Today the VFD could very well be the most common type of output or load for a control system. As applications are more complicated 
the VFD has the capacity to control the rate of the engine, the direction the engine shaft can be turning, the torque the engine 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-effective and take up less space.
The arrival of advanced microprocessors has allowed the VFD works as an exceptionally 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 improve during ramp-up, and a variety of settings during ramp-down. The biggest cost savings that the VFD provides can be that it can make sure that the motor doesn’t pull extreme current when it starts, therefore the overall demand factor for the whole factory could be controlled to keep carefully the utility bill only possible. This feature by itself can provide payback more than the cost of the VFD in less than one year after purchase. It is important to remember that with a traditional motor starter, they will draw locked-rotor Variable Drive Motor 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 often results in the plant spending a penalty for all the electricity consumed during the billing period. Because the penalty may be just as much as 15% to 25%, the cost savings on a $30,000/month electric bill can be used to justify the buy VFDs for virtually every engine in the plant actually if the application form may not require working at variable speed.
This usually limited how big is the motor that may be controlled by a frequency plus they weren’t commonly used. The initial VFDs used linear amplifiers to regulate 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 electric circuit converting the alternating current into a immediate current, then converting it back to an alternating current with the required frequency. Internal energy reduction in the automated 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 fans save energy by allowing the volume of surroundings moved to complement the system demand.
Reasons for employing automated frequency control may both be related to the efficiency of the application and for saving energy. For example, automatic frequency control is used in pump applications where in fact the flow is matched either to quantity 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 into prominence. The AC-induction motor can have its quickness transformed by changing the frequency of the voltage used to power it. This implies that if the voltage put on an AC 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 motor will run faster than its rated speed, and if the frequency of the supply voltage is definitely less than 50 Hz, the electric motor will run slower than its ranked speed. Based on the adjustable frequency drive working basic principle, it’s the electronic controller specifically designed to alter the frequency of voltage provided to the induction electric motor.