MULTIVARIABLE IDENTIFICATION OF ACTIVE MAGNETIC BEARING SYSTEMS

In many applications of magnetic bearings, high system performance (di sturbance rejection) is required, Often several eigenfrequencies of th e rotor must be actively damped. Advanced controller design is then ne cessary, which in ture relies on accurate plant models. System identif ication is therefore an important prerequisite for fast and reliable c ommissioning, Magnetic bearing systems are unstable MIMO(1) plants. I n case of current control, they are characterized by a set of poles on the positive and negative real axis (rigid body modes of the rotor), and a set of poorly damped poles along the imaginary axis (flexible mo des). Previously described identification algorithms fail with this ki nd of system. Therefore a novel algorithm has been developed, The syst em poles are identified from the determinant of the measured frequency response function matrix. The algorithm provides a state-space model of pre-defined order and structure, suited for controller design and v erification. Experimental results obtained using measurement data from a magnetic bearing system with a flexible rotor are presented.