Question

What is the working principle of VFD?

Answer 1

When AC (Alternating current) motors were first introduced by Tesla it was considered more reliable than DC motors. However, AC motors speed control requires some important conditions to be fulfilled. That it has to either vary the magnetic flux or change the number of poles. Therefore changing the frequency of the speed controls remained an extremely difficult task. And then this VFD (variable-frequency drive) came into play. Let us see the working principle of this VFD.

Complete answer:
VFD is a type of motor controller whose work is to drive an electric motor by varying the frequency and also the voltage supplied to the electric motor.
The working principle of the variable-frequency drive mainly depends upon the adjustable speeds and soft start or soft stop capabilities. These two important features make the variable-frequency drive a powerful controller to control AC motors.

Additional Information:
There are numerous variations in the design in which the VFDs are created. However, the main work of the VFD is to convert the incoming electrical supply of fixed frequency and voltage into a variable frequency and variable voltage. This refers to the output to the motor with a corresponding change in the motor speed and torque. The variation in the average speed of the motor can be varied from zero rpm, to $100 - 120\%$of its full rated speed.

Note:
There are four important sections in the variable frequency drive. Those important sections include a rectifier, intermediate DC link, inverter, and controlling circuit. This variable frequency drive not only offers variable speeds that can be adjusted but also can provide numerous benefits in terms of process control and conservation of energy.