Dynamic Behavior of Superconductor-Permanent Magnet Levitation With Halbach Arrays for Flywheel Design and Control

Abstract

Our research goal is to construct a general predictive model for the design and control of a flywheel energy storage system (FESS) that utilizes a superconductor-permanent magnetic levitation bearing. The FESS machine design is a hubless field-regulated reluctance machine for which the rotor of the machine is also the rotating mass for the flywheel. Reported are the results of several experiments that show the oscillatory reactions of the levitated systems. For these experiments, the levitation height and the amount of flux penetrating the superconductor is controlled by adding mass to the levitated Halbach array and by the initial cooling conditions. A small impulsive force is delivered to the levitated array, which is then allowed to freely oscillate until it has completely decayed. From this we can find an effective spring constant and damping coefficient for the levitated system as a function of the magnetic field densities and levitation height. The goal of the experiments reported is to understand the dynamic behaviors of a levitation system and incorporate those properties into the control model for the flywheel. Initial experiments have demonstrated near critically damped harmonic behavior when a magnet array levitated by a superconductor is delivered an impulsive force. Using the data from our experiments we aim to gain knowledge of the underlying physics of the forces of interaction and to create a predictive macroscopic model based on magnetic array and YBCO properties. We compare our measured results to those obtained by using the advanced image mirror method and finite element magnetic modeling.