Q5Electric Drives

An induction motor drive is a variable-speed electric drive system built around an induction motor (most commonly the robust, low-maintenance squirrel-cage type, though wound-rotor/slip-ring types are also used in specific applications, as discussed elsewhere in this paper) together with a power-electronic converter — typically a variable-frequency, variable-voltage inverter, controlled using scalar (V/f), vector (field-oriented), or direct torque control methods, as discussed elsewhere in this paper — that converts a fixed-frequency, fixed-voltage AC supply into the variable-frequency, variable-voltage supply needed to control the induction motor's speed. The primary purpose of an induction motor drive is to provide efficient, precisely controllable variable-speed and variable-torque operation of what is otherwise (without such a drive) essentially a fixed-speed machine (since a directly line-connected induction motor runs at a speed determined almost entirely by the fixed supply frequency and its small, load-dependent slip) — enabling induction motors, which are inherently simpler, more robust, and less costly to maintain than DC motors (having no brushes or commutator), to be used in place of DC motors for the vast majority of modern variable-speed industrial and commercial drive applications.