Today the VFD is perhaps the most common kind of result or load for a control program. As applications are more complicated the VFD has the capacity to control the acceleration of the Variable Drive Motor electric motor, the direction the motor shaft can be turning, the torque the engine provides to lots and any other electric motor parameter which can be sensed. These VFDs are also obtainable in smaller sizes that are cost-effective 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 motor, 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 savings that the VFD provides is that it can ensure that the electric motor doesn’t pull extreme current when it begins, so the overall demand aspect for the whole factory could be controlled to keep the utility bill only possible. This feature only can provide payback more than the cost of the VFD in less than one year after purchase. 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 outcomes 
in the plant paying a penalty for all the electricity consumed through the billing period. Since the penalty may end up being as much as 15% to 25%, the financial savings on a $30,000/month electric costs can be used to justify the purchase VFDs for virtually every electric motor in the plant even if the application may not require functioning at variable speed.
This usually limited how big is the motor that may be controlled by a frequency plus they were not commonly used. The earliest VFDs utilized linear amplifiers to control all areas 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 create different slopes.
Automatic frequency control contain an primary electrical circuit converting the alternating electric current into a immediate current, after that converting it back into an alternating current with the mandatory frequency. Internal energy loss in the automated frequency control is ranked ~3.5%
Variable-frequency drives are widely used on pumps and machine device drives, compressors and in ventilations systems for huge buildings. Variable-frequency motors on followers save energy by enabling 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 form and for saving energy. For example, automatic frequency control is utilized in pump applications where the flow is definitely matched either to volume or pressure. The pump adjusts its revolutions to confirmed setpoint with a regulating loop. Adjusting the circulation or pressure to the real demand reduces power consumption.
VFD for AC motors have already been the innovation that has brought the use of AC motors back into prominence. The AC-induction motor can have its rate changed 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 (used in countries like China), the motor works at its rated acceleration. If the frequency is improved above 50 Hz, the engine will run quicker than its rated speed, and if the frequency of the supply voltage is usually significantly less than 50 Hz, the electric motor will operate slower than its rated speed. According to the variable frequency drive working principle, it’s the electronic controller particularly designed to change the frequency of voltage supplied to the induction engine.