ABSTRACT
Flywheel systems have been proposed for several decades now and represent robust and powerful storage means. This chapter describes the basic properties of the kinetic energy storage, the rotor dynamics, the moment of inertia, and the specific energy of the rotor. A flywheel system is generally composed of an electric machine coupled to a rotating mass. Flywheels have been based for a long time on normal steel and reduced speed, but modern equipment benefit from advanced materials like carbon composites and fast-running permanent magnet motors that can rotate at several hundred thousand revolutions per minute. The first discharge profile corresponds to a discharge with a constant torque. This is not really corresponding to a real case of application but allows representing very easily the variation of the rotational velocity. Field-weakening strategies for permanent magnet synchronous machines (PMSM) exist but often lead to a reduced efficiency of the electric machine.
