Zero- and Low-Bias Control Designs for Active Magnetic Bearings

Abstract — In this paper we present several nonlinear control designs for a single one-degree-of-freedom (1-DOF) Active Magnetic Bearing (AMB). The primary control objective is to globally asymptotically stabilize the mechanical states of an AMB while reducing the AMB power losses. This suggests operation with zero or low bias flux. We derive a flux-based model for an AMB using a generalized complementary flux condition. This condition is imposed both for zero and low bias operations. A convenient model structure results, in which the zero-bias mode is a special case of the more general low-bias mode of operation. We next derive control laws for low- and zero-bias AMB operation. The control designs borrow ideas from the theory of control Lyapunov functions (clf’s) and passivity. The performance of each proposed control design is evaluated via numerical simulations with a highfidelity AMB model. Implementation issues are also discussed. Index Terms — Magnetic bearings, bias flux, passivity, nonlinear systems