Today the VFD could very well be the most common kind of result or load for a control system. As applications are more complicated the VFD has the capacity to control the quickness of the motor, the direction the motor shaft can be turning, the torque the electric motor provides to a load 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 motor, but protects against overcurrent during ramp-up and ramp-down conditions. Newer VFDs also provide ways of Variable Speed Drive Motor braking, power increase during ramp-up, and a number of regulates during ramp-down. The largest savings that the VFD provides is certainly that it can make sure that the engine doesn’t pull extreme current when it begins, so the overall demand aspect for the entire factory can be controlled to keep the domestic bill only possible. This feature by itself 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 traditional motor starter, they will draw locked-rotor amperage (LRA) if they are starting. When the locked-rotor amperage happens across many motors in a manufacturing plant, it pushes the electrical demand too high which frequently results in the plant paying a penalty for all of the electricity consumed during the billing period. Because the penalty may end up being just as much as 15% to 25%, the cost savings on a $30,000/month electric expenses can be utilized to justify the buy VFDs for virtually every motor in the plant also if the application may not require functioning at variable speed.
This usually limited the size of the motor that could be controlled by a frequency plus they weren’t commonly used. The initial VFDs used linear amplifiers to control all aspects 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 make different slopes.
Automatic frequency control consist of an primary electrical circuit converting the alternating electric 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 widely used on pumps and machine device drives, compressors and in ventilations systems for large buildings. Variable-frequency motors on followers 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 features of the application and for conserving energy. For instance, automatic frequency control is used in pump applications where the flow is 
certainly matched either to volume or pressure. The pump adjusts its revolutions to confirmed setpoint via a regulating loop. Adjusting the flow or pressure to the real demand reduces power intake.
VFD for AC motors have already been the innovation that has brought the use of AC motors back into prominence. The AC-induction electric motor can have its speed changed by changing the frequency of the voltage utilized to power it. This means that if the voltage applied to an AC electric motor is 50 Hz (found in countries like China), the motor functions at its rated swiftness. If the frequency can be improved above 50 Hz, the engine will run faster than its rated rate, and if the frequency of the supply voltage is less than 50 Hz, the motor will operate slower than its ranked speed. Based on the adjustable frequency drive working principle, it’s the electronic controller specifically designed to alter the frequency of voltage provided to the induction engine.