Analytical approach to determine the power limit of high-speed synchronous reluctance machines

The design of synchronous reluctance machines for high-speed applications is an issue that nowadays remains almost not dealt with. The thickness of the iron ribs that mechanically sustain the structure increases with the rotor speed, so that a high magnetic flux flows through them. Therefore, the available torque decreases with the rated speed required by the application. The aim of this paper is to tackle the design of synchronous reluctance machines for high-speed applications. The potentials of a high-speed synchronous reluctance machine are investigated. For a given operating speed, the mechanical structure is firstly designed, so as to achieve a robust rotor. Then the maximum torque is investigated according to the thermal limits. A tradeoff between increasing speed and decreasing torque is obtained, up to obtain an optimum value of the electromagnetic power. An advantage of the proposed procedure is its analytical nature: all the design steps are based on analytical relationships, so as to allow a rapid extrapolation of the obtained results to different machine size, operating requirements, and so forth. Finite element analysis is used only to validate the final results.