Today the VFD is perhaps the most common type of output or load for a control program. As applications are more complex the VFD has the ability to control the quickness of the electric motor, the direction the electric motor shaft is certainly turning, the torque the motor provides to lots and any other electric motor parameter which can be sensed. These VFDs are also obtainable in smaller sizes that are cost-efficient and take up much less space.
The arrival of advanced microprocessors has allowed the VFD works as an extremely versatile device that not only controls the speed of the motor, but protects against overcurrent during ramp-up and ramp-down conditions. Newer VFDs also provide ways of braking, power boost during ramp-up, and a variety of handles during ramp-down. The largest cost savings that the VFD provides can be that it can make sure that the engine doesn’t pull extreme current when it starts, therefore the overall demand factor for the entire factory can be controlled to keep the utility bill as low as possible. This feature alone can provide payback more than the price of the VFD in under one year after buy. It is important to keep in mind that with a normal motor starter, they will draw locked-rotor amperage (LRA) when they are Variable Speed Drive Motor beginning. When the locked-rotor amperage takes place across many motors in a manufacturing facility, it pushes the electrical demand too high which frequently outcomes in the plant having to pay a penalty for all the electricity consumed through the billing period. Because the penalty may be just as much as 15% to 25%, the cost savings on a $30,000/month electric expenses can be used to justify the purchase VFDs for practically every motor in the plant even if the application may not require functioning at variable speed.
This usually limited how big is the motor that could be managed by a frequency and 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 resistors into circuits with capacitors to produce different slopes.
Automatic frequency control consist of an primary electrical circuit converting the alternating current into a immediate current, then converting it back into an alternating electric current with the mandatory frequency. Internal energy loss in the automatic 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 allowing the volume of air moved to complement the system demand.
Reasons for employing automated frequency control can both be linked to the efficiency of the application and for conserving energy. For example, automatic frequency control can be used in pump applications where the flow is definitely matched either to volume or pressure. The pump adjusts its revolutions to a given setpoint via a regulating loop. Adjusting the circulation 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 to prominence. The AC-induction electric motor can have its velocity changed by changing the frequency of the voltage utilized to power it. This implies that if the voltage put on an AC engine is 50 Hz (found in countries like China), the motor functions at its rated quickness. If the frequency is definitely improved above 50 Hz, the electric motor will run 
faster than its rated quickness, and if the frequency of the supply voltage is definitely less than 50 Hz, the engine will run slower than its ranked speed. According to the variable frequency drive working principle, it is the electronic controller specifically designed to change the frequency of voltage supplied to the induction engine.