High Speed Synchronous Machines: Technologies and Limits

This article presents a comprehensive comparison of high-speed synchronous machines, encompassing synchronous reluctance, its permanent magnet variant, and surface permanent magnet synchronous motors. The evaluation of their maximum performance capabilities employs a hybrid analytical-finite element design procedure able to address electromagnetic, thermal, and structural requirements simultaneously. Indeed, the adopted design methodology takes into account all the machines nonlinearities, while also including the limitations introduced by the iron ribs of the reluctance machine, retaining sleeve of the surface permanent magnet machine and increasing iron losses. The aim of the outlined design exercise is to evaluate the effect of different design specifications on the maximum achievable performance of the three machine topologies. A wide range of maximum design speeds, airgap thicknesses, and cooling system capabilities has been assessed showing when and why one motor type outperforms the others. The cooling system capability increment required by the reluctance-based machines to achieve the performance of the surface permanent magnet one has been systematically quantified. The design assumptions have been verified by a thermal analysis supporting the final machine selection. Three different machines designed with a maximum speed of 80 kr/min have been prototyped and tested on an instrumented test rig, validating all the design considerations.