Resonance Reduction of Flexible Rotor with Hybrid Active Magnetic Bearings at Both Ends of the Shaft

This paper presents a hybrid active magnetic bearing (HAMB) system that uses both electromagnetic and permanent magnetic forces to support a flexible rotor. Unlike conventional active magnetic bearings, which require a bias current to generate bearing force, the proposed HAMB generates a bias magnetic flux using permanent magnets. This eliminates the need for a bias current and enabling reduced power consumption. The HAMB developed in this study exhibits negative stiffness in both the radial and tilt directions. Two HAMBs are installed at the ends of a horizontal flexible rotor to achieve magnetic levitation. To control levitation, a PD controller and an optimal controller based on the Linear Quadratic Regulator (LQR) method are employed. The LQR controller optimizes system performance while ensuring robustness against disturbances such as gravity-induced deflection and unbalanced forces during high-speed rotation. Sinusoidal disturbances were applied to the HAMB system, and the frequency responses in terms of rotor displacement and tilt were measured to model the resonance behavior of the elastic modes. Next, a motor was connected to one end of the rotor, and rotation tests were conducted. The results confirmed that the proposed LQR control allows stable passage through the critical speed associated with the first elastic mode. These two experiments demonstrate the effectiveness of the proposed control method in suppressing the resonance of the elastic modes.