Today the VFD is perhaps the most common type of result or load for a control system. As applications become more complicated the VFD has the capacity to control the acceleration of the engine, the direction the electric motor shaft is usually turning, the torque the motor provides to lots and any other engine parameter which can be sensed. These VFDs are also obtainable in smaller sizes that are cost-effective and take up much 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 electric motor, but protects against overcurrent during ramp-up and ramp-down conditions. Newer VFDs also provide ways of braking, power boost during ramp-up, and a number of settings during ramp-down. The largest savings that the VFD provides can be that it can make sure that the electric motor doesn’t pull extreme current when it starts, so the overall demand element for the entire factory could be controlled to keep carefully the utility bill as low as possible. This feature by itself can provide payback in excess of the price of the VFD in less than one year after purchase. It is important to remember that with a traditional motor starter, they’ll draw locked-rotor amperage (LRA) when they are beginning. 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 spending a penalty for all the electricity consumed through the Variable Speed Gear Motor billing period. Since the 
penalty may become as much as 15% to 25%, the savings on a $30,000/month electric expenses can be utilized to justify the buy VFDs for virtually every electric 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 managed by a frequency and they were not commonly used. The initial 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 create different slopes.
Automatic frequency control consist of an primary electric circuit converting the alternating electric current into a immediate current, after that converting it back into an alternating electric current with the mandatory frequency. Internal energy loss in the automated frequency control is rated ~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 enthusiasts 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 efficiency of the application and for conserving energy. For instance, automatic frequency control is utilized in pump applications where in fact the flow is usually matched either to quantity or pressure. The pump adjusts its revolutions to confirmed setpoint with a regulating loop. Adjusting the stream or pressure to the real demand reduces power usage.
VFD for AC motors have been the innovation which has brought the usage of AC motors back to prominence. The AC-induction engine can have its swiftness transformed by changing the frequency of the voltage utilized to power it. This implies that if the voltage applied to an AC electric motor is 50 Hz (used in countries like China), the motor works at its rated quickness. If the frequency can be increased above 50 Hz, the electric motor 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. Based on the variable frequency drive working theory, it is the electronic controller specifically designed to alter the frequency of voltage provided to the induction engine.