Abstract: In a high speed motor system supported by active magnetic bearings, the influence of permanent magnets in the motor rotor and the residual unbalance in the rotor is obvious. The active magnetic bearings have to work in nonlinearity and high speed running is hard to be achieved. To deal with the marked nonlinearity in the active magnetic bearing system, an exact linearization method is used to linearize the magnetic forces of the active magnetic bearings. Meanwhile, controller designs are improved. A gain schedule method is used to make the rotor running stable across its rigid critical speed. Through adding a zero-pole pair to a PD controller, the gain of the controller in the frequency domain near the running frequency of the rotor is effectively decreased and the rotor runs almost about its mass center. Then the saturation of the magnetic forces in the active magnetic bearings is avoided and stable running of the motor system at high rotation speeds is achieved with high nonlinearity in the active magnetic bearings.

Key words: Nonlinearity, Active magnetic bearing, High speed motor