Design and Performance Assessment of an Integrated Flywheel Energy Storage Systems based on an Inner-Rotor Large-Airgap SPM

An integrated flywheel energy storage system topology is presented in this paper, which is based on an inner-rotor large-airgap surface-mounted permanent magnet synchronous machine and which aims at achieving a unity energy to power ratio. The proposed synchronous machine is equipped with a thick carbon-fiber cylindric layer that acts as both the flywheel and the sleeve; as a result, this layer ensures permanent magnet containment and storing/delivering the required amount of energy simultaneously. In order to comply with all the design targets and constraints, a two-step design procedure is employed: a preliminary design is achieved analytically, by using an integrated mechanical-electromagnetic-energy modelling. Subsequently, the preliminary configuration is refined and validated through finite element analyses, which regard a performance assessment on mechanical, electromagnetic, energy, and thermal aspects at different operating conditions.