Analysis and control of a 6 DOF maglev positioning system with characteristics of end-effects and eddy current damping

Magnetic levitation technology has become the great candidate to provide ultraprecision motion in vacuum environment due to its characteristics, e.g., non-contact, frictionless, and unlimited stroke, etc. This paper presents the design, modeling, analysis, and control of a 6 Degrees-Of-Freedom (DOF) maglev positioning system, and the proposed system is able to achieve a planar motion of 50 mm × 50 mm while the levitation height is up to 4 mm. In this work, the model of eddy current damping for moving Halbach Permanent Magnet (PM) array is analytically established to predict the damping force in operating of the maglev positioning system. Furthermore, the magnetic field end-effect is analyzed in the maglev system, where two guidelines are provided to ideally avoid the model error due to end-effect during the design of the maglev system. To control the maglev positioning system to achieve good planar tracking performance, the system identification is carried out for x and y-axes, and a simple PID controller is designed and optimized according to the specifications characterizing on the closed-loop performance of the maglev system. Finally, the experiments are conducted on the maglev prototype to demonstrate the positioning performance, and the results show that the maximal static positioning error is less than 200 nm with the Root Mean Square Error (RMSE) around 60 nm.     

Experimental evaluation of the total shielding current in a bulkhigh-Tc superconductor [YBaCuO]

Total shielding currents of a melt processed bulk high-Tc superconductor (HTS) are evaluated from the measured voltage of a Rogowski coil when a permanent magnet is moved towards the HTS. The total shielding current and the levitation force between the magnet and the HTS show rapid growth and decay depending on the speed of the magnet. The dynamic levitation force and the magnetic relaxation are discussed from the experimental results     

基于TDD系统的高速磁悬浮软切换技术研究

磁悬浮列车是一种运行速度达600 km/h的陆地交通运输工具,对分区切换机制设计带来更大挑战。为保证列车运行过程中的可靠通信,首先对高速磁浮车地通信系统方案进行设计,面向磁悬浮车地通信软切换需求优化设计了MAC层帧结构,同时提出基于地理位置信息的软切换机制,包括分区内切换和跨分区切换;通过仿真得出列车在速度为600 km/h的情形下,切换重叠区距离设置为264 m,可以实现切换成功概率为99.6%。     

High Tc Superconductor Theoretical Models and Electromagnetic Flux Characteristics

High Tc Superconductors (HTS) have special electromagnetic characteristics and phenomena. Effort has been made in order to theoretically understand the applied HTS superconductivity and HTS behaviors for practical applications, various theoretical models related to the HTS electromagnetic properties have been developed. The theoretical models and analytic methods are summarized with regard to understanding the HTS magnetic flux characteristic which is one of the most critical issues related to HTS applications such as for HTS magnetic levitation application.     

Analysis of Vertical Oscillations of a Permanent Magnet Freely Levitated above an YBCO Bulk in an AC External Magnetic Field

The effect of the moving speed of permanent magnet （PM） on levitation force between PM and high temperature superconducting （HTS） bulk is analyzed and described in the PM-HTS levitation system. The PM vibration characteristic in the PM-HTS system is investigated. The PM may collide with the HTS in vibration if the amplitude and frequency of driving force satisfy the relationship Pmin=Afn. When the load of the system is below a threshold, the minimal collision amplitude of the driving force increases with the load increasing, however, it sharply drops to zero when the load exceeds the threshold. With the increase of the initial height of the PM, the threshold load increases, but the minimal driving force which causes a collision between PM and HTS decreases.     

High Tc Superconductor Theoretical Models and Electromagnetic Flux Characteristics

High Tc Superconductors （HTS） have special electromagnetic characteristics and phenomena. Effort has been made in order to theoretically understand the appfied HTS superconductivity and HTS behaviors for practical appfications, various theoretical models related to the HTS electromagnetic properties have been developed. The theoretical models and analytic methods are summarized with regard to understanding the HTS magnetic flux characteristic which is one of the most critical issues related to HTS appfications such as for HTS magnetic levitation application.     

Design,implementation and self-tuning adaptive control of maglev guiding system

This paper presents a self-tuning adaptive control (STA control) for a magnetically levitated (maglev) guiding system. The guiding system is a repulsive maglev system with a passive carrier and four active guiding tracks. Hybrid magnets exert the levitation forces, whereas the stabilizing forces are produced by electromagnets. Given such a system, an STA stabilizing controller is developed, and the thorough analysis of the stability property is also proposed. It is shown that without precise knowledge of various components, the overall system stability and the regulating precision are assured, which validates the hereby proposed system. From the simulation and experimental results, the performance of the system design and the enforced control mechanism is demonstrated successfully.     

Design and analysis of magnetically-drive actuator applied for linear compressor

A novel Magnetically Levitated Linear Actuator (MLLA), mainly consisting of a Halbach magnetized moving-magnet armature, a cylindrical frame, a rod and electromagnetic (EM) poles, is presented and analyzed for linear compressors applications. The Halbach magnetized armature naturally generates a periodically distributed magnetic field which is interacted with that induced by the EM poles. Therefore, an axially reciprocating thrust force is induced that is inherently suitable for high frequency drive for linear compressors. A lateral magnetic repulsive force, due to the eddy current induced at the cylindrical frame, to exert upon the rod is generated as long as the rod is deviated in the radial direction. Once the position of the rod is laterally deviated from the central position, the rod is automatically brought back by this magnetic repulsive force. The magnetic field distributions, axial thrust force and lateral magnetic repulsive force are numerically obtained by Governing Equations Analysis (GEA) under cylindrical coordinate. The Finite Element Method (FEM), by the commercial software ANSOFT Maxwell with Transient Solver, is employed to be compared with and validate the solutions obtained by GEA. It is shown that the GEA is extremely agreed with the results by FEM. At last, the efficacy of the proposed MLLA is examined and verified by intensive computer simulations and experiments.     

Analysis of magnetic field and circulating current for HTS transformer windings

In a high-temperature superconducting (HTS) transformer, the leakage magnetic field decreases the critical current and increases the ac loss in the tapes. Moreover, because of nearly zero resistance of HTS tapes, a slight unbalance of the branch inductances of the windings might result in heavy circulating current. So, the numerical analysis of the leakage magnetic field and circulating current is especially necessary for an HTS transformer design. In this paper, the influence of the winding configurations on the stray field and circulating current is studied. That is, the magnetic field distribution is analyzed by finite-element method and then, based on the inductance matrix obtained after a magnetic field analysis, the circulating current is calculated by circuit analysis. Some measures for improving the leakage field and circulating current distribution are also proposed to make HTS transformers more efficient.     

Independent Control of Average Torque and Radial Force in Bearingless Switched-Reluctance Motors With Hybrid Excitations

Radial force and torque are the control objectives that determine the machine performance of levitation and rotation in a bearingless switched reluctance motor (BSRM). This paper proposes a control scheme for rotating and levitating a 12/8 BSRM. The motor average torque and radial force are independently controlled with hybrid excitations in main windings and levitation windings. First, the mathematical relationship between radial force and currents, which is utilized in this paper, is derived by using the Maxwell stress tensor method. Then, the proposed control scheme is analyzed. The average torque of each phase generated in the levitation region equals zero for its symmetry of the aligned position. Accordingly, the current calculating algorithm is deduced to minimize the magnitude of instantaneous torque in the levitation region. The principle and realization of the proposed scheme are demonstrated with finite-element (FE) analysis. Experimental results show that the proposed scheme is effective for a stable levitation.      

Will maglev lift off?

Work on magnetic levitation (maglev) as a basis for ground transport systems has been going on since the 1960s, and although the future of maglev in land transport is still uncertain, the author gives an assessment of progress at a time when there is much interest both in high-speed trains and in people-moving systems. He deals first with the simpler low-speed systems, as these have now been proven safe for public service, and secondly with the high-speed systems on which decisions on implementation of projects for public-service use will be taken in the near future     

A Permanent Magnet Linear Synchronous Motor Drive for HTS Maglev Transportation Systems

A permanent magnet linear synchronous motor （PMLSM） for a high temperature superconducting （HTS） maglev system has been studied, including the motor structure, control strategy, and analysis techniques. Finite element analysis （FEA） of magnetic field is conducted to accurately calculate major motor parameters. Equivalent electrical circuit is used to predict the drive＇s steady-state characteristics, and a phase variable model is applied to predict the dynamic performance. Preliminary experiment with a prototype has been made to verify the theoretical analysis and the HTS-PM synchronous driving technology.     

Stabilization of one degree-of-freedom control type levitation table with permanent magnet repulsive forces

It is impossible to levitate an object by using only permanent magnets (PMs). Many researches have been reported to reduce the number of control degree-of-freedom (DOF) in magnetic levitation systems. This paper presents a one-DOF control type magnetic levitation table supported by repulsive forces of four sets of PMs. Each set of PMs is composed of two PMs on a fixed frame and one PM on the levitated table. The PMs are located at the four corners of the rectangular table and the corresponding positions of the frame. The magnetic poles of the PMs on the table are opposed to those of the fixed PMs, so that repulsive forces act on the table and the frame. This paper, first, discusses theoretically the relative position range of the sets of PMs to the center of gravity of the table from the viewpoint of the stability condition of the motion of equation. In the discussion, the repulsive force and stiffness produced by a set of the PMs are assumed to be known parameters because they can be numerically calculated. Then an experimental table is constructed, in which the unstable motion is actively stabilized by a linear motor. Dynamic responses are measured, and results prove that the proposed magnetic levitation table is successfully held in stable equilibrium by only one-DOF active control.     

Development of a MAGLEV superconducting magnet for the Yamanashitest line in Japan: vibration characteristics and analysis for design

A high-performance and high-reliability magnetically levitated (MAGLEV) superconducting magnet (SCM) was developed. Its heat generation per unit time by the electromagnetic forces due to the spatially fifth ripple magnetic fields from levitation coils is under 2 W at the frequency range in which vehicles are levitated. The vibration mode of inner vessels that makes the largest contribution to heat generation in SCMs is clarified, the torsion mode. A modeling method to analyze SCM vibration, which considers the effect of the bogie frames of a vehicle, is examined, and heat generation in SCMs is calculated from the vibration of the inner vessel. Using the numerical analysis method, new SCMs combined with new bogie frames for the Yamanashi Test Line are designed. Good performance in vibration and heat generation of these SCMs is predicted by numerical analysis     

Combined magnetic levitation and propulsion: The mag-transit concept

Mag-Transit is a unique combination of magnetic levitation and propulsion for people mover applications. Linear induction motors are used for levitation, propulsion, braking, and guidance. Since there are a minimum of moving parts there is a potential for a substantial increase in system reliability and availability as compared to conventional systems. Modern solid-state technology provides the capability to condition sufficient quantities of electrical energy to control motor excitation, and thereby levitation, within a closed-loop servo system. Real time measurements of air gaps and vehicle accelerations are used to compute the desired levitation force. In addition, the solid-state electronics provides the ability to control independently the speed of the vehicle by a continuously variable excitation frequency to the motors. An overview is provided of the Mag-Transit concept from a control system standpoint. Results from a dynamic simulation of a test vehicle configuration are presented.     

Design of high precision linear stage with double-sided multi-segmented trapezoidal magnet array and its compensations for force ripples

Generally, linear motor is used as actuators for high precision stage which requires long stroke, high speed and high precision capability. In order to meet the needs of high speed and high precision, it is important that the motor generates large force and has small size. In this paper we propose a linear motor with multi-segmented (MST) magnet array to maximize actuating force per unit volume. The MST magnet array is a modified version of standard Halbach magnet array. Each magnet in the MST magnet array has various shapes and dimensions while standard Halbach magnet array has identical magnets. In order to optimize the shapes and dimensions, design optimization of the motor is carried out and its performance is investigated. We conclude that the linear motor with the MST array can generate more actuating force per unit volume than the one with conventional magnet array and standard Halbach magnet array. A high precision stage is constructed using the optimized MST magnet array. Even though we obtain maximized actuating force, the flux density by the MST array is seriously distorted from ideal sinusoidal flux density with respect to mover position. This distorted flux density results in force ripples when we use three phase commutation. And no matter how small force ripples would be, serious tracking errors occur in high precision linear stages. Thus, force ripple must be compensated. In this paper, we proposed a simple method to reduce the ripple by current shaping.     

Trapped field and related properties in a superconducting-disk magnetized by pulse field

The distributions of the magnetic field and temperature in a superconducting-disk magnetized by pulse field, and the levitation force between this disk and a permanent magnet are calculated. The calculation is based upon the current motion and the heat diffusion equations in the disk. The critical current density as a function of magnetic field and temperature is taken into account. The dissipation power in the superconducting or the normal state region is distinguished. The trapped field may reach 17 T at 29 K by pulsed field magnetization. The effects of the amplitude of the current pulse on the distributions of magnetic field in the disk and on the levitation force are discussed.     

水轮机转子磁悬浮承重系统之电磁装置漏磁研究

面对传统推力轴承支承系统存在的问题,本着采用混合磁悬浮装置和传统推力轴承共同完成支撑的目的,研究了漏磁对电磁装置的影响。为此,引入了气隙比的概念,提出了通过改变气隙比的值来研究漏磁对系统悬浮力的影响,通过一系列仿真,得出了随着漏磁的增加,系统电磁悬浮力反而增大的结论。结合了陕西安康水电站水轮机组的数据,通过各方面的约束,在永磁装置确定的情况下,计算出了电磁装置较优的电气及结构参数。     

An automated loading and unloading system for a maglev wafertransport path

An automated loading and unloading system for placing silicon wafers on a carrier is discussed. Interest is particularly focused on the automated loading of wafers onto a carrier which is moved along a transport path using a magnetic levitation (maglev) drive mechanism. The system consists of a wafer carrier which can move along the path and is purely passive, and a loading and unloading device which uses vacuum and electrical power. A magnetic clamping mechanism presents the wafer from sliding when the carrier moves along the path. The electromagnetic loading and unloading device firmly holds the wafer using vacuum suction and may be carried out by a robot. Only the bottom surface and edge of the wafer are touched by the carrier and the loader-unloader. The loader-unloader described, when combined with a maglev transport path, is potentially useful for connecting the processing tools in a cluster or connecting the workstations along a semiconductor fabrication line     

Field tests on a MAGLEV with passive guideway linear inductor motortransportation system

A passive guideway linear inductor motor MAGLEV research vehicle intended primarily for urban transportation applications is presented. Solutions for magnetic levitation and propulsion control together with the main sensors (airgap, acceleration, and position) are described. Preliminary field tests on a 4-t 4-m-long research vehicle, named Magnibus-01, are given. Vehicle take-off and landing, response to perturbations in levitation, vehicle acceleration, and electrical braking at low speeds were recorded and are presented