MIMO PID Control of Rotors with Electromagnetic Bearings

Rotors with electromagnetic bearings are inherently unstable systems; hence feedback control is an integral part of their operation. While the rotor dynamics is linear and time-invariant at constant operation speed, electromagnetic bearing model is non-linear. Non-linear bearing dynamics can be linearized at an operating point using a constant bias current. In this paper we design a MIMO PID controller for horizontal rotor/active magnetic bearing systems and compare its performance with respect to SISO decentralized PID control. Dynamic coupling in rotor dynamics causes gyroscopic forces to act at orthogonal directions on the rotor. SISO PID control lacks sufficient performance as it has limited capability to compensate for the gyroscopic effects due to angular motions in transverse directions which can be caused by couple (dynamic) unbalance forces