A synchronous homopolar machine for high-speed applications

The design, construction, and test of a high-speed synchronous homopolar motor/alternator, and its associated high efficiency six-step inverter drive for a flywheel energy storage system are presented in this paper. The work is presented as an integrated design of motor, drive, and controller. The performance goal is for power output of 30 kW at speeds from 50 kRPM to 100 kRPM. The machine features low rotor losses, high efficiency, construction from robust and low cost materials, and a rotor that also serves as the energy storage rotor for the flywheel system. The six-step inverter drive strategy maximizes inverter efficiency, and the sensorless controller works without position or flux estimation. A prototype of the flywheel system has been constructed, and experimental results for the system are presented.