ΦAbstract -- This paper deals with peculiar design of high frequency 15 kW synchronous permanent magnet motor having raised technical and economic parameters. Reduction of losses is achieved by slotless stator core structure. Performance motor characteristics are increased by special rotor design: the rotor has two parts which are moving under inner stator diameter and over outer stator diameter, so the both sides of a coil create electromotive force. Some questions of optimal construction with electromagnetic characteristics are estimated. Recommendations at the choice of proper rotor dimensions are given and opportunities of decrease in losses are estimated.

Index Terms -- design methodology, frequency, losses, permanent magnets, synchronous machines

I. INTRODUCTION he permanent magnet high-speed synchronous machines (PMSM) are used more in different applications in recent years due to their high performance and to the relatively

low cost with a high quality of modern permanent magnets [1-11].

It should be noted that because of high value magnetization frequency for high-speed PMSM the stator-teeth and stator-yoke magnetic flux density must be decreased and the air gap magnetic flux density should be limited up to 0.5 Т. Reduction of losses can be achieved by slotless stator core structure. A number of authors have presented design, electromagnetic modeling and analysis of axial-flux coreless PMSM [1, 2, 4, 6, 10]. We suggest to investigate three various models of slotless motor with radial permanent magnets.

The proposed motor essential is the using of permanent magnets NdFeB for excitation to receive higher efficiency of a set of elementary magnets with non-magnetic inserts. The magnets and inserts are strengthened by non-magnetic strip cylinder. Two low resistance rings are also placed on the rotor. The damping and line-starting properties of rotor itself are improved by such decision.

The main data of motor are the following:

Rating, kW 15.0

Authors thank RFBR for support by grant № 10-08-00402_a. Janush B. Danilevich is with Russian Academy of Sciences, Institute of

Silicate Chemistry, St. Petersburg 199034, Russia (e-mail: jandan@isc.nw.ru).

Victor N. Antipov, is with Russian Academy of Sciences, Institute of Silicate Chemistry, St. Petersburg 199034, Russia (e-mail: bht@mail.ru).

Irina Yu. Kruchinina is with Russian Academy of Sciences, Institute of Silicate Chemistry, St. Petersburg 199034, Russia (e-mail: ikruch@isc.nw.ru).

Yuvenaliy Ph. Khozikov is with Russian Academy of Sciences, Institute of Silicate Chemistry, St. Petersburg 199034, Russia (e-mail: khozikov@isc.nw).

Anna A. Ponomareva is with Russian Academy of Sciences, Institute of Silicate Chemistry, St. Petersburg 199034, Russia (e-mail: jandan@isc.nw.ru).

Lubov Yu. Shtainle is with Russian Academy of Sciences, Institute of Silicate Chemistry, St. Petersburg 199034, Russia (e-mail: jandan@isc.nw.ru).

Voltage, V 220 Speed of rotation, rpm 3000 Number of phases 3 Number of poles 16 Frequency, Hz 400 Power factor 0.8 Stator winding connection «star»

II. DESIGN ASPECTS There is nothing more important to PMSM than line-

starting condition. The complicated configuration of line-starting PM motors, including cage and magnets, requires to look for another construction solution. The decision can be received by improvement of damping and line-starting properties of rotor in person. Such design has been made in [8, 12]. Rotor magnetic system consists of four elements: permanent magnets divided by nonmagnetic inserts, face flanges and the strip cylinder. Distinguish feature of this construction encloses in material of constructive elements: the face flanges are produced from material having the high conductivity, e.g. from copper, the strip cylinder is produced from nonmagnetic steel. Together with the strip cylinder they form starting winding that is important because the generator can also be used as a motor. The rotor design is distinguished simplicity and reliability, because construction has not many components.

For high frequency of excitation the iron losses, essentially at slot zone may be very significant. The way to restrict the iron losses is to exclude at design the slot zone. The several models of such motors are represented in Fig. 1, where two pole pitch is shown.

Fig. 1. The design models of the synchronous motor with permanent magnets (1 – stator core; 2 – stator winding; 3 – magnets; 4 – non magnetic inserts; 5 – the strip cylinder, 6 – rotor core; 7 – air gap)

The first model (a) is the basic model with traditional slot stator core. The second model (b) is the model with slotless stator core and with the rotor which is moving under inner stator core diameter. The third model (c) is the model with slotless stator core and with the rotor which is moving over outer stator core diameter. The last model (d) also has slotless stator core but with rotor consisting of two parts, one of them is moving under inner stator core diameter, another is moving over outer stator core diameter. The numerical

Peculiar design of permanent magnet synchronous motor

J. B. Danilevich, V. N. Antipov, I. Yu. Kruchinina, Y. Ph. Khozikov, A. A. Ponomareva,L. Yu. Shtainle

T

XIX International Conference on Electrical Machines - ICEM 2010, Rome

978-1-4244-4175-4/10/$25.00 ©2010 IEEE

calculations have been made for the same stator winding (slot number is 48, coil number is 16) but for different dimensions which is optimal for chosen model.

The results of numerical calculation for a), b), c) models are given in Table I.

TABLE I COMPARISON OF NUMERICAL CALCULATION FOR VARIOUS MODELS

OF 15 KW, 220 V, 3000 RPM PMSM

Data Value Model a) b) c)

Outer stator core diameter DSI, mm 204 180 180Inner stator core diameter DS, mm 170 170 170Rotor diameter DR, mm 168 162 190Active rotor length, la, mm 650 630 485Air gap Δ, mm* 3 6 5Magnet height hm, mm 7 7 6Copper mass GCu, kg 4.39 3.46 2.69Iron mass GFe, kg 34.3 12.6 9.7Magnet mass GM, kg 12.1 12.8 10.3Efficiency η, % 80.1 88.1 86.5

* including non magnetic strip cylinder From Table I data it is obvious that the model a) with slot

stator core has the worse result in respect to efficiency and the largest weight of copper and iron. The best result was received for model b) when the rotor has been moved along the under inner stator core diameter. The efficiency is increased at 8 point, expenses of copper are 25 % less, the expenses of iron are decreased almost two times. The model c) when the rotor has been moved over outer stator core diameter also has some advantages: the efficiency is increased at 6.4 point, expenses of copper and, iron more essential, the magnet volume is less than another models have. Nevertheless the model b) and model c) have grave disadvantage because only one side of stator winding coil is creating electromotive force. The special design has been created when the rotor has two parts which are moving under inner stator diameter and over outer stator diameter. In this case the both coil sides are creating electromotive force (model d)).

III. ELECTROMAGNETIC DESIGN OPTIMIZATION The choice set of the main dimensions, the air gap value,

the magnet height and stator winding parameters have been investigated for model d).

Fig. 2. The model for 2D-FEA calculations (1 – stator core; 2 – stator winding; 3 – magnets; 4 – non magnetic inserts; 5 – the strip cylinder and air gap, 6 – rotor core)

The model for 2D-FEA calculations is shown in Fig. 2. In

Table II you can see the data for the base synchronous motor, the calculations have been carried out separately for

“over” and “inner” parts of rotor with common stator core. Calculation has been made for 16 winding coils and for pole overlap α = 0.812.

TABLE II COMPARISON OF NUMERICAL CALCULATION FOR VARIOUS MODELS

OF 15 KW, 220 V, 3000 RPM PMSM

Data Value

Model Outer rotor

Inner rotor Total

Outer stator core diameter DSI, mm 188 188 188Inner stator core diameter DS, mm 170 170 170Rotor diameter DR, mm 198 156.4Active rotor length la, mm 370 370 370Air gap Δ, mm 5 8.8Magnet height hm, mm 4 3Copper mass GCu, kg 2.13 2.13 2.13Iron mass GFe, kg 13.6 13.6 13.6Magnet mass GM, kg 5.5 3.2 8.7Efficiency η, % 92.0 94.9 93.4

For hand-picked optimal set of 15 kW PMSM the

electromagnetic, mechanical, ventilation and thermal design have been fulfilled, and main characteristics have been received. The magnet diagrams for “over” and “inner” magnets are represented in Fig. 3. The distribution of vector magnetic potential for no-load, rated load and short circuit are depictured in Fig. 4-6.

0,001,002,003,004,005,006,007,008,009,0010,00

-7000 -6000 -5000 -4000 -3000 -2000 -1000 0

F, А

Ф,mWb

ФmФd0

Фmsc

Фs

Фм-Фs

0,001,002,003,004,005,006,007,008,00

-5000 -4000 -3000 -2000 -1000 0

F, А

Ф,mwb

Фm

Фd0

ФmscФs

Фm-Фs

Fig. 3. B-H characteristics of “over” and “inner” permanent magnets (Фm - magnet flux, Фd0 - open circuit flux, Фmsc - short circuit flux, Фs - leakage flux)

The magnetic vector potential has only the component in

z direction. The circuit equations only include the parts which are in the main magnetic field regions. The resistances and inductances of the ending parts of the windings and conductors are all included in the external circuit.

Electromagnetic torque is computed by the Maxwell stress tensor at all points of a bounding surface about the rotor and summed to find the resultant torque applying to rotor using calculation technique.

∫ ××= s r dsBJrM

1 2

3

4

6

5

where r − position vector; rJ − total current density,

vector; B − magnetic flux density vector; ds − area of the bounding surface.

Fig. 4. The distribution of vector magnetic potential over cross section 15 kW PMSM at no load

Fig. 5. The distribution of vector magnetic potential over cross section 15 kW PMSM at rated load

Fig. 6. The distribution of vector magnetic potential over cross section 15 kW PMSM at short circuit

As the calculations show the rotor upper part ensures 11.83 kW, but the lower rotor part only 3.6 kW. In the Fig. 7 the distribution of magnetic flux density over motor cross section is shown. In Fig. 8 and Fig. 9 the distributions of magnetic flux density along the air-gap for both rotor parts are shown.

Fig. 7. The distribution of magnetic flux density (T) over motor cross section

Fig. 8. The distribution of magnetic flux density (B) along the air-gap of “upper” rotor (DIST – air-gap length (m), y-axis – B (T))

Fig. 9. The distribution of magnetic flux density (B) along the air-gap of “lower” rotor (DIST – air-gap length (m), y-axis – B (T))

IV. CONCLUSION The electromagnetic calculations have been executed and

a new design of a high frequency permanent magnet synchronous motors has been proposed.

Numerical methods such as FEM have been used for electromagnetic field investigations to calculate power, flux and magnetic flux density.

The proposed motor design saves the active materials and greatly decreases iron losses. For 15 kW PMSM in comparison with slot core stator set the efficiency increases at 8.7 %, expenses of copper amount to 49 %, expenses of iron is 74 %, expenses of magnet is 96 %.

The motor construction of calculated model is represented in Fig. 10 and can be improved in future by decreasing air gap.

Fig. 10. The motor construction of calculated model

V. REFERENCES [1] F. Caricchi, F. Crescimbini, F. Honorati, G.L.Bianco, and E. Santini,

“Performance of coreless winding axial-flux PM generator with power output at 400 Yz-3000 rev/min,” IEEE Trans. Ind. Appl., vol. 34, No. 6, pp. 1263-1269, Nov./Dec. 1998.

[2] R.-J. Wang and M.J. Kamper, “Calculation of eddy current loss in axial field permanent magnet machine with coreless stator,” IEEE Trans. Energy Convers., vol. 19, No. 3, pp. 532-538, Sep. 2004.

[3] A. Binder, M. Klohr, T. Schneider, “Losses in High-Speed Permanent Magnet motor with magnetic levitation for 40000/min, 40 kW,” in Book of Abstracts 2004 International Conf. on Electrical Machines, paper 464.

[4] F. Marignetti and J.R. Bumby, ”Electromagnetic modeling of Permanent Magnet Axial Flux Motors and Generators,” in Proc. 2004 International Conf. on Electrical Machines, paper No. 588.

[5] J. B. Danilevich, V. N. Antipov, I. Yu. Kruchinina, “Permanent magnet generator for 200 kW station of a new type,“ in Proc. 2004 International Conf. on Electrical Machines, pp. 308-310.

[6] R.-J. Wang and M.J. Kamper, Van der Westhuizen, and J.F. Gieras, ”Optimal design of a coreless stator axial flux permanent magnet generator,” IEEE Trans. Magn., vol.41, No. 1, pp. 55-64, Jan. 2005.

[7] A.S. Nagorny, R.H. Jansen, D. M. Kankam, “Experimental Performance Evaluation of a High-Speed Permanent Magnet Synchronous Motor and Drive for a Flywheel Application at Different Frequencies” in Book of Abstracts 2006 International Conf. on Electrical Machines, p. 536.

[8] Danilevich Y. B., Antipov V. N., “High-speed (3000-15000 rpm) permanent magnet generator (design and testing),” in Book of Abstracts 2006 International Conf. on Electrical Machines, pp. 2-5.

[9] J. B. Danilevich, , I. Yu. Kruchinina, V. N. Antipov, Y. Ph. Khozikov, A. V. Ivanova, “Some Problems of the High-Speed Permanent Magnet Miniturbogenerators Development,” in Proc. 2008 International Conf. on Electrical Machines, Paper ID 942.

[10] S.M. Hosseini, M. Agha-Mirsalim, and M. Mirzaei, ”Design, Prototyping, and Analysis of Low Cost Axial-Flux Coreless Permanent-Magnet Generator,” IEEE Trans. Magn., vol. 44, No. 1, pp. 75-80, Jan. 2008.

[11] J. B. Danilevich, V. N. Antipov, I. Yu. Kruchinina, Y. Ph. Khozikov, Lower-power turbogenerators for decentralized energy supply systems. St. Petersburg: Science, 2009, p. 102 (in Russian).

[12] J. B. Danilevich, V. N. Antipov, A. D. Grozov, “Synchronous electrical machine rotor”. Patent of Russian Federation, No. Oct. 5, 2006.

VI. BIOGRAPHIES

Janush B. Danilevich was born in Vilnius in Lithuania, on December 6, 1931. He graduated from Leningrad Polytechnic Institute.

His employment experience includes Institute electromechanics ASSU, Institute of electric machine industry, Division of Electric and Power engineering problems RAS, Electrophysics and Power engineering Institute RAS, Institute of Silicate Chemistry RAS.

J. B. Danilevich received honorary degrees from institutions of higher learning including doctor of technical science, academician of Russian Academy of Sciences, Senior Member, IEEE, doctor Honoris Causa (Krakow Polytechnic University), the head of laboratory power and ecology of Institute of Silicate Chemistry RAS, guide of power and renewable energy. His special fields of interest include new methods of mathematical modeling of the electromechanical energy convertors, joint consideration both electromagnetic, thermal and mechanical problems, the solution of the problem of the abnormal operation of the generators in power systems, creating of a new local energy sources for integrated energy production.

Victor N. Antipov was born in Voronezh in the Soviet Union, on April 10, 1940. He graduated from Leningrad Polytechnic Institute.

His employment experience included Institute electromechanics ASSU, Institute of electric machine industry, Division of Electric and Power engineering problems RAS, Electrophysics and Power engineering Institute RAS, Institute of Silicate Chemistry RAS.

V. N. Antipov received honorary degrees from institutions of higher learning including doctor of technical science, Member IEEE, leading scientist associate of laboratory power and ecology of Institute of Silicate Chemistry RAS. His special fields of interest include electrical machines and drives, renewable energy.

Irina Yu. Kruchinina was born in Bryansk in the Soviet Union, on June 15, 1961. She graduated from Leningrad Polytechnic Institute.

I. Yu. Kruchinina received honorary degrees from institutions of higher learning including candidate of science, Member, IEEE, deputy director of Institute of Silicate Chemistry RAS.

Her special fields of interest include electrical machines, renewable energy, new construction materials.

Yuvenaliy Ph. Khozikov was born in Cheboksary in the Soviet Union, on October 26, 1943. He graduated from Leningrad Polytechnic Institute.

His employment experience includes Institute electromechanics ASSU, Institute of electric machine industry, Division of Electric and Power engineering problems RAS, Electrophysics and Power engineering Institute RAS, Institute of Silicate Chemistry RAS.

Yu. Ph. Khozikov is a senior staff scientist associate of laboratory power and ecology of Institute of Silicate Chemistry RAS.

His special fields of interest include electromechanics, mathematical modeling of electromagnetic, thermal and mechanical problems.

Lubov Yu. Shtainle was born in Leningrad in the Soviet Union on March 25, 1976. She graduated from Leningrad Polytechnic Institute.

Her employment experience includes Institute of electric machine industry, Division of Electric and Power engineering problems RAS, Electrophysics and Power engineering Institute RAS, Institute of Silicate Chemistry RAS.

Her special fields of interest include synchronous machines.

Anna A. Ponomareva was born in Shevchenko (Aktau) in Kazakhstan on October 23, 1985. She graduated from St. Petersburg Polytechnic University.

Her employment experience included Institute of Silicate Chemistry RAS. Her special fields of interest include synchronous machines.