Drives: Learn About Drives Here > Drives are electromechanical systems that employ an electric motor as the prime mover instead of a diesel engine, steam
and gas turbines, or hydraulics to control the motion and processes of various mechanisms. Examples in which electric
drives would be utilized include: conveyors, fans, ventilators, compressor pumps, cranes, hoists, excavators, escalators,
electric locomotives and cars.
Electric drives generally include both an electric motor and a speed control unit or system. The term drive is often applied
to the controller without the motor. In the early days of electric drive technology, electromechanical control systems were used.
Later, electronic controllers were designed using various types of vacuum tubes. As suitable solid state electronic components
became available, new controller designs incorporated the latest electronic technology.
In the past, a variety of terms have been used to describe a system that permits a mechanical load to be driven at user-selected
speeds. Some of these terms are Variable-Speed Drive, Variable Frequency Drive, Adjustable-Frequency Drive, and Adjustable-Speed
With these various names, the term "variable" implies a change that may or may not be under the control of the user. "Adjustable"
is the preferred term, since this refers to a change directly under control of the user. Lastly, the term "frequency" can only
be applied to drives with an ac output, while the term "speed" is preferred since this includes both ac and dc drives. The term
most commonly accepted is Adjustable-Speed Drive (ASD). Each of the general types of electric drives can be further divided
into numerous variations. Some of the most popular types of electric drives include adjustable voltage DC drives, adjustable
frequency AC drives, adjustable voltage AC drives, servo drives, eddy current drives and wound-rotor motor drives. For the
purposes of this document, some of the more common electric drives have been highlighted.