Passive magnetic bearing for flywheel energy storage systems

This paper proposes a novel type of passive noncontact magnetic suspension. An advantageous feature of passive suspension systems is that they are intrinsically stable, in contrast to active magnetic bearings and therefore can provide much higher reliability, which is known to be the crucial factor in applications requiring continuous noncontact suspension of high-speed rotors. An example of such an application is flywheel energy storage systems, which are considered to be an attractive alternative to conventional electrochemical batteries from both environmental and overall energy efficiency aspects. In such systems, a high-speed rotor is used to accumulate energy in the form of kinetic energy, and its continuous noncontact suspension may be needed for many years with no faults being tolerable. The suspension design addresses some drawbacks of other passive magnetic suspension systems, such as high rotational losses, high manufacturing accuracy, and dynamical problems. The authors have built and tested a bearing prototype, in which noncontact suspension of a 3.2 kg rotor is achieved when it rotates above 20 Hz.