Variable Frequency Drives

Variable Frequency Drives

Q. Variable Frequency Drives

1. The VDF operates on a very simple principle. 
2. The rotational speed of an AC induction motor depends on the number of poles in that stator and the frequency of the applied AC power.
3.  Although number of poles in an induction motor cannot be altered easily, variable speed can be achieved through changes in frequency.
4.  The VFD changes standard 50 cycle AC line power to DC, then converts the DC to a variable frequency AC output. Motors connected to VFD provide variable speed mechanical output with high efficiency. 
5. These devices are capable of upto a 9 : 1 speed reduction ratio (11 percent of full speed) and a 3:11 speed increase (300 percent of full speed).
6.  In recent years, the use of digital microprocessor control, along with high switching frequency IGBTs (insulated Gate Bipolar Transistors) power devices for variable frequency drives (VFD) has evolved largely.
7. The two most significant benefits from the evolution in technology have been that of cost and reliability, in addition to the significant reduction in physical size.