Grid-Tie Inverter Design

I think what you need is a grid interface. This allows you to control the phase and voltrage of your home system so that you can feed power into the grid when you have an excess for sales.

there should be a few clues in here.

http://www.google.ca/search?hl=en&q=%22solar+power%22+%2B%22grid+interface%22&btnG=Google+Search

I don't know for certain, but conversations I've had with an employee of a company that makes what you want lead me to believe that the solar array cells are series'd to exceed the peak line voltage of the grid. Essentially, an H-bridge switches the array (end-for-end) at the zero-crossings of the grid sinewave, and the voltage from the array is then switched at high freq, duty-cycled up and down a half-wave 60 Hz sine curve, and filtered to remove the switching frequency. No transformers needed, just a relatively small filter inductor. At each point on the sine curve, the array voltage must be a bit higher than the grid voltage in order to push current back into the grid.

It looks to me as though this is a cheap way to build an inverter, but since you're not extracting all the energy the array can produce on a continuous basis (steady DC), it's not too efficient. But, other than that, I think its kind of slick.

A 60 hertz sine wave is synthesized that is in phase with the line and they use PWN and a transformer to generate a high + and a high - bus which is then ramped inphase from the high + bus to the low - bus, through zero at a slightly higher voltage than the line so it feeds the line. It must also detect when the array declines and change the pulse widths to maintain the feed to the grid at the max while letting the house eat what it wants as well. It also has the ability to feed the line if you do not need the power and the sun declines and the array does not put out the full voltage.

Complex little devices, but just a few LSI chips inside.

read the documentation

http://store.altenergystore.com/Inverters/Inverter-Accessories/Grid-Tie-Interface/Xantrex-Gti-Grid-Tie-Interface-For-Sw-Inverter/p2128/

http://perfectpowernetwork.com/departments/T1,0009,0108/0/1/Inverters_.htm

http://www.solarelectricsupply.com/Inverters/sunny_boy/sunnyboy.html

http://www.solarelectricsupply.com/Inverters/Fronius/index.html

http://www.solarelectricsupply.com/systems/grid-tie/discount-gridtie.html

Better check the restrictions/ regulations on feeding power to a utility.

In most of Canada it is forbidden. The utilities are fearful for their linemen. They isolate a system only to find someone is back feeding the grid. Standby generation etc. has to go through an approved transfer switch.

Otherwise it is technically easy.

No need to reinvent the wheel so to speak. There are half a dozen big name companies who produce such devices. There are literally dozen if not hundred of retailers selling their products.

Outback, Magnum, and Xantrex are among the US company names that first come to mind. Look up Home Power magazine. This is a publication dedicated to off-grid and grid-tie systems for residential use. Their back issues contain a wealth of information on systems ranging from tiny 1000 watt capacity to very large systems.

In Europe look to Victron and Mastervolt brands. There are places with restrictions on interconnecting to the grid; but legislation has been passed by several states to allow tie installations provided the necessary safety interlocks are use. The technology is mature. I first worked in a grid tie system back in 1978. Things have improved tremendously since then. Outback has some good technical papers on their website you can download.

Collectively Outback engineers have expertise going back more than a decade on grid tie systems. They are located in Washington state - one juristiction which does allow grid tie.

Check out Home Power Magazine - they have good articles ranging from beginner to advanced, typically with schematics. The big companies advertise with them, so you can get a feel for who is out there. I would definitely stay with the brand names mentioned earlier, as they have been around and know what they are doing. Visit http://www.homepower.com/ for more.

Why don't you just buy one?

"Why don't you just buy one"

BECAUSE THEY ARE WAY OVER PRICED. That was yelled a the top of my lungs.

Solar panels cost about $4-5/Watt, inverters cost $1-2/watt. This is crazy. These grid tie inverters are no more complicated than a computer power supply which will cost you about $0.08/watt. The inherint nature of the grid tie inverters is to track the sinusoidal input and drive it to a higher voltage, thus selling the solar power on it. The IEEE 1547 require all kinds of hoops to jump thru and the inverter companies use this as an excuse to charge what they do. Again the hoops are simply jumped by a programed algorithum that monitors frequency and voltage levels. WOOOOO. I see this mans drive to find/build an inexpensive alternativ and do the gorella thing.

Mark,

You guessed it right. The idea here is to get some of these units made in China using one of my contacts there who makes the battery chargers and controllers for Electric scooters and wind turbines. They dont have experience in buiding a Grid Tie inverter, that too in 110V. Hence the request.

You have hit the nail right on the head - These are way too expensive to buy at the moment, like say $2000 for the Solar Grid tie made by Xantrax

the unit has to follow the phase angle of the line and stay at that angle, then it has to drive a slight extra voltage onto the line to the limit of the ability of the small power supply from th sun or ?? to supply it.

A lot of the cost is the certification for reliability that goes with the approval process. The usually low grade Chinese power supplies are not good enough.

There can also be patent issues.

Oh please. The original poster is sooo right. This stuff about "Chinese technology can't cut it" is such veiled biggotry. Chinese fabs produce silicon in products for Macintosh, HP and IBM. Don't give me that Chinese=crap argument.

The fact is, microcontrollers that have the power of what was considered a mainframe PC just a few decades ago have become incredibly cheap and easy to use. In the dollar per part range if you're buying by the reel. The Atmel AVR series, in particular, is easy to program in C and doesn't even require assembly. Do grid-tie inverters even need DSPs? Probably not. But DSPs are cheap and many DSP algorithms can be implemented in an Atmel AVtiny using software only making them practically free for such designs. Otherwise what have you got in this circuit? A bit of power circuitry? No big deal.

Do a little surface mount PCB, load up the pick and place and turn on the solder oven. You're cranking them out at a few dollars a pop.

There is a wide range in quality in Chinese parts, from very good to very bad. The US makers, like Macintosh have local quality control people who inspect and test. In addition, foundry machinery is not made in China and it produces parts as good as the operators are able to support with input silicon etc.

The small power supplies made by discrete part soldering are the cheapest. surface mount stuff is better and more reliable.

China is going through the same quality ramp the Japanese, Koreans and Taiwanese went through, and it makes products from many places on that ramp.

They still have hand labour removing parts from boards with solder pots and blowtorches and these salvaged parts are used for the lowest end products.

In case you say no....I have seen these places in person. China is slowly shuting these down, when the find them, but entrepreneurs arise all over the place buying containers full of scrap for recycling and doing it out in the far country areas where there are few watchers and labor is $10/week

Yeah, hey good to see this thread isn't completely abandoned. I should have been so critical, it was late and I wasn't being very civil. I'm just saying that the rules have changed in just the last few years and things that may have been beyond expectation in China are now doable and partly because of the revolution in microcontrollers. The white goods market in China, for instance, has benefitted hugely from the increasing ease of use, reduction in costs and openness of microcontroller design. I wouldn't have bought a coffee maker from China ten years ago. Now, I'd buy a washing machine or even a car and this has a lot to do with the rise of the easy-to-use high speed, fat memory networked microcontroller. It's not a nationalism issue, it's a global scale technology issue. The state of the art has risen to a new level and all boats rise simultaneously as the sea rises whether they're filthy old junks or shiny white yachts. Certainly micros have been around for decades but they haven't been so easy to use until quite recently.

DSPs are the same story. Twenty years ago only EE grad students has even heard of a DSP, in the nineties they became standard university fodder and now they're a high school level topic because everything in our environment is packed with them such as this net conntection we're conversing across. That is a game changing fact. Nowadays you have people like myself who have no formal training in electronics designing sophisticated electronic devices and loading them with custom code. Even surface mount which used to seem like the end of the line for the electronics hobbyist is doable these days. You can get tutorials on doing DIY surface mount in a toaster oven on YouTube for crying out loud. To pretend that all of this is somehow out of the range of Chinese factories and yet accessible to American high school kids seems like a fairly large presumption.

Anyway, I'm hoping the original poster comes back because I have a link for him. Not actual layout or PCB which is something I'm also looking for, but a company in China that is doing grid tie inverters. What caught my eye was that they do mention that the produce uses DSPs which was one of my assumptions. They also mention something called MPPT and an IPM module. I'm going to spend some time looking into those but I'll leave the link here in case the original poster comes back and wants to take a look.

http://www.tradeindia.com/selloffer/1166530/Grid-Tie-Inverter.html

Also, I would like to comment on the earlier mention about looking in Home Power magazine. I am a bit suspicious about the claim that an actual teardown or details of internal circuitry and much less printable traces for PCBs can be found in Home Power magazine because searching with any additional terms beyond "grid tie" gives me zero hits in their on-line database. I've read Home Power on a number of occasions through the years and I've seen some good stuff, but I kinda doubt they are going to scavenge their advertising dollars with something like that.

I'm sure it's just a matter of time till I get this one. Might have to go to some patents but it's out there somewhere. Any leads would be welcome.

Ooh, love the edit button.

Here's another thread on a home brew GTI system that is almost completed and offers input voltage flexibility beyond what's in the market. No home page but the builder is available to discuss his system. Also someone in that thread thinks certification for the UK can be done for less than GBP10K. No word on the US though.

http://www.fieldlines.com/story/2005/1/22/11194/0957

The problem with not going through the proper regulatory hurdles, testing and approval etc., is that simple mistake can end up killing a utility worker. "Cheap" is possible, safe is possible, safe and cheap are rarely possible.

JRaef,

The way the grid tie inverters work per the regulatory hurdles is it syncs in on the line power voltage level and sine wave siganture. If power goes down it shuts off, no harm can come to the line man. This type of statement from you or utility companies is old school old day problems stemming from someone hooking a rotatry generator or non-monitoring piece of equipmnet to the line. And if a lineman is doing as he is suposed to he grounds live wires to ground before working on a "dead line". (that's a rule)

Utility companies have this power thing locked up and are going to be very reluctant to let small producers get in the game. Utility companies should not fear small producers they should embrace them and buy their excess power and resell it at a profit without any over head. The largest source of funds to build the power supply sytem is in the pockets of consumers: let consumers build it.

And as far as the regulatory cost as a part of the inverter cost that to is a pile. When the cost of regulation of a certain product is spread over the number of units sold it is small. Again we have a situation of free market and what the buyer will pay. In verter builders are maximizing there profits because competition is nill. I am all for free market but too I am for some of the Chinese or Indian products to slap the US, German and Australan made manufactures into a stop gouging mode.

I talked to a lines man in Otario Canada and he told me that if there is power on a line they will ground it and burn out the supply My father was a lines man fo ontario hydro in the fifty's

Why dont you find out how Boeing plane works and get is made in China ??

China can make coppies of existing things, I have never seen a chineese company come up with their own product.

Before you run to china take the spec with you. These inverters have 97% and more efficiency. If you are an engineer you would know what 97% means.

Obviously you know little to nothing about China! Get a global education and use it instead of presenting such an infantile argument. Simply by the fact you have not "seen" any Chinese company "come up with their own product", must make it a fact? Have you ever been there?

If "you" are an Engineer, I'm sure you understand some code of ethics, which isn't represented by your narrow minded comments.

Sorry for being off topic for my first post, but that comment above thia was unecessary.

It's easy. and it's cheap. less then $15.00 for a 1500w device (perhaps)

I have tried and it works. It does not "kill" if the power outage. Work on as little as 12V (larger battery can use Zener diode)

It's not an inverter, it charge/pump your electrons to the grid

ALL You need a real H-bridge and a bridge.

(a) On one leg of your 220v you run it thru the H-bridge.

(b) Other leg you run it thru a bridge (rectifier). This you connect serially to your 12v battery

(c) Connect (a) & (b) parallel.

Technology:

The (a) create a 110v DC (1/2 upper hafts of sine wave) allowing exceed power to pump back to the AC source.

The (b) create a 110v DC (1/2 upper hafts of sine wave) but Not allowing exceed power to pump back to the AC source.

Then at B it is = 110 + 12 (way less then 132 upper limit that the utility requires)

Good luck ! ! !

Would you like to share a drawing of this circuit?

Thanks Dave

Yes please provide a circuit diagram. It is hard to picture by just reading words

What the poster was saying is, just add 12Vdc to the ac and then power will have to flow out of the battery into the grid. (He would be resuppling dc power to the battery from solar or wind, presumably). Instead of requiring two batteries, one connected +12 and one -12V, for the _+ and - sinewave halves, he is using one battery. This batt is in series with the + half waves from the fullwave rectifier. Then the H-bridge alternately inverts the boosted half sinewaves and applies them in parallel with the local power. If the local power is at 110V, his unit will be alternately applying (+110rms +12dc) and (-110rms -12dc), which will be symmetrical, if not exactly sinusoidal.

A fancy micro controlled GTI does the same thing: raises the line voltage so that power flows in reverse. One can do a fancy job of phase locking and phase leading. Or do the crude thing that the poster describes.

Of course, one will not be able to apply the full 12V. In the case of the poster's unit, the ac current will be limited by the total series resistance of the diodes, transistors, and wiring. Plus inductance. Thank the lord for small wire, in this case! If one were to do this with 00 cable and big-amp semiconductors, efficiency would increase from maybe 5% to 90% and there would be big power transfer...for a few seconds. One would have to lower the battery voltage if trying for the practical, big-amp circuit. And watch out: the battery is in series with line voltage. At least put it in series at the neutral leg.

. . . John, CI Solar

From the poster.

Thanks John for explaining. and sorry that I am unable to post the diagram.

NCD

Well, I found this idea interesting so I simulated it! I was able to produce a nice waveform for the 110RMS +/- 12VDC with the H bridge. I was also able to calculate real and reactive power in the primary source (used simulink) it turns out that since the grid is mostly inductive, this idea does not work very well, only a few watts can be injected back (with 12V ideal source). I think to pump real power into an ac inductive source you have to lead it! in other words you have to have a leading phase angle injected in your secondary source constantly. The technique proposed injects in-phase voltage with the primary source which results actually in reactive power flow more than real power flow because of inductance of grid. I used about 100uH in series with ideal 110 V RMS in simulation. happy new year everyone! I hope someone will come up with a really good and cheap solution to this problem

looking at this as a system in proper phase at all times in terms of voltage and current, then if you want to feed power to the grid, you then need extra voltage in perfect phase. This is just like charging a battery, except the battery wiggles, so you must track it closely. Modern systems do this well.

It's all about here:

- You don't need to create the waveform.

- Eliminate the need of transformers?

A Zener diode + resistor can do lot of good And I don't think that it need the full 12V but anywhere from 1 and up.

If you can make work at 3 watts then you can make 30 watts then 300w.... so on.

Am I right?

yes, at about 50 KW you will find it hard to find zeners..

Diac instead?

I am a old poster to this form, way back at number 14. It is good to see people still working on this. It seems a few more people have been able to understand the idea of using the H-bridge to make an inexpensive inverter. Before we go off an start working on 50K units, which hardly anyone has, how about a diagram post or a low power demonstration on YouTube.

Thanks

Mark

I think I licked it, but I'm not sure what my tongue just stuck to, so its a bit worrysome. O.K. so as not to dirty up the line dance. Use tee tiny little L.E.D.'s stuck to the sides of the wall outlets male ends. Right up next to the diodes is a little piece of solar photovoltaic cell or just even 1 little strand of fiber telling them cowboys when to shake it to the left and shake it to the right. Hey, its reinventing the good old fashioned power cord, but it's so small I might never see it!

From the 18th poster.

One of the reason I post this is it's for educational purpose

It's my opinion that:

1- Grid tie inverter will be "things of the past", It's gonna be a single chip (20 cent?) installed in every solar panel?

2- There is s no need for large power gird tie inverter to be use in other mechanical apps such as wind/water. Because as far as I know, it could be grid tied much less then the cost of PMA or other DC gen. or even today's scheme of induction gen? -- I think?

Grid tie inveters "a thing of the past" maybe when as you say each panel could have a built in interface, I could ses that. But what about all of us who already own panels and wind turbines who would like to tie to the grid in our life time. I am 53 years old and would like to unburden myself with the further care and cost of batteries, I need an inexpensive design soon.

I know anythig I built would not be acceptable to the power companies but if a design is as cheap as you say I am sure someone would design and UL certify it. If I could have built a 1000W grid tie inverter for less than $10 as you would indicate, and it being inherintly safe, can not back feed AC without an incoming signal, I would attempt to have it UL approved myself and sell them.

Single panel inverters can be purchased from Enphase. However, they are about $1/watt. A 200W grid tie inverter will run you $200. However, you can be guaranteed that the cost of goods in that system is no more than $100. This company (and others like it) are bound to team up with panel manufacturers and offer "AC Panels" and they will begin to dominate residential PV but I believe that larger systems will have a central inverter for the foreseeable future. http://www.enphaseenergy.com/products/

Example:

http://www.altersystems.com/catalog/enphase-energy-microinverter-m20032240so01-p-1745.html

For a schematic of a Grid-Tie Inverter see: http://www.electro-tech-online.com/alternative-energy/86777-grid-tie-inverter-schematic-7.html

For the real amateur such as myself, a parts list and assembly instructions would be worth paying for. Also, doesn't a wind generator grid tie need different design than a solar grid tie inverter? John

Any grid tie connection needs to be type approved by the electricity regulators in your area, no easy way for a home-made box to be used.

Recently the the Ontario Canada regulators have erected barriers to sales of home made energy to the system in the form of an annual licence, inspection and a monthly rental of a grid tie box. These ruin the economics of most home power systems.

Awesome thread! The design criteria for grid-tie is all about "economics of design." There are a bunch of really great insights here that need to be put into a "design matrix." We need to understand and define the most fundamental issues dealing with cost, performance and mass manufacturing. Let me pose a question to [CIT, MIT, MU] make this point painfully clear: LOL, [how & when] can I grid-tie a grapefruit [battery]?

how about taking a couple of SCR's and a micro with a decent adc and just making a pwm that follows the grid waveform in a short pulse duration square wave that only covers say the sin(pi/4) to sin(pi/2) for a positively 'wired' scr and then sin(5pi/4) to sin(3pi/2) for a negatively wired scr. you could go real stoneage and just hook up some diodes to the scrs that would trip once the grid is at the proper voltage.

how about a multiplexer hooked up to transistors coupled to varied levels of zener/cap banks to store energy at multiple voltages, and then just switch on/off transistors as the grid waveform changes.

or you could just do it the real way with a couple of transistors from a power supply to a transformer tied to the grid. you would just need to trigger using some kind of resistor divider, possibly diode protected, from the grid line. though using a micro would allow you to intelligently and reliably push and pull on the line on a waveform thats like 1% out of phase ahead of the grid.

having the micro would allow you to deal with power outages, where the system shuts down but then again if you planned it properly you could just use diodes and switches to accomplish the same thing. though it would be cheaper in the end to use the micro simply due to the parts cost, having enough pieces at the rated power could easily multiply the expense of the unit.

5 dollars for a micro and a 12v:30v -> 3v regulator, another 5 for passive parts ie caps and resistors just small smt stuff, high power switches can get expensive, but retail ur looking at like 100-500$ otherwise ebay for prototypes, dyi 'rs, etc can get decent scrs for under 50$. the transformer could be problematic, a 'center tapped' transformer to handle the power could cost a decent amount but you could probly just crack open a car inverter so like <$500 retial.

you could probly just crack open a car inverter and add some smarts to it to really 'tie' it to the grid properly. so then you are looking at like a <20$ kit and a <500$ inverter to hook up you solar or wind kit to the grid. ive seen 5kw inverters for <$1k so its still not really worth it unless you can cheaply get the switches and the transformer. then theres liability. someone uses your design and electrocutes themself or a line worker gets fried, you have to be able to defend against it showing you have taken such precautions. now your dealing with extensive and expensive testing.

skipping out on the things like fire hazard assurance and lethality and whatnot, will maybe save you a few hundred to a couple of thousand dollars. going from say 1kw-10kw but is it really worth it? I know i could easily make a grid tie system for cheaper than buying it but i think i would rather buy it than debug >1kw at 120-240vac.

Hello Guest,

To your response #37 you have a lot of Ideas. I understand the concepts you speak of but I do not have the knowedge to design such a circuit. I build lots of circuits to interact with my solar and wind but have had no luck designing a decently efficient circuit to intertie with. I am one of the earlier contributors to this string and have seen several people speak as you have (other strings and sites too) but it seems a tested circuit with parts list is never forth comming. Have you tried any of your concepts that you can share with us hobbiest? Don't get tied up in the cost of transfromeres and such, a design does not need to be 500-1000W as you say a garage sale 200W batery charger is good for a start and scalable by building more. I see the argument all the time the inverter has to be big, forget that most people make renewable a hobby and start small. Many hobiest have lots of parts to work with, design small to start with, give us a starting point.

Build a circuit and post it. You can't be sued for posting a circuit, if so every ham radio operator and computer hobbiest would be in jail by now.

Bring it on.

ill draw something up with some guidelines on scalability/garage parts.

what do you actually want as a reference point?

In relate to #18. I found;

warning-- These are patent pending technology-- Please check with the author if you try to do.

Bridge rectifier - MB152 (digikey.com)

About the H-bridge.

Things that needed:

1-1 At least 10 amp transformer 110v->110V.

2- 4 1/4 watt diodes (al least 200V) (RadioShack $1.99 for 3) Name its D1 to D4

3- 4 40 apms altermistor (Q8040K7 from mouser.com or digikey.com) name TT1 to TT2; each will have 3 terminals gate, MT1,MT2

4- 4- 10 AMP fuses (assume that the transformer already has a fuse built in)

Step 1- building the H-bridge. The purpose is to make a 4 terminal h bridge include two inputs (I1,I2) and two output (O1,O2)s. They are as:

. . a- I1 is the combination of D1 anode,D2 cathode + TT1 MT2 + TT2 MT2

. . b- Connect D1 cathode to TT1 gate, D2 anode to TT2 gate

. . c- I2 is the combination of D3 anode,D4 cathode + TT3 MT2 + TT4 MT2

. . d- Connect D3 cathode to TT3 gate, D4 anode to TT4 gate

. . e- O1 is the combination of TT1 MT1 + TT1 MT3 (two fuses should be placed right after the MT1s) - This is the positive of the H-bridge

. . f- O2 is the combination of TT3 MT1 + TT4 MT3 (two fuses should be placed right after the MT1s) - This is the negative of the H-bridge

Step 2:- Connect I1 and I2 to the output of the transformer

Step 3:- Connect O1 and O2 the serially connected of the bridge rectifier and the solar..

Step 4:-- Warning, (a) It's very very dangerous when you do anything with the high voltage AC.

Who can prevent one building one as this for home use?

One method to avoid transformer. (not yet tested but it's theoretically sounded).

Anode of the D1 also connected to the gate of the TT4

Cathode of the D2 also connected to the gate of the TT3

At TT3,TT4 - swap the MT1 and MT2.

If this one work then all you need is 2 diodes,4 altermistors, 4 fuses and 1 full wave bridge rectifier - Nothing is more simple then this.

Oops!!

Cathode of the D1 also connected to the gate of the TT4

Anode of the D2 also connected to the gate of the TT3

- I'st arrange to have one diode to connect to two gate of the altermistors instead of one

Hello,

I'm building a grid-tie inverter of my own. I have yet to prototype the unit but if the specs of the components I'm using on my design are any indicator, my unit shall have the following specs...

Voltage = 120VAC

Peak Apparent Power = 2400VA

Peak Current = 20A

Duty = 100%

I'm quite proud of the design. I've adapted the diode-clamped multilevel design for use on 120VAC systems and use fewer components than prescribed in the literature. The topology is a multilevel H-bridge hybrid. The beauty of it is that like a multilevel diode-clamped inverter it also supplies VARS but with FAR fewer parts. Remarkably the bill of material is close to $150 without the need for large transformers, excessive heating of parts or injecting loads of harmonics back onto the grid.

I can't seem to add pictures here so I'll describe the circuit as best as I can. There are several stages to the design. The circuitry is far simpler to grasp in schematic form, believe me.

1) Boost Converter DC-DC. Whatever the DC source you're using, you need to boost the signal up to peak dc grid voltage (170Vpeak = 120Vrms) and beyond. You will need to control the converter so that output power (to the next stage) is maximized depending on the available power at the input (wind, water, solar etc.)

2) Multi-Buck DC-DC converter. You convert the approximately 170VDC into several smaller DC voltage levels with buck converters. The more levels you use, the higher the current rating you will achieve overall and the less the THD (total harmonic distortion) on the output. I'm using 8 levels but the minimum you would want to use is 3 to significantly reduce the harmonics you would get with a PWM. The additional cost per level is about $10. Each voltage level is separated by a large 1000uF capacitor to form a ladder.

3) Switches. The output voltage of each level (in stage 2) connects to a common bus (stage 4) via 2 opposing N-channel mosfets (per level) with integral clamping diodes. This is CRUCIAL since this will allow you to supply and consume VARS which you need to do if you want to run motors, inductive loads and electronic power supplies. To save the cost of driving each mosfet you connect the mosfets such that you can use a high-side mosfet driver to turn both of them on simultaneously regardless of which side of the switches has the higher voltage.

4) Bus. The outputs of each pair of switches in stage 3 are shorted together, filtered with a capacitor (more on that in a minute) and then fed into an h-bridge using higher rated mosfets.

Principle of operation:

You convert your raw input power into a stepped up DC voltage. Use this voltage to both transmit your power to your inverter (since your copper losses will be significantly reduced compared to if you send 12V power to your inverter) and modulate the inverter power going back to the utility. The voltage of each stage 2 element is proporational to the secondary voltage of stage 1. A controller circuit (easlily done) would turn the switches of each successive level on and then off again forming a staircase waveform on the bus with as many "steps" as there are levels. This approach has the distinct advantage of reducing commutation loss that high frequency switching PWM inverters use which inevitably over-heat your switch and inject unneccessary harmonics into the grid. Several switches are used, switch on and off at the grid frequency (60 Hz where I live),share the I2Rdson losses evenly between eachother and eliminate the need for output filters. It is important to ensure that only one level's switch be on at a time to avoid a multilevel short circuit. A smoothing capacitor is placed on the bus to provide intermediate power during commutation. The H-bridge commutates when the step waveform reaches the crossover voltage and the cycle continues.

The strategy I'm using for synchronizing the output voltage waveform is by means of a microcontroller measuring the time between a half-cycle for each half-cycle and then starting the staircase waveform at a zero-crossover of the output/grid waveform (triggered by an op/amp to interrupt a microcontroller) to last as long as the previous half cycle. This way the circuit is immune to the smallest frequency variation on the grid's waveform, is easy to implement and gives total control of the phase angle. This is done with a tiny transformer (a spare ac adapter sitting around the house will do) between the line and neutral with the secondary connected to control voltage circuitry, being cleaned up with op-amps and fed into a microcontroller.

I realize this sounds complex but if you saw the circuit in schematic form, it is fairly elegant and simple considering what the circuit is being asked to do. I would not even think of using an isolation transformer as sourcing one is a big problem for most people. PWM in my mind is out of the question as it makes the output power very "dirty" and forces all the output power through a single switch, forcing you to pay for higher rated components whereas with the above approach you would buy more components but with lower required ratings.

If anyone is interested please post and I'll send a schematic.

Thanks,

Hi,

I got a membership and can therefore post images. I posted here last night regarding the 2400VA 120V grid-tie inverter. I'm interested to see if others can use this design in their own projects and would like to hear from them about their experiences. I'll have to add the controller circuit and low side current sensor but will have to get back to it later.

Hi. send me schematic please

dear Sir,

i have read your document on Grid Inverter, and please send me ircut diagram on my mail id that is saurabh044@gmail.com. I will be very thank full to you.

Saurabh singh

I'd really like to see your drawing for this design. Have you considered a shutoff in the case of the grid going down? (The shutoff would protect utility workers' safety.)

Hi: I've been following your conversation. Has anyone built the above circuit yet? I'm in Mexico, so while there is regulation, no one checks.. If you can tell me some results I'll duplicate here. Cheers

There is a great GTI at http://www.electro-tech-online.com/alternative-energy/86777-grid-tie-inverter-schematic-15.html and http://www.electro-tech-online.com/alternative-energy/90964-250-watt-grid-tie-inverter-build-8.html and in his personal blog here; http://www.timnolan.com/index.php?page=solar-grid-intertie-inverter enjoy

Your welcome!

It rather amazes me that those threads are still drawing the number of regular views that they are! I intended for them to be simple, basic, and workable within reasonable levels of electronics knowledge and to be built with nothing more than common electrical and electronics parts. What more could you want from free schematics!

And yes I really am the same tcmtech guy here as I am there.

Here is the link to my 2.0 writeup. http://www.electro-tech-online.com/alternative-energy/105324-grid-tie-inverter-schematic-2-0-a.html

Interesting, no PWM, another issue that will surface in the future is Frequency variations of GRID power to sync with say down to 56hz -63hz US. How would you compenstae or maybe just a simple add on circuit?

put your images on instructable.com

Please send me a copy of your schemaic. Could you also attach your description of operation along with it. I hope to be able to impliment this ona house I am currently in the process of building on our acreage.

To:

bhughes@rhughes.org

hi ,

sir i m also workin in grid tie inverter .problem is that i have only one month to do as much as i can . uptill nw what i have been doin is apparently jst studin the the topologies... if u could send me your schematics i might be able to follow a guide line to work on a straight track...

mail add is simplyshuja@yahoo.com

Yes,

We are all interested in a schematic diagram. It would be of great help to everyone on this list. I personally would be very interested in building one.

Tom Cornell

The system if it works it requires a constant frequency or at least it a predictable cross zero (at the future) tt may be anywhere between 60HGz +-10%. or 54Hz to 64Hz. It's not impossible but it's hard (though) to generate a amplitude that go in sync with the AC curve of the grid?

If your seriously looking for schematic and full descriptions of how to build one check out 'electro-tech.com'! Their alternative energy section is loaded!

They got loads of information and relevant discussion's about legality and the actual working circuits. Plus for the simpler guys they even have the full analog circuit systems and the recommendations from actual people that built them for more complex and bigger or smaller systems too!

Hello, This forum thread is very informative, but I would like to add a little twist to what has all been said about design and the implementation of a grid tie inverter. I have 3 grid tie inverters I buy online at www.buyerisland.net/gti-300.htm and it is fantastic. I have three 85 watt panels wired in parallel to the unit and plug the AC side right into my AC receptacle to feed the house and the grid. The unit does not have UL Listing but I do not produce more then I use (but it has drastically lowered my utility bill). Now for the twist... I like this grid tie inverter I am using as I can stack more as I build my system. I have seen on the website, and talked to the people of buyerisland in regards to their wholesale offer http://www.buyerisland.net/wholesale.htm so I can sell this simple grid tie inverter for a little profit and aid all of us in our "Green" quest. I read frequently about Grid Tie Inverters needing UL Listing. Is there any restrictions I should be aware of if I would venture into "selling" a Grid Tie Inverter without UL Listing ? The design is fantastic, and it is truly a "Plug-n-Play" inverter. Thanks, Sid Alan hkalan2007@yahoo.com

yes

Wow, I never thought engineers could write so many words

This is a good place to start.

It isn't a grid tie design, but I'm guessing you would have to sniff the grid voltage rather than making your own sine wave, with feedback to control the voltage output (i.e. change the amplitude of the triangular wave to control a constant current). Please don't shoot me down if this is wrong, it'd be nice to start a process whereby a working design evolves from a succession of responses.

Adrian

There are many companies currently paying top $$$ for such developments? What a about the bad guys, who want to make plenty of $$$ and fortune on the back on somebody for thanks.

did you ever get a schematic to the grid inverter

email me

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thanks

YOUTUBE has one for DIY + Schematic. (claimed penny per watt)

http://www.youtube.com/profile?user=PTranCypress#p/u/0/12E6bQ1OksU

http://www.neo-aerodynamic.com/GridTieInverter.html 3000+ watts