Unbalance Compensation for a 5-DOF Magnetic Rotor-Bearing System

The objective of this study is to design an unbalance force rejection controller by using the decoupling control law as a levitation controller. The system under study is a 5-DOF rotor magnetic bearing system. It is equipped with two sets of heteropolar radial active magnetic bearings and one axial active magnetic bearing. In this study, an unbalance force rejection control (UFRC) structure is proposed, which is inspired by the coordinate transformation of the decoupling control. By combining the proposed UFRC controller with decoupling control, the system can be divided into two independent parts, parallel mode and conical mode. That is, the system has been decoupled. By decoupling the system, the design and analysis of the UFRC controller can be more intuitive and easier. In addition, the advantage of decoupling control is maintained. The design method and stability analysis are given in the paper. After adding UFRC controller to the control loop, the stability becomes speed dependent. Thus, the UFRC controller parameter varies for different speed range. At the end of this paper, the performance of the proposed concept is verified by numerical simulation. In summary, the proposed method works and makes the rotor turn around its center of mass so that the imbalance force is rejected. Although only the static unbalance is considered in this study, the same concept can be extended to the case where both the static unbalance and the dynamic unbalance are present.