Abstract: An experimental setup of five degree-of-freedom active magnetic bearing (AMB) rotor system is built up. The modes of bias current and zero bias current are presented. Dynamic characteristics of the system with zero bias current are investigated by stamping modal test, method of model updating based on frequency response function (FRF) and actual operation of the system, and compared with the results of the system with bias current. The results show that, for the system with zero bias current, the stability region of control parameters, modal damping and stiffness and damping of AMB are reduced obviously and its vibration amplitudes in motion on the critical speeds are larger than the system with bias current, however it can still get across the first bending critical speed safely. If the design of the system is proper, the mode of zero bias current can be adopted in actual application, especially in the application of low rotation speed and stable load, so that the system has better over-all properties.

Key words: Active magnetic bearing, Bearing damping, Bearing stiffness, Modal parameter, Zero bias current