They were all motors and axles, wheels and engines. However, the introduction of maglev technology has broken that tradition. Developing these trains has required input from a number of different fields other than mechanical engineering, including physics and chemistry. Most importantly, though, it has brought electrical engineers to the table.
From the beginning, electrical engineers have been major contributors to developing maglev technology. Eric Laithwaite, an electrical engineer, developed the first linear induction motor, an important and necessary precursor to maglev trains. Hermann Kemper, who many believe to be the father of maglev, was also an electrical engineer.
German and Japanese electrical engineers worked to establish the maglev programs in their respective nations.
And today, electrical engineers are making the technology better and better so that it may appeal to countries all over the world. Maglev trains have surprisingly few moving parts.
They are all about electric currents, magnets, and wire loops. Some important topics to the field are electromagnetic fields and waves, circuit theory, feedback control systems, and power engineering. All these fall under the expertise of electrical engineers. Therefore it is electrical engineers that are needed to solve the biggest problems this technology faces. The trains need to be made faster and more energy efficient.
All the while they need to be kept well within boundaries of safety. The guideways need to be made cheaper, easier to implement, and perhaps more compatible with existing rails.
The control systems need to be made flawless. All of these issues and more are calling out for an electrical engineer to come unravel their answers. Maglev technology holds great promise for the future. It has the potential to be a cheaper, faster, safer, and greener form of transportation than we have today. And with the help of some electrical engineers, it will become all of these things. There are possible applications for this technology in anything from intercity public transportation to cross-country trips.
There are even proposals to build long underground tubes, suck the air out of the tubes, and place maglev trains inside of them. In this setting there would be virtually no wind resistance, so a train could easily reach speeds exceeding the speed of sound Thornton, While it may be a long time before this technology becomes prevalent, it is difficult to deny that it will at some point be prevalent.
The advantages are too hard to ignore. As of now there is only one commercial maglev train in use, and it has already eclipsed everything that has come before it.
How will this technology evolve and improve as we move into the future? Only time will tell. But it is highly plausible that we now stand at the precipice of a transportation revolution. I, for one, look forward to gliding across the countryside at mph in a levitating box of magnets. Abstract Maglev trains use magnetism to levitate above the tracks on which they travel. Introduction Imagine a train without wheels. History of Maglev The fundamental ideas behind maglev technology can be traced back to the early 20th century.
Figure 1 Transrapid on testing center in Germany near Bremen. Figure 3 Comparison of Wheel-Rail versus Guideways. Figure 4 Levitation, propulsion, and guidance in maglev. Levitation Levitation is the ability for the train to stay suspended above the track. There are two important types of levitation technology: Electromagnetic Suspension EMS : EMS Figure 5 uses the attractive force of electromagnets placed on the guideway and on the train to achieve levitation.
The benefits of this method are that it is simpler to implement than Electrodynamic Suspension discussed below , and that it maintains levitation at zero speed. The drawbacks are that the system is inherently unstable. At high speeds, it becomes difficult to maintain the correct distance between train and guideway. If this distance cannot be kept, the train will fail to levitate and come grinding to a halt.
To account for this, EMS requires complex feedback-control systems to ensure the train is always stable Lee, Electrodynamic Suspension EDS : EDS Figure 6 uses the repulsive force of superconducting magnets placed on the guideway and on the train to achieve levitation. The magnets move past each other while the train is running and generate the repulsive force. The benefits of this method are that it is incredibly stable at high speeds.
Maintaining correct distance between train and guideway is not a concern Lee, The drawbacks are that sufficient speed needs to be built up in order for the train to levitate at all. Additionally, this system is much more complex and costly to implement.
Propulsion Propulsion is the force that drives the train forward. Figure 7 Rotary motor versus linear motor. Guidance Guidance is what keeps the train centered over the guideway. Benefits of Maglev The most obvious attraction of maglev trains is that they can travel faster than traditional rail trains.
There are other, more subtle qualities that also make maglev attractive: Longevity: Conventional wheels and rails undergo a great deal of stress over time. They must be replaced and repaired periodically to remain functional. In maglev, there is no contact between train and guideway, so there is substantially less wear-and-tear. The lifespan of maglev parts are appropriately much longer due to this fact Powell, Economically, this is quite an incentive, as repair and maintenance are costly and time-consuming activities.
Safety: It might seem counter-intuitive that these trains are safer, as they travel so much faster than their wheeled counterparts. It is true nevertheless. Maglev trains are near impossible to derail Luu, These magnetic fields interact with simple metallic loops set into the concrete walls of the Maglev guideway.
The loops are made of conductive materials, like aluminum, and when a magnetic field moves past, it creates an electric current that generates another magnetic field. Three types of loops are set into the guideway at specific intervals to do three important tasks: one creates a field that makes the train hover about 5 inches above the guideway; a second keeps the train stable horizontally.
Both loops use magnetic repulsion to keep the train car in the optimal spot; the further it gets from the center of the guideway or the closer to the bottom, the more magnetic resistance pushes it back on track. The third set of loops is a propulsion system run by alternating current power.
Here, both magnetic attraction and repulsion are used to move the train car along the guideway. Imagine the box with four magnets -- one on each corner. The front corners have magnets with north poles facing out, and the back corners have magnets with south poles outward. Electrifying the propulsion loops generates magnetic fields that both pull the train forward from the front and push it forward from behind.
Figure 2 b shows the general block diagram representation of a maglev-based rail system. Therefore, in maglev systems, ground supply either energizes the track coils or it supplies the on-board system through magnetic coupling between the track coils and rail car, whereas in on-wheel rail systems, mechanical contacts fulfil this task.
Features like an automatic centralized control unit and in-cab signalling system differentiate the maglev systems from on-wheel rail systems [ 5 , 6 , 7 ]. Table 1 presents the basic differences between an on-wheel system and maglev-based system. Maglev technology has emerged as a breakaway from the conventional wheel-based technology for achieving higher speeds with better performance [ 8 ]. Although the capital cost of establishing a maglev system is high, its maintenance and operating costs, however, are much lower than the on-wheel railways due to less mechanical contacts.
Maglevs show much less specific energy consumption as compared to wheel-based rail systems for the same travel distance at the same operating speed [ 9 ]. On-wheel rail systems use adhesion between wheels and rails to move forward, while maglev systems use propulsion force generated by a linear electro-mechanical system, to move forward. This linear propulsion system replaces conventional rail wheels with electromagnets, by yielding sufficient force to levitate the train on the guideway [ 10 ].
This feature imparts a smooth ride to the vehicle along with increased speed. In some existing systems like Moscow monorails, linear motors are used to power the wheel-based rail systems.
Therefore, in higher-speed systems, maglev technology is currently used. The following sections of this paper describe maglev technology in detail. A maglev system comprises five major components, namely levitation, guidance, input power transfer, propulsion and control systems, as shown in Fig. Levitation force provides the upward lift to the vehicle, whereas propulsion force is responsible for propelling the vehicle forward.
Guidance force balances the lateral displacement of the vehicle to keep the vehicle centred on the guideway, as marked in Fig.
Input power transfer deals with the mechanism of transferring power from the groundside. The control system is designed mainly to control the previously described components, as shown in Fig. The following sub-sections include detailed discussions about these components [ 8 , 9 , 10 , 11 ]. Levitation technology is an integral part of every maglev system that enables the vehicle to glide over an air cushion. The method used to accomplish levitation can be either a magnetic repulsion-based system or a magnetic attraction-based system [ 12 , 13 ].
Based upon the method used for realizing levitation, maglev system can be classified as an electro-dynamic suspension EDS system, electro-magnetic suspension EMS system, a permanent magnet electro-dynamic suspension system PM-EDS or a hybrid electro-magnetic suspension system HEMS. This system employs magnetic repulsive force for accomplishing levitation, as shown in Fig. On-board magnets, when moving forward with the vehicle over the guideway consisting of inductive coils or conducting sheets, generate repulsive force due to interactions of on-board magnets with the currents induced in the guideway coils [ 13 , 14 ].
This repulsive force provides the required levitation to the vehicle. This technique can achieve levitation up to 10 cm. In addition, this system uses superconducting magnets SCMs which are super-cooled at frigid temperatures using a cryogenic system. These magnets not only raise the cost of the system, but the strong magnetic field generated by such magnets penetrates inside the train car even after shielding, making the travel uncomfortable for the passengers.
However, the SCMs can conduct electricity during power failure. The Japanese MLX01 vehicle uses this levitation technology [ 15 , 16 ]. This system is a modified form of the conventional EDS system.
It is a passive levitation system, also known as an inductrack system based on the principle of magnetic repulsion. It uses permanent magnets at room temperature, arranged in the form of a Halbach array, as shown in Fig. Unlike a conventional EDS system, this system does not require any super-cooled magnets, neutralizing any cryogenic requirements [ 15 , 16 ]. However, the system requires auxiliary wheels to accelerate the vehicle until it acquires some initial take-off speed, after which it starts levitating.
In case of power failure, the train can slow down and rest on its auxiliary wheels. This arrangement produces a sinusoidal magnetic field on the lower side of the array while cancelling it completely on its upper side. This magnetic field interacts with the insulated short-circuited coils forming the track to produce repulsive levitating force [ 14 ]. As this design does not require any super-conductor, it is a low-cost design.
Since an ideal Halbach array does not exist, the magnetic field produced by such an array is not purely sinusoidal [ 13 ].
Thus, for smaller levitation air gaps, irregularity in the magnetic field produces higher-order harmonics in the system [ 15 ]. These harmonics result in oscillations in the system even without external disturbances. This technology has been under trial by General Atomics, USA, with suspension magnets separated from propulsion magnets [ 13 ].
Other technology that uses super-conducting material levitating in a constant field of permanent magnets has also been under trial and research in Chengdu, China since [ 16 ]. This system uses magnetically attractive forces between the guideway and the on-board electromagnets installed below the guideway, for accomplishing levitation. This design produces levitation even at zero speed [ 17 , 18 ]. Unlike the EDS system, EMS system uses standard electromagnets, which conduct in the presence of electric power supply only [ 19 ].
This results in magnetic fields of comparatively lower intensity inside the passenger compartment, making the travel more comfortable for the passengers. However, lower intensity of magnetic field produces a levitation air gap of 1 cm.
A small levitation air gap makes the continuous controlling of the gap imperative because of the inherent instability of the suspension systems. Nevertheless, controlling the smaller air gap becomes more and more inconvenient with the increase in speed. This makes it suitable for low- to medium-speed applications [ 8 ]. This design not only decreases the number of power controllers and electromagnets required, but it also decreases the power supply rating required for the circuit, making it an inexpensive design [ 6 ].
However, in this arrangement, the interference between the two circuits increases with the increase in speed. Therefore, this integration is suitable for low-speed applications [ 18 ]. However, such arrangement increases the cost of the design due to the increase in number of power controllers used.
Electro-magnetic suspension system, a with levitation and guidance circuits integrated, b with levitation and guidance circuits separated. This is a modified form of the conventional EMS system, as shown in Fig. It uses permanent magnets along with electromagnets to reduce the electric power consumption of the conventional system and to achieve larger air gaps [ 20 , 21 ]. At the start, the system uses both the electromagnets and permanent magnets PMs to accomplish levitation.
However, after achieving a steady-state air gap, the PMs solely starts levitating the vehicle, nullifying the power of the electromagnets. The PMs generate a magnetic flux of constant magnitude.
Thus, the requirement for a controllable input source having larger variation becomes imperative for exciting the electromagnets [ 21 ].
Achieving stable suspension from hybrid magnets requires a complex control system. Nevertheless, this technology is under research because of its robustness and high stability. This technology shows many future prospects in the field of high-speed contact-less transport systems [ 21 ]. Based on the distinctive characteristics of maglev levitation systems, Table 2 gives the comparison of different levitation techniques, which summarizes this section based on the existing literature.
However, it may vary with several factors such as type of magnets used, location and arrangement of magnets with respect to the vehicle and track. In order to keep the vehicle centred on the guideway, the maglev vehicle requires a precise guidance mechanism so that the lateral displacement of the maglev vehicle can be controlled [ 22 ].
Such a guidance mechanism generally uses either magnetic-repulsive force or magnetic-attractive force [ 6 , 16 ]. In magnetic-repulsive guidance, the sideway track contains the guidance coils on both sides, as shown in Fig. Coils on either side of the guideway are connected together in such a way that net electromotive force emf induced in the coils becomes zero, in case of null lateral displacement [ 23 ].
As soon as the train displaces laterally towards one side, the net magnitude of induced emf increases and engenders a repulsive force on the vehicle to centralize it on the guideway. Japanese MLX technology integrates the guidance system with the levitation system, whereas Japanese MLU technology integrates the guidance system with the propulsion system. The German Transrapid also uses magnetic repulsive force between the on-board electromagnets and the side coils connected on either side of the train for accomplishing guidance.
Nevertheless, in the German system, the levitation and propulsion systems remain separated from each other to shun any interference between the two systems at higher speeds. In magnetic-attractive guidance, attractive force generated between the on-board electromagnets and reaction rail controls the lateral displacement, as shown in Fig.
A gap sensor senses the air gap between the electromagnets and reaction rail. As soon as the vehicle displaces laterally, the air gap increases which further increases the reluctance and decreases the inductance of the electromagnetic flux path.
This impels the system to reduce the reluctance for maintaining stability. This further pushes the vehicle towards the centre of the guideway.
In a maglev system, transfer of electricity from the groundside is crucial for powering the levitation and propulsion coils and other on-board accoutrements [ 24 , 25 ].
For such applications, linear transformers and linear generators together form the contact-less power delivery system. This system transfers the necessary power to the vehicle [ 23 ]. The power supply system of the Chinese Shanghai Maglev includes substations, feeder cable along with tracks, switch stations and other supply equipment.
In this system, high-voltage alternating current AC supply is taken at kV from the power grid which was stepped down to 20 kV and 1. This stepped-down AC is converted into direct current DC using rectifiers, then into a variable-frequency AC supply of 0— Hz using inverters [ 24 ]. After stepping up, this supply excites the long stator windings of linear motors on the guideway.
The German Transrapid uses linear generators embodied with levitation electromagnets for power transfer. These linear generators procure power from the traversing electromagnetic field that travels with the vehicle and generates frequency six times larger than the motor synchronous frequency.
Being mechanically contact-free, this transfer method is suitable for high-speed operation [ 23 ]. The Japanese MLX uses two linear generators of concentrated type and distributed type along with a gas turbine generator. On-board coils distributed along the vehicle form the coils of the distributed type of generator. These coils are fitted with on-board superconducting coils. In the concentrated type, generator coils are concentrated in the nose and tail part of the vehicle.
Superconducting coils and generator coils form the upper and lower part of the on-board assembly, respectively. When the vehicle moves with speed, DC flux produced by superconducting coils varies and links with levitation and guidance coils forming the sideways of the track. This variable flux in turn links with the on-board generator coils.
This converts the DC flux generated by the on-board superconducting coils into AC flux using on-board linear generators [ 24 , 25 ]. Pulse width modulation PWM -controlled voltage source converter systems supply and control the propulsion motor windings.
Future applications may use silicon carbide SiC , as it offers high switching speed, lower losses and a wider gap [ 25 ]. Cooling and encasing the input supply circuit are key techniques in maglev systems. The French TGV uses concentrated power cars with the input circuit encased and concentrated under the floor of the locomotive.
The Japanese Shinkansen uses distributed power cars with input circuit components fitted under the locomotive floor. A maglev train carries auxiliary power sources of several kilowatts for powering air-conditioning, lighting, cryogenic cooling and controlling systems [ 25 ]. Maglev systems need a contact-less propulsion mechanism to propel the vehicle body.
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