Design and Performance Analysis of Proposed Single-Sided Linear Induction Motor used in Elevator

In this paper, single-sided linear induction motor (SLIM) for driving the elevator system is designed. Differing from other motors, SLIM is simple in construction, less expensive, very suitable for linear application which is used from low speed to high speed application. Special machine adjustments and alignments are not necessary in SLIM because mechanical coupling and gears are not required. Thus, SLIM is superior to other linear and rotary motor. The single-sided linear induction motor (SLIM) design, performance equations and design procedure are developed and its performance is predicted by using equivalent circuit model. End effects and edges effects are neglected in this study. The performance of the SLIM for different value of mechanical air-gap are evaluated by using MATLAB. The effect of variation of such parameters on the performance of the machine is discussed.


INTRODUCTION:
Linear induction motor (LIM), is basically an advanced types of motor that is use to obtain rectilinear motion instead of rotational motion as in ordinary conventional three phase induction motors. They may be obtained by "cutting" and "unrolling" the rotary induction machines to yield flat, singlesided topologies, where the cage secondary may be used as such or replaced by an aluminium sheet placed between two primaries to make the doublesided LIM. Linear motor potentially have unlimited applications. Linear induction motors (LIMs) alone have found application in the following general areas: conveyor systems, material handling and storage, people mover (Elevators), liquid metal pumping, machine tool operation, operation of sliding doors and low and high speed trains. There are different types of LIMs, among them, single-sided linear induction motors (SLIMs) are widely used in transportation system. In this paper, single-sided linear induction motor (SLIM) with short primary has been studied for the vertical conveying application because its main characteristic is the linear motion, which takes place without transformation mechanisms, increasing efficiency and the reliability of the system and also eliminating the need for large machine room on the roof. The SLIM has the following advantages comparing with the rotary induction motor (RIM): simple construction, direct electromagnetic thrust propulsion, safety and reliability, precise linear positioning, separate cooling, all electro-mechanical controlled systems used for an induction motors can be adopted for a SLIM without any bigger changes, economical and cheap maintenance.

Equivalent Circuit Model
The equivalent parameters of SLIM can be determined using the per-phase equivalent circuit as shown in figure 3.
The electromagnetic force s F produced by a machine is given by The moving resistance of the system D, consists of two components in this specific case, which are Rolling resistance, r t 1 2 r D =m (c +c v ) Where g is acceleration of gravity, 2 9.8m/s .

Finally,
' ts FF  becomes a greatly important criterion to decide whether this machine design is satisfied or not.

Design of Secondary
The single-sided linear induction motor secondary (rotor) design contains conduction layer design and reaction plate design, it is illustrated in figure 4.  The secondary reaction plate design which can consist of either solid or laminated design. To improve performance, the reaction plate is coated with conduction sheet of either aluminium or copper. For standard operating, the reaction plate should not be any less than 6mm thick and the attached conducting sheet should not be any less than 3mm thick. The best thrust per size ratio is obtained. The design data sheet of electrical parameters of SLIM is presented in table 3.In the electrical parameters design, neglect the core losses.

PERFORMANCE CURVES OF SLIM
The input data used for SLIM design in MATLAB program was given in above section(3) along with the slot geometry. The performance characteristics of the SLIM are shown in following figures.

PERFORMANCN EVALUATION OF SLIM BY CHANGING PARAMETER
The performance of the SLIM based on this particular design is evaluated by varying certain parameter like the mechanical air gap. Based on this evaluation, the best possible value for this parameter is selected as shown in the following sections.

Effect of Mechanical Air Gap on Performance
The length of the air gap plays the most critical role determining the characteristics of the machine. A large air gap requires a large magnetizing current and results in a smaller power factor. In the case of SLIM, exit-end zone losses increase with a larger air gap.
Also, output thrust and efficiency decrease when the design incorporates a large air gap. The goodness factor is inversely proportional to the air gap. Thus, it is clear that the air gap should be as small as is mechanically possible. The different performance values with varying air gap are shown in figure 7 and 8. When the air gap is changed, keeping all other parameters fixed, the efficiency slightly decreases with increasing air gap and the output thrust decreases as the air gap is increased.

CONCLUSION
In this paper, the equivalent circuit has been derived to analyze the performance of the short primary SLIM. So, from the parametric analysis it can be concluded that the input parameter like the length of Page: 393 the mechanical air gap plays a very important role in the performance parameters, thrust and efficiency. As the length of the mechanical air gap of the machine increases thrust and efficiency of the machine decrease. Hence, based on the target values of rotor velocity and thrust, this parameter should be chosen which gives the best possible thrust closest to the target value at a required frequency.

ACKNOWLEDGMENTS
The author is deeply grateful to Dr. Nan Win Aung, my dissertation supervisor and Daw May Nwe Ye Tun, my co-supervisor. The author also thanks to all teachers at Technological University (Thanlyin) and all who provided her with necessary assistance for this paper. The author wishes to express her guidance to all persons who helped directly or indirectly towards the successful completion of paper. Finally, the author wishes to express her special thanks to her parents for their support and encouragement to attain her destination without any trouble.