Active Magnetic Bearing
The active magnetic bearing (AMB) is one of the most advanced and promising types of rotor supports. This is an environmentally friendly type of support, and it operates only on electricity. On the one side, AMB controller expands the possibilities of dynamic characteristics control, diagnostics and tuning both of the bearing and the supported rotor. On the other side, it requires much higher design and labour costs.
An AMB must hold the rotor in a reference position at various loads. Also it must limit the necessary levels of the rotor vibration and stability. Also it must providethe levels of rotor vibration and stability. In machines with rigid and flexible rotors the AMP controller differ significantly. Therefore it is necessary to use digital models, algorithms and software tools for the сontroller and magnetic actuator design and the whole system analysis.
Requirements for the Design of the Machines with AMB
Nowadays there are certain requirements for the design of machines with active magnetic bearing specified in the following standards:
Mechanical vibration — Vibration of rotating machinery equipped with active magnetic bearings
ISO 14839-1-2018 Part 1: Vocabulary
ISO 14839-2-2004 Part 2: Evaluation of vibration
ISO 14839-3-2006 Part 3: Evaluation of stability margin
14839-4-2012 Part 4: Technical guidance
The DYNAMICS R4 allows solution of the following design problems:
- Development of a flexible rotor model as an controller object;
- Analysis of the rotor system with AMB;
- Analysis of the rotor fall down to the safety bearings.
Development of a Flexible Rotor Model as an controller Object
An AMB controler significantly influences and determines the overall machine vibration state. For other types of support the problem of the “rotor-bearings” rotor system is solved, but design of a machine with AMB requires an analysis of the controller dynamic parameters and features. For its design and adjustment the special software is used where iteraction of all parts of the “rotor-controller-electromagnets” system is simulated.
Operation near the rotor natural frequencies is a key problem in development of a rotor on AMB. The system must provide supports damping at the oscillation modes that combine both movement in the support and the rotor bending. In controllerdevelopment it is necessary to take into account information about the flexible rotor as a control object. DYNAMICS R4 allows calculation of the frequencies and coefficients of the oscillation forms in all necessary points of the rotor and creates the rotor model as the controller object This model allows tuning the support flexibility taking into account the rotor and AMB inertial parameters, provides the information on natural oscillations frequencies and modes for the controller development.
Rotor System with AMB Analysis
DYNAMICS R4 allows investigation of the entire rotor system behavior. The parameters of stiffness and damping of the rotor model are input into the model. This opens the possibility to carry out a set of calculations according to the standards, critical speeds and maps of critical frequencies.
A Map of Critical Rotor Speeds on AMB with frequency adjustment. When Adjusting the Stiffness of AMB by Modes
Analysis of Rotor Drop down to Safety Bearings
A safety bearing is a necessary element of the active magnetic bearing machine. It protects the rotor from contact with the stator when the AMB is turned off or in the case of its failure. Our company research has shown that rolling bearings are the best choice for safety bearings. They protect the compressor from the possible exit of the rotor to the reverse precession movement in the case of AMB failure. That is why the safety bearingы are used in the AMB rotor systems. However, clearances in rolling bearings can reduce the resonant mode corresponding to the first flexural mode of oscillation, and transition through the rotor runout can be accompanied by high vibrations. DYNAMICS R4 has all necessary nonlinear models (models of radial and angular contact rolling bearings, a model of rotor-stator contact and dry friction bearings) and analysis tools for studying the rotor dynamics at falling on auxiliary bearings, both on rolling bearings and dry friction bearings.