Design and analysis of the magnetic suspension system in an energy storage flywheel

Over the past decade, there has been a rising need to develop more efficient, sustainable and environmentally friendly means of short term energy storage. Flywheel energy storage systems store kinetic energy by continuously spinning a compact rotor in a low-friction environment. Magnetic bearing suspension systems are desirable for this application since they significantly increase efficiency, reduce waste heat when operated in vacuum and reduce power requirements for the electronics. A demonstration flywheel energy storage test rig under development at the University of Virginia will use a five-axis active magnetic bearing support system. This paper discusses the design and analysis procedure of the flywheel magnetic suspension system. The magnetic suspension system will be controlled by a µ-synthesis controller, with an adaptive auto-balancing algorithm. Preliminary calculations are performed to determine the various design parameters such as nominal air gap, number of coil turns required, and stator/rotor diameter and thickness using linear magnetic circuit models. Finally, a 3-dimensional finite element analysis was conducted with commercial finite element software to verify the calculated design parameters. The flux path was visualized for both the thrust a nd radial magnetic bearings and important parameters such as load capacity, flux density, inductance and slew rate were calculated.