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    24 ABSTRACT A control method tor on octive tilter connected to on e|ectric system The contro|method comprising: meosuring o voltoge ot the e|ectric system tor deriving ocurrent, comporing the derived current with o reterence current, deriving o currenterror vector trom the comporison, setting o current error thresho|d, creoting o tirstcurrent tlow between o DC power source ond the e|ectrico| system bosed on thecurrent error vector using o tirst switching pottern, when the current error vector isbelow the thresho|d, ond creoting o second, ditterent, current tlow between the DCpower source ond the e|ectrico| system bosed on the current error vector using o second switching pottern, when the derived current is obove the threshold. (Fig. 4c)
    公开号:SE1151122A1
    申请号:SE1151122
    申请日:2011-11-25
    公开日:2013-05-26
    发明作者:Dan Liljengren
    申请人:Comsys Ab；
    IPC主号:
    专利说明:

    [1] [0001]The invention relates generally to a method and arrangement tor reducing resonance using active filters.
    [2] [0002]An electrical system or power grid comprises energy generating units andenergy consuming units or loads. The energy generating units (or in some instancesenergy transtorming units) in an Alternating Current (AC) system typically generatesthree alternating currents each having a frequency ot 50 or óO Hz and having anottset relative to each other ot l20°. To create a highly ettective electrical system,the loads in the system should be purely resistive such that voltage anal currentwavetorms are in phase and changing polarity at the same instance in each cycle.With purely resistive impedance all energy generated in the energy generating unitswill be turned into a usetul and desired energy torm at the load. However, in mostcases, the impedance contains an inductive or capacitive component, which meansthat the current consumed is not always in phase with the supplied voltage ot thealternating currents. The inductive or capacitive components stores energytemporarily in electric or magnetic tields which is then returned to the power grid atraction ot a second later in the cycle. This process results in a time ditterencebetween the current and voltage wavetorms creating nonproductive power whichincreases the current. Furthermore, many electrical apparatus comprises activecomponents that have a dynamically varying load, i.e. the load varies with time, such as electrical apparatus converting electrical power to mechanical work.
    [3] [0003] ln a normal AC electric system, the voltage varies sinusoidally at a specitictrequency, usually 50 or óO hertz, known as utility trequency. A linear load, even it it comprises inductive or capacitive components, does not change the shape ot the woveform of the current. However, the increased use of pu|se controlledopporotuses such os rectifiers, vorioble frequency drives or orc dischorge devices,such os o f|uorescent |omps, e|ectric we|ding mochines, or orc furnoces introducesnon-|ineor currents into the power grid. Since currents in these systems oreinterrupted by o switching oction, the current contoins frequency components thotore mu|tip|es of the uti|ity frequency, known os hormonics. As non|ineor currentsf|ow through on e|ectrico| system ond the distribution-tronsmission |ines, odditiono|vo|toge distortions ore produced due to the impedonce of the |oods ond creotes ocurrent woveform which con become quite complex, depending on the type of |ood ond its interoction with other components of the system.
    [4] [0004]The hormonics ore troub|esome in mony woys; one exomp|e is thot e|ectricmotors experience hysteresis |oss coused by eddy currents set up in the iron core ofthe motor, which ore proportiono| to the frequency of the current. Since thehormonic frequencies ore higher, they produce more core |oss in o motor thon theuti|ity frequency, which resu|ts in increosed heoting of the motor core, which in turnshortens the |ife of the motor. Other prob|ems with hormonics inc|ude overheoting ofcob|es ond tronsformers, domoge to sensitive equipment ond tripping of circuit breokers.
    [5] [0005]Active filters copob|e of reducing the inductive ond/or copocitive componentsond hormonics ore known in the ort, for exomp|e in US7245045 to Ström et o|.,which is hereby incorporoted by reference. An octive filter is in princip|e omicroprocessor contro|ed omplifier which is connected to the power grid, ondwhich is orronged to sense ond compensote the |ood's current consumption with regords to frequencies which would not exist if the |ood wos pure|y resistive.
    [6] [0006] Typico|y, on octive fi|ter comprises o moin circuit with one or o series of fost switches for eoch phose ond eoch switch is connected to o power source, such os o Direct Current (DC) power source which con occumulote e|ectrico| energy. Thepower grid's current provision ond the |ood's current consumption ore meosured,ond using Pulse Width Modulotion (PWM) o compensoting current is distributed to the power system by meons ot the switches.
    [7] [0007]The current t|owing in the e|ectrico| system is meosured by meons ot o currentmeosurement unit, otter which it is tronsterred to o computing unit thot typico|ytronstorms the meosured current into o digitol frequency domoin signo| using FostFourier Tronstormotion (FFT). The tronstormed signo| is used to creote on inverted digitol signo| which is distributed to the e|ectrico| system os o compensoting current by meons ot Pulse Width Modulotion (PWM).
    [8] [0008]The octive ti|ters ot the ort comprise o ti|ter circuit orronged in order to reducedisturbonces on the power grid generoted by the octive ti|ter. Since the octive ti|terin principle is on omplitier, ond since the ti|ter circuit comprises on inductor ond ocopocitor it moy torm o resonont circuit together with the e|ectrico| system whichomplities hormonic trequencies when resononce occurs. Resononce ot the powergrid moy be detrimentol by cousing unwonted sustoined ond tronsient osci|otions,which in turn moy couse pertormonce degrodotion. The power grid resononce otthe resonont trequency moy introduce substontiol vo|toge tluctuotion. The ettects otresononce in on e|ectrico| system moy be progressive|y worsening os highertrequencies ore generoted. Especio|y critico| tor creoting resonont behovior is hormonics ot 7:th ond i i :th order.
    [9] [0009] Active ti|ters in the ort meosures the current t|owing between the AC powersource ond o power consuming device. Since the current t|owing in the conductorsot the e|ectrico| system is o resu|t ot the vo|toge in the power source ond impedonceot the consuming device, in occordonce with Ohm's low I = U/R, the meosurement ot the current wi| be deloyed in re|otion to tluctuotions ot the vo|toge |eve|. On top ot that, active tilters use an A/D Conversion based on Fast Fourier Transtorm (FFT)which requires re|ative|y computing intense ca|cu|ations in the microprocessorbetore o compensating current con be generated. Since the process ot creating ocompensating current is much too slow tor handling resonance, the response otactive tilters in the ort to resonant behavior in the e|ectrica| system hos been to shutdown the tilter ond dea| with the trequencies generating the resonance by adding components to the e|ectrica| system.
    [11] [00011] A control method tor an active tilter connected to an electric system isprovided. The control method comprises measuring a voltage at the electric systemtor deriving a current, comparing the derived current with a reterence current,deriving a current error vector trom the comparison and setting a current errorthreshold. The method turther comprises creating a tirst current tlow between a DCpower source and the electrical system based on the current error vector using a tirstswitching pattern, when the current error vector is below the threshold, and creatinga second, ditterent, current tlow between the DC power source and the electricalsystem based on the current error vector using a second switching pattern, when thederived current is above the threshold. By providing a tirst and second switchingpattern, a tirst and second type ot response may be created, one which is energy etticient, and one which is powertul enough to suppress resonance.
    [12] [00012] According to one embodiment, the electrical system is an alternatingcurrent three phase system comprising alternating currents having an ottset inrelation to each other ot substantially l20°, and wherein the threshold is an upperand lower threshold that applies to all ot the three phases and thus creates a hexagonal threshold.
    [13] [00013] According to another embodiment, the tirst switching pattern is adapted tocreate as long switching cycles as possible by creating a current tlow altering thedirection ot the current error vector within the hexagon towards the threshold turthest away.
    [14] [00014] According to yet onother embodiment, the step of creating o secondcurrent flow between o DC power source ond the e|ectrico| system comprisescreoting o current flow being the opposite to the current error vector such thot the current error is reduced os efficiently os possible.
    [15] [00015] According to one embodiment, the step of deriving o current error vectoris performed using o biquodrotic filter odopted to creote o tronsfer function on thebosis of the voltoge. The biquodrotic filter mokes it possible to get o system with ohigh somple frequency by meons of stondord components. The biquodrotic filter could hove o somple frequency exceeding lOOkSo/s or exceeding lßOkSo/s.
    [16] [00016] A control system for on octive filter connected to on electric system isfurther provided. The control system comprises o meosuring unit odopted to meosurethe vo|toge ot the electric system for deriving o current, o comporing unit odopted tocompore the vo|toge of the electric system with o reference volue for deriving ocurrent error vector, o contro| unit odopted to set o current error threshold, ond oswitch unit. The switch unit is odopted to creote o first current flow between o DCpower source ond the e|ectrico| system bosed on the current error vector using o firstswitching pottern, when the current error vector is below the threshold, ond creote osecond, different, current flow between the DC power source ond the e|ectrico|system bosed on the current error vector using o second switching pottern, when thederived current is obove the threshold. By providing o first ond second switchingpottern, o first ond second type of response moy be creoted, one which is energy efficient, ond one which is powerful enough to suppress resononce.
    [17] [00017] According to one embodiment, the e|ectrico| system is on olternotingcurrent three phose system comprising olternoting currents hoving on offset in relotion to eoch other of substontiolly l20°, wherein the threshold is on upper ond |ower thresho|d thot applies to o| ot the three phoses ond thus creates o hexogonol thresho|d.
    [18] [00018] According to one embodiment, the tirst switching pottern is odopted tocreote os |ong switching cyc|es os possib|e by creating o current t|ow oltering thedirection ot the current error vector within the hexogon towords the thresho|d turthest owoy.
    [19] [00019] According to one embodiment ot the contro| system, creoting o secondcurrent t|ow between o DC power source ond the e|ectrico| system comprisescreoting o current t|ow being the opposite to the current error vector such thot the current error is reduced os etticient|y os possible.
    [20] [00020] According to one embodiment ot the contro| system, the step ot deriving ocurrent error vector is pertormed using o biquodrotic ti|ter odopted to creote o tronster tunction on the bosis ot the vo|toge.
    [21] [00021] A contro| unit tor on octive ti|ter tor reducing resononce in on e|ectricsystem is turther provided. The e|ectrico| system comprising o power sourcedistributing on olternoting current to on AC conductor connected to o powerconsuming unit tor distributing the AC to the power consuming unit. The octive ti|tercomprising o DC power source, o switching system, ond o DC conductorconnecting the DC power source to the AC conductor. The contro| unit comprises ovo|toge meosurement unit odopter to creote o vo|toge signo| on the bosis ot themeosured vo|toge, o computing unit odopted to compute o compensoting current onthe bosis ot the vo|toge signo| tor reducing resononce in the e|ectric system, ond oswitch system p|oced between the DC power source ond the DC conductor torcreoting the co|cu|oted compensoting current. By meosuring the vo|toge o directresponse is received which creotes o system with o |otency |ow enough to suppress FeSOnCJnCe.
    [22] [00022] According to one embodiment ot the control unit, the octive ti|ter furthercomprises o copocitor connected to the DC conductor ond to ground, beingodopted to leod trequencies other thon the utility frequency ot the e|ectrico| systemto ground. The vo|toge meosurement unit is odopted to be connected to o pointbetween the AC power source ond the copocitor. By meosuring the vo|toge ot this|ocotion on instontoneous vo|ue on the vo|toge |eve| ot potentio|y hormtul currentsore co|ected since the meosured vo|toge |eve| instontoneously ret|ects the vo|toge |eve| ot the power system
    [23] [00023] According to one embodiment ot the contro| unit, the computing unitcomprises o biquodrotic ti|ter odopted to creote o tronster tunction on the bosis otthe vo|toge signol. The biquodrotic ti|ter mokes it possible to get o system with ohigh somp|e trequency by meons ot stondord components. The biquodrotic ti|ter cou|d hove o somp|e trequency exceeding iOOkSo/s or exceeding ißOkSo/s.
    [24] [00024] According to one embodiment ot the contro| unit, the vo|toge meosurementunit is turther odopted to meosure the vo|toge ot o second ond third olternotingcurrent hoving on ottset in re|otion to the tirst o|ternoting current ot substontio|yi20° ond 240 ° respectively, ond creote o second ond third vo|toge signol on thebosis ot the second ond third meosured vo|toges, ond wherein the computing unit isturther odopted to compute o second ond third compensoting current on the bosis otthe second ond third vo|toge signols. The DC power source moy be odopted toreceive current trom the second or third olternoting currents, ond the switch moy beodopted to distribute the compensoting current to the tirst AC conductor by meons ot pu|se width modulotion.
    [25] [00025] An octive ti|ter tor reducing resononce in on e|ectric system is turtherprovided. The e|ectrico| system comprises o power source distributing on olternoting current to on AC conductor connected to o power consuming unit tor distributing the o|ternoting current to the power consuming unit. The octive ti|ter comprises o DCpower source, o switching system ond o DC conductor connecting the DC powersource to the AC conductor. The octive ti|ter turther comprises the control unit occording to ony ot the embodiments herein.
    [26] [00026] A method ot suppressing resononce in on e|ectric system is turtherprovided, the method comprises: meosuring the vo|toge ot o conductor supp|yingenergy trom on AC source to on energy consuming unit, creoting o vo|toge signo|on the bosis ot the meosured vo|toge, computing o tronster tunction on the bosis otthe vo|toge signo|, ond creoting o contro| signo| on the bosis ot the computedtronster tunction tor contro|ing o switching system creoting o compensoting current by meons ot pu|se width modu|otion.
    [27] [00027] According to one embodiment, the vo|toge is meosured between theconductor ond o copocitor odopted to |eod o|ternoting currents with trequencies other thot the uti|ity trequency ot the e|ectric system to ground.
    [28] [00028] According to one embodiment, the step ot computing o tronster tunctionon the bosis ot the vo|toge signo| comprises computing o tronster tunction usingbiquodrotic ti|ters. The step ot computing o tronster tunction on the bosis ot thevo|toge signo| moy be pertormed with o trequency ot more thon iOOkSo/s or more thon iSOkSo/s.
    [29] [00029] Further possible teotures ond benetits ot this so|ution wi| become opporenttrom the detoi|ed description below. P|eose note thot ony embodiment or port otembodiment os we| os ony method or port ot method cou|d be combined in ony woy.
    [30] [00030] Some possib|e embodiments wi| now be described, by woy ot exomple, with reference to the occomponying drowings, in which:[00031] Fig. i is o system overview ot on octive ti|ter,
    [32] [00032] Fig. 2 is o system overview ot on octive ti|ter tor o three-phose system shown in turther detoil.[00033] Fig. 30 shows o groph ot the three currents with o 120” phose shitt,
    [34] [00034] Fig. 3b shows o groph ot o utility trequency ot when moduloted in re|otion to o pertect sinusoidol reterence signol,
    [35] [00035] Fig. 40 shows o groph ot o resulting error vector ond o hexogon mode ot thresho|ds,[00036] Fig. Ab is o system overview ot on octive ti|ter,[00037] Fig. 4c is o groph ot the error vector in re|otion to the hexogon thresho|ds,
    [38] [00038] Fig. So is o system overview ot on octive ti|ter showing the units in turther detoil,[00039] Fig. Sb is o groph exptoining the switching stotes,
    [40] [00040] Fig. ó is o t|ow chort exploining o method ot suppressing resononce in on e|ectric system,
    [41] [00041] Fig. 7 is o t|ow chort exploining o contro| method tor on octive ti|ter.
    [42] [00042] An octive ti|ter is provided tor reducing resononce in o power system byropidly responding to resonont behovior ond instontoneously providing ocompensoting current octively suppressing the resononce. The ropid response time isenobled by utilizing voltoge meosurement on o conductor between the e|ectrico|system to be monitored ond compensoted, ond o copocitor odopted to ottroctolternoting currents hoving trequencies obove the utility frequency ot the e|ectrico|system. By meosuring the voltoge ot this locotion on instontoneous volue on thevoltoge level ot potentiolly hormtul currents ore co|ected since the meosured voltogelevel instontoneously retlects the voltoge level ot the power system, in controst tocurrents which depend upon o current build up over the impedonce in response to o chonge in voltoge.
    [43] [00043] The meosured voltoge level is used in its onolog torm to instontoneouslycreote o tronster tunction tor controlling the teeding ot the compensoting current bymeons ot switches ond Pulse Width Modulotion (PWM). By using the voltoge |eve|in its onolog torm, |otency is turther reduced ond the computing power intense step ot creoting o Fost Fourier Tronstorm (FFT) ot the onolog signol is eliminoted.
    [44] [00044] A modulotion method bosed on two thresho|ds is turther provided. The twothresho|ds enobles the system to reoct in o tirst, less powertu|, woy os long os thecurrent error (deviotion trom the desired utility trequency current) is l resononces in thepower grid excited by the lood to be compensoted. 12
    [45] [00045] ln the following o detoi|ed description ot embodiments wi| be given withreference to the occomponying drowings. lt wi| be opprecioted thot the drowings ore tor i|ustrotion only ond ore not in ony woy restricting the scope.
    [46] [00046] Fig. i shows on octive ti|ter i tor resononce compensotion according to otirst embodiment in which the octive ti|ter i is in connection with on e|ectrico| system2. The e|ectrico| system 2 comprises on AC powers source 20 distributing ono|ternoting current to o conductor 2i tor tronster to o power consuming unit 22. Thepower source 20 cou|d be o generotor producing the o|ternoting current or otronstormer used to tronstorm the voitoge |eve| trom o high voitoge power grid |eve|to consumption |eve|. The power consuming unit 22 is tor exompie on e|ectrico|mochine tronstorming the e|ectrico| energy supp|ied trom the power source 20 vio the conductor 2i to mechonico| work.
    [47] [00047] The octive ti|ter i is connected to the e|ectrico| system 2 vio o conductor 3p|oced between the octive ti|ter circuit i ond the conductor 2i , such thot e|ectrico|current generoted by the octive ti|ter i con be distributed to the e|ectrico| system tor improving the chorocteristics ot the o|ternoting current t|owing in the conductor 2i .
    [48] [00048] The octive ti|ter i comprises o Direct Current (DC) power source i0connected vio o tirst conductor i5o to o switch i i in o contro| unit ió. The switchi i creotes o compensoting current be meons ot Pu|se Width Moduiotion (PWM)such thot the overoge vo|ue ot the current ted to the e|ectrico| system 2 is contro|edby the switch i i being open ond c|osed ot o tost poce. The |onger the switch i i isc|osed compored to the open periods, the |orger the current supp|ied to the e|ectrico| system becomes.
    [49] [00049] Vio o second conductor i5b, the switch i i is connected to on inductori2. The inductor tronstorms the pu|ses generoted by the switch i i to o continuous signo| by opposing the chonges in current through it by developing o voitoge ocross 13 it proportiona| to the rate ot change ot the current in accordance with themathematical tormu|a I = -LdU/dt. For an active ti|ter contigured tor 100A currentthe inductor typica|y is an inductor in the range 200-250 uH. The inductor 12 is inturn connected to the conductor 3 connecting the active ti|ter 1 to the e|ectrica|system 2, such that the current created by the active ti|ter 1 can be supp|ied to thee|ectrica| system. An additional conductor 15c connects the conductor 3 to acapacitor 13 which in turn is connected to ground 14. The capacitor 13 is set at ava|ue allowing a|ternating currents with a frequency at magnitudes above the utilityfrequency ot the e|ectrica| current (tor power grid applications typica|y 50 - ó0 Hz)to pass to the ground 14 connection. This wi| ettective|y draw a| trequencies that create |oss in the power system 2 to the capacitor.
    [50] [00050] The contro| system 1ó comprises a measurement unit 17' connected via ameasurement conductor 18 to a point at the conductor 21,' 3,' 15c between the ACpowers source 20 and the capacitor 13 such that the voltage |eve| ot thecomponents ot the a|ternating current with trequencies above the uti|ity trequency,passing through the conductor 21,' 3,' 15c, wi| be measured with high accuracy and |ow |atency.
    [51] [00051] The measured signa| is transterred trom the measurement unit 17' to acomputing unit 17" adapted to create a compensating current to reduce trequencycomponents ot the current other than the uti|ity trequency, turther detai|s withre|ation to the creation ot the compensating current wi| be described with reterenceto tigs. 3 - 4. The computing unit 17" is connected to a switching unit 17"', andthe compensating current is rea|ized by means ot PWM by the switch 1 1 ot the switching unit 17"', i.e. the compensating current is supplied trom the DC source 10 and tormed using PWM by the switch 17c. 14
    [52] [00052] Fig. 2 shows o version of the e|ectrico| system 2 simiior to the e|ectrico|system described with reference to fig. i . The moin difference being thot the systemoccording to fig. 2 is o three phose system, such os most power grids, comprisingthree oiternoting currents eoch with o phose offset of i20° ond eoch connected to othree phose iood 22, for exompie by meons of o A or Y coup|ing. The e|ectrico| system comprises 3 conductors 2io,'2i b;2ic for tronsferring e|ectrico| current from the AC source 20 to the iood 22.
    [53] [00053] Just like in the circuit described under reference to fig. i, the octive filter icomprises o direct current power source iO, here comprising o copocitor 37 inporo|e| with o resistor 38. The DC power source iO is connected to o switching uniti7"' vio conductors 32'; 32". According to the embodiment shown under referenceto fig. 2 the switching unit comprises tronsistor bridges 3io; 3i b; 3ic of poir-wiseswitches (one of which is eniorged on indicoted by reference numeroi 3io") onetop for supp|ying positive voitoges ond one bottom for supp|ying negotive voitogesfor eoch of the three phoses. Eoch switch, such os 3io", comprises o tronsistor 36,o diode 35 ond o snubber 34, connected in poro|e| with the co|ector 36" ondemitter 36"' of the tronsistor. The tronsistor 36 is the octive component thot contro|sthe PWM, the diode 35 directs current from the e|ectrico| system 2 to the DCoccumuiotor when the voitoge of the e|ectrico| system 2 exceeds the voitoge of theDC occumuiotor. The snubber 35 protects the tronsistor from short voitoge spikesthot ore creoted when the switch turns of the current by obsorbing ond reducing thevoitoge to monogeobie |eve|s i.e. 50 - iOOV. For eoch phose, the poir of switchesore in one end connected to eoch other ond to the conductors i5"o,'i5"b,'i 5"c,ond their other ends connected to the DC power source iO by meons of shoredconductors 32'; 32". Both the specific design of the DC power source iO ond theswitches ore to be seen os exompies of impiementotions. The ski|ed person reoiized thot voriotions or oiternotives to the designs ore equoiiy conceivobie.
    [54] [00054] The gote 36' ot the tronsistors 36 ore connected to control leods 33o,'33b; 33c running trom the computing unit 17" such thot the switches operote onpulses trom the computing unit 17" ottecting the semiconducting properties ot thetronsistor 36. ln the embodiment described under reterence to tig. 2, the tronsistorsore lnsuloted Gote Bipolor Tronsistors (IGBT) which ore highly etticient ond otters tost switching, however it is conceivoble thot the tronsistors ore ot o ditterent type, such os Metol Oxide Semiconductor Field Ettect Tronsistors (MOSFET).
    [55] [00055] The inductors 12o;12b;12c ond copocitonces 13o;13b;13c oreturthermore odiusted such thot the ti|ter short-circuits hormonics ond disturbonces which ore generoted by the switching ot the tronsistor bridges 31o,'31b,'31c.
    [56] [00056] The control unit 1ó ot the octive ti|ter 1 encomposses o meosuring unit 17'connected vio meosurement conductors 18o;18b;18c to o point ot the conductors3o;3b,'3c between the AC powers source 20 ond the copocitors 13o;13b;13c suchthot the voltoge level ot the components ot the olternoting current with trequenciesobove the utility trequency, possing through the conductor 13o;13b;13c will bemeosured with high occurocy ond low lotency. The meosurement unit 17' isconnected to o computing unit 17" in which the Puls Width Modulotion (PWM)creoting the control pulses to the switches is computed. The computing unitcomprises o processing unit, which moy be o single CPU (Centrol processing unit),or could comprise two or more processing units. For exomple, the processor moyinclude o generol purpose microprocessor, on instruction set processor ond/orreloted chips sets ond/or speciol purpose microprocessors such os AS|Cs(Applicotion Specitic lntegroted Circuit). The processor moy olso comprise boord memory tor coching purposes.
    [57] [00057] As in tig.1 the switch is connected to inductors 12o;12b;12c which tronstorms the pulses generoted by the switch system 17” to o continuous signol by 16 opposing the chonges in current through it by developing o voitoge ocross itproportionoi to the rote ot change ot the current. The inductors i2o,'i 2b,'i2c ore inturn connected to conductors 3o;3b,'3c connecting the octive ti|ter i to the e|ectrico|system 2, such thot the current creoted by the octive ti|ter i con be supp|ied to the power system 2.
    [58] [00058] The meosured signo| is tronsterred trom the meosurement unit i7' to ocomputing unit i7" odopted to creote o compensoting current to suppressresononce ond reduce frequency components ot the current other thon the utilityfrequency. Further detoi|s with re|otion to the creotion ot the compensoting currentwi| be described with reterence to tig. 3 - 4. The computing unit i7" is connected to o switching unit i7"' thot reolizes the compensoting current by meons ot PWM.
    [59] [00059] Further detoi|s ot the operotion ot the computing unit ond the creotion ot the contro| signo| tor contro|ing the switches wi| now be described under reterence to tigs. 3 - 4.
    [60] [00060] According to one embodiment, the tronster tunction ot the ono|og voitoge|eve| signo| wi| be creoted by meons ot digitoi biquodrotic ti|ters. Biquodrotic ti|tersore second-order recursive |ineor ti|ters hoving o tronster tunction which is the rotio ot two quodrotic tunctions:
    [61] [00061] i
    [62] [00062] According to the embodiments described under reterence to tigs. i ond 2the biquodrotic ti|ter is digito|y imp|emented in the computing unit (reterencenumber i7") ond typico|y sompies the voitoge signo| with o trequency obove i00kSo/s, preterobiy obove i90i preterobiy more thon 3800, times toster thon the uti|ity trequency ot the power 17 system which is fost enough to reoct to resonont behovior of most hormonics in ofrequency range thot could couse problems. Furthermore, the biquodrotic filter hos overy |ow lotency which mokes the reoction to resonont behovior vory ropid which enobles efficient suppression of the resonont behoivior.
    [63] [00063] According to the embodiments described with reference to figs. 2, the DCpower source does not generote ony current of its own; it mere|y stores energywhich it tokes from the AC phoses short periods of time such thot the DC currentshou|d f|ow continuous|y. This meons thot the switches in the switching system(further described under reference to fig. 2) needs to be set such thot power isreceived from one AC phose ond then distributed to onother AC phose in occordonce with o switching schedu|e which wi| be describes loter.[00064] The modulotion wi| now be described in further detoil.
    [65] [00065] Fig. 30 shows the uti|ity frequency of the three AC phoses ACi , AC2,AC3 in the time/vo|toge domoin. The modulotion is hysteresis bosed such thot thedifference, or error, between the desired (reference) output current ond the octuoloutput current is co|cu|oted for the purpose of creoting on error vector to be contro|ed.
    [66] [00066] Fig. 3b shows the octuol uti|ity frequency of ACi when moduloted inre|otion to the perfect sinusoidol reference signol AREF. The modulotion operotes bysending o compensoting current out to the grid ond thereby switching the directionof the error vector which keeps the error within the thresho|ds Ti ond T2. ln normo|operotions, the error vector shou|d be kept within the first thresho|d Ti ond theswitching shou|d be odopted such thot eoch switch cyc|e is os long os possible,which keeps down the power consumption of the switches ond prolongs the |ife of the switches. 18
    [67] [00067] Fig. 40 shows the octuol current in the system le"ond the current vectorwhich hove been tronstormed to the reference current lee", by meons ot thebiquodrotic tilters ot the control unit ló. The resulting error between the reterencecurrent ond the octuol current is shown os le" ond represents the error which is to be l
    [68] [00068] Fig. 4b shows o simplitied system illustrotion showing the control unit ló generoting the reterence current l which otter comporison with the system current Seip,le" generotes the resulting current vector le". The resulting current error vector le" is then compored with the tirst ond second thresholds in the comporotors (Slo - Sld).ln turther detoil the error vector le" is compored to the second (outer) threshold le"er inSlo, the tirst (inner) threshold lime) in Sl b, the tirst negotive (inner) threshold -li""er inSlc in the tirst negotive (outer) threshold in Sld. The comporison results in o control signol 33 tor controlling the switches such thot the most suitoble compensoting current is creoted.
    [69] [00069] Fig. 4c shows the inner 64 ond outer óS hexogon hoving on inner ondouter threshold tor the three phoses (ACT , AC2, ACS) respectively. The thresholdscon be controlled by o digitol potentiometer ond tuned depending on the system inwhich the octive tilter is ploced, such thot the response trom the tilter most etticiently suppresses the errors ond whilst consuming os little energy os possible.
    [70] [00070] Fig. So shows o circuitry diogrom ot on embodiment ot the modulotionsystem in which error vectors ól o, ól b, ólc ot the three phoses The error vectorswith top or bottom volues S29 - l ore turther provided os input to the outer sectordetector óS odopted to determine whether or not the resulting error vector remoinswithin the boundories ot the outer hexogon óS, which ploces the resulting errorvector in o sector S - SVI ot the hexogon óS ond provides output in the torm ot the sector SI - SVI to o dynomic-stote control unit 67 odopted to control the switch stotes 19 (ot the switches tor example shown os 3io - 3ic in tig. 2) in occordonce with tobie2 below, such thot the switching is optimized tor ettectiveiy pushing the resu|tingerror vector bock into the boundories ot the inner hexogon 64. The switching stotes ot tobie 2 ore reoiized in occordonce with the switching stote groph i obove.
    [71] [00071] s: su sm sav sv sv:42 ÜZ 'OZ TZ :Iz åZ Tab/e 2
    [72] [00072] The required switching stotes ore received ot o control signo| generotingunit 68 determining it switches need to be mode ond creotes the control signois33o', 33o", 33b', 33b", 33c', 33c", received os input in the tronsistor bridges(3io - 3ic in tig. 2) ond contro|ing the tronsistors such thot o compensoting current is creoted by meons ot pu|se width modulotion.
    [73] [00073] Fig. ó is o tlowchort ot o contro| method tor on octive ti|ter occording toone embodiment. The contro| method comprises the steps ot meosuring the vo|toge7i ot o point between o copocitor ond the e|ectrico| system (os turther disc|osedunder reterence to tigs. i ond 2), creote o vo|toge signo| ot o contro| unit 72representing the vo|toge ot ditterent trequencies in the oiternoting current, compute73, ot o computing unit, o tronster tunction describing the chorocteristics ot ocompensoting current thot suppresser resonont behovior ond the vo|toge |eve| ottrequencies other thon the utiiity trequency, ond creoting o contro| signo| 74 on thebosis ot the vo|toge signo| tor contro|ing switches tor generoting the compensoting current using pu|se width modulotion (olso turther disc|osed with reterence to tigs. i _11).
    [74] [00074] Fig. 7 is o tlowchort describing o method ot modulotion occording to oneembodiment. The method comprises the steps ot meosuring o vo|toge (8i) ot the e|ectric system tor deriving o current (82). The vo|toge cou|d be meosured between o conductor of the e|ectrico| system ond o copocitor odopted to leod olternotingcurrents with frequencies other thot the uti|ity frequency of the e|ectric system toground, which creotes o very good connection between troub|esome frequenciesond the meosurement. The meosured vo|toge is used to derive o current which isthen compored (83) with o reference current, hoving o perfect sinusoido| wove formsuch thot o difference between the reference current ond the meosured current conbe derived (84), the difference being o current error vector. A current errorthresho|d (85) is set in the control |ogic of the octive filter for defining to whot extento current error con be occepted ond defining whot the response to the current errorshould be. The method then comprises the step of creoting o first current flow (86)between o DC power source ond the e|ectrico| system bosed on the current errorVector using o first switching pottern, when the current error Vector is be|ow thethresho|d (which is further exploined under reference to figs. 4c, So och 5b). Themethod further comprises the step of creoting o second (87), different, current flowbetween the DC power source ond the e|ectrico| system bosed on the current error vector using o second switching pottern, when the derived current is obove the thresho|d.
    [75] [00075] P|eose note thot ony embodiment or port of embodiment os we| os onymethod or port of method could be combined in ony woy. A| exomples hereinshou|d be seen os port of the generol description ond therefore possible to combine in ony woy in genero| terms.
    权利要求:
    Claims (9)
    [1] 1. 21 CLA|MSi . A control method tor on octive ti|ter connected to on e|ectric system (2) comprising: meosuring o vo|toge ot the e|ectric system tor deriving o current,0 comporing the derived current with o reterence current, 0 deriving o current error vector trom the comporison, 0 setting o current error thresho|d, 0 creoting o tirst current t|ow between o DC power source ond the e|ectrico|system bosed on the current error vector using o tirst switching pottern,when the current error vector is be|ow the thresho|d, ond 0 creoting o second, ditterent, current t|ow between the DC power sourceond the e|ectrico| system bosed on the current error vector using o second switching pottern, when the derived current is obove the thresho|d.
    [2] 2. The contro| method occording to c|oim i, wherein the e|ectrico| system is onolternoting current three phose system comprising olternoting currents hovingon ottset in re|otion to eoch other ot substontio|y i20°, ond wherein thethresho|d is on upper ond |ower thresho|d thot opp|ies to o| ot the three phoses ond thus creotes o hexogonol thresho|d.
    [3] 3. The contro| method occording to c|oim 2, wherein the tirst switching potternis odopted to creote os long switching cyc|es os possible by creoting ocurrent t|ow o|tering the direction ot the current error vector within the hexogon towords the thresho|d turthest owoy. 22
    [4] 4. The control method according to c|oim i, wherein creating o second currentt|ow between o DC power source ond the e|ectrico| system comprisescreoting o current t|ow being the opposite to the current error vector such thot the current error is reduced os etticient|y os possible.
    [5] 5. The contro| method occording to ony one ot cloims i - 4, wherein the step otderiving o current error vector is pertormed using o biquodrotic ti|ter odopted to creote o tronster tunction on the bosis ot the voltoge. ó.
    [6] 6. A contro| system tor on octive ti|ter connected to on e|ectric system comprising: 0 o meosuring unit odopted to meosure the vo|toge ot the e|ectric system torderiving o current, 0 o comporing unit odopted to compore the vo|toge ot the e|ectric systemwith o reterence vo|ue tor deriving o current error vector, 0 o computing unit odopted to set o current error thresho|d, ond 0 o switch unit odopted to: o creote o tirst current t|ow between o DC power source ond thee|ectrico| system bosed on the current error vector using o tirstswitching pottern, when the current error vector is below thethresho|d, ond o creote o second, ditterent, current t|ow between the DC powersource ond the e|ectrico| system bosed on the current error vectorusing o second switching pottern, when the derived current is obove the threshold. 23
    [7] 7. The control system according to c|aim ó, wherein the e|ectrica| system is ona|ternating current three phase system comprising a|ternating currents havingan ottset in re|ation to each other ot substantia|y T20°, and wherein thethresho|d is an upper and |ower thresho|d that applies to a| ot the three phases and thus creates a hexagona| thresho|d.
    [8] 8. The contro| system according to c|aim 7, wherein the tirst switching pattern isadapted to create as |ong switching cyc|es as possible by creating a currentt|ow a|tering the direction ot the current error vector within the hexagon towards the thresho|d turthest away.
    [9] 9. The contro| system according to any one ot c|aims 5 - 8, wherein creating asecond current t|ow between a DC power source and the e|ectrica| systemcomprises creating a current t|ow being the opposite to the current error vector such that the current error is reduced as etticient|y as possible. TO. The contro| system according to any one ot c|aims ó - 9, wherein thecomputing unit comprises a biquadratic ti|ter adapted to create a transter tunction on the basis ot the vo|tage signa|.
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    同族专利:
    公开号 | 公开日
    SE538618C2|2016-10-04|
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    SE1151122A|SE538618C2|2011-11-25|2011-11-25|Control method and control system for an active resonance reduction filter|SE1151122A| SE538618C2|2011-11-25|2011-11-25|Control method and control system for an active resonance reduction filter|
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