An AC Drive is an electronic device that converts a fixed frequency and voltage to an adjustable frequency and AC voltage source. It controls the speed, torque, horsepower and direction of an AC motor. AC Drive is also a term used for an AC inverter and is sometimes used to describe a particular section of an AC drive.
The section uses the DC voltage from a previous circuit stage (DC Bus) to produce an AC current or voltage having the desired frequency. AC Drives are also referred to as Variable Frequency Drives (VFD's) or Adjustable Speed Drives (ASD's). These drives are gaining in popularity due to the energy savings that can be obtained related to the AC technology. In addition, AC motors are simpler than DC and usually an "off-the-shelf" item compared to DC motors. Advances in technology have made the size, cost, reliability and performance of AC drives very appealing in industrial variable speed applications. The AC Drive system is very simple. It consists of three components: