Design methodologies for the output power maximisation of synchronous reluctance machines

Synchronous reluctance (SyR) machines can constitute a promising alternative to permanent magnet machines for low-cost applications. The recent literature reports some guidelines for choosing the proper number and position of the rotor flux barriers capable of enhancing the electromagnetic performance in low-speed applications. However, as the rotational speed increases, the electromagnetic and structural mutual interactions become relevant; therefore, an optimal design requires a proper trade-off between torque production and stress reduction, which can be difficultly predicted analytically. This work proposes an approach based on optimisation algorithms in order to find ‘non-conventional’ geometries able to improve the power density: genetic algorithms coupled to magneto-static finite elements analysis and structural analytical models, are adopted to co-design SyR machines with different numbers of stator slots and rotor barriers subjected to the same thermal constraints. This study investigates two design procedures aimed at maximising the output power of SyR machines by increasing the rotational speed. Both procedures allow determining the power limits for a given volume of active parts and a fixed amount of admissible losses; moreover, the second procedure automatically finds also the rotational speed which maximises the output power.