Dear Kai,

Thanks for your kind reply,

Perhaps an intelligent machine? Starting with a fix table and then adding correction data, after measuring actual current they had with fix table data?

Yes these controllers are certainly very intelligent and they seem to be updating their data continuously.

If the caliberation firing angles are fixed by the controller and are not modifiable by user does the risk you mentioned do exist. If my controller always fire three positions maximum, minimum and middle and measure currents to calculated the polynomial co-efficient?

Antoher trap is rounding errors of calculation of coefficients. There are certain situations, where higher precision is needed than expected, otherwise the coefficients can look very strange. So, calculation of coefficients can be troublesome.

Thats true, Thanks for this helpful note.

In your situation I would first try to improve the table entries. Check, whether the deviations are from mains distortion or voltage dips. If everything is checked out, then your table will very probably compensate all machine typical effects. Then you should try the whole stuff at a total different location, maybe a factory of friends, where you can check your machine again. Then, there should not develop further deviations.

On Monday I will move my setup to another city 'Surat' for trials on a seam welding machine. I will measure the currents attained and calculated and will post the table here. Surat is 250Km from Mumbai :)

Regards,
Prahlad Purohit