Disturbance Attenuation Using a dc Motor for Radial Force Actuation in a Rotordynamic System

This paper presents a technique for attenuating the external disturbances acting on the rotor of a prototype flywheel energy storage device. The approach uses a three-phase axial flux brushless dc motor to simultaneously produce a torque and a radial force. This is accomplished by using two phases of the motor for torque generation, and one phase to produce the radial force. The paper develops a set of equations that can be used to predict the forces generated by the motor coils. These equations are used to implement a feedback control system to suppress the effects of external excitations. The nonlinear controller requires the velocity measurements and the angular displacement of the flywheel. The controller essentially adds damping to the system, and the constant feedback gains solve an optimization problem that involves a $H∞$ bound on the disturbance attenuation. The experimental results clearly demonstrate that the dc motor can be used to suppress unwanted radial vibrations due to external disturbances.