Design of a pure synchro-reluctant machine with asymmetrical poles for high-speed applications

In this article, the authors present the various choices made to design a magnet free and directly recyclable pure synchro-reluctant (Pure-SynRel) machine with asymmetrical poles operating at a maximum speed of 21,000 rpm dedicated to automotive. This project was carried out by identifying design levers and optimizing the magnetic circuit in order to remove 3 well know issues of this topology: maximizing the power factor to reduce the inverter rating and cost, minimizing sources of NVH and torque ripples in particular, and finally maximizing the efficiency in use to close the gap with magnet technologies (PMaSynRel). The sizing of stator components such as the choice of winding (concentric or distributed, full or fractional pitch, round or hairpin wire) and rotor components (number of poles pairs, shape and number of barriers, etc.) are explained. The optimizations methods and the mechanical solutions used to reach the max speed are also detailed. A machine with symmetrical poles was firstly designed, with torque ripples of 24%. Based on this version, an adjacent asymmetrical pole was created, reducing the torque ripple by 44% and limiting the torque drop to 4%. The final machine has a DC voltage of 750V, generates 172 N.m/220kW, and the torque ripple and power factor at Pmax are 14% and 0.64 respectively. A prototype is currently being built and will be tested on a test bench at IFPEN. The theoretical expectations will be verified and presented.