Vibration analysis of a motor/generator for flywheel batteries

Energy storage is key piece of the energy transition, since it can be tailored for intermittent energy sources, such as wind and solar resources. Chemical batteries represent the de facto standard of storage systems but are affected by several drawbacks, hence research is focusing on viable alternatives. Mechanical storage systems, i. e. flywheel batteries, are a promising solution thanks to their lower costs, lower environmental footprint, immediate charging time and higher lifetime. However, in order to exploit this technology for a domestic scenario, the self-discharge duration must be increased. In order to achieve that, all losses must be minimized, i. e. electromagnetic and mechanical losses. A motor/generator prototype to be coupled with the flywheel has been specifically designed to reduce the electromagnetic losses. Mechanical losses, on the other hand, must be minimized by an optimal design of the remaining structure, such as transmissions and bearings. In this paper the vibration analysis of the machine structure is proposed as a fundamental methodological step for the development and optimization of the overall system. Mechanical losses of the motor/generator coupled to the flywheel are assessed and the resonance frequencies of the structure are estimated by spectral analysis. In addition to that, this vibration analysis paves the way for a modal analysis and an optimal redesign of the mechanical system. Experimental acquisitions were realized both in stationary and variable speed conditions and the results are here illustrated.