Active Short Circuit Tolerant Design of Permanent Magnet Assisted Synchronous Reluctance Machines

Abstract

The functional safety standard fulfillment could necessitate the active short circuit manoeuvre regardless the pre-operating condition of the electrical machine used in traction applications. This poses an additional and computationally-challenging requirement to the machine design as the permanent magnet (PM) demagnetization risk needs to be evaluated in the worst condition during the short circuit transient. This manuscript proposes a comprehensive design procedure of a PM assisted synchronous reluctance machine able to evaluate the full performance in the torque-speed plane including the short circuit current transient and the worst PM demagnetization condition in a time-efficient way. The computational efficiency is achieved evaluating the flux-current maps with a non-linear magnetic equivalent circuit carefully balancing the compromise between a faithful representation of the machine flux paths and computational effort. The methodology is adopted to perform a parametric design study varying two independent design variables and the number of poles considering the space and performance requirements of a heavy duty electric vehicle application. The compromise between overload capability and PM demagnetization during the short circuit is investigated defining the rationals of the final machine selection. One machine candidate is refined, manufactured and tested and the experimental results support both design procedure and design insights.