Active magnetic bearings for a flywheel peak power buffer for electric vehicles

The performance of electric vehicles may be improved significantly by incorporating a flywheel peak power buffer into the power-train. An annular carbon fibre composite flywheel rim offers a high specific energy capability, although a high rotational speed is necessary for a high stored energy, whilst operation in a vacuum is conducive to a low aerodynamic loss, and necessitates the use of magnetic bearings. The electromagnetic design of such a flywheel system is described, and a dynamic analysis that predicts the free vibration modes and frequencies, is presented. Finally, the magnetic bearing control system is described, and it is shown that the vibration damping capability of the bearings is such that natural vibration frequencies within the flywheel operating speed range can be accommodated, and performance objectives commensurate with operation in a vehicle drive-train can be achieved.