Design And Simulation Of An Inverter-fed Im For Electric Vehicles

Design and Simulation of An Inverter-fed Induction motor for Electric Vehicles Huijuan liu. Yihuang zhang, Qionglin zheng, Dong wang and Sizhou guo of inverter-fed induction motor for electric vehicle. As an example, the integrated design and control simulation method is presented and programmed in VB software, which take the design specification, in terms of geometry constraints, supply characteristics, required static performance, required dynamic performance, and generates an optimal geometry of the machine. It is apparent that the design requires a compromise

Abstract-The variable-frequency induction motor used in electric vehicle is investigated in this paper. Firstly the design method of a voltage inverter-fed induction motor is introduced, and then the calculation methods of electromagnetic parameter are presented and programmed in VB (Visual Basic) software.

Based on the geometrical dimensions and parameters, a simulation model in the vector control system is used to predict the performances of this machine. The comparison between the simulation results and the experimental results shows that the performances of the design machine are matched for its

between achieving low losses on one hand and high power density and wide speed range on the other. The experimental results show that the performances of the sample motor are match for the requirements of the electric vehicle.

application.

II.

Index Terms-Induction motor, Motor design, Simulation,

Voltage inverter-fed

MOTOR DESIGN

A. Initial Parameter Design The machine design process involves finding a suitable set of machine dimension variables to satisfy a set of performance . . . requirements taking into account minimization of cost, weight etc. The basic design parameters include number of poles, base frequency, geometry parameters, and winding distribution, among other things. Factors, like switching-

I. INTRODUCTION

JNDUCTION~~~ ~ MOOShv.ayadatgsoe ~ Iconventional DC motor, such as robustness, low cost, and h

well established manufacturing techniques, weight, efficiency. With the developing of the power electronic and inverter techniques, Induction motors fed by voltages source inverters are used in variety of industrial, residential and commercial applications, such as electric vehicle traction system, the frequency, electric-magnetic load, core losses, harmonic papermaking and the steelmaking system. The structure of the current, and the flux distribution play an important role in the design of variable-frequency induction motor. variable-frequency induction motor is same as the general . ~~~The choice of p Jole number involves a comdromise between asynchronous motor. However due to the inverter-fed supplies .p machine weight and efficiency. The high inverter frequency and the requirements of the applications, such as electric vehicle traction system, the performances of the variable- reqiedb a motor chi or. morel thei frequency induction motor differ greatly from those of the between a two- or four-pole motor. Since the inverter can general~~~~. asnhoosmtr.uhaswd pe ag,hg supply the range of frequency for a two- or four-pole motor to operate at the same speed, then from the motor design point of ftor, densit hi , density, high dependability and minimumesize. So the view it is merely a matter of selecting the pole number that gives the maximum torque per pound or per unit volume. On equen or different from those of the general induction motor. is thisThe the four-pole motorofis stator basis,harmonic superior.mmf wave may be content paper will pay attention to the discussion of the design feature minimized by an appropriate choice of the stator slot number

wihsxpoles

effiiency,lahighpower high powie ht varsity,hiablef nductliomtandesignimehsis mosthe

and coil pitch. The magnitude of the n'th harmonic mmf component is proportional to the n'th harmonic winding factor

Liu huijuan is with the School of electric engineering Beijing Jiaotong University, Beijing 100044 China, (phone:86-10-51684831; fax: 86-10-

51687101; e-mail: hjliu@ bjtu.edu.cn).

and inversely proportional to n.

Zhang yihuang is with the School of electric engineering Beijing Jiaotong

Aljudicious ofstheeffects of harmonicisfluxes such as, alleviate the undesirable choice

University, Beijing 100044 China, (phone:86-10-51687105; fax: 86-10-

51687101; e-mail: yhzhangl@ bjtu.edu.cn).

rotor slot number

necessary to

Zheng qionglin is with the School of electric engineering Beijing Jiaotong University, Beijing 100044 China, (phone:86-10-51688281; fax: 86-10-

iron loss, noise, vibration and cogging, crawling and synchronous torques

Wang dong is with the School of electric engineering Beijing Jiaotong University, Beijing 100044 China, (phone:86-10-51687084; fax: 86-10-

In the sample motor, the stator winding iS a conventional double layer type in 36 slots with a coil pitch of 8 slots. The

51687101; e-mail:

qlzhengs bjtu.edu.cn)t.

51687101).

rotor winding is a squirrel cage type with 33 copper bars.

Guo sizhou is with the School of electric engineering Beijing Jiaotong

University, Beijing 100044 China, (phone:86-10-5 1687084; fax: 86-10-

B. Magnetic Design

51687101).

O-7803-9761-4/07/$20.OO ©2007 IEEE

The variable-frequency induction motor torque-speed 112

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*1 * 1r~ ~Selctionfmateril

supply characteristics, required static performance, required dynamic performance, and generates an optimal geometry of the machine. This approach combines the results obtained from a modified magnetic equivalent circuit method with a dynamic simulator in which various control strategies can be programmed. Fig. 1 shows a frame of the inverter-motor vector control system. Fig.2 shows the design methodology of inverter-fed induction motor. Owing to this analysis model is coupling with the closed loop control method; it is the prefect approach in variable frequency induction motor design. [5,6]

envelope shows that rated current at high speeds cannot be maintained due to the effect of leakage reactance and the maximum torque is limited by the pull out torque. Evidently the speed range of the motor is limited by its pull out torque at high speed. This is proportional to the product of flux, which is proportional to the ratio of voltage and frequency and the maximum q axis rotor current. In the field-weakening region of operation, flux falls with increasing frequency and the consequent reduction in pull out torque is exacerbated by the fall in voltage due to the effects of leakage reactance. To achieve a wide speed range it is necessary to minimize the leakage reactance. For an induction motor in an electric vehicle it is necessary to limit the leakage reactance in order to achieve the desired speed range. Evaluation of leakage reactance is facilitated by dividing it into a number of components, i.e. slot, end, harmonic and skew leakage. All this leakage reactance can be estimated by experiential expression [5], although there are different leakage fluxes contribute to them respectively. The variable frequency induction motor losses are greater than those using a sinusoidal supply. The losses increase is due mainly to increases of iron losses and the additional rotor copper losses, due to a strong increase of eddy current. The reason for the increase in losses can be attributed to the switching frequency, to the fundamental frequency, and to the modulation technique. Hence, the motor losses calculation is divided in two parts: the losses with a sinusoidal supply and the additional losses due to the PWM supply. The losses calculation is based on the equivalent circuit method [5]. And the induction motor design program must be modified for traction applications with PWM inverter supply. With regard for the requirements of the electric vehicle, the design parameters of an inverter-fed induction motor are given in table I.

|U

+ju5te3 F<

or

+

curren

uinverterX|

|_|_______I

Fig. 1. Inverter-motor vector control system. Design of induction motor

Determination of initial geometry of the motor

Calculation of

electromagnetic parameters

Due to inherent dependency of control strategies on the

Calculation static

characteristics of the motor

TABLE I

THE DESIGN PARAMETERS OF THIS MOTOR

Number of poles

4

Number of phases

3 Y

Type of winding

connection Power (kW) Rating voltage (V)

40 200

Core length (mm) Number of stator Number of rotor slots

Rating frequency

slots

Stator interior diameter (mm)

170

Stator exterior diameter (mm) Rotor interior diameter (mm)

268

Rotor exterior diameter (mm) Overall gear ratio

169 11

4.831

205 36

Total losses (W) Power factor

2579.71 0.7992

33

Rating efficiency

0.9394

(A/mm2)

Control strategy

58

Density of stator current

100

Static requirements

Dynamic performance of the motor Dynamic requirements | End

magnetic design of the machine, an integrated design and control simulation tool is needed. To achieve this, we have

Fig. 2. Design methodology ofinverter-fed induction motor.

developed user-friendly program in VB (Visual Basic), which take the design specification, in terms of geometry constraints, 113

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and ac current is nearly constant. This produces a nearly constant torque. Of course, the power out of the motor is proportional to speed, so power increases linearly with speed. This method of control is possible until the ac voltage reaches the maximum available from the inverter. This point is the end of the constant torque region and the beginning of the constant power region. In constant power region the inverter supply adjustable frequency to the motor. AC voltage is no longer adjustable since the inverter is producing the maximum voltage, so ac voltage is constant. This results in the flux density decreasing as the reciprocal of speed. The slip frequency is increased an ac current is nearly constant. This produces a torque that decreases as the reciprocal of speed, while power out of the motor is nearly constant. The motor performances of each operation point during constant power region are shown in table III. During this region, the pullout power of motor is 40.13kW.

III. MOTOR PERFORMANCE CALCULATION The design method in Fig.2 employs the equivalent circuit to provide the specified pull out power and torque over the full speed range. Values of the circuit parameters are calculated during an iteration of the design process and the machine performance subsequently evaluated by combine analysis of the equivalent circuit and the control strategies. This will allow us to perform a timely efficient optimization while accessing the detailed performance of the electric vehicle drive, and to perform fine adjustments on the motor design, thereby improving the compactness, quietness and providing more room for development of efficient control

strategies.

An integrated design and control simulation method is presented to take the motor design specification. The electromagnetic loads on typical operating points in the

TABLE II

ELECTROMAGNETIC LOADS ON TYPICAL OPERATION POINTS

Starting point

Stator frequency (Hz) Power Power (kW) Torque (N.m) Line voltage (V) Line current(A) Magnetic density of stator tooth (Gs) Magnetic density of stator yoke (Gs) Magnetic density of rotor tooth (Gs) Magnetic density of rotor yoke (Gs) Magnetic density of

5

Rated

operation

point

100

TABLEIII

End of constant power region

THE PERFORMANCE OF THIS MOTOR DURING CONSTANT POWER REGION Line Line Stator Torque Speed Efficienc Power

frequency ~~~(Hz) 100

162

40.13

40.13

17512

200 136.965 12061

15456

15456

9500

16462

16462

11337

118 121 124

15619

15619

9601

127

8911

8911

6137

4.78

4.84

Cuatrretd

.1 3.11

Curroto deoop Stator copper losses (W) Rotor copper copperWlosses losses IrOn losses (W) Stray lOSSeS (W) MOSt tOrqUe mUltiPle

air gap (Gs)133

Current density of stator (A/mm2) CUrrent denSitY oOf rotor bar (A/mm2) CUrrent denSitY t Of ( 2)) rOtOr loop (A/mm

(W)

(kW)

1.59

129.13

11.91 152.22 17512

129.13 199.92 154.26

79.57

103 106 109 112 115

(N.m)

voltag e (V)

current (A)

)

.9394 .9404 .941 .9412 .9415 .9414 .9411 .9413 .9413

.7992 .8172 .8314 .8436 .8536 .8612 .8673 .873 .8775

200

139.28

.9412

.8808 .8841

99.03

200 200 200 200 200 200 200 200 200

153.87 150.33 147.65 145.49 143.73 142.45 141.47 140.51 139.81

factor atr

(m

(rpm) rm

128.72 124.97 121.44 118.09 114.93 111.93 109.09 106.39 103.81

2967.39 3056.45 3145.48 3234.49 3323.49 3412.47 3501.44 3590.42 3679.39

101.36

3768.36

130

200

200

138.36

.941

.8869

96.79

3946.27

4.301

136

200

138.04

.9408

.8891

94.66

4035.2

3.1 D3.12

3.18 3J.18OU

3.33

3.35

3.414

139 142

200 200

137.81 137.65

.9405 .9397

.891 .8927

92.62 90.66

4124.15 4213.04

145

642

659

520

148

200 200

137.42 137.29

.9398 .9393

.8941 .8954

88.79 86.99

4301.99 4390.92

446

451

469

151

200

137.21

.9388

.8964

85.27

4479.82

20 8 3.23

988 201 4.76

717 200 2.608

154 157

200 200

137.09 137.02

.9386 .9383

.8974 .8982

83.61 82.01

4568.74

160

200

136.97

.9379

.8988

80.47

4746.55

162

200

136.96

.9377

.8991

79.57

4800.48

Most_____torque _______multiple________3__23____4__76____2__608

__

138.74

.9414

3857.33

4657.64

control system are given in table II. IV. TESTING AND RESULTS To illustrate the effectiveness of this electric vehicle drive system, this drive system is tested while the control strategy of the system is closed loop vector control and the motor is full load. The experimental results of this motor are shown in table IV, such as line voltage, line current, pullout power, motor efficiency, motor speed and torque. Table V shows the test results contrast with the design data. Fig.3 shows the experimental voltage, current and FFT analysis at rating speed

The motor torque-speed curve has characterized by two regions operation, constant torque and constant power. The constant torque region lies from standstill to the base speed. In this region the inverter is operated in PWM mode to supply adjustable voltage and frequency to the motor. The ac voltage is adjusted as speed (frequency) changes to maintain constant flux density in the motor. The ac voltage, therefore, basically increases proportionally with speed (frequency). The frequency of the voltage induced in the rotor is held constant 114

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(n=2967rpm). It can be observed from Table V that the control strategy and the motor design is match for the requirements of the electric vehicle.

efficiency and power factor throughout the region and available inverter currents. The motor leakage inductance cannot be based solely on motor design issues or required pullout torque but must also consider the effects on harmonic ripple current, chopping frequency, fundamental ac current, and peak transistor current. An integrated design and control

TABLE IV THE TESTING RESULTS OF THIS MOTOR Stator

Line

Line

(V)

current

(A)

EEfficienc 7

100.9 124.69

150.42

.896

153.89 154.08 154.22

.915 .923 .935

frequency

voltage

51.21

(Hz)

63.58

76.15 88.68 98.12

154.39 178.14 195.96

153.65

.908

Pullout

Power

Torque

(N m)

(12) 19.28

24.13

30.14 35.09 39.15

129 129

129 129 129

peak method cis rrent.o simulation presented to take design the motor design specification. The comparison between test results and design

Speed

(rpm)

1466

results shows that the control strategy and the motor design is match for the electric vehicle traction system.

1825

2278 2635 2908

[1] TABLE V THE TEST RESULTS CONTRAST WITH THE DESIGN DATA Pullout Speed Input (rpm) power Power Efficiency test design test

design

test

design

test

design

test

design

test

design

test

design

747 750 1107. 1110 1466 1470 1825 1830 2278 2280 2635 2640 2908 3000

(kW)

11.715 12.25 16.48 16.85 21.52 22.14 26.57 27.09 32.94 33.16 38.01 38.37 41.87 42.11

(kW)

10.11 10.82 14.42 14.93 19.28 20.17 24.13 24.95 30.14 30.87 35.09 35.84 39.15 39.84

[2]

0.863 0.883 0.875 0.886 0.896 0.911 0.908 0.921 0.915 0.931 0.923 0.934 0.935 0.946

[3] [4] [5] [6] [7]

[8]

[9]

REFERENCES Vlado. Ostovic, "A method for evaluation of transient and steady state performance in saturated squirrel cage induction machines," IEEE Trans.

On Energy Conversion, vol. EC-1, 1986, ppl90-192 Eugene A.K.,"Polyphase Induction Motor Performance and Losses on Nonsinusoidal Voltage Source," IEEE Trans. On PAS, No.3.1968,

pp625-634

B.J. Chalmers, "Induction-Motor Losses due to nonsinusoidal Supply Waveforms,"Proc,IEEE,vol. 115,No.12, 1968,ppl777-1782 S.D.T. Robertson, K.M. Hebbar. "Torque pulsation in induction motor with inverter drivers," IEEE, Trans.Ind.Gen.Appl. vol, IGA-7, 1971,

pp318-323

Li yifeng, Gao peiqing, "The characteristic curve calculation of the induction traction motor fed by inverter," Electric Drive for Locomotive, No.6, 1997, pp8-11. Gao peiqing, "The development and application of the induction motor for electric traction," Electric Drive for Locomotive, No.5, 1998, pp2326. G. A. Kaufman and A. B. Plunkett, "Steady-state Performance of a voltage source inverter synchronous machine drive system," in conf: Rec. 1981 Annu. Meet. IEEE Ind. Appl. Soc., pp. 881-887. Shanghai electrical apparatus research institute, "The designing manual of S & M Electric machine", China Machine Press, Beijing. 1995.pp2426 Chen shikun, "The design of electric machine", China Machine Press,

Beijing.

1985.pp3-32

Fig.3 The voltage, current and FFT analysis at rating speed

V. CONCLUSION Induction motor is an attractive solution for the motor propulsion of electric vehicles. In this paper, an inverter fed induction motor drive is developed and tested using the closed

loop vector control system successfully to achieve induction motor torque-speed characteristics suitable for electric vehicle applications. During the motor design, the selection of the number of poles cannot be based solely on selecting the pole structure for minimum volume or weight. The constant power region of the speed-torque depends upon the variations in

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