Paralleling VFD outputs to one motor 1

[Billgas]

For capacity reasons can two (or more) VFD outputs be tied to a common bus and then used to power a motor load greater than the rating of one VFD?

Any experiences?

Any manufactures doing this?

 

[DickDV]

Absolutely not! Manufacturers do put power blocks in parallel to acheive higher currents but this cannot be done in the field as very precise IGBT firing is necessary.

Did I say "NO"?

 

[itsmoked]

That would be a smoke-a-thon.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[jraef]

As DickDV said, some manufacturers do this for large drives, and some even have mid-size designs that can be "stacked" (parallel) in the field to create larger units, but they are specifically designed up-front to do this with specialized firing control systems that accommodate it. Not something that you can rig in the field. One microsecond off and your transistors release their magic smoke.




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[MAGTiger]

Couldn't this be done if a carrier stripping sinewave filter (resulting in <5%Vthd) were used on each drive, then the filter outputs be summed at the bus?

Neil

 

[LionelHutz]

Neil - Both VFD's still have to produce outputs that match each other so they need to be operating synchronized with each other. So, the short answer is no, sine wave filters would not be enough. From what I've seen, a reactor is required once the VFD output sections are synchronized.

All manufacturers use paralleled output devices in their larger VFD's. They typically have 3 IGBT output sections running in parallel. The drive will use a lower current rated 3-phase output "brick" with the 3 output sections paralleled. Paralleling drives can be looked at as an extension of this practice. Some extra precautions are needed such as reactors because of the lead lengths between drives.

 

[roydm]

I guess you could somehow use the firing circuit of one VFD to fire the transistors in both but that would be a major exercise.
Roy

 

[Guardiano]

I believe the answer is still NO for two identical VFDs.

Guardiano

 

[Phaneas]

For example KEB has Master-Slave units, but the only reason is, they do not have bigger converters and to supply converter at higher power range they are coupling them together