Design and practical Realization of an innovative Flywheel Concept for industrial Applications

The joint industry project ‘ETA-Fabrik’ at TU Darmstadt demonstrates different approaches to improve the energy efficiency of manufacturing processes. Within this project an innovative flywheel concept was designed and realized in order to provide energy storage and load smoothing services. The flywheel design is an outerrotor setup. The rotor is a hubless hollow cylinder made of fiber reinforced plastic (FRP). All functional components are fully integrated into the rotor. For the radial suspension homopolar active magnetic bearings (AMBs) made of soft magnetic composite are used. A permanent magnetic bearing provides axial levitation. In order to increase the systems robustness a newly developed backup bearing system in a planetary arrangement with multiple independent bearing elements is integrated. The motor generator unit is a permanent magnet synchronous machine which is connected to the factory gird via a frequency inverter. The system is operated in high vacuum in order to reduce gaseous friction. Design challenges are the segmented sensor planes for the AMBs, the diametric enlargement of the rotor due to centrifugal forces, the anisotropic FRP as well as the thermal stability of the rotor in vacuum environment which leads to the demand of very low rotor losses. The paper describes the system and component design process and solutions which were incorporated in order to meet the design restrictions and challenges