Performance Analysis of Shunt Active Power Filter using PLL based Control Algorithms Under Distorted Supply Condition

Transcription

1 Performance Analyss of Shunt Actve Power Flter usng PLL base Control Algorthms Uner Dstorte Supply Conton Rajesh K Patjosh Electroncs an Communcaton Engg.Dept. atonal Insttute of Technology Rourkela, Ina rajeshpatjosh@gmal.com Kamala kanta Mahapatra Electroncs an Communcaton Engg.Dept. atonal Insttute of Technology Rourkela, Ina Kmaha@gmal.com Abstract Ths paper presents three fferent PLL base control algorthms for shunt actve Power flter (SAPF uner the storte supply conton. Dfferent synchronsaton technues such as Mofe SRF (MSRF-PLL, Transformaton angle etector an SRF base PLL have been apple to SAPF an analyze uner fferent storton contons of supply voltage. From the smulaton results, t s foun that the MSRF- PLL acheves better performance as compare to other two stanar PLL technues on the bass of THD% (total harmonc storton. The MSRF-PLL s fast n transent response an robust aganst sturbances on the gr voltage wave. Here smulaton has been carre out usng MATLAB uner storte lne voltage contons. Ine Terms Mofe SRF, Angle Detector SRF, SRF PLL, harmonc storton, storte lne voltage. I. ITRODUCTIO Interfacng of power electroncs converters to the supply lne, partcularly for the meum an hgh power lne reures proper synchronzaton for the purpose of better operaton an control of power electroncs base eupments[.the synchronzaton s base on conserng the phase angle of supply voltage an current.the sgnal n the utlty are often corrupte by power lne sturbances such as harmoncs, voltage sag an swell, phase jump, commutaton notch an unbalance contons[ [4.The phase-angle of the voltage/current funamental component at the pont of common couplng (PCC shoul be tracke onlne n orer to control the energy transfer between the actve power flter an the ac mans., so sutable synchronzaton algorthms have been evolvng for proper operaton of the actve power flter. The P- Q operaton pont of actve power flter epens on the phase angle of the utlty. In general, the controllers of power electronc converters mplement synchronzaton algorthms to assess echanges of electrcal energy. Measurements at the PCC are mae n orer to estmate voltage/current absolute phase-angles. The PLL control algorthms were consere for three-phase electrc systems, Kaura at [5, an he establshe a PLL technue for Synchronous Reference Frame, whch prove goo performance an fast transent response uner less storton level an small unbalance conton. Any conton fferent from these specfcatons proves poor phase synchronzaton, lock loss, storte output sgnal resultng n uncorrecte harmonc compensaton. Utlty connecte systems such as UPS, PWM rectfers an Actve Power Flters have ts performance epens on PLL accuracy, especally those n whch the controllers are base on SRF. An open loop system, name low-pass transformaton angle etector, was able to synchronze wth the postve-seuence of the funamental vector of a three-phase voltage/current system, presente n [6. Ths system was propose as a Transformaton Angle Detector PLL. The PLL Algorthm propose n [7, was base on Mofe Synchronous Reference Frame technue (MSRF an offers uckly lock feature wthout PI controller an uses only phase-a voltage measurement by reucng sensors even f n three phase utlty case. Also, voltage unbalance an harmonc o not sturb the performance of the PLL. Ths paper presents three fferent topologes of PLL such as Mofe SRF (MSRF-PLL, Transformaton Angle Detector, an SRF base PLL for etecton of postve seuence sgnal from the storte supply voltage for proper operaton of the actve power flter. Here three fferent storte contons of supply voltage have been consere n comparatve analyss of the above mentone PLL structures. Comparson result shows the superorty of MSRF-PLL as compare to others on the bass of THD% (total harmonc storton. II. COTROL STRUCTURE OF PLL SYSTEM arous methos of synchronzaton technues are outlne n ths secton. They are categorze as open-loop an close-loop methos. Open-loop methos rectly estmate the phase angle of the voltage an current sgnal base on frame sgnal. In close-loop methos, whle the frame voltages are beng processe, the estmaton of the phase s aaptvely upate through a loop mechansm. Ths loop s ame at lockng the estmate value of the phase angle to ts actual value. The paper consers both open an close loop PLL control technues for synchronzaton of the actve power

2 flter. In open loop technue, the Transformaton Angle Detector an n the close loop system, both SRF PLL an Mofe SRF (MSRF-PLL are use. b as as as A. Open-Loop Synchronzaton Metho Transformaton Angle Detector s consere here for three-phase actve power flter connecte to the utlty gr. The performance of ths synchronzaton metho s analyze uner storte gr voltages. Fg. shows the control scheme of the Transformaton Angle Detector. A three-phase system voltages ( a, b, c are transforme to ts euvalent Clarke s Transformaton (transformaton from abc to. c 3 3 a as / / = 3 3 It s assume that there s no negatve-seuence of funamental freuency an the phase angle of the postveseuence s estmate from ˆ an ˆ, whch are obtane by flterng harmoncs from an through ornary lowpass flters (s. The fltere sgnals are normalze an passe through the rotaton matr to compensate for the phase lag ue to the s. In esgnng s, a traeoff shoul be mae between robustness an transent convergence spee. The smaller cutoff freuency of the flters results n less storton n the estmate angle. However, ths results n a slower rate of convergence. A major efcency of ths metho s ts senstvty to the gr freuency evatons [8. If the center freuency vares, there s no control on the phase lag ntrouce by the s an hence ts full compensaton s not possble. Another shortcomng of the -base metho s ts senstvty to voltage unbalance. To overcome ths ownse, the followng two methos are approache. B. Close-Loop Synchronzaton Metho A close-loop metho operates on regulatng an error sgnal to zero. Here both SRF PLL an MSRF-PLL are consere for synchronzaton. Synchronzaton Base on SRF PLL Synchronous reference frame strategy s a popular metho use n the generaton of the current reference by co-ornate transformatons. For ths purpose, t employs the well known Clarke s Transformaton (transformaton from abc to an Park s Transformaton (transformaton from to, whch are shown graphcally n Fg.. v a v b v c Clarke Transformaton v v ˆv ˆv vˆ vˆ v ˆnorm v ˆnorm Fg. Control scheme of the Transformaton Angle Detector ( a tan θˆ ( (a (b Fg.(a Clarke' Transformaton, (b Park s Transformaton * PI regulator ω s abc Fg.3 SRF base PLL structure θ = ωt a b c Operaton of a three phase SRF base PLL can be schematcally shown n the Fg.3. To obtan the phase nformaton, the three phase voltage sgnals ( a, b, c are frst transferre nto statonary two phase systems ( an an further reference frame ( an. Where, a transferre nto synchronously rotatng = snωt ( m = sn( t b m ω (3 = sn( t c m ω (4 = a b c 3 3 = c b (5 (6 = cosθ snθ (7 = cosθ snθ (8 ow phase angle (θ can be obtane by settng the reference * eual to zero an compare wth. The PI sτ controller ( K P. s use to regulate ths - sτ component an the output of ths PI controller s the gr

3 freuency. After the ntegraton of the gr freuency, the utlty voltage angle s obtane. As ωt s the angular freuency, snω t s n phase wth the funamental of the - component an the cos ω t s 9 phase-shft wth the - component. The controller gans are esgne such that follows the reference value an the estmate phase angle (φ shoul be eual to the phase angle (θ. ow f θ φ then the space vector of voltage gets algne to as. Synchronzaton Base on Mofe SRF(MSRF-PLL The PLL algorthm [9 s esgnate as mofe SRF- PLL (MSRF-PLL because t consers only one phase voltage (.e., a wave n place of three phase voltage waves use n the SRF-base algorthms. The PI control n the SRF PLL control loop s elmnate by MSRF PLL, because the PI controller use n SRF PLL gets sluggsh uner hghly storte utlty conton. The MSRF-PLL uses an algorthm whch s base upon the prncple of Coulon oscllator [. Block agram of the Coulon oscllator s shown n Fg. 4, where the nput sgnal ( t s harmoncally rch, an s gven by ( t = A sn( ω t φ Where s the harmonc orer, A (9 s the harmonc ampltue, an φ I s the phase angle. The Coulon oscllator freuency s efne as f r = ω r /π, whch generates the sn(ωrt an cos(ωrt sgnals. Therefore, after multplcaton wth the sgnal (t, t generates two corresponng sgnals (t an (t respectvely, by = ( t A sn( ω t φ.sn( ωr t = ( t A sn( ω t φ.cos( ωr t Input ( ( E.( & ( can be wrtten as sgnal π sn( ω r t cos( ω r t Oscllator Fg.4 Block Dagram of Coulon Oscllator A r φ r. ( t ( t A {cos[( ω ωr t φ = ( cos[( ω ω t φ } A {sn[( ω ωr t φ = (3 sn[( ω ω t φ } By takng f = ω /π, an ω =ω, ω r = rω ( an r are harmonc orers, E( an (3 can be epresse as ( t ( t A {cos[( r ωt φ = (4 cos[( r ω t φ } A {sn[( r ωt φ = (5 sn[( r ω t φ } In orer to etract the funamental freuency of ( t the oscllator freuency ω shoul be tune to be the same freuency asω,.e., r = =. Therefore, A A ( t = cos( φ cos( ω t φ A {cos[( ω t φ (6 = cos[( ω t φ } ( t = A A sn( φ sn(ω t φ A {sn[( ω t φ = r r sn[( ω t φ } (7 Frst term of the euaton (6 an (7 s the DC component relate to the funamental magntue A an phase angle φ, an the secon term relates to the secon harmonc component, an the remanng terms n the euaton are hgher freuency components. A low-pass flter, flters out the DC component of each sgnal whch are gven as A = cosφ (8

4 A = snφ (9 Therefore, the output of the Coulon oscllator can be erve as A ( = ( ( = tan ( φ ( When the phase of the oscllator conces wth the phase of the funamental component of nput sgnal (t.e., φ =, then =.5A an =. It can be shown that the Coulon oscllator not only flter out the funamental component of the nput sgnal, but also other harmonc components can be fltere out by approprately tunng of the couple oscllator. Fg.5 shows the block agram of the MSRF PLL structure, where sa s the phase A utlty voltage at 5Hz, an, can be epresse as A cosφ A snφ φ = arcsn( an A =.. = ( = = (3 = Where The phase angle φ of the output can be fe back to the oscllator to lock ts freuency an phase so that φ approaches to zero. In ths conton, sn( ω e t an cos( ω e t can be efne as unt phase voltage sa.the avantage of the MSRF-PLL n comparson wth the SRF-base scheme s that t s erve from only one phase voltage, an the unt vector output s not affecte by harmonc storton, unbalance or sag/swell of the utlty voltage. III. FUCTIOAL STRUCTURE OF SAPF The complete control structure of SAPF s shown n Fg.6. The -as loa current when hgh pass fltere (DC alone remove wll gve the harmonc content of the loa current, an the -as loa current gves the reactve content of the loa current. The outputs of the an as current controllers are ae to the nverter an -as currents respectvely to get current references reure for generaton of the gatng pulses, The output of the voltage controller represents the actve current reurement of the actve power flter to compensate for the varous losses. sa X sn( ω t cos( ω t e e Lock uptable FC = samples = Hz samples ( Φ Fg.5 Block agram of the MSRF PLL structure X Φ Φ( la lb lc ca cb cc cref c abc cosθ snθ PLL abc abc cosθ snθ cosθ snθ PLL Fg.6 Functonal Structure of SAPF I SIMULATIO RESULTS AD DISCUSSIOS refa refb refc The performance of the SAPF wth fferent PLL structure such as a Transformaton Angle Detector, SRF-PLL an Mofe SRF (MSRF-PLL s evaluate through MATLAB programmng n orer to moel an test the system. To verfy the SAPF wth fferent PLL structures, the parameter values consere here are; Lne to lne source voltage (, 5 Hz, Source mpeance of R S an L S (. Ω an.5 mh, the Flter mpeance of R c an L c (. Ω an.7 mh; Loa mpeance of R L an L L (Ω an mh, DC se capactance C DC ( µf.the power evces are bult by IGBT wth ant parallel oes. The smulaton s eecute uner steay state usng oe rectfer wth RL loa. The smulaton results for loa current, compensatng current, capactor voltage, an source current waveforms at low storton (.8% of lne voltage are shown n Fg.7. From Table I, t s shown that the performances of all three PLL structures (TAD, SRF-PLL, an MSRF-PLL are nearly same as a low storton conton of supply voltage. Fg. 8 shows the source current waveforms, whch are n phase wth the source voltage for the above PLL structures n meum storton (7.99% conton, but MSRF-PLL gves slghtly better performance accorng to THD% calculaton. The source current waveforms along wth ther spectrums for TAD,SRF-PLL an MSRF-PLL methos n hgh storton (9.99%conton of supply voltage are shown n Fg.9, an respectvely. Table I shows that MSRF-PLL (THD-.9% s foun to be much better than the other two methos. (A

5 (a (b SOURCE CURRET SOURCE OLTAGE (A OLTAGE( (b (c (c Fg.8 Source current & source voltage waveforms after compensaton for (a TAD, (b SRF-PLL an (c MSRF-PLL methos wth meum storton conton. - SOURCE CURRET SOURCE OLTAGE 5 SOURCE CURRET SOURCE OLTAGE TIME(s (a Ampltue ( Fg.7(aLoa current,(bcompensatng current,(c Capactor voltage,(source voltage & source current waveforms after compensaton for low storton conton. 5 SOURCE CURRET SOURCE OLTAGE Harmoncs (b Fg.9(a Source current & source voltage waveform, (b Source current spectrum after compensaton for TAD metho wth hgh storton conton. 5 SOURCE CURRET SOURCE OLTAGE (a ( a 5 SOURCE CURRET SOURCE OLTAGE Ampltue Harmoncs (b

6 Fg. (a Source current & source voltage waveform, (b Source current spectrum after compensaton for SRF-PLL metho wth hgh storton conton. Ampltue AM PLITUDE - SOURCE CURRET SOURCE OLTAGE TIME(s (a Harmoncs (b Fg. (a Source current & source voltage waveform, (b Source current spectrum after compensaton for MSRF-PLL metho wth hgh storton conton. Source oltage (THD% ΤΑΒLE I (THD% COMPARISO OF PLL METHODS Synchronzaton Metho Source Current Before Compensaton (THD% Source Current After Compensaton (THD% TAD SRF-PLL MSRF-PLL TAD SRF-PLL MSRF-PLL TAD SRF-PLL MSRF-PLL COCLUSIOS Harmonc current compensaton for SAPF has been performe usng TAD, SRF-PLL an MSRF-PLL base synchronzaton methos.three fferent storte contons (.88, 7.99 an9.99% THD of supply voltage have been consere for comparatve analyss of the above mentone PLL structures. From the smulaton results, t s foun that the MSRF- PLL acheves better performance as compare to other two stanar PLL technues on the bass of THD% (total harmonc storton. The superorty of MSRF-PLL s prove n all three storte contons of lne voltage. The MSRF- PLL s fast n transent response an robust aganst sturbances on the gr voltage wave. REFERECES [ J. Svensson, Synchronzaton methos for gr-connecte voltage source converters, n Proc. Inst. Elect. Eng. Generaton, Transmsson, Dstrbuton, vol. 48, May, pp [ Gary W. Chang, A novel reference compensaton current strategy for shunt actve power flter control, IEEE Trans. power elvery, vol. 9, no.4, pp , Oct. 4. [3 Hlmy Awa, Operaton of statc seres compensator uner storte utlty contons, IEEE Trans. power systems, vol., no., pp , Feb. 5. [4 Chrstoph Meyer, Optmze control strategy for a meumvoltage DR theoretcal nvestgatons an epermental results, IEEE Trans. Power Electron, vol. 3, no.6, pp , ov. 8. [5. Kaura an. Blasko, "Operaton of a phase locke loop system uner storte utlty contons," IEEE trans. on Inustry Applcatons, ol.33, no., pp , 997. [6 R. F. e Camargo an H. Pnhero, Synchronsaton metho for Three-phase PWM converters uner unbalance an storte gr, Electrc Power Applcatons,IEEE Proceengs -, vol. 53, no. 5, pp , Sep. 6. [7 Carlos Henrue a Slva, A gtal PLL scheme for three- Phase system usng mofe synchronous reference frame, IEEE Trans. In. Electron., vol. 57, no., pp , ov.. [8 Masou Karm, A Metho for Synchronzaton of Power Electronc Converters n Pollute an arable- Freuency Envronments, IEEE Trans. Power Syst.,vol.9,no.3,pp.63-7,Aug.4. [9 Carlos Henrue a Slva, DSP Implementaton of Three- Phase PLL usng Mofe Synchronous Reference Frame, n IEEE nustral electroncs socety,pp.697-7,ov.7. [ S. Tnan, M. Mazauer, A. Berthon, an S. Dop, Comparson between fferent real-tme harmonc analyss methos for control of electrcal machnes, n Proc. PED, 994, pp