igbt H bridge current regulator. noobish

[psychosteve]

ok so i get this fantastic idea to make a new case for my amp, got some 5mm alu plate from work, go to tig weld it and PUFFFF, welder goes up in smoke. boss says well we dont use it so i aint replacing it, chuck it in the skip!

well, i aint gona do that so in the back of the truck it goes.

now i go through it and strip it down, not much left, good transformer, and the bridge rectifier, thats about it.

what i need help with is an ac current regulator, i was goin to use op amps to generate an adjustable freq. square wave with adjustable duty cycle 50% to 99% witch is what i need, and can just about design myself, but how to get that to regulate dc current, i was looking at some igbt H bridge modules or single igbt transistors that will hold the current. but i need the voltage to fluctuate and only regulate the current, adjustably upto 150amps!!

any help at all greatly appreciated, cheers, steve.

[psychosteve]

any one??

even a "go look at this site noob!!"

cheers guys, steve.

[S.G. Mahbub]

Do you have any idea how current is controlled in modern smps based welding machine? Slightest idea- theoretical knowledge? In conventional AC welding machine, current is controlled by wire wound resistor/inductor. But the system is bulky and inefficient. I have studied one Chinese Heavy Welding Machine, where current is controlled through saturable core transformer. Hope, you can put some light on it.
With thanks.

____________________________________________
IDEAS ARE MONEY IF THEY CAN BE USED ON GROUND.
বাস্তবে ব্যবহারযোগ্য চিন্তাধারাই মানুষের প্রকৃত সম্পদ।

[Eva]

They use average-current mode loops (search the forum and google for documents on that subject). Primary side current is usually sensed with transformers and secondary side current with shunts. An input or output inductor is also required in order to limit di/dt and allow the control loop to operate (depends on topology).

Anyway, this is not an easy job. Consider repairing the welder rather than redesigning it.

[S.G. Mahbub]

Dear steve,
Want to know something practical from you. You are a brave man, I must admit. Instead of purchasing a new one, you ventured to construct/ make one with modern smps route. It is like the soldiers, who prefer to fight and die in the battlefield, rather than showing the back and flee away from the battle field to the safe home and enjoying a cowardice life-which is adopted by most. I like the spirit.

It is easier to control an instrument which require to control 1or 2 parameters, rather than the welding machine, which require min. voltage and variable current.

However, I have formulated a system to control current and it will be put for your comment shortly. By the time let me see your practical oriented suggestion -if any.

____________________________________________
IDEAS ARE MONEY IF THEY CAN BE USED ON GROUND.
বাস্তবে ব্যবহারযোগ্য চিন্তাধারাই মানুষের প্রকৃত সম্পদ।

[golam]

Dear s.g. mahbub,
Please put forward your plan for current control. I think it is easier if you try to control using backyard parameter, that is first controlling the Mains AC through Phase Angle Control with Microcontroller and then finally use a modality for final and finer regulation.
Thanks.

[alexnwolf]

you can use transistors to control your current and use some feedback to modify the gate voltage to hold the current per the varying voltage