Development and Performance Investigation of Permanent Magnet Synchronous Traction Motor

Abstract-- The paper deals with the design of permanent magnet synchronous traction motor PMSM that was based on volume and stator windings of asynchronous traction motor with an outpu

Abstract The paper deals with the design of permanent

magnet synchronous traction motor (PMSM) that was based

on volume and stator windings of asynchronous traction

motor with an output power 210 kW The proposed PMSM

was built with permanent magnets (PM) placed on the

surface of the rotor There will be described the basic

parameters as well as analytical analysis of losses in the

machine, with emphasis on losses in PM, that depend on the

size of PM and they may form a significant component of

loss in the paper In the paper will be also described the

results of measurements realized on PMSM with rotor made

in the initial versions of the rotor and three other

modifications realized on the built rotor and their

experimental verification and valuation in comparison with

the theoretical knowledge Finally they will be compared to

the parameters of asynchronous traction motor (ATM) and

PMSM with recommendations for mass production of the

PMSM for applications in the traction vehicle

Index Terms analysis and design of electrical machines,

losses, measurement, permanent magnet, permanent

magnet synchronous motor, traction motor

I INTRODUCTION Target requirements for design of PMSM for traction

application are:

- the expected higher efficiency of PMSM as ATM

(due to the absence of losses in the rotor winding),

- lower weight and volume PMSM as ATM,

- PMSM with excitation by rotor PM provides the

ability of motor brake in resistors in case of failure of

the traction converter,

- PMSM made with a larger number of poles enables to

make the drive powered rail vehicle (HDV) without

gearbox, that is a drive component with major

dimensions, weight and price have a direct impact on

the final transfer efficiency of the engine torque to the

driving wheel-set

Noted parameters and especially efficiency of PMSM

over ATM led us to intent design, construction and

performances investigations of the traction motor of this

type

II PMSMDESIGN Electromagnetic and thermal design of PMSM based

on volume of ATM foreign manufacturer [10],

characterized with the internal stator bore pack is the

same for the power range of ATM from 70 to 210 kW

and single dimensional types differ only with an active

length of the stator and rotor For these varieties have

been designed some variants of rotor with different PM arrangements This approach to the solution of unifying design as ATM and PMSM, allows the customer to offer traction motor of the same size and weight, but at a slightly higher price with higher efficiency

In this paper attention is paid to design of PMSM that was based on ATM with an output of 210 kW Basic parameters of the ATM were verified on the test as EVPÚ j.s.c laboratory as with sinusoidal supply and as the traction power frequency converters, and thus it can

be based on real measured operating parameters Based

on the measured temperature increase winding of the real ATM 210 kW, considering the available real PM, we rate

as the target power of the PMSM set as rated power of

160 kW and reduce the temperature class from C to F Basic parameters of the ATM are shown in Table I

TABLE I T HE N AME P LATE AND O THER P ARAMETERS

OF THE B ASE ATM (P RODUCER [10])

type ATM210C70Hz425V

rated power P N 210 kW voltage U 425 V

nominal current I 1 332.2 A rated torque T N 1018.5 Nm

nominal frequency f N 67 Hz nominal speed n N 1971.1 min -1

pole pairs 2p 4

efficiency η 0.94 power factor cos φ 0.909

isolation class C 240°C

Content research and development work of the design PMSM was:

- selection of the appropriate rotor configuration and arrangement of the permanent magnets (on the surface, inside, combined);

- calculation of the PMSM magnetic circuit - determining the volume of PM, the calculation of the magnetic field distribution in the air gap, the calculation of moments, reactances et al

In these works were tested several alternatives of configuration rotor layout with PM on surface PM or in a rotor For the design and implementation of a prototype

160 kW PMSM was chosen variant with PM mounted embedded to the rotor surface, which seemed like the easiest way of implement the first prototype PMSM Simulation results of magnetic field distribution of the selected configuration option with PM embedded to the

Development and Performance Investigation of Permanent Magnet Synchronous Traction Motor

M Franko*, J Kuchta*, J Buday*

* EVPÚ a.s., Electrotechnical Research and Projecting Company, j.s.c., Trencianska 19, SK - 018 51 Nova Dubnica (Slovakia), franko@evpu.sk, kuchta@evpu.sk, buday@evpu.sk

2012

International Symposium on Power Electronics,

Electrical Drives, Automation and Motion

surface of the rotor in no-load state can be seen in Fig 1 in the state with nominal current in Fig 2

Fig 1 2D magnetic flux distribution in cross section of PMSM at no load state and air gap magnetic flux density waveform and harmonic analysis of PMSM magnetic flux density

Fig 2 2D magnetic flux distribution in cross section of PMSM at nominal current I=332.3; torque M=1191.9 Nm

and air gap magnetic flux density waveform 4 harmonic analysis of PMSM magnetic flux density

III PERMANENT MAGNET LOSSES

To determine the efficiency of an engine is necessary

to determine the motor losses In addition to known

components of losses such as losses in the stator

windings, stator iron losses, iron losses in the stator tooth

and mechanical losses is necessary for machines with PM

on surface consider also the losses in the PM of rotor

Rotor losses in synchronous machines with permanent

magnets are usually neglected, because the main rotor

flux is constant However, when running from converter

to be a time-dependent harmonic field, which is not

neglected Alternating flux penetrates into magnets and

causes losses in them Theory of losses calculation in

permanent magnets due to eddy currents that are

described in [5,11,12] In Fig 3 is a sketch of one pole of

the machine with the appropriate size and shape and

dimensions of the permanent magnet:

 dimensions of the permanent magnet (h M x w M x l M):

4.3 x 14°( 27.16 mm) x 50 mm;

 one rotor’s pole is divided into (n Mx x n Mz): 5 x 13

pc, totally 260 pc

 switching frequency f sw 750 Hz Overall losses in the permanent magnets are calculated as:

M

gM h sw Mz Mx M

k B f n pn P



2



 where:

- p is number of pole pairs;

- n Mx is the number one magnet pole arc in the direction

of the x-axis;

- n Mz is the number one magnet pole arc in the direction

of the z-axis;

- B h harmonic flux density in the air gap;

- M resistivity of magnet;

- k gm coefficient of geometry, that calculated according

the magnet’s dimension at which the equation is dependent on relation between length and width of

magnets

The sum of the losses of individual harmonic components without addition to the 3-and the multiple to acquire permanent magnet losses in the rotor P r

(highlighted in Table II.)

9 x

22

4,5

70°

Permanentný magnet

R109

14°

50

Fig 3 PMSM: Cross section of motor pole, shape, dimensions and radius of the permanent magnet,

3D model of designed rotor, photography of rotor’s sheet Permanent

magnet

TABLE II T HE I MPACT OF A C HANGE OF PM N UMBER TO R OTOR ’ S L OSSES

Number of PM 2 x 3 2 x 4 2 x 5 5 x 10 5 x 12 5 x 13 10 x 13 10 x 20 10 x 26

PM w M 67.89 67.89 67.89 27.16 27.16 27.16 13.58 13.58 13.3

Coefficient of k gm3 k gm1 k gm1 k gm1 k gm1 k gm1 k gm3 k gm1 k gm1

PM geometry 2.429.10 -8 1.627.10 -8 9.772.10 -9 4.167.10 -10 2.726.10 -10 2.311.10 -10 4.49.10 -11 2.61.10 -11 1,44.10 -11

PM losses (W) 25599 22865 17162 3659 2872 2638 1024 915 660

Quotient of losses to

nominal power P N =210kW 12.2% 10.9% 8.2% 1.7% 1.4% 1.3% 0.5% 0.4% 0.3%

Table II refers to the effect of changing dimensions of

PM and therefore pieces of the PM too, that make one

pole of the machine The increasing number of magnets

means reduction of losses For realization was chosen

arrangement with 5x13 pieces of PM per machine pole

that has been a compromise in consideration of work time

consuming and lower cost of PM’s acquisition Doubling

the number of PM (10x13) would reduce the loss of

0.75% (relative to total output), but would increase the

labour intensive construction as well as the price

Effect of loss depends on the size of the magnet and it

reflects the variable that describes the geometry of the

permanent magnet, coefficient of geometry k gM1 where

index 1 expresses assumptions that are basis for deriving

the relation of the loss in the PM (l M > w M)

IV RESULTS OF DESIGN AND VERIFICATION

OF PMSM,MODIFICATIONS EXECUTED

ON THE PROTOTYPE OF PMSMROTOR Designed prototype of rotor for PMSM was verified by tests such as no-load test at the generator running, as well

as fed by sinusoidal supply and traction power converter Because during the measurement was found that the rotor is susceptible to mechanical vibration, which was due to the large disparity between the length of iron and the stator bore, what at default induction motor is unknown, was built prototype of PMSM used for further research in order to improve its properties

A)

0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000

0

60

120

180

240

300

360

420

480

540

600

f (Hz)

No load characteristics of PMSM at generator runnig

U0 v1 U0 v2 U0 v3 straty v1 straty v2 straty v3

P 0

U i0

f

U i0 ver.1 U i0 ver.2 U i0 ver.3 loss ver.1 loss ver.2 loss ver.3

B)

-1000 -800 -600 -400 -200 0 200 400 600 800 1000

U1 U3

C)

D)

Fig 4 No load test of PMSM at generator running A) No load characteristics and B)-D) comparison of instantaneous value

of voltage curve of motor against to modifications at nominal speed: B) Version 1 of Prototype, C) Version 2 after first modification ( rise), D) Version 3 after second (skew) and third (PM size reduction) modification

After test of rotor’s prototype the rotor was regrinding

so that the air gap was increased to 2 mm (the original

ATM has =1 mm, and rotors prototype had =1.5 mm)

After rotor’s modification was PMSM tested by measuring selected characteristics This correction meant

decrease of induced voltage U i0, and it reduces the ripple

in the curve of actual value U i and also no-load losses

(see Fig 4)

In order to optimize the parameters of PMSM and

thereby reduce losses and increase efficiency of PMSM

we made further modifications of the rotor version,

namely:

of one slot - in order to reduce the ripple of magnetic

flux density - the suppression of harmonics in the

curve of magnetic flux density and hence reduce pulsations of voltage and torque ,

magnet losses - an initial using permanent magnet

(27.16 x50x4.3 mm) was divided into four parts (i.e.:13.58 x25x4.3 mm Proposed modification would have reduce of PM losses from 2640 W to 660 W in compliance with calculation, it was confirmed by efficiency measurement

TABLE III S ELECTED E LECTRIC P ARAMETER OF THE PMSM

Ver.1

(before)

Ver 3

(after modification)

No load EMF U i0 (V)

Coupled magnetic flux M (Wb) 0.9339 0.8472

No load losses P 0 (W) 6 125 4 062

Synchronous inductance L d (mH)

L q (mH)

1.63 1.9

2.36 2.8

Leakage inductance L 0 (mH) 0.3791

Stator resistance R s (m) 11.0679

-300 -200 -100 0 100 200 300 400 500 600 700 800 900 1000 1100 1200

Meas Torque at I=300 A Sines Torque Reluct Torque Meas Torque at I=330 A Torque calculated by FEM

Fig 5 Calculated and measured and dependency of the torque on load angle for PMSM

0 1000 2000 3000 4000 5000 6000 7000 8000

90

91

92

93

94

95

96

97

98

Current (A) Efficiency Losses

0 35000 70000 105000 140000 175000 210000

0 200 400 600 800 1000 1200

P p1

P mec

T mec

U s

Current (A) Mech torque Term voltage Voltage -1harm

Input power Mech.-output power

Fig 6 Load characteristics of PMSM at f=50 Hz, U DC=680 V

56 60 64 68 72 76 80 84 88 92 96 100

200

350

500

650

800

950

1100

1250

0 200 400 600 800 1 000 1 200 1 400 1 600 1 800

U s

U s1

82 84 86 88 90 92 94 96 98

50 70 90 110 130 150 170 190 210

P m

rotational speed (min -1 )

Output power Efficiency

Fig 7 Mechanical characteristics of PMSM U DC =680 V, I=330 A

Because of the limited extent of the contribution, we

have chosen only selected experimental results and much

more information can be found in details in [1,2,3]

V CONCLUSIONS Objective, which led us to a specific analysis of

performance of PMSM and investigation of analytical

results from the theoretical development and practical

implementation, was the feature of the machine found in

the type test The pilot realization of a prototype PMSM

was built on basis of ATM with power 210 kW, that have

stator bore D e =230 mm and stator length l Fe=650 mm

Such ratio D e /L Fe of the stator bore to the length has

proved unsuitable for the construction of PMSM from

mechanical point of view and it results in limitations of

maximum speed Rotor PMSM has just sheets and

magnets and its mechanical natural frequency

significantly decreased and shifted to the operating

frequency area, this caused vibration and mechanical

scrubbing of the rotor This feature led us to use the

prototype rotor for the purpose of research and review in

order to obtain theoretical knowledge in practical

application ATM has rotor composed of sheets with

reinforced rotor bars and therefore the mechanical

limitations did not occur there The realization of the

rotor, but most of all bonding technology for PM on rotor

plate requested address range of material and

technological issues that significantly affect the resulting

behavior of the machine Comprehensive tests of the

prototype brought an important knowledge for

re-designed construction machinery in question (namely: the

choice of the size of NdFeB magnets in relation to the

amount of eddy loss, ratio limits the length of the active

rotor and stator to the stator bore diameter l Fe /D e, skew,

etc.)

TABLE IV C OMPARISON OF P ARAMETERS D ESIGNED AND

I MPLEMENTED THE P ERMANENT M AGNET S YNCHRONOUS T RACTION

M OTOR FOR P UBLIC T RANSPORT V EHICLES WITH THE D EFAULT

P ARAMETERS OF A SYNCHRONOUS T RACTION M OTOR

Nominal voltage U s_conver (V) 425 U mot =475 (U gen=420)

Nominal current I s (A) 332.2 300

Rated input power P p (kW) 223 171

Rated output power P mech (kW) 210 163 *

Shaft torque T mech (Nm) 1018 1040

Nominal frequency f n (Hz) 66.7 66.7

Rated speed n n (min -1) 1971 2010

Efficiency  (%) 94 96

Type of permanent magnet NdFeB

(BH)max (kJ/m3)

Dimensions W x H x L (mm)

Mass of PM G PM (kg)

Number of PM (pc)

Max working temperature (°C)

42SH

344 13.3 x 4.3 x 24.8 11.55

1056

150

because it was decreased temperature class due to used PMs

Experimentally confirmed obtained parameters of a realized prototype of the PMSM into stator winding pack from ATM are listed in Table IV., which the most significant parameter is the increase of the machine efficiency by 2%

ACKNOWLEDGMENT This work was supported by the Slovak Research and Development Agency under the contract No APVV-0530-07 and realization of project “Research on Highly Efficient Electric Propulsion Systems Components of Locomotives and Public Transport Vehicles” No 26220220078, founded by European Regional Development Fund under Operational Programme Research and Development

REFERENCES [1] Annual report of project solutions by contract APVV-0530-07, per year 2010, archive EVPÚ a.s , January 2011, (in Slovak)

[2] Annual report of project solutions by contract APVV-0530-07, per year 2009, archive EVPÚ a.s and Slovak Research and Development Agency, January 2010, (in Slovak)

[3] Annual report of project solutions by contract APVV-0530-07, per year 2008, archive EVPÚ a.s and Slovak Research and Development Agency, January 2009, (in Slovak)

[4] Franko, M.: Permanent magnet synchronous motor for

traction applications PhD Thesis, Univesity of Zilina,

Slovak republic, May 2009, (in Slovak) [5] Kuchta, J.: Some design issues of asynchronous traction

motor for locomotives with electric power transmission

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P.: Electromagnetic design of ironless permanent magnet

synchronous motor, SPEEDAM 2008, International

Symposium on Power Electronics, Electrical Drives, Automation and Motion, Ischia, Italy, 2008, June, 11.-13., AFC, p.: 721-726

[7] Franko, M.; Grman, Ľ.; Hrasko, M.; Kuchta, J.; Buday, J.:

Experimental Verification of Drive with Segment Slotless Synchronous Motor with Permanent Magnet, IECON

2009, Porto 3-5.11 2009, abstract proceeding p.360 [8] Kuchta, J.; Franko, M.: Advantages and limitations of

using a permanent magnet synchronous motor in the traction drive 20 International conference „Current

problems in rolling stock“- ProRail 2011“; 21 – 23 September 2011, Žilina, Slovakia, vol II, p.183-191 ISBN 978-80-89276-31-8 (in Slovak)

[9] http://www.skd.cz/EN/index.htm

[10] Polinder, H.; Hoeijmakers, M.J.: Eddy-current losses in

the permanent magnets of a PM machine, Proceedings of

the Eighth International Conference on Electrical Machines

and Drives, IEE, Cambridge, UK, 1997, pp 138{142

[11] Nipp, E.: Permanent Magnet Motor Drives with Switched

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[4] Franko, M.: Permanent magnet synchronous motor for

traction applications... [8] Kuchta, J.; Franko, M.: Advantages and limitations of

using a permanent magnet synchronous motor in the traction drive 20 International conference „Current ... Slovak Research and Development Agency under the contract No APVV-0530-07 and realization of project “Research on Highly Efficient Electric Propulsion Systems Components of Locomotives and Public