Grid Tie Inverter Schematic

Re: Another Example

I got the the PWM software working and scoped the microprocessor output to see that it was locking-in with the power line. Everything looked good. I then got busy with a couple of large projects and put the Inverter on the back burner. I never got to power up the high voltage section. I am not so busy this year and might resurrect this project. I am glad to see that there is lots of interest in this area.

Hi Robby here, I read your article with interest, and I would like to build a 250 watt
230 volt, 50 hrtz Grid tie inverter, but I need your help with design and parts list please, I am a very interested newby, Not sure if I should put my e mail address, but I gess someone will tell me,thanks, robert@xnet.co.nz

Sure. I have been wondering if someone would eventualy come along. What do you have to work with? And what level of system are you looking to make?

IF you dont have any parts yet a 20 amp battery charger transformer will make a good start.

Would you mind doing this one in a new thread? Say "250 watt Grid Tie Inverter Build"

It will make it a better reference point. Thanks!

Vakl;
What a beautiful and professional looking board you got there.
Hopefully you'll be able to finish it succesfully.

How much pwer do you calculate your IGBTs will be dissipating?

Hi everyone.
I have been completely blown away by the amount of effort that has gone into creating the last 7 pages! Particularly I would like to thank tcmtech and Val for their obvious technical expertise, and the time that has been shared on this board.
My interest in electronic projects has has grown slowly over the past years, but I still lack the technical know-how to tackle this sort of large project without serious help.

My interest here is that my family has a holiday shack in an area of full Australian sun and abundant wind supply. I would like to build a small GTI with PV cells to slowly trickle power back to the grid for the outcome of a $0 power bill. As the shack is not occupied for around 6 months of the year I don't see that a large system is required- however being able to add PV cells as they come to me would be nice.

If no-one else does then I will start a new thread to help myself and other newbies design and build a low power GTI.

Many thanks,

Julian

Thanks Fernando

I don't know how much power the IGBTs will be dissipating. I may find that at a switching frequency of 60KHz the power dissipation is too high. Since this is a software driven device, the switching frequency can be reduced easily. The cost is a slightly coarser sine wave.

Val

Information

Here are some URLs for additional information on grid-tie inverters.
Freescale1
Freescale2
Freescale3
**broken link removed**

Grid tied inverter

This is my first post -- so Greetings to all.

I have kind of perused this thread - more or less lightly.

I see that is seems that one or more like to develop a Grid Tied Inverter uisng Non-sinosoidal waveforms like square or modified Sine waveforms.

I have designed DC/AC inverters from low power to high kilowatt power, including the Grid tied Inverter.

Regulations demand certain things like Islanding, current leakages and power drop when the Grid drops within certain number of hertz, of deviation of frequency plus other requirements to fill.

The logical way is to produce a sine wave voltage and current ( in phase) to the Grid reference points -- any other way - problems will appear.

One can make it using a half bridge or a full bridge, or a dual half bridge to produce in this case, 117-0-117 or 234 volts AC.

Any other scheme using non sinosoidal or equivalent waveforms are NOT allowed. ( these, as well, means that a step sine wave is acceptable if the distortion is within the regulation level ) - so a MSW is not permitted.

Regards

Nando

mvocray said:

Hi again,

I have a few things I'd hope you could clarify re current source inverters vs voltage source inverters. I'm assuming an H-bridge configuration in all cases. Sorry it's quite off the main topic since I'm quite a newb in this.

1. I understand that DC current would be fed in current source inverters, not voltage sources, i.e., voltage sources should first be transformed to fixed current sources right?

2. If instead I use the H-bridge to switch and form a voltage source whose fundamental is greater than the line (with the same phase as the line) and connect it to the line using a impedance (low valued resistor or a low valued inductor perhaps to limit the current amplitude), would that circuit cause troubles?

To sum it up: I'm thinking of getting away with making a grid-tie inverter using an H-bridge that does an in-phase modified sinusoid (PWM) with fundamental's amplitude greater than the line. And connecting this modified sine wave to the line in phase with a small filter inductor. DO you think there will be problems with this setup? Thanks

Click to expand...

I have kind of perused this thread - more or less lightly.

Click to expand...

Hahaha Me too! And I did most of the technical write up!

Got any practical design tips to share?

Practical designs or things that should be watched for as the power levels get further up.

But if you have actualy built them, also Feel free to share some knowlege with us.
It is always appreciated by all.

I dont know everything (yet)!

Being this is a new subject to many you may have seen I am trying to start out with the basics so we can work up from there.

Any other scheme using non sinosoidal or equivalent waveforms are NOT allowed.

Click to expand...

He did share one thing and one more

step sine wave is acceptable if the distortion is within the regulation level

Click to expand...

I would like to no more about half bridge
and dual half bridge I have seen them in inveter of ups.

Yea I caught that too. But I can only assume he is talking about the line side of the system. I know the utilities are picky about that. Most of his statements are rather vague though.

Everything I have ever experimented with and built over the years has been able to give a good clean output waveform just using the power transformer and PFC and a good line filter. No matter what method of operation I used on the H-bridge input side.
But all my stuff requires some form of satep up isolation so the standard tranformer design is what I have always been working with and I know that has always worked well.

I dont know about direct connecting the H-Bridge right to the lines though. I think then what he is talking about could be where you could run into those problems real easy.

I hope he elaborates more.

Half bridge or dual or full bridge can be isolated or not isolated, this depends on how the power source is implemented.

Recentley isolation transformers have been used, this for human protection, and the isolation can be made after the half bridge or in between the power source and the high voltage conversion -- like 58 volts to the conversion to 200+ - 0 200- for the sine wave generation.

The job to develop one , this if you have a good technical experience and know-how, may be close to 2000 to 10,000 man-hours -- so think about it !!

The bridge, any type may need a high voltage isolation between the upper and lower semiconductors and to the circuitry driving the devices and this isolation has to have a low delay time which should not me more than 0.03 to 0.1 % of the pwm maximum width to avoid response problems.
Current detection either pulse by pulse and/or at the output Grid frequency .

GRID tied inverter DO REQUIERE additional parameters which are somechat complicated and not very easy to implement because the inverter needs to detect the Grid frequency and the sine wave generation synchronized in accurate phase -- these are the simple basics which really need deep understanding - reason why there are not many companies producing Grid Tied Inverters.

Does this help ?.

Nando

Your location would help, as the technical standards vary.

Some yes. The 2000 to 10000 man hour part could use a little more explanation.

If your refering to designing a grid tie inverter system taking that long I think you may need to take some over paid and grossly underworked developers out for a good beating!

As far as synchroniozing, line frequency and line voltage monitoring thats easy! I will be covering that in the "250 watt grid tie inverter build" thread in a few days. They will be basic but reliable analog circuits.

Additional control such as RMS voltage and peak voltage monitoring, thermal limits, and switching device current control is not hard either. And as far as isolation of different voltage sources and levels in relation to the control circuits thats not much either.

I can knock that all out in analog if need be. But I prefer to go to some level of micro proccesor based control system at that point. I prefer PLR or PLC myself, Its what I am most familiar with and have fair programming knowlege in.

If I turn over my design for my 15 KW GTI can I have the engineering pay equivilant of the 2000 hours?

But I am not speaking for everyone here just myself.

However there are some super Miroprocessor people here! Give them a challenge!

But over all I am delighted to have you keep giving pointers and tips!

And always feel free to give pointers and comments along the way. Most threads here are a group effort. Everyone has there own strong areas.

Mine is power conversion systems.

tcmtech said:

and it will be on some enviro-nutter website for free in the over unity devices section with all the input watt numbers divided by 3 and the output watt numbers multiplied by 500!

So if any of you have a size you would like to see and everyone can agree on I will consider it!

Click to expand...

I think you are mixing "environmental nutters" with "con men"

Inverter Design

Hi, I have done it with the TL494, Your idea is right and it works. You only have to scale the input and rectify at the error amplifiers in the TL494. You can use a Microcontroller to create the sine wave also & it will give you the logic also to turn on the desired pair in the H Bridge. You leave on the high side for 8.3 ms and switch the lower side at HF, & then change switches to change polarity.... If you leave on the low side & switch the High side it will be easier to sense the output Voltage.

mvocray said:

Hi! I got interested as I'm thinking of building one myself, otherwise I won't graduate next semester. LoL. My idea is to build an H-bridge with the high side switches connecting at 60 Hz (it's 60 Hz here) and the low side ones running at high freq SPWM as Hero suggested.

The current harmonics will be filtered out by a low value sense inductor in series with the line. The focus of my project is proper timing of the control switches.

The problems I've encountered with the design so far are
1. getting proper line voltage feedback (I believe an unknown value lag would come from feeding back using a transformer)
2. I'm thinking of using FET switches with snubbers. With a DC current source feeding current into the H-bridge, overlap times would be necessary otherwise, there would be no path for the current, right? Following this argument, how will the SPWM scheme (requires off times) work with a current source?

As far as I've heard, most applications nowadays use MC. I would want to make one using only analog components though.

Also, this is my first time making the circuit, so any help/criticism of the work will do. Thanks.

PS. First time joining a forum. How do I post my schematics? LoL

Click to expand...

Gti

Greetings to everyone, it's also my first day. One possible way is to use an interleaved PFC IC, and take the reference signal directly from the grid. You will get a sinusoidal in phase current, you will only need to change current direction with an H-Bridge every 8.3 ms.

Kind regards,

Felipe Kobeh.

nando37 said:

This is my first post -- so Greetings to all.

I have kind of perused this thread - more or less lightly.

I see that is seems that one or more like to develop a Grid Tied Inverter uisng Non-sinosoidal waveforms like square or modified Sine waveforms.

I have designed DC/AC inverters from low power to high kilowatt power, including the Grid tied Inverter.

Regulations demand certain things like Islanding, current leakages and power drop when the Grid drops within certain number of hertz, of deviation of frequency plus other requirements to fill.

The logical way is to produce a sine wave voltage and current ( in phase) to the Grid reference points -- any other way - problems will appear.

One can make it using a half bridge or a full bridge, or a dual half bridge to produce in this case, 117-0-117 or 234 volts AC.

Any other scheme using non sinosoidal or equivalent waveforms are NOT allowed. ( these, as well, means that a step sine wave is acceptable if the distortion is within the regulation level ) - so a MSW is not permitted.

Regards

Nando

Click to expand...

Self-Installed PV Project

Here is someone who actually did it all.

**broken link removed**

I didn't see any grid tie inverter schematic there. Just a lot of talk and a "partial" H-bridge with no drive and even then, it wouldn't work without about 50 times more circuitry ! OK, maybe only 45 times more parts.

I do see a picture of something that is supposed to be an inverter, (and maybe an IGBT nodule)

Do we see a picture of a wind turbine, a solar panel ? I didn't see that either.

It would have been a lot more interresting to get a complete hand writting shematic than spending all this time putting long answer to this tread.

Otherwise, this might be called "Guerrilla Wind".

tcmtech, to prove me that I am completely wrong could you send me your grid tie shematic ?

Thanks a lot

I was not overly impressed with the information on that link either. Everything was factory built. Granted they did install it themselves which is great but the actual pictures and overall information was rather lacking I thought.

And if your going to be advertising your build on the INTERNET at least put a shirt on!

Actually I have the full Schematic for the power system already in the 250 watt grid tie build thread.
That thread has a far better descriptive write up of how and why things work.
I have the basic control system circuit schematics there too. But I have not gotten around to drawing up the full analog control circuit. Sorry about that. All of the individual comparator circuits are shown along with a fair writeup of what they do and where they are used.

Granted it is a full analog design and its rather simplistic as far as the power handling is concerned but it is based on several real life units I have and one has been running for a few thousand hours without trouble!
And it does infact give you a good clean sine wave on the grid despite the simplistic switching and filtering design.

The design information I have been posting here is admittedly basic but it has proved very reliable. I do have much more complicated and sophisticated designs than what I am giving out here.
But this is all done for free just to show that its possible to do a full grid tie inverter using basic and common components.
The higher end designs are not for free! Sorry!

I hope this helps you out some. If you need more information just ask!