2012 IEEE Vehicle Power and Propulsion Conference, Oct. 9-12, 2012, Seoul, Korea

Analysis on Electromagnetic Vibration Source

Permanent Magnet Synchronous Motor for Compressor of Electric Vehicles

Hyeon-Jae Shin\ Jang-Young Choil, Han-Wook Cho2, Seok-Myeong Jangl

Dept. of Electrical Engineering, Chungnam National University, Daejeon, Korea Dept. of Electric, Electronics & Communication Engineering Education, Chungnam National University, Daejeon, Korea

E-mail : godnow@cnu.ac.kr

Abstract- This paper analyzes the electromagnetic vibration

sources affect mechanical vibration the PMSM type motor for

full electric driven compressor of electric vehicles. 2-D FEM

solutions for cogging torque, torque ripple and radial force

density are obtained magnetic field solutions. And find natural

frequencies the stator of this electric machine using 3-D FEM.

Finally, compare vibration sources from electromagnetic

harmonics with natural frequencies stator of the motor.

Keywords ; IPM,compressor motor, cogging torque, radial force, natural frequnecy

I. INTRODUCTION

It is widely documented that the continuously increasing energy consumption is linked to population and economic growth. The acceleration of industrialization and economic growth is accompanied by an increase of mobility demand, but most of transportation system still using fossil fuels.[I] The study of eco-friendly cars going around the world and also increasingly expanding the scope of its application is becoming the trend. Eco-friendly cars are classified hybrid vehicle, fuel cell electric vehicle, electric battery charging vehicle and etc. All kind of Electric vehicle car (EV -car) is still expensive, takes a lot of time for charging and has few infrastructures than gasoline and diesel engine vehicles. To overcome these disadvantages EV -cars have to high-efficiency, miniaturization of components. The permanent magnet synchronous motor (PMSM) is suitable for components of EV -car systems. Because the PMSM being studied as promising candidate for many industrial applications owing to its high torque density and high efficiency.[2-3] Suitable for automotive refrigerant compressor motor is considered vehicle's weight and volume efficiency. Permanent magnet motor is divided interior permanent magnet motor (IPM) and surface-mounted permanent magnet motor. Especially IPM is using magnetic torque and reluctance torque that has wide speed range and high efficiency. In addition, mechanical strength can be greater than SPM because of the rotor magnets are fixed to the internal, sensor-less drive is available to using a salient-pole characteristic about d-axis inductance and q-axis inductance. The vehicle system also needs quietly and good ride comfort. There are many electromagnetic sources affect noise and vibration of the PMSM; cogging torque, normal force, torque ripple, etc.

(a) (b) (c)

Fig. I. Concepts and components about automotive refrigerant compressor (a) engine belt driven compressor (b) full electric driven compressor

( c) hybrid compressor

In this paper, focuses on the electromagnetic source affect mechanical vibration of IPM type compressor motor. 2-D FEM solutions for cogging torque, torque ripple and radial force density are obtained from the derived analytical magnetic field solutions. And find natural frequencies the stator of this electric machine using 3-D FEM.

II. MOTOR SPECIFICATIONS AND CONFIGURATIONS

Ordinary fossil-fuel vehicles using engine belt driven compressor system (BDC) for air conditioning, but these systems always wasting fuel even though idling time. Full electric driven compressor (FEDC) and 2-way or hybrid compressor is shown fig. 1. Classified according to the output performance of the electric motor, when the engine and the electric motor can operate independently is called power hybrid (or strong hybrid) or using main engine power with electric power as needed in the way that is called mild hybrid. In this paper focuses IPM type FEDC system. Table. I Show motor specification.

TABLE/, MOTOR DESIGN SPECIFICA nONS

Parameter Value Parameter Value Nominal

6.6Nm Cogging torque 0.25Nm Torque

Operating! 6540rpml

Efficiency Maximum (S.5Nm, 92%

speed 8000rpm

3000rpm) Max Power 4.SkW THD 10%

Torque ripple 8 % Weight 3kg

978-1-4673-0954-7112/$31.00 ©2012 IEEE

200

Fig. 2. 3D-Model of rPM type compressor motor for FEDC

Fig. 3. Rotor and stator for Prototype rPM compressor motor

III. ELECTROMAGNETIC ANALYSIS

A. Cogging Torque

Fig. 2 show designed interior permanent magnet type compressor motor for electric vehicles. It is consists of 27-stator slots, 6 poles rotor. The cogging torque is least common multiple of stator slots number and rotor poles.

(1)

Where, 51 is number of stator slots and p is number of rotor magnetic poles. LCM(p. 51) is least common multiple of stator slots number and rotor poles. The 54th is major harmonic from cogging torque. Fig. 3 show number of pole pairs and stator slots for prototype IPM compressor motor. If the magnetic saturation and armature reaction are negligible, the cogging torque is independent of the stator current.[4] The Cogging torque result using FEM analysis is shown in fig. 4. Also Fig.5 is show test result about cogging torque at 3rpm during one revolution. Compare analysis results with measured results, test result is shown higher than FEM result and including multiples of 6th harmonics form number of magnetic poles.

E 40

z .s 20

!!l [! 0 (? g -20

'5> 8' <.l -40

50

40 E z 30 .s " '0 20 :E Ci E 10 «

20 40 60 80 100

Angular Position [Deg] Harmonic Order

(a) (b)

Fig. 4. Cogging torque analysis results of 2D-FEM (a)torque wave form and (b) FFT analysis result

E 60

§. 40

� 20 cr � 0

g -20 '5> g -40 <.l

-60

90 180 270 Angular Position [Deg]

(a) 360

E Z .s " � � «

50

40

30

20

10 6th 12th 24th

.1 1 18'"J o 20

54th

40 60 Harmonic Order

(b)

80

Fig. 5 Cogging torque measured results at rotor speed 3rpm (a)torque wave form and (b) FFT analysis result

Fig. 6. Positions where Radial force density is calculated

B. Radial Force

100

Fig. 7 show radial force characteristics at maximum torque with current and phase angle conditions. Radial force density waveform using the finite element analysis can be obtained from the following formula.

B2 F= -g , 2110

(2)

Where, Bg is magnetic flux density at load condition by permanent magnet flux density and armature current given by the sum of the magnetic flux density or no-load flux density that is the permanent magnet flux density can be given alone.

f.1o is permeability of vacuum, 41tx 10-7[H/m] .

C. Torque Ripple

Torque ripple due to shape and distortion of the electromotive force (EMF) and current waveforms. Containing A phase back-EMF harmonics are the following expression.

''E E 0.4

� ;:;. 0.3 .� � 0.2

� o

L1. 0,1

I I • I . " 0,00 5 10 15 20 25 30 35 40 45 50

Mechanical Angle [Deg] Harmonic Order

(a) (b)

Fig. 7. Radial force density analysis results of 2D-FEM (a)radial force density wave fonn and (b)FFT analysis result

201

E �

!!l e-0 f-"

� 0> OJ E

� Q) Lij

� C � "

u « 3: OJ � U.

8 7

E 6

6 � Q) "0

4 � Ci. E «

3

2 !!l 2 e-o

18th 54th f-0 0

0 0 20 40 60 80 Time [msJ Harmonic Order

(a) (b)

Fig. 8 . Torque anaJysis results at rotor speed 6540rpm of 2D-FEM (a) torque waveform and (b) FFT anaJysis results

Measeured@6540rpm 120 PI

Q) "0 90

. .E! Ci. 60 E «

30

3"

100

0.0':-00=---0

::-C .0::CO::-C

2 ----:-0.0::

0-:-4 -

---:-0.-:-'006

0 0�-....... n

�-

-c':10

'-----1-:-5

--:'20

Time[sec] Harmonic order

(a) (b)

Fig. 9. Back EMF measured data at rotor speed 6540rpm (a) Back EMF wave form and (b) Phase-A FFT analysis results

40 40 1>'

30

Q) "0 . .E! 20 Ci. E «

10 5"

0 I�. 0 10 15

Time[secJ Harmonic order

(a) (b) Fig. 10. Phase-A current Measured data at rotor speed 6540rpm

(a) Current wave form and (b) FFT analysis results

00

20

kA(B)= K,cos(B)+ I Kncos(nB) (3) n=3.odd

The instantaneous electromagnetic torque is the same as that obtained from Lorentz Equation. Fig.8 show torque analysis results using the finite element analysis can be obtained from the following formula.

1 T= -[kAiA +kBiB +kcicl (4)

OJp

Where, OJ is electric angular velocity, kA is phase-A back EMF and i is phase current. Fig. 9, 10 show voltage and current measuring speed at 6540rpm, torque 6.6Nm. Dominant harmonic orders of measured back EMF are 1, 3 harmonic orders. Also, dominant harmonic orders of measured current are 1 and 5.

TABLE II. STATOR CORE NATURAL FREQUENCIES

--- m=2 m=3 n=1 2305 Hz 5815 Hz

n=2 4192 Hz 8829 Hz

(a)

(c)

N � >-u C Q) ::J CJ �

u.

(b)

(d)

Fig. I I. Deformation of the stator core of 3D-FEM (Circumferential mode: m, axial mode: n)

(a) m= 2, n= 1 (b) m= 3, n= 1 (c) m= 2, n= 2 (d) m= 3, n= 2

8000 6540rpm 60

Stator Natural 54 Frequencies 48

6000 .... ...... ...... ..................................... 42 36

4000 .... ...... ...... ................................... 30 24 18

2000 12 6

00 0 4000 6000 8000 Rotor speed [rpm]

Fig. 121 Natural Frequency with rotor speed and harmonic order

IV. MECHANICAL ANALYSIS

I Ql

3 0 ::J n' 0 a. �

Noise and vibration in PM machines can be classified into three categories based on its source: aerodynamic, mechanical and electromagnetic. Electromagnetic source is the dominating on in low to medium power rated machines.[7] The noise and vibration of the motor structure are the direct responses of the excitation by those electromagnetic sources. There are three different types of vibration for a stator of an electric machine: axial, torsional and radial. Axial stator vibration may be produced by axial forces which are out of phase, but this kind of vibration probably arise only rarely, except in large generators. Torsional vibration may occur in machines with skewed slots or salient poles, radial vibration of the stator structure is usually the most important type of vibration.[] If the frequency of the radial magnetic force is equal to, or near, the natural frequencies of the stator system and the force order r is the same as the circumferential vibrational mode m of the stator system, significant vibration and acoustic noise can be produced.[4] Fig. 10 shows deformation of the stator core using the [mite element analysis and table II is values about stator core natural frequencies. Where, m is circumferential mode and

202

n is axial mode. In the fig. 11, the dash lines showed the natural frequencies and electromagnetic harmonic orders are shown as solid lines. At the driving point 6540rpm, the 54th harmonic from electromagnetic vibration frequency 5889Hz is nearby stator natural frequency 5815Hz. But, amplitude of 5461

harmonic is very small. For accurate determination, it is has to need vibration measuring and compare these results.

V. CONCLUTTON

This paper presents electromagnetic analysis to find cogging torque, radial force and toque ripple about proto model IPM type automotive refrigerant compressor motor. Also compare with cogging torque, back EMF and current measured data. The stator natural frequencies are found using 3-D FEM compare with electromagnetic harmonics. It is shown about possible to noise and vibration at the some operating points. Specificall�, electromagnetic vibration harmonic from cogging torque 54!1 harmonic has small amplitude. But, stator m=3 mode is closed to 5889Hz. For accurate determination, it is has to need vibration measuring and compare these results. In addition, motor vibration studies need to compare with electromagnetic analysis.

ACKNOWLEDGMENT

This research was supported by basic Science Research Program through the National Research Foundation of Korea(NRF) Funded by the Ministry of Education, Science and Technology(20 12-0003363)

REFERENCES

[1] P. Corbo, F. Migliardini, O. Veneri, Hydrogen Fuel Cells for Road Vehicles, Springer 2011

[2] S. Vaez-Zadeh, "Variable flux control of permanent magnet synchronous motor drives for constant torque operation," IEEE Trans. Power Electron., vol. 16, no.4, pp. 527-534, 2001.

[3] Edward C. Lovelace, Thomas M. Jahns, and Jeffrey H. Lang, "Impact of saturation and inverter cost on interior PM synchronous machine drive optimization," iEEE Tran. ind. Appl., vol. 36, no. 3, pp. 723-729, June 2000.

[4] Jacek F. Gieras, Chong Wang, and Joseph Cho Lai, Noise of polyphase electric motors, Boca Raton: CRC Press, 2006.

[5] A. Cassat, C. Espanet, R. Coleman, E. Leleu, L. Burdet, D. Torregrossa, 1. M'Boua and A. Miraoui, "Force And Vibrations Analysis in Industrial PM Motors Having Concentric Windings", Energy Conversion Congress and Exposition (ECCE), pp.2755-2762, 2010

[6] Islam, R. and Husain, T. "Analytical model for predicting nosie and vibration in perrnanet magnet synchronous motors," Industry Applications, iEEE Transactions on, vo1.46, pp.2346-2354, 2010

[7] 1. Ellison and SJ Yang, "Natural frequencies of stators of mall electric machines," lEE Proc. of elect. Power Control and SCience, vol. 1 18, n. I, pp.18 5-190, 19 71

203