Identification of Active Magnetic Bearing System Using Magnetic Force Measurement

An active magnetic bearing(AMB) system is developed, which is equipped with two sets of piezoelectric-type force transducers so that in-plane forces generated by a pair of magnetic bearings can be measured. Each magnetic bearings are mounted on each set of force transducers, consisting of four shearIype cells. In the process of modal testing, the radial bearings in the stabilized closed loop system are excited by the random and sinusoidal voltage inputs to power amplifiers, and then the forces and displacements at the bearings are measured simultaneously, all quantities being defined in the complex domain. The modal properties of AMB system are then effectively Identified from directional frequency response functions (dFRFs) defined between the complex inputs and outputs. It is shown that we can also identify the position and current stiffnesses from the relations between forces, displacements and currents.