Today the VFD is perhaps the most common kind of output or load for a control program. As applications are more complex the VFD has the ability to control the acceleration of the motor, the direction the engine shaft is turning, the torque the engine provides to lots and any other engine parameter which can be sensed. These VFDs are also available in smaller sized sizes that are cost-efficient and take up less space.
The arrival of advanced microprocessors has allowed the VFD works as an extremely versatile device that not merely controls the speed of the motor, but protects against overcurrent during ramp-up and ramp-down conditions. Newer VFDs also provide methods of braking, power increase during ramp-up, and a variety of regulates during ramp-down. The largest cost savings that the VFD provides is certainly that it can make sure that the engine doesn’t pull excessive current when it begins, therefore the overall demand element for the whole factory could be controlled to keep carefully the domestic bill as low as possible. This feature by itself can provide payback more than the cost of the VFD in less than one year after purchase. It is important to remember that with a traditional motor starter, they will draw locked-rotor amperage (LRA) when they are beginning. When the locked-rotor amperage happens across many motors in a manufacturing plant, it pushes the electrical demand too high which frequently outcomes in the plant paying a penalty for all the electricity consumed through the billing period. Since the penalty may be as much as 15% to 25%, the savings on a $30,000/month electric expenses can be utilized to justify the purchase VFDs for virtually every engine in the plant even if the Variable Speed Drive Motor application form may not require working at variable speed.
This usually limited how big is the motor that could be controlled by a frequency plus they were not commonly used. The earliest VFDs used linear amplifiers to regulate all areas of the VFD. Jumpers and dip switches were used provide ramp-up (acceleration) and ramp-down (deceleration) features by switching larger or smaller sized resistors into circuits with capacitors to create different slopes.
Automatic frequency control consist of an primary electric circuit converting the alternating current into a immediate current, after that converting it back to an alternating electric current with the mandatory frequency. Internal energy reduction in the automatic frequency control is ranked ~3.5%
Variable-frequency drives are widely used on pumps and machine device drives, compressors and in ventilations systems for large buildings. Variable-frequency motors on enthusiasts save energy by enabling the volume of surroundings 
moved to complement the system demand.
Reasons for employing automatic frequency control may both be related to the functionality of the application form and for conserving energy. For example, automatic frequency control can be used in pump applications where in fact the flow is matched either to volume or pressure. The pump adjusts its revolutions to confirmed setpoint with a regulating loop. Adjusting the movement or pressure to the actual demand reduces power intake.
VFD for AC motors have been the innovation which has brought the use of AC motors back into prominence. The AC-induction electric motor can have its acceleration transformed by changing the frequency of the voltage used to power it. This implies that if the voltage put on an AC electric motor is 50 Hz (used in countries like China), the motor works at its rated rate. If the frequency is certainly increased above 50 Hz, the engine will run faster than its rated acceleration, and if the frequency of the supply voltage can be significantly less than 50 Hz, the engine will run slower than its ranked speed. Based on the adjustable frequency drive working principle, it is the electronic controller particularly designed to change the frequency of voltage provided to the induction engine.