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Modelling and Simulation in Engineering
Volume 2011, Article ID 414286, 10 pages
Research Article

Performances Comparison for a Rotating Shaft Suspended by 4-Axis Radial Active Magnetic Bearings via πœ‡ -Synthesis, Loop-Shaping Design, and Sub ( 𝐻 ) ∞ with Uncertainties

Dipartimento di Ingegneria Chimica, Gestionale, Informatica e Meccanica, Universita' di Palermo, Viale delle Scienze, 90128 Palermo, Italy

Received 3 March 2011; Revised 8 April 2011; Accepted 9 May 2011

Academic Editor: Jing-song Hong

Copyright © 2011 G. Barbaraci and G. Virzi' Mariotti. 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.


The control systems applied on active magnetic bearing are several. A perfect levitation is characterized by maintaining the operating point condition that is characterized by the center of stator coincident with the geometric center of shaft. The first controller implemented for this purpose is PID controller that is characterized by an algorithm that leads the amplifier to produce control current until the operating point condition is not reached, this is obtained by an integration operator. The effect of an integrator is essential but not necessary for a centered levitation for example in the robust control characterized by a dynamic model depended on plant of system so that it depends on angular speed as LQR controller does. In LQR there is not integrator so there is not a perfectly centered section of shaft with center of stator. On contrary PID controller does not depend on angular speed and it can be easily implemented according some simple rules. Predictive control is another interesting controller characterized by a multiple controller operating in different condition in order to get the minimum of cost function, but also in this case the angular speed is introduce for the same reason discussed before.