SRM control algorithm for electric vehicles drives applications

Transcription

1 Krzysztof TOMCZUK, Marcn PARCHOMIUK Electrotechncal Insttute, Power Converters Department SRM control algorthm for electrc vehcles drves applcatons Abstract. In the artcle author descrbes a measurements of generated torque and flux n SRM for dfferent rotor postons. The measurements are compared wth smulatons results. At the end of the artcle author descrbes a algorthm of realzaton tracton drve characterstc requred by mechancal vehcles. Streszczene. W artykule autor prezentue wynk pomarów momentu oraz strumena elektromagnetycznego dla różnych położeń wrnka. Wynk pomarów porównano z wynkam otrzymanym drogą symulac komputerowych. Przedstawony est także algorytm realzac charakterystyk trakcyne wymagane do napędy poazdów mechancznych. (Algorytm realzac charakterystyk trakcyne wymagane do napędy poazdów mechancznych Keywords: SRM, Swtched reluctance motor, torque, flux Słowa kluczowe: SRM, slnk reluktancyny przełączalny, moment, strumeń Introducton Swtched reluctance motors (SRM belong to a group of motors wth electronc commutaton, where the phenomenon of varable reluctance s used n ther operatons. Because of the absence of rotor wndngs and of a relatvely smple machne phase wndng system they belong to motors wth the lowest producton costs and they are characterzed by hgh durablty, smlar to that of nducton machnes. The SRM have several advantages whch cause that they are deally sutable for use n certan applcatons for drves. These machnes do not have mechancal commutator, that s there are not any problems related to commutator operaton. They can be operated n explosve envronments and n conons of hgh dustness, wthout any specal casng. In case of any damage to one wndng, ther operaton can be contnued at a reduced load whch consttutes an essental advantage for fans and pumps. The SRM do not have permanent magnets or rotor wndngs whch permts the machnes to operated at much hgher temperatures, and permts the machne to be desgned wth reduced dmensons. A drve wth a reluctance motor (SRM and converter has hgher effcency [6] than one realzed usng an nducton motor wth converter. It s of basc mportance to mnmze the amount of energy consumpton by vehcles wth electrc drve. Measurements of SRM parameters A 6/4 swtched reluctance motor wth a power of 1kW was used for laboratory tests. Fg. 1 presents a schematc dagram of a swtched reluctance motor wth ndcated method of determnng poston of the rotor and of the wndngs n the motor. The torque was measured by means of a sutable lever, mounted on the rotor shaft. Ths lever permtted a precse control of the rotor poston wth respect to the stator by means of the worm gear used. Fg. presents varatons of the statc electromagnetc torque generated by one phase wndng of the motor wth a blocked rotor. If the machne has to operate n the range of motor operaton the control angles must be set n the range of α = -45, whle n order to work n generator mode the angles must be n the range of α = 45. Fg.. Varatons of the statc electromagnetc torque generated by the SRM wndng Measurements of electromagnetc flux values flowng n the magnetc crcut of the machne s presented In Fg. 3. Calculatons of the flux were made basng on current tme varatons recorded (wth rotor blocked n known poston flowng n the wndng, and on voltages across ts termnals. Fg. 1. Desgnaton of poston angles Fg. 3. Tme varatons of U(t, I(t and adonal curve U(t-RI(t 7 PRZEGLĄD ELEKTROTECHNICZNY (Electrcal Revew, ISSN 33-97, R. 88 NR 1a/1

2 Measurement of the electromagnetc flux value generated by the motor phase wndng was connected wth determnng an adonal curve U(t-RI(t, and by ntegratng t then accordng to Formula (1. t (1 ( t [ U( t R I( t] where: U voltage [V], I - current [A], R wndng resstance [Ω], Ψ - flux [Wb] Measurements of the flux were repeated for other rotor postons. The value of the voltage appled across wndng termnals was selected n such a way that t forced the flow of rated current n the wndng n statonary state. Fg. 6. Grd n the whole cross-secton of the motor Fg. 4. Varatons of the electromagnetc flux Fg. 7. Magnetc flux lnes for the poston α= and current I=1A Fg. 5. Varatons of the electromagnetc flux Fg. 4 shows varatons of the electromagnetc flux as a functon of rotor poston for varous values of the current flowng n the motor phase wndng, whle Fg. 5 presents electromagnetc flux varatons as a functon of the current n the motor phase wndng for dfferent postons of the rotor. The results were ntroduced nto the smulaton (Formulas 3 and 4. Fg. 8. Magnetc flux lnes for the poston α=-.5 and current I=1A Verfcaton of the motor parameters A feld of the motor was elaborated n the programme FEMAG-DC n order to verfy the values of torque and flux. Model of the reluctance motor was made ntroducng the real machne dmensons and the characterstc of magnetc crcut materal. On the bass of feld tests there were determned magnetc flux values and varatons of electromagnetc torque generated n the motor for dfferent rotor postons. The results are shown n Fgs. 11 and 1. Fg. 9. Magnetc flux lnes for the poston α=-45 and current I=1A PRZEGLĄD ELEKTROTECHNICZNY (Electrcal Revew, ISSN 33-97, R. 88 NR 1a/1 71

3 M [Nm] A 8A 6A 4A A Fg. 1. Varatons of the electromagnetc flux determned on the bass of feld tests In the FEMAG-DC programme [Wb] deg + - deg Prąd [A] Fg. 11. Varatons of electromagnetc flux determned on the bass of feld tests In the FEMAG-DC programme [Wb].35 1A α [deg] Mathematcal of SRM Formula ( show the voltage equaton for the SRM phase wndng. ( U R d (, where: U supply voltage, R wndng resstance, Ψ flux, wndng number, α - rotor poston, wndng current The value of electromagnetc flux depends on the rotor poston α and on the value of current n the wndng, thus partal dervatves of the varables appear n Formula (3. d (3 d The voltage equaton for one phase wndng wth partal dervatves s shown by Equaton (4 whch was used n the smulaton programme. d (4 d U R The rotaton speed of rotor was calculated accordng to Formulas (5 and (6. d d d (5 M J D T f sgn TL where: M sum of torques generated by motor phases, J rotor nerta, D frcton, T f frcton, TL external load (6 t where: α rotor poston, ω rotaton speed, α startng poston A 4A 3A A Selected laboratory test results and verfcaton of the mathematcal.5 1A [deg] Fg. 1. Varatons of electromagnetc flux determned on the bass of feld tests In the FEMAG-DC programme Table 1. Comparson between laboratory and feld results Max. values of the torque Max. values of the flux [Nm] [Wb] Current [A] Laboratory (Fg. 1 Feld (Fg. 1 Laboratory (Fg. 4 Feld (Fg Satsfactory convergence of measurement results was obtaned from both s. The obtaned results were used as nput data for the smulaton realzed n the Matlab-Smulnk programme. The results are shown n Table 1. Fg. 13. Characterstcs M=f(n for Uz=3V ; UG=4V ; α on =var ; α off =-1.4 Fg. 13 presents a famly of M=f(n characterstcs for varous current swtchng angles α on and for a constant current swtchng angle α off = The measurements presented were performed on a laboratory of a drve wth a reluctance motor, n order to verfy the mathematcal. Fg. 1 presents selected measurements results of the M=f(n characterstcs obtaned from the laboratory and smulaton. A satsfactory convergence of measurements was obtaned from both s. Thus t can be assumed that the mathematcal s correct. 7 PRZEGLĄD ELEKTROTECHNICZNY (Electrcal Revew, ISSN 33-97, R. 88 NR 1a/1

4 Fg. 14. Comparson of results obtaned from the smulaton wth the measurement for Uz=3V ; UG=4V; α on = -11. ; α off =- 1.4 Fgs. 15a, 15b, 15c presents exemplary test results of the smulaton of the varables of rotatonal speed (rys. 15a, torque rpples (rys. 15b and of the effcency (rys. 15c, at changes of the frng angle α on and of the current conducton angle ( on = α on - α off. The tests were performed for the converter supply voltage Uz=3V, UG=64V, motor load torque TL=4Nm. and a constant power. Durng the controllng wth a constant torque the force appled to the vehcle wheels s constant and t does not depend on speed. The power consumed by the motor ncreases as well as the temperature of wndngs. The moment of gong over from the frst method to the second one s determned by the thermal safety lmt whch should not be exceed, as t can lead to overheatng the motor wndngs. If a further ncrease n the vehcle speed s requred, then the control algorthm shall be changed to another one, n whch the force appled to the vehcle wheels decreases wth rse n the rotaton speed. The power suppled to the motor s then constant and consequently, so s also the wndngs temperature. Fg. 16. Descrpton of the tracton characterstc Fg. 15a. Varablty of the rotaton speed Fg. 15b. Varablty of the torque pulsaton The realzaton algorthm of tracton characterstc was defned on the bass of tests of the smulaton. The results are presented n Table II. Table. Tracton characterstc realzaton algorthm I Speed range [RPM] α on [ ] on [ ] max [A] Torque rpples , , , ,7 > ,5 where: α on frng angle, on conducton angle, I max current lmtatons n motor wndngs The hghest values of the torque generated were acheved when the phase currents were fred at α on = -45 and conducted by the angle on = 45. The current conducton angle shall undergo reducton when the rotaton ncreases. The varaton of the torque shown n Fg. 17 s not mld, there are two local decreases of the torque value for n = RPM and n = 4 RPM. It s related to the fact that the conducton angle on n the algorthm was reduced n steps of 5 (see Table II. Fg. 15c. Varablty of the effcency of the motor wth converter Accordng to the test results t s possble to obtan smultaneously a mnmum of torque pulsaton and maxmum of SRM and converter effcency. It s possble to obtan these parameters for α on = and on = Tracton characterstc realzaton algorthm Two control methods can be dstngushed durng realzaton of the tracton characterstc: at a constant torque Fg. 17. Graphcal nterpretaton of Table II PRZEGLĄD ELEKTROTECHNICZNY (Electrcal Revew, ISSN 33-97, R. 88 NR 1a/1 73

5 If smulaton s performed by steps of 1, then the varaton of torque becomes smooth. At the same tme the number of rotaton speed ranges descrbed In Table II, must be ncreased. Fg. 1. Vew of the converter laboratory Fg. 18. Lmt-wse nterpretaton of Table II n case of the number of control ntervals ncreased by fve tmes wth a reducton step on every 1. C-DUMP Converter A C-DUMP converter was used to supply the laboratory of a swtched reluctance motor wth power suppled from mans of 3V, 5Hz. It permtted the currents n motor wndngs to be swtched on and off n precsely defned postons, determned by the α on and α off angles. Durng swtchng off the currents n wndngs, the energy collected n the magnetc felds L1, L, L3 charges the CG capactor through the D1, D, D3 dodes. The system has the possblty of controllng the UG voltage whch nfluences the speed of the current decay n motor wndngs. Such a capablty of the system s partcularly useful n the range of hgh rotaton speeds (hgh voltage across UG. The value of the UG voltage s controlled by the TG transstor. The control system of the converter had the possblty to control the α on and α off n the range from -45 to 45. The value of UG could be set n the range from 35 Vdc to 1 Vdc. Conclusons The present paper descrbes a method of measurng the torque and the electromagnetc flux n a swtched reluctance motor. The nvestgatons carred out determne the possblty of applyng SRM n electrc and hybrd vehcles. An algorthm of realzaton of a tracton characterstc requred for the drve of mechancal vehcles s presented. Characterstcs of M=f(n for constant α on and α off angles used n smple control algorthms are shown. REFERENCES [1] X. D. Xue, K.W.E.Cheng, J. K. Ln, Z. Zhang, K. F. Luk, T. W. Ng, N. C. Cheung. Optmal Control Method of motorng Operaton for SRM Drves n Electrc Vehcles. IEEE Transactons on Vehcular Technology, vol. 59, No. 3, March 1. [] V. L. Do, M. C. Ta. Modelng, Smulaton and Control of Reluctance Motor Drves for Hgh Speed Operaton. Energy Converson Congress and Exposton. September 1-16, 1. IEEE. [3] P. Krshnamurthy, W. Lu, F. Khorram, A. Keyhan. Robust Force Control of an SRM-Based Electromechancal Brake and Expermental Results. IEEE Transcatons on Control Systems Technology, vol. 17, No. 6, November 9 [4]. W. Jazdzynsk, M. Machrowcz. An Approach to Fnd an Optmum Desgned SRM for Electrc Vehcle Drve. Proceedngs of the 8 Internatonal Conference on Electrcal Machnes [5] Ch. Mademls, I. Koskerds. Smooth Transton between Optmal Control Modes n Swtched Reluctance Motorng and Generatng Operaton. Internatonal Conference on Power Systems Transents (IPST 7 n Lyon, France on June 4-7, 7 [6] P. Andrada, B. Blanqué, J.I. Perat, M. Torrent, E. Martínez, J. A. Sánchez. Comparatve effcency of swtched reluctance and nducton motor drves for slowly varyng loads. Internatonal Conference on Renewable Energy and Power Qualty (ICREPQ 6, Palma de Mallorca, 5, 6, 7 Aprl,6 Fg. 19. Connecton topology of the C-DUMP converter Authors: Ph.D. Krzysztof Tomczuk, Electrotechncal Insttute, Power Converters Department, Pozaryskego Street 8, 4-73 Warsaw, e-mal: k.tomczuk@el.waw.pl M.S. Marcn Parchomuk, Electrotechncal Insttute, Power Converters Department, Pozaryskego Street 8, 4-73 Warsaw, e-mal: m.parchomuk@el.waw.pl Fg.. Vew of the motor wth an electrc dynamometer 74 PRZEGLĄD ELEKTROTECHNICZNY (Electrcal Revew, ISSN 33-97, R. 88 NR 1a/1