Applied Power Electronics

Most of the electric machines had a conventional design for speed –control. Previously, the speed regulation of these motors was done via traditional or mechanical contacts, for example: inserting resistors to the armature circuit or controlling the excited circuit of DC motor, and other methods of control. These classical methods, however, lead to non-linearity in mechanical or electromechanical characteristics [ω= f(M) or ω= f(I)], which in turn lead to increased power losses as the result of the non-soft regulation of speed, as well as the great inertia of classical control methods that rely on mechanical and electromagnetic devices.