Today the VFD could very well be the most common type of result or load for a control program. As applications become more complicated the VFD has the capacity to control the speed of the electric motor, the direction the motor shaft can be turning, the torque the electric motor provides to a load and any other electric motor parameter that 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 merely 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 enhance during ramp-up, and a variety of settings during ramp-down. The biggest savings that the VFD provides is definitely that it can make sure that the electric motor doesn’t pull excessive current when it begins, so the overall demand aspect for the entire factory could be controlled to keep the utility bill as low as possible. This feature by itself can provide payback in excess of the cost of the VFD in under one year after buy. It is important to keep in mind that with a normal motor starter, they’ll draw locked-rotor amperage (LRA) when they are beginning. When the locked-rotor amperage takes place 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 every one of the electricity consumed through the billing period. Because the penalty may be as much as 15% to 25%, the financial savings on a $30,000/month electric expenses can be utilized to justify the buy VFDs for virtually every Variable Drive Motor engine in the plant even if the application may not require operating at variable speed.
This usually limited the size of the motor that may be controlled by a frequency plus they were not commonly used. The initial VFDs utilized linear amplifiers to control 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 develop different slopes.
Automatic frequency control consist of an primary electric circuit converting the alternating electric current into a immediate current, then converting it back to an alternating electric current with the mandatory frequency. Internal energy loss in the automatic frequency control is rated ~3.5%
Variable-frequency drives are trusted on pumps and machine tool drives, compressors and in ventilations systems for large buildings. Variable-frequency motors on followers save energy by permitting the volume of atmosphere moved to complement the system demand.
Reasons for employing automatic frequency control can both be linked to the efficiency of the application form and for saving energy. For instance, automatic frequency control can be used in pump applications where the flow can be matched either to quantity or pressure. The pump adjusts its revolutions to a given setpoint with a regulating loop. Adjusting the flow or pressure to the actual demand reduces power consumption.
VFD for AC motors have been the innovation which has brought the use of AC motors back to prominence. The AC-induction engine can have its swiftness transformed by changing the frequency of the voltage used to power it. This means that if the voltage applied to an AC motor is 50 Hz (found in countries 
like China), the motor functions at its rated acceleration. If the frequency is usually increased above 50 Hz, the motor will run faster than its rated quickness, and if the frequency of the supply voltage is less than 50 Hz, the engine will operate slower than its rated 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 motor.