Doctoral school of energy- and geo-technology January 1520, 2007.

Kuressaare, Estonia

Application and analysis of linear induction motors in mechatronic systems

Roma Rinkeviien, Saulius Lisauskas, Vygintas Batkauskas Vilnius Gediminas Technical University roma.rinkeviciene@el.vtu.lt

Abstract
This paper introduces electronic engineers into the mechatronic systems based on the linear induction motors. Article discusses the advantages and disadvantages of the linear induction motors (LIM) employed in mechatronic systems. The list of the LIM application areas is presented. The integrated environment of modeling created for analysis starting and breaking transients is presented. Simulation results made for LIM with windings connected in series-parallel.

Keywords
Mechatronics, linear induction motor, application, starting and breaking transients, simulation, model.

Easy expansion for any linear motion of system topology. Exact positioning in closed loop systems. Possibility to provide inductor and windings separate cooling. The power factor developed by naturally cooling LIM is 1 N / cm 2 . Almost 2 N / cm 2 can be obtained with an air cooling and from 2,5 3 N / cm 2 with liquids [3]. All electro-mechanical controlled systems used for an induction motors can be adopted for a LIM without any bigger changes.

Introduction
Integrated mechanical electronic systems emerge from a suitable combination of mechanics, electronics and control information processing. Thereby, these fields influence each other mutually. Mechatronic systems are developed for mechanical elements, machines, vehicles and precision mechanic devices [1]. Electromechanical energy conversation devices change electrical energy to mechanical. Motor of any type can be used as electromechanical converter. The most of actuators operate in the transient mode. The frequent starting, breaking and reverse modes characterizes operation of these drives.

Disadvantages: Power factor and efficiency are less than of rotary motors because of a ratio of large air gap between inductors and pole pitch (g / ) > 1 / 250 . The longitudinal end effect reduces power factor and efficiency. This can be noticed only with fast speed and small pole number motors. Influence of the longitudinal end effect can be reduced with special motor design methods. Extra vibrations with distortions can be noticed because of uncompensated normal force [3]. Linear induction motors invented by Charles Wheatstone in 1840 m., since this time linear induction motors are investigated, produced and improved and nowadays are used in mechatronic systems whose examples are presented below. High-speed transport and catapult, Industry transport systems, Batching systems, Vertical transport systems, Semiconductors and electronics industry, Explosion localizing systems, Industry robots and machine-tools, Protection and control systems of power energetic, Medical instruments, Computer engineering.

Linear induction motor in applications

High-acceleration linear motors are normally quite short, and are designed to accelerate an object up to a very high speed and then release the object. They are usually used for studies of hypervelocity collisions, as weapons, or as mass drivers for spacecraft propulsion [2]. LIM characteristics are worse than rotary motors those because of there construction, but some disadvantages can be omitted in different areas of applications. Below some advantages and disadvantages are presented. Advantages: Direct electromagnetic force (no mechanical elements, no limitations for speed). Economical and cheap maintenance.

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Analysis of LIM application areas shows problems of developing and investigation of linear drives being topical and urgent. In Automation department of VGTU electric drives of catapults, high voltage circuit-breakers, fast speed dampers, used to localize dust explosions, pneumatic transport damper drives

with linear induction motors have been developed and investigated [4]. Investigations of linear induction motors began in Automation department in 1970. The structural scheme of applications for LIM presented in Fig 1.

Fig. 1. Classification of linear induction motor application areas

Modeling software of linear induction motor

Developed integrated environment of modeling allows easy to analyze of different linear induction motor modes and can be used for investigation and developing new linear electric drives.

Developed models and their control system gives possibility to analyze influence of motor construction parameters or the static load on the motor dynamic characteristics. Created integrated environment of modeling execution window is presented in the Fig. 2.

Fig 2. Integrated environment of modeling

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The integrated environment of modeling allows choosing a windings connection type, operation mode, motor construction parameters, acceleration and braking time. For results program uses a special Matlab arrays. Then they are used to draw braking time dependences against secondary element resistance by braking with continuous and alternating current. Created software gives possibility to control model and investigate various non-symmetrical modes (breaking with direct current, single phase breaking), to compare obtained characteristics and consider influence of motor parameters to dynamic characteristics [5]. Fig. 3 shows the main program active window for all entering parameters of the construction of the LIM.

( R1 , R 2' , X m , X 1 , X 2' , , m , FSt )

Fig. 4. Program execution algorithm Fig. 3. Active window of developed program In a lower part of the program window these parameters can be entered: inductor phase resistance , R 1 ; resistance of the secondary element, R '2 ; the main magnetizing reactance, X m ; leakage reactance of inductor, X1 ; leakage reactance of the secondary element, X '2 ; secondary element weight , m; pole pitch, ; static load force, Fst . By pressing button Parametr sk. the parameters of the model are calculated. By pressing Modeliuoti button begins algorithm of the model presented in Fig. 2. The results are loaded to all available arrays. At this time dependences of variables can be chosen from a right side of the window Fig. 3. The program execution algorithm presented in the Fig. 4. The notations A, B, C, used in Fig. 4 correspond to different winding connections: two windings connected in series, one phase winding and serialparallel connection. The program allows to calculate these dependences:

v = f ( t ), F = f ( t ), S = f ( t ), I s = f ( t ), I ant = f ( t ), I A = f ( t ), I B = f ( t ), I C = f ( t ), I a = f ( t ), I b = f ( t ), I c = f ( t ). Research of the motor parameters influence to the dynamic characteristics requires making a lot of simulation and all the time measure the LIM steadystate. To shorten time of simulation the program for an automatic parameters change and LIM transition time measurement was developed. The integrated modeling interface is created for easy exchange of parameters and comparing of different dynamic characteristics of the drive.

Simulation results
There were already made some experiments of the LIM modeling with connecting windings in a two serial and one phase connection [6]. Here we present

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the modeling results when the linear induction motor windings at the braking mode connected in seriesparallel at breaking by single phase current [6]. Fig. 5 shows the transient current flowing in the inductor windings. The phase B and C are connected in parallel at the braking mode so the current decreases but the A phase winding current remains the same.
A 20 10
i iA iB iC

gets the minimal value at the same braking voltage (Fig. 8).
s 17 16 15 14
tp.p.

13 12 11 10 9 20 40 60 ' R2 80 100

0 -10 -20 1.4 1.45 1.5 t 1.55 1.6 s

Fig. 8. Dependence of breaking time against resistance of the secondary, when the applied breaking voltage of 100 V Fig. 8 indicates, that the minimum value of breaking time can be achieved by changing resistance of the secondary element.

Fig. 5. Inductor phase current alternation

A 4
ia ib ic

Conclusion
1. Integrated environment of modeling was developed to control the model, change its parameters and inductor windings connection way, process and compare results of simulation 2. Linear induction motors can be used in many mechatronic systems. The biggest advantage of linear induction motor is to expand a linear motion topology. 3. Developed integrated environment of modeling program has a friendly user interface and allows to model different types of LIM constructions.

3 2
i

1 0 -1 -2 1.5 1.52 1.54

t

1.56

1.58

1.6 s

Fig. 6. LIM secondary element currents without load at breaking Induced currents in the secondary element presented in a Fig. 6, the amplitude of the windings B and C at any instant of time equals a half of a phase winding current amplitude. Dependence of breaking time on breaking voltage and secondary element resistance is shown in Fig 7.
s 40

References
1. 2. Rolf Isermann. Mechatronic Systems, Fundamentals. Springer, USA. 2003, 624 p. Budig P. K. The application of linear motors. The third Intenational Power Electronics and motion Control conference 2000, Vol.3. p. 1336-1341. Lisauskas S. Investigation into nonsymmetrical modes of linear induction motors. Summary of Doctoral dissertation. Technologija, Vilnius. 2006. 108 p. Smilgeviius A., Rinkeviien R, Poka A. Special Systems with Low Speed Linear Induction Motors. In Proceedings of the International Conference on Robotics. 1999, Rinkeviien, R. Lisauskas, S. Simulation of linear induction motor dynamic breaking. In proceedings of the International Conference Electrical and control technologies. Kaunas: Technologija, 2006, p.446-449. Rinkeviien, R., Lisauskas, S., Petrovas, A. Dynamic Modes of Single Phase Braking of Linear Induction Motors. Doctoral School of Energy and Geotechnology. Kuressaare, Tallinn University of Technology, 2006, p. 72 77. ISBN 9985-69-036-2.

R2=48.83

' ' '

3.

30
tp.p.

R2=80 R2= 20

20

4.

10

5.
0 50 100 150 200 Um 250 300 350 V

Fig. 7. Dependence of breaking time on braking voltage when the voltage is attached to one phase winding Breaking time decreases with increased voltage at any value of secondary element resistance. Breaking time with the change of resistance of the secondary

6.

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