Perspectives on safe operating region and field weakening operation in electrical machines

Abstract

This paper discusses the issue of safe operating speed torque zone and field weakening in electrical machines from a somewhat different viewpoint than in the existing literature, including textbooks. At present, field weakening in electrical machines is viewed as an issue due to limitation of available input voltage which prevents a desired current to flow into the motor due to back emf at high speeds. This issue, along with the issue of safe operating zone, is examined in this paper with elaborations on the total loss in the machine which includes magnetic loss, copper loss, and also rotational and windage losses. The author believes that this gives a more complete and accurate picture of the situation and leads to a more scientifically accurate reasoning towards implementation of field weakening (if necessary), and also describing the safe operating zone in electrical machines.