Single Linear Induction Motor Research Articles

Comparison of dynamic models of SLIM

The Single Linear Induction Motor (SLIM) is a specialized electrical machine that produces linear motion instead of the rotary motion produced by a traditional rotary induction motor. SLIM's accurate dynamic model is required to analyze the performance of the motor under different operating conditions. Dynamic modelling of SLIM using the traditional DQ- axis equivalent circuits is difficult due to the time-varying parameters such as end effect, air gap flux, saturation, and half-filled slot. The two methods for modelling SLIMs were compared, namely the conventional method and the split method. The results of the comparison showed that both methods provided similar results, but the split method offered a more detailed analysis of the components and provided deeper insight into the behavior of the motor. The choice between the two methods depends on the specific requirements and objectives of the analysis. In this paper, the dynamic model of SLIM is modelled using conventional and split methods in MATLAB/SIMULINK. The results of the two modelling methods are compared with each other, and it is concluded that the splitting method provides better transient performance than traditional D-Q axis methods.

A new method to reduce end effect of linear induction motor

A new method to compensate the end effect of a linear induction motor (LIM) in low-speed maglev vehicles is proposed. With this method, the motors are close to each other so that the front motor’s exit-end magnetic field extends into the next motor’s entry zone. As a result, the motor’s magnetic field traveling wave become continuous and the end effect of short primary LIMs is greatly weakened. In the analysis of the air-gap magnetic field distribution, the LIM is assumedly divided into two identical motors with the distances of 20, 40, 60, and 80 mm. The results show that the air-gap magnetic field is still continuous within these distances due to LIM’s end effect. As the distance between two motors increases, the distortion of the air-gap magnetic field becomes more severe. Then, we investigate the relationship between the secondary speed and the thrust in three cases, i.e., a single LIM, two motors divided with 72 mm with pole pitch corrected, and two motors divided with 60 mm without the pole pitch being corrected. We find that the thrust has a small decrease when the speed increases, which means that the magnetic field is already continuous and its amplitude is approximately a constant. Furthermore, the thrust loss of case 3 is more than that of case 2, which indicates that the pole pitch correction is effective.

Contact-free planar stage using linear induction principle

The feasibility of using a linear induction motor as a driving actuator for a contact-free planar stage is investigated for various situations. In this stage, the features of an induction motor such as no cogging force, ease of workspace enlargement, and a simple metrology process may be advantageous. The induction principle has inherently limited performance. So, a novel control method and a structural modification are suggested to compensate for the poor characteristics of the induction system. First, a modified vector controller, in which the normal force is controlled with direct current (dc) current biased to three-phase current under settled d-axis flux, replaces the general dq-based controller. Secondly, a pair of linear induction motors, in which the traveling direction of the moving part changes not by a phase change of three-phase current but by a difference of thrust forces from each linear induction motor, substitutes for a single linear induction motor to compensate for discontinuity due to the phase shift of alternating current (ac). Therefore, the stage with a dynamic characteristic, such as a double integrator in the planar direction, is preloaded in the planar direction. Finally, the influence of air stiffness on the ripple of normal force due to the ac drive is analyzed for two types of air-supporting mechanisms. All the aforementioned methods are verified experimentally.