An Experimental Estimation of a Rotor Speed MRAS Based on ANN for Sensorless Control of IM

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1 An Expeiental Estiation of a Roto Speed MRAS Based on ANN fo Sensoless Contol of IM Kai Negadi Ibn Khaldoun Univesity, BP 78 iaet, Algeia, aboatoy of Autoatics and Systes Analysis (.A.A.S.), Depatent of Electical Engineeing, E.N.P. Oan BP 53 El M naoue, Oan, Algeia kai.negadi@yahoo.f Abstact In this pape an expeiental evaluation of a novel Model Refeence Adaptive Syste (MRAS) speed obseve fo induction oto dives based on stato cuents is pesented. In this schee the easued stato cuents ae used as the efeence odel fo the MRAS obseve to avoid the use of a pue integato. A two-laye Neual Netwok (NN) stato cuent obseve is used as the adaptive odel which equies the oto flux infoation that can be obtained fo the cuent odel. Speed estiation pefoance of the new MRAS schee is studied and copaed with the classical oto flux MRAS when applied to an indiect vecto contol induction oto dive. Expeiental esults ae shown fo the two schees in the low speed egion of opeation including tests fo the egeneating ode. hese esults copleent the siulation esults pesented fo the poposed schee in a ecent wok. Keywos IM (Induction Moto), MRAS, Sensoless Contol, ANN (Aticial Neual Netwoks). I. INRODUCION Accuate speed infoation is necessay to ealize high pefoance and high-pecision speed contol of an induction oto. he speed is achieved by using echanical sensos such as esolves o pulse encodes. Howeve, these sensos ae usually expensive and bulky. heefoe, the cost and size of the dive systes ae inceased []. Since the late 98s, speed-sensoless contol ethods of induction otos using the estiated speed instead of the easued speed have been studied. hey have estiated the speed fo the instantaneous values of stato voltages and cuents using the induction oto odel. Recently, othe appoaches such as odel efeence adaptive syste (MRAS) ethods, extended Kalan filte algoiths, etc., have been ipleented to achieve oe accuate and obust speed estiation pefoance []. Howeve, an induction oto is a highly coupled, nonlinea dynaic plant, and its paaetes vay with tie and opeating conditions. heefoe, it is vey difficult to obtain good pefoance fo an entie speed ange and tansient states using pevious ethods. Recently, the use of atificial neual netwoks (ANN) to identify and contol nonlinea dynaic systes has been poposed [3, 4] because they can appoxiate a wide ange of nonlinea functions to any desied degee of accuacy. Moeove, they have the advantages of exteely fast paallel Abdellah Mansoui aboatoy of Autoatics and Systes Analysis (.A.A.S.), Depatent of Electical Engineeing, E.N.P. Oan BP 53 El M naoue, Oan, Algeia aansoui@yahoo.f coputation, iunity fo input haonic ipples, and fault toleance chaacteistics. Since 99, thee have been soe investigations into the application of ANN to powe electonics and ac dives, including speed estiation [5]. In [6], tow-laye NN was used with offline taining (befoe the oto is woking). his technique gives a faily good estiate of the speed and is obust to paaete vaiation. Howeve, the atificial neual netwok speed estiato should be tained sufficiently with vaious pattens to get good pefoance. In [4], a two-laye NN was used to estiate induction oto speed with online taining, but this lies oe in the eal of adaptive contol than ANN. he speed value is not obtained at the output, but at one of the weights. Moeove, only one weight is adjusted in the taining. heefoe, it would be vey sensitive to paaete vaiations and syste noises. In this pape, a new speed estiation ethod of an induction oto is poposed. In the new appoach, a ultilaye NN with one hidden laye is used. he speed value is obtained at the NN output and the feedback is connected between the output and the input node. he ultilaye and ecuent stuctue akes it obust to paaete vaiations and syste noises. he weights of the neuons ae continuously odified by backpopagation duing the speed-sensoless dive with online taining. heefoe, no offline taining and taining pattens ae needed. II. USE OF A MRAS WIH AN FIED ORIENED CONROER A. Dynaic Model of Induction Moto and Vecto Contol Stategy he induction oto atheatical odel in d-q cooinates established in a oto flux oiented efeence fae can be witten as: d v Rsi e () d v Rsi e () d Ri sl (3)

2 d Ri sl (4) whee the stato and oto flux linkages ae given by: (5) s s (6) (7) (8) he state space epesentation of the induction oto with the stato cuents and the oto flux linkages coponents as state vaiables can be witten as: R s d. i s s s i d R s i. s s s i d p d p s v s v (9) whee is the oto tie constant and is the leakage coefficient. he electoagnetic toue and the oto speed ae given by: whee: esistances;, and s e 3 p ( i i ) () J d p B p e l () J J J R and R ae the stato and oto winding s ae the stato, utual and oto inductances; p is the nube of pole pais; e, and sl ae the synchonous, oto and slip speed in electical ad/s; v, v i, i, and ae stato voltage, stato, cuent and oto flux d-q coponents in the oto flux oiented efeence fae; e and l ae the electoagnetic toue and the load toue espectively; J and B ae the oto inetia and viscous fiction coefficient espectively. Unde the oto flux oientation conditions the oto flux is aligned on the d-axis of the d-q oto flux oiented fae and the oto flux equations can be witten as: () i (3) he slip fequency can be calculated fo the efeence values of the stato cuent coponents epesented in the oto flux oiented efeence fae as follow [7]: * * i sl e (4) i and the electoagnetic toue equation can be witten as: 3 e p i Kti (5) whee K is the toue constant. t B. Model Refeence Adaptive Syste (MRAS) he classical oto flux MRAS speed obseve stuctue consists of a efeence odel, an adaptive odel, and an adaptation schee which geneates the estiated speed. he efeence odel, usually expessed as a voltage odel (VM), epesents the stato equation. It geneates the efeence value of the oto flux coponents in the stationay efeence fae fo the stato voltage and onitoed cuent coponents. he efeence oto flux coponents obtained fo the efeence odel ae given by [8, 9]: d di v Rsi s d di (6) v Rsi s he adaptive odel, usually epesented by the cuent odel (CM), descibes the oto equation whee the oto flux coponents ae expessed in tes of stato cuent coponents and the oto speed. he oto flux coponents obtained fo the adaptive odel ae given by: dˆ i ˆ ˆ ˆ dˆ (7) i ˆ ˆ ˆ he MRAS-based schees descibed in the pevious section contain a efeence odel and an adaptive odel. Howeve, geate accuacy and obustness can be achieved if the atheatical odel is patially eplaced by a neual netwok. III. ARIFICIA INEIGENCE-BASED MODE REFERENCE ADAPIVE SYSEM he MRAS-based schees descibed in the pevious section contain a efeence odel and an adaptive odel. Howeve, geate accuacy and obustness can be achieved if the atheatical odel is patially eplaced by a neual netwok. It is then also possible to eliinate the need of the sepaate PI contolle, since this can be integated into the tuning echanis of the neual netwok-based odel.

3 he neual netwok-based odel can take vaious fos: it can be an atificial neual netwok (ANN) o a fuzzy neual netwok etc. and thee is also the possibility of using diffeent types of speed tuning signals. It is believed that soe of these solutions can give high accuacy and ae elatively obust to paaete vaiations even at exteely low stato fequency. One specific ipleentation of the ANN-based MRAS speed estiato syste which is popula in acadeic wok, as shown in figue., which is siila to the conventional MRAS syste. In this new odel, the adaptive odel is eplaced by a siple two laye neual netwok, which enables the whole syste with fast esponse and bette accuacy than the conventional MRAS []. Fig.. MRAS-based oto speed estiato containing a two laye. o obtain the equied weight adjustents in the ANN, the sapled data fos of equations (6) and (7) ae consideed. By using the backwa diffeence ethod, the sapled data fos of the equations fo the oto flux linkages can be witten as (8) and (9), whee is the sapling tie. ˆ ˆ ( k ) ˆ ( k ) ˆ ( k ) i ( k ) (8) ˆ ( k) ˆ ( k ) ˆ ( k ) ˆ ( k ) i( k ) (9) hus the oto flux linkages at the k th sapling instant can be obtained fo the pevious (k-) th values as ˆ ˆ ( k ) ˆ ( k ) i ( k ) () ˆ ( ) ˆ ( ) ˆ k k ( k ) i ( k ) () It can be seen that w and w 3 ae constant weights, but w is a vaiable weight and is popotional to the speed. hus equations () and () take the following fos: wˆ ( k ) w ˆ ( k ) w i ( k ) () ˆ 3 ˆ( k) w ˆ ( k ) w ˆ( k ) w3i ( k ) (3) hese equations can be visualized by the vey siple two laye ANN shown in figue.. Fig.. Neual netwok epesentation fo estiated oto flux linkages. he neual netwok is taining by the backpopagation ethod; the estiated oto speed can be obtained fo: w ( ) ˆ ˆ k ( k ) w ( k ) ˆ ( k ) ˆ ˆ ( k ) ˆ ˆ ( k ) / w ( k ) (4) Whee η is the leaning ate and α is a positive constant called the oentu constant. he inclusion of the oentu te into the weight adjustent echanis can significantly incease the convegence, which is exteely useful when the ANN is used to estiate in eal tie the speed of the induction achine. IV. HE EXPERIMENA SYSEM he MRAS ANN based speed obseve has been tested in siulation and expeientally. A test bench has been set up fo this pupose. he test bench shown in figue 3 consists of: IM + oad Autotansfoe Fig. 3. Photogaph of expeiental setup. Powe Electonic Convete Contol Panel 3

4 i, i (A) e (N) i, i (A) e (N) Speed (p) Eo speed (p) Speed (p) Eo speed (p) One thee-phase induction oto with ated values shown in able (Appendix A), synchonous achine fo loading the induction oto, electonic convete powe (thee-phase diode ectifie and VSI coposed of thee insulated-gate bipola tansistos IGB odules, electonic ca with voltage sensos (odel EM V 5-P) and cuent sensos (odel EM A 55-P) fo onitoing the instantaneous values of the stato phase voltages and cuents, inceental encode (odel RS , 5 pulses pe ound), dspace ca (odel DS4) with a PowePC 64e at 4 MHz and a fixed-point digital signal pocesso (DSP) MS3F4. Fo eal-tie ipleentation, a eal-tie Siulink odel is developed and then downloaded to the DSP boa utilizing dspace ContolDesk softwae. V. EXPERIMENA RESUS AND DISCUSIONS he pefoance of the poposed obseve is investigated by following five tests on induction oto dive. then applied at 6.8, 9.45,.9 and 4.4 s espectively to the oto shaft. he axiu speed eo is 5 p (.8%). he estiated speed eplicates well the easued one, and its ipple is sall. his is an indication that the cuents obseves ae also accuate, since the speed was calculated fo the stato cuent estiate. he cuent eo is also sall, confiing the coect estiation opeation of the dive. ) Sensoless FOC speed evesal unde no load : No-load opeation is pesented in Fig. 6 - Fig. 7. he tansient of speed in slow evesing is pesented in Fig. 6. It is obvious, that the speed contol can be pefoed even at vey low fequencies. he quality of speed estiation is pesented in Fig Refeence speed Estiated speed Eo speed Estiated speed Refeence speed Eo speed 5 5 ie (s) Fig. 4. he oto speed esponses and eo speed estiation ie (s) Fig. 6. he oto speed esponses and eo speed estiation. iest ies iest iest e iest ies iest ies e ie (s) Fig. 5. Diect and evese stato cuent, electoagnetic toue.. In Figue 4, the achine has been initially set to opeate at 49 p in steady state. A sudden esistive load has been ie (s) Fig. 7. Diect and evese stato cuent, electoagnetic toue. he estiation eo is elatively low, having the peak at zeo speed, as expected. Anothe ipotant issue is the quality of toue tacking, pesented in Fig. 6. he absence of toue senso akes it ipossible to easue the actual toue, thus only the desied and estiated values can be pesented. It is obvious that egaing the high dynaics of the signal, the toue tacking is vey good, as pesented in Fig. 7. It has to 4

5 i, i (A) e (N) i, i (A) e (N) Speed (p) Eo speed (p) Speed (p) Eo speed (p) be taken into account that evey obseve has the liited fequency ange, which cannot he exceeded by the contolle. ) ± p speed evesal at load applied : 5 Estiated speed Refeence speed Eo speed Estiated speed Refeence speed Eo speed ie (s) ie (s) Fig.. he oto speed esponses and eo speed estiation. Fig. 8. he oto speed esponses and eo speed estiation. iest ies iest ies e eest ies iest iest ies ie (s) ie (s) Fig. 9. Diect and evese stato cuent, electoagnetic toue. In Figues 8 and 9, a DC geneato supplying a vaiable esistive bank has been connected to the oto as a load. In this case, as it can be seen fo these figues, the achine needs oe cuent. he evese stato cuent incease as it is diectly popotional to the electoagnetic toue. he diectstato cuent eains constant indicating the decoupling is guaanteed. he MRAS optiized obseved speed and the easued one follow the taget indicating the high pefoance of the poposed ethod. As it is seen fo the expeiental esults the poposed speed sensoless diect field oiented induction oto dives has good pefoances. 3) Invesion of the speed unde load toue change : o test the dive behavio unde tansient conditions, a dive statup to 43 p with evesal speed at 9 sec with Fig.. Diect and evese stato cuent, electoagnetic toue. load followed by a step change of load toue has been pefoed. he estiated oto speed, the eo speed, the estiated toue and the stato cuent coponents ae depicted in fig. and fig.. 4) Sensoless FOC at low speed : Duing the five tests, the dive opeation at low speed has been investigated to test the dive stability and the efficiency of the poposed ethod. In Fig., 3 the speed, eo speed, d-q axis cuents and estiated electoagnetic toue ae shown when the oto speed is p at no load. Due to low fequency egion, the estiated speed is consideably distoted with oscillation, the steady state eo is obtained. At such speeds and below, the MRAS based ANN sensoless schee fails to povide stable opeation giving lage oscillations. 5

6 i, i (A) e (N) Speed (p) Eo speed (p) Refeence speed Estiated speed Eo speed 5 APPENDIX A ABE I. HE INDUCION MOOR PARAMEERS Coponents Rating values Stato esistance Roto esistance Rs=.8Ω R=.385Ω Stato/oto inductance s==.5568h - -5 Mutual inductance =.6585H Moent of inetia J=. Kg ie (s) Viscous fiction f=3.65e-4n./ad/sec Nube of pole pais p= Fig.. he oto speed esponses and eo speed estiation. Rated Powe Rated speed P= kw = 49 p 4 3 ies iest iest ies ie (s) Fig. 3. Diect and evese stato cuent, electoagnetic toue. VI. e CONCUSION In this pape a ANN-based stato cuent MRAS is used fo speed estiation in sensoless induction oto dives. Roto flux estiation is equied fo the speed obseve. Using a voltage odel fo oto flux estiation causes pobles at low speed due to stato esistance sensitivity and the pue integation fo flux. A cuent odel can be used instead to estiate the oto flux fo the easued stato cuents and the estiated speed. Expeiental esults ae shown fo the pefoance of the poposed cuent MRAS schee at low speed when copaed to the classical oto flux MRAS obseve. he poposed schee shows bette speed estiation pefoance at low speed. Howeve in contast to the classical schee, the poposed schee shows instability in the egeneating ode of opeation. Pefoance ipoveent of the poposed schee ay be achieved by bette estiation of the oto flux duing egeneation REFERENCES [] K. Seong-Hwan, Speed-Sensoless Vecto Contol of an Induction Moto Using Neual Netwok Speed Estiation, IEEE ansactions on Industial Electonics, VO. 48, NO. 3, June [] M. G. Shady, D. Giaouis and J. W. Finch A Neual Netwok Based Stato Cuent MRAS Obseve fo Speed Sensoless Induction Moto Dives, 8 IEEE [3] B. Kaanayil, M. F. Rahan, and C. Gantha, "Online Stato and oto esistance estiation schee using atificial neual netwoks fo vecto contolled speed sensoless induction oto dives," IEEE ansactions on Industial Electonics, vol. 54, pp , 7. [4] Shady M. Gadoue, Daian Giaouis, and John W. Finch, Senio Mebe, IEEE Sensoless Contol of Induction Moto Dives at Vey ow and Zeo Speeds Using Neual Netwok Flux Obseves IEEE ansactions on Industial Electonics, VO. 56, NO. 8, August 9. [5] V. Vasic and S. Vukosavic, Robust MRAS-based algoith fo stato esistance and oto speed identification, IEEE Powe Eng. Rev., vol., no., pp. 39 4, Nov.. [6] Q. Gao, C. S. Staines, G. M. Ashe, and M. Sune, "Sensoless speed opeation of cage induction oto using zeo dift feedback integation with MRAS obseve," in Poc. Euopean Confeence on Powe Electonics and Applications, 5. [7] K.Sedhuaan, S.Hiavathi and A.Muthuaalinga, "Pefoances Copaison of Neual Achitectues fo On-ine Speed Estiation in Sensoless IM Dives", Wold Acadey of Science, Engineeing and echnology, Iss. 6, pp.38-35, Dec. [8] B. Kaanayil, M. F. Rahan, and C. Gantha, "Online Stato and oto esistance estiation schee using atificial neual netwoks fo vecto contolled speed sensoless induction oto dives," IEEE ansactions on Industial Electonics, vol. 54, pp , 7. [9] M. Kainski, M. Dybkowski, "Analysis of the Sensoless Vecto Contol of Induction Moto with MRAS(CC) Estiato and Neual Model Applied fo Speed Calculation", Pzeglad Elektotechniczny, Vol. 88, No. 4B, pp. 6-,. [] M. Pyne, A. Chattejee, S. Dasgupta, Speed estiation of thee phase induction oto using atificial neual netwok, Intenational Jounal of Enegy and Powe Engineeing, pp 5-56, 3(), ach 4. 6