| stuartsjg |
Hi,
This isnt really anything to do with audio, but this forum is one of the best SMPS design forums on the web!!
I need a controlled DC 300v power supply for a plasma cutter. This will need upto 30A, which is 9kW.
The largest SMPS ive made is a full bridge 100kHz 2kW unit so this is a jump.
The input will be single or 3 phase 230vAC, rectified to DC. Output will be 300vDC. Output control im planning is via a hall effect sensor on the output DC terminal.
I could use the direct mains rectified but this is very dangerous without an isolation transformer. 9kVA 50Hz transformers are not cheap, i think SMPS is the way to go, i also can control things without using resistive heating elements etc.
This will feedback to the SMPS IC, and ill have a Pot, which together with the hall effect sensor, will control the maximum output current. full duty will correspond to the 300vDC open circuit i need to srtike the arc. The current limit will back off the duty and cut the voltage. Ideally, for plasma cutting, the current will be such that about 200vDC is present.
Are there any commonly avaliable cores for handling this power?
For the 2kW unit, i made it from two 1 kW stages and paralleled the output.
I would be v-happy with a single 9kw stage, happy with two 4.5kW stages, and border line with three 3kW stages.
Does anybody have any core recomendations?
im happy with higher than 100kHz, ive made upto 500W smps at 250kHz!! but i prefer to keep 100kHz as a maximum.
Thanks,
Stuart |
|
|
| Alexsch |
Well lets see...
6 pulse 3ph rectified 230Vac gives 563Vdc. Derating of 30% places you in 900V IGBT range. So you cannot switch at a high frequency anyway.
Core type U93/76/30-3C94 Gives Al=6.4uH, Ae=8.4cm.
Working at 50KHz full bridge and 85% DC:
N*B=114,000.
For Bpp=3KG you have 39T, on primary and 24T on secondary.
Ploss=21W U+U core set.
Lp=5mH.
Im=1.91A
Lo= 90uH for dIL=10Ap-p.
Do NOT use CT secondary, you will loose a lot from Trr. Use either a full bridge rectifier or better still, split the secondary and use 2 of them.
Use phase-shift PWM with IGBT. Current mode will be better here, it allows DC coupling of the primary. |
|
|
| stuartsjg |
Hi,
Thanks for that, was planning on using only a standard uncontrolled "3 wire" bridge rectifier, the AC supply will be a star (Wye) supply with no neutral, so the voltage i get will be lower than indicated 230x1.414=325v as im basically rectifying 3 AC supplied. (unless ive got my 3-phase thinking the wrong way round)
Im happy enough to take 9kW from single phase AC, its just that 3 phase is avaliable to me and it makes smothing to DC much easier.
I had looked into IGBT but ive never gone there before, if the voltage im dealing with is 325v then MOSFET still works, but is pushing it.
IGBT's do come in handy full or half-bridge packs which have insulated heat-sinks and easy termination.
What core power are you calculating for? I see you say "Bpp=3KG" should KG be kW, meaning Bpp=3kW?
Are you suggesting using 4 "U" core half to make an "E" core? Id looked to this but bobbins get hard to find.
Also, something to bear in mind, a 50%-75% duty cycle is not uncommon for the cheeper plasma cutters so i can push the core etc further thermally - im not running 9kW all the time.
Finally, do you know a supplier (UK, or ship to UK) of this core?
Thanks,
Stuart |
|
|
| stuartsjg |
Just wondering if it would be easier using a push-pull toplogy (similar to the ESP 350w system?)
My thought is, i can with much greater ease utilise pulse-by-pulse current limiting.
Ensuring the coils are both the same does become more critical thought?
Stuart |
|
|
| Alexsch |
| quote: | | Thanks for that, was planning on using only a standard uncontrolled "3 wire" bridge rectifier, the AC supply will be a star (Wye) supply with no neutral, so the voltage i get will be lower than indicated 230x1.414=325v as im basically rectifying 3 AC supplied. (unless ive got my 3-phase thinking the wrong way round) |
What exacly you have in mind? A schematic can help a lot...
| quote: | | Im happy enough to take 9kW from single phase AC, its just that 3 phase is avaliable to me and it makes smothing to DC much easier. |
A single phase usage at 9kW level? Too low. 3 phases are better.
| quote: | | I had looked into IGBT but ive never gone there before, if the voltage im dealing with is 325v then MOSFET still works, but is pushing it. |
At the power levels we are talking about, first consider IGBT, then MOSFET. You dont nessesary need modules, TO247 or something like that may be enouth.
What core power are you calculating for? I see you say "Bpp=3KG" should KG be kW, meaning Bpp=3kW?
3KG=3kilo-Gauss (magnetic flux level).
| quote: | | Are you suggesting using 4 "U" core half to make an "E" core? Id looked to this but bobbins get hard to find. |
Actually i had in mind U+U as they are, one against another. No need to construct E core from them.
Bobbins? There are NO bobbins. You go to a winding shop and they will do it for you. Also as extreme solution you may design and MILL a bobbin from a plastic material (Delrine?) for yourself.
| quote: | | Also, something to bear in mind, a 50%-75% duty cycle is not uncommon for the cheeper plasma cutters so i can push the core etc further thermally - im not running 9kW all the time. |
You prefer to use 50-75% DC? OK. Go ahead. But the output choke will be larger.
| quote: | | Finally, do you know a supplier (UK, or ship to UK) of this core? |
Well, i am Israeli, we have plenty of our own supply sources. Up to a few days ago i never even knew the option of Amidon+VISA or EBAY. Such a wonder was dislosed for me by Tolik in his thread on "My first 12V SMPS".
| quote: | | Just wondering if it would be easier using a push-pull toplogy (similar to the ESP 350w system?) |
No push-pulls at this level! What is ESP350?
| quote: | | Ensuring the coils are both the same does become more critical thought? |
Which coils? |
|
|
| stuartsjg |
Hi,
I've attatched a schematic, i was thinking that i want to beable to run on both single and 3-phase depending on the situation.
To make this a bit easier the unit would have 3 inlets, each with its own AC filter and rectifier. This way, i can plug it into 3 mains outlets, if each outlet is on a diffirent phase, that would be the best thing, if not, provided each is on a diffirent breaker then that would be fine.
I have never used U+U core, i guess you wind the coil on each half of it then pair together.
I have several ETD59. Some of N97(Al=5500) material, some of 3C90 (Al=6000) material and good for up to 200kHz.
These have an Ae min of 368mm.sq and a Ve min of 51200mm.cu
I have seen people on the forum push 2kW through at 75kHz. What would you think at 100, 150 or 200kHz full bridge.
When i referr to "duty cycle" i perhaps was confusing things. I am not talking about the PWM duty, but the duty of operation.
Most welding and cutting tools have a continuous duty, for example, a welder can operate at 100% duty (all the time) at say 80A current, however, at 140A current can only operate at 30% duty. So, 3 mins of welding then a 7min cool down.
Most plasma cutters can be operated for 5 mins before a 2.5 to 5 minute cool down period is required. This is because the components can then be sized much smaller and hence cheeper.
The ESP system, i am referring to the common design http://sound.westhost.com/project89.htm |
|
|
| Alexsch |
I dont think that this schematic will work... Also, there is no individual phase return in 3PH systems. Only delta or a Y wiring with the forth conductor (N) may be absent. And you need a soft start for the bridge, so use thyristor semi-controlled 6 pulse bridge.
Check semiconductor companies for 3ph rectifier modules. |
|
|
| stuartsjg |
Hi,
Running through my logic for the AC/DC input rectification.
if running from 3 phase, it will be from star. In most buildings it provides 3 individual single phases (N+L1, N+L2, N+L3).
What ive done is parallel 3 standard bridge rectifiers DC output. I can also paralleling the AC input (as in a single phase situation), OR, having 3 seperate AC supplies, i.e. 3 phase.
I could put this into a single block 3 phase rectifier which makes single phase use slighly awkward.
Also, the sockets in the area i am using it in are all on a diffirent phase, so getting the 3 phase is easy.
I may just stick with single anyway as i do have a 50A single phase outlet avaliable to me which gets used with a welder.
Soft starting the AC supply is a good point given the smothing capacitors and the high voltage diffirence, large currents may ensue!
Whats your thoughts on the power handling capacity of the ETD59 core?
Other posts indicate 2.6kW possible at 75kHz full bridge, what would be possible at higher frequencies, bearing in mind i can push the core further than usual given that it wont be used for any more than a 1-2 minutes before a no-load break of 4-6 minutes?
Thanks,
Stuart |
|
|
| Alexsch |
On rectification.
I do not fully understand what you have posted, but know this:
A SPICE simulation of any rectifier circuit will save you from a lot of trouble.
On ETD59.
Well lets see:
Ae=3.7cm instead of 8.4cm.
Increase primary turns to 88 and secondary to 55.
Ww=41mm.
41/(88/2)=0.93mm diameter wire (in sandwitch interleave 2 layers) at ~19A primary current. Looks bad.
And also you may use powerful fan only for the trafo. Going to high frequency gives very little. You have a lot of AC current to conduct and the skin effect will demolish any attempt to go beyound, say 150KHz.
By the way, using planar core technology may be of an advantage here.
Is this SMPS is intended for mass production, or a learning project? Anyway its most definitely a bold step into a power-electronics minefield. |
|
|
| DigitalJunkie |
Sorry to interject:
| quote: | | I could put this into a single block 3 phase rectifier which makes single phase use slighly awkward. |
9KW from a single phase? :eek:
That much power from a single phase might be a bit awkward anyways. :confused:
I would think at least 2-phases would be needed,for practicality's sake,if nothing else. |
|
|
| Eva |
| If the output voltage does not need to change quickly or a pulsed output current waveform is allowed, consider three independent transformer-coupled PFC stages, one per phase. This is a difficult topology, though, due to the active clamp requirements, but it's single stage with isolation and allows to use 600V MOSFET/IGBT. |
|
|
| S.G. Mahbub |
Dear Stuartsjg,
You have put forward a project, which requires theoretical knowledge and also concrete practical experience.
I want to share my little experience with you. Recently I was associated with a project of similar nature.
First, you have to rectify the line voltage(considering star connection) in the way prescribed by Alexsch. It should be six pulse 3 phase rectified AC, which will give you 564 volt dc not 325 volt dc as you have stated. In Star connection, if Phase voltage is 230v, then the Line voltage would be 230v x 1.73 =400v approx. When you rectify, the voltage will be 400v x1.41=564v dc (uncontrolled).
You can use rectifier module as different companies made rectifier module for 3 phase.
I am attaching a schematic of 6 pulse rectification. It is termed as 6 pulse rectification as the pulsation of the output voltage is 6 times the input frequency.
Next is the conversion of 564v dc to 300v dc. Alexsch has correctly pointed out that it will be difficult for you to convert it to 300v dc in high frequency with Big Ferrite Core. Moreover, what is the requirement of high frequency?
If you adopt modern sophisticated technology evolved recently instead of older technology, you should not bother for high frequency and also forger about using ETD xxx and other Type of Transformer as modern technology made things easier. You don't require Transformer at all.
You can use 1200v IGBT Module as these are easily available because now a days these became the essential requirements for modern power electronics.
Now the modality of conversion. You will use a controller to convert 564v dc to required AC voltage, so that after further rectification, you get 300v DC. I have done in the following manner.
I use Pic Microcontroller 18F4550. It is having inbuilt Hardware Module known as ECCP and it is given for PWM full bridge application and for that 4 pins are assigned in the Pic. Programme is made for required voltage and PWM ed signal is given to the IGBT drivers (2) through ECCP module of the PIC and excess voltage is killed as dead time through delay calculation in between opposite phased signals. So, you get modified sinewave as output and rectify that through rectifier module and you get your required 300V DC output.
To get the controlled output, I used internal 10 Bit ADC Module and also 2 internal Comparators.
To supply my required output I have used AC phase control before final dc conversion and 2 DATA TABLES are made and stored in Pro gramme memory of the PIC. One is for Voltage stabilization and another for Power Control through AC PHASE control. After each half cycle, ADC collects the data and comparator compares the output with the DATA Table and corrects the output through corrected PWM ed signal in the next half cycle. In this way output is stabilized.
I donot understand of controlling output through hall effect sensor. If you elaborate it kindly, I can study about the process for further use.
Thanks. |
|
|
| S.G. Mahbub |
Hi,
Microcontroller is not yet a common instrument for most of those who is having interest in Electronics. My post is just to show how this can be utilized in Power Electronics. Not to bother those, who don't use it.
Some one who is not conversant with it, need not to venture in it. Life is full of trade off.
However if anybody is interested in Pic Microcontroller and if I can be of any use, he is always welcome.
-----------------------------------------------------------------------------------------
Ideas are money, if it can be applied on ground - not in forum only
----------------------------------------------------------------------------------------- |
|
|
| luka |
| What the ?!?! Those are some really big cores, FTW |
|
|
| S.G. Mahbub |
Hi mflorin,
Useful address. Thanks. German products are always excellent. |
|
|
| S.G. Mahbub |
Hi stuartsjg,
| quote: | | This will feedback to the SMPS IC, and ill have a Pot, which together with the hall effect sensor, will control the maximum output current. |
I am interested to know the process of controlling the output through hall effect sensor. Interesting idea. Hope, you will elaborate.
Thanks. |
|
|
| psychosteve |
do you need that much voltage? ive used a modified 100 amp stick welder with a plasma torch.(£30 from ebay) voltage is about 58v before arc strike, then just regulate current. hf start you can find online then just sense main current to open air solenoid.
or is it cheaper to take a cheap cutter from ebay (£80 / £100) and use that, or strip and uprate the components inside to up the duty cycle/ cutting capacity?
just a thought, steve. |
|
|
| S.G. Mahbub |
Dear psychosteve,
Since you are acquainted with plasma cutter, I want to know some information from you.
What is the max. voltage required for plasma cutter? Arc welding/stick welding voltage- 45v-60v isn't low for plasma cutting? If voltage range is same as stick welder, then your advice is really worthy.
Please let me know and thank you for providing a valuable information. |
|
|
| psychosteve |
i have used a clarke 120 amp stick inverter from machine mart. torch from ebay. arc starter from a hobart stick welder, cut was good.
from what i know, plasma cutters use higher voltage because its easier to get the arc started inside the torch, known as pilot arc, which is used to superheat the air flow turning it to plasma state allowing it to burn through painted surfaces, and in turn through base material. but it isnt necisary to have the higher voltages.
if you want to experiment for your self find a mig or tig welder with some spare tips / tungstens as this will probly burn them a fair bit. disconect the sheild gas, argon or co2, and plug it into an air line, make sure its a regulated supply at around 60 psi and try welding, taking saftey as per normal welding. if air presure is high enough and base metal thin enough, it will cut.
failing that there are multi use machines that will do tig, stick and cutting. try looking at those to find the pre strike voltage.
hope this helps, steve. |
|
|
| wakibaki |
| quote: | Originally posted by S.G. Mahbub
excess voltage is killed as dead time through delay calculation in between opposite phased signals |
Sorry, I didn't understand this bit. Could you show a schematic of a real circuit, please? And point out critical features?
w |
|
|
| S.G. Mahbub |
Dear psychosteve,
Thank you very much for your information. It will be useful for me.
Thanks. |
|
|
| S.G. Mahbub |
| quote: | Originally posted by wakibaki
Sorry, I didn't understand this bit. Could you show a schematic of a real circuit, please? And point out critical features?
w |
This project is done with Pic Microcontroller. If you are acquainted with Microcontroller, then it will be easier to understand. Please go through my posting again and I am sure you will understand. If not, I will try to make you understand.
I have disclosed the main idea and modality in detail. Schematic and critical features can not be divulged as it is having commercial value and the company for which I worked, will not allow to disclose.
With thanks. |
|
|
| wakibaki |
I am acquainted with PIC16F87x which have PWM and A/D.
Why do you have a full bridge generating modified sine followed by a bridge rectifier? Why not just have single-ended? What kind of filter do you have and where?
w |
|
|
| psychosteve |
http://www.cutting-tool.americanmac.../bdeee29_1.aspx
this is a good basic explanation of the mechanics behind plasma arc cutting, the explanation gives two examples the lower one (70v at 12amps) is a good indicator, if you assume general principals and keep the same wattage, then at about 40 to 50 volts from an arc welder unit you should aim for around 18 to 19 amps.
if this is for your work is it as a manurfacturing concern or for use in your work? if you only making them to use in your work place, a 1kva transformer at 50v ac is about 20amps. rectified should give around 70v.
costing around £60 upto £100 for a transformer, OR 1.5kva 100v for £130, is the development and parts cost worth trying smps?? |
|
|
| S.G. Mahbub |
Dear wakibaki ,
If you are acquainted with Pic 16F87x, then it is easier to understand.
After getting the output from full bridge configuration with 4 Mosfets, Bridge Rectifier is required to convert modified sine AC to DC. I have used normal LC filter as my requirement is DC. I have adopted modified sine wave/quasi sine wave route to remove the extra voltage in dead time/off period through calculated delay routine and ultimately to obtain the required voltage by hardware pwm module of ECCP of Pic Microcontroller.
Hope, I could make you understand.
With thanks.
____________________________________________
IDEAS ARE MONEY IF THEY CAN BE USED ON GROUND.
বাস্তবে ব্যবহারযোগ্য চিন্তাধারাই মানুষের প্রকৃত সম্পদ। |
|
|
| S.G. Mahbub |
Dear steve,
Thank you a lot for your help. I got useful information from the address you have provided.
I am thinking for trial making plasma cutting M/C for Metal Cutting purpose and plasma heating machine for preserving molten metal heat, so that heat is not reduced before casting and it will be through smps route.
However, have you used smps Arc Welding machine of 400-500A range? What should be the max. voltage ratings? Can you apprise me regarding this- as I find you are very knowledgeable regarding this.
With many many thanks.
____________________________________________
IDEAS ARE MONEY IF THEY CAN BE USED ON GROUND.
বাস্তবে ব্যবহারযোগ্য চিন্তাধারাই মানুষের প্রকৃত সম্পদ। |
|
|
| psychosteve |
unfortunately ive never used an smps welder with over 200 amps, in welding if its old and its still working, it will keep working!!
to translate for non welding people, if youve got a 400 amp transformer thats been working for 15 years, it isnt going to melt anytime soon.
if you are still looking for that kind of power what thickness are you looking to cut? and what material? aluminium takes about twice the power of steel. and imho, if your looking for that kind of power for work, buy it! import from china, they do some HUGE industrial cutters for around £2000, or go c.n.c machine cutting for around £8000 that will cut 25mm steel.
try this for a bit of inspiration, its a tig welder, and uses a transformer (ac buzz box) but the controle, gas valve and arc starting are there, just way more complicated than you or me need.
http://www3.telus.net/public/a5a26316/TIG_Welder.html
glad i can help, just wish some one could help me with my problem, steve. |
|
|
| S.G. Mahbub |
| Thank you steve for providing useful information. |
|
|
| DACMan1 |
| I am also contemplating building something similar. would be a PSU for pulsed MIG spray welding, though. According to EPCOS, you should be able to get 4.5kW through an ETD59 with N87 material at about 125khz. |
|
|
| golam |
HI DACMan1,
Please elaborate your plan so that we can help you and also can learn something from youl
Thanks. |
|
|
| DACMan1 |
ATM, I am just thinking about it. Actually, the software from EPCOS calculates the power handling of the ETD59 @100kHz to be 9056W with dB = 324 mT and J = 5.2 A/mm^2. I am considering using 4 of these cores to get between 10-12kW and running them with 4 seperate full bridges. on the output side I will also have 4 full active mosfet bridges for rectification, which should enable me to generate an AC output for TIG welding with the right controll. not sure of the effects of 4 paralel bridges and still have to look at all possible current paths with the active rectification and how to controll that. But I have a lot of projects that need to get finished first...
What do you guys think of this? |
|
|
| luka |
| I would use them in series rather then in parallel, all would have same output current, but only 1/4 of the voltage |
|
|
| DACMan1 |
| quote: | | I would use them in series rather then in parallel, all would have same output current, but only 1/4 of the voltage |
That makes no sense at all! It would seriously affect efficiency adversely! |
|
|
| luka |
Hi
How do you know that? Didn't you ever see say car amp with more then one transformer inside?? There were, 1/2 of them in series to make + rail, other 1/2 also in series to create - rail. Same in more powerful inverters, all primarys were driven by its own set of fets, all secondarys (ALL!!) in series to make 330Vdc.
I don't know where is one pic from this forum that shows that. Same you could use. Or you could use all of them in ||, every secondary its own rectifiers and after them they would go to same caps...but one trafo can be here loaded more, and it will be, the one that makes biggest voltage will be loaded first, then after sagging durring load all others will start to contribute some, but not the same as that first one...think aout this |
|
|
| DACMan1 |
| Oh, you mean the secondary windings of the transformers in series, I thought you meant the bridges in series - that would make no sense. Series trafos would not necerarily affect the efficiency that much, but might not be practical: The number of primary windings are determined by the dB you want the core to operate at. Since the output voltage would be around 32V, placing all in series means 8V, which might mean that you end ub with 0.8 turns on the secondary(for example, would probbly be more than that). Anyway, ending up with a too low number of secondary turns is not ideal for tranformer design. I would rather wind more turns, matching trafos exactly, and end up with less current in the secondaries of the trafos. Of course, this approach would mean that the components must be matched very closely. But I will definitely look into this approach, and do the calculations when designing, thanks for the insight. |
|
|
| luka |
Hi
Ahh ok, I though that there is higher voltage, around 100v, probably is for something else...well in this cas you have right, best of luck and do post any pic that you will take, would like to see how it will go |
|
|
|
