DESIGN CONSIDERATIONS FOR PERMANENT-MAGNET SYNCHRONOUS MOTORS FOR FLUX WEAKENING APPLICATIONS

The required parameter values of a permanent magnet synchronous motor designed for very large power-speed range are determined based on a li near dq model. It is shown that unconventional motor constructions wit h the d-axis inductance equal to, or bigger than, the q-axis inductanc e can provide superior torque, power factor and control characteristic s. The initial sizing stage of a design procedure is described. Analyt ical equations are developed and used to illustrate the influence of t he rotor configuration, electromagnetic loading and airgap length on t he performance of a relatively large range of medium-sized motors. Sug gestions regarding the improvement of efficiency, power factor, overlo ad performance and PM protection against permanent demagnetisation are also given, The results of the analytical design procedure have been checked against finite element computations and experimental data.