Achieving a constant power speed range for PM drives

The authors question the desirability of the flux weakening approach for a number of applications where energy efficiency is of prime importance, such as in electric vehicles. They point out that, for an acceptable increase in the rating of some of the semiconductor devices, standard PM (permanent magnet) commutator motors and switched PM motors with surface-mounted magnets can be used, and a significant reduction in power loss can be achieved. At the cost of an increased rating of the chopper or inverter switching devices, a substantial reduction of energy loss in the windings can be achieved for all operations in the constant power range above the base speed. The attractiveness of the constant-flux approach proposed here depends on the value system of the particular application. In part, it depends on the capital cost of the chopper or inverter relative to that for the flux-weakening approach