Parallel Operation of Induction Motors of Different Pole Pair under a VFD

[danishdeshmuk]

[h=3]Parallel Operation of Induction Motors of Different Pole Pair under a VFD[/h]
What if two induction motors of different Pole Pair are connecte in Parallel to a VFD. What all should we look then. Will the system run properly ?
Ofcourse the motor speed ratings would be different.
When we enter the motor parameters we enter power, current ratings as sum of the two. But what about speed and pole pair?

 

[Jraef]

If you want Vector Control, it will not work. If simple V/Hz (Scalar) control is OK, then the VFD will not know, or care, what is connected down stream of it. There are numerous other major considerations however, starting with motor protection issues. The VFD will not be able to discrtiminate between one motor or the other, so the motor short circuit and overload protection features will become null and void and must be re-instated separately for each motor on the load side of the VFD.

Why do you ask?

 

[transient]

hi

hi

If possible can you please elaborate vector control , please ?

 

[Jraef]

If possible can you please elaborate vector control , please ?

Long, detailed subject requiring a lot of time that I don't have right now.
Assuming you already have a grasp of how a basic VFD works, here is something I cowrote a long time ago for another forum on the subject as your homework assignment. If this doesn't do it for you, post your follow up questions.

 

[weressl]

Parallel Operation of Induction Motors of Different Pole Pair under a VFD


What if two induction motors of different Pole Pair are connecte in Parallel to a VFD. What all should we look then. Will the system run properly ?
Ofcourse the motor speed ratings would be different.
When we enter the motor parameters we enter power, current ratings as sum of the two. But what about speed and pole pair?

Due to the advancement in the sophistication of the ASD's drive control modes, even with identical motors and cable lengths/configuration, multiple motor drives are less-and-less recommended.

If you really want to do that I would consult with the factory engineers directly. Not your middle-man sales "engineer" or anybody in the distribution chain.

 

[danishdeshmuk]

If you want Vector Control, it will not work. If simple V/Hz (Scalar) control is OK, then the VFD will not know, or care, what is connected down stream of it. There are numerous other major considerations however, starting with motor protection issues. The VFD will not be able to discrtiminate between one motor or the other, so the motor short circuit and overload protection features will become null and void and must be re-instated separately for each motor on the load side of the VFD.

Why do you ask?

It means all the VFD's control method would be v/f , right ?

IF the motors have encoders then would we still use v/f control method for all drives connected to these motors ?