Linear Machines for Long Stroke Applications: a review

This document reviews the current state of the art in the linear machine technology. First,the recent advancements in linear induction, switched reluctance and permanent magnet machines arepresented. The ladder slit secondary configuration is identified as an interesting configuration for linearinduction machines. In the case of switched reluctance machines, the mutually-coupled configuration hasbeen found to equate the thrust capability of conventional permanent magnet machines. The capabilities ofthe so called linear primary permanent magnet, viz. switched-flux, flux-reversal, doubly-salient and verniermachines are presented afterwards. A guide of different options to enhance several characteristics of linearmachines is also listed. A qualitative comparison of the capabilities of linear primary permanent magnetmachines is given later, where linear vernier and switched-flux machines are identified as the most interestingconfigurations for long stroke applications. In order to demonstrate the validity of the presented comparison,three machines are selected from the literature, and their capabilities are compared under the same conditionsto a conventional linear permanent magnet machine. It is found that the flux-reversal machines suffer froma very poor power factor, whereas the thrust capability of both vernier and switched-flux machines isconfirmed. However, the overload capability of these machines is found to be substantially lower than theone from the conventional machine. Finally, some different research topics are identified and suggested foreach type of machine

A Complete Equivalent Circuit for Linear Induction Motors With Laterally Asymmetric Secondary for Urban Railway Transit

Since the linear induction motor commonly work with a laterally asymmetric secondary as it is applied to pull rail vehicles, this paper presents a complete equivalent circuit model considering the asymmetry to predict thrust, vertical and transversal forces. First, six correction factors are presented to quantify the variations in the air-gap magnetic flux and secondary induced current as the linear induction motor operating with a laterally asymmetric secondary. Second, it develops a circuit model based on the existing T-model for the rotary induction motor and two correction factors for the magnetizing branch, which is used to indicate the electromagnetic variations in the air-gap flux and secondary plate due to the asymmetry. Third, the mathematical expressions for the thrust, vertical and transversal forces are derived by applying the equivalent circuit model. Then, the six correction factors are calculated with a prototype motor, and the results of them are comprehensively analyzed. Finally, the characteristics in the prototype motor are calculated with the mathematical expressions in a range of rated speed，and validated by the experimental measurements carried out on a test rig and line for linear motors

A prototype of an energy-efficient MAGLEV train : a step towards cleaner train transport

The magnetic levitation (MAGLEV) train uses magnetic field to suspend, guide, and propel vehicle onto the track. The MAGLEV train provides a sustainable and cleaner solution for train transportation by significantly reducing the energy usage and greenhouse gas emissions as compared to traditional train transportation systems. In this paper, we propose an advanced control mechanism using an Arduino microcontroller that selectively energizes the electromagnets in a MAGLEV train system to provide dynamic stability and energy efficiency. We also design the prototype of an energy-efficient MAGLEV train that leverages our proposed control mechanism. In our MAGLEV train prototype, the levitation is achieved by creating a repulsive magnetic field between the train and the track using magnets mounted on the top-side of the track and bottom-side of the vehicle. The propulsion is performed by creating a repulsive magnetic field between the permanent magnets attached on the sides of the vehicle and electromagnets mounted at the center of the track using electrodynamic suspension (EDS). The electromagnets are energized via a control mechanism that is applied through an Arduino microcontroller. The Arduino microcontroller is programmed in such a way to propel and guide the vehicle onto the track by appropriate switching of the electromagnets. We use an infrared-based remote-control device for controlling the power, speed, and direction of the vehicle in both the forward and the backward direction. The proposed MAGLEV train control mechanism is novel, and according to the best of our knowledge is the first study of its kind that uses an Arduino-based microcontroller system for control mechanism. Experimental results illustrate that the designed prototype consumes only 144 W-hour (Wh) of energy as compared to a conventionally designed MAGLEV train prototype that consumes 1200 Wh. Results reveal that our proposed control mechanism and prototype model can reduce the total power consumption by 8.3 x as compared to the traditional MAGLEV train prototype, and can be applied to practical MAGLEV trains with necessary modifications. Thus, our proposed prototype and control mechanism serves as a first step towards cleaner engineering of train transportation systems

Fractional kVA Rating PWM Converter Doubly Fed Variable Speed Electric Generator Systems:An Overview in 2020

Variable speed generator systems (VSGs) are at work in the now 600 GW installed wind power plants (parks). Also, they are used as vehicular and on ground stand-alone generators. VSGs imply full kVA rating PWM converters in permanent magnet (PM) or in electrically excited synchronous or in cage rotor inductance generators. But, to reduce cost in absence of PMs at a reasonable initial cost (weight) and efficiency, the fractional kVA PWM converter doubly fed induction generators (DFIG) cover now about 50% of all installed power in wind generators. The present paper reviews recent progress in DFIG and various forms of brushless DFGs (doubly fed generators) characterized in terms of topology, design, performance and advanced control for healthy and faulty load conditions in the hope of inspiring new, hopefully ground breakings, progress for wind and hydro energy conversion and in vehicular and on the ground stand-alone generator applications

Performance analysis for a shaded-pole linear induction motor

Bibliography: pages 129-148.The induction motor remains the prime mover of present day industry with it's associated components in drive applications. In many such applications, fractional horse-power motors find ready use in small mechanisms where three-phase power supply is not available. In Southern Africa, these motors can be used is rural areas with simple reticulation systems, hence the renewed interest in the development of these low-power electrical motors, especially specialised models such as linear versions of such motors for special applications. This research is in the area of single-phase LIMs. The objective has been to model the shaded-pole LIM, in an attempt to enhance it's performance through improved design methods. This was carried out using an integrated analysis approach, involving circuital and field theory in the analysis of the practical motor, and computer simulation of it's equivalent model using the finite element method. Linear counterparts are possible for all the various forms of rotating electrical machines. All cylindrical machines can be 'cut' along a radial plane and 'unrolled' [32]. LIMs convert electrical energy directly into mechanical energy of translatory motion. Some advantages of linear version of induction motors are: they are gearless and often require minimal material thus minimising cost. While their scope of application are somewhat limited when compared to rotary versions, they do however give excellent performance in special situations where translator motion is required. However, the output power-to-mass and output power-to-volume of active materials ratio is reduced compared to rotary induction motors[45]. These disadvantages are caused by the large air-gap and the open magnetic circuit, which produces parasitical effects

Superconducting electromagnetic launch system for civil aircraft

This paper considers the feasibility of different superconducting technologies for electromagnetic launch (EML) to assist civil aircraft take-off. EML has the potential of reducing the required runway length by increasing aircraft acceleration. Expensive airport extensions to face constant air traffic growth could be avoided by allowing large aircraft to operate from short runways at small airports. The new system positively affects total aircraft noise and exhaust emissions near airports and improves overall aircraft efficiency through reducing engine design constraints. Superconducting Linear Synchronous Motors (SCLSMs) can be exploited to deliver the required take-off thrust with electromagnetic performance that cannot be easily achieved by conventional electrical machines. The sizing procedure of a SCLSM able to launch A320 in weight is presented. Electromagnetic and thermal aspects of the machine are taken into account including the modelling of ac losses in superconductors and thermal insulation. The metallic high temperature superconductor (HTS) magnesium diboride (MgB2) is used and operated at 20 K, the boiling temperature of liquid hydrogen. With modern manufacturing technology, multifilament MgB2 wires appear to be the most cost-effective solution for this application. Finally the impact of the cryocooler efficiency on the machine performance is evaluated

Performance of Induction Machines

Induction machines are one of the most important technical applications for both the industrial world and private use. Since their invention (achievements of Galileo Ferraris, Nikola Tesla, and Michal Doliwo-Dobrowolski), they have been widely used in different electrical drives and as generators, thanks to their features such as reliability, durability, low price, high efficiency, and resistance to failure. The methods for designing and using induction machines are similar to the methods used in other electric machines but have their own specificity. Many issues discussed here are based on the fundamental achievements of authors such as Nasar, Boldea, Yamamura, Tegopoulos, and Kriezis, who laid the foundations for the development of induction machines, which are still relevant today. The control algorithms are based on the achievements of Blaschke (field vector-oriented control) and Depenbrock or Takahashi (direct torque control), who created standards for the control of induction machines. Today’s induction machines must meet very stringent requirements of reliability, high efficiency, and performance. Thanks to the application of highly efficient numerical algorithms, it is possible to design induction machines faster and at a lower cost. At the same time, progress in materials science and technology enables the development of new machine topologies. The main objective of this book is to contribute to the development of induction machines in all areas of their applications

THREE-DIMENSIONAL STEADY STATE AND TRANSIENT EDDY CURRENT MODELING

Maglev transportation using electrodynamic wheels is a promising new technology aimed at providing a low cost, high-speed and environmental friendly mode of transportation. In this technology, Halbach permanent magnet rotors, termed electrodynamic wheels, are simultaneously rotated and translationally moved above a conductive non-magnetic guideway. The time-changing magnetic field created in the airgap between the rotors and guideway induces eddy currents in the guideway which in turn interact with the magnetic rotor field to produce suspension and propulsion or braking forces which are required for maglev transportation. This technology offers an integrated suspension and propulsion system. In this dissertation the eddy current distribution in the conductive guideway has been modeled in three-dimension. An approach for the computation of the static magnetic fields due to the Halbach rotor has been presented using novel magnetic charge sheet concept. Finite element models have been developed to study the steady state and transient eddy current field distribution. Three analytic models have been developed to compute the electromagnetic forces and torque acting on the rotor as well as joule loss in the guideway. The models include the heave, translational and rotational motion of the magnetic rotor for dynamic simulation. The developed analytic and finite element models are highly generic and thus can be applied to any magnetic source. The developed finite element models have been validated by comparing it with commercial finite element software and previously developed boundary coupled steady state finite element model. Commercial finite element software and two experimental setups have been used to verify the developed analytic models. Computational efficiency of the presented models has been compared with the previously developed finite element model and commercial software. Good performance of the developed models has been achieved