Asymptotically exact linearizations for active magnetic bearing actuators in voltage control configuration

We consider the exact linearization of a standard, single-axis, active magnetic bearing actuator in voltage control configuration. The actuator is modeled using the magnetic circuit law, with edge effect, flux leakage, and permeability nonlinearity omitted. Exact linearization of such a plant has been studied by other authors using the systematic Lie-algebra-based approach. In this paper, we present linearizations that turn out to be not obtainable by the systematic approach. Three such linearizations are given. They are asymptotically exact and more simple than the existing linearizations. In addition to position signal, they use flux feedback, current feedback, and observer-based feedback, respectively. Their performances are investigated and compared by experiment. While they are observed to be not so exact (due to modeling errors), they do significantly improve the linearity and closed-loop stability robustness. Then, one of them is revised by taking account of edge effect and flux leakage, which gives very satisfactory results. Finally, effects of variation in coil copper resistance are investigated.