One of the enabling technologies for practical flywheel energy storage is the magnetic bearing. As part of an effort to develop flywheel energy storage for use in hybrid electric vehicles, we have designed and constructed a self-sensing, homopolar magnetic bearing. This bearing would make it possible to spin flywheels at very high speeds, thus increasing power density and efficiency.
Homopolar magnetic bearings feature extremely low rotating losses. The term homopolar refers to the arrangement of the DC permanent magnet flux and the AC control flux in our design. The term self-sensing refers to the fact that our design senses the position of the rotor through the same coils that are used to actuate the rotor, so no external sensors are needed to operate the bearing. Eliminating the need for extraneous sensors is a major advantage because it reduces complexity, eliminates sensor reliability problems, and eliminates difficulties with locating sensors in tight areas.
We have successfully demonstrated a prototype self-sensing homopolar magnetic bearing, and are currently working on integrating the bearing into a flywheel system.
Figure 1: Cutaway view of magnetic bearing
Figure 2: Plot of sensor output versus rotor displacement