Today the VFD is perhaps the most common type of output or load for a control program. As applications are more complex the VFD has the ability to control the quickness of the motor, the direction the engine shaft can be turning, the torque the engine provides to a load and any other electric motor parameter which can be sensed. These VFDs are also obtainable in smaller sized sizes that are price-effective and take up much 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 motor, but protects against overcurrent during ramp-up and ramp-down conditions. Newer VFDs provide methods of braking, power increase during ramp-up, and a number of settings during ramp-down. The largest savings that the VFD provides is that it can ensure that the engine doesn’t pull extreme current when it starts, therefore the overall demand element for the whole factory can be controlled to keep the utility bill only possible. This feature by itself can provide payback more than 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 occurs across many motors in a manufacturing facility, it pushes the electrical demand too high which often results in the plant paying a penalty for all the electricity consumed during the billing period. Because the penalty may become as much as 15% to 25%, the savings on a $30,000/month electric expenses can be used to justify the purchase VFDs for virtually every engine in the plant even if the application may not require working at variable speed.

This usually limited the size of the motor that could be controlled by a frequency plus they were not commonly used. The earliest VFDs used linear amplifiers to regulate all areas of the VFD. Jumpers and dip switches were used provide ramp-up (acceleration) and ramp-down (deceleration) features by switching bigger or smaller resistors into circuits with capacitors to create different slopes.

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