Today the VFD is perhaps the most common kind of result or load for a control system. As applications become more complicated the VFD has the capacity to control the velocity of the motor, the direction the motor shaft is certainly turning, the torque the engine provides to lots and any other engine parameter which can be sensed. These VFDs are also available in smaller sized sizes that are cost-efficient 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 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 controls during ramp-down. The biggest savings that the VFD provides can be that it can ensure that the electric motor doesn’t pull excessive current when it starts, so the overall demand factor for the whole factory can be controlled to keep carefully the domestic bill as low as 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 will draw locked-rotor amperage (LRA) when they are beginning. When the locked-rotor amperage happens across many motors in a manufacturing facility, it pushes the electrical demand too high which often results in the plant spending a penalty for all of the electricity consumed during the billing period. Because the penalty may become as much as 15% to 25%, the savings on a $30,000/month electric expenses can be utilized to justify the purchase VFDs for virtually every electric motor in the plant even if the application form may not require working 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 earliest VFDs utilized 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 develop different slopes.
Automatic frequency control consist of an primary electrical circuit converting the alternating electric 
current into a direct current, after that converting it back to an alternating current with the mandatory frequency. Internal energy loss 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 supporters save energy by Variable Drive Motor allowing 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 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 a given setpoint via a regulating loop. Adjusting the flow 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 electric motor can have its velocity changed by changing the frequency of the voltage used 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 functions at its rated velocity. If the frequency is usually improved above 50 Hz, the electric motor will run quicker than its rated velocity, and if the frequency of the supply voltage is less than 50 Hz, the motor will run slower than its ranked speed. According to the variable frequency drive working theory, it’s the electronic controller specifically designed to modify the frequency of voltage supplied to the induction motor.