VFD DC Link Choke?

LMAO

Senior Member
Location
Texas
I have seen a lot of high power (+1000HP) VFD systems (Alstom, Siemens, Yaskawa, AB, etc.) and most of them do not use a DC Link inductor (choke). But some require placing a swinging choke in between rectifier and inverter to reduce DC ripple and line harmonics.
How/why some manufacturers don't use the DC link inductor? How do they compensate for not using it?
Thanks
 

LMAO

Senior Member
Location
Texas
Effectively, their product looks less expensive that way.
They don't, really. Instead, they simply say it is the responsibility of the customer to provide something.
this was my perception as well; smaller size and lower cost in return for more harmonics and shorter capacitor life cycle (due to ripple voltage).
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
It's basically a tradeoff between the cost of capacitors vs the cost of iron and copper. For the Japanese and some of the biggies like Siemens who actually MAKE capacitors, it's often cheaper for them to use their own components. For others who have to BUY the capacitors from their competitors, it's often cheaper to wind some copper around some iron. The choke then comes with other benefits, but many of those go unappreciated because most people just look at price first.

FYI, for A-B if you are referring to MV drives, they are Current Source Inverters, there is no benefit to a DC choke on those.
 

Besoeker

Senior Member
Location
UK
D'oh!
Don't know what I was thinking.... slightly different purpose, same device though.
Happens to us all from time to time.
We used to build inverters from component level*. Mostly voltage source but we did dabble with a couple of current source units.
*We still do from time to time for applications where there is no standard unit available to do what we want it to do.
 

LMAO

Senior Member
Location
Texas
A bit more information:



Note that the current, I, is constant.
There are no IGBTs on the inverter side; all diodes. So how are they controlling the load voltage and frequency? What kind of inverter is this?
Am I missing something here?

edit: never mind, I found them, S1-S6. Should have looked harder.
 
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