A new modulated permanent magnet twin stator machine for high torque density and better magnet utilisation

Abstract

Given the recent interest in the replacement of internal combustion engines with electric machines, the main aim of this research is to design a high torque density permanent magnet machine to an electric vehicle’s specification. A new design concept for increasing the torque density of a conventional permanent magnet machine is introduced and described theoretically and mathematically. The proposed method involves splitting the stator teeth in order to introduce a magnetic gear ratio into the torque equation. The introduced machine is also further modified to improve its magnet utilisation. An investigation is carried out on the impact of different slot to pole combinations on torque density and an optimum combination found. Thereafter, two optimisation methods are applied. The first method is carried out manually by varying a single parameter and investigating its effect on torque density. The second method is conducted automatically using OptiNet to validate the results achieved with the manual optimisation. Further analysis is carried out, including mechanical evaluation against centrifugal forces in order to determine the mechanical strength of the rotor. Finally, a prototype is constructed and tested with detailed discussion on the results achieved and comparison with finite element calculations in order to validate the design and determine its level of performance. The final design is then compared to the Toyota Camry and Prius electrical motors.