Field Experiences with a Highly Unbalanced Magnetically Suspended Flywheel Rotor

This paper describes the behaviour of a highly unbalanced flywheel rotor. The unbalance leads to rotational synchronous harmonic bearing forces which may cause amplifier saturation. It will be shown that the balancing of the rotor can be achieved with data obtained from the magnetic bearings. Additionally, it will be shown that the housing dynamics can have an enormous influence on the balancing data. Furthermore, experiences with unbalance compensation are given. The results presented in this paper show that the rotor does not, as often written, rotate "force-free" and therefore does not spin around its principal axis of inertia. Moreover, for rotors with high gyroscopic coupling an undamped resonance occurs. In this frequency range it is impossible to use unbalance compensation. The results presented in this paper are crucial for magnetic bearing systems and have to be considered in their design.