Performances Comparison for a Rotating Shaft Suspended byud4-Axis Radial ActiveMagnetic Bearings via μ-Synthesis,udLoop-Shaping Design, and Sub(H)∞with Uncertainties

摘要

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