Global design optimization strategy of a synchronous reluctance machine for light electric vehicles

Synchronous Reluctance (SynRel) machines are considered a competitive alternative to the induction motors for variable speed drive applications due to their comparable performances and low cost. The absence of rare earth permanent magnets makes them very attractive also in the automotive sector especially for light electric vehicles. The design of SynRel machines has been formalized by many authors in the last three decades but it is still an open challenge since it involves many competitive design objectives and a higher number of geometrical variables compared to other kind of machines. This paper is focused on the joint optimization of both stator and rotor of a SynRel machine with the aim of obtaining the highest torque density with the minimum iron and joule losses as well as smooth torque. The aim is to carry out a machine design that suits best the requirements of a small electric car for urban mobility, i.e. 30 kW with a base speed of 3000 rpm and a maximum speed of 6000 rpm. The proposed optimization strategy is global because it considers a geometry design that takes into account several stator and rotor parameters together. The design method consists in a two steps procedure: in the first stage the torque density and the losses are optimized, while the quality of the torque profile is improved in the second design stage. The results, satisfying the project requirements, are presented and compared to the initial reference machine. Finally a comparison between two design approaches allowing the improvements of the constant power speed range is presented and discussed.