Richard M. Stephan

Vector control methods for induction machines: an overview

In the last three decades, different vector control methods (field-oriented control (FOC), field acceleration method (FAM), universal field orientation (UFO), direct self control (DSC) and Takahashi method among others) have been proposed. It is difficult for students and nonspecialists to understand the drawbacks and advantages of each one. With this in mind, the objective of this paper is to propose a clear classification and comparison of them.

Tests on a Superconductor Linear Magnetic Bearing of a Full-Scale MagLev Vehicle

A full-scale MagLev vehicle prototype has been developed by the team of the Laboratory for Applied Superconductivity from the Federal University of Rio de Janeiro. This vehicle is named MagLev-Cobra (cobra means snake in Portuguese), because it is composed by several modules and its motion in curves resembles the movement of a snake. The suspension technology proposed for this vehicle is the levitation of bulk superconductors above a rail made with Nd-Fe-B magnets and steel. The main advantages of the MagLev-Cobra vehicle are low energy consumption, negligible noise emission, curvature radius of 45 meters and capability to ascend ramps of 15%. These properties allow the vehicle to be perfectly adjusted to big cities layout and to be constructed along roads and rivers. One of the most important parts of this project is the superconductor linear magnetic bearing (SLMB) development for the MagLev. In this work, some new results of the SLMB are presented. Measurements of the vertical levitation force of the SLMB and the effect of the flux creep on this force are presented. Also, some tests were made to investigate the influence of the load variation on the levitation force and the SLMB levitation gap. Finally, some tests were made to measure the levitation force and torque in the cryostat for an angular displacement between it and the magnetic guideway. These tests simulate the vehicle operation in real conditions.

Flywheel Energy Storage System Description and Tests

This paper presents test results of a flywheel energy storage system (FESS) prototype. The bearing system is composed of a superconducting magnetic thrust bearing (SMB) and a permanent magnet bearing (PMB). The SMB was built with Nd-Fe-B magnet and YBCO superconducting blocks. The PMB has the function of positioning radially the switched reluctance machine (SRM) used as motor/generator and reduce the load over the SMB. The SRM drive is responsible to convert electrical into mechanical energy, and vice versa. The prototype still operates at low speeds, but the dynamical simulations of the SRM drive showed that the system can work at high speed, supplying the required energy during disturbances. In the tests performed with the FESS prototype, the system took or delivered energy from/to the grid when requested.

Optimization of a Linear Superconducting Levitation System

The Laboratory for Applied Superconductivity of the Federal University of Rio de Janeiro (LASUP) has been developing a superconducting magnetic levitation urban train named MagLev-Cobra. It is a kind of light rail vehicle where the conventional wheel-rail track is substituted by a rail of Ne-Fe-B magnets and carbon steel interacting with superconductor bulks installed in the vehicle to promote levitation. The main cost of this levitation system is the magnetic rail. Therefore, any improvement in the shape and configuration of magnets and iron has a significant budgetary impact. In this paper, the optimizations carried out with the feasible direction interior point algorithm, extensive search, and genetic algorithm of magnetic rails are presented. The objective is to find the geometry that minimizes the total cost, for a given levitation force, considering some practical restrictions. The levitation force restriction is calculated using a finite-element method. During the optimization process, the superconductor null permeability model is used. Finally, the results are checked with the Bean model and verified experimentally. Measurements of the levitation force and the field mapped over the magnetic rails are presented. Significant reduction of soft and hard ferromagnetic materials was reached.

Experiments in a real scale maglev vehicle prototype

A Brazilian real scale magnetically levitated transport system prototype is under development at the Federal University of Rio de Janeiro. To test this system a 180 m long line has been projected and it will be concluded by the end of 2010. A superconducting linear bearing (SLB) is used to replace the wheels of a conventional train. High temperature superconductor bulks placed inside cryostats attached to the vehicle and a magnetic rail composes the SLB. To choose the magnetic rail for the test line three different rails, selected in a previous simulation work, were built and tested. They are composed by Nd-Fe-B and steel, arranged in a flux concentrator topology. The magnetic flux density for those magnetic rails was mapped. Also, the levitation force between those rails and the superconductor cryostat, for several cooling gaps, were measured to select the best rail geometry to be used in the real scale line. The SLB allows building a light vehicle with distributed load, silent and high energy efficient. The proposed vehicle is composed of four modules with just 1.5 m of length each one and it can transport up to 24 passengers. The test line having two curves with 45 m radius and a 15% acclivity ramp is also presented.

Levitation force and stability of superconducting linear bearings using NdFeB and ferrite magnets

Abstract In the frame of a project on the development of a reduced-scale-levitating rail-vehicle prototype, the performance of two different permanent magnets have been tested in linear bearings using YBa2Cu3O7−y bulk superconductors. The levitation forces, the stiffness and the vibration damping have been measured using two different rail assemblies: one mounted with NdFeB magnets and another with ferrite ones. The levitation force of the NdFeB rail is more than one order of magnitude larger than that of the ferrite one. The stiffness of those linear bearing and the vibration damping were measured for several cooling heights from the rail. The stiffness increases with the decrease of the cooling height and is larger in the NdFeB rail. The vibration damping is rather low in both systems. Finally, we conclude that the NdFeB magnets are the most suitable for applications on linear levitating bearings.

Tests With One Module of the Brazilian Maglev-Cobra Vehicle

Approximately a decade ago, superconducting maglev train prototypes started to be developed. Researchers from China, Germany, and Brazil have built prototypes carrying people based on superconducting levitation technology. The Brazilian MagLev project, named MagLev-Cobra, started in 2000 with a small-scale prototype that was concluded in 2006. After that, efforts toward a full-scale test vehicle for 30 passengers began. This vehicle will be composed of 4 modules, each one 1.5 m long, with six levitation cryostats and a linear induction motor. The first module and 12 m of test track are already constructed and this paper will describe the following tests: air gap as a function of load, temporal air gap stability, linear motor traction force, and vehicle acceleration. The paper will also describe the construction details of module, linear motor, and the rail.

Superconducting Light Rail Vehicle: A Transportation Solution for Highly Populated Cities

This article describes the construction and operational advantages of a superconducting magnetically levitated (MagLev) vehicle in comparison with wheel-rail traditional options and applied to urban transportation. The technology was tested with a small-scale prototype. A comparison with other MagLev technologies is presented and application niches are identified. The steps for a full-scale implementation and commercialization will also be addressed.

Superconducting axial bearing for induction machines with active radial magnetic bearings

A superconducting passive axial bearing has been developed for an induction machine with vertical rotor and two active radial magnetic bearings, resulting in a fully levitating system. This prototype has been designed on the basis of a previous one reported by Salazar-Stephan as a 4-pole 2-phase induction machine using windings of a standard motor. Each active radial bearing measures four shaft-positions using eddy-current sensors, each displaced by 90 degrees. The levitation has been performed using two NdFeB permanent magnets and bulk pieces of seeded-melt-textured YBCO. The YBCO pieces have been characterized by measuring the levitation forces and mapping the remanent magnetic field with Hall probes. The radial stability of the system is modeled and discussed.

MagLev Cobra: Test Facilities and Operational Experiments

The superconducting MagLev technology for transportation systems is becoming mature due to the research and developing effort of recent years. The Brazilian project, named MagLev-Cobra, started in 1998. It has the goal of developing a superconducting levitation vehicle for urban areas. The adopted levitation technology is based on the diamagnetic and the flux pinning properties of YBa2Cu3O7−δ (YBCO) bulk blocks in the interaction with Nd-Fe-B permanent magnets. A laboratory test facility with permanent magnet guideway, linear induction motor and one vehicle module is been built to investigate its operation. The MagLev-Cobra project state of the art is presented in the present paper, describing some construction details of the new test line with 200 m.