VFD uses less frequency to control the speed.But when the frequency decreases, the current will increase.There is a chance that the current may go beyond the rated current .Then how VFD is an option for speed control??

 

VFD uses less frequency to control the speed.But when the frequency decreases, the current will increase.There is a chance that the current may go beyond the rated current .Then how VFD is an option for speed control??

You're right. Nobody should ever use a VFD because nobody knows about the speed/current response curves of electric motors. That includes the manufacturers of the VFD drives. They were just guessing.

 

Pulse Width Modulation.

Read about it.