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Multi KW Grid-Tie Inverter Build

Thread starter #1
After looking at the 250 W Grid-Tie inverter build, i'm interested to know what it would take to build a larger 3-5KW (or larger) inverter. Thanks.


Most Helpful Member
Well lets start out with the basics.

What country is it located in?
What is the primary power source?
Will it ever be getting an increase in the input power sources capacity?
What is the input voltage and current range it will need to run on?
What is the output line voltage and frequency?

(I was hoping you would show up!):D
Thread starter #3
Well, to start with it's in North America, Tn to be exact. Primary power source would be wind power, probably around 3-5Kw. I don't really see a need in increase in power needed since it might actually be hard to come up with 3-5Kw for the average person (maybe that will include me depending on funds). Do you think that it might be better off to go with a 3Kw unit since that would probably be the high-limit for most people? Most people around the forums run the axial generators that are 3-phase rectified to DC. The largest i've ever seen was 232A at 13V DC (in the 3kw range). TLG has that farm that puts out 370A at 14.5VDC for 5Kw. To be honest i'm really weak in the area of 3-phase to DC rectifiers (just haven't studied up enough). If you put 700V 3-phase into the rectifier wil it output 700VDC at low amps, or 13VDC at mega amps? That's the only area i can't really help with. Most wind turbines can really crank out the volts 600+. So i'll have to leave the input capacity math up to you for that one, sorry. Output voltage is either 110 or 220 60Hz. Oh, yeah. I scored some monster UPS's the other day!! They're the "Best" brand Micro Ferro UPS 3.1KVA, 2.2KW beasts. The transfermer weighs more than my wife, i can barely pick the end of it up (238lbs). I tried to R-E it, but i can't for the life of me figure out that they've done. They have 4 half-bridges, two to drive the transformer, and it looks like one to turn on the ac and the other has what looks like a DC line going to it to/from the transformer (n addition to the two other 6-8Guage DC wires going to it, center tap maybe?) I've never seen a transformer like this before, it's definately custom (says so on sticker..lol). It looks like all AC going into the unit goes into the transformer and back out for isolation. The thing that i don't understand is that all of the AC lines are tiny!!, There's probably a 14-16 guage output (load side) to the two caps (metal, bigger than beer cans), in series, then maybe a 12g going to the output (Leg). Definately wouldn't want to put 30A through that wire personally. This thing's a beast, cooling fan for the half-bridges' heat sink and caps. I just can't figure out the transformer and all of the myriad of wires going in/coming out of it. It does look like they used two separate transformers to drive the h-bridge. There is a seperate set of input wires going to the side of the board where the transformers are so that's probably the sync, but since everything is electrically isolated from everything else it's confusing me. I did see that there are separate inputs (L & N), and outputs (L & N), so i don't really know if this thing runs 24/7 even if AC is applied but it sure likes it. There's a SSR that does kill the input AC so it can't backfeed, but it runs off of a separate board that looks like it just monitors the input voltage and if low enough breaks the connection so that it can't backfeed (even thought it's isolated, i guess it still might be able to backfeed). Do you think that with a tweak or two this beast could be used as a 2.2Kw GTI and not have to build one? I still would like to learn to build one though, i'd rather know how to do it myself and understand it, than rely on these 17 year old units (built like a brickhouse though). Also, supposedly with their software, the output frequency is adjustable +/-1Hz to +/-3Hz on-line and +/- 0.005 on inverter. Output voltage is adjustabe +5%,-8.3% for any line/load/battery condition. I'm assuming i could rig it up to apply voltage to the board (making it think it was online and drive the control transformers) and up the Hz and voltage a little so it would feed the grid? (once again, separate input and output (L+N input, and L+N output). All of this might just be a pipe dream, but at the least i can rob the parts out of it!!! (If you'd like some pics let me know and i'll post some). Thanks for all of your help!!!
tcmtech, Have you discovered any robust way to dump the Kick Back Voltage from the Transformer directly into the Supply Voltage if it were a battery bank? Wouldn't this increase the overall efficiency by recharging the battery bank instead of wasting the kick back energy as heat? I would think that many people who do not have a Reversable Electric Meter (or who sell back at half price vs. billed useage) would NOT want to run a GTI continuously or only when Wind was blowing but run the GTI only to offset any energy Usage which saves the most $$$. I am not sure if the Battery losses would be greater than the $ savings at the meter by controlling and optimizing when the GTI was activate. Your thoughts?
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Most Helpful Member
The reverse conduction diodes on the switching devices just dump that spike back into the big capacitor thats in between them and the feedback blocking diode on the DC side. Its automatically recycled as it runs. The actual energy in those spikes is very small and does not represent enough power to be worth being concerned about when compared to the total power being handled by the system overall.

I have not had any time this summer to work on any of the GTI systems so much of this stuff has been floating on hold since last winter.
Now that winter is coming and the work I do is about over for the year I will be getting back into these threads and updating things in the next month or so.
Expect to see more information and related stuff coming around the end of December and later. Until then I still have other more important things I need to work on.

Sorry for the summer long delay but all of this GTI stuff is side line hobby work for me and only gets worked on when there is time and money. :)
Thread starter #6

How's things going? Have you had any time to work on your CD? I'm really anxious to purchase one! I've been gathering parts but most of the transformers i've found have so many wires coming out of them it's confusing, but that's minor. I think i could piece one together by now but i would really like to have the guidance of someone that knew more about what they were doing. The selection of (correct) parts is my major holdback (uF, uH, R, etc). I could probably figure it out but i'd rather not blow too many parts if i can avoid it! I'm looking for a good stout 3-5Kw unit, preferrable 5Kw. I have a couple of 2.2Kw transformers, as well as some 2.2KVA, 1.4KVA, and 750VA trannies that i could use. I'm really anxious to learn here. If you could PM me or something (if need be) i'd greatly appreciate it. I'm willing to compensate for your time/knowledge. I just need a little help with the larger units. I'm looking at 0-500VDC input (wind turbine) with either 120/240VAC 60Hz output. I really need to understand how 48VDC input and 400VDC input will still equal 120/240VAC output just with different amps. Thanks much!


Most Helpful Member
The CD made it to about 3/4 of the way through the rough draft before my business tanked last summer.
I lost two customers that represented about 1/3 of may annual income when they went out of business last summer. Shortly after that my wind generator crashed and I had no practical testing system to work with and no money to rebuild it or justify putting toward experiments so it was not a good summer for the AE projects and every thing basically just stopped right there.
I picked up some business last fall and restarted work on the AE stuff for a few weeks until my mom died. Unfortunately I had to deal with all the stuff that relates to someone dieing unexpectedly which used up any time and motivations I had to continue on with the AE work as winter set in. Plus once the snow piles up around here all the wind generator work gets put on hold simply due to not being able to get around in the deep snow.
It just ended up being a very bad year for this type of work all around and everyone here who has been patiently waiting didn't get what they have been waiting for once again.

As you may have seen in the **** chat area I did get my wind generator up and going again a little while back, http://www.electro-tech-online.com/threads/wind-generator-up-again.104543/ , so I have been working on a new multistage GTI design that will run in the 2-3 KW range.
The working range for this one will be for a roughly 25 - 180 volt input split over three stages. 25 - 50, 50 - 100, and 100 - 180 volts.
I ordered parts for it this week and did have plans to use it for a 'Grid Tie Inverter Schematic 2.0' thread but I just got offered a truck driving job, http://www.electro-tech-online.com/threads/going-back-to-work.105194/ , that is too good to turn down so I likely will not have time to work with much of this stuff for a long time now.

I had hoped to have more time this spring to work on finishing much of this GTI stuff but the weather warmed up about 6 weeks early unlike last year where it was 6 weeks later that normal. Around here when its warm enough to work I tend to go and leave the hobby stuff behind until later.

Sorry for the delays and inconveniences but thats sort of how life goes.
I am still working on this stuff but I have no idea of when I will get much of it done. After all most of this is basically just a hobby for me after all so its always been on the low priority list for being worked on right from the beginning.

Thanks for the offer to pay but I do all of this for free so I can work on it at my pace and as my time permits. In the long run more people will benefit from it that way.
Sorry for the continuing delays but at least now you know why.

But just for a little tease here is a picture of the new version of the 20+ Kw direct connection GTI partially assembled. At least I got some of the big GTI worked on for part of last summer. :)



Most Helpful Member
Read all of the other GTI threads carefully.

They have all the schematics and descriptions of what has to be done and how to make your own unit of most any size.

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