Nathan Black
L01/Kenny
Team MagLev
MagLev Propulsion Systems
Since high speed transportation patents were granted to various inventors in the 1970s,
there are seven working magnetically-levitating (Maglev) trains in operation, three under
construction, and dozens of proposed projects [1]. The state-of-the-art propulsion technology in
Maglev trains involves a linear motor, which is an electric motor that produces motion in a
straight line as opposed to rotational motion. Linear motors are currently being used in a wide
variety of applications including Maglev train tracks, armor-piercing weapons, crane arms, and
amusement park roller coasters. Research is being done by the U.S. Navy regarding using linear
motors to propel aircraft for takeoff from aircraft carriers [2].
Linear Motors for Maglev Use
The main use of linear motors is Maglev propulsion systems. There are two types of
linear motors used in current Maglev trains. The Linear Induction Motor (LIM) is used primarily
in Japan, and the Linear Synchronous Motor (LSM) is used primarily in Germany [3]. Propulsion
in a LIM is caused by induced voltages across four individual linear motors that combine to
produce a massive repulsive force that pushes the train car forward. A LSM creates propulsion
by alternating magnetic poles on either side of the track such that the front of the train car is
being pulled forward while the rear is pushed forward [4]. The speeds for LIMs are determined
by “the ratio of length of the vehicle magnet system to the length of the energized block, the sum
of the coupling coefficients between vehicled magnets and the guideway coils, applied voltage,
and the current flowing in the coils [4].” In the LSM case, the train’s speed is limited by the
frequency of the alternating current.
A linear motor can either be placed on the train or in the track to achieve propulsion. A
big disadvantage of carrying the motor on the train is that not only would an on-board power
supply be necessary, but both the motor and power supply will add more weight to the train. The
driving power is much more flexible with the motor in the track. For example, in sections of the
track where acceleration is heavy, more robust wiring can be installed compared to sections
where the train is likely to be simply maintaining a constant speed [5]. For these reasons, most
operating Maglev trains use a linear motor in the tracks. For example, the Transrapid in
Germany, the Shanghai Maglev in China and the current world’s fastest train, the JR-Maglev
(361 mph top speed) in Japan all use linear motors in the track.
A linear motor in the track operates the same as a DC motor, but with the stator unraveled
and stretched the length of the track. By altering the frequency and intensity of the current, speed
and thrust can be adjusted accordingly [6]. The direction of energy flow can be reversed (motor
operating as a generator) and contactless, magnetically-powered braking can be achieved.
Energy can also be saved using a linear motor in the track because only the section of track that
the train is on needs to be powered. This also eliminates the potential for two trains colliding
because only one can operate per track.
References
[1] U.S. Patent 3,736,880 , January 21, 1972. Page 10 Column 1 Line 15 to Page 10 Column
2 Line 25.
[2] Wikipedia, “Linear Motor,” [Online document] Available:
http://en.wikipedia.org/wiki/Linear_motor
[3] Luu, T, Nguyen, D. “MagLev: The Train of the Future,” Fifth Annual Freshman
Conference, Tesla Society, Paper # 270, April 9, 2005.
[4] He, J. L., Coffey, H. T., Rote, D.M. "Analysis of the Combined MagLev Levitation,
Propulsion, and Guidance System", IEEE Transactions on Magnetics, Vol 31, No. # 2,
March 1995, pp 981-987.
[5] “Transrapid Maglev Train,” Gizmo Highway, [Online] Available:
http://www.gizmohighway.com/transport/maglev_train.htm
[6] Vranich, J. “Supertrains: Solutions to America's Transportation Gridlock,” New York: St
Martin's, 1991.