Today the VFD is perhaps the most common kind of output or load for a control system. As applications are more complex the VFD has the capacity to control the speed of the motor, the direction the motor shaft is turning, the torque the engine provides to lots and any other electric motor parameter that can be sensed. These VFDs are also obtainable 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 only controls the speed of the 
engine, but protects against overcurrent during ramp-up and ramp-down conditions. Newer VFDs also provide ways of braking, power enhance during ramp-up, and a number of controls during ramp-down. The biggest financial savings that the VFD provides is certainly that it can make sure that the motor doesn’t pull excessive current when it starts, so the overall Variable Drive Motor demand factor for the whole factory can be controlled to keep the domestic bill as low as possible. This feature alone can provide payback in excess of the price of the VFD in less than one year after purchase. It is important to keep in mind that with a traditional motor starter, they’ll draw locked-rotor amperage (LRA) if they are starting. When the locked-rotor amperage occurs across many motors in a manufacturing plant, 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 end up being as much as 15% to 25%, the cost savings on a $30,000/month electric costs can be used to justify the buy VFDs for virtually every electric motor in the plant even if the application may not require working at variable speed.
This usually limited how big is the motor that could be managed by a frequency plus they weren’t commonly used. The initial VFDs used 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 resistors into circuits with capacitors to generate different slopes.
Automatic frequency control consist of an primary electrical circuit converting the alternating current into a immediate current, after that converting it back to an alternating electric current with the mandatory frequency. Internal energy reduction in the automatic frequency control is rated ~3.5%
Variable-frequency drives are widely used on pumps and machine tool drives, compressors and in ventilations systems for huge buildings. Variable-frequency motors on supporters save energy by enabling the volume of air flow moved to match the system demand.
Reasons for employing automatic frequency control can both be related to the functionality of the application and for conserving energy. For instance, automatic frequency control is used in pump applications where in fact the flow can be matched either to volume or pressure. The pump adjusts its revolutions to confirmed setpoint with a regulating loop. Adjusting the flow or pressure to the real demand reduces power consumption.
VFD for AC motors have already been the innovation which has brought the use of AC motors back to prominence. The AC-induction motor can have its speed 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 works at its rated swiftness. If the frequency is increased above 50 Hz, the electric motor will run faster than its rated acceleration, and if the frequency of the supply voltage is less than 50 Hz, the engine will operate slower than its rated speed. Based on the adjustable frequency drive working basic principle, it is the electronic controller specifically designed to modify the frequency of voltage supplied to the induction engine.