Experimental validation of a current-controlled three-pole magnetic rotor-bearing system

We report on an experimental study of a three-pole active magnetic bearing (AMB) system. Two cases (with and without a motor) are investigated. For the system without a motor, we designed and implemented three controllers: a linear state feedback controller (LC), feedback linearization with a linear state feedback controller (FLLC); and feedback linearization with an integral sliding mode controller (ISMC). We found that both LC and FLLC will result in a limit cycle at the steady state, and ISMC yields the best transient and steady-state performance. We also implemented ISMC for the system with a motor. We found that when the rotor speed is zero, the system performance is as good as that of the system without a motor, which shows that the ISMC controller is robust. When the rotor is spinning, a steady-state limit cycle exists. The size of the limit cycle increases with the rotor speed. We discuss the effects that cause the limit cycle and suggest ways to improve the results. The results clearly indicate that the three-pole AMB is indeed feasible. However, delicate calibration and a robust nonlinear controller are necessary to yield good performance.