
Quasi variable frequency soft start method!
#1
Posted 05 September 2003 - 12:05 PM
There is no changes in a power schematics, only in software algorythm... Why no one do not realize this starting mode in their production???
#2
Posted 05 September 2003 - 05:41 PM
You cannot change the output frequency without changing the power structure. Phase-angle fired SCRs are gated on, but are self commutating so the frequency output will always be the same as the fundamental. Anything else would be a VFD.
If what you are thinking of is a GTO (Gate Turn Off ) thyristor system, we refer to those as 6-step or Current Source inverters. Load Commutated Inverters are frequently used for soft starting large loaded motors, but again, we consider those to be Drives, not soft starters.
If you know of something new, let us know! We would love to here it. I see nothing in their website (English version) that mentions this. Being that most of us are Anglophiles, we would love to see a translation.
#3
Posted 05 September 2003 - 08:38 PM
I think that AB were using this technique for their creep speed option some years ago, not sure, just a suspiscion.
Best regards,
Mark Empson | administrator
Skype Contact = markempson | phone +64 274 363 067
LMPForum | Power Factor | L M Photonics Ltd | Empson family | Advanced Motor Control Ltd | Pressure Transducers | Smart Relay | GSM Control | Mark Empson Website | AuCom | Soft Starters
#4
Posted 06 September 2003 - 10:14 AM

And one more image... This is quasi VF start method phase voltage diagramm

As we see the current frequency can be chanhed by fixed values... 1, 2, 3, 4, 5, 6, 7, 8, 10, 12, 17, 25 Hz... while voltage frequency is still 50 Hz...
I think that it is usefull method... I am waiting your comments!!!
;f;
#5
Posted 06 September 2003 - 10:31 AM
Yes, this is a form of cycloconverter as in my last post.
If you go a stage further and add SCR from each phase input to all phase outputs, i.e. 9 sets of SCRs, you have a full blown cycloconverter and can have a much better control over the pseudo frequency. The frequency is reduced by this method, but it has effectively a 50Hz carrier so ther frequncies that can be synthesised are limited, especially when you only use three SCR sets.
Best regards,
Mark Empson | administrator
Skype Contact = markempson | phone +64 274 363 067
LMPForum | Power Factor | L M Photonics Ltd | Empson family | Advanced Motor Control Ltd | Pressure Transducers | Smart Relay | GSM Control | Mark Empson Website | AuCom | Soft Starters
#6
Posted 06 September 2003 - 09:43 PM
#7
Posted 08 September 2003 - 01:23 AM
Not sure if they will ever get this one off the ground. Take a look at;
http://www.acdrives.com/tec.htm
The same message has been posted for over 12 months now. No joy in obtaining further information.
Regards,
GGOSS
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