[2009] IEEE. Reprinted, with permission, from Guo, Youguang; Zhu, Jianguo; Dorrell, David; Lu, Hai Yan; Wang, Yi. 2009, 'Development of a Claw Pole

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1 [2009] IEEE. Reprinted, with permission, from Guo, Youguang; Zhu, Jianguo; Dorrell, David; Lu, Hai Yan; Wang, Yi. 2009, 'Development of a Claw Pole Permanent Magnet Motor with a Molded Low-Density Soft Magneti Composite Stator Core', Proeedings of IEEE Energy Conversion Conferene & Expo, pp This material is posted here with permission of the IEEE. Suh permission of the IEEE does not in any way imply IEEE endorsement of any of the University of Tehnology, Sydney's produts or servies. Internal or personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for reating new olletive works for resale or redistribution must be obtained from the IEEE by writing to pubs-permissions@ieee.org. By hoosing to view this doument, you agree to all provisions of the opyright laws proteting it.

2 Development of a Claw Pole Permanent Magnet Motor with a Molded Low-Density Soft Magneti Composite Stator Core Youguang Guo, Jianguo Zhu, David Dorrell, Haiyan Lu, and Yi Wang Faulty of Engineering and Information Tehnology University of Tehnology Sydney 1 Broadway, PO Box 123, NSW 2007, Australia youguang@eng.uts.edu.u, joe@eng.uts.edu.au, david.dorrell@eng.uts.edu.au, helenlu@it.uts.edu.au, yiwang@eng.uts.edu.au Abstrat SMC (soft magneti omposite) materials and SMC eletrial mahines have undergone signifiant development in the past deade. For the molding of the SMC ore, if a high produtivity low pressure press is used, the manufaturing ost an be dramatially redued. However, the magneti properties of the SMC ore and the mahine performane are highly dependant on the mass density of the ore. This paper presents the development of a law pole permanent magnet motor with a low mass density SMC stator ore molded at low pressure whih an replae the existing single phase indution motor in a dish washer pump. The developed SMC motor has been prototyped and tested. Both the parameter omputation and performane predition are validated by the experimental results. These show that the low mass density SMC ore is suitable for low ost mass prodution of SMC eletrial mahines. Index Terms Claw pole motor; Low pressure molding; Magneti field finite element analysis; Molded ore; Phase variable model; Permanent magnet motor; Soft magneti omposite (SMC). I. INTRODUCTION Soft magneti omposite (SMC) materials have many unique properties. These properties inlude good design flexibility due to magneti isotropy, very low eddy urrent harateristis beause of the partile oating, and high potential for low-ost mass prodution through the powder metallurgial molding tehnique. Their use in eletrial mahine manufature has undergone signifiant development in the past deade, and the results are very promising [1]. A large amount of researh has been onduted by various researhers on designing and prototyping various types of eletrial mahine. These studies fous on the axial field permanent magnet (PM) mahine [2]-[6], law pole motor [7]-[10], transverse flux motor [11]-[13], hybrid axial and radial flux motor [14], PM radial field servo motor [15]-[16], DC motor [17], universal motor [18]-[19], indution motor [20], and swithed relutane motor [21]. They overed a variety of appliations. Among these mahines, the most signifiant types are the law pole and transverse flux motors whih feature omplex strutures and 3-D flux paths [22]- [23]. These features mean that it is diffiult to use laminated steel so that SMC material appears to be an ideal substitute. The main onstraint of steel laminations, i.e., the magneti flux must flow within a 2-D lamination plane, is then removed. This offers greater design flexibility for exploiting novel-struture eletrial mahines, whih may lead to improved performane and new appliations. However, SMC materials do have disadvantages. They have low magneti permeability so that most of the SMC mahines that have been developed are PM mahines whih have high magnet thikness. Hene the magneti iruit is not very sensitive to the permeability of the ore. Beause the magnets have a permeability whih is lose to air the magnet relutanes dominate the magneti iruit. Most of the SMC motor prototypes investigated so far used the iron ores ut from existing pre-forms whih were previously ompated with high pressure in a simple shape mold suh as ylinder or bar. This tehnique might be appropriate for prototyping but not suitable for mass prodution beause of the ost issue. Furthermore, the utting proess may signifiantly redue the magneti and mehanial properties of the SMC ore. SMC is brittle so that in ore prodution it is better to use a molding tehnique rather than mahining a pre-formed sample. Some papers have addressed the molding of parts, i.e., a modular tehnique [24]-[25], but this still needs a large number of ostly pressing and assembly stages. The ideal proess should be that the ore is pressed in one single step and that the oils an be easily fitted. In ommerial prodution, the manufaturing ost of the SMC motor an be dramatially redued if a highprodutivity low-pressure press is used in the molding. However, the magneti properties of SMC material, and hene the motor performane, are very dependant on the mass density of the ore. Therefore areful designing is neessary to obtain a good ompromise between the molded ore density and the mahine performane. To investigate the industrial prodution-ready produts, the authors reently developed tehniques for designing and prototyping PM motors with low-density molded SMC ores [26]. This paper further reports on the development of the law pole PM SMC motor whih ould replae an existing single phase indution motor in a dish washer pump. A mold for pressing the SMC law pole disk was designed and fabriated. SMC ores were ompated at two different pressures and the orresponding magneti properties were measured and ompared. The lower mass density ore was used in the development of an SMC motor. Finite element

3 magneti field analysis was arried out for aurate alulation of the key motor parameters, suh as winding flux, bak-emf, winding indutane and ore loss. An improved phase-variable model was developed in Simulink for the predition of motor performane. A prototype was fabriated with the low-density molded SMC ores, and tested to validate the motor parameter omputation and performane analysis. The theoretial analyses and experimental results illustrated that the lowdensity molded SMC ore is suitable for mass prodution. II. MOLDED SMC CORE AND MOTOR PROTOTYPE As desribed in the last setion, SMC is very suitable for developing omplex-strutured PM motors beause of its unique magneti and mehanial properties. This paper desribes the development of a three-phase three-stak permanent magnet law pole motor with SMC stator ore whih takes advantage of these unique properties. The onventional mahine has a torque output whih is proportional to the produt of the air-gap magneti flux and the eletri loading, and is not very salient, even for an internal PM mahine. The law pole mahine is highly salient so that it is very torque dense with high pole number (if magneti saturation and leakage is ignored). Therefore, the law pole motor usually has a large number of poles. Here, the law pole motor is hosen to have 12 poles so that an exitation frequeny of 300 Hz is required for a synhronous speed of 3000 rpm. The 300 Hz frequeny is not unrealistially high for SMC material [22]-[23]. The low eddy urrent loss property due to the oated insulated partiles allows the mahine to operate at higher frequeny, resulting in smaller size and weight for a given output. The motor is designed to replae an existing indution motor for a dish washer pump, so the major dimensions (e.g. outer diameter and overall axial length) should be within the available spae and deliver the same output. Fig. 1 shows the SMC law pole disks after ompation in a mold with a single step press (no further mahining required). Fig. 2 shows the assembled 3 phase stator ore. Eah phase onsists of two disks with one onentrated axially-orientated global (i.e., spanning all poles) oil in between eah molded disk. The simple struture allows a very high fill fator to be ahieved. The stator is formed by staking three phases axially with a irumferential spatial shift of 120 o eletrial from eah other. The major geometrial parameters are: stator inner diameter = 43 mm, stator outer diameter = 67 mm, effetive axial length = 55 mm, and air-gap length = 1 mm. 12 NdFeB magnets with dimensions of mm 3 are mounted on the surfae of a mild steel rotor. The motor is designed to operate at 3000 rpm, delivering 60 W of mehanial power. The stator ore disks were ompated in a mold with a pressure of 20 ton fore (about 179 MPa) or 100 ton fore (895 MPa). This is slightly higher than 800 MPa, whih is the nominal pressure for the SMC material [27]. The average mass densities are 5.8 g/m 3 and 7.2 g/m 3, respetively. As shown in Fig. 3, the measured B-H urve of the 5.8 g/m 3 ore is muh lower than that of the 7.2 g/m 3 ore. However, the low density ores an be ompated at lower pressure, whih yields muh higher produtivity ompared to the higher density ores. This an be attrative for industry appliation. In this paper, the 5.8 g/m 3 molded SMC ore is used to fabriate the mahine. Fig. 1. Six Molded SMC law pole disks for the motor stator ore. Fig. 2. Stator of a 3-phase law pole motor Fig. 3. Measured B-H urves of ompated SMC ores with pressure of 20 ton and 100 ton

4 III. PARAMETER COMPUTATION AND PERFORMANCE ANALYSIS A. Magneti Field Finite Element Analysis and Parameter Computation Due to the omplex struture and 3-D magneti flux path of the law pole motor, a 3-D numerial analysis of the magneti field by, for example, finite element analysis is neessary to aurately determine the magneti field distribution and major parameters. Strutural symmetry means that only a pole region is needed for the field analysis, as shown in Fig. 4(a). On the two radial boundary surfaes, the salar magneti potentials should obey the following halfperiodial boundary onditions: ϕ m (r,θ, z ) = ϕ m (r,θ + Δθ, z ) where Δθ = 30 o is the angle of one pole pith. The onditions for magneti flux density at the two boundary planes are: B r (r,θ, z ) = B r (r,θ + Δθ, z ) B θ (r,θ, z ) = B θ (r,θ + Δθ, z ) B z (r,θ, z ) = B z (r,θ + Δθ, z ) (1) (2a) (2b) (2) (a) Fig. 4. (b) Flux density vetor plot at no-load Fig. 4(b) illustrates the magneti flux density vetor plot at no-load and θ = 0 o for the arrangement shown in Fig. 4(a). The law poles fae rotor magnets so that the main magneti iruit has the lowest magneti relutane and the stator winding has maximum magneti flux linkage. It an be seen that the major magneti flux flows along a 3-D path, i.e. starting from the north pole of a rotor PM, radially passing aross the air-gap to enter one law pole, flowing into the SMC stator ore (mainly axially in the law pole, radially in the side wall, and irumferentially in the yoke), radially passing aross the air-gap again into the south pole of another rotor PM, and finally through the mild steel rotor yoke to form a losed loop. It an also be found that a onsiderable amount of flux leakage exists between the side and end surfaes of the law poles of the two separated disks. Considerable attention should be paid in the design stage to the redution of the flux leakage. From the no-load magneti field distribution, a number of major motor parameters an be determined. For example, Fig. 5 plots the omputed waveform of the flux linkage of one phase winding with the rotor PMs. This was obtained by alulating the flux at different rotor positions, e.g., by rotating the rotor magnets for one pole pith in 24 steps. To redue the omputation error aused by meshing, separate fixed meshes are reated for the stator and rotor parts and then merged in the middle of the air-gap when the rotor moves to a new position. It an be seen that the flux waveform is almost sinusoidal. Fig. 5. Per-turn flux of a phase winding produed by rotor PMs When the rotor rotates, a bak-emf is indued into the stator phase winding. The frequeny of the bak-emf depends on the rotor speed while its waveform is determined by the phase winding flux-linkage waveform. Aording to Fig. 5, the bak-emf is lose to sinusoidal (the differential of this waveform). The bak-emf onstant an be omputed: K = p N φ max E s 2 2 where p = 12 is the number of poles, N s = 256 the number of turns of a stator phase winding, and the peak phase winding flux-linkage φ max = mwb. The EMF onstant an then be alulated to be Vs/rad. From the no-load magneti field solutions, the ogging torque urve an be obtained by using the virtual work method or the Maxwell stress tensor method. The winding indutane is one of the major parameters affeting the motor performane. The behavior of an eletrial iruit is determined by the inremental indutane rather than the apparent indutane [28]. Fig. 6 plots the selfindutane of a phase winding using a modified inremental energy method [29]. The inremental indutane is omputed using the following steps: (1) For a given rotor position, perform a non-linear (3)

5 analysis whih aounts for the saturation due to the rotor PMs (assuming the magneti field produed by the PMs is dominant); (2) Save the inremental permeability in eah element; (3) Swith off the rotor PMs, and perform a linear field analysis with the saved permeabilities under a perturbed urrent exitation; (4) Calulate the value of the inremental magneti oenergy for the urrent exitation; (5) Finally, the self inremental indutane an be omputed from The oeffiients β, k, k e and C e are obtained by urve fitting the measurements on to a ubi SMC sample by using a 3-D magneti property tester [33]. The time stepping FEA and ore loss omputation are arried out on an elemental basis. The total ore loss is obtained by summing the ore loss in eah element. Fig. 7 plots the omputed transient ore loss against rotor angle. L in 2ΔW (Δi) 2 (4) The apparent self indutane an also be omputed by the above method if, in step 2, the apparent permeability is saved. The mutual indutane between phase windings an be onsidered as zero if eah stak is assumed to be magnetially independent. It an be seen that unlike onventional mahines, law pole SMC motors have large indutane variation due to their salieny, whih may affet the dynami performane [30]. Fig. 7. Transient ore loss Fig. 6. Inremental and apparent indutanes of a phase winding The SMC mahine is different from a onventional mahine where the opper loss dominates; the ore loss and opper loss in an SMC mahine are more omparable. Therefore, it is very important to aurately predit the ore loss. This an be done by taking into aount the waveform of the flux density lous in eah element of the ore when the rotor rotates [31]. Due to the large value, the ore loss variation an be signifiant aross the dynami performane simulation range. In this paper, the variation is obtained using a magneti field time-stepping finite element analysis (FEA) B. Improved Phase Variable Model and Motor Performane Predition An improved phase-variable model [34] is applied to analyze the performane of the motor when it is driven by a sensorless brushless DC (BLDC) ontroller (as developed at the University of Tehnology Sydney), whih an produe a reasonably sinusoidal phase voltage waveform to math that of the motor bak EMF. The eletro-mehanial equations of the phase-variable model are desribed below where L jk is the apparent indutane (whih is independent of the stator urrents), and L jk the inremental indutane. All other parameters are used in their onventional meaning. It should be noted that the mutual indutane for this motor is quite small sine eah phase stak is almost magnetially independent. The three phase windings are onneted in star with a entral point for experimental measurement. The eletro-mehanial equations are: v j = r j i j + dλ j / + e j, j=a,b, (6) λ j = = a L jk i k k d λ j λ j di = k + λ j dθ r and an improved three-term formula [32] where k =a i k θ r z db 2 β z k db z 3 k db di dl jk P fe ={ H j } + ( ) + { ( ) } (5) = (L jk + i k ω r ) 2π 2 C j β 2 j 2 e j 2 4 j=x j=x e j=x = k a dθr k (7) (8)

6 J dω r = T T em = ( e j i j ) / ω r + T og (9) j = a r j = r k, L jk = L kj, P dθ fe r em T L δω r r ωr j = a, = ω (10) i j = 0 (j, k=a, b, ) (11) Suppose that the terminal potentials (voltages) of the staronneted three-phase phase windings are U a, U b and U, respetively, then the entral star point voltage U N an be alulated from and referring to (8), we get v a = (r a i a + L a a di a ) + v am + e a (19) dia v a = v a v am = (r a i a + L a a ) + e (20) a Similarly, v bm, v b, vm and v an be defined. Based on the above equations, an improved phase-variable model an be developed in Simulink for simulating both the steady-state and dynami performanes of the motor, as illustrated in Fig. 8. v j = U j U N, (j=a, b, ) (12) U N = j = a r di a L ja + e a j=a k =b A (U j v j ) / 3 (13) By substituting (6) to (8) into (13), and with due onsideration of (11), we have 1 T di dl k U jk (14) N = U j l L jk + 3 dθ i k ω r I e j j =a 1 k =a A r The values of U j (j = a, b, ) are deided by the swithing states of the inverter, whih represent the PWM states that are used to ontrol the 3-phase winding urrents. Under BLDC ontrol, there are only two phase windings that are energized at any moment, e.g., the urrent flows into phase b and then out of phase via the entral point, and phase a is nonenergized (120 degree ondution). U N and U a an be obtained from U = 1 N 2 U a = U N + j =b A di j lu j L jj dl jj dθ i jω r e j I (15) di k dl ak + l L a k + i k ω r I (16) dθ r When the phase urrent is not zero and the PWM is in the off state, U a is obtained from U a = U bus if I a > 0, U a = 0 if I a < 0 (17) where U bus is the potential of the power bus line. Using (15)-(17), we an derive the potentials of the input ports and the entral star point of the three phase windings, and hene the three phase voltages. By defining the voltage v am = k =b L a k di k + k =a dl ak dθ r i k ω r (18) Fig. 8. Simulink implementation of an improved phase-variable model Compared to the magneti field FEA, the improved phasevariable model an predit the motor using a muh shorter time but with the same level of auray. The dependene of key parameters on time or rotor angle has been previously obtained using a series of time-stepping FEA solutions. The variations of parameters against rotor position are stored in a lookup table and will be retrieved during the performane simulation. From Fig. 8, key motor performane harateristis an be

7 predited. For example, Fig. 9 illustrates the simulated speed urve from start-up, showing that the motor an aelerate smoothly to the rated speed of 3000 rpm at the rated torque of 0.2 Nm. Fig. 10 shows the simulated steady-state eletromagneti torque with ripple, whih is aused by the ogging torque, transient ore loss torque and phase urrent swithing. Fig. 11 plots the simulated applied voltage, bak- EMF and phase urrent. Fig. 9. Simulated speed urve from startup to steady state Fig. 11. Simulated phase voltage, bak EMF and urrent Fig. 10. Simulated steady eletromagneti torque IV. EXPERIMENTAL RESULTS The motor parameter alulations have been verified by measurements on the prototype. For example, the bak-emf waveform (open-iruit voltage) was reorded on a CRO when the rotor was rotated. From the approximately sinusoidal waveform, the peak-to-peak EMF was found to be 46.5 V at 39.7 Hz. It an be dedued that the per-turn winding flux-linkage (with the rotor PMs) is mwb, whih is very lose to the alulation. With the voltageurrent method, the equivalent phase winding indutane was found to be 50.9 mh, whih is lose to the average value of 54.1 mh (differential) or 56.2 mh (apparent) in Fig. 6. The mutual indutane was measured as only about 5% the self indutane. Fig. 12 illustrates the experimental setup for measuring the motor performane. The SMC motor prototype is on the right and a dynamo load ell is on the left. A torque transduer is mounted between the motor and the load for measuring the shaft torque and speed. Fig. 13 plots the measured mehanial harateristis, i.e., the motor speed against applied DC link voltage of the inverter with different loads. The motor an suessfully deliver a torque of 0.2 Nm at 3000 rpm.

8 Fig. 13. Fig. 12. Experimental setup Speed vs. DC link voltage with onstant torque V. CONCLUSION This paper presents the development of a three-phase permanent magnet motor with a molded low density soft magneti omposite (SMC) stator for driving a dish washer pump. 3-D magneti field finite element analyses were arried out and these aurately omputed the key motor parameters suh as winding flux-linkage, bak-emf, ogging torque, winding indutane and ore loss. An improved phase-variable model was developed in Matlab/Simulink for analyzing the motor performane. In this model, the rotor position dependene of key parameters an be aounted for. The developed motor has been prototyped and tested, validating the design and analysis. It is antiipated that the molded low-density SMC ore would be a ost-effetive tehnique for mass prodution of SMC eletrial mahines. ACKNOWLEDGMENT The authors gratefully aknowledge the finanial support of the Australian Researh Counil (Linkage Projet Grant: LP ) whih allowed this work to be arried out. REFERENCES [1] The latest development in soft magneti omposite tehnology, SMC Update, Reports of Höganäs AB, Sweden. ( ). [Online]. Available at [2] M. Persson, P. Jansson, A. G. Jak and B. C. Merow, Soft magneti omposite materials use for eletrial mahines, in Pro. 7 th IEE Conf. on Eletrial Mahines and Drives, Durham, England, Sept. 1995, pp [3] F. Profumo, A. Tenoni, Z. Zhang and A. Cavagnino, Novel axial flux interior PM synhronous motor realized with powdered soft magneti materials, in Pro IEEE Industry Appliation Soiety Annual Meeting, St. Louis, USA, Ot. 1998, pp [4] G. Cvetkovski, L. Petkovska, M. Cundev and S. Gair, Improved design of a novel PM disk motor by using soft magneti omposite material, IEEE Trans. Magn., vol. 38, no. 5, pp , Sept [5] M. A. Khan, Y. Chen, and P. Pillay, Appliation of soft magneti omposites to PM wind generator design, in Pro IEEE Power Engineering General Meeting, 4 pages. [6] G. S. Liew, N. Ertugrul, W. L. Soong, and D. B. Gehlert, Analysis and performane evaluation of an axial-field brushless PM mahine utilising soft magneti omposites, in Pro. IEEE Int. Eletri Mahines and Drives Conf., May 2007, pp [7] A. G. Jak, B. C. Merow, C. P. Maddison and N. A. Wahab, Claw pole armature permanent magnet mahines exploiting soft iron powder metallurgy, in Pro. IEEE Int. Conf. on Eletri Mahines and Drives, Milwaukee, USA, May 1997, pp. MA1/ [8] J. Cros and P. Viarouge, New strutures of polyphase law-pole mahines, in Pro. IEEE 37 th Industry Appliations Soiety Annual Meeting, Ot. 2002, pp [9] R. Qu, G. B. Kliman, and R. Carl, Split-phase law-pole indution mahines with soft magneti omposite ores, in Pro. IEEE 39 th Industry Appliations Soiety Annual Meeting, Ot. 2004, pp [10] Y. G. Guo, J. G. Zhu, P. A. Watterson, and W. Wu, Development of a law pole permanent magnet motor with soft magneti omposite stator, Australian Journal of Eletrial & Eletroni Engineering, vol. 2, no. 1, pp , [11] B. C. Merow, A. G. Jak and C. P. Maddison, Permanent magnet mahines for high torque, low speed appliations, in Pro. Int. Conf. on Eletrial Mahines, Vigo, Spain, Sept. 1996, pp [12] R. Blissenbah and G. Henneberger, New design of a soft magneti omposite transverse flux mahine with speial attention on the loss th mehanisms, in Pro. 4 Int. Symp. on Advaned Eletromotion, Bologna, Italy, June [13] Y. G. Guo, J. G. Zhu, P. A. Watterson, and W. Wu, Development of a permanent magnet transverse flux motor with soft magneti omposite ore, IEEE Trans. on Energy Conversion, vol. 21, no. 2, pp , June [14] A. G. Jak, B. C. Merow and C. P. Maddison, Combined radial and axial permanent magnet motors using soft magneti omposites, in th Pro. 9 Int. Conf. on Eletrial Mahines and Drives, Canterbury, UK, Sept. 1999, pp [15] A. G. Jak, B. C. Merow, P. G. Dikison, D. Stephenson, J. S. Burdess, N. Fawett and J. T. Evans, Permanent magnet mahines with powdered iron ores and pre-pressed winding, IEEE Trans. on Industry Appliations, vol. 36, no. 4, pp , [16] J. Cros, P. Viarouge and C. Gelinas, Design of PM brushless motors using iron-resin omposites for automotive appliations, in Pro. IEEE 33 rd Industry Appliation Soiety Annual Meeting, St. Louis, USA, Ot. 1998, pp [17] J. Cros, P. Viarouge and A. Halila, Brush DC motors with onentrated windings and soft magneti omposites armatures, in Pro. IEEE 36 th Industry Appliation Soiety Annual Meeting, Chiago, USA, 2001, pp [18] A. G. Jak, B. C. Merow, P. Dikson, P. Jansson and L. Hultman, Design and testing of a universal motor using a soft magneti omposite stator, in Pro. IEEE Industry Appliations Soiety Annual Conferene, Rome, Italy, Ot. 2000, pp [19] J. Cros, P. Viarouge, Y. Chalifour and J. Figueroa, A new struture of universal motor using soft magneti omposites, in Pro. IEEE 36 th

9 Industry Appliation Soiety Annual Meeting, Chiago, USA, 2001, pp [20] T. Fukuda and M. Morimoto, Load harateristis of indution motor made of Soft Magneti Composite (SMC), in Pro Int. Conf. on Eletrial Mahines and Sys., Wuhan, China, Ot. 2008, pp [21] K. Vijayakumar, R. Karthikeyan, G.K. Sathishkumar, and R. Arumugam, Two dimensional magneti and thermal analysis of high speed swithed relutane motor using soft magneti omposite material, in Pro. TENCON IEEE Region 10 Conf., Nov. 2008, pp [22] A. G. Jak, Experiene with the use of soft magneti omposites in eletrial mahines, in Pro. Int. Conf. on Eletrial Mahines, Istanbul, Turkey, 1998, pp [23] Y. G. Guo, J. G. Zhu, P. A. Watterson, and W. Wu, Comparative study of 3-D flux eletrial mahines with soft magneti omposite ore, IEEE Trans. on Industry Appliations, vol. 39, no. 6, pp , Nov [24] W. Ouyang and T. A. Lipo, Multiphase modular permanent magnet drive system design and realization, in Pro. IEEE Int. Eletrial Mahines and Drives Conf., 2007, pp [25] G. S. Liew, E. C. Y. Tsang, N. Ertugrul, W. L. Soong, D. Atkinson, and D. B. Gehlert, Analysis of a segmented brushless PM mahine utilising soft magneti omposites, in Pro. 33 rd Annual Conf. of IEEE Industrial Eletronis Soiety, 2007, [26] Y. G. Guo, J. G. Zhu, and D. G. Dorrell, Design and analysis of a law pole PM motor with molded SMC ore, IEEE Trans. Magn., 2009, in press. [27] Soft Magneti Composites from Höganäs Metal Powders - SOMALOY 500, Höganäs Manual, [28] M. Gyimesi and D. Ostergaard, Indutane omputation by inremental finite element analysis, IEEE Trans. Magn., vol. 35, pp , [29] Y. G. Guo, J. G. Zhu, and H. Y. Lu, Aurate determination of parameters of a law pole motor with SMC stator ore by finite element magneti field analysis, IEE Proeedings Eletri Power Appliation, vol. 153, no. 4, pp , July [30] Y. G. Guo, J. G. Zhu, Z. W. Lin, H. Y. Lu, X. L. Wang, and J. X. Chen, Influene of indutane variation on the performane of a PM law pole SMC motor, Journal of Applied Physis, vol. 103, no. 7, pp. 07F , 1 Apr [31] Y. G. Guo, J. G. Zhu, J. J. Zhong, and W. Wu, Core losses in law pole permanent magnet mahines with soft magneti omposite stators, IEEE Trans. Magn., vol. 39, no. 5, pp , Sept [32] D. Lin, P. Zhou, W. N. Fu, Z. Badis, and Z. J. Cendes, A dynami ore loss model for soft ferromagneti and power ferrite materials in transient finite element analysis, IEEE Trans. Magn., vol. 40, no. 2, pp , Mar [33] Y. G. Guo, J. G. Zhu, Z. W. Lin, and J. J. Zhong, Measurement and modeling of ore losses of soft magneti omposites under 3D magneti exitations in rotating motors, IEEE Trans. Magn., vol. 41, no. 10, pp , Ot [34] J. X. Chen, Y. G. Guo, J. G. Zhu, and J. X. Jin, Performane analysis of a surfae mounted permanent magnet brushless DC motor using an improved phase variable model, in Pro. 42 nd IEEE Industry Appliations Soiety Annual Conf., New Orleans, USA, Sept. 2007, pp