Modeling and control of a new horizontal-shaft hybrid-type magnetic bearing

This paper reports on the development of a new horizontal-shaft hybrid-type magnetic bearing system. The bearing system will be used for a horizontal- shaft machine. The rotor is levitated due to the repulsive force between a stator and a rotor permanent magnet (PM). A lower cost and higher radial st iffness have been achieved by using a strontium-ferrite magnet on the rotor and an Nd-Fe-B PM above and below the rotor magnet. A finite-element analy sis was performed to calculate the levitation force and radial stiffness. A n upper stator magnet subtending an angle of 45 degrees provides the best c ompromise between a large levitation force and radial stiffness. A model fo r the horizontal-shaft hybrid magnetic bearing system has been developed an d includes the effect of the rotordynamics and the electromagnetic forces. An integral servocontroller was designed to stabilize the axial position. T he controller has been implemented in a digital signal processor, Experimen tal results performed on a prototype system are in agreement with the theor etical results.