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Author Topic: Current control for SMPS Arc Welding Machine  (Read 29439 times)
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MAXPAYNE
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« Reply #25 on: January 19, 2009, 10:54:32 10:54 »

If u r sensing current by placing CT in the primary side, then u can't accurately control output current.u can place a CT for over current protection but for accurete current controlling u have to sense the output current directly. r u using full bridge topology ?
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tAhm1D
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« Reply #26 on: January 19, 2009, 01:27:23 13:27 »

Hi abcsantosh,
What is the frequency you used? Is your test completed? What is the efficiency of your inverter? What Topology you have used? If you don't have any objection, you can post your schematic. I will also post my schematic when I finish my final tie up. Please keep up your good effort.
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abcsantosh
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« Reply #27 on: January 20, 2009, 05:02:35 05:02 »

Hi tAhm1D, I am using main fullbridge stage at 200Khz. The estimated efficiency is 80+ because of phase shifted ZVT . The topology above 1KW is of course Full Bridge. Yes, although I have tested the prototype successfully but there is still some problems. Too much noise, voltage spikes are generated. So that I am testing it at 25 % load. After correction of switching waveforms I will go to full load testing. The schematic is still on papers only. I am going to verify some basic building block. If every thing goes well sure I can. (Actually, I am developing it for commercial purpose) :-) May be I can show you photographs of test assembly.
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tAhm1D
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« Reply #28 on: January 20, 2009, 07:05:21 07:05 »

Hi abcsantosh,
Please don't disclose anything which is related to commercial interest. My Topology is also Full Bridge. I am actually interested regarding your output current control process so that for different requirement, different Amperage can be supplied to the output. Keep apprised regarding your problems/success with design parameters so that we can consult for upgrading those. Mutual help will ease our burden.
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abcsantosh
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« Reply #29 on: January 20, 2009, 08:31:28 08:31 »

Hey tAhm1D, your understanding is appreciable. We can share our knowledge. To help you, I found this Image on net. http://www.china-power.net/psta/dzkw/504/tu/yj2.bmp. Take a look at it. I think this is the best solution to fit your needs. Soon I will draw a block diagram to suggest you secondary side current sensing to connect to above mentioned Control scheme. First I will have to study it. :-)
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newboy
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« Reply #30 on: January 20, 2009, 12:35:10 12:35 »

Too much noise, voltage spikes are generated. So that I am testing it at 25 % load. After correction of switching waveforms I will go to full load testing. The schematic is still on papers only.

How do you know there are voltage spikes generated but you said 'The schematic is still on papers only' ? Do you simulate it in PC ? What software you use simulation ... hope I can learn from both of you.

Just newbie in this area Smiley
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abcsantosh
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« Reply #31 on: January 20, 2009, 02:38:08 14:38 »

newboy, voltage spikes are generated. I know because I tested and viewed it on O'scope. 'The schematic is still on papers only' - By this statement I mean schematic is not final, although I build it, test it. but, it is at conceptual level. may be I can change the part of circuit or completely change the design. I do not simulate it on PC because I don't have enough of spice simulation (Spice models of Components). You can get the SPICE Simulation Fundamentals Series by following this link. I hope it is useful for you.

http://zone.ni.com/devzone/cda/tut/p/id/5413
 
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abcsantosh
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« Reply #32 on: January 20, 2009, 03:47:37 15:47 »

During the tests, I blew up the Full bridge board. Actually it is my mistake. I am trying to improve the waveforms. In this attempt, I remove the fast turn off diodes of mosfet gates. I thought it might slow down the turn on and turn off. Attached are the Photographs of my Test Prototype.
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tAhm1D
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« Reply #33 on: January 21, 2009, 07:23:11 07:23 »

Hi,
Proper simulation of smps circuit as close to practical one is very difficult to formulate and I have not found one that useful. I have studied the schematics. Good effort. You have blown up the circuit- that means you are in the right track. It is a proverb in China that the person who has not destroyed minimum 1doz Fets and 1doz Drivers, can not earn proficiency in Full Bridge circuit in smps. I am now very confident with this type of circuit but I had  destroyed many. I find that,if properly use, this type of circuit is very reliable. You are probably testing with less power as I could see the Transformer you use is small. What type of transformer you used? EE or ETD? What is the number? One advice to you if you don't mind. When using frequency > 150 KHz, be very careful to use Flux density much less than higher flux density possible for that core and calculate turn ratio basing on that or your core will attain saturation easily and the Fets and circuit will be destroy. Another thing- when you use> 100KHz Frequency, check whether the Freewheel diodes inside the Mosfets can withstand that speed. Better to use 4 more high frequency diodes with 4 Mosfets as freewheel diodes, discarding internal ones. Please let us informed regarding your progress. Hope for the best.
« Last Edit: January 21, 2009, 07:35:32 07:35 by tAhm1D » Logged
abcsantosh
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« Reply #34 on: January 21, 2009, 02:05:20 14:05 »

 Hi, you suggested very good points. I have to use external freewheel diode. I am using IRFP460 and it's internal body diode is bit of slow. The full bridge transformer is EE42/21/20 N87 material from Epcos. Also the pfc inductor is built using same core with air gap. I am using the cores considerably inside the boundaries.   The core underneath the big capacitor and in front of mosfets is the full bridge Tx. Output power is 1500W, but when I tested, I put the load for 25% power, as you can see from photo. The green one is my load resistor. I will make the changes and tell you about further results.
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Walkura
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« Reply #35 on: January 24, 2009, 05:55:17 17:55 »

Good evening Tahmid .

I have a few schema's for you ,but unfortunatly the text is in Polish and Russian .
On the other hand i know your understanding of smps's by now so i'm confident you will understand by the schematics itself.
The first one is from a Polish magazine ,its a article where they build a welding inverter .
http://www.ep.com.pl/pobierz.php?id=12163
http://www.ep.com.pl/pobierz.php?id=530
The schema is complete with pcb ,for translating segments of the text you can use the poltran website .
(Sorry but since Polish isn't my native language, i can read some of it but my Polish is far from perfect)
The second schema is from a russian website and its also a welding inverter .
http://imajr.com/Original.aspx?Id=spawark1100_393678
Somewhere in the coming week i will post another schema (although that would be photo's from the magazine)
Last month they published a welding inverter in another Polish magazine but the second part of the article comes out this month .
When i have the second part i will post the schema .
Last but not least i have some other schema's of welders (mostly Polish or Russian) but they are on another computer .
Those i will also post when i get to my other computer monday .

Good luck and be carefull .
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tAhm1D
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« Reply #36 on: January 28, 2009, 08:20:10 08:20 »

Hi Walkura,
Good material. The Russian one seems to be very interesting. I am studying those. If you have more schematics, please post. If you have any other material regarding Polish and Russian smps and welding inverter, please don't forget those also. I will consult you regarding the schematics you posted after detail study.
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Walkura
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« Reply #37 on: March 02, 2009, 07:11:20 19:11 »

Good evening Tahmid .

Sorry i reply so late but i didn't have a chance earlyer .
I uploaded you another welding inverter ,again its in Polish but its a well documented schema with pcb,s and pictures .
http://rapidshare.com/files/204508135/dokumentacja_spawarki_inwertorowej_140a.rar

Some time ago you asked about calculating current transformers .
In the book bij Ron Lenk they explain how to calculate and design them (chapter 5 from what i recall) .
The book was already uploaded here so i didn't put it again ,if the links are dead just let me know and i'll reupload it .

Also i would consider to use those allegro sensors i use them a lot and am very pleased by them .
(i would use them primary side followed by opamp to fit it to the smps controller)
Saves you the hassle of calculating a current transformer .

When i found the rest of the schema's i'll upload them here .

Good luck and be carefull .
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9thwonder
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« Reply #38 on: March 07, 2009, 12:17:25 12:17 »

why not to use a DCCT which were used in the sine wave inverters for load sencing.
i think this is better solution to sence and control dc current.
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MAXPAYNE
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« Reply #39 on: March 07, 2009, 05:31:27 17:31 »

HI 9thwonder,
       please give details info abt DCCT.....
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tAhm1D
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« Reply #40 on: July 11, 2009, 04:37:09 16:37 »

Hi all,
If I use AC phase control to control current in welding machine, is there any problem? In one German schematic, I found that in a DC smps welding machine, they use high current but very low voltage(As low as 10v) but in AC type of welding machine,voltage less than 30v create problem in Arching. I am not sure whether in DC type welding machine, that type of low voltage is enough or not. Can anybody provide any suggestion/idea on this?
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tAhm1D
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« Reply #41 on: July 17, 2009, 12:47:45 12:47 »

I did not find yet the Linear Technology reference.
Anyway, any power supply has set point and feedback, or should be.
Suppose a configuration with “voltage” set point.
Add a current measurement circuit  and a comparator with a threshold set point (current set point) that when the current exceed (current set point) will reduce the voltage set point. That is the basic idea.
A linear simple conceptual implementation can be made by OP AMP (as a comparator) driving an open collector transistor that shunt the voltage set point.
On SMPS the power stage (pulse generation) cut off for one or more cycles may be easy to do and simple to balance (loop stability).





Hi,
Your Idea is correct. I am trying this using shunt resistor and external comparator driving the compensation of SG3525. I have tested a simple circuit like this and found to be working properly according to the Oscilloscope reading. If actually it works properly,it will be an easy and simple method to control current.
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tAhm1D
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« Reply #42 on: November 10, 2009, 04:30:54 16:30 »

Hi all,
I have successfully applied the Phase Angle Control and Pulse Skipping Method in Input side for effectively control the current in SMPS Arc Welding Machine. Both process works satisfactorily. I applied these methods successfully in Butt Welding Machine and Spot Welding Machine also. These processes are not for precision control. can anybody suggest any other process for precision control of Current in SMPS Welding Machines?
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lillbear
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« Reply #43 on: November 10, 2009, 05:29:29 17:29 »

But I think, CT is best for large current output.

or

http://en.wikipedia.org/wiki/Rogowski_coil and from IEEE there is lots of papers about Rogowski Coil.
And commercial one ->http://www.powertekuk.com/cwtmini.htm
if we are talking about large currents..  Grin

yours
« Last Edit: November 10, 2009, 05:36:19 17:36 by lillbear » Logged
tAhm1D
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« Reply #44 on: November 11, 2009, 07:04:56 07:04 »

Hi,
Current control is a process which have 2 types of mechanism. One is sensing current and other is controlling the amount of current according to requirement. We can control the upper limit of current by using shunt resistor and external comparator driving the compensation of SG3525. Or we can sense the current by Rogowski Coil as stated by lillbear and many other process. But the second part is important- that is controlling current precisely according to requirement. Precise control of current in the circuit is the name of the game. That is exactly require for application precisely in many smps circuits like micro butt welding machine etc.
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alien
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« Reply #45 on: November 11, 2009, 09:27:08 09:27 »

Hi Tahmid,
Please provide some more details on your phaseangel controlled/cycle skipping based spot welding implementation....I just completed a project on same....commercially available units have many features....many programmable schedules is among one of them...
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arash_tah
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« Reply #46 on: November 11, 2009, 12:38:52 12:38 »

Hi Tahm1d
Did u reach final idea? Current control in SMPS is a very chalengable issue and it takes u alot of effort to achive the gole please inform us what stage are u in? I also want to say u to use current mode control I mean average current mode controlin this control mode you will have a system that inherently limit the current and protect your switches have look at ti.com and search average curent mode control I am sure u can fine mane helpful articles
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tAhm1D
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« Reply #47 on: December 02, 2009, 05:17:28 17:17 »

Hi Tahmid,
Please provide some more details on your phaseangel controlled/cycle skipping based spot welding implementation....I just completed a project on same....commercially available units have many features....many programmable schedules is among one of them...

Please elaborate regarding your project. I hope to provide some details regarding my application of phase angle controlled/cycle skipping based spot welding implementation soon.

arash_tah,
I have not decided finally but testing different processes in practical application. You are correct that by using current mode technique, current control can be done. I will test with those soon and will test with current mode I.C. and with Pic microcontroller.
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