Flywheel energy storage is an important technology for power quality systems and uninterruptible power supplies. The high power density, environmental friendliness, and high reliability of flywheel systems make them a very attractive alternative to existing battery technologies for these applications. However, reductions in cost and complexity need to be achieved before they become more widely used.
Other flywheel systems have been built using carbon fiber or other expensive composite materials for their flywheel rotor. This drives up the material and manufacturing costs significantly. By using a slotless synchronous homopolar motor design and integrating the containment and vacuum housing with the motor housing, a much simpler flywheel system can be constructed . The single-piece steel rotor design can achieve comparable performance at lower cost and higher reliability. A prototype 30 kW, 140 W-hr flywheel energy storage system has been built, and we are currently conducting performance tests.
Other flywheel-related research conducted by the UC Berkeley Power Electronics Group includes the design of high-speed, low-loss synchronous reluctance motors and self-sensing magnetic bearings [2, 3].
Figure 1: Cross-section of prototype flywheel energy storage system
Figure 2: Stator and rotor