compon~ and will be ava~abb ~ support a~ 1~ a par~ion of thc internal losscs of the ~ontuctance ~mplifier 18. ~ :
~Ihc third CU~lt component of Il is a cur~ent proportional 10 ~e fundarnental *equcncy compone~t of ~e voltage Vl on the AC: pow~ line 12.
30 Th~ rcfe~ence voltage V"~ ed to thc compua~r amplifler 38 is chosen ~o ~at ' 94/95~67 PCr/USs3/07985 g a flow of power from the AC power line I tD the ~ansconducunce amplifier 18 is pr~duced to maintain the DC energy storage of the nansconductance ampllfier i8 ar~le a~te 1evel, thus compen~dng for powcr losscs within ~hat de~nce 18: ~his flow of power is typically only a fc~ per~nt of the appara~t power al 5 x Yl) produccd by Ihe ~ansoondu~ce amplifier 1~.
FIG. 3 is a more ddailet ~chana~c diagtam of one cmbodiment of ~c invcntion. The cu~sent sensing t~nsducer 20 uses ;~ cu~Tcnt ~ansfonner Crl and a ~urdcn resis~r 1~1 to providc ~he wlta~e V2 which is pK~r~nal to the loQd cu~rens ~L. 'Ibc first voltage sa~ ~cuit 22 co~ ul ~aior~ amplifi~
io ~0 wi~ gain ~tors R2 ant R3 connectot to provide a phase inveTsion and the d~red ampL~de of ~oltagc sen~ng signa~l Y3. The sumnnng j~nction 24 com~ an opelational al.nplificr42 and rcsistors R4, R~, and ~6 to piovide ~e ou~ut signal V4 equal to -~2-V3 (V4~ V33. Ille notch fllter 26 compris¢s, ~ d~is anbodimcnt, a ~n~r ~ filt~r comprising ~:sist~s 1~ through R9 and 15 cspo~ C1 ~ough C3 fooding a buffer an~liffer 4~ to prodlloe output wltage VS, `Ihe notch filter 26 i~ mad~ s}~ in Ws emSodiment by the use of posl~
feedbacl~ through res~stor divider RlO ~nd R~ l, ant ~c buffcr amplifio~ 46 to ~e T elanent of dlc twin T circuit.
The second wltage sonsulg ~i~ 30 con~rises divida rcsistors R14 ant 20 RlS to provide a voltage v7 to ~e ~x" input of thc analog muldplier 32. Thc ~ g citcuit34 compdses an ope~ational ~ 48 and ~ :~rs R16 ~ugb Rl9 to producc ~e vol~gc V8. Thc diffeaencc bctween the Yol~
V8 and the ~oncc ~ol~go V,~f ~ dd~mined by zene~ diode VRl b~asod by R2~ is ampll~ed by dle ap~onal amp1ifier 49 in conjuncdon ~4 th gain resistoss 23 R20, R21, and R23 and f~equalcy ~nsc ca~tor C4 to result in ctror ~olt~ge V9. The output at ~e ~Z~ t of ~ analog muldplier 32 is the~efore voltslge V7 adjusted in amplitude or polarit~r by aror voltage V9 applicd at the ~Y~ input of the a~alog m~tipL;er 32. Tbe output ~roluge at the "Z~ port of the analog muldpli~ 3~ ltered by a band pass filter 39 compnsing a ~esistor R24 ~nd 30 c:~acitors C5 and C: 6 to produce control signal V10, which is thus prapordonal ,:
~ " wo 94/05067 2 1 2 2 1 2 9 P~/USg3/07985 -10- .
to the fundamental frequcncy component of dle v~ltage Vl on ~he AC power line 1~. .
~ ltc summing junction 28 fceding dle trans:onductance arnplifier 18 recel~es thc vol~agc V10 from the band pass filte~ 3g, ap~lies it tnrough resistor 5 R25 to ~e ncgative input tenninal of an opeIatio~al amplifie~ ~1. Also provited to dle negativc input termind of ~c op~a~o~al ampl~fier51 is ~he ou~tputvoltage VS from ~he notch filt~r 26. Voltage V~ is appliod ~rough ~sistor R12. Comrol sign~l ~6 to the ~ansconductance amplifi~s 18 is thueforc ¢ql~al to -~S^V~O
(V6=-YS-V10).
FIG. 4 is a schemadc diag~sm show~g one~ble circuit implementation for ~c ~ansconductancc amplifier 18. The ~an~nd~cc amplifier 18 of E:IG.
i . ^ .. , ACITVE ~ILTER FOR REDUClNG
NQN-~UNDAMENTAL CUR~15 AND VOLTAGES
. .
.,, lhis invendon relates gen~y to imp~ovcmcnts in power dis~ibu~on s~stems ant, m~ par~cularly, to clee~rical current inj~on for more effccd /ely r~duang non-fundam0tal cu~rents and voltages in a powe~ distribu~on sys~m.
Ihe wide usc of nonlillear loads, suc~ as ~ose presented by dcc~mic S power conv~rs for co~nputers and other decu~nic eq~ment, has incre~ed the ha~c content of ~e vol~e ~nd current wa~efomls in alt~na~ng c~ (AC) power di~ribudon s3~ems. ~e probl~n has become espciaDy acute in largc of ~e buildin~s wl~ ~e AUmbe~ of such de~ic og ~pment are oq~adng t~ causing a corre~onding incrcase in po~Ycr line ~momcs. In some of ~ése b~3dings, ~e cu~t disbordon levels may reach 80~
Such harmo~c cmrents h conjun~tion with ~cir assoctated source in~prDduced~donofthelincvolt~gcsand ~esedis-oned lineYoltages ca~ cause eq~dpm~nt to Alalfi~l~ The eloc~pletic fields a~sociatod with tbe basmonic c~ents can int~rfere with tel~hone and o~er communication sy~ems, and ~e h~nonic cum~ts can dso result in averheated conduc~rs in conduits and panel bax~s ~nd in ove~ud Ls~ibution t~ansform~s. Under ~ loa&g, neu~al conduc~rs ~ three phasc pow dis~ibu~on ~gstems, : which normally carry inslgdficant CU~lt3 for linear loads. are now car~ying currents up to approximately 73X g~ r than the ac~ual line cu~ents.
Pnor systems for cont~olling or limidng the hannonic currents and the distor~on Yohages they p~duce havc included; (1) plac~ng limits on the arnount of harmonic cu~ent tha~ loads are ~ed to draw by ~etter load design; (2) .
~O 94/0s~67 2 1 2 2 1 2 9 Pcr/US93/079B5 - - using passive filters; (3) adding power line conditioners which effcc~cly isolate Ioads ~rotn the power sys~em; (4) runn~ng the genera~ing or dis~ibution system b~low~d capacity lo reduco lbe sou~ impedance and also reduce ~osses; (S) Ising zl~-zag and phase-shifdng tJansr~ormers: and (63 using aaive ~l~g S techniques.
s The technohgy exist~ f~r substan~ally reduc~ng the harmonic cunents drawn by most offentin~ loads through bcttet load design. Howcve~ e requisite additional power components ant contro1 circuhy atd to manuf~c~ring costs. and the costs of retro-fitdng ~ng oquipm~t, such as the la~e inmlled 10 base of personal compu~s, can be prohibidve. Therefore, this ap~oach is not -~ likdy to bc implcmcnt~d in thc near future.
In~ c ant shunt passi~e filters can be designed and inscallod to remove I~monics tbat occur at ~ic f~quencics. Passiv~ fil~e~ usc capacitoq~ and inductors to shunt unwanted hannonic currents. 'rnc usc of ~eact;vc compo~s IS can p¢ovidc cffec~vs filtcdng if p~pe ly designed and~nt~ into the po~
~m. Howevcr. passhre fltcrs gcn~all~ ap~te in a ~row f~quency band ant ba~ omc severe disadvan1ages wl~`i~h ohen outweigh ~c sdvant~ges. Sucll disad~t~ges inclùdc catastrophic fi~ilure of f~ta componems ~vhen une~d harmonic cu~nts are ~, dc~da~on of filt x pcrformancc wh~n load 20 ot powor souroe cha~ d~ange, and deg~adadon of the dectri~
di~ibudon system due to harmordc reson~noes created ~y the passive filter i~self.
Power line oondi~onen which ~lize A~-~DC and DC~AC tandem power conve~sion s~ages iso1ate load l~nonlc cunents *om the input AC li~e.
To be effec~ve in reducing Iw3ide harmonics, howev~, the input AC~ DC
25 comc~sion circuit must use low ~ic con~ ion t~chnology. Because tbls ype of power condi~ feeds all ~e load power ~rough ~vo power conve~on stagcs, ~e power loss is substandal on a rdad~ basls. The power line condidone~ is a Ye~ expensi~e so1u~on if the sole funcdon is tho reducdon of hannonic cu~cnts.
~ WO 94/05067 2 1 2 2 1 2 9 P~r/US93/07985 Running the system below rated capacity is also an undesi~able app~ach.
The system then would not be used tO the full extent of i~ abilities, thus lost `. ca~ity reSults witb thc associa~d loss of e~ficiency and increasc in cos~
zag connec~ons on the socondasy windirl~s of sh~ee-phase distribLtion 5 ~ansformcrs havc been used in an a~empl to rcduce thc flow of ~ird hannon~
(and othcr ~iplc) cutrents through thc ~ansform ineo d~e "u~s~casn~ pnmaly ~ts. This method of controlling harmonic cur~ents does not rcmoYe no~-tdpae l~rA~ and is less cff~cdve when the third hannonic cu~rents are not balancod 3 between the phascs. Exccssive powe~ loss in the soconda~ windings duc to 10 hannoniccurr~nts ~acon~deration. AddiQonally, zig-zagphase-shif~
transfonne~s cannot be usct for singl~pbasc c~ts.
A p~.shif~ng ~ansfiorma which ouq)uts two th~ phase volta~c scts ha~ing ~ s of p~ Shif~ bc~n than can p~ovide c~on of Sf~h and sG~nth harmor~c a-rrents ~ the ups~cam pow a~cuit. Best result~ occur 1~ when loads ha~ g ~imilar fif~ and scvcnth hannonic cu~eats can be eguallsr di~ded bdw~en tb~ ~wo th~ee phase ou~uts. ~he addidon of pl~shi~ng ~o~s u~ ~B pow t~ ins~atioas C?~ be an ~e ha~c cu~ent ~olu~on. In adti~on lo the co~ of ins~lling thc t~ansform~s, load circuits must be dividod and connec~ uough se~ate di~t~ibll~on circuits, . 20 ~fl ~sfonoer~ also c~nnot be u~od for sul~e phase cirwits.
Ihe use of acthre cusrent i~jecdon ~or thc oompeAsa~on of lurmon~c a~ts ~as pmposod ln thc arlg 1970'8. In the hannonic ausent ~oc~on filt, an inJo~don power sou~e i~ connested ac~oss the AC power liAC at a point ~t ~ the power s~rce and the load and provides a con~rolled output 25 curJent. C~ent to thc load is set~ and analyz d, and the harmonic componantS arc input to thc injection power source. Il~ ection pow souroe p~duces thc appropriate input-dgnal-tooutput~ent ~atio to supply the ha~ ~ic cu~ents trawn by tho load, and the~cfore thc harmonic cuurent~ drawn ~y ~e load from the AC power sourc~ arc ideally reduced to zero.
~o 94/05067 Pcl/US93/0798s . ~
The conventional current injecion filter pr~duc~s an undesi-able response, howev, in the Glse where distortion in the AC volta~c source is par~i?~ly res~s~1e~for the existence of dis~orted cu~ents tO the load. Due to the habili~
of pnor cuIrent injec~on filters to de~mine ~he sourcc of thc distortcd load 5 cu~q~s, such traditional cum!nt injection filters ~11 supply the load wi~ ~c ssune harmonic cu~ents that ~e voltage source was supplying ~ereby ~mlo~ing~
the distDned AC voltagc source for the harmonic vol~ages. ll~e distorted voltagesource may now produce increasct harmonic volugcs. Similarly, t~ansient dlsmrbances dlat a~e no~mally tamped by the laad can becomc undarnpct by ~bc 10 ~c~on of thc uadi~ional cu~ent injecuon filter if it is made ~ wnsive to ~ient . currents.
Hence, those concemed unth tcducing she non-fundamental wn~ent in power distnbudon systems ha~c r~ri~d a neot for a more effective ~lter sy~em; one ~hlch can ~educe cu~rent di~orion causod by ~e load without idng voltage tis~ion produc~d by thc voltage sourcc. ~ddit`ionally, thr~
a~an~dfor~ding ~uch aflltersy~m withoutuntuee~andwithout dls~bing d~ in~ed ba5e of a~i~dng load equipmcnt. T~e present f~fills ~ neods.
Bridly ant h ~netal te ms, dle present invcndon employs cu~t cu~en~ fl~g ~o thc load and thc other controi signal is propordonal to Ihe line vollagc. Ea~h contrcl signal is fll~red to ren~e she fiJ_tal f~equcnC3~; e-8-2S 60 Hz, ~ is a~pL;ed to tll~e cunent gen~adng mea~s. In one embotimcnt, thocon1rol s~gnals are conlbinod and a single ~wit~ng-modc ~ansoondu~nce an~lificr r#iponsive to ~e control signal comUna~on is usct as ~e cu~t gene~adng means.
The cumn~ gencratillg means is controlled by the con~aol signals to irUoct 30 into the power lln~ a cu~ent component prapordonal to the ha~monic and ot~
:~ `
~0 ~4/05~67 PCr/US93/0~985 -s- :
- non-fundamental frcq~ency currents flowing toward the load and a cu~rent com~onent propor~onal t~ the non-fundamcntal frequtc~ line Yoltages but oppo~ite~in phase. Because thc second componcnt of the inje~cd current is propor~onal t~ ~he non-iundamental ~equency linc voltages on lhc power line but ~ ;
S is out of phase witll them, the cu~ent generadng ~ acts as a ~sis~ve load ~ thesc vollages and powcr will flow into thc cunent 8en~a~ng means at these non-fundamen~ equency voltag~s thcr~by loading thcm and reducing thar amplitudes.
ln one ~nent. thc powa flowing into the c~em generadng mcans -! lo as a result of the loadin~ of ~e non-fundamcntal frequen~y voltages coun~a~s c int~nal losses of the o~nt gale~ng means and, if the power fhwing in excoods ~ose losscs, the excess powcr is conYcrted to power at the filndamental fr~qua7c~ and supplied baclc ~ the AC power line.
Other aspec~ and advaD~ges of ~e invention will becomc ~ppa~ent fir~m thcfollowing ddailcd dcscs~on, and ~caooornpanyi~g draw~gs, mt~g by way of a~npk the fca~s of the mven~on.
BRI~: ~SCR.~ON OF 7~11~k~
FIG. I is a bloclc diag~am of an acive f~ter in acoordance wi~ Ihe p~ ples of the inven~ion;
PIG. 2 is an ova~l blaclc dia~n illustrating one embodlnxnt of ~e p~ent inventdon;
FIG. 3 iS a nwrc de~ilet ~chemadc diag~n illustrating ~e ci~cUit of ~a.
2;
FIG. 4 is a ~chemadc dis~am illust~ting one embodimcnt of a ::
25 t~nductance amplirler using a voltage-modc, switching-mode amplifier and intcn~al cun~nt feedbaclt control and PI~S. 5A tbrough SC p~scnt examploe of cu~rent wavofonns.
~ED DES~ON
Ref~ing now tO tbe d-awings with more par~icularit~r, wherein lilce ~ ~
30 refer~ce numelals are used to indicate li10e or co~esponting elemcnts among the ~ :
, ' '"" `' , ~ vo 94/0s067 2 1 2 2 1 2 9 PCr/US93/0798s seve a~ YieWS, in FIG. 1, an AC power source 10 provides voltage V5 through in~nal impedance Z~ ~o AC power line 12. The voltage Vs has a fundamcntal - f~u~ component o and may includc non-fundamental frequency componeDts suclr as harmonics of the fun~arnen~al frcquency or t~nsient voltages. Ihe '. 5 voltage V1 on the AC power line 1~ is applicd to load 14 which may produce nonlinear loading reprcsented by non-fiJndamcntal *~u~ncy load uurent sourcc ~, IN- ThC ;mPOdanCC ZL of thc laat is shown in paralld with the load cu~e~t SOU~Ce IN- l~pically, POWer SOUrCe 10 alSO hCdS Other IOadS 15 Wh;Ch ~Y alSo 'j produce nonlin~ar h6ding r~p~sented by non-fimdamental *~quency load cusrcnt source IN' and impedance ZL'-,. In ~he embodiment of ~G. 1, an acuYe ~lter 16 has ~vo conne~ions with dlc AC power linc 12. The fi~ connoction comprises a point 19 where ~c wltage Vl sf thc AC pow~ linc 12 is s0~d and wh~e thc mjecdon curren~ I1 ~s provitod to thc AC pow line 12. The ~ocond connestion ¢omprises a a~
~ ~anstucer 20 which is conn~ed to the ~C power line 12 be~wee~ the load 14 and the point of connec~on 19 for the injec~on currcnt.
Refcrring now ts E~l¢. 2, thc cu~ent ~ng t~ansducu 20 p~ovides a voltage V~ which is pr~ o~l to thc load cu~ent IL on the AC line 12 dr~wn by ~c 1aad 14. A first vol~ge sa~ng arcuut 22 ps~id~s a volt~ge V3 whlcl~
i~ p~oporti~ to thc vol~e Vl on the AC pcwer l~nc 12 serlsed at a point 19 but with a phase inve~ion. ln ~ embodiment, the ac~e filter 16 complisa a bi~di~ficnal trans~ntuc~nce amplifia 18 and thc first vol~ge ~g ci~dt 22 connects to the oulput of the transconduc~nce amplificr 18. Voltages V2 a~
~3 arc combincd in a j~ ion 24 so that thc output voltagc V4 oquals a linear combilladon of voltages Y2 and V3. Voltage V4 is filte~et by a notch filter 26 to r~novc thc fund~mcntal f~uon~y coJs ponent ~O. ~e ou~ut voltage VS of ~he nott h fil~er 26 i~ combincd vnth an input powe~ cont~ol signal V10 (descdbed bdow) in a junc~on 28 to providc an output voltage V6 which is a l~r comb~ation of volta~es VS and V10. Thc tlansconductance amplifier 18 30 p~tuces an output ~njection cunent I1 whiCh is propor~onal to this analo~ input 94~5067 2 1 2 2 1 2 9 Pcr/US93/07985 vol~age signal V6. As us~d herein, a transconductance ampli~cr is an amplifier whic~ produces a cu~ent ou~ur in responsc to a ~ input. ~n this ~nibodi*lent, the ~nsconduc~nce amplifier 18 is bi~donal; i.e., power efficien~y flows in either direc~on between its output and its en~gy stolage bus.
In the ~t shown in FICi. 2, the voltage ~f2 is a current sensc con~o1 signal and thc vol~gc ~f3 is a vo1tage se~sc contro1 si~al. These control sig~
are filtered by no~ fil~ 26 ~o remove the fi~ menlal f~quenc~ oomponcnt fO ~d src spplied lo a cUSl~lt SOU~CC 18 tO con~l that cll~lt SOI~Ce tO illjeCt a cumcnt into thc AC power L~ne. Although in FIG. 2, the control sig~als V2 and V3 havc been oombined, ~is has bcen donc in this cmbodimcnt to incn~ase effi~. Only onc notch filter a~d one cu~eAt source arc neodod. Ir~ er ~dimeJ~ hc oon~ol signals mar be sepasately ~'il~d ant may be ~ded to sepa3a~ cu~ent souroes. Ea:h curr~t souroo wo~ inject ~ cun~ to th¢ AC pow~ linc ~ponsive to its respe~vc control sig~ owcv tbc lS embodiment of FIG. 2 uscs ody a sin~c filt~ and a singlc cu~nt source thus low~n~ the number of parts ~n tl sctive ~ t~is embo~nent, thc transco~uc~nce a~aifier 18 does not tequirc ~
Ir~nt pow sollrcc ot se~c connec~on to the AC powe~ line 12.
~4bead, it draws sny nooted power from the AC power linc 12 through ~ts ou~ut 2t) pott U i8 dibod in morc de~l bolow.
~ seoond volta~e sensing clradt 30 provides a re~res~ta~e volt;~ge Y7 whi~ is ~b~o p~por~oùal to thc ~aJ~ge ~ c AC power line 12.
R~scn~vc ~ age V~ isap~ied to the inputpo~ Q~ of a gain con~ 32, ~vhich in this cmbotimcnt is an el~onlc gain con~ller implenunted by an 25 a~og multipli~. A sen~ng ampliffer 34 conne~s to th~ DC bus 36 of the t~Dsconduc5~ancc 5~nplifi 18 to ps~fide a s~roltage V8 which is ~or~ond to tho DC parame~ at rela~es to the DC ene~r sborago d~vice in the t~conduc~ am~lifier 18. When the tr~nsconduct~ncc 5~nplifier 18 u~lizc~
a ~tage-snotc switchin~ ~Implifi fior cxatnple, thc voltage V8 is made 30 p~l to the DC voltage on the an~lificr's DC voltage bus capa~tor. On - .. ~, .,. . .... ,., . :,.. ~. . .. . .... .
vo s4/0so~7 2 1 2 2 1 2 9 PCr/uS93~07s#s the other hand, when the ~nsconduclance amplifier 18 u~lizes a current-mode swit:hing amplifier, thc voltagc V8 is m~de propor~onal lo d~e DC C~Ent in the ain'plifie~'s DC current bus inductor.
The voltage V8 is compa~d to a refc~enoe voltage V"~ at a comparing S ~fier 38 to produce a I)C eIror vd~c W. 'rhe enor voltage V9 is a~plied to thc controll ~nput (Y) of the gain controller 32 eo control the ~ol~ge at ~eoutput po~t ~ of thc gau~ controllcr 32. The output (Z) of ~he ga~n contro31er 32 is flltetod by a band pass fllter 39 to rcmovc non-fundamaltal *~queocy co~onents and dlc filtacd ~igaal, designatçd as ~oltage V10, is ~pliod to ~e junction 28 to control the t~ansconductance amplifi 18. The voltage V~" is se~ected so d~at suffia~t power is dsawn *~m dl¢ AC pow~ linc 12 bo n~air~i~
thc desi~ C bus ~roltagc or cu~t to run ~e l~an~onductancc ~nplifier 18.
Ttlc output current 11 ôf thc tQ~nsoonduclance a~ er 18 is ~refo~e a :
combina~on of thrcc cu~t components. Ihc first cumilt component of Il a a~ ordonal to the non-~ntd *equa~r ameAt5 inc~
load cur~nt IL flow~g tow~d the laad 14. lhc salsit~r ~ ~e rent t~ansdu~r 2~ and the vollage-t~ent gain of thc tra~sconduc~oc ampl~i 18 are chos~ to malce t~is curr~t component oqual to thc non-f~mdan~t~
*oquenc~ cutrcnt~ of IL flOWjng tOWard the ~ 4.
Z4 Tl~ sooond cu~rcnt component of Ii is a a~ent propa~donal to the non-1imdament~1 froqucnc3~ volt~Bc on d~e AC power llne 12 but a~ositc in ph~se.
Ibc ~vity of the fi~st ~ age ~g cu~ uit 22 i~chosen to provide a des~ot rstio oî cu rent to voltagc, so that the output of ~e ~soonduaance ~ier 18 funaions as a r~sdve load on non-fimdam~l ~reque~ vollage oo~nts on thc AC power Une 12. Power ~ flow into tbe t~sn~ool~duc~nce ampl~fier 18 for those volt~ge compon~ and will be ava~abb ~ support a~ 1~ a par~ion of thc internal losscs of the ~ontuctance ~mplifier 18. ~ :
~Ihc third CU~lt component of Il is a cur~ent proportional 10 ~e fundarnental *equcncy compone~t of ~e voltage Vl on the AC: pow~ line 12.
30 Th~ rcfe~ence voltage V"~ ed to thc compua~r amplifler 38 is chosen ~o ~at ' 94/95~67 PCr/USs3/07985 g a flow of power from the AC power line I tD the ~ansconducunce amplifier 18 is pr~duced to maintain the DC energy storage of the nansconductance ampllfier i8 ar~le a~te 1evel, thus compen~dng for powcr losscs within ~hat de~nce 18: ~his flow of power is typically only a fc~ per~nt of the appara~t power al 5 x Yl) produccd by Ihe ~ansoondu~ce amplifier 1~.
FIG. 3 is a more ddailet ~chana~c diagtam of one cmbodiment of ~c invcntion. The cu~sent sensing t~nsducer 20 uses ;~ cu~Tcnt ~ansfonner Crl and a ~urdcn resis~r 1~1 to providc ~he wlta~e V2 which is pK~r~nal to the loQd cu~rens ~L. 'Ibc first voltage sa~ ~cuit 22 co~ ul ~aior~ amplifi~
io ~0 wi~ gain ~tors R2 ant R3 connectot to provide a phase inveTsion and the d~red ampL~de of ~oltagc sen~ng signa~l Y3. The sumnnng j~nction 24 com~ an opelational al.nplificr42 and rcsistors R4, R~, and ~6 to piovide ~e ou~ut signal V4 equal to -~2-V3 (V4~ V33. Ille notch fllter 26 compris¢s, ~ d~is anbodimcnt, a ~n~r ~ filt~r comprising ~:sist~s 1~ through R9 and 15 cspo~ C1 ~ough C3 fooding a buffer an~liffer 4~ to prodlloe output wltage VS, `Ihe notch filter 26 i~ mad~ s}~ in Ws emSodiment by the use of posl~
feedbacl~ through res~stor divider RlO ~nd R~ l, ant ~c buffcr amplifio~ 46 to ~e T elanent of dlc twin T circuit.
The second wltage sonsulg ~i~ 30 con~rises divida rcsistors R14 ant 20 RlS to provide a voltage v7 to ~e ~x" input of thc analog muldplier 32. Thc ~ g citcuit34 compdses an ope~ational ~ 48 and ~ :~rs R16 ~ugb Rl9 to producc ~e vol~gc V8. Thc diffeaencc bctween the Yol~
V8 and the ~oncc ~ol~go V,~f ~ dd~mined by zene~ diode VRl b~asod by R2~ is ampll~ed by dle ap~onal amp1ifier 49 in conjuncdon ~4 th gain resistoss 23 R20, R21, and R23 and f~equalcy ~nsc ca~tor C4 to result in ctror ~olt~ge V9. The output at ~e ~Z~ t of ~ analog muldplier 32 is the~efore voltslge V7 adjusted in amplitude or polarit~r by aror voltage V9 applicd at the ~Y~ input of the a~alog m~tipL;er 32. Tbe output ~roluge at the "Z~ port of the analog muldpli~ 3~ ltered by a band pass filter 39 compnsing a ~esistor R24 ~nd 30 c:~acitors C5 and C: 6 to produce control signal V10, which is thus prapordonal ,:
~ " wo 94/05067 2 1 2 2 1 2 9 P~/USg3/07985 -10- .
to the fundamental frequcncy component of dle v~ltage Vl on ~he AC power line 1~. .
~ ltc summing junction 28 fceding dle trans:onductance arnplifier 18 recel~es thc vol~agc V10 from the band pass filte~ 3g, ap~lies it tnrough resistor 5 R25 to ~e ncgative input tenninal of an opeIatio~al amplifie~ ~1. Also provited to dle negativc input termind of ~c op~a~o~al ampl~fier51 is ~he ou~tputvoltage VS from ~he notch filt~r 26. Voltage V~ is appliod ~rough ~sistor R12. Comrol sign~l ~6 to the ~ansconductance amplifi~s 18 is thueforc ¢ql~al to -~S^V~O
(V6=-YS-V10).
FIG. 4 is a schemadc diag~sm show~g one~ble circuit implementation for ~c ~ansconductancc amplifier 18. The ~an~nd~cc amplifier 18 of E:IG.
4 Is a bi-dircctional dc~ice betw~n its AC output and DC bus ports. A vol~
~ode, switching^mode amplifi~ SO is used in conjunc~ with a suies ~nduc~r I3 to p~duc~ ~c desircd ou~put ament. Ol~tpUt cu~ent control is p~ b3f 15 a a~ent feedback control loap compsising pdma~ly a cutrent sensor 52 a~d a feod~ck control ampL;ifier 54. T~c switding-modc ~ie~ SO, also callet a class D an~lifi~ (volta~c modc), i~ based on ~c circuit des~dbod in U.S. Paleat No, 4,020,361 to ~ucklc c~ al. inco~po~d ha~ by refaes~c~
The ~witching-modc an~pl~er 50 com~scs xm~oonductor powe~ sw~hcs 20 Ql ~rough Q4 with L;~ Dl tbrou~h D4 und d~ive ci~i~ PRl t~h DR4 ananged ~n ~ R~ e ~on. Ihc DC ~oltage bu~ 36, at ~o~tage V12, is ~uppor~d for AC cu~ts by a41acitot C7. llle tl~ieo~ swhchcd voltagc waveform V13 ~om the H~idge i9 filt~t by induc~s Ll ant L~! ~nd by c~or C8 tv removc thc sqh~g &oquenc~, e.g. S0 kHz. *om ~e Yol~gc 25 V14 ac~s the capa~bor C8. The con~ol logic circu~y S6 reGe~es analog input oontrol voltage Yl-5 ~nd gene~ates thc ~prhtc swluh~ng control s~gnals, su~
e tcs~bed h U.S. ~tent No. 4,020,361, so that Y14 is proportional to V15, the ~nput con~ gnal to ampUfler ~0.
Whcn ~C power line voltage Vl is iru~ally a~lied~ the DC bus 36 30 capacitor C7 is char~ rough thc ~soft-start~ ~istor R~6, ~c inducD~ss L1 ' .
~ g4/05067 PCr/US93/07985 ~rough L3, and the diodes Dl ~hrough D4. As the ~ac~tor C7 charges, the AC
~,rol~age Vll will ~e. When the voltagc V11 rea~hcs a~mately 80% of the A~pow* linc vol~gc Vl, a contactor K1 will be eng~ed there~y short-circi~i~ng the soft-s~ res~stor R26.
The voltage aaross th~ inductor ~3, V14 - V~ ces out~ut cu~nt Il. Cu~ent sensor 52, a Hall current sensor for nple, ~des voltage V16 which is propordonal to cur~cnt I1 but o~te in phase. Voltage ~16 is compa~d to vo1ta~c V6, thc input~ontrol ~gnal ~o thc t~ans~nduc~ance unplificr 18, at amplifia S4 to ~dc output c~t feedback c~ion signal VlS.
Output cu~t Il ls tl~y made propor~onal to thc ~alog conlrol signal Y6, red transcooduclance amplifier 18 cha~acseristic. The r~ors R~7 and R28 and ~e capacito~s C9 and C10 a-e selected to pr~nde a s~able a~ra~on of lhe current contro1 feod~ck 100p.
~n the casc ~vherc ~c ~o1tage on the AC pow linc ~ncludes non-t~l frequalcg components, the co~t~o1 sign~ V6 will causc the t~ucta~cc amp1ifier 18 to appe r ~esistive to the sou~ce 10 at ~e non h~odamaltal frequen~r components and cumnt at ~ese non~fi~ndamental *eqoascics will tlow ioto the transconduc~ncc amplifier. The pow~r draw~ at d~ese *equenci~s will charge thc DC b~ capacitor C7 as controlled by ~
~0 the pow fl~8 irlto the amplificr 18 at ~ese non-fundamental froq~encles is ~t in itself to ~p~ate the acd~e ~Ites 16 and Xeep C7 char~ed so the vd~gc sct Sy V"", thal control si~nsl V10 ~ill notca~sc any ~r to be dta~n firo~ d)e AC pow~ l~ne l2 at ~e fimdamental f~equenc3r fO. If ~e power flowing into ~e amplifia 18 at the non-fitndamental ~equalcies exceeds tho ~
2S ~quircd to sup~on the int4~ losses of ~e ac~w filtcr, the t~anscoJ~ductan~c ampllfier will, in rcsponsc to control signal V10, cause suffi~ent ~t a~d consoqu~t powe~ to flow to the AC po~lver line 12 at thc fi~ndamental f~oquency to maintain the ~olta~c alXOS5 C7 at the valuc set by V"r. This cumnt will then be availablc for use by other lo~ds 15 conncctcd to the AC power sourcc IQ
~ ' A
~ ~o 94/05067 PCrJUS93/0798s FIG. 5 depicts alrrent wave~orms measuFed on a prototypc emb~d~g the pnnciples of ~he invennon. Thc ve~ical and honzon~al scalcs are twcnty ampaes p~ ~ion and hVO milliscconds pcr di~on, r~tely. FIG. SA shows thc lasd curswt IL trawn by a nonli~ar ant linear load combin~on. The no~li~ear S poni.on, exemplifiet by the highly~ ced cur~:nt component, i~ ~pical of t~c cun~t dlawn by clo~onic 4uipmcnt such as pesso~al comps. FIG. SB
sbows the cu~rcnt Il i~e~ by t~c ~e filtet in ~dance w~ e h~
FIG. SC shows the cu~ Is provided by the AC power sourcc ~hich results from t~e bcnc~ effccts of an activc filter cmbodying d~e p~inciples of thc 10 invention. 1hc harrnonic cuncnt conlponems of ~e load cu~sent I~ ase subslanially sbsent from th~ so~cc cqtr~nl 15. The harmordcs in thc ~
voltage wavefonn ca~sed by ~hose harmo~ic load cu~alts a~e consoquently 'The u:8~re filter as desded abovc and shown in ~c fg~es co~s to 15 a si~-phase AC power line a~d uscs load~t sensor 20. ~:or poly-phasc acduc filte~s can be emp3~yed. Por a ~phase, four-wirc s~stem ~ee ac8vc filtets can bc anployed. Each would coMect betweal one of thc ~hot~ lines, u~llyda A,~ ~B,"or~Candthen~ aductor. Theloadalm:nt 20 scl~sor 20 would connect to ~ espcnding A, 8 or C load cir~uit. Far a ~wire, ~phase powcr s~ o ~ve filte~ can b¢ empl~. ~ this c~se, one of the thrcc coodctQrs, "C~ for exa~b, would b¢ used for the co~nmon c~necdon of both dcvices. Ihe ~hot~ connec~ons and load c~ment mo~itcring would be ma~e to conduc~rs A and B, respa:~vdy. lt should bc 2S ~otet t~at bocause Ihe~su~ of 1he duec ~e curre~ts is ze~o ~n shc 3-wi~e sysoem, the ~moval of wn-fimdamuual f~equcn~ a~t componalts from the A-ph~sc and B~hase powe~ sourcc c~ts rcsults ~ ~e removal of such compalents f~om ~c C-phasc powcr sour~c current.
Refcmng again to FIG. 2, dle op~adon of thc ac~ve filter ~ill be .30 dcscribed. l~e cuITcn~ sor 20 will providc to ~e 3uncdon 24 a voltage . . ~ , .
I
represenuuve of thc sensed current wavefonn of the cunent ~ drawn by the load1~. The first voltage sensin~ eircuit 22 will sense the voltage on the AC power ~ e 12 and will provide a voltage sepresentative of tha~ sensed voltage to ~e colmbined~at the junction 24 with the voltage representative of the cur~cnt 1 S sensed. Tbe combination of thc two volta~es is then filtered by a notch filter 26 to rçmove the fundamenul frequcslcy, e.g. 60 Hz. The resultD~g sign~l V5 is comb~ncd wid~ ~flO and is fcd to the ~sconduc~ncc amplificr 18. Tbc result of combining the filtered Yoltage sensc signal V3 and the filte~d current sense sig~l V2 is that the t~wonduc~nce amplifier 18 supplies to the AC po~ver line 10 12 the non-fi~ndamcntal components o~ load culTent ~. less thc non-fundamcntal frcquency currcnt ~at would flow into a predeteImined rcsis~ve load a~ the result of the non-funda~nental frcquency components of the volta~e on thc AC pow linc This predetennined resisdve load valuc could, for exarnple, be selocted to app~ma~: thc nominal "full loat" ~sist;~cc of the laat citcuit.
lS ~s an c~nplc. if ~ure we~e no distord~n in the AC power linc voltage, thc ~anscondu~;c amplifies 18 would pro~ide all of the n~n-fu~damenEII
froquenc3~ current d~aw.n by thc load and no non-fundamenlal frequency a~t would bc dlawn ~n d~c AC power source 10.
As a second e~le, if thc load 14 were an o~al arcuit (no load) and ahc 20 linc vohagc Vl containcd non-fundamèntal frequency vol~age components, non-fu~ cy aurent prapordonal to non-fundamental frequcncy co~onen~ of voltage~e sitnal V3 wol~ld flow in o the ~sconductance amplifi 18 from the AC poY~er li~e 12. In othe~ wotds, for non-fi~ndamen~l h~quenc~ voltage components of AC power linc voltagc V1, ~e a~ve filte~
25 &mcdons as a dis~ ng ~tor of pretctenr~ned value connected to AC power li~e 12. The non-fundamen~l f~quc~ power flowing into thc acti re filter is a~ailabl¢ to support some ponion of ~e ac~e filkr's inte~s~al losses. If ~c flowof non-fundamens~ quency power into the active filter were to exceed the intanal losscs, ~c e~ccss power would bc ruum~d to the AC power soura: 10 30 ~n ~c form of power at ~c fundarncntal frcqucncy.
.
E ~
~ W o 94/05067 2 1 2 2 1 2 9 P(~r/US93/07985 As a ~rd exam ple~ if the ~ne vol~ge Vl con~ned no~-fundamens~
vol~ge componen~ and the load were rc~sd~e and oqua~ to the predet~nninod resisd~cl ~ value ofLheacdve f~ter,dhenon-fIndiunen~fi~uquency oomponcn~
of voltagc sense signal V3 and the non-fundbunen~ frequency componen~ of S a~lent sGnse ~gn~ V2 urould canccl one another, and, Yqth the ~ on of a snna~ annount of currcnt drawn by the acdve fi~ter in nesponsc to corltnol s~
V10 to compcnsate for intemal losscs, no curtent would flow benvecn ~e AC
pow~ linc 12 and d~e aaive filter.
Although spo~fic cmbodimalts,of d~e inv~ have boen doscribcd and 1~ illu~ it is clear that the 1nven~on is susceptible so numerous modifica~ions and embodimalts u~i~in the abili~ of those sl~ n ~e art, and without the exe~se of the inventive facult~r. Ihus, it shou~d bc unde~stood ~at ~
changes in fonn, ddail and applicadon of d~o present imendon may bc madc vn~out dc~ng from the ~pirit a~d SCOpC of the ~nvcn~
:
: ~
~ode, switching^mode amplifi~ SO is used in conjunc~ with a suies ~nduc~r I3 to p~duc~ ~c desircd ou~put ament. Ol~tpUt cu~ent control is p~ b3f 15 a a~ent feedback control loap compsising pdma~ly a cutrent sensor 52 a~d a feod~ck control ampL;ifier 54. T~c switding-modc ~ie~ SO, also callet a class D an~lifi~ (volta~c modc), i~ based on ~c circuit des~dbod in U.S. Paleat No, 4,020,361 to ~ucklc c~ al. inco~po~d ha~ by refaes~c~
The ~witching-modc an~pl~er 50 com~scs xm~oonductor powe~ sw~hcs 20 Ql ~rough Q4 with L;~ Dl tbrou~h D4 und d~ive ci~i~ PRl t~h DR4 ananged ~n ~ R~ e ~on. Ihc DC ~oltage bu~ 36, at ~o~tage V12, is ~uppor~d for AC cu~ts by a41acitot C7. llle tl~ieo~ swhchcd voltagc waveform V13 ~om the H~idge i9 filt~t by induc~s Ll ant L~! ~nd by c~or C8 tv removc thc sqh~g &oquenc~, e.g. S0 kHz. *om ~e Yol~gc 25 V14 ac~s the capa~bor C8. The con~ol logic circu~y S6 reGe~es analog input oontrol voltage Yl-5 ~nd gene~ates thc ~prhtc swluh~ng control s~gnals, su~
e tcs~bed h U.S. ~tent No. 4,020,361, so that Y14 is proportional to V15, the ~nput con~ gnal to ampUfler ~0.
Whcn ~C power line voltage Vl is iru~ally a~lied~ the DC bus 36 30 capacitor C7 is char~ rough thc ~soft-start~ ~istor R~6, ~c inducD~ss L1 ' .
~ g4/05067 PCr/US93/07985 ~rough L3, and the diodes Dl ~hrough D4. As the ~ac~tor C7 charges, the AC
~,rol~age Vll will ~e. When the voltagc V11 rea~hcs a~mately 80% of the A~pow* linc vol~gc Vl, a contactor K1 will be eng~ed there~y short-circi~i~ng the soft-s~ res~stor R26.
The voltage aaross th~ inductor ~3, V14 - V~ ces out~ut cu~nt Il. Cu~ent sensor 52, a Hall current sensor for nple, ~des voltage V16 which is propordonal to cur~cnt I1 but o~te in phase. Voltage ~16 is compa~d to vo1ta~c V6, thc input~ontrol ~gnal ~o thc t~ans~nduc~ance unplificr 18, at amplifia S4 to ~dc output c~t feedback c~ion signal VlS.
Output cu~t Il ls tl~y made propor~onal to thc ~alog conlrol signal Y6, red transcooduclance amplifier 18 cha~acseristic. The r~ors R~7 and R28 and ~e capacito~s C9 and C10 a-e selected to pr~nde a s~able a~ra~on of lhe current contro1 feod~ck 100p.
~n the casc ~vherc ~c ~o1tage on the AC pow linc ~ncludes non-t~l frequalcg components, the co~t~o1 sign~ V6 will causc the t~ucta~cc amp1ifier 18 to appe r ~esistive to the sou~ce 10 at ~e non h~odamaltal frequen~r components and cumnt at ~ese non~fi~ndamental *eqoascics will tlow ioto the transconduc~ncc amplifier. The pow~r draw~ at d~ese *equenci~s will charge thc DC b~ capacitor C7 as controlled by ~
~0 the pow fl~8 irlto the amplificr 18 at ~ese non-fundamental froq~encles is ~t in itself to ~p~ate the acd~e ~Ites 16 and Xeep C7 char~ed so the vd~gc sct Sy V"", thal control si~nsl V10 ~ill notca~sc any ~r to be dta~n firo~ d)e AC pow~ l~ne l2 at ~e fimdamental f~equenc3r fO. If ~e power flowing into ~e amplifia 18 at the non-fitndamental ~equalcies exceeds tho ~
2S ~quircd to sup~on the int4~ losses of ~e ac~w filtcr, the t~anscoJ~ductan~c ampllfier will, in rcsponsc to control signal V10, cause suffi~ent ~t a~d consoqu~t powe~ to flow to the AC po~lver line 12 at thc fi~ndamental f~oquency to maintain the ~olta~c alXOS5 C7 at the valuc set by V"r. This cumnt will then be availablc for use by other lo~ds 15 conncctcd to the AC power sourcc IQ
~ ' A
~ ~o 94/05067 PCrJUS93/0798s FIG. 5 depicts alrrent wave~orms measuFed on a prototypc emb~d~g the pnnciples of ~he invennon. Thc ve~ical and honzon~al scalcs are twcnty ampaes p~ ~ion and hVO milliscconds pcr di~on, r~tely. FIG. SA shows thc lasd curswt IL trawn by a nonli~ar ant linear load combin~on. The no~li~ear S poni.on, exemplifiet by the highly~ ced cur~:nt component, i~ ~pical of t~c cun~t dlawn by clo~onic 4uipmcnt such as pesso~al comps. FIG. SB
sbows the cu~rcnt Il i~e~ by t~c ~e filtet in ~dance w~ e h~
FIG. SC shows the cu~ Is provided by the AC power sourcc ~hich results from t~e bcnc~ effccts of an activc filter cmbodying d~e p~inciples of thc 10 invention. 1hc harrnonic cuncnt conlponems of ~e load cu~sent I~ ase subslanially sbsent from th~ so~cc cqtr~nl 15. The harmordcs in thc ~
voltage wavefonn ca~sed by ~hose harmo~ic load cu~alts a~e consoquently 'The u:8~re filter as desded abovc and shown in ~c fg~es co~s to 15 a si~-phase AC power line a~d uscs load~t sensor 20. ~:or poly-phasc acduc filte~s can be emp3~yed. Por a ~phase, four-wirc s~stem ~ee ac8vc filtets can bc anployed. Each would coMect betweal one of thc ~hot~ lines, u~llyda A,~ ~B,"or~Candthen~ aductor. Theloadalm:nt 20 scl~sor 20 would connect to ~ espcnding A, 8 or C load cir~uit. Far a ~wire, ~phase powcr s~ o ~ve filte~ can b¢ empl~. ~ this c~se, one of the thrcc coodctQrs, "C~ for exa~b, would b¢ used for the co~nmon c~necdon of both dcvices. Ihe ~hot~ connec~ons and load c~ment mo~itcring would be ma~e to conduc~rs A and B, respa:~vdy. lt should bc 2S ~otet t~at bocause Ihe~su~ of 1he duec ~e curre~ts is ze~o ~n shc 3-wi~e sysoem, the ~moval of wn-fimdamuual f~equcn~ a~t componalts from the A-ph~sc and B~hase powe~ sourcc c~ts rcsults ~ ~e removal of such compalents f~om ~c C-phasc powcr sour~c current.
Refcmng again to FIG. 2, dle op~adon of thc ac~ve filter ~ill be .30 dcscribed. l~e cuITcn~ sor 20 will providc to ~e 3uncdon 24 a voltage . . ~ , .
I
represenuuve of thc sensed current wavefonn of the cunent ~ drawn by the load1~. The first voltage sensin~ eircuit 22 will sense the voltage on the AC power ~ e 12 and will provide a voltage sepresentative of tha~ sensed voltage to ~e colmbined~at the junction 24 with the voltage representative of the cur~cnt 1 S sensed. Tbe combination of thc two volta~es is then filtered by a notch filter 26 to rçmove the fundamenul frequcslcy, e.g. 60 Hz. The resultD~g sign~l V5 is comb~ncd wid~ ~flO and is fcd to the ~sconduc~ncc amplificr 18. Tbc result of combining the filtered Yoltage sensc signal V3 and the filte~d current sense sig~l V2 is that the t~wonduc~nce amplifier 18 supplies to the AC po~ver line 10 12 the non-fi~ndamcntal components o~ load culTent ~. less thc non-fundamcntal frcquency currcnt ~at would flow into a predeteImined rcsis~ve load a~ the result of the non-funda~nental frcquency components of the volta~e on thc AC pow linc This predetennined resisdve load valuc could, for exarnple, be selocted to app~ma~: thc nominal "full loat" ~sist;~cc of the laat citcuit.
lS ~s an c~nplc. if ~ure we~e no distord~n in the AC power linc voltage, thc ~anscondu~;c amplifies 18 would pro~ide all of the n~n-fu~damenEII
froquenc3~ current d~aw.n by thc load and no non-fundamenlal frequency a~t would bc dlawn ~n d~c AC power source 10.
As a second e~le, if thc load 14 were an o~al arcuit (no load) and ahc 20 linc vohagc Vl containcd non-fundamèntal frequency vol~age components, non-fu~ cy aurent prapordonal to non-fundamental frequcncy co~onen~ of voltage~e sitnal V3 wol~ld flow in o the ~sconductance amplifi 18 from the AC poY~er li~e 12. In othe~ wotds, for non-fi~ndamen~l h~quenc~ voltage components of AC power linc voltagc V1, ~e a~ve filte~
25 &mcdons as a dis~ ng ~tor of pretctenr~ned value connected to AC power li~e 12. The non-fundamen~l f~quc~ power flowing into thc acti re filter is a~ailabl¢ to support some ponion of ~e ac~e filkr's inte~s~al losses. If ~c flowof non-fundamens~ quency power into the active filter were to exceed the intanal losscs, ~c e~ccss power would bc ruum~d to the AC power soura: 10 30 ~n ~c form of power at ~c fundarncntal frcqucncy.
.
E ~
~ W o 94/05067 2 1 2 2 1 2 9 P(~r/US93/07985 As a ~rd exam ple~ if the ~ne vol~ge Vl con~ned no~-fundamens~
vol~ge componen~ and the load were rc~sd~e and oqua~ to the predet~nninod resisd~cl ~ value ofLheacdve f~ter,dhenon-fIndiunen~fi~uquency oomponcn~
of voltagc sense signal V3 and the non-fundbunen~ frequency componen~ of S a~lent sGnse ~gn~ V2 urould canccl one another, and, Yqth the ~ on of a snna~ annount of currcnt drawn by the acdve fi~ter in nesponsc to corltnol s~
V10 to compcnsate for intemal losscs, no curtent would flow benvecn ~e AC
pow~ linc 12 and d~e aaive filter.
Although spo~fic cmbodimalts,of d~e inv~ have boen doscribcd and 1~ illu~ it is clear that the 1nven~on is susceptible so numerous modifica~ions and embodimalts u~i~in the abili~ of those sl~ n ~e art, and without the exe~se of the inventive facult~r. Ihus, it shou~d bc unde~stood ~at ~
changes in fonn, ddail and applicadon of d~o present imendon may bc madc vn~out dc~ng from the ~pirit a~d SCOpC of the ~nvcn~
:
: ~
Claims (26)
We Claim:
1. An active filter connected to a power line between a power source providing power at a fundamental frequency and a load, the active filter comprising:
current sensing means connected to the power line for sensing the current flowing to the load and providing a current sense signal representative of the sensed current;
voltage sensing means connected to the power line for sensing the voltage on the power line and for providing a voltage sense signal representative of thesensed voltage;
filtering means for filtering the fundamental frequency out of the current sense signal and for filtering the fundamental frequency out of the voltage sense signal; and current generating means for providing a first current to the line in response to the filtered current sense signals and a second current to the power line in response to the filtered voltage sense signal.
current sensing means connected to the power line for sensing the current flowing to the load and providing a current sense signal representative of the sensed current;
voltage sensing means connected to the power line for sensing the voltage on the power line and for providing a voltage sense signal representative of thesensed voltage;
filtering means for filtering the fundamental frequency out of the current sense signal and for filtering the fundamental frequency out of the voltage sense signal; and current generating means for providing a first current to the line in response to the filtered current sense signals and a second current to the power line in response to the filtered voltage sense signal.
2. The active filter of claim 1 wherein the first current is substantially in phase with non-fundamental frequency current components on the power line sensed by the current sensing means.
3. The active filter of claim 1 wherein the second current is out of phase with non-fundamental frequency voltage components on the power line sensed by the voltage sensing means.
4. The active filter of claim 3 further comprising power supply means for receiving the second current and providing power to operate the current generating means from said second current.
5. The active filter of claim 1 wherein:
the first current is in phase with non-fundamental frequency current components on the power line sensed by the current sensing means; and the second current is of opposite phase to non-fundamental frequency voltage component on the power line sensed by the voltage sensing means.
the first current is in phase with non-fundamental frequency current components on the power line sensed by the current sensing means; and the second current is of opposite phase to non-fundamental frequency voltage component on the power line sensed by the voltage sensing means.
6. The active filter of claim 1 wherein the current generating means provided the first and second currents to the power line farther from the load than the point on the power line at which the current sensor means senses the power line current.
7. The active filter of claim 1 wherein the current generating means provides the first and second currents to the power line at the same point at which the voltage sensing means senses the voltage on the power line.
8. The active filter of claim 1 further comprising a combiner coupled to the current sensing means and the voltage sensing means to receive the current sense signal and the voltage sense signal, the combiner provides a control signal which is a combination of the current sense signal and the voltage sense signal;wherein the filtering means comprises a filter coupled to the combiner which filters the fundamental frequency from the control signal; and wherein the current generating means is responsive to the filtered control signal to provide the first and second currents.
9. The active filter of claim 1 further comprises power supply means connected to the power line for receiving power from the power line to operate the current generating means including providing power to the current generatingmeans from which the current generating means generates the first and second currents.
10. The active filter of claim 9 wherein the current generating means is also supplying a third current to the power line when the power supplied to the current generating means by the power supply means exceeds the power required by the current generating means for its operation, the third current being at the fundamental frequency.
11. An active filter connected to a power line between a power source providing power at a fundamental frequency and a load, the active filter comprising:
a current sensor connected to the power line which provides a current sense signal proportional to the current on the power line;
a voltage sensor connected to the power line which provides a voltage sense signal proportional to the voltage on the power line;
a fundamental frequency filter which receives the current sense signal and the voltage sense signal, filters the fundamental frequency from the signal and provides a filtered current sense signal and a filtered voltage sense signal; and a current generator connected to the power line at a location closer to the power source than the current sensor and connected to the fundamental frequency filter and which provides a first current to the power line in response to the filtered current sense signal and a second current to the power line in response to the filtered voltage sense signal, the first and second currents being provided at the point at which the voltage sensor sense the voltage on the power line.
a current sensor connected to the power line which provides a current sense signal proportional to the current on the power line;
a voltage sensor connected to the power line which provides a voltage sense signal proportional to the voltage on the power line;
a fundamental frequency filter which receives the current sense signal and the voltage sense signal, filters the fundamental frequency from the signal and provides a filtered current sense signal and a filtered voltage sense signal; and a current generator connected to the power line at a location closer to the power source than the current sensor and connected to the fundamental frequency filter and which provides a first current to the power line in response to the filtered current sense signal and a second current to the power line in response to the filtered voltage sense signal, the first and second currents being provided at the point at which the voltage sensor sense the voltage on the power line.
12. The active filter of claim 11 further comprising a combiner connected to the current sensor and the voltage sensor and which combines the current sense signal with the voltage sense signal and provides a control signal representative of the combination;
wherein the filter receives the control signal and filters the fundamental frequency out of the control signal; and wherein the current generator receives the filtered control signal and provides the first and second currents to the power line in response thereto.
wherein the filter receives the control signal and filters the fundamental frequency out of the control signal; and wherein the current generator receives the filtered control signal and provides the first and second currents to the power line in response thereto.
13. The active filter of claim 11 wherein the first current is equal to and is substantially in phase with non-fundamental frequency current components flowing to the load on the power line.
14. The active filter of claim 13 wherein the second current comprises a current proportional to and out of phase with non-fundamental frequency voltage components on the power line sensed by the voltage sensor.
15. The active filter of claim 14 further comprising a power supply which receives the second current and provides power to operate the current generator from the second current.
16. The active filter of claim 11 further comprising a power supply circuit connected to the power line which receives power from the power line to operate the current generator including providing power to the current generating means from which the current generating means generates the first and second currents.
17. The active filter of claim 16 wherein the current generator also supplies a third current to the power line when the power supplied to the current generator by the power supply circuit exceeds the power required by the current generator for its operation, the third current being at the fundamental frequency.
18. A method of providing current to a power line connected between a power source providing power having a fundamental frequency and a load, comprising the steps of:
sensing the current on the power line flowing to the load and providing a current sense signal representative of the sensed current;
sensing the voltage on the power line and providing a voltage sense signal representative of the sensed voltage;
filtering the fundamental frequency from the current sense signal and from the voltage sense signal; and injecting a first current into the power line in response to the filtered current sense signal and injecting a second current into the power line in response to the filtered voltage sense signal.
sensing the current on the power line flowing to the load and providing a current sense signal representative of the sensed current;
sensing the voltage on the power line and providing a voltage sense signal representative of the sensed voltage;
filtering the fundamental frequency from the current sense signal and from the voltage sense signal; and injecting a first current into the power line in response to the filtered current sense signal and injecting a second current into the power line in response to the filtered voltage sense signal.
19. The method of claim 18 wherein the step of injecting a first current comprises injecting a first current which is substantially in phase with non-fundamental frequency current components on the power line.
20. The method of claim 18 wherein the step of injecting a second current comprises injecting a second current which is out of phase with non-fundamental frequency voltage components on the power line.
21. The method of claim 20 further comprising the step of generating the first current from the second current.
22. The method of claim 18 wherein the step of injecting the first and second currents to the power line comprises the step of injecting the first and second currents to the power line at a point located farther from the load than the point on the power line at which the current is sensed.
23. The method of claim 18 wherein the step of injecting the first and second currents to the power line comprises the step of injecting said currents at the same point at which the voltage on the power line is sensed.
24. The method of claim 18 further comprising the step of combining the current sense signal and the voltage sense signal prior to the step of filtering and providing a control signal from said combination;
wherein the step of filtering comprises the step of filtering the fundamental frequency from the control signal; and wherein the step of injecting first and second currents comprises the step of injecting first and second currents in response to the filtered control signal.
wherein the step of filtering comprises the step of filtering the fundamental frequency from the control signal; and wherein the step of injecting first and second currents comprises the step of injecting first and second currents in response to the filtered control signal.
25. The method of claim 18 further comprising the steps of receiving power from the power line and forming the first and second currents from said received power.
26. The method of claims 25 further comprising the step of supplying a third current to the power line when the power received from the power line for forming the first and second currents exceeds the power required to form said first and second currents, the third current being at the fundamental frequency.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US934,924 | 1992-08-25 | ||
| US07/934,924 US5397927A (en) | 1992-08-25 | 1992-08-25 | Active filter for reducing non-fundamental currents and voltages |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2122129A1 true CA2122129A1 (en) | 1994-03-03 |
Family
ID=25466282
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002122129A Abandoned CA2122129A1 (en) | 1992-08-25 | 1993-08-25 | Active filter for reducing non-fundamental currents and voltages |
Country Status (8)
| Country | Link |
|---|---|
| US (1) | US5397927A (en) |
| EP (1) | EP0609434A1 (en) |
| AU (1) | AU4837993A (en) |
| CA (1) | CA2122129A1 (en) |
| MX (1) | MX9305150A (en) |
| TW (1) | TW281821B (en) |
| WO (1) | WO1994005067A1 (en) |
| ZA (1) | ZA936216B (en) |
Families Citing this family (24)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2716045B1 (en) * | 1994-02-04 | 1996-03-15 | Schlumberger Ind Sa | Active filter. |
| US5483148A (en) * | 1994-02-14 | 1996-01-09 | Rensselaer Polytechnic Institute | Single-phase active power filter for multiple nonlinear loads and method therefor |
| US5548165A (en) * | 1994-07-18 | 1996-08-20 | Regents Of The University Of Minnesota | Hybrid filter for reducing distortion in a power system |
| AT404527B (en) * | 1994-07-20 | 1998-12-28 | Johann Walter Kolar | ACTIVE MAINS VOLTAGE FILTERING WITH A PRESETABLE INNER IMPEDANCE |
| US5594630A (en) * | 1995-06-27 | 1997-01-14 | Sundstrand Corporation | Add-on distortion scrubber for AC power systems |
| US5567994A (en) * | 1995-09-29 | 1996-10-22 | Allen-Bradley Company, Inc. | Active harmonic filter with time domain analysis |
| US5977660A (en) * | 1996-08-09 | 1999-11-02 | Mesta Electronics, Inc. | Active harmonic filter and power factor corrector |
| SE514498C2 (en) * | 1997-03-13 | 2001-03-05 | Abb Ab | Control equipment for an active filter and HVDC system including such control equipment |
| US6320392B1 (en) * | 1997-03-13 | 2001-11-20 | Asea Brown Boveri Jumet S.A. | Active filter device |
| GB9713878D0 (en) * | 1997-06-30 | 1997-09-03 | Roxburgh Electronics Ltd | Mains filtering circuit |
| GB2376819A (en) * | 2001-06-21 | 2002-12-24 | Ericsson Telefon Ab L M | Electronic circuit having series connected circuit blocks |
| GB2389973B (en) * | 2002-06-18 | 2006-02-15 | Alstom | Improvements relating to electrical filters |
| CN1323477C (en) * | 2003-04-30 | 2007-06-27 | 华中科技大学 | High-capacity tandem type active electric power filter |
| US7465872B1 (en) * | 2003-12-15 | 2008-12-16 | General Electric Company | Photovoltaic power converter system with a controller configured to actively compensate load harmonics |
| FR2910734B1 (en) * | 2006-12-26 | 2009-02-06 | Univ Poitiers | ACTIVE FILTERING OF A THREE-PHASE CURRENT |
| WO2008106550A2 (en) * | 2007-02-27 | 2008-09-04 | Osisoft, Inc. | Impedance measurement of a power line |
| US7834480B2 (en) * | 2007-06-20 | 2010-11-16 | Mesta Electronics, Inc. | Energy converter system with reactive-power-management |
| JP5345148B2 (en) * | 2007-10-10 | 2013-11-20 | シャフナー・エーエムファウ・アクチェンゲゼルシャフト | EMC filter |
| EP2559123B1 (en) * | 2010-04-15 | 2016-09-07 | System Electric GmbH | Module assembly for the application-specific construction of power factor correction systems, filter systems, and absorption circuit systems |
| WO2014174667A1 (en) * | 2013-04-26 | 2014-10-30 | 富士電機株式会社 | Resonance suppression device |
| US11289940B2 (en) | 2013-06-14 | 2022-03-29 | Abb Schweiz Ag | Systems and methods for multi-use multi-mode ups |
| DE102014110672B4 (en) * | 2014-07-29 | 2016-06-30 | Infineon Technologies Austria Ag | Circuit with an RC filter |
| JP6515588B2 (en) * | 2015-02-27 | 2019-05-22 | 富士電機株式会社 | Resonance suppression device and resonance suppression method |
| US11169187B2 (en) * | 2019-06-28 | 2021-11-09 | King Fahd University Of Petroleum And Minerals | Zig zag based load flow method and system for extended radial distribution systems |
Family Cites Families (16)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3531652A (en) * | 1968-03-20 | 1970-09-29 | Allen Bradley Co | Active narrow notch filter |
| US3628057A (en) * | 1970-06-19 | 1971-12-14 | Allen Bradley Co | Corrective circuit for an active narrow notch filter |
| US4020361A (en) * | 1974-10-04 | 1977-04-26 | Delta Electronic Control Corporation | Switching mode power controller of large dynamic range |
| DE2716153C2 (en) * | 1977-04-12 | 1982-04-29 | Siemens AG, 1000 Berlin und 8000 München | Circuit for the compensation of harmonic currents in an electrical consumer arrangement |
| US4135101A (en) * | 1977-07-08 | 1979-01-16 | Power Monitors, Inc. | Method and apparatus for controlling loads in electric power systems by reduction of peak loads |
| US4206398A (en) * | 1978-04-26 | 1980-06-03 | Esb Incorporated | Method of and apparatus for detecting ground faults in isolated power supply systems |
| US4224660A (en) * | 1979-01-22 | 1980-09-23 | The Regents Of The University Of Minnesota | Composite filter for suppressing harmonic frequencies on electric power transmission lines |
| JPH0834669B2 (en) * | 1986-06-26 | 1996-03-29 | 三菱電機株式会社 | Harmonic suppressor |
| JP2554261B2 (en) * | 1987-07-24 | 1996-11-13 | 三菱電機株式会社 | Active filter device |
| JPS6485574A (en) * | 1987-09-28 | 1989-03-30 | Toshiba Corp | Power converting device |
| JPH0655009B2 (en) * | 1987-11-16 | 1994-07-20 | 三菱電機株式会社 | Control device for active filter |
| HU202338B (en) * | 1988-01-18 | 1991-02-28 | Budapesti Mueszaki Egyetem | Active filter for filtering upper harmonics generated by a nonlinear consumer coupled on power network |
| JPH063861B2 (en) * | 1990-02-14 | 1994-01-12 | 株式会社東芝 | Active filter |
| JP2893882B2 (en) * | 1990-07-11 | 1999-05-24 | 三菱電機株式会社 | Active filter device |
| US5172009A (en) * | 1991-02-25 | 1992-12-15 | Regents Of The University Of Minnesota | Standby power supply with load-current harmonics neutralizer |
| US5198746A (en) * | 1991-09-16 | 1993-03-30 | Westinghouse Electric Corp. | Transmission line dynamic impedance compensation system |
-
1992
- 1992-08-25 US US07/934,924 patent/US5397927A/en not_active Expired - Fee Related
-
1993
- 1993-08-25 ZA ZA936216A patent/ZA936216B/en unknown
- 1993-08-25 MX MX9305150A patent/MX9305150A/en unknown
- 1993-08-25 EP EP93921185A patent/EP0609434A1/en not_active Ceased
- 1993-08-25 CA CA002122129A patent/CA2122129A1/en not_active Abandoned
- 1993-08-25 AU AU48379/93A patent/AU4837993A/en not_active Abandoned
- 1993-08-25 WO PCT/US1993/007985 patent/WO1994005067A1/en not_active Application Discontinuation
- 1993-10-21 TW TW082108778A patent/TW281821B/zh active
Also Published As
| Publication number | Publication date |
|---|---|
| WO1994005067A1 (en) | 1994-03-03 |
| ZA936216B (en) | 1994-06-29 |
| AU4837993A (en) | 1994-03-15 |
| EP0609434A1 (en) | 1994-08-10 |
| MX9305150A (en) | 1994-05-31 |
| US5397927A (en) | 1995-03-14 |
| TW281821B (en) | 1996-07-21 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Discontinued |