Study On Related Theories And Design Method Of Large Air-Gap Hybrid Magnetic Bearings

Magnetic bearing technology uses controllable electromagnetic force to levitate the object, realizing no mechanical contact between the object and the basis. Thereby it has many advantages, such as no mechanical friction, no wear, no lubrication, low power consumption and high speed. Meanwhile its supporting characteristics (stiffness and damping) can be adjusted online by changing control parameters, which can enhance the system stability. Therefore, magnetic bearing technology is known as a revolution of supporting technology. Hybrid magnetic bearing is a kind of magnetic bearing system which formed by combining electromagnetic bearings and permanent magnetic bearings. It takes into account the advantages of both electromagnetic bearings and permanent magnetic bearing. So it has been widely studied at present. However, in the applications such as wind turbines and artificial heart pump, the working air-gap of hybrid magnetic bearing is large, which causes basic assumption in the conventional magnetic bearing design theory such as uniform magnetic field, no magnetic flux leakage are no longer correct. Therefore, a new design theory and method need to be developed.In this paper, a typical kind of hybrid magnetic bearing has been discussed, and the structures of hybrid magnetic bearings with different air-gap have been designed by using conventional equivalent magnetic circuit method. The bearing capacity models of those hybrid magnetic bearings have been built, and the bearing forces have been analyzed by ANSYS. By comparing the calculation results of traditional equivalent magnetic circuit method and ANSYS, it shows that the conventional equivalent magnetic circuit method cannot meet the requirement of structural design and bearing capacity analysis of large air-gap hybrid magnetic bearings.The characteristics and variation rules of equivalent magnetic circuit method model calculation error in large air-gap hybrid magnetic bearings are studied. What’s more, impact factors which caused equivalent magnetic circuit method calculation error and impact rules of each factor on the error are studied.For the main factor, magnetic flux leakage that causes errors of conventional magnetic circuit method, leakage coefficients are introduced to describe magnetic flux leakage. Furthermore, the magnetic circuit model of large air-gap hybrid magnetic bearings based on leakage coefficients is estabilished. The changing laws between air-gap magnetic flux leakage and structural parameters are studied. The description method of leakage coefficients is presented and application range of this description method is studied. Based on the description method, large air-gap hybrid magnetic bearings are demarcated from conventional air-gap ones.An air-gap magnetic flux leakage model based on leakage permeance has been built by using a combination method of magnetic field and an equivalent magnetic circuit bearing capacity model of hybrid magnetic bearings based on magnetic flux leakage has been built. On this basis, the application range of this model is studied and the results show that this model can satisfy the majority of practical engineering hybrid magnetic bearing capacity analysis needs. Then, a single degree of freedom hybrid magnetic experimental device is designed and manufactured. And the model is validated by utilizing that device.Finally, the main reason that conventional equivalent magnetic circuit method can not be used for structure design of large air-gap hybrid magnetic bearings is analyzed. Furthermore, the structure design method of large air-gap hybrid magnetic bearings based on leakage coefficient correction model and leakage permeance correction model is proposed. And the structural of large air-gap hybrid magnetic bearings is designed by using improved magnetic circuit method.