Development of a High-power Motor/Generator for the ARPA-E Hub-Less Flywheel

Recognizing the advantages of energy storage flywheels in rapid-response, high cycle-life applications, ARPA-E has funded Beacon Power to develop critical components for a low cost flying ring hub-less flywheel under the GRIDS program. The funded system will provide 100 kW for 1 hour for firming and smoothing of intermittent-renewable power generation. The goal is to reduce the cost per kWh by a factor of 8. For this large, low-cost flywheel to be applicable to either Frequency Regulation or Frequency Response applications, the motor/generator capability will need to be increased to 400 kW. The permanent magnet motor/generator (PMMG) configuration proposed in the ARPA-E project is based upon the use of bonded magnets (which give up a significant amount of remnant flux density (Br) in exchange for strain capability) together with a stator with no back-iron (and so, no negative spring constant). The questions for the SBIR project are: 1. Can some of this Br be regained with other bonded magnet materials and/or processes? 2. Can the bearing system be designed to accommodate the negative stiffness from adding back-iron? 3. Is the resulting stator size reasonable? and 4. Can the losses in the resulting high-power design be dissipated? The Phase I effort has resulted in a 400 kW motor/generator design using the same rotor magnet and stator winding as the ARPA-E design. The 4 times increase in power has been achieved with a combination of concentrating the magnetic field by adding some iron to the stator, and with additional cooling of the stator winding. The proposed Phase II project is to demonstrate that the design approach developed during Phase I will achieve the required four-times improvement in power capability for the motor/generator. This will involve building a full-scale version of the machine, and obtaining operational test data up to rated speed on a dynamometer. Commercial Applications and Other Benefits: The new high-power motor/generator will make it possible to commercialize at least six major energy balancing grid-scale applications at a cost equal to one-fourth the cost of our current Gen4 flywheel that is currently operating in our 20 MW Frequency Regulation plant in Stephentown, NY. These are: 1. Frequency Regulation and Frequency Response; 2. Primary and Secondary Reserve, which is what Europe and parts of the rest of the world use to balance system frequency; 3. Super Primary Response, a derivative of our core technology that can replace conventional spinning reserve for event contingencies; 4. ramp mitigation for solar PV; 5. load following and ramp mitigation for wind-diesel-storage hybrid applications; and 6. micro grid stabilization.