Performance Evaluation of Synchronous Reluctance Motors With and Without Permanent Magnets

Transcription

1 Performance Evaluation of Synchronous Reluctance Motors With an Without Permanent Magnets M. N. Ibrahim 1,, Stuent Member IEEE, Peter Sergeant 1, Member IEEE an E. M. Rasha, Senior Member IEEE 1 Department of Electrical Energy, Systems an Automation, Ghent University, Ghent 00, Belgium Electrical Engineering Department, Kafrelshiekh University, Kafr el-sheikh 11, Egypt Electrical Power an Machines Department, Tanta University, Tanta 7, Egypt m.nabil@eng.kfs.eu.eg Abstract Nowaays, a growing interest in the efficiency an the cost of electrical machines has been notice. Therefore, Synchronous Reluctance Motors (SynRMs) have become more attractive, thanks to their higher efficiency an nevertheless acceptable cost compare to inuction machines. The rotor esign of SynRMs with or without permanent magnets (PMs) has a huge effect on the motor efficiency, torque ensity an power factor. This paper introuces an evaluation for the performance of SynRMs with an without PMs in terms of efficiency, torque an power factor maps. Three ifferent rotor esigns for the same machine have been compare. For one machine, the experimental measurements have been obtaine an the valiation of the simulation results have been confirme. Inex Terms PM, Synchronous Reluctance Motors, Design, FEM, sensitivity analysis, flux-barriers. R I. NOMENCLATURE i, i q Direct an quarature axis stator current respectively, A L, L q Direct an quarature axis stator inuctance of SynRM respectively, H P Number of pole pairs p Differential operator (/t) R s Stator resistance of the motor, Ω T e Electromagnetic torque of the motor, N.m V, V q Direct an quarature component of stator voltage respectively, V V m Maximum input voltage of the motor, V λ s Stator flux linkage of the motor, V. sec I m Maximum input current of the motor, A δ, α Loa angle an current angle, ra ω r Mechanical spee of the rotor, ra/s Rotor position, Deg. θ r II. INTRODUCTION ecently, Synchronous Reluctance Motors (SynRMs) with or without permanent-magnets (PMs) are becoming attractive machines for inustrial application especially electrical vehicles [1]. This is thanks to their merits of wie constant power spee range an high torque ensity. The power factor an efficiency are goo compare to inuction machines [], []. Several papers stuie the SynRMs an PMaSynRMs[1], [11]. For example, in [1], SynRM esign suitable for electric The authors acknowlege the Egyptian Ministry of Higher Eucation (Cultural Affairs an Missions Sector) an Special Research Fun of Ghent University (BOF) for the financial support uring this work. vehicles has presente. In aition, a comparison between ifferent flux-barrier esign for the same stator is investigate. The effect of four ifferent steel grae on the performance of SynRMs is stuie in []. It is notice that the lower thickness steel grae has the higher efficiency, however it has not the higher output torque. In [], the esign characteristics of SynRM with ferrite magnets an stator skew has investigate. In aition, mechanical stress an emagnetization of ferrite has stuie as well. This paper investigates the performance evaluation of SynRMs an PMaSynRMs. The moelling of PMaSynRM is introuce in Section III. Performance evaluation of SynRMs is investigate in Section IV. Experimental results are implemente to valiate the simulation results as epicte in Section V. At the en, conclusions are figure out in Section VI. III. PMASYNRM MODELLING A. Mathematical q moel of PMaSynRM The q moel of PMaSynRM can be represente in the rotor reference frame [], [], []. The reference frame rotates at ω r, so that the voltage equations are represente by: V R i p ( i, i ) P ( i, i ) P (1) V q s q r q q q( i rp ( i, iq R i p ) () s q The flux-linkage relations are given by: ( i L ( i i, q( i Lq ( i iq () The electromagnetic torque can be calculate as follows: Te P( ( i iq q( i, iq ) i pmi ) () The currents can be performe as a function of the current angle (α), which is the angle of the stator current space vector with respect to the -axis of the motor as escribe in Fig.1. i I m cos(), iq I m sin( ) () The supply voltage can be obtaine as follows: V V m sin( ), Vq V m cos( ) () where δ is the machine loa angle as shown in Fig. 1. The power factor (PF) of the PMaSynRM can be calculate by: r pm

2 V cos( ) Vq sin( ) PF cos( ) (7) V V q The torque ripple can be etermine as follows: max( Te ) min( Te ) Tripple () avg( Te ) where max, min an avg are the maximum, the minimum an the average values of the electromagnetic torque respectively. The SynRM moel can be obtaine by inserting λ pm=0 in the previous equations. R s i ω r Pλ m -ω r Pλ q ω r Pλ i q R s i q δ ϕ α V m I m i Fig. 1. Vector iagram of PMaSynRM -axis The iron losses of the SynRM are calculate base on the statistical losses theory of Bertotti. The theory epens on the separation of the losses into hysteresis (hy), classical (cl) an excess (ex) losses [], [7]. m P a B f hy. m p B Pcl. ( t) bm t (9) B B Pex. ( t) cm 1 m 1 t t Piron ( Phy. Pcl. Pex. ) where a m, α m, b m, c m, m an σ are material epenent parameters, an f is the frequency of the applie fiel. On the other han, the SynRM copper losses can be easily compute using the measure phase resistance as follows: P copper I R () Ph ph The efficiency of the motor can be obtaine by : Po (11) P P P o copper iron where P o is the mechanical output power of the motor calculate using the compute torque from the FEM moel by: P () o T e IV. r PERFORMANCE EVALUATION OF SYNRMS AND PMASYNRMS Three ifferent rotors with the same stator an other geometrical an electromagnetic parameters have been consiere. On the one han, the stator has slots an 1 turns/slot with conventional star-connecte winings. The stator esign is similar to that of inuction machines. Several specifications for the stator of the machine are liste in table I. On the other han, all the rotors have -flux-barriers per pole as seen in Figs. an. The first rotor has been esigne by a manufacturing company. This motor is calle a reference SynRM an it is the motor for which the experimental valiation has been one. The geometrical rotor parameters of the reference motor are shown in table I. The secon rotor has been optimize by a conventional optimization technique with D FEM for the twelve rotor parameters, epicte in Fig.. This motor is calle an optimal SynRM an its rotor parameters are given in table II. The final rotor has been obtaine by filling all the three flux-barriers of the optimize rotor (secon one) with ferrite PMs. The ferrite PM is selecte ue to the lower cost an the availability in the market. In aition, it can withstan higher temperature []. The aopte ferrite PM properties are shown in []. This motor is calle a PMaSynRM. TABLE I PROTOTYPE SYNRM PARAMETERS Parameter Value Parameter Value Number of rotor flux Rotor shaft mm barriers per pole iameter Number of pole pairs Axial length 0 mm Number of stator slots Air gap length 0. mm Number of phases Rate spee 000 RPM Stator outer iameter 10 mm Rate 0 Hz frequency Stator inner iameter 1 mm Rate current A Rotor outer iameter 9. mm Material M00-0A grae θ1 7. W1 mm θ. W mm θ. W mm L1 mm p1. mm L 19 mm p mm L mm p mm L1 W 1 L W L p p p 1 W rib raius -axis Fig.. Quarter rotor geometry of SynRM The following results have been obtaine by D-FEM at the same conitions. In FEM, only one pole of the consiere four-poles machine nees to be simulate. Sinusoial currents are injecte in the machine winings at ifferent spees up to the rate value (000 r/min). The currents have ifferent values up to the rate value (I m= A) at fixe current angle α=.. The selecte value of the current angle (. ) is the angle at which the machine can give approximately the maximum output power, for the ifferent currents an spees. θ θ 1 θ

3 The FEM fiel pattern of the reference motor for quarter geometry at rate conitions, is epicte in Fig.. It can be notice that there are some iron regions having higher flux level (re color). These regions are calle flux-barrier tangential ribs. The thickness of these ribs has a big influence on the SynRM performance. TABLE II OPTIMAL SYNRM ROTOR GEOMETRICAL PARAMETERS Parameter Value Parameter Value θ1.0 W1. mm θ 1. W. mm θ. W. mm L1. mm p1.7 mm L mm p. mm L 1. mm p. mm θ r=0 o -axis θ r= o Fig.. Flux paths for the reference SynRM using FEM for a quarter geometry for two rotor positions Figure shows the output torque of the reference, optimal an PM assiste SynRMs at ifferent spees an currents up to the rate values. On the one han, for the same current an spee, the output torque of the machine epens on the rotor esign which is affecte strongly by the esign of the twelve rotor parameters, shown in Fig.. Therefore, an optimize rotor geometry for the SynRMs is necessary an unavoiable to maximize the machine performance. The SynRM performance mainly epens on the irect () an quarature (q) inuctances that epen on the rotor flux-barrier geometrical esign. On the other han, when comparing the subfigs. of optimal SynRM an PMaSynRM, it can be notice that aing ferrite PM in the optimize rotor of the SynRM leas to an increase of about % in the motor torque. This is because of the effect of PMs on the inuctance of the SynRM. The PMs saturate the tangential ribs (see: Fig. ) of the motor. By consequence, reuce the inuctance, this leas to a higher output torque. Figure shows the compute losses (iron an copper) of the reference, optimal an PM SynRMs for ifferent currents an spees up to the rate values. The copper losses are constant for all the machines ue to the same stator winings an currents. The iron losses epen on the material properties, the currents an the geometry esign of the machine. Only, the rotor esign is ifferent between the reference, optimal an PM SynRMs. The variation of the flux-barrier parameters, shown in Fig., has a notable effect on the machine iron losses. This is ue to the variation of the saturation regions of the iron especially, the stator teeth an rotor tangential ribs. This can be observe in fig., by comparing the subfigs. (reference, optimal an PMaSynRM). For the same current an spee, the iron losses increases for the PMaSynRM that has the higher output torque (Fig. ) compare to the others. In aition, for one machine as expecte, the iron losses increases with increasing the spee an current, approximately in proportional way Torque map[n.m] Optimal SynRM Fig.. Motor torque maps for ifferent rotor esigns Losses map[w] Fig.. Motor power losses maps for ifferent rotor esigns

4 PF. map Fig.. Motor power factor maps for ifferent rotor esigns E,. map% inication for PMaSynRM to be attractive motor for inustrial applications. Moreover, the efficiency of SynRMs is better than inuction motors [] an is inferior compare to the permanent synchronous motors [9] as euce in Fig. 7. As the output power an total losses were affecte with the rotor esign, the efficiency of the machine epens on the rotor esign as well (Fig. 7). The efficiency of the PMaSynRM can reach 9% for half rate conitions. V. EXPERIMENTAL VALIDATION The FEM results have been valiate by the experimental measurements. The experimental set up shown in Fig., consists of: a three-phase inuction motor as a braking loa, kw a prototype SynRM (reference esign), kw an A three phase Semikron inverter, A an 00 V torque sensor of Lorenz Messtechnik, DR-1-R power analyser Tektronix, PA000 a Space platform, DS1 DC power supply, 17 A an 00 V The measure an simulate valiation results have been obtaine at 00 rpm an. A Fig.. Photograph of the experimental setup Fig. 7. Motor efficiency maps for ifferent rotor esigns The power factor of the SynRMs epens on the saliency ratio (L /L q) which is affecte by the rotor esign. As the optimal SynRM has the higher saliency ratio than the reference motor, then it has higher power factor. However, although the SynRM rotor is optimize, the power factor is still low about 0. at the rate conitions. Hence, aing PM in the optimize rotor reuces the phase angle between the voltage an current as seen in Fig.1 hence, increases the power factor. The power factor is increase to about 0.91 at the rate conitions as observe in Fig. (PMaSynRM). This is goo 9 Motor output torque [N.m] 9 7 Experimental Simulation Current angle [Deg.] Fig. 9. Compute an measure output torque of SynRM with ifferent current angles Figure 9 shows the compute (FEM) an the measure

5 output torque of the SynRM. There is a goo agreement between the simulate an the measure values. However, the ifference between the measure an compute results is ue to ifferent reasons: the cutting an punching effects on the steel properties, the manufacturing tolerance an the measurement error. VI. CONCLUSION This paper has iscusse the performance evaluation of Synchronous reluctance motors (SynRMs) with an without permanent-magnets. same Three ifferent rotors having the stator esign an other geometrical an electromagnetic parameters are consiere. The three rotors are reference, optimize an optimize assiste by ferrite PMs (PMaSynRMs) in its flux-barrier. Different performance inicators for the machine are compute by FEM an compare at the same conitions. The performance inicators are efficiency, torque, total losses an power factor maps. It is foun that the PMaSynRMs can reach efficiency an power factor higher than 9% an 0.91 respectively at the rate conitions. This means that the PMaSynRMs are much better than both the inuction machines an switche reluctance machines. In aition, they can be goo competitors compare with the permanent magnet synchronous machines ue to lower cost. Finally, measurements are obtaine an valiate FEM moel. VII. REFERENCES [1] M. Ferrari, N. Bianchi, A. Doria, an E. Fornasiero, Design of synchronous reluctance motor for hybri electric vehicles, IEEE Trans. In. Appl., vol. 1, no., pp. -, Jul/Aug. 1. [] M. N. Ibrahim, P. Sergeant, an E. M. Rasha, Synchronous reluctance motors performance base on ifferent electrical steel graes, IEEE Trans. Magn. vol. 1, no. 11, Nov. 1, Art. ID 70. [] R. Vartanian an H. A. Toliyat, Design an comparison of an optimize permanent magnet-assiste synchronous reluctance motor (PMa-SynRM) with an inuction motor with ientical NEMA frame stators, in Proc. IEEE Electr. Ship Technol. Symp. (ESTS), Apr. 09, pp [] Y. H. Jeong, K. Kim, Y. J. Kim, B. S. Park, an S. Y. Jung, Design characteristics of PMa-SynRM an performance comparison with IPMSM base on numerical analysis, in Proc. th ICEM,, pp. 170 [] S. Morimoto, M. Sanaa, an Y. Takea, Performance of PM-assiste synchronous reluctance motor for high-efficiency an wie constant power operation, IEEE Trans. In. Appl., vol. 7, no., pp. 0, Sep./Oct. 01 [] H. Huang, Y. Sh. Hu, Y. Xiao, an H. Lyu, research of parameters an antiemagnetization of rare-earth-less permanent magnet-assiste synchronous reluctance motor, IEEE Trans. Magn. vol. 1, no. 11, Nov. 1, Art. ID 1. [7] G. Bertotti, "General properties of power losses in soft ferromagnetic materials," IEEE Trans. Magn., vol., no. 1, pp. 1 -, 19 [] _sintere_1.pf [9] T. Ahonen, J. Tamminen an J. Montonen, Comparison of electric motor types for realising an energy efficient pumping system, in Proc. 1th Eur. Con. Power Electronic. Appl. (EPE'-ECCE Europe),, pp. 1 9 [] Ch.T. Liu, T. Y. Luo, Ch. C. Hwang, an B.Y. Chang, Fiel path esign assessments of a high-performance small-power synchronousreluctance motor, IEEE Trans. Magn. vol. 1, no. 11, Nov. 1, Art. ID 0. [11] R. Lohninger, H. Grabner, G. Weienholzer, S. Silber, an W. Amrhein, Moeling, simulation, esign of permanent-magnet-assiste synchronous reluctance machine, IEEE Trans. In. Appl., vol. 1, no. 1, pp. 19-, Jan./Feb. 1. VIII. BIOGRAPHIES Mohame N. Ibrahim was born in Kafrelshiekh, Egypt on September 1, 19. He has grauate from Faculty of Engineering, Kafrelshiekh University, Egypt on 0. He receive his MSc. egree in Electrical Power an Machines Engineering from Tanta University in. Since, he is working as an assistant lecturer at the Department of Electrical Engineering, Faculty of Engineering, Kafrelshiekh University, Egypt. He is currently working towars the PhD at Ghent University, Belgium. His research interests are in Electrical Machines, Electrical Drives, Power Electronics an Renewable Energy. Prof. Essam M. Rasha was born in Shebin El-Kom, Egypt in 1. He receive his BSc egree from the epartment of Electric Power an Machines Engineering., Faculty of Engineering, Shebin El-Kom, Menoufiya University, Egypt in May 19. In 197 an 199 he receive MSc an PhD, respectively both from faculty of Engineering Alexanria university, Egypt. In 199 he has joine Faculty of Engineering, Tanta University, Egypt, where he is currently a Professor an Hea of Electrical Power an Machines Engineering. From Feb. to Aug 00, he was a visiting researcher in Faculty of Engineering, Nagasaki University, Japan. In summer 0, he was a visiting researcher at Faculty of Engineering an Applie Science, Memorial University of Newfounlan, St. John s, NL, Canaa. From 0 to 09, he was Hea of Electrical Technology Department, Burayah College of Technology, Kingom of Saui Arabia. From 11 to, he was Vice Dean for Eucation an Stuent affairs of Faculty of Engineering, Tanta University, Egypt. Prof. Rasha research interests inclue electrical machine analysis an esign, electrical rives, power electronics an renewable energy systems. Peter Sergeant receive the M.Sc. egree in electromechanical engineering in 01, an the Ph.D. egree in engineering sciences in 0, both from Ghent University, Ghent, Belgium. In 01, he became a researcher at the Electrical Energy Laboratory of Ghent University. He became a postoctoral researcher at Ghent University in 0 (postoctoral fellow of the Research Founation - Flaners) an at Ghent University College in 0. Since, he is associate professor at Ghent University. His current research interests inclue numerical methos in combination with optimization techniques to esign nonlinear electromagnetic systems, in particular, electrical machines for sustainable energy applications.