Research On Redundant Design Of Weak Coupling Radial Magnetic Bearing

With no mechanical friction inside, magnetic bearings have a lifespan whichcan be really long theoretically and a relatively higher reliability. But it is still notenough for the magnetic bearings applied in hi-tech equipment with a higherreliability requirement. So it has become a hot research point that how to improvethe reliability of magnetic bearing one step further.Redundant design of magnetic bearing is an effective way to improve thereliability and in this paper, the redundant design of radial magnetic bearing isresearched in detail. Firstly, a redundant design scheme for weak coupling radialmagnetic bearing is put forward as well as two failure styles when combined withthe features of radial magnetic bearing in this kind. Based on the idea of forcebalance, compensation strategies are then proposed for the two failure styles aboveand they are researched on a weak coupling radial magnetic bearing with6magneticpole pairs as an example when the rotor is at both the equilibrium position and theposition with a maximum displacement. The result indicates that a full compensationcan be achieved during both failure styles through force balance compensation whenpremised on certain surplus capacity of both current and saturation in magnetic coreiron.The expression of additional bending moment caused by the axial magneticbearing under unbalanced failures is deduced and then its influence on the weakcoupling radial magnetic bearing is analyzed.Combined with the redundant design requirement of magnetic bearings, amagnetic suspension device with redundant scheme is designed and the illustrationsof redundant styles for radial magnetic bearing, axial magnetic bearing anddisplacement sensor are given with a stress on the key points of the redundant designfor weak coupling radial magnetic bearing.To experimentally verify the plausibility of the proposed control strategy forredundant reconfiguration based on the idea of force balance, the weak couplingradial magnetic bearing with6magnetic pole pairs is simplified to only onemagnetic pole pair. Then experiments are carried out on it including the rotorproperty research of the rising process and reconstruction process under certain coilfailures. The experiment draws a conclusion that the armature can be stably sus-pended with any coil in failure using the idea of force balance compensation, whichwill lead to a successful transfer in operative mode of the system from normal tofault-tolerant. Moreover, the system keeps a good suspension property at last.