| Common structure and components of attractive type, radial active magnetic bearings (AMB) were identified. Mathematical modelling and control analyses have been performed with clear separation of stiffness and damping. Eight essential parameters governing the AMB load capacity, stiffness and damping have also been identified. A 3-step AMB sizing method using non-dimensional formulation is proposed for design use.; Furthermore, special circuit elements, namely, velocity observer and acceleration observer were formulated and analyzed for AMB control. The velocity observer estimates the AMB journal velocity based on the measured journal displacement without performing differentiation and thus it is noise free. The feedback control using the estimated velocity provides the AMB damping. The acceleration observer estimates the journal acceleration from the same displacement measurement. The feedback control using the estimated acceleration creates a rotating force which cancels the imbalance force and other external disturbances.; A test rig with an AMB was designed according to the proposed design method. The velocity and acceleration observers were implemented in the control circuit. The test data correlates well with the analyses. The AMB stiffness and damping are adjustable, each by a separate potentiometer in the circuit. The acceleration observer was built into a feedback loop with an on-line/off-line switch. When it is on-line continuously, it totally suppesses the synchronous responses during start-up or coast-down transients. It can be switched on or off in the designed speed range without causing rotor instability. This additional vibration suppression mechanism greatly enhances the versatility of AMB. |
