Experimental Analysis and Modification of the Rotor System with Passive and Active Magnetic Bearings to Improve its Dynamic Characteristics

The paper discusses a laboratory operating model of a rotor in full magnetic suspension. It is considered as a prototype for small and medium-sized energy machines. The suspension is implemented using two radial passive magnetic bearings made of ring permanent magnets and one axial active magnetic bearing with double-sided stator armored cores of power electromagnets and a control system to create the necessary stabilizing forces depending on the current state (rotor position, and, as an option, rotor speed, as well as currents in the windings). To measure and analyze the dynamic characteristics of this rotor system, a developed specialized software and hardware complex is used. The use of this complex made it possible to determine the vibration amplitudes of the rotor support sections and the trajectories of their motion at various rotational speeds in the range from 0 to 3000 rpm. The results are presented in the form of three-dimensional spectrograms and amplitude-frequency characteristics for each degree of freedom of the rigid rotor, namely the radial displacements of the centers of two radial support sections of the rotor in two orthogonal directions (horizontal and vertical) and the center of the axial support section in the axial direction. The analysis of these data allowed identifying and generalizing the linear and nonlinear phenomena of rotor dynamics in the considered system with passive and active magnetic bearings. This gives an idea of the possible critical modes in systems of this type, and ways to suppress them to avoid resonances in the operating speed ranges or reduce the amplitudes of resonant vibrations. For the laboratory rig, a design modification option was proposed, which made it possible to improve the dynamic characteristics with a decrease in the range of nonlinear vibrations when the rotor moves in the form of cylindrical and conical precession.