Stability Analysis for a Flexible Rotor on Active Magnetic Bearings subject to Aerodynamic Loads

The development of advanced control algorithms to guarantee stability and high performance of a rotor-AMB system subject to uncertainties and disturbances is an active area of research. The model based control paradigm entails consideration of the dynamics of all components that will affect the stability and performance of a system. Control design for a flexible rotor supported on active magnetic bearings provides an additional challenge since uncertainties such as the magnitudes of cross-coupled stiffness forces strongly affect the stability of the closed-loop system. Recent work has highlighted the use of sensitivity functions in determining stability margins for AMB supported turbomachinery. The output sensitivity function provides a means of quantifying the disturbance rejection and reference command tracking properties of the closed-loop system. Our work presents an analysis of the closedloop AMB sensitivity functions of the rotor-AMB system. We present simulations of the effects of varying mid-span aerodynamic cross-coupled stiffness on stability and performance of several µ-optimal controllers designed in a mixed-sensitivity framework, measurements of experimental sensitivity functions from the levitated rotor, and recommendations on the selection of weighting functions to improve the performance.