Compensation of nonlinearities in active magnetic bearings with variable force bias for zero- and reduced-bias operation

Compensation of the active magnetic bearing actuator nonlinearities for a variable force bias control is demonstrated. Instead of the classical premagnetization current, a force bias is applied. In the proposed novel compensation method, the magnetic force bias is produced by an on-line tunable set bias current, which may be adjusted by some upper control scheme. The compensation of the nonlinearities for the zero- and reduced-bias operation is implemented as a part of the inner current control loop. In the outer position control loop, an optimal stabilizing controller is employed. With a controller applying the compensation of nonlinearities and the zero-bias current, it is possible to achieve a dynamic performance comparable with that of a controller with the classical bias current. Stable operation under step position references and external impulse disturbance forces with the zero force bias is shown. Additionally, the initial lift up of the rotor with the zero force bias is presented and the robust stability of the compensated controller is verified using sensitivity functions.