Analysis and Suppression of the Suspended Rotor Displacement Fluctuation Influence for Motor System

Suspended rotor displacement fluctuation would result in unbalanced magnetic pull and inaccurate speed measurement, which degrades the suspended rotor stability and motor performance. In order to reduce the blight, some research studies have been conducted. First, the influence on the motor magnetic field has been analyzed between motors with iron-cored and coreless stator structures. It is found that with the coreless stator, the air-gap magnetic flux density variation can be neglected. Second, the law of the speed fluctuation caused by the rotor runout has been studied. In addition, two methods, which are based on the use of notch filter and speed correction, have been proposed for suppressing the fluctuation. Third, the performances of the closed-loop systems with the proposed speed fluctuation suppression methods have been analyzed. Finally, experimental results are presented to demonstrate the correctness of the analysis and the validity of the proposed methods.

Nomenclature

Centrifugal force.

Rotor rotational speed.

Speed fluctuation induced by the rotor runout.

Rotor geometric center position along the -axis.

Mass unbalance distance.

Rotor initial phase.

Encoder radius.

Speed detecting time.

Center frequency of the notch filter.

Damping ratio of the notch filter.

Damping ratio margin.

Maximal rotational frequency fluctuation.

Rotor acceleration.

Original estimated rotor speed.

Corrected rotor speed.

Length of the unilateral protection gap.

Coulomb friction torque.

External disturbance torque.

System disturbance torque.

Estimated disturbance torque.

Viscous friction coefficient.

Motor inertia.

Nominal motor inertia.

Torque coefficient.

Nominal torque coefficient.

Electromagnetic torque.

Output torque.

Estimated output torque.

Torque command.

Low-pass filter cutoff frequency.

Speed disturbance.

Motor winding current.

Current command.

Compensation current.

Current reference, which is the sum of the current command and the compensation current.