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SECTION III-A
MAGNETODYNAMIC SUSPENSION ( MDS)
The MDS implements the idea of self-regulating magnetic suspension (see above) by employing non-linearity of saturated steel. The MDS consists of four identical interconnected magnetic units (Fig.1). Each unit consists of two parts movable (located on the vehicle) and stationary (extended along the track), (Fig.2). The movable part contains four long permanent magnets with rectangular cross-section and assembled into a quadrupole with the help of a steel insert. The stationary part consists of two laminated steel cores of unlimited length with "C"-shaped cross-section. Each core has a long back covered by aluminum layer and two thickened unsaturated tips. The cores are located mirror-symmetrically to each other and extend along the whole length of the guideway. There is a constant air gap between the thickened tips pertained to the right- and left-hand cores. The quadrupole is inserted in this air gap and can move freely within it in all directions.
The lateral shift of the quadrupole from its symmetrical position (equilibrium) results in a destabilizing force that attracts it to the nearest core tip. This force is proportional to the difference of magnetic fluxes coming into left-side and right-side core tips. The vertical shift of the quadrupole results in a stabilizing force bringing it back to equilibrium. Necessary and sufficient condition for magnetic suspension to be stable is that with the same size of both shifts of the quadrupole stiffness of stabilizing force exceeds stiffness of destabilizing force in each unit. In the MDS this condition is attained by maintaining certain level of saturation in a part of the core backs passed by a quadrupole during vehicle’s motion.
The unit forms two-contour magnetic circuit with the sources of mmf (permanent magnets) and magnetic reluctances both linear (a distance between a steel insert and core tips) and non-linear (saturated steel core backs). The non-linear reluctance in the magnetic circuit reduces dependence of the magnetic flux in the steel cores on the lateral shifts of the quadrupole. To maintain a needed level of saturation (reduction of a leakage flux) in the core back the latter is covered by an aluminum layer which performs function of electro-magnetic barrier for the leakage flux during the vehicle motion [3].
Fig.3 shows graphs of stabilizing force Fs and its stiffness F¢s and also destabilizing Fd, produced by the shift d of the MDS levitator according the calculations made in [5]. A cross-section of the unit (in scale) is shown in Fig.2. Superscripts “o” and “s” mean forces in the levitator at unsaturated (when its speed V=0) and saturated (when its speed > 100m/s) core backs respectively. The curves P and Po are the traces of paraboloids of magnetic potential energy on the cross-sectional plane (P, d). Stabilizing force FsE and its stiffness F¢sE for EDS are shown in the same scale for comparison.
