The experiment setup of five degree-of-freedom active magnetic bearing (AMB) system was built up. The working principle of variable bias current control was presented. H∞ control strategy was adopted for the digital controller design. Weight functions were selected according to the vibration amplitudes of the rotor operating at the natural frequency of the system. The signal of the rotation speed was introduced into the digital controller. The dynamic performance of the system with variable bias current was investigated

and also compared with the result of the system with fixed bias current. The results show the variable bias current control will not deteriorate dynamic performance of the system and it reduces the total currents of AMBs more than 25%.