03-05-2011, 09:25 AM
I. INTRODUCTION
ALONG with the increase of population and expansion
in living zones, automobiles and air services cannot
afford mass transit anymore. Accordingly, demands for innovative
means of public transportation have increased. In
order to appropriately serve the public, such a new-generation
transportation system must meet certain requirements such
as rapidity, reliability, and safety. In addition, it should be
convenient, environment-friendly, low maintenance, compact,
light-weight, unattained, and suited to mass-transportation. The
magnetic levitation (Maglev) train is one of the best candidates
to satisfy those requirements. While a conventional train drives
forward by using friction between wheels and rails, the Maglev
train replaces wheels by electromagnets and levitates on the
guideway, producing propulsion force electromechanically
without any contact.
The Maglev train can be reasonably dated from 1934 when
Hermann Kemper of Germany patented it. Over the past few
decades since then, development of the Maglev train went
through the quickening period of the 1960s, the maturity of
the 1970s–1980s, and the test period of the 1990s, finally
accomplishing practical public service in 2003 in Shanghai,
China [1]–[4].
Since the Maglev train looks to be a very promising solution
for the near future, many researchers have developed technologies
such as the modeling and analysis of linear electric
machinery, superconductivity, permanent magnets, and so on
[5]–[25].
The Maglev train offers numerous advantages over the conventional
wheel-on-rail system: 1) elimination of wheel and
track wear providing a consequent reduction in maintenance
costs [26]; 2) distributed weight-load reduces the construction
costs of the guideway; 3) owing to its guideway, a Maglev train
will never be derailed [96]; 4) the absence of wheels removes
much noise and vibration; 5) noncontact system prevents it from
slipping and sliding in operation; 6) achieves higher grades and
curves in a smaller radius; 7) accomplishes acceleration and deceleration
quickly; 8) makes it possible to eliminate gear, coupling,
axles, bearings, and so on; 9) it is less susceptible to weather conditions. However, because there is no contact between
rails and wheels in the Maglev train, the traction motors
must provide not only propulsion but also braking forces
by direct electromagnetic interaction with the rails. Secondly,
the more weight, the more electric power is required to support
the levitation force, and it is not suitable for freight. Thirdly,
owing to the structure of the guideway, switching or branching
off is currently difficult. Fourthly, it cannot be overlooked that
the magnetic field generated from the strong electromagnets for
levitation and propulsion has effects on the passenger compartment.
Without proper magnetic shielding, the magnetic field in
the passenger compartment will reach 0.09 T at floor level and
0.04 T at seat level. Such fields are probably not harmful to
human beings, but they may cause a certain amount of inconvenience.
Shielding for passenger protection can be accomplished
in several ways such as by putting iron between them, using the
Halbach magnet array that has a self-shielding characteristic,
and so on. [27], [79].
Table I shows the comparison of Maglev and wheel-on-rail
systems. In all aspects, Maglev is superior to a conventional
train. Table II represents the comparison of characteristics of the
mass transportation systems provided by the Ministry of Transportation
in Japan. It is appreciable from the tables that the tendency
of global transportation is toward the Maglev train. Accordingly,
it is necessary to be concerned and understand all technologies including magnetic levitation, guidance, propulsion,
power supply, and so on.
II. TECHNOLOGY ASPECTS
State-of-the-art Maglev train technologies are investigated.
Fig. 1 illustrates the difference between the conventional train
and the Maglev train. While the conventional train uses a rotary
motor for propulsion and depends on the rail for guidance and
support, the Maglev train gets propulsion force from a linear
motor and utilizes electromagnets for guidance and support.
A. Levitation
Typically, there are three types of levitation technologies:
1) electromagnetic suspension; 2) electrodynamic suspension;
and 3) hybrid electromagnetic suspension.
1) Electromagnetic Suspension (EMS): The levitation is accomplished
based on the magnetic attraction force between a
guideway and electromagnets as shown in Fig. 2. This methodology
is inherently unstable due to the characteristic of the magnetic
circuit [28]. Therefore, precise air-gap control is indispensable
in order to maintain the uniform air gap. Because EMS
is usually used in small air gaps like 10 mm, as the speed becomes
higher, maintaining control becomes difficult. However,
EMS is easier than EDS technically (which will be mentioned
in Section II) and it is able to levitate by itself in zero or low
speeds (it is impossible with EDS type).
In EMS, there are two types of levitation technologies: 1) the
levitation and guidance integrated type such as Korean UTM
and Japanese HSST and 2) the levitation and guidance separated
type such as German Transrapid. The latter is favorable
for high-speed operation because levitation and guidance do
Fig. 2. Electromagnetic suspension. (a) Levitation and guidance integrated. (b)
Levitation and guidance separated.
Fig. 3. Electrodynamic suspension. (a) Using permanent magnets. (b) Using
superconducting magnets.
not interfere with each other but the number of controllers increases.
The former is favorable for low-cost and low-speed operation
because the number of electromagnets and controllers
is reduced and the guiding force is generated automatically by
the difference of reluctance. The rating of electric power supply
of the integrated type is smaller than that of the separated type,
but as speed increases, the interference between levitation and
guidance increases and it is difficult to control levitation and
guidance simultaneously in the integrated type [29].
In general, EMS technology employs the use of electromagnets
but nowadays, there are several reports concerning EMS
technology using superconductivity, which is usually used for
EDS technology [30]–[33]. Development of the high-temperature
superconductor creates an economical and strong magnetic
field as compared with the conventional electromagnets even
though it has some problems such as with the cooling system.
2) Electrodynamic Suspension (EDS): While EMS uses
attraction force, EDS uses repulsive force for the levitation
[34]–[46]. When the magnets attached on board move forward
on the inducing coils or conducting sheets located on
the guideway, the induced currents flow through the coils or
sheets and generate the magnetic field as shown in Fig. 3. The
repulsive force between this magnetic field and the magnets
levitates the vehicle. EDS is so stable magnetically that it is
unnecessary to control the air gap, which is around 100 mm,
and so is very reliable for the variation of the load. Therefore,
EDS is highly suitable for high-speed operation and freight.
However, this system needs sufficient speed to acquire enough
induced currents for levitation and so, a wheel like a rubber tire
is used below a certain speed (around 100 km/h).
Download full report
http://electricalandelectronicswp-content/uploads/2008/11/01644911.pdf
ALONG with the increase of population and expansion
in living zones, automobiles and air services cannot
afford mass transit anymore. Accordingly, demands for innovative
means of public transportation have increased. In
order to appropriately serve the public, such a new-generation
transportation system must meet certain requirements such
as rapidity, reliability, and safety. In addition, it should be
convenient, environment-friendly, low maintenance, compact,
light-weight, unattained, and suited to mass-transportation. The
magnetic levitation (Maglev) train is one of the best candidates
to satisfy those requirements. While a conventional train drives
forward by using friction between wheels and rails, the Maglev
train replaces wheels by electromagnets and levitates on the
guideway, producing propulsion force electromechanically
without any contact.
The Maglev train can be reasonably dated from 1934 when
Hermann Kemper of Germany patented it. Over the past few
decades since then, development of the Maglev train went
through the quickening period of the 1960s, the maturity of
the 1970s–1980s, and the test period of the 1990s, finally
accomplishing practical public service in 2003 in Shanghai,
China [1]–[4].
Since the Maglev train looks to be a very promising solution
for the near future, many researchers have developed technologies
such as the modeling and analysis of linear electric
machinery, superconductivity, permanent magnets, and so on
[5]–[25].
The Maglev train offers numerous advantages over the conventional
wheel-on-rail system: 1) elimination of wheel and
track wear providing a consequent reduction in maintenance
costs [26]; 2) distributed weight-load reduces the construction
costs of the guideway; 3) owing to its guideway, a Maglev train
will never be derailed [96]; 4) the absence of wheels removes
much noise and vibration; 5) noncontact system prevents it from
slipping and sliding in operation; 6) achieves higher grades and
curves in a smaller radius; 7) accomplishes acceleration and deceleration
quickly; 8) makes it possible to eliminate gear, coupling,
axles, bearings, and so on; 9) it is less susceptible to weather conditions. However, because there is no contact between
rails and wheels in the Maglev train, the traction motors
must provide not only propulsion but also braking forces
by direct electromagnetic interaction with the rails. Secondly,
the more weight, the more electric power is required to support
the levitation force, and it is not suitable for freight. Thirdly,
owing to the structure of the guideway, switching or branching
off is currently difficult. Fourthly, it cannot be overlooked that
the magnetic field generated from the strong electromagnets for
levitation and propulsion has effects on the passenger compartment.
Without proper magnetic shielding, the magnetic field in
the passenger compartment will reach 0.09 T at floor level and
0.04 T at seat level. Such fields are probably not harmful to
human beings, but they may cause a certain amount of inconvenience.
Shielding for passenger protection can be accomplished
in several ways such as by putting iron between them, using the
Halbach magnet array that has a self-shielding characteristic,
and so on. [27], [79].
Table I shows the comparison of Maglev and wheel-on-rail
systems. In all aspects, Maglev is superior to a conventional
train. Table II represents the comparison of characteristics of the
mass transportation systems provided by the Ministry of Transportation
in Japan. It is appreciable from the tables that the tendency
of global transportation is toward the Maglev train. Accordingly,
it is necessary to be concerned and understand all technologies including magnetic levitation, guidance, propulsion,
power supply, and so on.
II. TECHNOLOGY ASPECTS
State-of-the-art Maglev train technologies are investigated.
Fig. 1 illustrates the difference between the conventional train
and the Maglev train. While the conventional train uses a rotary
motor for propulsion and depends on the rail for guidance and
support, the Maglev train gets propulsion force from a linear
motor and utilizes electromagnets for guidance and support.
A. Levitation
Typically, there are three types of levitation technologies:
1) electromagnetic suspension; 2) electrodynamic suspension;
and 3) hybrid electromagnetic suspension.
1) Electromagnetic Suspension (EMS): The levitation is accomplished
based on the magnetic attraction force between a
guideway and electromagnets as shown in Fig. 2. This methodology
is inherently unstable due to the characteristic of the magnetic
circuit [28]. Therefore, precise air-gap control is indispensable
in order to maintain the uniform air gap. Because EMS
is usually used in small air gaps like 10 mm, as the speed becomes
higher, maintaining control becomes difficult. However,
EMS is easier than EDS technically (which will be mentioned
in Section II) and it is able to levitate by itself in zero or low
speeds (it is impossible with EDS type).
In EMS, there are two types of levitation technologies: 1) the
levitation and guidance integrated type such as Korean UTM
and Japanese HSST and 2) the levitation and guidance separated
type such as German Transrapid. The latter is favorable
for high-speed operation because levitation and guidance do
Fig. 2. Electromagnetic suspension. (a) Levitation and guidance integrated. (b)
Levitation and guidance separated.
Fig. 3. Electrodynamic suspension. (a) Using permanent magnets. (b) Using
superconducting magnets.
not interfere with each other but the number of controllers increases.
The former is favorable for low-cost and low-speed operation
because the number of electromagnets and controllers
is reduced and the guiding force is generated automatically by
the difference of reluctance. The rating of electric power supply
of the integrated type is smaller than that of the separated type,
but as speed increases, the interference between levitation and
guidance increases and it is difficult to control levitation and
guidance simultaneously in the integrated type [29].
In general, EMS technology employs the use of electromagnets
but nowadays, there are several reports concerning EMS
technology using superconductivity, which is usually used for
EDS technology [30]–[33]. Development of the high-temperature
superconductor creates an economical and strong magnetic
field as compared with the conventional electromagnets even
though it has some problems such as with the cooling system.
2) Electrodynamic Suspension (EDS): While EMS uses
attraction force, EDS uses repulsive force for the levitation
[34]–[46]. When the magnets attached on board move forward
on the inducing coils or conducting sheets located on
the guideway, the induced currents flow through the coils or
sheets and generate the magnetic field as shown in Fig. 3. The
repulsive force between this magnetic field and the magnets
levitates the vehicle. EDS is so stable magnetically that it is
unnecessary to control the air gap, which is around 100 mm,
and so is very reliable for the variation of the load. Therefore,
EDS is highly suitable for high-speed operation and freight.
However, this system needs sufficient speed to acquire enough
induced currents for levitation and so, a wheel like a rubber tire
is used below a certain speed (around 100 km/h).
Download full report
http://electricalandelectronicswp-content/uploads/2008/11/01644911.pdf