Separately Excited DC Machine

Abstract

Direct current (DC) motors have been dominating the field of adjustable speed drives for over a century; they are still the most common choice if a controlled electrical drive operating over a wide speed range is specified. This is due to their excellent operational properties and control characteristics; the only essential disadvantage is the mechanical commutator which restricts the power and speed of the motor, increases the inertia and the axial length and requires periodic maintenance. With alternating current (AC) motors, fed by variable frequency static power converters, the commutator is eliminated, however at the cost of increased complexity. This is one of the reasons why controlled AC drives could not immediately supplant DC drives, once the semiconductor-technology had sufficiently advanced.