Abstract: The relationships between dynamic stiffness properties and PID parameters of active electrostatic bearing and rotor systems based on a stiffness compensated model are investigated. The analytical and experimental results via a three-degrees of freedom electrostatic bearing supporting a spherical rotor demonstrated that the frequency response curve of the bearing stiffness is in a bathtub shape with a minimum value in intermediate frequency range. The dynamic stiffness is mostly determined by controller parameters within the closed-loop bandwidth of electrostatically levitated systems, while the stiffness above the system bandwidth is determined by the inertial stiffness of the rotor. As a result, the stiffness properties may be varied over a certain range by changing the controller parameters within the stable region.

Key words: Dynamic stiffness, Electrostatic bearing, Electrostatic levitation, PID control, Aero-engine, Fault diagnosis, Synchrosqueezing transform, Time-frequency analysis