Nonlinear control design for rotating stall with magnetic bearing actuators

Rotating stall is one type of aerodynamic instability limiting the performance of aeroengines. A set of magnetic bearings supporting the compressor rotor is a potential actuator for active control of rotating stall. Based on a first-principles model we show that using this type of actuation, the first harmonic mode of rotating stall is linearly controllable, but the zeroth and the second harmonic modes are linearly uncontrollable. For systems with a stable zeroth (surge) mode, we give an explicit procedure for designing feedback laws such that the Hopf bifurcation of the second mode stall inception is supercritical. We also investigate the effects of magnitude saturation on the size of the region of attraction. We demonstrate the theoretical results by numerical simulations of a model for a transonic compressor at the NASA Glenn Research Center