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Grid Tie Inverter Schematic

>>>I have read up on some methods of using two or more inductors or transformers being ran with a switching time phase difference between them. Does that actually increase efficiency greatly or just power handling capacity?

One thing this multi-phase method achieves is lower ripple current which can increase efficiency in the capacitors and somewhat in the inductors if done right. PC-computer supplies use this multi-phase buck converter technology all the time. I ≈believe≈ my MX60 was the first battery MPPT controller to use this topology.

Mr. RB... Did you work on a battery-less grid tie MPPT unit, or was that a battery charging unit ?

boB ΩΔ
Washington, AC


Active Member
I only read a few pages back, but I'm not sure everyone is aware of the safety issues with a GTI.

It's not just that it's hooked up to 110v and may catch fire or electrocute you when improperly designed or made with less-than-spec components.

IF the power company chops power to work on your line, and your GTI continues to keep it "live" with 110VAC, that AC feeds back through the transformer because transformers work both ways. This can step up to 7200v or more on a line which is "supposed" to be dead because it's disconnected from the supply, although of course the current available is limited by how much wattage you can source. It is plausible to test 0v at first and then the sun comes out or whatever brings the GTI back on and then it has high voltage at some time later.

It's called a "power island", and the power companies are "concerned" about the possibility.

It's not all that likely, since your power source must be able to power everything "on" at your end, and any neighbors on the same transformer. If the power cuts off at first, many computers and A/C won't start back up by design, and a smaller supply might be able to power the clocks and such left on. A large solar array can plausibly do this, although it's less plausible with a small array. And I think the industry is supposed to use a shorting cable to short-circuit such a supply, but I'm not sure how common that is.

What worries me is just that I'm having to include a lot of "probably" and "I don't think" when talking about risks to people's lives. If the power company knows and approves of a product, probably one which is somehow able to be remotely disconnected, that's one thing. Rogue projects are more alarming.


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Already covered a few months ago! Or around pages 5 - 9 and again some other places. ;)
Read the full thread. Its almost considered educational by some! :eek: :D

The safety issue is real and relevant but on the logical side are you going to be building multi kw GTI with a constant enough power source to be able to hold its own island with all of your neighbors and who knows what else drawing off it? All the while providing a clean regulated sine wave with the right frequency, voltage, and current capacity simultaneously? ;)

The GTI designs we have posted and are developing here are line voltage and wave form following by design so as soon as the line voltage drops out they will inherently get very unstable and either shut down safely on purpose or crash and burn if someone builds one without the necessary monitoring and protection circuitry and actually has a power source feeding it that can supply a far greater peak power than the GTI they built can support.

I covered the original and basic all analog cheapo proof of concept design and Val Gretcheve has been developing a very nice and far more sophisticated design as of the last few pages/month or so. :)


Well-Known Member
Oznog I don't think any one has said to build a GTI that will feed the main with the power out. No power on the main No feed the GTi is checking the main for phase and voltage so it can go on line in phase. So no phase no voltage no feed. But you have a good point sure don't want it to try to feed the a dead main so any one building one should make sure
that can't happen.


Most Helpful Member
Postem if you got em! We would love to see what others have came up with!
I came here looking for useful information about Grid Tie Inverter systems. What I found was a bunch of posts that should have been moderated as spam. A good portion of the spam was from amateur want-to-be lawyers, and other types of ninnies and know-it-alls. Some of you are so smart that you already knew how Original Poster's neighbors would react to OP's silly ideas. And OP's ideas were indeed silly; for example, he thought this was a place to discuss electronics. OP by the way, appears to be long gone; and has left you all here to argue amongst yourselves.

The safety problem, by the way, is not a new one. Power companies have been dealing with it for years (ever since they installed a second generator). And Linesmen don't just sidle up to any old wire they find and test it with their tongue to see if it is hot. They have tools and procedures to keep them safe. And, they have more to worry about than your little home-built .1-10kW solar system.

If you're genuinely interested in the safety and power quality issues, and not just in browbeating or berating the naive, and the un-knowledgeable; you might be happy to learn that ANSI / IEEE-1547 is a standard (as of 2003) meant to deal with precisely these issues. The standard was developed at the behest of the US DOE, and NREL. It includes approved methodologies to test distributed electrical generation equipment for safety / suitability.


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Two posts and some how I already like you! :D
Pure Sine Wave Inverter

hello, im a student, i have been looking for a most advance Pure Sine Wave Inverter, from 12Vdc to 240Vac inverter. Please send me a full circuit diagram with it full explanation to my email- jeffrey_5097@yahoo.com or here.

I have read all the pages of this forum as well as the one that started for the 250watt specific unit. I am starting to produce a circuit design similar to the ones described here hoping that the power company will work with me.

I was looking to use a wind design and live in the middle of a city, but the city requirements for a tower is that it has to be less then 100 ft tall (I don't plan on making mine anywhere near that), but I was looking for monitoring software that I could tie some type of tach unit to and stick up at various heights to test which elevation would work best.

Any ideas what and where I could find this, I have been looking around, but haven't found anything that fits the bill.


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Hi there,

First thing you should check with your local power company.
You have to at least find out if they allow grid tie inverters in your area.
Second, you have to find out what the required spec's are for something
that is tied to the line like that, such as what is the maximum level of
the harmonic distortion allowed and maybe even how often you can allow
your unit to tie and untie from the line in any given day. There may be
other spec's that they demand so you better check first.
Maybe I missed it, but has anyone here talked about PFC for a Grid Tie Inverter? I'm trying to figure out how it would be done, since you are trying generate a voltage waveform to closely match the grid, how would you regulate the current to track the voltage?

(First time post)


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Most Helpful Member

Actually, if you set the voltage to match the line before contact, then switch
to current generator mode, you turn the inverter into a current generator and
then you just regulate the current. The voltage goes to whatever it has to
be to match the line...that's how a current generator works.


Most Helpful Member
It depends on how you build the GTI for the most part. I prefer simple and rugged and use a simple LC tank setup on the line side both for filtering and for power factor correction.
Without knowing what you are working with its impossible to say exactly. Still to correct possible line hash or harmonics issues a filtering system is needed. And if the filter capacitors are of the correct size the power factor will say fairly close to 1.
A couple of things to keep in mind.

1) the mains waveform, when loaded, may not be a perfect sine wave - if you use it as a reference, you only make it worse. Best to create your own.

2) reactive loads will cause back-emf - ie, the load will produce a possibly quite high voltage and you need to absorb it somehow.


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How to filter the inverter output?
I have 250V pk at the MOSFETS.
10 volts pk at the output of the first LC filter.
0.4 volts pk at the output of the second LC filter.
I am 25db over FCC specs.
I can see that a simple LC filter will never work.
Any ideas?
Question for Val

Hi Val, nice elegant line waveform tracker with digital adjustable attenuator for power point tracking via microcontroller. But how will you mitigate the feedback coupling when HVDC and both "240 VAC" line connections are hooked up together? Won't the circuit behave differently since it will then be sensing its own output?

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