Study On Design And Control System Of A BLDC Motor With Passive Magnetic Bearings

Magnetic bearings, having the merits of non-contact, without lubricant system, lack of mechanical wearing, and low level of noise respecting to conventional mechanical bearings, are attracting more and more interests in the high speed rotating machines and some special fields. Active magnetic bearings and the bearingless motor can realize stable magnetic suspension. But the two main advantages- high level of load capacity and controllable suspension of them are some kind being counteracted by the disadvantages of complicated control system reliability of system, low level of reliability and high costs along with the using of numerous of devices and thereby limited their application. The bearing system that can achieve stable suspension with a simple structure is very attractive.Passive permanent magnet bearing is one kind of magnetic bearing using permanent magnet providing the magnetic suspension force. With the advantages of simple structure and control system, high reliability, no friction, low level of energy consumption, it is widely used in many fields. It is well known that passive magnetic bearing can't realize the stable suspension in all degrees of freedom. But with the introducing of the compensation in one freedom, stable suspension can be easily achieved.hi this paper, a brand new type of radial bearings and its application in a BLDC motor is introduced. The radial bearings' mechanical characteristics and stability is fully probed using the infinite elements method and has been tested by some experiments. And the axial self-alignment of the stator and rotor of each motor that is in favor of the stability of radial bearings is discussed. Then a special BLDC motor using this kind of radial bearings, having a simply ML4425 control system, is design and tested. The results show that the magnetic suspension is achieved and the motor meets the demands expected.