V/f profile and current drawing

[abfer]

1- How does the current change with a 3ph induction motor which is drived in v/f principle and unloaded?

2- I'm trying to determine a v/f profile for a delta connected motor. But i couldn't be able to find a good profile. Due to dead time it's not good at very low frequencies. As frequency goes up it smoothes but at some frequencies it begins to vibrate. If i increase voltage it begins to stabilize but current also rises and a noise sounds up like it's forced. If i decrease voltage at the same frequency, it stabilizes again but torque output reduces dramatically.

3-Sometimes when i increase the frequency by 1 Hz, it suddenly stucks and continues to revolve.

What may be the reason of these? How should i create a v/f profile? All my tests are held while the motor is unloaded by the way.

 

[Skogsgurra]

Yes - and no.

As you know, the name of the site is Eng-Tips. Which infers that engineers exchange tips within their respective field of expertise. And that's the way it works best.

I now understand that you are in the category "Learning by doing" and that is not quite what these fora are there for. Learning by doing means that you do lots of mistakes, find out what the mistakes are and correct them. The finding out process mostly means using instruments like oscilloscopes, DMMs, logic analyzers and the likes.

It also means that you gradually master the physics and mathematics behind the different parts of the system. What you have set out to do is quite complex and it also involves dangerous voltages and power levels. Such projects require formal training and lots of practice.You cannot get that here and you will soon find that the members stop answering your questions. Sometimes because you overtax their benevolency, sometimes perhaps out of pure exhaustion.

Learning about frequency inverters is good - really good. It is among the best things an electric engineer can undertake to stay competitive in the market. But I think that a good text-book or a good engineering course will take you to the goal a lot faster than repeated postings here.

I do not write this to discourage you. More to set you off in the right direction. Also, I am worried about the shock and fire risks that you expose yourself and your vicinity to.



Gunnar Englund

http://www.gke.org

 

[CJCPE]

Skogsgurra has made some good comments. I have also had some concerns about what you are trying to do and how you are trying to do it. Part way through the above discussion, I realized that some of the discussion seemed familiar and looked for your previous posts. Your previous explanations make your project seem more reasonable. The fact that you have progressed to the point that you have successfully turned a shaft tells me that you are more qualified to undertake this project that I might have suspected from some of your questions.

I hope that others here continue to be willing to help you.

 

[electricuwe]

abfer, for several months you are continously asking question on operation of induction motors on VFDs in this forum. I would stronlgy recommend to read some basic books or conference papers on that and to use this forum only to discuss question going beyond the basics.