POWER QUALITY IMPROVEMENT USING SELF-TUNING PI CONTROLLED STATCOM BY PARTICLE SWARM OPTIMIZATION

Transcription

1 Internatonal Journal of Power Control Sgnal an Computaton (IJPCSC) Vol. 4 No. Aprl- June - gopalax journals,sngapore ISSN:976-68X Avalale at : POWER QUALITY IMPROVEMENT USING SELF-TUNING PI CONTROLLED STATCOM BY PARTICLE SWARM OPTIMIZATION K.PARVENTHAN Department of Electrcal an Electronc Engneerng Dr Pauls Engneerng College Vllupurum Dst, Taml nau, Ina raja_737@yahoo.com Astract In recent years, there has een an ncreasng nterest on applyng avance an ntellgent control esgns n power engneerng area. As a heurstc optmzaton technque, Partcle Swarm Optmzaton (PSO) s use for tunng the parameters of the STATCOM. Regulatng the DC capactor voltage n STATCOM s a common task an can mprove the system ynamc. The nonlnear control s ase on exact lnearzaton va feeack. A PI controller exsts n ths control system to regulate the capactor voltage. In conventonal heme, the tral an error metho has een use to etermne PI controller coeffcents. In ths project, the effect of PI gans on responses of V, I an Moulaton Inex (M) s presente. The exact calculaton of optmze PI coeffcents can e carre out to reuce sturances an steay state error n DC lnk voltage. An effcent formula for the estmaton of system loa mpeance usng real-tme measurements s erve. Base on the estmate system loa, a PSO algorthm, whch takes the est partcle gans, the est gloal gans, an prevous change of gans nto account, s employe to reach the esre controller gans. To emonstrate the effectveness of the propose PSO self-tunng PI controller for a STATCOM, expermental results for a system uner fferent loang contons are presente. Results from the self-tunng PI controller are compare wth those from the fxe-gan PI controllers. Keywors- STATCOM, FACTS, self-tunng PI controller, Partcle swarm optmzaton, Voltage Source Converter MATLAB / SIMULINK I. INTRODUCTION Recent evelopments n power electroncs play a major role n the accomplshment of more effcent power systems. The man reason for that s the alty of power electronc evces to control M.BALAMURUGAN Department of Electrcal an Electronc Engneerng Dr Pauls Engneerng College Vllupurum Dst, Taml Nau, Ina alasngar.m@gmal.com power flow n transmsson lnes. The technology of flexle AC transmsson systems, whch are ase on power electroncs, s Flexle AC Transmsson Systems (FACTS) have ecome very mportant applcatons of power electroncs n controllng power flow avancng an t has fferent applcatons n power control. They were the soluton to the ffcultes that were arsng wth the geographcally uneven growng power eman. FACTS met the transmsson system rurement to use the exstng power facltes wthout ecreasng system avalalty an securty. In aton, the use of FACTS proves voltage support to prevent voltage collapses when the electrcty network s uner heavy loang. The man ojectves of FACTS are to ncrease transmsson capacty of lnes an to control the power flow over chosen transmsson routes []. FACTS offer the posslty of meetng many recent power emans. FACTS evces are routnely employe n orer to enhance the power transfer capalty of the otherwse unerutlze parts of the nterconnecte network [].FACTS coul e connecte n seres wth the power system Workng as a controllale voltage source or n shunt wth the power system workng as a controllale current source. The STATc synchronous COMpensator (STATCOM) s a shunt FACTS evce an t was ntrouce an evelope n the last ecae. It s use to regulate voltage values at fferent ponts n the transmsson lnes. In the lterature, ecouple control of - an q-axs currents an voltages has een propose to regulate the capactor voltage an the ac system (loa) voltage, respectvely, n STATCOM controller esgn [3] [6]. Proportonal-ntegral (PI) controllers have een esgne for the ac system voltage regulator, the voltage regulator, an the current regulators. Satsfactory ynamc responses have een reporte for the STATCOM wth PI controllers. 76

2 Internatonal Journal of Power Control Sgnal an Computaton (IJPCSC) Vol. 4 No. Aprl- June - gopalax journals,sngapore ISSN:976-68X Avalale at : In the fxe-gan PI controller [3] [6], the controller gans for the STATCOM were usually esgne ase on a Lnearze system uaton for the system uner a nomnal loa conton [3] [6]. These controller gans remane fxe n aly operaton of the STATCOM. Snce system loa changes wth tme n aly operaton of the STATCOM, the system matrx, the close-loop Egen values, an the ynamc performance wll change. Therefore, to mantan goo ynamc responses at all possle loang contons, the controller gans nee to e aapte. II POWER SYSTEM CONFIGURATION WITH STATCOM Fgure shows the confguraton of the system wth STATCOM connecte n loa us. A three phase non lnear loa (a rectfer wth resstor) s connecte n loa us. Where Rp represents the ON state resstance the swtches whch are n Voltage Source Inverter nclung couplng transformer leakage resstance, L p represents the couplng transformer leakage nuctance. A Voltage Source Inverter s the core element of the STATCOM.t generates a alance an controlle three phase voltage V p. RsjωLs represents the source mpeance whereas RtjωLt represents the lne mpeance. system are then erve. When the ynamc uatons for the system are Lnearze aroun a nomnal loang conton, we can procee to esgn a fxegan PI controller for the STATCOM usng the Lnearze state uatons. Then, a self-tunng PI controller for the STATCOM s esgne usng the PSO metho III SYSTEM MODEL A. Loa Moel As shown n Fg., the three-phase loa voltages n ac coornates can e wrtten as Vla la la () Vl Rl l l t V lc lc lc where alance three-phase loas are assume (R la R l R lc R l an L la L l L lc L l ). By usng the wellknown Park transformaton π π cosθ cos θ cos θ 3 3 π π T snθ sn θ sn θ () Equaton () can e transforme to the synchronously rotatng reference frame as Vl l follows l ω Rl Vlq lq t lq ω Note that θ tan - (V lq /V l ) an V l s neglecte n (3)snce the system s assume to e alance. Snce the angle θ s calrate y the PLL at each cycle, the error wll not e accumulate. When l s replace y the sum of the source current s an nverter current e, we have V V l lq Rl s slq Rl e t s t e ω ω Fgure : Confguraton of the system wth a STATCOM ω ω s ω ω e (4) The contents of ths paper are as follows. Frst, the confguraton of the system wth a STATCOM s ere. The ynamc uatons for the loa, the VSC ac-se system, an the VSI -se 77

3 B. VSI AC-Se Moel When the loa current l n Fg. s replace y s e, the source voltage V S an nverter output voltage e can e Wrtten as V V V sa s a sa s ea a e e c sa s t t Internatonal Journal of Power Control Sgnal an Computaton (IJPCSC) Vol. 4 No. Aprl- June - gopalax journals,sngapore ISSN:976-68X Avalale at : IV. DESIGN OF FIXED-GAIN PI CONTROLLER FOR STATCOM ea ea ea c e e e L l ec ec ec (5) sa ea V sa c s e Vs L l ec V (6) Transformng (5) an (6) to the synchronous reference frame an rearrangng, we have t s e ω L a ω a ω ω a c c Where vs s the rms value of vsa. c ω s e V s e C. VSI DC-Se Moel The power alance uaton of the VSI se an ac se s expresse as [5] 3 V e e (8) ( ) e q In aton, the ynamc uaton for V can e erve from a current alancng formula as follows: V (9) V t R c C From (8), the current n (9) can e expresse n terms of the state varales V, e, an as follows: ( e e ) 3 e () q V Fgure.. Fxe-gan PI controller for STATCOM Wth the ynamc moel for the system at han, we can procee to esgn a fxe-gan PI controller for the STATCOM n orer to regulate a loa us voltage uner sturance contons. Fg. shows the lock agram for the fxe-gan PI controller for the STATCOM. It s oserve from Fg. that the STATCOM controller s compose of four fxe-gan PI controllers: the -axs current regulator, the q-axs current regulator, the voltage regulator, an the ac voltage regulator. The prmary functon of the - an q-axs current regulators s to regulate the - an q- axs nverter currents e an to the esre values * e an * y ajustng the nverter output voltages e an. The esre MI an angle α can e compute from these nverter output voltages e an e q, as shown n the fgure. Note that the -axs s algne to the loa voltage vl n the PI controller esgn process, whle the -axs for solvng the VSI ac-se uatons n (7) s algne to the source voltage vs. As a result, the compute phase angle α must e augmente y the phase angle fference etween vs an vl,.e., θ, efore t s sent to the PWM generator to generate the swtchng pulses for the nverter swtches n orer to have correct phases for the nverter output ac voltages e a, e, an e c. The voltage v for the capactor s regulate to the esre value v y the voltage regulator. On the other han, the loa voltage v l s kept at the esre value vl y the ac voltage regulator. Detals on the esgn of the four regulators have een ere n [] []. It has een foun n [] [] that, as far as the ynamc performance for loa us voltage regulaton uner sturance contons s concerne, the controller gans for the ac voltage regulator,.e., KP an KI, play a more mportant role than those for the other three regulators. As a result, only the esgn of the controller gans for the ac voltage regulator s usse n ths 78

4 Internatonal Journal of Power Control Sgnal an Computaton (IJPCSC) Vol. 4 No. Aprl- June - gopalax journals,sngapore ISSN:976-68X Avalale at : paper. To etermne proper gans for the PI controllers, the nonlnear ynamc uatons () an (3) for the system are Lnearze aroun a nomnal loang conton, an the resultng Lnearze state uaton s gven y. X ( t) AX ( t) BU ( t) where X(t) [ s e ] T s the state vector an U(t) [e e q ] T s the control vector. In ths paper, heavy loa conton s chosen as the nomnal operatng conton. V DESIGN OF SELF-TUNING STATCOM CONTROLLER Fgure. 3. Block agram of the propose PSO self-tunng STATCOM controller. In the esgn of the fxe-gan STATCOM controller n the prevous secton, the PI controller gans KP an KI have een etermne ase on a partcular loang conton (heavy loa conton n ths paper), an these gans are fxe n aly operaton of the STATCOM. Snce these controller gans have een esgne to gve goo ynamc responses for that partcular loang conton, t may happen that unsatsfactory responses are oserve as loa changes wth tme. Thus, t s esrale to ajust the PI controller gans when there s a sgnfcant change n system loa. In ths paper, the PI controller gans KP an KI are ajuste y the ANN self-tunng controller as shown n Fg. 4. general prncples for the PSO algorthm are state as follows. Suppose that the search space s n mensonal, an then the th partcle can e represente y a n-mensonal vector, X [ X, X,..,X n ] an velocty s V [ V, V,..V n ] Where,,..., N an N s the sze of populaton. In PSO, partcle rememers the est poston t vste so far, referre to as P I [P, p,..p n ] T An the est poston of the est partcle n the swarm s referre as G [g,g, g n ] T Each partcle ajusts ts poston n next teratont Where ω (t ) s nerta coeffcent whch graually ecreases from at frst teraton to a small magntue aout zero on a straght lne. χ s constrcton factor whch s use to lmt velocty. c an c enote the cogntve an socal parameters respectvely. r an r ranom real numers rawn from unformly strute nterval [,]. The nerta coeffcent n () s employe to manpulate the mpact of the prevous hstory of veloctes on the current velocty. Therefore, ω (t ) resolves the traeoff etween the gloal an local exploraton alty of the swarm. A large nerta coeffcent encourages gloal exploraton whle small one promotes local exploraton. Expermental results suggest that t s preferale to ntalze t to a large value, gvng prorty to gloal exploraton of search space, an graually ecreasng as to otan refne soluton. VII. DESIGN OF SELF-TUNING STATCOM CONTROLLER USING PSO VI. PARTICLE SWARM OPTIMIZATION (PSO) Optmzaton methos often etect optma n ffcult optmzaton prolems faster that tratonal methos []. One of the most powerful swarm ntellgence-ase optmzaton methos, name PSO, was ntrouce y Kenney an Eerhart The Fgure. 5Desgn of self-tunng statcom controller usng pso 79

5 Internatonal Journal of Power Control Sgnal an Computaton (IJPCSC) Vol. 4 No. Aprl- June - gopalax journals,sngapore ISSN:976-68X Avalale at : The proceures followe y the propose PSO self-tunng STATCOM controller to ajust the PI controller gans are summarze n Fg. 4. Detals for these proceures are ere as follows. Determne Stale Regons for PI Controller Gans KP an KI : In the esgn of the self-tunng PI controller for the STATCOM, t s essental for the system to reman stale when the PI controller gans are aapte y the PSO algorthm. Therefore, the stale regons for the PI controller gans KP an KI must e frst etermne. Ths s one y computng the Egen values of the lnearze state uaton () for all possle comnatons of KP an KI. The results are shown n Fg. 5 where the stale regons are epcte for the system wth heavy loa, meum loa, an lght loa, respectvely. Measure Loa Voltage vl an Current l: The three phase loa voltages vla(t), vl(t), an vlc(t) an currents la(t), l(t), an lc(t) are measure wth a samplng pero of /536 s, whch s uvalent to 56 samples per cycle for a 6-Hz system. The analog sgnals fetche y the Hall sensors are frst converte to gtal sgnals through a multchannel ata acquston car, as shown n Fg., efore they are sent to the gtal computer. Estmate Loa Impeance: To estmate the uvalent loa resstance Rl an nuctance, the measure three phase loa voltages vla(t), vl(t), an vlc(t) an currents la(t), l(t), an lc(t) are frst transforme to - an q-axs components vl, vlq, l, an lq usng the transformaton matrx T n (). Then,the esre values for Rl an can e erve from (3), anthe results are gven as follows: Step ) Determne ntal partcle postons K() P, veloctes V () P, an weght w(). As shown n Fg. 6, the PSO algorthm egns wth the selecton of ntal postons K() P, ntal veloctes V () P (P,..., ) for the ten partcles, an weght w().5 at teraton. In ths paper, ten partcles were use for each teraton, an a total of teratons were execute y the PSO algorthm. Note that the numer of partcles an numer of teratons were selecte such that satsfactory gans coul e acheve n a short pero. The ntal postons (controller gans) K()P [K() PPK() IP ]T were selecte ranomly wthn the stale regons for PI controller gans. On the other han, the ntal veloctes (controller gan ncrements) V()P [ΔK()PPΔK()IP]T were selecte ranomly etween an. Step ) Determne the est partcle postons Pest KP(pest) an the est gloal poston gest K(gest) for ntal partcle postons K() P. The performance of the system wth the PI controller gans KP an KI can e ere y the evaluaton Functon E. Note that the ntegral of asolute error (IAE) n loa us voltage vl has een employe as the evaluaton functon. It has een mentone that a controller wth mnmum IAE wll result n a response wth relatvely small overshoot an short rsng tme. Thus, satsfactory stalty, as well as fast response, can e acheve y the propose controller esgne usng IAE crteron. Step 3) Upate partcle veloctes V()P,postons K()P,an weght w(). For a partcle P at teraton, ts poston K()P [K()PPK()IP]T an velocty V () P [ΔK () PPΔK () IP] T Check f There Is a Sgnfcant Change n R l an L ll : When there s no sgnfcant change n system loa, t s not necessary to upate the PI controller gans KPesre an KIesre. These controller gans are upate when there s a change of more than % n system loa mpeance Z l R l jωl l. Upate Kesre [KPesre KIesre]T usng the PSO Algorthm: When there s a sgnfcant change n the system loa, the followng steps are followe to upate the PI controller gans KPesre an KIesre. Fgure. 7. Flowchart for the proceures of ajustng PI controller gans y the PSO selftunng STATCOM controller. 8

6 Internatonal Journal of Power Control Sgnal an Computaton (IJPCSC) Vol. 4 No. Aprl- June - gopalax journals,sngapore ISSN:976-68X Avalale at : IX. CONCLUSIONS A STATCOM moel has een evelope wth all the necessary components an controllers n orer to emonstrate ts effectveness n mantanng smple an fast voltage regulaton at any pont n the transmsson lne. The values of the DC lnk capactor an attery source were optmze usng the PSO an the smulatons results were compare wth that of the system wthout compensaton an wth STATCOM, uner oth optmze an un-optmze contons. The comparson of voltage compensaton for nuctve as well as capactve loa contons show that the performance of STATCOM tune wth PSO was the est an closest to the nomnal value of voltage of per un REFERENCES. L. Gyugy, "Dynamc compensaton of ac transmsson lnes y solstate synchronous voltage sources," IEEE Trans. On Power Delvery, vol. 9, No., pp 94-9, Aprl 994. ]T. An, M.T. Powell, H.L. Thanawala an N. Jenkns, "Assessment of two fferent STATCOM confguratons for FACTS applcaton," n Power Systems, Staffor, Englan, UK: IEEE 3. Schauer an H. Mehta, Vector analyss an control of avance statc VAR compensators, Proc. Inst. Elect. Eng. C, vol. 4, no. 4, pp , Jul G. Joos, L. T. Moran, an P. D. Zogas, Performance analyss of a PWM nverter VAR compensator, IEEE Trans. Power Electron., vol. 6, no. 3, pp , Jul ] B. S. Chen an Y. Y. Hsu, A mnmal harmonc controller for a STATCOM, IEEE Trans. In. Electron., vol. 55, no., pp ,Fe S. Chen an Y. Y. Hsu, A mnmal harmonc controller for a STATCOM, IEEE Trans. In. Electron., vol. 55, no., pp ,MFe S. Chen an Y. Y. Hsu, An analytcal approach to harmonc analyss an controller esgn of a STATCOM, IEEE Trans. Power Del., vol., no., pp , Jan T. Chang an Y. Y. Hsu, Desgn of an ANN tune aaptve UPFC supplementary ampng controller for power system ynamc performance enhancement, Electr. Power Syst. Res., vol. 66, no. 3, pp , Sep S. Mohaghegh, Y. el Valle, G. K. Venayagamoorthy, an R. G. Harley, A proportonal-ntegral type aaptve crtc esgn-ase neuro controller for a statc compensator n a multmachne power system, IEEE Trans. In. Electron., vol. 54, no., pp , Fe S. Mohaghegh, R. G. Harley, an G. K. Venayagamoorthy, An aaptve Maman fuzzy logc ase controller for STATCOM n a multmachne power system, n Proc. ISAP, Nov. 5, pp S. Mohaghegh, G. K. Venayagamoorthy, an R. G. Harley, Fully evolvale optmal neurofuzzy controller usng aaptve crtc esgns, IEEE Trans. Fuzzy Syst., vol. 6, no. 6, pp , Dec. 8. ] C. Schauer an H. Mehta, Vector analyss an control of avance statc VAR compensators, Proc. Inst. Elect. Eng. C, vol. 4, no. 4, pp , Jul Schauer an H. Mehta, Vector analyss an control of avance statc VAR compensators, Proc. Inst. Elect. Eng. C, vol. 4, no. 4, pp , Jul S. Chen an Y. Y. Hsu, A mnmal harmonc controller for a STATCOM, IEEE Trans. In. Electron., vol. 55, no., pp , 3. T. Chang an Y. Y. Hsu, Desgn of an ANN tune aaptve UPFC supplementaryampng controller for power system ynamc performanceenhancement, Electr. Power Syst. Res., vol. 66, no. 3, pp ,Sep