Exact linearization of a voltage-controlled 3-pole active magnetic bearing system

Most magnetic radial bearings adopt the configuration of eight magnetic poles. Such a configuration usually requires four power amplifiers and has high power loss, resulting in high cost. In this study, a 3-pole active magnetic bearing (AMB) is investigated, which requires only two power amplifiers. In addition, it has lower power loss. Thus, the overall cost can be reduced. However, the 3-pole AMB system is strongly nonlinear due to magnetic flux coupling. If the actuator dynamics are also considered, the overall system will be much more complicated. Nonlinear control is thus necessary. By taking magnetic fluxes as part of the system states, the state equations of the voltage-controlled 3-pole AMB system admit a quadratic nonlinear form. It is shown that this quadratic nonlinear system is feedback linearizable. An admissible domain for the initial states such that the resulting system responses will not hit the bearing boundary (or back-up bearing, if exists) is also obtained via a Lyapunov analysis. Numerical simulations are carried out to verify the theoretical results.