Today the VFD could very well be the most common type of result or load for a control program. As applications become more complex the VFD has the capacity to control the quickness of the motor, the direction the electric motor shaft is turning, the torque the electric motor provides to a load and any other electric motor parameter which can be sensed. These VFDs are also available in smaller 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 only controls the speed of the engine, but protects against overcurrent during ramp-up and ramp-down conditions. Newer VFDs provide ways of braking, power boost during ramp-up, and a variety of controls during ramp-down. The largest savings that the VFD provides is definitely that it can make sure that the motor doesn’t pull excessive current when it begins, so the overall demand element for the whole factory could be controlled to keep carefully the utility bill as low as possible. This feature only can provide payback in excess of the price of the VFD in less than one year after buy. It is important to keep in mind 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 facility, it pushes the electrical demand too high which frequently outcomes in the plant spending a penalty for all the electricity consumed through the billing period. Since the penalty may become just as much as 15% to 25%, the cost savings on a $30,000/month electric bill can be utilized to justify the purchase VFDs for virtually every engine in the plant even if the application form may not require operating at variable speed.
This usually limited the size of the motor that may be controlled by a frequency and they weren’t commonly used. The earliest VFDs used 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 contain an primary electric circuit converting the alternating electric current into a immediate current, after that converting it back into an alternating electric current with the required frequency. Internal energy loss 
in the automatic frequency control is rated ~3.5%
Variable-frequency drives are trusted on pumps and machine device 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 functionality of the application form and for saving energy. For example, automatic frequency control can be used in pump applications where the flow is matched either to quantity or pressure. The pump adjusts its revolutions to a given setpoint with a regulating loop. Adjusting the movement or Variable Speed Drive Motor pressure to the real demand reduces power usage.
VFD for AC motors have already been the innovation which has brought the use of AC motors back to prominence. The AC-induction motor can have its quickness changed by changing the frequency of the voltage utilized to power it. This implies that if the voltage applied to an AC electric motor is 50 Hz (found in countries like China), the motor works at its rated quickness. If the frequency is certainly increased above 50 Hz, the engine will run quicker than its rated speed, and if the frequency of the supply voltage is certainly significantly less than 50 Hz, the motor will operate slower than its rated speed. According to the adjustable frequency drive working principle, it is the electronic controller particularly designed to change the frequency of voltage provided to the induction motor.