Variable frequency drive VFD VVFD Direct torque controller DTC

What is the function of a VFD with an electric motor?

Variable frequency drive VFD is sometimes known as VVVFD is a special type of motor drive that runs an induction motor on the variable frequency and variable voltage. By varying the frequency and voltage of an induction motor, the variable motor speed is achieved. Variable frequency drive is also capable of ramping up or ramping down a motor. Ramping up and ramping down feature provides a motor soft starting and soft starting feature which is a very useful feature for an industrial motor to control starting torque and jerk on an induction motor. Also, the ramping-up feature reduces electrical jerk on the power line when a motor is started from a standstill. The following circuit diagram illustrates the basic electrical wiring for a VFD system. In this diagram single phase, AC input is shown and the VFD provides three-phase power to the delta-connected three-phase motor. There are several VFDs available that accept three-phase line power as input and provide three-phase controlled power to the three-phase induction motor to control the motor speed and torque.

VFD motor drive circuit diagram
VFD motor drive wiring circuit diagram


Why do we use a VFD with an induction motor?

Motors with variable speed use VFDs. Input power supplied to the VFD is converted from AC to DC, Smooth by filter electrolytic capacitors and then inverted back to AC power of desired voltage and frequency to run the motor with the required variable speed. VFD supplies controlled and adjustable voltage and frequency so that a variable and adjustable desired motor speed is achieved.

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