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Actuators 2017, 6(1), 2;

Active Magnetic Bearing Online Levitation Recovery through μ-Synthesis Robust Control

Department of Engineering, Hofstra University, Hempstead, NY 11549, USA
The Center for Rotating Machinery Dynamics and Control, Department of Mechanical Engineering, Cleveland State University, Cleveland, OH 44115, USA
Author to whom correspondence should be addressed.
Academic Editor: Eric H. Maslen
Received: 1 December 2016 / Revised: 30 December 2016 / Accepted: 5 January 2017 / Published: 8 January 2017
(This article belongs to the Special Issue Active Magnetic Bearing Actuators)
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A rotor supported on active magnetic bearings (AMBs) is levitated inside an air gap by electromagnets controlled in feedback. In the event of momentary loss of levitation due to an acute exogenous disturbance or external fault, reestablishing levitation may be prevented by unbalanced forces, contact forces, and the rotor’s dynamics. A novel robust control strategy is proposed for ensuring levitation recovery. The proposed strategy utilizes model-based μ-synthesis to find the requisite AMB control law with unique provisions to account for the contact forces and to prevent control effort saturation at the large deflections that occur during levitation failure. The proposed strategy is demonstrated experimentally with an AMB test rig. First, rotor drop tests are performed to tune a simple touchdown-bearing model. That model is then used to identify a performance weight, which bounds the contact forces during controller synthesis. Then, levitation recovery trials are conducted at 1000 and 2000 RPM, in which current to the AMB coils is momentarily stopped, representing an external fault. The motor is allowed to drive the rotor on the touchdown bearings until coil current is restored. For both cases, the proposed control strategy shows a marked improvement in relevitation transients. View Full-Text
Keywords: AMB; levitation; recovery; robust control; touchdown bearing AMB; levitation; recovery; robust control; touchdown bearing

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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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Pesch, A.H.; Sawicki, J.T. Active Magnetic Bearing Online Levitation Recovery through μ-Synthesis Robust Control. Actuators 2017, 6, 2.

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