Harmonic Disturbance Suppression for Magnetic Bearings via Output Regulation

In a magnetic bearing system, rotor imbalance and sensor runout problem are inevitable, which will not only bring about the synchronous and harmonic disturbances in rotor dynamics, but also cause amplifier saturation and system instability. Moreover, these two types of disturbances affect the system states through two different channels. Therefore, a novel method which combines the disturbance observer and output regulation is designed to suppress the harmonic disturbances. An exogenous system is firstly presented, which refers rotor imbalance and sensor runout as matched disturbance and measurement error, so that the harmonic disturbance attenuation is transferred to an output regulation problem. Then, an observer is designed to estimate not only synchronous disturbances but also harmonic disturbances. By using the estimated states and the measured ones, a state feedback method is designed to suppress the harmonic disturbance, so that the real displacement could converge to the reference, rather than the measured states. Furthermore, the condition for displacement stabilization is derived, and the stability of the closed-loop system is proved. The results of simulations and experiments illustrate that the proposed method could simultaneously reduce the disturbances in multiple frequency bands.