Advanced Controller of a Hybrid Foil-Magnetic Bearing

A hybrid foil-magnetic bearing (HFMB) is combination of a gas foil bearing (GFB) and a active magnetic bearing (AMB), which takes advantages of both bearings while compensating each other’s weaknesses. It is a solution of friction and wear of the GFBs at low speeds and limited load capacity of the AMBs. Furthermore, load sharing and control of dynamics can be achieved in a hybrid foilmagnetic bearing. However, in order to achieve the ideal performances of the HFMBs, an advanced controller must be designed based on the static and dynamic performances of the HFMBs. Since the AMBs are ‘smart’ devices that the working condition can be measured and actively controlled, it is quite natural to design an advanced controller for the HFMBs to use the AMBs to identify the characteristics of the GFBs and with the function of load sharing between the GFBs and the AMBs. In this paper, a 4-DOF model of bearing-rotor system supported by two HFMBs was established firstly, and then an advanced controller with the function of identification and load sharing was presented. Finally, experiments were done on a test rig whose rotor is supported by two journal HFMBs and a thrust AMB. The test results show that when change the load shared by the GFBs and the AMBs, advanced controller can find the new proper working position of the HFMBs rapidly and smoothly. More importantly, HFMBs with advanced controller based on the identified characteristics of GFBs can work steadily at the speed range of 0~2,2000r/min.