Just like the soft starter, a Variable frequency drive (VFD) can vary the voltage as well as the frequency of the supplying current. It is mainly used for controlling the speed of the induction motor as it depends on the supply frequency.
The AC from the supply line is converted into DC using rectifiers. The pure DC is converted into AC with adjustable frequency & voltage using pulse width modulation technique through power transistor like IGBTs.
It provides full control over the motor speed from 0 to rated speed. The speed adjust option with the variable voltage provides a better starting current & acceleration.
Advantages of Variable Frequency Drive
- It provides a better and smooth acceleration for large motor
- It offers full speed control with smooth acceleration & deceleration.
- It increases the life span due to the absence of electrical & mechanical stress
- It offers forward & reverse operation of a motor
Disadvantages of Variable Frequency Drive
- It is relatively expensive unless speed control is necessary
- There is heat dissipation
- VFDs create harmonics in the electric lines which can affect electronic equipment & power factor.
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