A Frequency Dividing Control Method Using Wavelet for Active Magnetic Bearing System

Benefiting from the features such as zero-friction and active control, Active magnetic bearings (AMBs) have several advantages over conventional mechanical bearings and are getting more applications. Various control strategies and algorithms have been applied and designed to deal with the nonlinear characteristic as well as the complex rotor dynamics. However, most control schemes are in time domain, while the control in frequency domain, which is also essential for stability of rotor system, is rarely considered. In this paper, a frequency dividing control method is proposed for AMB-rotor system. Wavelet theory is applied for frequency dividing control. The control scheme is implemented by filter banks for Wavelet Transform (WT) and a group of PID controllers for multifrequency control. Simulation on a 4-DOF AMB-rotor system in different cases is run and vibration of the system is analyzed. Simulation results demonstrate that the proposed approach has an obvious control effect with better precision and quicker response than conventional PID control. This research provides a time-frequency control approach for AMBs, and this low-hardware-cost approach can also be adopted in other vibration control, especially in multi-frequency applications.