design and comparison of linear synchronous motor and linear im for electromagnetic aircraft launch...

8/14/2019 Design and Comparison of Linear Synchronous Motor and Linear IM for Electromagnetic Aircraft Launch System

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Design and Com parison of Linear Synchronous Motor and Linear Induction Motorfor Electromagnetic Aircraft Launch SystemGorazd hm berger , Damir h k o 3 , Mehmet Timur Aydemir, Thomas A. Lipo3University of M aribor, Faculty of Electrical Engineering and Com puter Science, Smetanova 17,2000 Maribor, SloveniaGazi University, Departm ent of Electrical and Electronics Enginering,06570 Ankara, Turkey3University of Wisconsin-Madison, Department of ECE, 1415 Engineering Dr., MadisonWI 3706,US A

AbstracI-Tko basic linearmotor designs suitable for an electro-magnetica i d annchsystem (EMALS)have been presented inth e paper. Themotors have beeo designed with an emphasis oneasy assembly and replacement even at the cost of sligbtlyreducedperformances. Both,hear permanent magnet synchronousmo-tor (LPMSM) and linear nduction motor (LIM ) are assembledfrom modular stator segments which can be quickly and easfiy~ p h c e d . erformances and eqnivalentdr mi t parameters of th eLPMSM and LIM designs are comparedat the end of the paper.

I. INTRODUCTIONThe replacement of the steam catapults used in the aircraftlaunch systems with electromagnetic ones has attracted the at-tention of several authors [I ] to 141. Two important candi-dates to be u sed in these systems are linear permanent mag-net synchronous motors (LPMSM) and linear nduction motors(m). I b i s paper initially defines the design problem fo r the Elec-tromagnetic Aircraft Launch System (EMALS). The motorsuitable for EMALS must produce enough thrust with the suf-ficient level of redundancy, it must be easy to assemble and

maintain, while its total rotor mass must be limited. The de-signs of the LPMSM and the LIM presented in this work aredetermined with the emphasis on easy assembly and replace-ment. Therefore, they are composed of modular stator seg-ments. The stator coils in the segments can be connected innumerous ways. The most prom ising connections for whichthe num erical analysis has been carried out are half phase perpole (HPP) and one phase per pole (OPP). None of thesestructures is a ble to produce sinusoidally distributed armature(stator) MMF like a standard1ap winding, but they still pro-vide acceptable electromagnetic propenies o f the motor an d,moreover, they satisfy previously stated requirements of theEMALS.In the representative publications, [5 ] to [81, the air gap fluxdensity is determined in more than one dimension using mul-tidimensional approach to magnetic circuit analysis. However,in this work only simple one-dimensional(1D)nalysis of themagnetic circuit is performed [81. The ID analysis togetherwith 191to [I71 s used to determine the designs of the LPMSMwith the HPP and OPP tator structures. However, the compar-ison of the results obtained by ID analysis of the magneticcircuit and by 2D finite element method (FEM) shows thatthe approxim ation of the stator and rotor MMFs, air gap flux,EMFs and thrust only with the fundamental harmonic compo-

nent would be accurate enou$h to design the LPMSM .The LIMs with the HPP and OPP stator structures are de-signed with consideration of only fundamental harmonic com-ponent of the MM F in the air gap. The stator (primary) hasthe same structure as n the case of the LPMSM w hile the sec-ondary of the LIM consists of a copper sheet. In the designprocedure the copper sheet is approximated by a dense meshof conductors. The results obtained analytically are confirmedby the results of the FEM calculations.The comparison of the physical, operational and equiva-lent circuit parameters of the LPM SM and LIM designs show sthat all presented designs are valid candidates for the EM ALS.However, at the present state of the art the LPMSM seems tobe a better candidate for this project. It has much better powerfactor, which facilitates the power inverter design.

11. D E S I G N ROBLEMThe problem considered in this work is to design a mo-tor to be used in an Electromagnetic Aircraft Launch System(EMALS) 1 to [4]. The system is composed of a linear motor,power electronic components and control system designed toaccelerate an aircraft to its take off speed and then to abruptlystop the moving rotor portion. The time interval between twotake-offs s 45 s. The design param eters which were used are asfollows: airaalimass = 23000 g, ly away speed Y = 103 s ,maximal available path for acceleration= 310 ft (94.49 m) andthe maximal available path fo r deceleration = 19 A (5.79 m).If the necessary calculations are carried out, it can be foundthat the required value of the acceleration and the length ofthe acceleration period are 56.01 ml s and 1.84 s, respectively.Similarly, the required d eceleration and the length of the decel-eration period needed to bring the rotor from its highest speedof 103 mJs to a stop within the distance of 5.79 m are found tohe 919.64 m/s2 and 0.112 s, respectively. Neglecting all kindsof friction, the motion of the entire system can he described by

d 2sdr2 -m - - F or m a = F

where m s the mass of the moving part of the entire system, sis the rotor position and F is the force required for accelerationa. The mass to be accelerated is the sum of the aircraft massand the rotor mass. The mass to be decelerated is only the rotormass. The required force or thrust F that must be prov ided hythe EMA LS for acceleration and deceleration is given in Fig. 1as a function of the rotor mass.

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- ~ L . d4 . . : . . . . , . . . . .-E , . . : .. : . . . . : . . . . . . . . . . .~ . rotor aircrafiaccele timc

lax, 2 w o 3 w o m 5worotormass [kglFig. 1. Thml required for acceleration and dccclcntion given as a functionof m o r mass.

The results presented in Fig. 1show that a thrust of 2 MNis sufficient to accelerate the aircraft and the rotor if the rotormass is less than 5000 kg. With the same thrust only rotorswith a m ass less than 2183 kg can be stopped w ithin the pre-scribed distance. Thus. without consideration of the requ iredpower electronics supply and its limitations, a motor w ith thebest possible power factor should bedesigned which is able toproduce a thrust of 2 MN with a rotor mass less than 2183 kg.111. MO DULARTATOR ST RU CT U RE

The b asic design principleis to fabricate both, the linear per-manent m agnet synchronous motor (LPMSM) and the linearinduction motor (LIM), from modular stator segments. Theconcept is shown in an idealized fashion in Fig. 2. Coordi-nate z is assumed to be the directionof m otion, coordinate ythe vertical depth and coordinate x the thickness of the m otor(directionof the air gap).

Fig. 2. One modular segment of Ihc stafm composed of a laminatedpoldlwlh envelopd hy an mature coil.

In general, each stator segment is composed of a laminatedpole (or stator tooth) and a concentrated m a t u r e winding en-veloping the pole with the emp hasis on easy assembly and re-placement. In the case of a winding fault the stator segmentassociated with the fault can be quickly and easily replacedwith a new segmen t without disturbing the healthy segments.Two poles of the complete stator are assembled as a stringof these stator segments. The stator coils can be connectedin a variety of ways to realize a three-phase magnetomotiveforce @IMF). From many possible connections of the statorcoils only two are sufficiently promising to be d iscussed here.The first connection of the stator coils defines the 1/2 phase

LPM MMF

~I I I I porilizzFig.3. HP P SUUctuTeof Ux LPMSM with the smor and rotorMMF

waveforms (io = I , ib = -0.51 and i = -0.50.

L*U ition zI U

\PM MMF

1 I poaitiaorIFig.4. OPP svuctm of lheLPMSM wiIh the6mmandmlmMM Fwaveforms ( =I. b = -051 nd & = -0.50.

per pole (HFP) stator structure. This structure is shown inFig. 3 for the LPMSM together with the corresponding arma-ture and permanent magnet (FM) MM F waveforms. m e sec-ond connection of the stator coils defines the one phase perpole (OPP) stator structure. This arrangement is shown inFig. 4for the LFMSM together with the corresponding m a -ture and PM MM F waveforms. The distribution of fluxes inthe HPP and OPP stator structures is shown in Fig. 5 while theparameters of the motor geom etry are shown in Fig. 6.In both cases presented here, the permanent magnets are em-bedded into the rotor frame that consists of a non-magneticand non-conducting material. In the case of LIM the perma-nent magnet rotor is replaced by a massive copper sheet, while

the stator HPP or OPP structures and their MMFs remain thesame as n the case of LPMSM. The prop osed realization of theLPMSM for the EMALS is schem atically presented in Fig. 7.Specifically, four independent stators (HPP or OPP) are ori-

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OPPIC pitch

b a - a s030 10 0.50le pitch W P pole pilchI p o I

0.50 0.5os0 0.50

Frg. 5. Distribution of fluxes in OPP and HPP srmnures lor & = I , a = -0 51and i = -0.51.OFT

l q , I

1

Rg . . Paramerers of the motor geomeuy.ented vertically and act on a single rotor with embedd ed per-manent magnets. The system is d esigned with sufficient redun-dancy so that in the case of rem oval of one of the four stators,the remaining three statorswill be sufficient to produce 2 MN ,which is enough for an aircraft launch. T he realization of theLIM difers from the described LPMSM realization only in therotor portion, which is made of a single copper she etTh e aim of th is work is to find designs of the LPMSM andLIM with the HPP and OPP stator suuchues and to evaluatetheir physical, operational and equivalent circuit parameters.The motor designs must be able to produce a thrust of morethan 2MN with a rotor mass less than 2183 kg.Iv. LINEARERMANENT MAGNET SYNCHRO NOUS MOTORTo design LPMSMs with the HPP and OPP stator sbuc-tures, the one-dimensional (1D) analysis of the m agnetic cir-

RE.7. Reposed four-sator-single-morrealization01&e LPMSM lor heEMALS.

cuits [8],[9] is applied. The flux eakage, fringing, skin effectand iron core losses are neglected. The permeability of theiron core is assumed to be nfinite. Only twopoles of the upperstator shown in Figs. 3and 4 and one half of the permanentmagnet (PM) thickness I , =x,/2 shown in Fig. 6 are involvedin the calculations. The effects of the armature slotting are ac-counted for by the po sition dependent permeance A(z) [91

where is the permeability of vacuum L is the position alongthe stator, zo is the displacement of the PM with respect to thestator,g. is the length of the effective air gap, ;\a is the meanairgap permeance in per unit,A, is the k-th lolting permeancein per unit, N is the number of the armature slots per twopole pitches, k is the order of the armature slot permeance.The m ean permeance is calculated by (3) and the k-th slottingpermeance in per unit is calculated by (4), where Kc; is theca ne r factor for the armaNre sloning.

1K C S

% = - - < 1 (3 )

The length of the effective air gap is g. = g+ 1, outside thePM and g, = g+ L nside the PM, where g is the length ofthe air gap and pr IS the relative recoil permeability of the PM[81,[11],[12]. Th e air gap flux density17g(z ,zo,f) at the instantf is g iven by (5 ) , where S a ( z , f ) and S P M ( L , ~ , ~ )xe the ar-

B.

4%



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mature MMF and the PM M MF, respectively.B,( z , zo , t ) = h ( z , z o ) 9 , , ( z , f ) + ~ P M ( z , z o , ~ ) )

The thrust produ ced by th e two pole pitches is given by( 5 )

(6)whereA(z,t) =9 s the armature current sheet, T p is thepole pitch and Y is the motor length in th e y direction. Thephase a EM F eo(!) is determined by

2VF ( z o , t ) = A(z,t) B g ( z , z o , t )Y dz

(7)

(8)ZZPW)= N l 4 2 ) B,(z,zo,t)Y d zwhere I&(I) is the phase a flux l i g e , N is the number ofturns while w&) is the function describing distribution of thephase a winding along two pole pitches. In the case when themotor terminals are opened the EMF,e.o(t) caused by the PMmoving at the speed v can be determined. The phase a voltage& ( I ) at load can be calculated by

(9)di ( I )d tU&) = R i . ( r ) +L -5- + e , a ( t )where R and L are the ohmic resistance and the inductance ofthe phase a winding while io(r) is the phase a current. Thepower P and the power factor PF are calculated by (IO) and( l l ) , espectively.

The time dependent phase a, b an d c currents and voltages aredenoted by i n ( f ) , ic(t) U,&), ub(f). i c ( ! ) , theirRM S val-ues are denoted by la ,$, I,, U,, ~ b ,,, while T =2 s the pe-riod of the current and voltage waveform s. If only fundamentalharmo nic componen ts of the voltages and currents are consid-eredin(lO)and(Il),thepowerfactorPF becomescos(cp).Two LPMSM designs, one with the HPP stator structure(Fig. 3) and the other with the OPP stator structure (Fig. 41,were determ ined by using ID analysis of the m agnetic circuitand equations (2) to (1 1). Both des igns produce the thrust ofmore than 2 MN with three stators (Fig. 7) while their rotormass is less than 2183 kg. Their physical, operational andequivalent circuit parameters are summarized in Table I. It isassumed that both LPMSM s are supplied by three symm etricalsinusoidal currents.The EMF s due to the moving PMs and the supply voltages inthe phase a, phase b and phase c windings for one pair of polesare given in Fig. 8for the HPP stator structure and in Fig. 9fo r

- ,mM0 - . . .. . . . . . . . . . . . . . . . . . .z x = O ' " . ' , ' '.,m.. ~ . . . . . . . . . . .Im . . . . . . . . . . . . . . . . .

I I I 1

. . . . . . .. . . . .

0 O.J I 0 0.5 I' I n s ] ,Imp1- , -~ 0f lnsl lmpl.

. . . . . . . . . . .. . . . . . . . . . . . . -,m . . . . i . . . . . . . .. ' ' ' " 1 " '.Im

0 0.3 I 0 0.5 I

Fig. 8. HPP smucly~c EMFs e d , em. em due o the PM moving a1Y = 103 m l s and line volrages zb.ub. uc 81 full load.

-"lm-lmom-elmom'

. . .0 an 0 ' '. . . . . . . . . . . . . . . . . . .lm . . . .

0-Iw . . . . . . . . . . . . . . . . .]m . . . . . . . . . .

.....-I M . . . . . . . . . . . . . . . . .m . . . . . . . . . . . . . .

Fig.9.OPP smcm - EhfFs e d , em, em due IOhe PM moving 81Y = 103 m l s and ine valrages %. "6. uc81 full load.

the OPP tator structure. The EM Fs e&, em an d ero are givenfor the case when the rotor with the PM s moves at the speedv = 10 3 m l s and the motor terminals are opened. The voltagesu., ub and uc are given for the case when the rotor moves atv = 103m l s , three stators (Fig. 7) produce the thrust of 2 MN,PM and armature MMFs are displaced by rJ2. and the motoris supplied by sin usoid al curre nts.

The t h s t character ist ics calcu lated by 1D analysis of hemagnetic circuit (ID nalysis), their fundam ental harmoniccomponents (1. harm. compone nt) and thrust characteristicscalculated by 2D finite element method (FEM) are given inFigs. 10 to 1 3 for the HPP nd OPP tator structures. Resultspresented in Figs. 10and 11 are given for the co nstant statorcurrent excitationwhile the rotor with the PMs moves over two

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n n tposition z [mlFig. I O . HPP mctm: thrust per 2 5 with a single stator conimtm a t u r eMMF. mo r moves over 27,.

20 I

I0 0.05 0.1position z lm lFig.1 . OPP smclm: Ihrun per 27, with B single sfator.c o n ~ m t rmatureMMF, m m oves over 2r,.

0 ' I0 0.05 0.1position z [mlFig. 12.HPP meture: thrust pcr 2 5 with a sin& stator; otorand statorUMFs move over 21, displaced by rJ2.

2 0 , I

I0 0.05 0.position L lm lFig. 13. OPPsmaw: h s t er 2rPwith a single stator;m o r and statorMMFs mwe over 2r, displaced by rP/2 .

pole pitches. Th e thrust characteristics shown in Figs. 12 and13are given for the case when the stator M MF and the rotorMMF move over two pole pitches displaced by 7J2. In termsof twc-axis mod els this means that the motor is controlled toproduce the maximal thrust with the quadrature axis currentwhile the direct axis current equals zero. In all cases presented,the sinusoidal currents with the maximum amplitude given in

Table I were applied.Results presented in Figs. 10and 11 show a good agreementbetween the fundamental harmonic component of the thrustobtained by 1D analysis and the thrust calculated by FEM . Thethrust charac teristics calculated by FEM given in Figs. 12and13show a low position dependent thrust pulsation. H owever, ifit is required, even this low thrust pulsation can be reduced byskewing or even simpler by displacing each of the fo ur statorsin Fig. I by on e quarter of the slot pitch.

v. L I N E A RNDUCTION MOTORThe design of the LIM has the same HPP or OPP statorstructure as in the case of the LPMSM while the rotor withembedded PMs is replaced by a single copper sheet.The design of the LIM and param eters of the equivalent cir-cuit are determined on the assumption that only fundamentalcomponent of the MMF in the air gap exists. The magn etic re-luctance of iron is neglected. Therefore, the inductances ofthe LIM depend only on the magnetic reluctance of the airgap. The influence of skin effect on the values of equivalent

secondary resistance and inductance is included in the calcula-tions. The parameters of the equivalent circuit are determinedfor two stators (primaries) (upper and lower stator in Figs. 3and 4) and two pole pitches assuming at the same time that themachine has only two poles.The parameters of the secondary (rotor) circuit cannot becalculated in a straightforward manner because the secondaryconsists of the copp er sheet. Unlike the motor of the squirrelcage type where an equivalent impedance of the bar and end-ring can be fairly easily calculated, in this case there are nophysical conductors whose impeda nm can be calculated. Thethrust isproduced by edd y currents induced in the copper sheetwhose distribution and direction is difficult to predict. How-ever, f it is assumed hat sinusoidally distributed magnetic fieldin the air gap induces sinusoidal currents in the copper sh eetthen the copper sheet can be approximated by the dense meshof segmen ts connected as shown in Fig. 14.The secondary of the machine is generally wider than theprimary. Therefore the magnitude of the flux density in y direc-tion varies. Consequently, the voltages induced in the ve dc alsegments that are positioned along he s ame l i e have differentmagnitudes, but the phase angle is the sam e. In the horizon-tal segments there are no voltages induced because they arealigned with the direction of motion. However, since they arethe part of the entire circuit and they are connected to the ver-tical segments inwhich the voltages are induced, there are CUT-rents flowinghrough them. The currents in all the segmentsof the mesh can be calculated systematically if it is assumedthat the voltages and currents in the segm ents adjacent in thedirection of motion are of the sam e amplitude, but displaced inphase by an angle a = 2 n / m .

This circuit can replace the copper sheet if the numb er ofsegments is large enough. The basic principle of solving thecircuit is to apply Kirchhoffs current and voltage laws to the

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. . .. .. ;.L_-_- .- .-1Fig. 15. C u m n t distribution n Ihe c op p r sheet obtained from L e meshmodel.

loops of the mesh. The current distribution in the copper sheetcalculated by solving the circuit in Fig. 14 is shown in Fig. 15.Two parallel horizontal lines mark the boundaries of the pri-mary which is narrower than the co pper sheet of the secondary.One must bear in mind that the solution for currents 11, 11 2and 113 in Fig. 14 can be obtained only if the voltages el ; areknown. These voltages can be difficult to calculate becausethey depend on the m agnitude of the flux density in the air ga pwhich is the function of both, primary and secondary MMF.The secondary MMF is at the same time the function of cur-rents 111, 112 an d 113 which should be determined. The bestapproach to this problem is to find the equivalent impedanceof an imaginary bar by applying the principle of equivalenceof active and reactive power in the imaginary bar and the seg-ments as it is done in the rotary squirrel cage induction ma-chine [ lo] . This bar replaces all the vertical and horizontalsegments where, according to Fig. 14, the currents have thesame first index in their notatio n, i.e. 111, 112, . . . I I+I ) , 1121,

1122, . ' . 1 1 2 ~ .With this approach the how led ge of the inducedvoltages el , is no longer necessary. The total number of imag-inary bars equals m. With this equivalent impedance the stan-dard analysis of the ind uction machine based on the equivalentcircuit can be used.

TABLE1PHYSICAL, OPERATIONAL AN D EQUIVALENT CIRCUIT PARAMETERS FOR

TH E L P M S MThicblerr rl (mm) I 37.8 I 25.4Lenlrth in 7 8reeti"" T I" I 47.0 I 54.6PMGeometry I HPP I OP P

Pole&h b ( m m ) ~Slotpitch T (mm)Tmthwid~h; (mm)SIN opting (T, I ; ) (mm)T& height T, (m) 26.0 38.6Yoke kight r, (mm) I 6.8 I 6.8co n Geometry ICoil widfh e . (mm) I 11.91 8.4coil kiehl e. kn" I 2 6 3 I 38.6" . . ,Cod le@ (mm) I 5001 500Number o f m ~ I I1 1

VI. RESULTSThe design parameten of the H PP and OP P stator structures

are given in Table I for the LPMSM and in Table II for theLIM.All presented designs produce a thrust of more than 2 MNwith the rotor mass less than 2183 kg. which means that all ofthem fulfill the fimdamental requirements. For both machines,HPP structure yields a higher cos(q) compared to the OPPstructure, while both designs of PMSM have a better cos(q )than LIM. he maximum currents in the case of LPMSM de-signs are under l l kA,which is acceptable from the point ofview of the power inverter design. In the case of LIM designsthe maximum currents are in the range of 100kA,which couldbe a problem for the inverter design. On he othe r hand the fre-quencies are mode rate in the case of LLM designs , w hile theyare rather high in the case of LPMSM designs. The small dif-

ference between the cos (q) and the power factor in the case ofLPMSM and relatively small thrust pulsation in characteristicscalculated by FEM prese nted in Figs. 12 and 13 show that thenonsinusoidally distributed armature MM F does not suhstan-

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TABLE IIP H Y S I C A L , O P E R A T I O N A L A N D Q U I V A L E N TC I R C U I T P A R A M E T E R S FO R

supply current requirements and especially low cos(p). Thedrawb acks of the LPM SM aTe higher sta tor frequency and itsTYL 1 1M

8.87

. .rotor structure with embedded PMs, w hich is not as robust asthe copper sheet in the case of LIM. The most important ad-vantage of the LPMSM is much better cos(p), which facili-tates the power inverter design. At the presen t state of the artthe LPMSM s e e m to be a better candidate for the EMALS.IIolrpitch 7, (mm) 265 650I71 211 ACKNOWLEDGEMENTSupport for thisprojectfrom the Wisconsin Elecuic Machines andPower Electronics Consortium (WEMPEC) is gratefully acknowl-edged. Dr. Mehmet T.Aydemir was supported through Fulbrightscholarship forperforming research at UW-Madison.

REFERENCES[ I ] R. R. Bushway, E l e c m ~ e t i cunafl launch system developmentconsiderarions, IEEE T m n r ~ ~ t i ~ n sn Magnrficr. vol. 37. no. 1. pp.52-54.2001.121 H. D.Fair. The science and technology of electric launch, IEEETmnroeriomon Mognctics. vol. 37. no.1.pp.25-32.2WI.131 M. R. Dayle, D. I . Samuel,T.Conway, and R. R. Klimowski,UecvO-

magnefic a i d 1 aunch System - em&, IEEE Tmnsocliom on Mag-nelies, vol. 31, no. 1,pp. 528-533. 1995.141 R. . Wwell. R. W. Garman. and M. Doyle, 7hermal mansgemcm tech-niques form advenced linearmotor in an electric aunaft recovery sys-tem, IEEE Tm(1~ac60mn Mogncricr, vol. 37, no. I. pp. 476479.2001.151 Y. Zhang. S. Ho, H.Wong. and G. Xie, Analytical prediction ofarmam-reaction field in diw-lyPe permanent magnet gcncrarors:IEEE Tmnracrions on Emgy Conversion, vol. 14, no. 4,pp. 1385-1390,1999.161 Z. . Zhu,D. HOWGE. Bolte. and B.A c h a n n , 1wmm~usag-netic field distribution in brushless permanent m ap et dc motors.pan IOpen-e+uil field, EEE Tmnrocriom onMagnetics. vol. 29, no. 1 pp.124-135.1993.171 Z.Q. Zhu and D.Howe, hsmmeour magnetic field distributionin brushless permanent magnet dc motors. pm U Armamre-reactionfield IEEE Tmmacfiom on Mogmticr. vol. 29, no. 1 pp. 136142,1993.181 2.Q. hu and D. Howe. ?nstantancous mapietic field distribution inbrushless permanent magnet dc motors. pan m. ffect of SWOTlot-ting: IEEE Tmmocliom on Magnetics. vol. 29. no. I, pp. 143-151.1993.191 S. Hum& M. Aydin, and T.A. Lipo, Toque quality -men1 andsizing optimization lor surface mountedpermanent magnet machines:in Thiq-Sinh IAS Annwi Mecling. Conference Reco d of rhe 2001IEEE. vol. 3, E E E . Chicago: IEEE,2001, pp. 161!&1625.

[IO] T.A. L i p . Intmducfion loAC Mochine Design Vol.1. Madison,W.University of Wiseonsin, 1996.[I I ] J.EGieras andZ . Piech, Linear Synchronous Molors (Tmrponarion

and Automotion *stem).[I21 1.E Gieras and M. Wing, P e m n r Mogncl Moror Technology (De-sign and Applications). New York: Marcel Dekker, Inc., 1997.

1131 I . Hendeshot andT.Miller,Design ofbnrrhlerspcrmoncnr-mgnel mo-101s. Oxford ClarendonPress, 1994.

[I41 T.Miller, B m h l e r r p e r ? - mo g n c l ond nlunant mlo r dt iws .Oxford: Oarendon Press, 1989.[IS] I. Boldea and S. A. Nasar, Lineor rlccrric ~ ~ e l w i o nnd gcncmlon.New York:Cambridze University Press, 1997.[161 S. A. Nasar and 1. Boldea. Linear clcnric molors : heory, design ondpmn ical applicariom.1171 1. Boldea and S. A. Nasar. Linear motion eleclmmgnetic sysremr.New York:Wiley, 198.5

New Y a k CRC Press.2033.

Englewood Cliffs N. 1 Prentiee-Hall,1987.

t i d y reduce the LPMSM performances.VII. CONCLUSION

Two designs of LPMSM and two designs of LI M are pre-sented in the paper. They are determined with the emphasis oneasy assembly and replacement, which means that they havemodular stator structures. In the case of a fault, the damagedmodule can be easily and quickly replaced without disturbingthe healthy modules. The price for the modular stator struc-ture is the nonsinusoidally distributed armature MMF. How-ever, the comparison between the powe r factor and the cos(cp)as well as the thrust characteristics calculated by E M n thecase of LPMSM show that the nonsinusoidally disuibuted ar-mature MMF does not substantially deteriorate motor perfor-mances.

Although all designs presented herein fullill the conditionsrequired for their use in E MAL S, there are still considerabledifferencesbetween them. The results presented show that bet-ter cos(9) can be reached with the H PP stator structures thanwith the OPP stator structures. That difference in cos(cp) isquite significant in the case of LIM, while it is small in thecase of LPMSM. The advantages of the LIM are ts ro bus t IO-tor structure and low stator frequency. Its drawbacks are higher

design and comparison of linear synchronous motor and linear im for electromagnetic aircraft launch...

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