Futterama said:But Lebowski, if you seperate the 12 FET in the second picture, you get two 6 FET, but then you connect them with a wire the same place you just cut the busbar. To me, it seems like it's the same thing.
Did you see my picture where I split it up? If that is series connected, then you have to show me the parallel connection cause I can't image it then.Lebowski said:Yeah but you make 'm star connected (so parallel to a common point), while what you suggest is series connected...
In what kind of situation would that happen?Lebowski said:...maybe some inductance in the power supply wire going to each individual stage would be a good thing, it helps the case where for instance some current from phase A in one 6FET wants to go out via the B and C of another 6 FET...
Tja, I got the feeling Murphy has a big interest in ebikes, his law seems to apply everywhere.Futterama said:In what kind of situation would that happen?Lebowski said:...maybe some inductance in the power supply wire going to each individual stage would be a good thing, it helps the case where for instance some current from phase A in one 6FET wants to go out via the B and C of another 6 FET...
In my round design, the 3 low side FETs are sitting right next to each other, and so do the 3 high side FETs. The inductance I tried to calculate here: http://endless-sphere.com/forums/viewtopic.php?p=848585#p848585Lebowski said:Tja, I got the feeling Murphy has a big interest in ebikes, his law seems to apply everywhere.
The unequal current sharing is possible in theory so it'll probably happen. Inductance in the lines to
the common power star-point will help to prevent it, so having some is a good thing.
For equal resistance and inductance in the busbar, yes, I see why you mention this.Lebowski said:Just looked again at your picture, I would swap one of the 6 FETs such that both have phase A close
to the power point and phase C furthest away...
Lebowski said:It will however not solve the higher inductance you get when making the whole
structure longer for parallelling FETs. You still have all the motor currents running
between the phase wires, first in one copper busbar plate and all switching over to
the othe busbar plate in the other half of the PWM cycle. The caps don't help against
this, however artfully you arrange them.
liveforphysics said:Most triple phase-leg modules before this generation just have a single power input point, which makes it almost impossible to balance inductance. It seems industry is picking up on the design advantages (cap placement options, balanced paths, etc) we're discussing in this thread.
http://ixapps.ixys.com/DataSheet/MTI145WX100GC.pdf
Or how about something like this... For a little more.... http://www.pwrx.com/Product/PM600CLA060liveforphysics said:With respect to cap placement, and balanced inductance layout, you will notice on the new IXYS triple phase-leg modules give you the input high current leads in 3 separate sections with even spacing adjacent from each bridge's output pins. Most triple phase-leg modules before this generation just have a single power input point, which makes it almost impossible to balance inductance. It seems industry is picking up on the design advantages (cap placement options, balanced paths, etc) we're discussing in this thread.
http://ixapps.ixys.com/DataSheet/MTI145WX100GC.pdf
they sky's the limitOr how about something like this... For a little more.
I basically agree with you guys, closer together is better so thin twisted magnet wire is better than the thick isolated stuff i used in the first post.Futterama said:Punx0r, yes, you are right about the fact that twisting them also increases wire length, so it is actually better to have them parallel. I don't expect common-mode noise to be an issue in a gate drive.
If twisting is only for keeping the wires close together, there are other ways to do that, like shrink tube or wire mesh and these methods would not increase wire length as twisting does.
Lebowski, please comment on this