Quasi-Synchronous Operation Principle of a Variable Air-Gap Doubly Fed Linear Motor for High-Speed Maglev Application

Abstract

Compared to a long-stator linear synchronous motor (LLSM), a long-stator doubly-fed linear motor (DFLM) exhibits two distinct advantages for high-speed maglev application: 1) It has two additional degrees of freedom with both the frequency and the phase angle of the mover to improve its control accuracy and dynamic responses; 2) It can use the slip power to feed the mover contactlessly and directly. In order to achieve the propulsion, the levitation, and the contactless power transfer through the common air-gap magnetic field, the "quasi-synchronous operation (QSO)" principle of the DFLM is proposed for highspeed maglev train. Based on the DFLM modeling and distinctive constraints for maglev train, the operation point analysis of the performance evaluation is further investigated. To validate the feasibility of the DFLM application for high-speed maglev train, a unit DFLM prototype is designed and tested, and the corresponding simulation studies of the QSO control structure are investigated.Index Terms-Doubly-fed linear motor (DFLM), quasisynchronous operation (QSO), high-speed maglev train, unit DFLM prototype, multiphase DFLM. I. INTRODUCTIONB Y replacing traditional wheels with electromagnets, a maglev (from magnetic levitation) train is able to achieve high-speed through both a contactless levitation system and a contact-free propulsion system, which has been proven to be a promising transportation system [1], [2]. For the maglev application, three basic functions of the propulsion, the levitation, and the contactless power transfer should be achieved through the design of the electric drive system [3], [4]. Currently, there are two main technical solutions for the high-speed maglev train, one is German Transrapid (TR) maglev train, the other is Japanese MLX maglev train [1], [4]. The electromagnetic suspension (EMS) technique is considered for the levitation by TR maglev system, while electrodynamic suspension (EDS) technique is used by MLX maglev system. Both of them adopt the long-stator linear synchronous motor (LLSM) for the propulsion. The electromagnets with iron-core are utilized by TR system, while the superconducting magnets with aircore are used by MLX system. Due to the combination of the EDS and the superconducting magnets, MLX system has relatively higher system cost and maintenance cost, and the superconducting magnets have stronger magnetic field and higher failure risks [1], [4].