Self-Bearing Motor-Generator for Flywheels

Self-bearing or ?bearingless? motors perform both motor and bearing support functions but such devices have not yet achieved speeds above 15,000 rpm. The innovation proposed for a self-bearing motor-generator (M-G) will achieve speeds above 30,000 rpm, moving the technology to a new frontier, not only for the motor but the generator functions as well. As applied to a flywheel energy storage system (FESS), the concept replaces the permanent-magnet bearings, conventional M-G, as well as the need for the active damper. The self-bearing function is implemented with a proportional integral derivative control and has adjustable damping as in conventional active magnetic bearings. As a result, the flywheel end rotors are shortened substantially and could enable running at much higher speed without concerns regarding the first bending critical speed. Further, elimination of rotor parts will enhance the reliability of the mechanical system. Although a self-bearing approach could result in a less efficient magnetic bearing combined with a less efficient motor, the proposed approach will solve the efficiency problem, making it ideal for the high energy efficiencies required for FESS. With such improved efficiencies and reliability, the self-bearing M-G will serve as a modular building-block technology for the power management and distribution systems used in observation platforms for earth science missions.