Study on PID tuning strategy based on dynamic stiffness for radial active magnetic bearing

Abstract

The development of industry technology requires magnetic bearings to work in high speed conditions. However, the current stiffness and displacement stiffness of the magnetic bearing will decrease significantly due to the consequent eddy current effect, and that decrease will make the system unstable and even result in the rotor drop and instrument damage. Therefore, the traditional Proportional-Integral-Derivative (PID) method based on constant stiffness is not adaptable for high speed conditions. This paper proposes a PID parameters tuning strategy based on dynamic stiffness for the radial active magnetic bearing (RAMB). The dynamic stiffness model under eddy current effect is established by analyzing the equivalent magnetic circuit model in which parameters are frequency-dependent. The PID parameters tuning method for RAMB control system including dynamic stiffness model is put forward according to the characteristic equation and Routh-Hurwitz criterion. Different PID parameters are set in simulations and several corresponding experiments are conducted. Satisfactory control effects consistent with the theoretical analysis are obtained and thus the proposed PID tuning strategy is verified to be good. Simulations and experiments in this paper provide theoretical guidance for the design of controller parameters and have research significance for structural optimization of RAMB.

Keywords: Dynamic stiffness; Eddy effect; Equivalent magnetic circuit model; PID tuning strategy; Radial active magnetic bearing (RAMB).