Design Features of an Innovative Synchronous Reluctance Machine for Battery Electric Vehicles Applications

The widespread of hybrid and battery electric vehicles is vital for the future of low-carbon mobility. In this context the delivery of affordable and efficient electric motor technologies together with high energy density storage devices are key aspects to enable the mass market take-off of electrified vehicles. The objective of this paper is to provide the scientific community with the results and design features of an innovative and rare-earth free electric motor technology based on the synchronous reluctance machine concept. This technology is capable to provide sufficient power density and higher driving cycle energy efficiency compared to the current state-of-the-art rare-earth permanent magnet synchronous machines used for automotive applications. The motor is designed to be integrated within a hatchback rear driving axle vehicle, achieving the maximum energy efficiency in urban operational conditions. The paper shortly presents the motor design objectives, to then focus on the main design steps undertaken, i.e. stator winding design, electromagnetic and mechanical design, power electronics hardware design and integrated thermal design. The final motor design and its preliminary performances are presented, showing a maximum torque performance of 133 Nm at 3,700 rpm and a maximum power of 56.7 kW at 4,900 rpm, with peak efficiency above 96% around 4,000±500 rpm and 50±20 Nm, decreasing to 93-94% by including the inverter efficiency (i.e. system efficiency). The proposed motor design constitutes a step ahead in the development of a market-ready permanent magnet assisted synchronous reluctance machine technology for automotive applications, potentially enabling the developed solutions to be successfully implemented in the next generation of electric motors for hybrid and electric vehicles.