Today the VFD could very well be 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 engine, the direction the engine shaft is definitely turning, the torque the engine provides to lots and any other motor parameter that 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 merely controls the speed of the motor, but protects against overcurrent during ramp-up and ramp-down conditions. Newer VFDs provide methods of braking, power boost during ramp-up, and a variety of controls during ramp-down. 
The largest financial savings that the VFD provides is certainly that it can make sure that the electric motor doesn’t pull excessive current when it begins, therefore the overall demand factor for the entire factory can be controlled to keep the domestic bill only possible. This feature by itself can provide payback more than the price of the VFD in under one year after purchase. It is important to keep in mind that with a normal motor starter, they will draw locked-rotor amperage (LRA) if they are beginning. When the locked-rotor amperage occurs across many motors in a manufacturing facility, it pushes the electric demand as well high which often results in the plant spending a penalty for every one of the electricity consumed during 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 bill can be utilized to justify the purchase VFDs for practically every electric motor in the plant also if the application may not require functioning at variable speed.
This usually limited the size of the motor that could be controlled by a frequency and they were not 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 bigger or smaller sized resistors into circuits with capacitors to develop different slopes.
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