Today the VFD is perhaps the most common kind of output or load for a control system. As applications become more complex the VFD has the capacity to control the swiftness of the electric motor, the direction the engine shaft can be 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 much less space.
The arrival of advanced microprocessors has allowed the VFD works as an exceptionally versatile device that not only controls the speed of the engine, 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 settings during ramp-down. The largest financial savings that the VFD provides is certainly that it can make sure that the engine doesn’t pull extreme current when it begins, so the overall demand element for the entire factory could be controlled to keep carefully the domestic bill only possible. This feature alone can provide payback more than the price of the VFD in less than one year after buy. It is important to keep in mind that with a traditional 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 facility, it pushes the electric demand too high which often results in the plant having to pay a penalty for all of the electricity consumed during the billing period. Because the penalty may be just as much as 15% to 25%, the savings on a $30,000/month electric costs can be used to justify the buy VFDs for practically every electric motor in the plant even if the application form may not require working at variable speed.
This usually limited how big is the motor that may be managed by a frequency and they were not commonly used. The initial VFDs used linear amplifiers to regulate 
all aspects 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 produce different slopes.
Automatic frequency control consist of an primary electric circuit converting the alternating current into a immediate current, then converting it back into an alternating current with the required frequency. Internal energy reduction in the automatic frequency control is ranked ~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 permitting the volume of air moved to match the system demand.
Reasons for employing automated frequency control can both be related to the functionality of the application form and for saving energy. For instance, automatic frequency control can be used in pump applications where the flow is certainly matched either to volume or pressure. The pump adjusts its revolutions to confirmed setpoint via a regulating loop. Adjusting the Variable Drive Motor movement or pressure to the actual demand reduces power consumption.
VFD for AC motors have been the innovation that has brought the use of AC motors back to prominence. The AC-induction motor can have its swiftness transformed 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 speed. If the frequency is increased above 50 Hz, the engine will run quicker than its rated velocity, and if the frequency of the supply voltage can be less than 50 Hz, the electric motor will operate slower than its rated speed. Based on the adjustable frequency drive working theory, it is the electronic controller specifically designed to change the frequency of voltage supplied to the induction electric motor.
