Today the VFD is perhaps the most common kind of output or load for a control system. As applications become more complicated the VFD has the ability to control the speed of the Variable Drive Motor electric motor, the direction the motor shaft is usually turning, the torque the 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 exceptionally 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 enhance during ramp-up, and a variety of settings during ramp-down. The biggest financial savings that the VFD provides can be that it can make sure that the electric motor doesn’t pull extreme current when it begins, therefore the overall demand factor for the whole factory could be controlled to keep the utility bill only possible. This feature alone can provide payback in excess of the cost of the VFD in less than one year after buy. It is important to remember that with a traditional motor starter, they’ll draw locked-rotor amperage (LRA) if they are beginning. When the locked-rotor amperage happens across many motors in a manufacturing 
facility, it pushes the electric demand too high which often outcomes in the plant paying a penalty for all of the electricity consumed during the billing period. Since the penalty may become just as much as 15% to 25%, the savings on a $30,000/month electric bill can be used to justify the buy VFDs for practically every motor in the plant actually 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 and they were not commonly used. The earliest VFDs used linear amplifiers to regulate all aspects 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 generate different slopes.
Automatic frequency control consist of 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 reduction in the automated frequency control is rated ~3.5%
Variable-frequency drives are trusted on pumps and machine tool drives, compressors and in ventilations systems for huge buildings. Variable-frequency motors on fans save energy by permitting the volume of air 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 utilized in pump applications where in fact the flow is matched either to volume or pressure. The pump adjusts its revolutions to confirmed setpoint with a regulating loop. Adjusting the stream or pressure to the actual demand reduces power consumption.
VFD for AC motors have already been the innovation which has brought the use of AC motors back into prominence. The AC-induction electric motor can have its speed transformed by changing the frequency of the voltage used to power it. This means that if the voltage applied to an AC motor is 50 Hz (used in countries like China), the motor works at its rated velocity. If the frequency is usually improved above 50 Hz, the motor will run faster than its rated acceleration, and if the frequency of the supply voltage is usually less than 50 Hz, the motor will operate slower than its rated speed. Based on the adjustable frequency drive working theory, it’s the electronic controller particularly designed to modify the frequency of voltage supplied to the induction engine.