Motor drives are used in a wide range of power values, from few watts up to many thousands of kilowatts, in applications ranging from high precision position control in robotics to variable speed drives for regulating the rate of flow in pumps.
In all drives where speed and position must be controlled, a power electronics converter is needed as interface between input power and motor.

Constant, or slightly variable according to load, speed drives use almost exclusively induction motors, thanks to their simple, robust and cheap construction, in addition to the fact that they do not need special maintenance. However, the multi‐phase motors supplied at constant network voltage and frequency have a rigid relationship between supply frequency and speed.

Direct current motor drives are mainly used in applications requiring the control of the speed of the motor (DCA 205.1). In variable speed drives direct current machines are used everywhere; however, today, with the development of power electronics, induction motor drives are also widely used .
In these cases, the speed of the motor can be varied in three different ways: by varying the number of polar couples, by varying the slip speed (DCA 205.2), by varying the supply frequency (DCA 205.3).

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