Design and Evaluation of Electrical Motors for Flywheel Energy Storage Systems: A Multi-Criteria Decision Framework for Optimal Selection

Abstract Flywheel energy storage systems (FESSs) are considered one of the most promising options in the field of energy storage because of their high reliability, long lifetime, low maintenance requirements, and fast dynamic response to power fluctuations. The electrical machine, as the heart of FESS, plays a key role in determining its technical and economic characteristics. For this reason, the selection of a suitable structure has a direct influence on the performance, dimensions, cost, and lifetime of the FESS. Therefore, the main objective of this paper is to select the optimal structure of the electrical machine for use in FESS considering the mechanical, magnetic and thermal aspects. Subsequently, a comprehensive design algorithm is presented for various system components containing the electrical machine, bearings, cooling system, and rotating mass. Furthermore, a dedicated algorithm is developed to design the electrical machine according to the FESS application. Based on these two algorithms, thirteen different topologies of electrical machines suitable for FESS applications are designed. The Finite element analysis (FEA) is performed to extract the electromagnetic and thermal characteristics of these topologies. In this paper, two major FESS applications, namely frequency regulation in power systems and electric vehicle applications, are considered. Then, by defining a set of key criteria and applying application-specific weightings, the TOPSIS multi-criteria decision-making (MCDM) method is employed to prioritize the machine structures. The results indicate that the choice of machine topology is strongly dependent on the FESS application and no single topology can be definitively introduced as the best option.