## Designing a Grid-Tie Inverter Circuit

A grid tie inverter works quite like a conventional inverter, however the power output from such inverter is fed and tied with the AC mains from the utility grid supply. As long as the mains AC supply is present, the inverter contributes its power to the existing grid mains supply, and stops the process when the grid supply fails.

The concept is indeed very intriguing as it allows each of us to become an utility power contributor. Imagine each house getting involved in this project to generate overwhelming amounts of power to the grid, which in turn provides a passive income source to the involved residences. Since the input is derived from the renewable sources, the income becomes absolutely free of cost.

Making a grid tie inverter at home is considered to be very difficult as the concept involves some strict criteria to be observed, not following may lead to hazardous situations.

The main few things that must be observed are:

The output from the inverter must be perfectly synchronized with the grid AC.

The output voltage amplitude and frequency as mentioned above must all correspond with the grid AC parameters.

The inverter should switch OFF instantly in case the grid voltage fails.

In this post I have tried to present a simple grid-tie inverter circuit which according to me takes care of all the above requirements and delivers the generated AC into the grid safely without creating any hazardous situations.

Let's try to understand the proposed design (exclusively developed by me) with the help of the following points:

Again, as usual our best friend, the IC555 takes the center stage in the entire application. In fact only because of this IC the configuration could become apparently so very simple.

Referring to the circuit diagram, the IC1 and IC2 are basically wired up as a voltage synthesizer or in a more familiar terms a pulse position modulators.

A step down transformer TR1 is used here for supplying the required operating voltage to the IC circuit, and as well as for supplying the synchronization data to the IC, so that it can process the output in accordance with the grid parameters.

Pin#2 and pin#5 of the both the ICs are connected to the point after D1, and via T3 respectively, which provides the frequency count and amplitude data of the grid AC to the ICs respectively.

The above two information provided to the ICs prompts the ICs to modify their outputs at the respective pins in accordance with these information.

The result from the output translates this data into well optimized PWM voltage that's very much synchronized with the grid voltage.

IC1 is used for generating positive PWM, while IC2 produce negative PWMs, both work in tandem creating the required push pull effect over the mosfets.

The above voltages are fed to the respective mosfets, which effectively converts the above pattern into a high  current fluctuating DC across the involved step up transformer input winding.

The output of the transformer converts the input into a perfectly synchronized AC, compatible with the existing grid AC.

While connecting the TR2 output with the grid, connect a 100 watt bulb in series with one of the wires. If the bulb glows, means the ACs are out of phase, reverse the connections immediately and now the bulb should stop glowing ensuring proper synchronization of the ACs.

You would also want to see this simplified design

Assumed PWM Waveform (bottom trace) at the Outputs of the ICs

Parts List

All resistors = 2K2
C1 = 1000uF/25V
C2,C4 = 0.47uF
D1,D2 = 1N4007,
D3 = 10AMP,
IC1,2 = 555
MOSFETS = AS PER APPLICATION SPECS.
TR1 = 0-12V, 100mA
TR2 = AS PER APPLICATION SPECS
T3 = BC547
INPUT DC = AS PER APPLICATION SPECS.

WARNING: THE IDEA IS BASED SOLELY ON IMAGINATIVE SIMULATION, VIEWER DISCRETION IS STRICTLY ADVISED.

You would also want to see this simplified design

After receiving a corrective suggestion from one of the readers of this blog Mr. Darren and some contemplation, it revealed that the above circuit had many flaws and it wouldn't actually work practically.

The revised design is shown below, which looks much better and a feasible idea.

Here a single IC 556 has been incorporated for creating the PWM pulses.
One half of the IC has been configured as the high frequency generator for feeding the other half IC which is rigged as a pulse width modulator.

The sample modulating frequency is derived from TR1 which provides the exact frequency data to the IC so that the PWM are perfectly dimensioned in accordance with the mains frequency.

The high frequency makes sure the output is able to chop the above modulation information to precision and provide the mosfets with an exact RMS equivalent of the grid mains.

Finally, the two transistors make sure that the mosfets never conduct together rather only one at a time, as per the mains 50 or 60 Hz oscillations.

Parts List

R1,R2,C1 = select to create around 1 kHz frequency

R3, R4,R5,R6 = 1K

C2 = 1nF

C3 = 100uF/25V

D1 = 10 amp diode

D2, D3, D4, D5 = 1N4007

T1, T2 = as per requirement

T3, T4 = BC547

IC1 = IC 556

TR1, TR2 = as suggested in the previous section design

The above circuit was analyzed by Mr. Selim and he found some interesting flaws in the circuit. The main flaw being the missing negative PWM pulses of the AC half cycles. The second fault was detected with the transistors which did not seem to isolate the switching of the two mosfets as per the fed 50 Hz rate.

The above idea was modified by Mr. Selim, here are the waveform details after the modifications. modifications:

Waveform Image:

CTRL is the 100 Hz signal after the rectifier, OUT is from PWM from both halve waves, Vgs are the gate voltages of the FETs, Vd is the pickup on the secondary winding, which in sync with CTRL/2.

Disregard the frequencies as they are incorrect due low sampling speeds (else it gets too slow on the ipad). At higher sampling freqs (20Mhz) the PWM looks quite impressing.

To fix the duty cycle to 50% at around 9kHz, I had to put a diode in.

Regards,
Selim

For enabling the detection of the negative half cycles, the control input of the IC must be fed with both the half cycles of the AC, this can be achieved by employing a bridge rectifier configuration.

Here's how the finalyzed circuit should look according to me. The transistor base is now connected with a zener diode so that would hopefully enable the transistors to isolate the mosfet conduction such that they conduct alternately  in response to the 50 Hz pulses at the base T4.

Hello Swags,

I have tried the zener-diode approach (no-luck), CMOS gates and, much better, op-amps worked best. I've got 90VAC out of 5VDC and 170VAC from 9VDC at 50Hz, I believe it's in sync with the grid ( can't confirm as no oscilloscope). Btw the noise goes if you clamp it with a 0.15u cap. on the secondary coil.

As soon as I put a load on the secondary coil, it's voltage drops to 0VAC with only a slight increase in input DC amps. The Mosfets don't even try to draw more amps. Perhaps some mosfet drivers like IR2113 (see below) could help?

Although in high spirits, I feel that PWM might not be as straight forward as hoped. It definitely is good to control torque on dc motors at low pwm freqs. However when the 50 Hz signal gets chopped at higher freq, it for some reason looses power or the PWMd mosfet can't deliver the needed high amps on the primary coil to keep the 220VAC going under load.

I've found another schematic which is very closely related to yours, except PWM. You might have seen this one before.

The power handling circuit is an H drive with IGBTs (we could use mosfets instead). It looks like it can deliver the power across.

It looks complicated but actually is not too bad, what do you think? I will try to simulate the control circuit and let you how it looks.

Regards,

Selim

Some very interesting modifications and information were provided by Miss Nuvem, one of the dedicated readers of this blog, let's learn them below:

Hello Mr. Swagatam,

I am Miss Nuvem and I'm working in a group that is building some of your circuits during an event about sustentable living in Brazil and Catalonia. You have to visit some day.

I've been simulating your Grid-Tie Inverter Circuit, and I'd like to suggest a couple of modifications to the last design that you had on your post.

First, I was having problems where the PWM out signal (IC1 pin 9) would just blank out and stop oscillating. This was happening whenever the Control voltage at pin 11 would go higher than the Vcc voltage due to the drop across D4. My solution was to add two 1n4007 diodes in series between the rectifier and the control voltage. You might be able to get away with just one diode, but I am using two just to be safe.

Another problem I was having was with the Vgs for T1 and T2 not being very symmetric. T1 was fine, but T2 was not oscillating all the way up to Vcc values because whenever T3 was on, it was putting 0.7V across T4 instead of letting R6 pull up the voltage. I fixed this by putting a 4.7kohm resistor between T3 and T4. I think any value higher than that works, but I used 4.7kohm.

I hope this makes sense. I am attaching an image of the circuit with these modifications and the simulation results that I am getting with LTspice.

We'll be working on this and other circuits for the next week. We will keep you updated.

Warm regards.
Miss Nuvem

1. Hi Swagatam,

what is the perfect TR2 and MOSFETS to use in this circuit?

if i have a 12-0-12 1500watts transformer, how many FETS will i use for iRFZ44n?

Regards,

1. I would suggest you to first check whether the circuit works proposed in the explanation, if it does then you can proceed with the selection of the other sections like mosfets etc.

By the way any type of N mosfet should work here, just make sure they are accurately matched with the transformer primary rating.

2. is this the circuit that can lower your electric bill?

Regards,

3. No this circuit will not lower your electric bill, but in countries where production and selling of excess electricity is allowed, this type of inverters can become a source of passive income.

4. what is the Grid-Tie inverter that i saw in you tube that the meter runs in backward? is it true or just a joke?

5. I haven't tried this circuit practically so have no idea how it would respond...

6. can i use 500mA for TR1?

7. yes, can be used.

8. Hi
You can get H bridge modules with the built in drivers and automatic dead time

Regards
Snuf

9. Hi Mr. Swagatam,

2. hi swagatam this is kurush karanjia here. This circuit of yours can be very help full in the PCU i am trying to make by synchronizing inverter output to the AC mains output and then suppling to loads. So please help and tell me how can i implement this circuit in the way i want.

1. Hi Kurush,

as mentioned in the bottom warning message, the idea has not been tested practically.

So you will have to check it practically using an oscilloscope and other equipment to confirm its working.

If the IC responds just as mentioned in the article then our job is done, we can be sure of the results.

3. thanks swagatam but some changes will have to be made to use it to supply load by synchronizing inverter and mains. so what changes will have to be made?

1. I have assumed the IC to handle a few things which have been mentioned in the article, if that happens correctly rest of the things will automatically shape up.

Synchronizing phase amplitude and frequency are the only things which are important. And also the inverter should switch OFF when mains is not available. All these things have been taken are of in the above circuit.

Unless the circuit is tested practically nothing can be said.

4. here you have shown how to supply the power back to grid after synchronization but i dont wanna supply back to the grid i want to synchronize both the supplies and then supply the load from it

1. OK, by synchronization you mean you want the inverter AC to replace the mains AC immediately when mains AC fails? Right?

2. no by synchronization i mean i want to synchronize the output of inverter and the ac mains and then supply to load when the inverter is not able to supply the load completely..

3. Yes i have tried to design exactly that in the above circuit, the ICs synchronizes the inverter AC output with the grid AC so that both merge together adding up the overall power to the appliances.

4. so please tell what should be the values of T2, mosfets and how much dc input should i use

5. T2 = BC547

mosfet = sk1058

please be cautioned: you are taking a huge risk by making something which has not been confirmed, and it involves potentially dangerous AC currents.

6. ok no problem i will take all possible precautions and will use a mcb before this entire device
And i will be directly using the inverter output so which part of the circuit should i eliminate and where to collect the load

7. and what should be the values of the TR2

8. i think by mistake you have replied to this question in another post but its ok i got what you said but my question now is that i am gonna use the inverter output directly so will need to eliminate some portion of this circuit so what portion should i eliminate...?

9. This circuit cannot be used like a normal inverter because for that we may have to eliminate a few stages and also introduce additional new stages.

You may refer to this circuit for making a simple inverter:

10. i am gonna make the inverter using another circuit and then want to synchronize the output of that inverter with ac mains and then supply to loads

5. i will try making this at home so please tell what should be the values of T2, mosfets and how much dc input should i use

1. The above circuit is of a grid tie inverter, I don't think you are looking for a grid-tie inverter circuit......???

6. The meter will run in the reverse if being fed.
I have seen grid tie inverter and they have a complex a/c synchronization ic circuit and they work in a range of the ac voltage.
Does this circuit also have a working voltage for the grid a/c and also frequency since frequency might drop due to heavy loads being used

1. As per my assumptions, the above circuit derives the frequency and the amplitude information from the existing AC grid input and processes the circuit output accordingly, therefore the circuit should be producing perfectly synchronized AC back to the grid.

2. Thanks but is there any issue w.r.t grid voltage fluctuations

3. The inverter output will follow the grid voltage data accurately so there should not be any issues.

7. Hi Swagatam,

what is the type of capacitors C2,C4?

Regards,

1. They are ordinary ceramic types.

8. Hi Swagatam,

10amps diode is not available in my area. only 6amps. can i use it?

Regards,

1. Use two 6 amps in parallel.

9. Hi Swagatam,

i almost finish with the first circuit but suddenly you modified it, what is wrong with the first circuit?
what is the function of BC547 in the modified circuit?

i would like to know the T1 and T2, is it the same value of FET's?

the T1 Source is connected to T2 Drain?

Regards,

1. I keep modifying my circuits to improve them more.

Both the ICs should produce waveforms in tandem by translating both the halves of the grid AC cycles, therefore BC547 is added so that the bottom IC is able to translate the negative half cycles into the required PWM.

T1 and T2 are same.

"sources" are made common and connected to ground, and the drains are connected to the transformer taps.

2. thanks Swagatam for your quick response...

i just want to clarify the connection of the FET's. because in the diagram my understanding the source and the drain is connected.

i can put the FET's and parallel it into one heatsink?

for testing purposes, can i use a lower wattage for a light bulb?

Regards,

3. Yes in the diagram it's wrongly shown, the source should be made common and connected to ground.

A common heatsink can be used for T1/T2

low wattage bulb can be used for testing, but without oscilloscope you cannot judge the waveforms.

Regards.

4. Hi Swagatam,

it is not sure if the wave form is sine wave even if it is tested with the light bulb?

what will happen if it is not synchronized with the local power?

i already finished with this circuit and i don't have a oscilloscope.

Regards,

5. First test the inverter separately, do not connect the output of the inverter to the grid, instead connect the output to a 100 watt bulb, next connect a DC power source may be a battery 25AH 12Vand to the shown points, check the bulb illumination.

TR1 must be connected to the AC mains as shown for the above testing.

If the bulb illuminates fully then we can proceed further.

WARNING: THE SUGGESTIONS ARE BASED SOLELY ON MY IMAGINATIVE SIMULATION.....

6. can i use DM for testing the output?

7. with DMM you cannot check RMS and amplitude....

10. Hi Swagatam,

i want to clarify the testing procedure.

While connecting the TR2 output with the grid, connect a 100 watt bulb in series with one of the wires. If the bulb glows, means the ACs are out of phase, reverse the connections immediately and now the bulb should stop glowing ensuring proper synchronization of the ACs.

- is TR1 connected to the grid?
- do i need to connect the battery?

Regards,

1. TR1 is connected to the grid so that the 555 circuit is able to assess and the synchronize the waveform accordingly.

Battery is required at the shown DC source points.

Pls read the warning message at the end of the article.

2. so it is not sure if the testing of this circuit will run and safe?

how do i test the wave form? on which point do i connect the probe?

Regards,

3. It seems you are very much new in the field so I will recommend not to build this circuit, it may be dangerous for you.

The output from TR2 can be fed to an oscilloscope to read the waveforms.

11. What kind of simulation tool did you use?
Thank you

1. mind simulation

12. Seems that pin 7 cannot go to + or it will short.

1. OK, thanks, you may add a 1K resistor in series with it.

2. Hi Swagatam,

the 1K resistor is going to the positive of the battery?

pin#4,6,7&8 of IC1,2 will put a 1K resistor going to the +?

Regards,

3. No, the 1K resistors will go from pin#7 to the postive of the respective ICs (pin#4/#8....)

4. Ok i got it... thanks

5. Hi Swagatam,

6. yes both of them should be connected to the 1K resistor.. since they are both joined together...

7. Hi Swagatam,

just for clarification...

pin# 6 and 7 with 1K resistor will connect to pin# 4 and 8? or is it going to the + of the Battery?

Regards,

8. pin#6 and 7 with 1K resistor will connect to pin# 4 and 8....NOT to the positive of the battery.....

Regards.

13. Hi Swagatam,
Been following this post for a while now and cannot beleive the amount of novice`s trying to build this un-tested project with no idea of what the components are doing. Do some research guys before you kill yourselfs.

Looked at the circuit myself and I can understand the half wave entering the chip at pin 5 which will follow the mains frequency but cannot see what you are trying to do with pin 2 as this is also at the same frequency.

You state that the chip is wired as a pulse position modulator which would be fine if it had another higher frequency either injected into pin 2 plus a timing cap or simply ocilating the chip at a higher frequency.

The tall and short of this is where is the higher frequency derived from other than the 50/60Hz that is injected ?.

Regards Darren.

1. Hi Darren,

I have already provided the necessary warning in the article and during the conversations.

Yes pin#2 needs a high frequency for enabling the PWMs at the output.

I'll reconsider the design soon and hopefully correct it.

Thanks!

14. Hi Swagatam,

Having done some more research about the 555 timer chip it seems you would have problems with the duty cycle only operating from 10%-90% which could cause both outputs to be on at once.

I am thinking that a better aproach to this problem would be op-amps.

Using something like a LM324N, 2 op-amps creating a high frequency saw-tooth and fed to the neg of the remaining two op-amps then half waves (50/60Hz) fed to the positive of the op-amps creating two seperate pwm outputs.

Maybe this would be a easier option and only one chip to buy. All off the top of my head at the moment !!!.

Hope this may help. Good Luck !.

Regards, Darren.

1. Hi Darren,
Thanks!

Yes surely opamps can be used also as suggested by you, but since I have already done some hard work in studying IC555, in my new design I employed them yet again, and hopefully eliminated the previous issues in this design.

I have presented the revised design in the above article, I hope this time you won't have any trouble with it :)

Regards.

2. Hi Swagatam,

Good work!

The circuit is shaping up to be a buildable project of which I might even have a go at for my 100w turbine. MANY THANKS!.

Only one error i can see is that T3 and T4 emitters I reckon should go to the low voltage earth point and not the LIVE mains section.

Keep up the good work and thanks again.

Regards Darren.

3. Hi Darren,

Thanks for correcting the diagram yet again, indeed it was a silly mistake from my part, I have corrected it now.

Thank you for making this happen!

15. Hi Swagatam,

May i know if the connection of t1 and t2 is correct? The drain of t2 connected to source of t1?

Regards,

1. Thanks, Good observation!

No it's not correct, the sources should be made common and connected to ground and the drains should go to the taps of the transformer...I'll have to correct the diagram one more time...I'll do it soon hopefully.

16. Hi Swagatam,

to get the 1KHz frequency for the value of R1,R2 and C1. what would be the duty cycle?

Regards,

1. good question! I think it should be preferably 50%, actually I am not very sure, will need to be investigated deeply.

2. Hi Swagatam,

This is what i got in my 555 calculator:

Frequency: 1kHz
Duty Cycle: 50%
Period (T) = 1 Milliseconds
Mark = 500 Microseconds
Space = 500 Microseconds

R1 = 7.143 Kilohms
R1 Preferred Value = 6.8 Kilohms

R2 = 71.429 Kilohms
R2 Preferred Value = 68 Kilohms

what about the testing of this circuit?

Regards,
Mike L

3. Thanks Mike!

That looks neat.

testing may be done just like an ordinary inverter by initially keeping the TR2 output disconnected with grid mains.

Once the waveforms, frequency and power are confirmed using appropriate equipment, the output may be connected to the mains with correct polarity.

17. Hi Swagatam,

what about the testing of the new circuit? is it the same with the first circuit?

Regards,

1. yes it will be the same...

18. Hi Swagatam, great project, I tried the schematic on a breadboard and it worked so far. I changed T2 drain/sorce pins, used IRF740PbF Mosfets and 15VA toroidal TR2. I used a bench power supply as a DC source and went up to 5VDC/0.04A, which produced a 80VAC. Didn't go any higher as the noise levels went up (around 0.8kHz). Also, I did not connect TR2 to TR1 as I have no oscilloscope to confirm wave form and phase. R1 was 6.8k, R2 68k, C1=10n and R7 was 1k (it wasn't mentioned). In your prev. schematics you used capacitors beteween R5 and T1 and (R6 and T2). Could this filter out the 0.8-0.9kHz noise from the transformer TR2? Also, would you suggest that running the timer from a stabilised power source like 78L12 could reduce the noise while feeding in the control frequency through an optical coupler? Could an optical coupler provide both frequency and amplitude data? Thanks for your advise. Br, Selim

1. Hi Salim,

Without an oscilloscope it would be quite dangerous to go head with this circuit...... for reducing the noise you may try increasing the frequency to above 20 kHz by reducing he value of C1.

Regards.

19. Hi Swagatam,

is there any way to check if LM556 is working?
i built this circuit but i got a low output voltage to tr2.

Regards,
Mike L

1. Hi Mike,

Since the output is a PWM, it cannot be checked with a DMM, you will have to incorporate an oscilloscope.

what output are you getting?

Regards.

2. Hi Swagatam,

i only got 6vac...

i will try to find first a oscilloscope to test it again.

Thanks and Regards,
Mike L

3. Hi Mike,

6V at the output of the transformer or at the output of the IC??

4. Hi Swagatam,

6v at the output of tr2.

Regards,
Mike L

5. Hi Mike,
check the voltage at the "PWM out" of the IC.

6. Hi Swagatam,

I still dont have an oscilloscope. Can it be tested with the DMM? What woulb be the output voltage of the ic?

Regards,

7. yes, check the voltage with a DMM at the output of the IC....

8. what is the voltage at the output of the IC?

9. I would like to know it from you....

20. hi swagatam !
great project !
we want to know if is posible to get 240V and 50 hz output

thanks
regards ! !

1. Thanks! since the input is synchronized with the grid voltage, the frequency would be followed accurately..... wattage can be upgraded by using appropriately rated mosfets

21. Those who are asking most of these newbie questions do not know enough to do this safely. Many dangers lurk here, electrocution, fire, damage to connected equipment, etc. Great project, but seriously not one to undertake without a good understanding of whats going on!

22. Hi Swagatam, could you please help me understand the function of T3/4. I know it's important that both FET-gates should not be positive at the same time. Using breadboard, and iCircuit simulator, I always got the same results. Only one FET was operating (10V pulse at gate) and the other one at 0.8V pulse at gate, not enough to open the gate (>2V) . So I tried using 3 NOR gates of a 4001 and it switched sides at 50Hz. Was this the purpose of T3/4 or did you put them in to prevent the FETs T1/2 conducting at the same time only? BTW, can I contact you by email?
Regards,
Selim
ps disregard prev msg

1. Hi Selim,

That's correct, T3/T4 has been introduced so that the mosfets conduct alternately and never together.

23. Thanks, Swagatam.

Somehow T3/4 won't work, but with 4001 it will alternate at 50Hz.

On iCircuit (iPad) and on the breadboard, I get at the gates: T1=+12.2V, and T2=+0.845V PWM-signals, same phase, not alternating between T1/2.

So effectively only one side of the primary winding coil (6V-0-6V) is energised. Leaving T3/4 running on the breadboard, using 2.5VDC/0.05A input, I get around 90VAC at 820-870Hz (wobbling at around 50Hz, I think).

Using NORs from 4001, I can get it alternated in sync between T1/2, now here comes the next question.
On iCircuit, I noticed that the positive wave gets PWM modulated properly where as the negative wave (or the missing bit/flat line between 2 positive waves) is only PWM modulated as a series of short pulses (no width/no power). The output would be distorted, such as larger positive waves vs. smaller negative waves. Is there a way to capture the negative side as well? Maybe another NE555/6 could do this job using the same 1kHz chopper.

Please keep this project up. It seems like it could work well.
Regards

1. Thanks for the observations and suggestions Selim!

OK, If cmos gates work better we can use them instead of the transistors, no issues.

In the first diagram I tried to take care of the negative wave forms also but in the improved version I completely forget about it.

We'll have to incorporate another IC555 for this, and feed the two mosfets with separate signals from the two 555 ICs.

I'll try to present the finalized design soon...

Regards.

2. Hi Swagatam, Any update on promising finalized design diagram with another incorporated IC555?
I was building one when your post came out, so now I'm waiting. Please!

3. Hi Kevin,

The design was updated a long time ago, an additional 555 was not felt necessary as the negative half cycles could be simply derived by using s bridge rectifier network.

please refer to the second last diagram which hopefully satisfies all the conditions.

4. ....sorry, I misspelled you name.

24. Hi Swagatam, I managed to pickup both waves, and PWMed them and then run through 4013 to divide the 100Hz by two. The results look good on iCircuit. Both wave halves are PWMed at 9kHz and alternated on T1/2 evenly. The secondory winding phase in-sync with control input. I'll email you the pics later today. Two 4001 can be used iso 4013, but would require more wiring on the breadboard is needed. I think two 555s could do a much better job. I haven't figured out how to feed a 555 with a negative wave yet.
Regards,
Selim

1. Hi Selim,

Thanks! it would be interesting to see how you derived both the halves of the AC for the required sync. will wait for the images.

25. Hi Swagatam,

I got a little concern about what would happen if this circuit was disconected from the mains but still getting a DC input from say a solar panel/turbine. The way i see it is that TR2 will keep trying to feed TR1 and the whole circuit will go out of control resulting in the end of the plug being live. A normal mains failure will most likely drown TR2 out due to not being able to feed a whole city !!.
Hope i am missing something here.

Best regards and keep up this project.

1. Thank you for the interesting observation!

However if TR2 drowns, TR1 would also stop producing the required data supply to the circuit, and the whole system would stall:-)

But yes your point is noteworthy, and the issue should be checked practically for a reliable solution.

Regards.

26. Hi Swagatam,

What is the value of the zener diode?

Maybe we can put a relay to cut the source coming from tr2.

Regards,
Mike L

1. Hi Mike,

It can be anything from 3V to 8V....we just want to delay the switching fractionally between the transistors.

Yes a relay would be a good idea for correcting the above issues.....

Thanks.

27. Hi Swagatam,

what is the value of zener diode?

R1,R2 and C1? what is the frequency to be use?

Regards,
Mike L

1. Hi Mike,

You will have to calculate them using any online 555 calculator software.

Regards.

2. Is it 1kHz or 20kHz?

3. It has to be a high frequency, the figure does not matter...

4. I am using 1K (R7) resistor and a 5.6 volts zener.

5. That should be OK, the idea is to keep the transistor conductions well isolated, and in an alternate manner.....the zener diode makes sure that the transistor conductions do not overlap (as far as I thing).

28. Hi Swagatam,

what is wrong if the voltage coming out to the PWM out of IC 556 is not stable? i measured it from 10V and then going down to 3V.
Pin#3 (not connected)output is stable to 10V.

Regards,
Mike L

1. Hi Mike,

The output PWM should vary with the control voltage......

29. hi i also trying to do one
can i send it to u

30. http://imageshack.us/photo/my-images/694/img3181oi.jpg/
hi this is the link for my diagram
regards dumidu

1. Good design should work, thanks!

31. can be used for recharge baruti.themigambo @ yahoo.co

32. Hello Sir,

I have a solar panel of 150W, 24V. It is currently hooked up by a charge controller and a lead acid battery. I just need an inverter which directly converts pv supply (24v dc) into 220v ac, without having a battery.
I only need to run an 80w fan on it. Can you please help me in this regard.

Thank you.

Rashid

1. Hello Rashid,

you can make the following circuit, just change the transformer to a 20-0-20V/5 amp.......any nearby type will also do:

can i increase its wattage by adding more mosfets in parallel??

Rashid.

3. Thanks Rashid, yes it can be done.

33. Hi Swagatam
What is the u1 that part no is not clear
Bandula

1. Hi Bandula,

Where's it? can't see it.

34. Hi Sir,
I want final circuit diagram and component list of Grid-Tie Inverter for solar panel for 70-80 watt in home. And give me cost for designing this circuit. Plz reply me sir....

Mohini

1. Hi Mohini,

The second last circuit is the finalized design, but please note that it's only the concept which I have tried to produce, the person who intends to build it should have a sound knowledge regarding electronics and inverters, only then will he or she be able to implement the design correctly for practical feasibility.

If your not an expert in the field please don't even think of making such complex circuits, you will end up wasting a lot of money and time.

2. hi,i have solar panel 58v amorfni 128w 4 pieces do i go in serial 220v then adjust your circuit for it (220vdc) or do i make in paralel 4 x 58v then adjust your circuit for 58v what do you mean by that two cobination?

3. Hi,
the above design is yet to be verified, so I would recommend you to first test the second last design shown above, if it performs as per the expectations, you could go on upgrading it from there....

By the way, putting solar panels in series makes more sense and is always more efficient.

35. Hello Mr. Swagatam,

I am Miss Nuvem and I'm working in a group that is building some of your circuits during an event about sustentable living in Brazil and Catalonia. You have to visit some day.

I've been simulating your Grid-Tie Inverter Circuit, and I'd like to suggest a couple of modifications to the last design that you had on your post.

First, I was having problems where the PWM out signal (IC1 pin 9) would just blank out and stop oscillating. This was happening whenever the Control voltage at pin 11 would go higher than the Vcc voltage due to the drop across D4. My solution was to add two 1n4007 diodes in series between the rectifier and the control voltage. You might be able to get away with just one diode, but I am using two just to be safe.

Another problem I was having was with the Vgs for T1 and T2 not being very symmetric. T1 was fine, but T2 was not oscillating all the way up to Vcc values because whenever T3 was on, it was putting 0.7V across T4 instead of letting R6 pull up the voltage. I fixed this by putting a 4.7kohm resistor between T3 and T4. I think any value higher than that works, but I used 4.7kohm.

I hope this makes sense. I am attaching an image of the circuit with these modifications and the simulation results that I am getting with LTspice.

http://i.imgur.com/jkOoU8k.png
http://i.imgur.com/XpOsQKd.png
http://i.imgur.com/9uv0TGx.jpg

We'll be working on this and other circuits for the next week. We will keep you updated.

Warm regards.
Miss Nuvem

36. Dear Sir
I have to Sun grid tie inverters. One input 10-30 volts and other 22-60.
For my wind turbine I have conclude the best range is 15-40 volts. Is suitable to change them to thiese range? If yes how?.
Best regards
Jose Castanho - Portugal
Email: castanho.jose@gmail.com

1. Dear Jose,

Changing inverter voltage specs would be difficult, you will have to dimension your windmill output as per the inverter requirements, may be by using a buck-boost circuit or other similar concept.

37. Hi Mr Swagatam,

Ryner here, I'm a student doing GTI for my Final Year Project. I would like to raise a more theoretical question: why is there a need to synchronize the output of the GTI with the grid? What would happen if it is not synced?

1. Hi Ryner,

since the involved current is varying from positive to negative every split second, if the two counterparts are not synchronized, would result in possible clashing of their opposite cycles in their AC phases which would in return result either in short circuiting of the power or one of the counterparts dragging the power toward lower levels thereby heating up the inverter devices.
That's why perfect synchronization becomes the ultimate crucial thing in GTI systems.

38. Hi Mr Swagatam,

Ryner here again, sorry to trouble you with another question, but from what I understand, the output of the GTI has to be channeled back to the grid. Does this mean that my output from the GTI should have a slightly higher amplitude compared to that of the grid? (by theory, a potential difference is required for current to flow) On that note, are we transmitting energy in terms of voltage or current? Thank you in advance!

1. Hi Ryner,

Imaging putting batteries in parallel for increasing the backup time, yes, it's the current that is being added here.

If we increase the inverter voltage would load the inverter more than the AC mains input, so both counterparts must bear equal and uniform potential sharing.

39. Hi Mr Swagatam,

Ryner here once again. How exactly do I get the output waveform to synchronize with the grid? Would I be able to do it with a Phase Lock Loop (PLL) Chip? Is there a simpler way to do the synchronization process? Thank You!

1. Hi Ryner,

I have already taken care of and have correctly implemented waveform synchronization in the explained designs,
regarding other options I cannot say much, that will require further investigation.

40. I am doing my final year project with renewable energy, i prefer doing this circuit. I am doing it for a grid of 230V what must be my transformer TR2's ratings? Can i have the full final circuit?

1. The final circuit is already updated in the above article. The concept was designed by me but is not yet tested practically, so pls be cautioned

TR2 wattage will be equal to the required power output from the inverter

2. How will this circuit behave to different voltages from the dc source, however its not a battery being connected to deliver a constant voltage?

3. the DC input could be from a battery or any regulated source. yes we'll have to add a comparator sensing stage for ensuring that the battery supply is cut off as soon as its voltage drops below the input DC ripple voltage from TR1 at pin#11 of the IC

41. Dear sir
In India THD,Freq,voltage all these thing at a time varries, then that how can adjust...if always less then 10 % thd...what is effect on perfomance..of GTI OR ONLOAD

1. Dear Dharamveer, if the DC input to the circuit is maintained at some constant, safe higher level say at 15V for a 12V system, the circuit will automatically take care of all the other factors associated with the mains supply (according to me)

42. dear sir
how can adjust GTI, THD, freq. voltage always varries....thd more then 5%

43. Sir, I need 10 Kw grid tied three phase solar inverter circuit diagram. If you have please send me on "ajinkya.brahma@gmail.com". If you have circuit giagram, please send me as early as possible.

1. Presently i don't have it, I'll try to find it.....

44. hi Swagatam Majumdar
can I connect directly to the solar dc source. can save a lot of costs.
but I have one problem, if larger loads feeds from tie circuit .circuit continues to operate or shut down
thanks

1. Hi Khang,

yes you can connect it directly to a solar panel, however the supply to the ICs must not exceed 15V.
The circuit output will follow the grid voltage proportionately...if the grid voltage drops so will the output from the inverter and vice versa...so with larger loads the output will adjust in accordance with the grid voltage.

45. hi Swagatam Majumdar
iI tested the circuit on the output voltage but only 4vac, f = 1kHz
I use fe core transformer (EI). transformer frequency more than. 100hz. perianth do fire transformer
can i change BC547 to 2N3904 ?

1. BC547 can be changed to 2N3904, .........cant troubleshoot without seeing practically.

46. hi Swagatam Majumdar
can you help me design and calcular an turbin wind capacity 200w.
thanks so much

1. hi khang, pls give complete specification in terms of voltage ad current.

2. Hi Swagatam Majumdar
i need technical specifications
U=24VAC
I=10A
V=0~10m/s (wind speed)

3. do you need the technical specification of the motor??

4. hi Swagatam Majumdar
yes i want it.
choice and calcular :wire size(mm),round wire,magnet.

5. khang, you can refer to this link:

http://www.alibaba.com/product-detail/YC-Series-Single-Phase-24vac-motor_1535220820.html

47. hi Swagatam Majumdar
my problem.
DC input 12v (power supply DC 3A)
transformer 12-0-12
i choice R1=100k,R2=20k,C1=10nF(~1khz)
output(pin 9 IC)=988hz,
current=0.01(DC IN)
output transformer=4VAC,frequency=100hz
Can you give me a guide
thanks

1. Khang, use a 6-0-6V transformer, you will get the required level of output..........but 4v is way too low... something may be wrong in your construction

2. hi Swagatam Majumdar
i send to you a picture result I measured.

3. email is in the "contact" page, pls see it.

48. HI Swagatam Majumdar
I checked the construction .output transformer 200vac.I have a problem ,output frequency is not 50hz .it's >300hz.
can you give me a opinions

1. Hi khang,
I can't get the picture..please post all the details regarding what you are referring to and what exactly have you made so far.

49. ok i understood your point....connect a 1uF/400 cap at the output and then check the frequency, it will show 50Hz.

50. Hi Swagatam Majumdar
Have you received a picture yet.
I have checked output bulbs but no light .it's synchronization phase on grid.
thanks

1. Hi Khang, yes i have seen the pictures sent by you.

I think you should first make the inverter separately, make it to produce the required 220V, once it's confirmed you can proceed with the integrations.

2. Hi Swagatam Majumdar
I sent you that image on meter

3. Hi Khang, yes, I have seen it but could not interpret much...

4. Hi sir
I checked the device by connecting 1 100w bulbs .It's not light . circuits sync phase grid.can I connect on grid?
thank's

5. Hi khang,
something may be wrong in your circuit or you may be using a small battery/trafo..., try using a 12V 25ah battery and a 9-0-9/20amp transformer for getting a valid output

6. Hi sir
I'm using one 3A power supply and 1A tranfo 18-0-18 to check circuit.result check in meter
Thank's

7. for 18-0-18 trafo you will need 24V DC input....... and in that case the mosfet gates will need zener diode clamping for safety

8. hi sir
I'll check back
thank's,

9. Hi Swag
i have a question?
Why create 1kHz instead of 50 hz in output ?

10. khang, 1khz at pin14 of IC 4017 will produce 50Hz on the gates of the mosfets and from the trafo, that's how it works

11. Hi Sir
schematic diagram not ic 4017.
output pin 9 Ic 556 is 1khz.output tranfo 220v 1khz.can't I connect to grid?

12. OK sorry, i confused it with the other circuit...the frequency will is locked with grid frequency so it will be always 50Hz at the trafo output, the 1khz is for generating the PWMs, it's not relevant to the output frequency.

13. hi sir
saving bill
thanks so much.

51. hi Swaggatam, Quick question irfz44n will be ok with 12 0 12..yeah..im going to check if this gonna work. or have you any latest update on grid tie inverter. Thanks

1. Hi Barbe, yes IRF44n will work with 12-0-12 trafo.

Please proceed only if you have understood the concept well, and it's strongly recommended to do it in a stagewise manner

No I do not have any further updates regarding the above circuit, I would appreciate if anybody provides the test results of the same.

2. Sure...the only missing with me is the 68k i hope i can find this afternoon and try to blow in the evening..anyway i let you know once it work smoothly..also i found some diagram from the net but not sure with it...but too many blogs says it works???

3. OK, great!
Try only those which you understand and are able to simulate in mind, otherwise it could be a waste of money and time.

4. I try.. Its busted...any way its fine...im waiting for my scope..its hard to check all of this..!!! I will try your other design and let see we were going to blow that one aswell...i will inform you what ever i found...but this one...my 10amps transformer get hot aswell..its reallly busted.i want to follow only what is in the doagram to check if its actually working but i put all the nessisary precaution..!!!!

52. Hi Miss Nuvem,

Is your Project works...as currently I don't have the scope...with me? Thanks

53. hi Swagatam

I have made ​​such a design above. but I do not see the output of the R5 and R6 using osiloscop. and I have tried to synchronize between the inverter and generator 1 phase using a 30 watt lamp. I see there is a change from the original load dim lights become bright.

when there is no load voltage and frequency phenomenon after the sync is 220 volts to 210 volts and 50Hz be 49.5 Hz. but the mosfet is used even though I use a cooler heat. what should I do to reduce the heat? and what will not be a burden inverter generator?

1. Hi Agung,

Please refer to the following article, I have addressed the heating issue at the end of the article:

54. I want to ask you a schematic, for it is connected to the battery TR2 or mosfet?

55. Great job!... This idea can be extrapolated by the class "D" amplifier implementation with AC grid reference signal employing comercial ASIC!

1. Thanks for the great suggestion! yes it could be feasible.

56. "The inverter should switch OFF instantly in case the grid voltage fails." Why Sir?

1. to make the Grid free from an AC mains potential which could otherwise kill or hurt an electrician who may be possibly at work across a faulty grid line without any caution, assuming the line to be switched OFF and safe.

57. hi swagatam.
i cannot find in your post. what zener diode should use. and how much power it could handle.?

1. Hi kikiloaw,

D10 in the last diagram can be a 6V zener diode, 1/2 watt rated

58. As I understand about the diagram. Any DC voltage can be a source. But depend on how many volts your MOSFET can handle right? And the transformer is depend also of how many power the your DC source can give right?

1. yes that's right....

2. as the mains voltage drops the inverter voltage also drops. when the inverter voltage drop. does it affect the power to be feed to the mains grid? and what is the efficiency of this inverter? and why does the tr2 only 6-0-6 ct?

3. I have only presented the concept only, it needs to be tested practically for all these answers

59. Hi Mr. Swagatam and Miss Nuvem,

Mr Swagatam a great design which was implemented by you. Miss Nuvem, is it possible that I can have the .asc file of your schematic? Because me too tried this in LTPice but output simulation was not as I expected. Thank you

Regards
Lovindu

1. You are welcome Lovindu, I hope Miss Nuvem will respond and fulfill your request.

By the way simulation softwares are never reliable and are no match to a human brain simulation...

60. Dear Sir,
Mr swagatam
good day.
My name is Zeal Njoku
i have been trying to have you in discussion, i am lover of electronics and i have bin going through your circuit designs so i picked interest on them. I must appreciate you for being so king and a generous man and having such time and giving people all this lectures, i say thanks to you.

I have some issues that i will like to discuss with you out of this site, i have some ideas that i brought up to ,my self about most inverter circuit which i want to try but i will like discuss it with you before i will start it then after i found possibility in it after practicing for success it can be post to your site and the explanation and diagram can be uploaded to your site so that all can see.

I will appreciate if you will send to me or type to me in my email address on zealthehightech@yahoo.co.uk so that we can discuss this issue at mail first before it can come up to this site.

Thanks as i waits to see your mail soonest.

zeathehightech@yahoo.co.uk

1. Dear Zeal,

I appreciate your interest, however due to lack of time and many comments pending it would be difficult for me to discuss through email.

So please feel free express your doubts here, I'll try to help

61. dear swagatam,
A great design which was implemented by you,i need a big help from you.I have dsp sine wave solar Hybrid inverter(offgrid) design and all.I want to convert my solar inverter in to bidirectional inverter.That means my inverter output 230v will be fed to ac grid.kindly help me

1. Thanks greens, it can be a little difficult,because to convert a normal inverter into a GTI would require modifying the internal circuitry of the unit and insert an external PWM to it with a duty cycle synchronized with the grid AC

2. Hi Swagatam continueing with Mr Green comment so which internal part of an off grid have to be modified for a GTI?
I half an ups and thought if I could use it's circuit for a GTI.
Thanks

3. Hi Aborg, the mosfet section of the uPS will need to be synchronized by appropriately tailoring its conduction rate with respect to the AC waveform...it will need to be done quite as shown in the second schematic from this article