16th NATIONAL POWER SYSTEMS CONFERENCE, 15th-17th DECEMBER, 2010 453 Sclab/Sccos Modelng, Smulaton and PC Based Implementaton of Closed Loop Speed Control of VSI Fed Inducton Motor Dre Vjay Babu Korebona, Student Member, IEEE Department of Electrcal and Electroncs Engneerng, B. M. S. College of Engneerng, Bangalore, INDIA jaybabukorebona@gmal.com Shankar J Magajkond, Raju A B, Member, IEEE Department of Electrcal and Electroncs Engneerng, B. V. B. College of Engneerng and Technology, Hubl, INDIA shankar_jm06@yahoo.co.n, abraju@bb.edu Abstract Modelng, smulaton and mplementaton of Voltage Source Inerter (VSI) fed closed loop speed control of 3-phase nducton motor e s presented n ths paper. A mathematcal model of the e system s deeloped and s used for the smulaton study. Smulaton s carred out usng Sclab/Sccos, whch s free and open source software. The aboe sad e system s mplemented n laboratory usng a PC and an add-on card. In ths study the ar gap flux of the machne s kept constant by mantanng Volt/Hertz (/f) rato constant. The expermental transent responses of the e system obtaned for change n speed under no load as well as under load condtons are presented. expermental results are presented n secton V and are compared wth that of smulaton results. II. DRIVE SYSTEM CONFIGURATION Keywor- Inducton motor, Mathematcal model, Smulaton, V/f Control, VSI. I I. INTRODUCTION NDUCTION machne s the most wdely used motor n ndustry because of ts hgh robustness, relablty, low cost, hgh effcency and good self-startng capablty. In spte of ths popularty, the nducton motor has two nherent lmtatons. They are () the standard motor s not a true constant-speed machne, ts full-load slp ares from less than 1% (n hgh hp motors) to more than 5% (n fractonal-hp motors). () It s not nherently capable of prodng arable-speed operaton. These lmtatons can be soled through the use of adjustable speed controllers. The basc acton noled n adjustable speed control of nducton motor s to apply a arable oltage magntude arable frequency to the motor so as to obtan arable speed operaton. Both the oltage source nerter and current source nerters are used n adjustable speed ac es [1, 2]. In ths study, VSI fed 3-phase nducton motor e system wth constant /f control method s modeled, smulated and s mplemented usng PC and an add-on card, as ths method prodes good runnng and transent performance [3]. The closed loop speed control of VSI fed nducton motor e system s descrbed n secton II. Secton III descrbes the modelng, smulaton model deeloped and smulaton results of the e system usng Sclab/Sccos. Secton IV descrbes the mplementaton of the e system usng PC and an add-on card. The Fgure 1. Dre system confguraton Fgure 2. Block dagram of closed loop /f control Fg. 1 shows the oerall e system whch conssts of 3-phase nducton motor, conerter and controller. The ac oltage from the supply system s rectfed usng 1-phase dode rectfer and s gen as nput to the 3-phase VSI. The output of nerter s feedng the nducton motor. Block dagram of the e system confguraton s shown n Fg. 2. The actual speed of the nducton motor s sensed and s compared wth the reference speed. The error so obtaned s processed n a Proportonal Integral (PI) controller and ts output sets the nerter frequency as well as the modulaton
16th NATIONAL POWER SYSTEMS CONFERENCE, 15th-17th DECEMBER, 2010 454 ndex. The slp regulator sets the slp speed command ω sl, whose maxmum alue s lmted to lmt the nerter current to a permssble alue. The synchronous speed, obtaned by addng actual speed ω f and the slp speed ω sl, determnes the nerter frequency. The reference sgnal for the closed-loop control of the machne termnal oltage V s s generated from frequency f. A step ncrease/decrease n a speed command ω r produces a poste/negete speed error. The slp speed command ω sl, s set at the maxmum alue. The e accelerates/ decelerates at the maxmum permssble nerter current, producng the maxmum aalable torque, untl the speed error s reduced to a small alue. The e fnally settles at a slp speed for whch the motor torque balances the load torque. III. MODELING AND SIMULATION OF DRIVE SYSTEM Mathematcal modelng of system In order to smulate the e system usng Sclab/Sccos, t s requred to model the arous components of the system n terms of ther mathematcal equatons. A. Inducton Motor Model Based on the appled stator oltage and flux lnkages the mathematcal model of the squrrel cage nducton motor n the statonary reference usng standard nomenclature as gen n [2]: (1) an L d a ( ) / cn bn (( 1/ Lm ) (1 ) (1/ Llt L ad 1/ L ad Laq L ad / dt ( Rs )( ) 3 (2) (3) (4) (5) (6) B. Modelng of Inerter The nerter output phase oltages and correspondng phase currents are obtaned by the followng equatons: Three phase nerter output oltages are gen by 2 ) / 3 (16) an bn cn Three phase nerter output currents are gen by C. Modelng Of Controller (17) (18) (19) (20) (21) The controller used s a PI controller. The error n speed s fed to PI controller as nput, t generates the slp command ω sl. The workng of PI controller s based on the followng equaton. t y( t) k e( t) k e( (21) PI controller n dscrete form s gen by (22) Where k p and k are proportonal and ntegral gan constants. D. V/f characterstcs b c ( ao bo co ( 2bo co ao) / 3 ( 2co ao bo) /3 a ( 1/ 2) ( 3 / 2) ( 1/ 2) ( 3 / 2) y( k p p error( k V/f characterstcs play a promnent role n /f control mechansm of speed control of nducton motor. It prodes a relatonshp between oltage and frequency as shown n Fg. 3. From the fgure we obsere that upto base frequency the /f rato s mantaned constant and aboe base speed oltage s kept constant. k 0 k n0 error( n) d / dt ( Rs )( ) d / dt ( R / L )( ) s s lr d / dt ( R / L )( ) lr r r (7) (8) (9) L ad (( ) ( / Llr (10) L ( ) / L aq (( ) ( / Llr ( ) / L ls te ( 3P / 4)( ) 1 p t e tl br dt J 2 ls (11) (12) (13) (14) (15) E. Sclab/Sccos Smulaton Fgure 3. V/f characterstcs Sclab s a freely dstrbuted and open-source software package prodng a powerful computng enronment for engneerng and scentfc applcatons. Matlab beng a commercally expense smulatng tool, Sclab s ganng mportance n research centers, educatonal nsttutes and ndustres. Sclab can be downloaded from
16th NATIONAL POWER SYSTEMS CONFERENCE, 15th-17th DECEMBER, 2010 455 http://www.sclab.org/products/sclab/download. Sclab conssts of Sccos toolbox whch prodes block dagram edtor for constructng smulaton models. Sccos s renamed as Xcos n ersons aboe 5.1.1. Models deeloped by Matlab/Smulnk can be reasonably modeled n Sclab/Sccos by moderate addtonal effort [4, 5]. The smulaton model of closed loop speed control s as shown Fg. 4 [6]. F. Smulaton Results The nducton motor parameters whch are lsted n Appendx are determned expermentally usng no-load and blocked rotor tests. These parameters are used n Sclab to determne /f characterstcs for frequences zero to base frequency.e. rated frequency. Fg 5 shows the smulated /f characterstcs. 800 rpm and then from 800 rpm to 1000 rpm at no load condton. Here, error s maxmum at start, then PI controller corrects the error and the motor pcks up the speed equal to new set speed. Fg. 9 shows the e response obtaned for closed loop system when the load torque on the motor s changed from zero to 1 Nm, durng ts runnng condton at 1000 rpm reference speed. Here, ntally speed ops when load s appled then the error n change of speed s controlled by PI controller and makes the motor to run agan at the set reference speed. Fgure 6. Speed response under no load condton Fgure 5. Smulated /f characterstcs. Fg. 6. Shows the speed response under no load condton, where the speed of nducton motor attans the set reference speed 1000 rpm from 0 rpm, t can be obsered that the error nput to the PI controller reaches 0 rpm from maxmum error 1000 rpm as can be seen n Fg. 7. As the error decreases, the speed of the machne bul up. Fg. 8. shows change n the speed wth respect to tme when reference speed s changed from 0 rpm to Fgure 7. Error ersus tme under no load condton Fgure 4. Smulaton model of e system
16th NATIONAL POWER SYSTEMS CONFERENCE, 15th-17th DECEMBER, 2010 456 Fgure 8. Speed response for step change n speed Fgure 10. PC based closed loop mplementaton Start Intalze the reference speed (ω ref ) Actual speed s sensed (ω) ADC Conerson IV. Fgure 9. Speed response for step change n load IMPLEMENTATION OF CLOSED LOOP SPEED CONTROL OF VSI FED INDUCTION MOTOR DRIVE The ac oltage from the supply system s rectfed and s gen to three phase oltage source nerter as nput whch fee nducton motor. The speed of the motor s sensed. The reference speed s set as ω ref and then the error between the requred speed and the actual speed s calculated. Ths error s processed by a PI controller and ts output ges the correcton whch wll mnmze the error. A. Implementaton The aboe mentoned closed loop control system s mplemented n laboratory usng a PC and ts add-on card. PC wth an nexpense add-on card offers the adantages of flexblty and conenent dsk storage of data and programs [7]. Add on card conssts of analog to dgtal conerson (12-bt 16 channels), dgtal to analog conerson (12-bt 2 channels) and dgtal nput output (12 lnes). Oerall closed loop block dagram s as shown n Fg 10.The requred speed s entered as one of the nput to the computer. The motor speed s sensed by optcal speed sensor, whose output s gen to the F to V conerter. Ths sgnal s fed to one of the ADC channel where t s conerted nto dgtal form and s taken as another nput to the computer [8]. A C program s deeloped to mplement the closed loop control of the e. Fg 11 shows the flowchart of algorthm. The expermental setup of the e system s as shown n Fg. 12. Error = ω ref - ω Proportonal Integral (PI) Controller DAC Conerson To Inerter Control termnal Fgure 11. Flowchart of controller program. Fgure 12. Expermental setup of closed loop VSI fed nducton motor e
16th NATIONAL POWER SYSTEMS CONFERENCE, 15th-17th DECEMBER, 2010 457 B. ExpermantalResults Fg. 13. Shows the speed response under no load condton wth reference speed as 1000 rpm. Fg. 14. Shows the error response under no load condton Fg. 15. Varaton of speed wth respect to tme under no load condton. The reference speed s changed from 0 to 1000 rpm and then rased from 1000 to 1200 rpm. Fg. 16. shows the speed araton wth respect to tme under loaded condton. Intally the motor s runnng at 1000 rpm under no-load condton. The machne s loaded after 187 secon. From fgure t can be seen that, at the nstant of loadng, the actual speed of machne ops slghtly, but then retans set speed of 1000 rpm wthn 3 secon. Fgure 13. Speed erses tme under no load condton Fgure 16. Speed response for step change n load V. CONCLUSION The smulaton of a VSI fed closed loop /f method of speed control of an nducton motor s studed and the same s mplemented n laboratory usng PC and an add-on card. The smulaton results show that the arable oltage arable frequency control allows nducton motor e wth good runnng and transent performance. Also t s obsered that the araton n the speed of nducton motor wth change n load torque s reduced wth the help of closed loop control. The mplementaton of the same usng PC and an add-on card results show that the C program deeloped to carry out the functon of speed control of the system, contnuously montors the actual speed and changes the control oltage n such a way as to make the motor speed and reference speed same. APPENDIX Inducton motor specfcatons and parametrs at rated frequency: 1 HP, 415 ±10% V, 1.7 A,50±5% Hz, 1410 rpm. R 1 =12.38 Ω, R 2 =15.3 Ω, X 1 =X 2 =6.48 Ω, X m =0.299-j1.227 Ω Fgure 14. Error response under no load condton Fgure 15. Speed response for step change n speed ACKNOWLEDGEMENT The authors would lke to thank Prncpal and Head of Electrcal and Electroncs Engneerng Department, B. V. B. College of Engneerng and Technology, Hubl for the necessary faclty proded. REFERENCES [1] A. E. Ftzgerald, Charles Kngley, Jr, Stephen D. Umans, Electrc Machnery. 5th Edn. McGraw-Hll. 1990. [2] P. C. Krause, Analyss of Electrc Machnery, McGraw-Hll, 1986. [3] G. K. Dubey, Fundamentals of Electrc Dres, Narosa publshng House, New Delh, 2002. [4] Lao Wenjang, Dong Nanpng and Fan Tongshun, The Applcaton of sccos for automatc Control Theory, OCSC 2009, IEEE. [5] Paolno Tona, Teachng Process Control wth Sclab and Sccos, Proceedngs of the Amercan Control Conference, Mnneapols, Mnnesota, USA, June 14-16, 2006. [6] Sclab/Sccos manual. http://www.sclab.org/download/5.2.2/manual_sclab.2.2_en_us.pdf [7] Thura Vnay, Computer Aded Laboratory n Dgtal Control 1996, IEEE. [8]Adanced Electronc Systems (ALS) PCI add-on Card Manual.