High Power Vsds In Parallel

[joze]

Hello all!

 

Does anybody have any experience in running many VSDs (high power) in parallel?

 

Problem: harmonic distrortion. Somebody gave me an idea of connecting VSDs in such way that phases between different VSDs would be "reversed" and harmonic distortion of one VSD would cancel another one.

 

Any comments?

 

Thank you very much

 

joze

[jraef]

What you are describing is the basic principal behind what is called a "12 pulse" drive topology, but it is not nearly as simple as that. For one thing, it is not necessary to have two entire VFDs in parallel, just two separate front-end converters. But they need to have a phase shift between them, usually done by having a Delta Wye transformer on one supply, and a Wye-Wye transformer on the other. Furthermore 12 pulse topology does not completely eliminate harmonics on it's own, it just reduces them, making filters etc. less expensive. The also make 18 pulse and 24 pulse front ends as well, all in an attempt to mitigate harmonics.

 

If you do a net search on the term "12 pulse VFD" you will find a lot of information on that topic.