68 Ë 3 Magnetic levitation
the normal conductive EDS scheme. In the initial development, Germany adopted two
schemes, EDS and EMS, simultaneously, later abandoning the first, but continuing
to develop EMS. At the beginning of development, Japan also adopted two sche-
mes simultaneously, high-speed EDS with superconducting magnets and low-speed
EMS with normal conductive magnets, and adhered to the two project development
thereafter.
Magnetic levitation has many types, for example, permanent magnet (PM), nor-
mal conductive coil magnet, LTS coil magnet, HTS coil magnet, and HTS bulk material
Maglev, etc. These Maglev types can be differentiated into EMS and EDS Maglev. Thus
far, the normal conductive coil Maglev only has an EMS version, because the magnetic
field of a normal conductive magnet is much lower.
The development and application of Maglev in bearing and ground transportation
(sometimes called a linear bearing) areas have made good progress [38, 52]. and it is
likely to become the most promising means of transport of the 21st century [14, 53].
The flywheel energy storage device with a HTS Maglev bearing is probably the most
competitive energy storage system for the 21st century.
3.6 Permanent magnet Maglev
The levitation technology based on attractive forces of magnets is a PM suspension
(PMS) which has favorable effects in respect to energy consumption in comparison to
the electromagnetic suspension (EMS). PMS and EMS both have a lift-to-weight ratio
of about 7:1. At maximum speed, the PMS control requires only 50 W/Mg with a gap
of 20 mm as compared to more than 1 kW/Mg for EMS with a gap of 10 mm [54], i.e.
the power consumption for suspension unit weight in the PMS with a gap of 20 mm
is 1/20th of that in the EMS with a gap of 10 mm under high-speed condition. Many
schemes for levitating vehicles with PMs, usually combined with propulsion by a
linear electric motor, have been proposed in the past few years. Ferrite, alnico, and
rare-earth PMs can be used in magnetically supported and propelled Maglev transport
systems [55, 56].
Although the suspension vehicle using PM were started in the early 1960s, sub-
stantial researches were conducted after the advent of Rare-earth permanent magnets
(RePM) in the 1970s and especially with neodymium-iron-boron (NdFeB) magnets in
the mid-1980s [57]. In the middle of 1970s, tests with the PM Maglev system were
commenced [58]. A dozen years ago, the magnetic energy product from NdFeB PM
has reached 55 MGOe [59]. Thus far, the magnetic energy product of batch produced
NdFeB PM (N52) in China is about 400 kJ/m^3 (50.3 MGOe), clearly suitable for Maglev
application [31]. In contrast, the thermal and chemical stability of cobalt-samarium
(Sm-Co) is better than NdFeB. However, NdFeB is cheaper. PMs in the vehicle un-
dercarriage serve a dual function, as part of the levitation and of the propulsion
systems.