Some questions related to Vfd ( used for controlling induction motor speed) .

[Fatima Ali]

i have some questions related to VFD ( variable frequency drive ) used for controlling the speed of induction motor .I would be thankful for your answers . My questions are following .
1) Can VFD provide smooth control of induction motor speed ?
2) How does it avoids high in rush starting currents of the induction motors ?
3) What is the function of using a microcontroller connected with the inverter ? Is it used for generating pwm ? if yes than how generated pwm controls the inverter's output ?
Kindly explain it to me based on concepts of power electronics and electronics engineering . thanks

 

[chuckey]

1. Yes
2. VFDs have got a proper ramp up to full power, so you can accelarate your motor over a wide time, say fro .5 -100 Seconds - useful for conveyor belts.
3. Because VFDs have many functions built in, they need a processor to get them, such as : speed control, max current, current ramp up time, current ramp down, emergency stop, jog, max torque, max speed, and a readout of all these parametres most which can be controlled remotely. Read a hand book for one, search on Google, there are loads of them out there.
I would think that the PWM is actually generated in a separate chip which is then divided in frequency to the output frequency and to provide the three outputs which would then be accurately phase locked.
Frank