Folks,

I need help.

I am an engineer working on an oil project and I am doing studies in harmonic distortion on a power system. We have got some big three-phase heater banks with phase controlled thyristors. I have been searching the internet for information on the spectrum of harmoic currents vs. firing angle, or, failing that, maximum values of harmonic currents over the whole range of firing angles. I have drawn a blank. So I have gone back to first principles and started doing some sums based on Fourier analysis. But it has been about 35 years since I did this sort of calculus and I feel a bit out of my depth.

I have attached two documents: one summarising the maths and the other a spreadsheet cacluating the harmonics. I would like some verification that the methodology is ok.

regards


David Bamber

 

Attached pdf includes some harmonic analysis of single phase controlled AC regulator.

It presumably get's more complex with 3-phase systems.

 

Thanks TNK for the pdf file with lesson #28. The methodology described is suitable for 3 phase systems' analysis since balanced three-phase systems are normally analyzed as single phase equivalents anyway. The main difference between the method given in #28 paper and the one chosen by me appears to be in the reduction of the trigonometric terms (before integration) to forms that are more easily integrable. I used an integration by parts metghod (because that was the form that I first found on the web) and lesson #28 uses a trigonometric identity. The results should be the same anyway but I will check my maths since I now have something more authoritative to check against.

The paper states that the final results providing the harmonic spectrum are given in lesson #26. Do you have a copy?

regards

David

 

The entire series of lessons is available here ...

http://nptel.iitm.ac.in/courses/Webcourse-contents/IIT%20Kharagpur/Power%20Electronics/PDF/

Good to hear you are reviving the old skills.

Perhaps another more direct approach is to use the Fast Fourier Transform of the phase controlled function. It can be done in Excel or you could use Matlab or a comparable application.

I was able to generate the harmonics graph in the lesson #26 fairly quickly using Scilab.