Today the VFD could very well be the most common kind of result or load for a control system. As applications are more complex the VFD has the capacity to control the velocity of the motor, the direction the motor shaft is definitely turning, the torque the electric motor provides to a load and any other motor parameter that can be sensed. These VFDs are also available in smaller sized sizes that are cost-effective 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 provide methods of braking, power increase during ramp-up, and a variety of controls during ramp-down. The largest savings that the VFD provides is that it can make sure that the motor doesn’t pull extreme current when it begins, therefore the overall demand aspect for the entire factory can be controlled to keep carefully the domestic bill only possible. This feature alone can provide payback more than the price of the VFD in under one year after purchase. It is important to remember that with a normal motor starter, they’ll draw locked-rotor amperage (LRA) if they are starting. When the locked-rotor amperage occurs across many motors in 
a manufacturing plant, it pushes the electrical demand too high which often results in the plant having to pay a penalty for all of the electricity consumed through the billing period. Since the penalty may end up being as much as 15% to 25%, the savings on a $30,000/month electric expenses can be used to justify the buy VFDs for virtually every electric motor in the plant actually if the application may not require Variable Drive Motor working at variable speed.
This usually limited how big is the motor that may be controlled by a frequency and they were not commonly used. The initial VFDs used linear amplifiers to control all areas of the VFD. Jumpers and dip switches were utilized provide ramp-up (acceleration) and ramp-down (deceleration) features by switching larger or smaller sized resistors into circuits with capacitors to generate different slopes.
Automatic frequency control consist of an primary electrical circuit converting the alternating electric current into a immediate current, then converting it back to an alternating current with the required frequency. Internal energy reduction in the automated frequency control is rated ~3.5%
Variable-frequency drives are widely used on pumps and machine tool drives, compressors and in ventilations systems for large buildings. Variable-frequency motors on enthusiasts save energy by enabling the volume of atmosphere moved to match the system demand.
Reasons for employing automatic frequency control can both be related to the features 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 certainly matched either to volume or pressure. The pump adjusts its revolutions to a given setpoint via a regulating loop. Adjusting the flow or pressure to the real demand reduces power intake.
VFD for AC motors have already been the innovation which has brought the usage of AC motors back into prominence. The AC-induction engine can have its speed changed by changing the frequency of the voltage utilized to power it. This means that if the voltage applied to an AC engine is 50 Hz (found in countries like China), the motor functions at its rated rate. If the frequency is definitely improved above 50 Hz, the motor will run quicker than its rated velocity, and if the frequency of the supply voltage can be less than 50 Hz, the engine will run slower than its rated speed. According to the adjustable frequency drive working principle, it is the electronic controller specifically designed to modify the frequency of voltage provided to the induction engine.