This article has been accepted for inclusion in a future issue of this journal. Content is final as presented, with the exception of pagination. IEEE TRANSACTIONS ON MAGNETICS 1 Algorithm of Linear Induction Motor Control for Low Normal Force of Magnetic Levitation Train Propulsion System Hyunuk Seo 1 , Jaewon Lim 2 , Gyu-Ha Choe 1 , Jang-Young Choi 3 , and Jae-Hoon Jeong 3 1 Department of Electrical Engineering, Konkuk University, Seoul 05029, South Korea 2 Department of Magnetic Levitation and Linear Drive, Korea Institute of Machinery and Materials, Daejeon 34103, South Korea 3 Department of Electrical Engineering, Chungnam National University, Daejeon 34134, South Korea This paper presents the analyses and experimental results of a single-sided linear induction motor (SLIM) thrust and normal force for the propulsion of semi-high-speed magnetic levitation (maglev) trains. These trains are composed of a levitation system that uses electromagnetic suspension and a propulsion system that uses SLIMs. The propulsion system of maglev trains using SLIMs has better low noise and dynamic characteristics compared with those using rotators. However, it has nonlinear characteristics due to the effect of slip that occur in the secondary eddy-current induction process; the normal force generated by the SLIM can negatively affect the levitation control. Therefore, a new slip-control algorithm is proposed for the safe operation of maglev trains, reflecting the normal force of the motor in propulsion control. First, the SLIM thrust and normal force are analyzed through the finite-element method (FEM) for a precise analysis of the slips. Furthermore, a slip range with a low normal force was derived based on the FEM analysis results, and these results are reflected in the propulsion control algorithm. Finally, the new algorithm was validated by an application to a full-sized testing apparatus. Index Terms— Levitation, magnetic levitation (maglev), normal force, power consumption, propulsion. I. I NTRODUCTION S INGLE-SIDED linear induction motors (SLIMs) have advantages such as the construction costs, high initial thrusts, simple structures, flexible mechanisms, absence of dust emission, and low noise [1]. Thus, they are widely adopted as traction components in several industrial applications, par- ticularly in magnetic levitation (maglev) transportation sys- tems or urban subway systems. They can provide higher passenger comfort with lower noise, because SLIM is that it generates linear motions without rotary-to-linear motion conversion devices [2]. The 200 km/h-class semi-high-speed maglev train, which is under development in Korea, uses SLIMs for the propulsion system because they are lightweight and inexpensive. How- ever, their driving characteristics are inferior to those of linear synchronous motors due to their low power factor and effi- ciency. In addition, they generate a normal force perpendicular to the moving direction, according to the slip frequency and thrust, which has adverse effects on the levitation system. The normal force in the SLIM can be described by the relationship between the thrust and slip [3]. The normal force can be reduced by adjusting the slip frequency [4]. However, one disadvantage of the constant slip frequency operation is that the best performance cannot be achieved because the optimized slip frequency is determined based on the force and the normal force at each speed. Because the slip is determined according to the speed in consideration of the normal force, it cannot be operated at the optimum driving condition in terms of propulsion efficiency. Therefore, Manuscript received March 16, 2018; revised May 6, 2018 and May 23, 2018; accepted May 24, 2018. Corresponding author: J.-H. Jeong (e-mail: tpts@cnu.ac.kr). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TMAG.2018.2842222 to increase the stability of the levitation characteristic and propulsion efficiency, it is important to analyze the charac- teristics of the normal force, thrust, speed, and slip to iden- tify the optimal operating points. Nevertheless, the constant slip-frequency control has been applied as a control method in maglev trains because it can limit the vertical fore irrespective of the thrust and speed. In this paper, the thrust and the normal force of the SLIM are analyzed at the available speed and slip ranges of rated voltage, using the 2-D finite-element method (FEM) analysis. A speed-slip condition with a stable normal force at the rated input is derived. Furthermore, the effectiveness of the slip limitation area is determined by analyzing the thrust and normal force according to the speed and slip. To verify the proposed slip pattern, the variation in the normal force is tested by implementing the general indirect field-oriented control (IFOC) and the constant slip-frequency indirect vector control (CSIFOC). The proposed algorithms are validated by simulation and by a full-sized SLIM experiment. II. MAGNETIC FIELD ANALYSIS ACCORDING TO THE SLIP AND SPEED A. Analysis Model A 200 km/h-class maglev train has six cars in one set, with each car having six bogies. The car length is 20 m, and the length of the SLIM is 2.5 m. A diagram of the semi-high-speed maglev train and the associated SLIM is shown in Fig. 1. The detailed specifications for the SLIM are listed in Table I. The motor is composed of 12 poles with 77 slots, and the required base velocity is 90 km/h. B. Rate-Characteristic Analysis The base speed of the SLIM for the 200 km/h-class semi- high-speed maglev train is 90 km/h. The base speed is defined 0018-9464 © 2018 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.