Variable Speed Drives

The speed of a motor can be controlled by using some type of
electronic drive equipment, referred to as variable or adjustable
speed drives. Variable speed drives used to control DC motors
are called DC drives. Variable speed drives used to control AC
motors are called AC drives. The term inverter is also used to
describe an AC variable speed drive. The inverter is only one
part of an AC drive, however, it is common practice to refer to
an AC drive as an inverter.

Before discussing AC drives it is necessary to understand some
of the basic terminology associated with drive operation. Many
of these terms are familiar to us in some other context. Later in
the course we will see how these terms apply to AC drives.