System identification and re-engineering controllers for a magnetic bearing system

In this paper, a model of an MBC 500 magnetic bearing system is identified using data collected in the frequency domain. The difficulties encountered in system identification using the MATLAB /spl mu/-Analysis and Synthesis toolbox are addressed. Since there are two resonant modes that threaten the stability of the system, two resonant frequencies have been correctly identified and then notched out by using two notch filters. Lead compensators have been designed to stabilise the four axial channels of the magnetic bearing system. The problem with attempting to design a lead compensator with too large a phase margin is also addressed. Finally, the designed notch filters and lead compensators are implemented in real-time.