Sensitivity analysis of torque ripple reduction of synchronous reluctance and interior PM motors

The main drawback of reluctance machines is a high torque ripple, due to the interaction between the stator magneto-motive force and the rotor structure. Adopting a rotor configuration characterized by several flux barriers per pole, there is a high influence of the rotor geometry on the machine performance, in terms of both average torque and ripple. An optimization is often required to determine the optimal rotor geometry so as to achieve a high and smooth torque. Then, the geometry determined above should guarantee good performance for various operating points (i.e., changing the current amplitude and phase), as well as for small variations of the geometry. This paper investigates this aspect, showing the results of optimizations carried out on various machines. The impact of the geometry parameters is taken into account and the sensitivity of the optimal solution to the geometry variation is pointed out. The paper highlights the difficulty to get a robust geometry as far as the torque ripple reduction is concerned. Finally, a few experimental results on a Synchronous Reluctance motor prototype will be presented, compared with Finite Element Analysis simulations for validation.