Novel Observer Based Force Control for Active Magnetic Bearings

摘要

State of the art active magnetic bearings are con-trolled using a current reference, a current observer or thecurrent as a state variable in a state-space controller. Using thecurrent to express the state of a magnetic bearing has severaldisadvantages such as an unstable zero, hidden information suchas stray flux, eddy currents, magnetization or hysteresis of theiron core material. Above all, it is in a nonlinear relation withboth the generated force and the air gap. In this paper a novel method is presented to directly and linearlycontrol the force of a magnet using a force controller that is basedon a flux estimator. The method is verified with simulationsas well as with measurements. It decouples the magnet andposition controllers, eases the modeling of non-ideal parametersof magnetic bearings, reduces noise, has a larger range ofdisplacement and behaves intrinsically linear.