A high-efficiency magnetic suspension actuator with reluctance-balanced permanent magnet biasing and flux-based control✩

To reduce power consumption of active magnetic bearings (AMBs), permanent magnets (PMs) may be employed to generate a bias flux through the magnetic circuits connecting the actuators with the rotor. In this way, control algorithms based on zero-current operating points and linearized models may be used. This paper describes a new modular design of PM-biased AMB actuator involving a balanced-reluctance topology where the bias flux is set by an auxiliary air gap within the magnetic circuit. A theoretical model and design methodology for achieving a specified range of actuation forces are also defined. Each actuator unit within an AMB suspension system may by positioned freely and operated independently because, unlike many previous PM-biased designs, there is no flux linkage between actuators. To improve the robustness of the actuator control to uncertainty in material properties and air gap sizes, a feedback control scheme is proposed based on inductive sensing of the mean flux density at the actuator pole faces. Testing of the actuator with a current -cancelling flux-based control scheme shows that stable suspension with very low power consumption can be achieved over a range of operating conditions involving both static loading and unbalance excitation.