Robust sliding mode control for axial AMB systems

Axial motion of a rotor in AMB (active magnetic bearing) systems is modeled and controlled by the sliding mode control law. A prefilter is embedded to provide the integral action so that the steady state error of position regulation can be eliminated. Computer and experimental simulation are both reported to verify the validity of the hybrid design of the SMC (sliding mode controller) cascaded with the prefilter. A test rig of unbalanced beam is implemented to be appropriately real-time controlled, exhibiting satisfied performance and robustness with respect to the system parameter uncertainties. The magnetic force is generated by a DSP-based digital microprocessor. In comparison, a counter example of conventional PI (proportional and integral) controller that is mostly employed in axial rotor motion, is presented to illustrate potential instability.