Flywheel batteries are a possible solution for adding storage to various grid applications including wind-electric systems. Possible applications are energy buffers for a fluctuating grid, energy storage for voltage support devices, and frequency control for generating systems. In flywheel batteries, it is desirable for the motor/generator to operate in an enclosure that either maintains a vacuum or is filled with a low windage loss gas such as hydrogen. In either of these cases, low amounts of heat will transfer from the rotor. Therefore, the motor/generator's rotor must have low loss and be able to withstand high temperatures. The synchronous reluctance machine is able to meet both of these requirements. To investigate the best way to design a 2 MW motor/generator, a 10 kW small-scale machine is designed, fabricated, and tested. The results of the testing are combined with electromagnetic and thermal finite element simulations to design a synchronous reluctance machine with the low rotor loss needed for flywheel battery applications. Finally, a control scheme for the synchronous reluctance motor/generator is presented that maximizes both efficiency and power output.
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