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Grid-tie Inverter (GTI) Circuit Using SCR

Grid-tie Inverter (GTI) Circuit Using SCR

Grid-tie inverter concepts may appear to be complex due to the many criticalities involved with them, however with some intelligent thinking it could be actually implemented using primitive technologies. One of the ideas has been explored here.


The discussed idea of a simple grid-tie inverter circuit was suggested by one of the interested readers of this blog, Mr. RTO.

The images sent by him are shown below. In the first image we find the simple circuit diagram comprising a step down transformer for translating the grid data, a mosfet triggering circuit which accepts the grid data and a corresponding inverter transformer which is used to amplify the DC conversion of the grid data from the mosfet network.

A Smart Looking GTI Circuit

The idea looks pretty simple, and indeed very smart:

The left side step down transformer feeds the half wave rectified voltage to the corresponding mosfets which begin conducting in-sync with the grid input and convert the DC source into a corresponding AC across the inverter transformer at the right hand side. The output from the inverter transformer which is now a grid synchronized AC feeds the grid with the intended GTI results.

The idea has been tested by Mr RTO, but he complains about lower efficiency from the unit.

This could be because of one major issue in the design, that is the absence of a "neutral" wire across the output of the inverter transformer.

With the shown set-up, the output would respond with a push-pull action across the secondary of the right hand transformer, meaning both the ends would become "HOT" or "LIVE" alternately during the operations.
The grid will take this as a "short" for every inverted half cycle from the transformer, because the grid voltage always has one wire as the neutral which is never a "LIVE" terminal.

We don't want this to happen.

Using a Center Transformer

A simple solution is to use a center tap winding for the secondary of the inverter transformer. This would render the center as the "dead" or "neutral" wire relative to the outer taps of the trafo. The upper tap may be configured with the grid while the lower tap to a balancing load or more effectively fed back to the primary side for charging the battery or reinforcing the DC source itself.

The test set-up of the above design can be witnessed here:

Another issue which could remotely transpire is the conduction from the mosfet which wouldn't be exponential, rather an "awkward" and unrecognizable sinewave.

The mosfets could be replaced with SCRS, as shown below. This would allow a perfect sine wave to be induced across the inverter transformer and the grid.


Using SCRs for the GTI

A much improved grid-tie inverter circuit using the above concept and SCRs is shown below. The idea looks greatly simplified, and quite impressive.

The output of the right and transformer could be seen converted to a center tap topology, wherein one half winding is integrated with the grid, while the other half is subjected to a balancing load so that the center tap is appropriately conditioned to be the neutral for the system.

The balancing load could be replaced with a charger circuit for charging the inverter battery itself, this would reinforce the input with additional power and more backup time.

SCRs will not Latch

At first glance it appears that the SCRs would get latched since a DC is being used across its anode/cathode, however according to me it won't happen, because the gate of the SCR is subjected with an alternately reversing AC which would prevent the SCR from getting latched everytime the gate AC feed changes its polarity


About the Author

I am an electronic engineer (dipIETE ), hobbyist, inventor, schematic/PCB designer, manufacturer. I am also the founder of the website: https://www.homemade-circuits.com/, where I love sharing my innovative circuit ideas and tutorials. If you have any circuit related query, you may interact through comments, I'll be most happy to help!

113 thoughts on “Grid-tie Inverter (GTI) Circuit Using SCR”

  1. Good day Mr. Swagatam. Is it possible to grid tie connect to the ac output of pure sine wave inverter? I want to add power to my existing solar system in this case a 1kW PSW inverter using 1kW GTI. The reason I want to connect it that way because my electric meter will add my solar generation if I connect the GTI to the grid. Other solution to this is with the use of limiter. Is my idea for PSW inverter being grid tied possible or doomed for failure?

    • Good day Roel, it may be possible only if your sine inverter is specifically designed for a GTI integration, if it is a normal inverter then I won’t recommend this at all. So make sure the inverter includes the synchronization feature with the grid sine waveform and only then you may be able to use it as a GTI

      • Good day Mr. Swagatam. What I mean is that I had an existing off grid solar inverter with 1000W pure sine and I want to add more power using another solar but in this case the inverter is 1000W pure sine grid tie type BUT I don’t want it to connect it to the grid but to the AC output of my existing off grid 1000W pure sine inverter. Is this possible?

        • Ok so you mean to say you want to join two 1000W inverter outputs in parallel? I think that may not be recommended, because their waveforms could be out of phase and cause catastrophic results, I personally won’t recommend that! I hope I understood your issue correctly?

          • Yes Sir Swagatam it seems that the two inverters are to be connected parallel because that’s the only way to connect the grid tie inverter and I think grid tie inverter will automatically sync the grid requirement but my concern to this idea is during a moment where the load is lower compare to the capacity of the grid tie inverter which in this case will throw that extra power back to the ordinary inverter. And I know and think that there is going to be a fight of power in that case whoever is the strongest wins. I only need to confirm through your broad knowledge of inverter circuits if this is so. I heard some idea also that the extra power generated by the grid tie inverter and will flow towards the ordinary inverter will charge the battery of that ordinary inverter. Thanks by the way Mr. Swagatam to your knowledge and sharing that knowledge to everyone. Your circuit are very simple yet very applicable. Thanks Sir Swagatam.

            • Hello Roel, When we refer to synchronization, that implies excess power can neither be sent or received from the two sources. When the amplitudes of the grid and the inverter output voltages are in sync, their voltage peaks and cycles become exactly equal and synchronized, and when voltages of two power two sources are exactly similar, transfer of current cannot take place.

  2. Good Morning! for the initial design with the 6v transformer, the batteries would give from 6v or 12v ????
    I’m going to ride one of these to play.

  3. Hello mr swagatam
    Thank you for answering so quick
    I already have the capacitor on the output which makes the square wave perfect .The question now is , can i connect this signal to the grid or i would have a sine wave ? I will try the
    trick with the bulb

    • Hello Thrasos, if the secondary of the transformer is generating voltage equivalent or higher than the grid level then you can try connecting it with the grid. make sure to connect a fuse in series with the mosfet drains or SCR anodes

  4. Hello sir
    I tried this disign above and the signal on osciloscope it is not sguare wave or clean sine wave .
    I found other design and i have a clean square wave .I can not communicate with the designer.
    I was wondering if i have square wave ,as i read above can i connect to the grid ,is this is going to become sine when it will connct to the grid ?
    Thank you

    • Hi Thrasos, as you can see the design does not have any special circuit processor, therefore the output waveform will be solely dependent on the switching pattern of the devices…you can perhaps improve the waveform by adding a 0.33uF/400V capacitor across the output leads of the transformer

  5. Hi Mr.Swagatam,
    I check in datasheet that NTE5538 can hold up to 800 volts and 50 Amperes. So if I have DC source maybe about 600 volt (from a lot of solar cell in series), do I only need change the right side transformer from 6-0-6 to 600-0-600 ? or I also need to upgrade the SCR ?

    can I avoid using balancing load in this schema ? it's make the GTI not independent.

    thank you

    • Hi Greenmoon,

      yes the 6-0-6 winding will need to be upgraded as per the input voltage and should be equal to the input voltage rating.

      SCRs also will need to be upgraded as per the input voltage and current specs

    • to avoid the balancing load…you can try connecting only one wire from the output of the GTI transformer…connect this to the Phase line of the Grid, don't connect the other wire….even this will need some consideration by ensuring that the both the cycles GTI and grid are in sync

    • My friend is Brazilian and I live in Africa faso volunteer work here I set up the first circuit with mosfet only the transformer 6-0-6 heats up so much and it burns in minutes I do not know where I'm going wrong can give me an idea

    • 6-0-6 transformer will heat up only under the following conditions:

      if the mosfets are not oscillating and/or the DC supply to its center tap is much higher than 7V….otherwise there's no reason it can burn.

      first test the set up without connecting the 6-0-6 output with the grid.

      and if possible change the mosfets with new ones.

    • Hi i just wany to know which gti cirucit gives the best efficiency.
      Because i read a lot of previous posts by barbe israel but he did not clear the confusion about the efficiency of his experiments. Anyone plz clarify if know sonething about it. I am electrical engineer, i want to start with the most optimal design and refine it. So plz help me out.

    • Hi, I think you should try it yourself practically by making small models of the above designs, and verify which one works more efficiently, there are hardly any components in the design and the set up looks quite cheap.

      make sure not to connect the output with the grid line while testing the set ups.

  6. hello swagatam.
    is this suitable for high and low voltage dc?. i want to build this one for my diy turbine generator.
    how much current it can handle? can it be modefied to produce high power generator?

  7. Hello Thrasos, I am afraid a two wire transformer can never work for the above shown designs,….. where did you feed the DC positive?

    The 115V that you might be getting could be something else but not because of the GTI functioning.

    PWM feature can be executed by feeding pulses across the gates of the SCRs…we'll discuss it in detail once you correctly and successfully implement the above designs.

  8. Hello Thrasos,

    If you are referring to the designs presented in the above articles, then yes these can be used with a 100AH batteries also, you just have to makes sure the power devices are rated accordingly.

    However you will strictly require a center tap transformer for making the above explained circuits, I am unable to simulate how a two wire transformer could be configured using the above concepts.

    I would recommended that you first try the designs using smaller transformers and a smaller battery, if the mini prototype works as per the expectations only then you may want to go for the bigger models.

  9. hi Sir. I have seen this circuit in your blog and it fits perfectly for my final project in industrial electronics. It is a power inverter that uses scr. The problem is i can't simulate it correct. The program that i use is NI Multisim. Also , what is the 12V -0-12V in the step down transformer? is it dc source or no. of turns? Please help me. Thanks! I hope you read this very soon. 😀

    • Hi Prymella, it would be better to build the last design practically using two small step down transformers….

      for testing purpose you could use a 12-0-12V 1amp for the left trafo and a 6-0-6v 1amp for the right trafo….do not connect the right trafo output to grid initially, check its output with a multimeter if it reads 220V the circuit could be assumed to be working OK.

      The battery could be a 12V 7ah or smaller…

      the 12-0-12 is an ordinary step down trafo.

  10. Hello, I'm from Brazil and I'm using google translator …
    Well I wonder if the first circuit presenting can use mosfet IRFZ44N.

    In the picture the transformer has a secondary of 6-0-6 because not 12-0-12

    • yes mate, it has been already invented successfully using HHO fuel engines….I don't have much idea of the mechanical stages of the engine, though.

  11. Hi Swag, I made some simulation for mosfet vs scr. I don't if this is right, I get curve line on mosfet and straight line on scr. Please see this link postimg.org/gallery/96dgt9ge/

    • Hi RTO, may be the simulator was not specified regarding the AC polarity, the AC would be changing polarity alternately at 50Hz rate,

      I think you should simulate the last circuit above exactly as it's given

  12. Thanks Swag, this information will help to me.

    Btw, how about the gates voltage, if I will give it 2volts vs 5volts. What would be the result? It is the same with mosfet that the more voltage on gates will get less resistance on Drain and Source?

    • yes, only upto the saturation level, once the Vgs crosses the saturation point which could be at about 6V, the drain/source conduction will tend to reach a constant level

  13. Hi Swag, this is my first time using SCR. According to my research, once the scr triggered it will always ON and the scr will turn off if we disconnect the source voltage. On the circuit diagram above, I can't see how scr goes OFF.

    • Hi RTO,
      you are correct, but there's another way of breaking the latch, it's by providing a negative voltage to tge gates, that's what exactly would happen for tge gates of the SCRs shown above.

      With every alternating voltage, the transformer taps will change polarity, supplying a negative voltage to tge ScR gates…according to my theory.

    • It will using optocoupler..it will switch and off..im sure..using 555 to be simple or if you want some noise used relay to switch it off and on very fast…i see that one in action actually its cool if u just want some fun on your gti used relay..but optocupler for the scr is the best..

      Hi mate actually..i dont see yet the scr works..just have doubt on it…because i check the scr on the net i dont see a very fast switching which we need on gti…like what happen to me my scr juz blow mate i used high amps..aswell 500/60amps…i waste my 10 dollars mate

    • Not sure mate..but my friend here suggest it will possibly working on his theory if we used triac…

    • whenever some doubtful and critical parameter is required to be confirmed, it must be scaled down proportionately to avoid mishaps, the above concept can be tried using a 1amp 12-0-12V transformer for the inverter transformer. and BT151 may be used for the scrs.

      for extra protection fuses may be atached at the scr anodes.

    • I research again mate with the scr…the issue is the switching on and off..is to complicated circuit to be used if u want scr…i tried again..mate sorry not working…!

  14. For the gti..i would suggest this igbt. Gt30j324 or gt30j322 im sure with this…!!! Take cage with the gate,,,, as always….make sure bout the current flow…like i said a resistor needed..for unstable current…maybe 1 ohms 50 watts will handle….! Series to the positive of the battery or solar…

    But my design will activated only when connected to grid…! So at the moment im on trial on switching via relay…to amke more my gti in safe mode…and after one ahour of used my big transfo become hot…but all the igbt in very cool… I thnk i need to search some good ventalation for my transfo…

    • IGBT gate is voltage dependent just like mosfets.

      mate the transformer too should not become hot..I suggested the use of a center tap configuration at the output, did you do it?

      before carrying out critical and dangerous projects like this one we should be very sound with the required info and knowledge, especially the basics, otherwise it could lead to hazardous situations….

    • Mate not too hot…is actually normal….kind of hot…but im thinking im going to use this one 24hrs..im sure..it will be hot…so need some air on the transfo same on the gti i both online…

      Im not using center top…i found some dificulties with center top…when i look into scope it is hard to align the movement…i dont really understand…coz i really not focus to trouble shoot that thing…so i made it no center top much easy…and perfect..

      Anyway i will look that one and try but so far without center top i found the waveform perfect…and no noise or interfernce…very nice square wave also compare with the center top the square wave is not smooth..and frequency somtimes become 600 to 10 khz while without center top..stable at 90hz or 80 hz juz put the caps boom 49 to 51hz..clean squarewave and when u put to the grid automatic very neat sinewave…compare again with the center top…you need to clean the power factor…mate u will not be happy if u see to mch scratch on sine wave..and after 5mins your igbt become too hot and transfo…

    • OK mate, that's fine.

      The inverter output must be an exact replication of the grid AC.

      The grid AC has a neutral which is never LIVE, the same should be obtained from the inverter output, that's why I am suggesting on having a center tap at the output.

    • Hi mate..base on my research and friends aswell we should not worry bout the voltage we get from neutral on gti…is just actually some kind of harmonic..static but no current at all..that is why when i touch it nothing happen…

      My friend told me which he have lot of knowledge on gti..he said just make sure build a lot of wattage to fight with the grid…and make your meter reverse…i will ask him a more solid xplanation on gti..but most of his gti design was not actually much or tie with grid but is working and effeciency is high like 90 to 95 percent…!

    • Sorry Mate, but your inverter doesn't need to fight the grid, that's horrible, rather you have to make sure your inverter output "shakes hands" with the grid output, that's why it's so important to have everything in order.

      for confirming whether your inverter output has a neutral or not you can do the following simple steps.

      take a 25 watt bulb, connect one of its ends to one of the taps of the inverter output, connect the other end of the bulb to your home earthing or to any water tap.

      Switch ON the inverter, check if the bulb glows or not,of course it'll glow.

      repeat the procedure for the other tap of the invetter output, check the results.

      You'll find that the bulb glows on both the occasions, proving that both the ends of your inverter are producing "LIVE" voltages…..that could be very undesirable for a grid integration.

    • I did as usual touch it by my hand… The line that i believe its neutral..and like u sugest insted i used meter…zero mate the reading and no elctrc shock…i can confirm its all harmonic only…nothing more….and when you put filter neutral became zero….

      Thats wat i found….

    • Also have nothing much knowledge on gti so i deside base on suggestion and help on others and share aswell to everyone…he told me gti is build to give extra to your grid…the more you put the more the wattmeter reverse…or slow when using ac..i really dont understand… But being compuse..i see that my wattmeter reverse..quick…with no shake hand….no pwm…nothing..just simple inductive circuit..he just told me bout if your circuit is purely capacitive or inductive no current used….but hence he said i generate…more the wattmeter no choise but to reverse..which actually work..same on wat i made…!!! I need xplaination here mte…that little crazy qwxdx…made me mad..for some kind…but he made it…

    • OK, if you are confident with your assumptions, then there's no problem you can go ahead with your plans.

      but according to Wikipedia a GTI should have the following features:

      The grid tie inverter must synchronize its frequency with that of the grid (e.g. 50 or 60 Hz) using a local oscillator and limit the voltage to no higher than the grid voltage. A high-quality modern GTI has a fixed unity power factor, which means its output voltage and current are perfectly lined up, and its phase angle is within 1 degree of the AC power grid. The inverter has an on-board computer which will sense the current AC grid waveform, and output a voltage to correspond with the grid. However, supplying reactive power to the grid might be necessary to keep the voltage in the local grid inside allowed limitations. Otherwise, in a grid segment with considerable power from renewable sources voltage levels might rise too much at times of high production, i.e. around noon.

  15. Sure mate…youre my mentor..and prof. Definitely i will…!!! Also im not sure if this gona work perfect…but im sure it will be minor adjustment on amps…i think my issue will be caps or my transfo computation….anyway let yoy know mte as alwys…your the boss here mate…

  16. Hi Swagatam,

    can u make a circuit witch after the battery is fully charge the solar panel will switch to the GTI for not wasting the solar panel power.

    thanks in advance,

  17. No prob..mate for the welding machine im starting collecting parts..i will try build inverter thing kind of welding machine but im goin to use round ferite nothng to found in dubai i buy online 2dollars so i have to wait for 2weeks

  18. I thnk one issue on your scr design is the diode going to transfo..when you plug in it to the grid the reverse current will flow back to the battery result to damaged the batt..which just happen to me the water came out from it…and also the gate when activated not really sure but it create short circuit may be mate not sure but my scr just wasted…!

    Sorry mate..do you have any suggestion…on this one…

    • No mate, the battery or any DC source will never be at risk from the reverse current, because you will see such diodes included in all types of circuits whenever inductors are used…in order to protect the switching devices.
      However for scrs this may be not true, they are never at threat from back EMFs, so anyway the diodes can be removed.

      The scrs must be rated to handle the transformer current, I think BT151 is not the correct option, I'll replace it with the appropriate ones soon.

    • Ah ok mate…it just blow..ok mate we will try that one aswell…by the way whre is our welding machine

    • mate, I am looking for a 12V 100amp smps circuit online, because it would be difficult for me to design, as soon as i get it will post it for you. it may be then applied for welding purpose

  19. I attached my frequency monitoring circuit…the link mate


    • It just optional…if you are in 110 110 output…bu can be also used in this one..o mak sure youre always 50hz…anyway no need..as i will buy just normal hz meter.that dis sign is one of my friend monitoring circuit for defferent purpos..anyway…

      The most mportant is the auto switch of to prevent the igbt from damaging..

      But so far all is perfect for 4days now..i will start feeding via solar now…but at the moment im using battery…so far both wattmeter my test wattmeter and our general kilowattmeter is spinning backward when no load..with load its to slow..actually

    • Hi barbe, can you provide the efficiency?
      Mine, I only got 92watts (40-50% efficiency) from 200watts solar panel.

    • Im not using it through solar though..but using battry and some math..not really sure is running 80 to 90 percent rto.

    • Yes correct bridge type..im using…!!..the only thing u may on this is that is to heavy becoz of too many transfo…but nterms of efficiency i thnk u will definitly happy.

      Im just waiting for the meter from my friend to double check but it will not less than 80percent…

  20. Hi mate i attached the working gti…the wattmeter actually move backward but hence i think there is some kind of lock i dont know after one round it just stop and not moving…


    • that's interesting mate, I'll research more about watt meters and let you know how these are specified to work.

    • I found the lock mate…actuallt is not the lock…i need to make sure that the meter is in 90degrees otherwise…it will lock or it will not move properly…

  21. He need a frequency control on the output..of his grid tie…i seen this one is actually working…just make sure that the polarity of the transfo is correct..! I already build one of that..its perfect…regarding the scr design mate it blows…:( i dont know why…i think the issue is with the gate not really sure..it seems short circuit or something not sure i use small transfo and small scr..

    • It needs to be matched with the DC source wattage,

      more wattage would contribute more to the grid and vice versa.

    • Hi rto…i think atleast you need 20amps transfo 6 0 6 primary and feed aprox 18 to 24 volts and your zener diode make it 15v make it two 6 0 6 make it in parallel it will make it more wattage…more spin aswell but make sure you have good input aswell…also try to put SSR on your output 220 and scr on your input..it will help make your grid tie..always in grid.. But your design is seems perfect…no need pwm…the only thing i dont like in this design is the heavy transfo while on ic grid tie small transfo but good in generating watts.

    • Also put 100uf on you dc source it will help on pp voltage to much with your control transfo switch

  22. I think IGBT is much better on RTO design..i already seen that one other blog not from him some french guy made that one but he complaint became very hot in long run…suggestion made an igbt..which solve the issue..some also made using ir2113.., but this simple one i really like its work…actually but im wondering if ur using battery is not feeding while if your are using solar or dynamo it is feeding?

    • yes that's correct, IGBTs are much rugged than mosfets and better protected against avalanches and parasitic voltages.

    • Barbe, the DC source can be from any source, but the issue here is that the generated output from the inverter transformer is not tied-up with the grid voltage…..here the inverter voltage could rise or drop independently causing imbalance and heating up of the devices.

    • I'm using this circuit about 2 weeks. The temperature was fine using that tiny heat sink.

      The other problem is when the grid fail the output voltage will increasing until the mosfet damage. To fix this problem, I use your Low/High voltage cut-off


      The relay cut the line from input transformer to output.

    • I dont know mate im generating 356vac/90hz..and tune it with 2uf and become clean square wave..and plug it to the circuit…nothing happen…its start feeding into the grid..i dont understand but the more i generate watts the more backward i get…for my experenmt…

    • RTO, that's strange how can the voltage increase, because if mains fails, the mosfets wouldn't receive any gate feed and would stop conducting instantly, there could some other issue in the circuit which needs to be checked.

    • Barbe, the voltage must be tied-up with the grid voltage level, otherwise the inverter may be subjected to unnecessary stress, because allowing more voltage into the grid would cause more load on the mosfets, while lower voltage wouldn't add anything into the grid, so the rise and fall must be synchronized with the grid voltage

    • Swag, I tried this circuit as normal inverter and the output voltage is 300vac. When this output transformer connected to the primary input transformer the secondary input transformer will also increased and feed to mosfet gate. The more voltage on gate the more voltage on output transformer. Then from output feed again the input transformer again and again until the secondary input transformer reached to 21volt the mosfet get damage.

    • Yeah mate, but its work…i made the wattmeter move backward and no issue….!all temperature is perfect…noise is perfect aswell…thats the work of thr control transfo…automatic when it tied up…its align with the frequency…i also have voltage on neutral…but it just because of the harmonic…i get it all and understand by scope…

      If no grid the grid tie will auto switch off to prevent from damaging the igbt…i will try to put some video on reversing wattmeter mate

    • RTO, we have 12V zeners clamped at the gates of the mosfets, so how could the voltage increase at the gates??

    • Sorry, the 12v zeners were not yet clamped during that burst. I'm newbie of zener, I just read your conversation with barbe about damaging of 4017 and 555. Then I applied that on my circuit. I just add that low/high cut-off just for double protection and system will automatically shut off. Without it, the system still have output even without grid.

    • OK, I thought you were referring to the first circuit in the above article…anyway zeners are crucial in either of the designs, at their respective positions.

    • Regarding on the gate issue u need atleast 1 to 5 ohms 50watts resistor on your input from battery to limit the current..to save you from damaging the gate…!!! U can check it with the scope..as wellit will help alot

    • not for the gates, rather for the drain and source, because gates are voltage dependent not current dependent, so gates won't be affected by high currents.

      to protect the gates you'll need make sure the voltage does not exceed 15V, therefore zeners are required for te same

    • I mean the igbt…and correct u need zener diode atleast 1 watt…i use 15 volts with one kilo ohm in seires.

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