Magnetic bearing apparatus and a method for operating the same

Electrical generator or motor structure – Dynamoelectric – Rotary

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F16C 3906

Patent

active

061304948

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The invention relates to a magnetic bearing apparatus and to a method for operating the same in accordance with the preamble of claim 19.
It is known from EP 0 612 928A to use active magnetic bearings for the contact-free journalling of rotors. The principle of the active magnetic bearing is based on the attractive force of regulatable electromagnets on a ferromagnetic rotor. In order to determine the position of the rotor in the radial direction, three U-shaped electromagnets are distributedly arranged over the periphery of the rotor. These three magnet pairs form a so-called radial bearing. In a manner similar to a ball bearing, the radial bearing can hold the rotor fixed at one location in a plane (x-y direction). Since a tilting of the rotor must often also be prevented, the latter is preferably held by two radial bearings arranged at different locations.
This known magnetic bearing apparatus has the disadvantage that the electromagnets are designed in the shape of a U. Therefore this bearing apparatus has a larger number of pole changes over its periphery, which causes increased eddy current losses. A further disadvantage of the known bearing apparatus is to be seen in the fact that the electromagnets are specially manufactured and correspondingly expensive; and in that an individual, special power amplifier is required for each U-shaped electromagnet so that a total of three separate direct current controllers are required for the operation of a radial magnetic bearing.


SUMMARY OF THE INVENTION

The object of the present invention is to provide an economically more advantageous magnetic bearing apparatus.
The object is satisfied in particular by a magnetic Maxwell bearing apparatus for a magnetizable body, in particular a rotatable shaft, with the bearing apparatus comprising at least one rotary field machine stator with a two-pole rotary field winding, with the two-pole rotary field winding being of three, phase design, and with the at least one rotary field machine stator forming a stator, and with the bearing apparatus having first means which produce a unipolar flux in the rotary field machine stator. These first means can for example be designed as an axial coil or as a permanent magnet.
In an advantageous embodiment of the invention the magnetic bearing apparatus comprises two rotary field machine stators which are arranged so that they are displaced in an axial direction with respect to the magnetically suspended rotatable shaft so that a stator with two spaced-apart, active magnetic bearing positions is formed in this manner in order to hold the shaft without contact using magnetic forces.
In the present discussion the term rotary field machine stator is understood to denote an arrangement known from the technical field of electrical machinery, namely a stator with electrical windings for the production of a magnetic field, with it being possible to produce a rotary magnetic field through the number and position of the windings in the stator and with appropriate excitation. A two-pole field is understood to mean a two-pole magnetic field extending in the radial direction within the rotary field machine stator as illustrated in FIG. 1b. A two-pole rotary field winding is understood to mean a winding which is designed in such a manner and can be excited in the rotary field machine stator in such a manner that a two-pole rotating magnetic field can be produced in the rotary field machine stator. For the production of a rotary field in a rotary field machine stator, windings with at least two different phases, i.e. with different excitations, are required. In a preferred embodiment the rotary field winding of the rotary field machine stator is of three-phase design, i.e. with three current branches. A two-pole, rotating magnetic field can be produced in a rotary field machine stator, and the rotational frequency can also be zero, so that the two-pole magnetic field stands still or is stationary. The direction of this two-pole stationary magnetic field, which extends

REFERENCES:
patent: 3877761 (1975-04-01), Boden et al.
patent: 4732353 (1988-03-01), Studer
patent: 4794290 (1988-12-01), Nagasaka
patent: 5066879 (1991-11-01), Yamamura
patent: 5111102 (1992-05-01), Meeks
patent: 5703423 (1997-12-01), Fukao et al.

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