Today the VFD is perhaps the most common kind of output or load for a control program. As applications are more complicated the VFD has the capacity to control the speed of the electric motor, the direction the electric motor shaft is Variable Drive Motor turning, the torque the electric motor provides to a load and any other engine 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 methods of braking, power increase during ramp-up, and a number of controls during ramp-down. The largest financial savings that the VFD provides can be that it can make sure that the electric motor doesn’t pull excessive current when it starts, so the overall demand element for the entire factory could be controlled to keep carefully the domestic bill as low as possible. This feature alone can provide payback more than the cost of the VFD in under one year after purchase. It is important to remember that with a traditional motor starter, they will draw locked-rotor amperage (LRA) if they are beginning. When the locked-rotor amperage happens across many motors in a manufacturing plant, it pushes the electrical demand too high which often results in the plant paying a penalty for every one of the electricity consumed through the billing period. Because the penalty may become just as much as 15% to 25%, the cost savings on a $30,000/month electric costs can be used to justify the purchase VFDs for practically every engine in the plant also if the application form may not require working at variable speed.
This usually limited the size of the motor that could be controlled 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 utilized 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 contain an primary electrical circuit converting the alternating current into a direct current, then converting it back to an alternating electric current with the required frequency. Internal energy loss in the automatic frequency control is ranked ~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 supporters save energy by allowing the volume of air flow moved to match the system demand.
Reasons for employing automatic frequency control may both be related to the functionality of the application and for saving energy. For instance, automatic frequency control can be used in pump applications where in fact the flow is definitely matched either to quantity or pressure. The pump adjusts its revolutions to confirmed setpoint with a regulating loop. Adjusting the flow 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 into prominence. The AC-induction electric 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 motor is 50 Hz (found in countries like China), the motor works at its rated acceleration. If the frequency can be increased above 50 Hz, the motor will run quicker than its rated speed, and if the frequency of the supply voltage is definitely less than 50 Hz, the engine will operate slower than its rated speed. Based on the variable frequency drive working basic principle, it’s the electronic controller specifically designed to modify the frequency of voltage supplied to the induction engine.