Achieving a constant power speed range for PM drives

Flux weakening has long been a standard approach in obtaining a constant power speed range for traction drives with commutator motors. There is much interest in using permanent magnet (PM) commutator motors or, preferably, electronically commutated PM motors for such applications. Some PM motor designs, such as those using inset or buried magnets, have been proposed to achieve flux weakening. This paper questions the desirability of the flux weakening approach for a number of applications where energy efficiency is of prime importance, such as in electric vehicles. For an acceptable increase in the rating of some of the semiconductor devices, standard PM commutator motors and switched PM motors with surface-mounted magnets can be used and a significant reduction in power loss can be achieved