Stability analysis of self-sensing magnetic bearing controllers

The controllers designed for position-sensorless voltage-controlled active magnetic bearings (AMBs) are investigated from the viewpoint of strong stabilization. First, magnetic bearings with laminated iron cores are treated in which the effects of eddy currents are negligible. It is shown that full- and reduced-order observer-based stabilizing controllers differ in stability; any reduced-order observer-based stabilizing controller is always unstable while most of the full-order observer-based stabilizing controllers are stable. Second, self-sensing suspension in magnetic bearings with solid iron cores is discussed. It is shown that the full-order observer-based stabilizing controller is destabilized by a modification including the effects of eddy currents flowing through the cores. It accounts for the difficulty of actual self-sensing suspension in solid-cored magnetic bearings.