Experimental comparison of nonlinear tracking controllers for active magnetic bearings

This paper presents an experimental comparison of position tracking controllers for an active magnetic bearing system. Two nonlinear designs are presented, each based on a different actuating constraint. The first design uses the constant current sum (CCS) biasing condition, and the second uses the current almost complementary (CAC) switching condition. While both designs achieve accurate tracking for a non-rotating shaft, a comparison of unbalance responses shows that the CCS-based design is more robust to disturbances for a given voltage saturation level. The nonlinear designs are compared to an industry standard decentralized PID controller. Experimental results are obtained using a commercially available five degree-of-freedom test stand.