using an appropriate controller for independent current control for motoring of force windings of bearing less induction motor

a bearingless induction machine has combined characteristics of induction motor and magnetic bearings. therefore, the advantages are small size and low-cost. in the magnetic suspension of the bearingless motors, suspension forces are generated based on the feedback signals of displacement sensors detecting the movement of the rotor shaft. the suspension forces are generated taking an advantage of the strong flux distribution of a revolving magnetic field in the air gap between the stator and rotor. thus, information of the instantaneous orientation and amplitude of the revolving magnetic field is required in a controller of the bearingless motor. therefore, vector control methods are necessary for transient conditions. for control improvement of vector control, a pid controller can be used in horizontal and vertical force paths. radial positions x and y are detected by displacement sensors.