Optimal design of magnetically-levitated flywheel energy storage system considering system stability

Flywheel energy storage systems (FESS) are a viable alternative for power storage. With an increasing interest in green technology and energy savings, flywheel energy storage systems are receiving a renewed attention for the applications in wind farms, subway stations, and large cranes. Since the stored energy of a FESS is proportional to the principal mass moment of inertia times the square of running speed, it is important to have a design that maximizes the principal inertia while running at as high speed as possible. In this paper, we present a parametric study showing that the optimum design must consider not only the structural constraints, but also the system stability and the vulnerability to disturbances. It is also found that a cross feedback control in combination with a conventional proportional-derivative (PD) controller is essential to reduce the effect of gyroscopic coupling and to increase the stored energy as well as the specific energy density.