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While I'm not an expert at grid tie inverters, the obvious reason seems your control strategy.
Wouldn't any grid tie inverter have closed loop current control by default? So either your reference generator is generating high currents, which it definitely shouldn't, or your current controller is unstable, which can be the more likely reason (although you can't rule out an issue being in the reference current generator itself).
Does the overcurrent occur at a certain point in each mains waveform? When mains voltage amplitude is near zero (twice per cycle), is your amplitude high? Then that means your waveform is pouring current at the wrong point in the mains waveform. It could be a power factor issue.
Does the overcurrent occur at a certain point in each mains waveform? When mains voltage amplitude is near zero (twice per cycle), is your amplitude high? Then that means your waveform is pouring current at the wrong point in the mains waveform. It could be a power factor issue.
so an unexpected voltage spike across my zero point is possibly the reason of the overcurrent? and the solution should be to produced a perfect sine wave in my output?
so an unexpected voltage spike across my zero point is possibly the reason of the overcurrent? and the solution should be to produced a perfect sine wave in my output?
This simulation is an inverter which shows (more or less) how to take the control signals from mains AC. (If the output were connected to mains, then I guess we might call it a grid-tied inverter.)
The output waveform needs to be a sinewave, and it needs to coincide with the grid. As you can see, my waveform is lopsided on both counts.
My waveform tries to push juice onto the grid at wrong times in the cycle.
Perhaps this inverter can be fooled with enough so it operates properly (the values are not necessarily working values). As it appears now it illustrates a concept which is important if you want to avoid burning up your project.
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Of course I do not know for sure whether this is the cause of your error.
If you have a transformerless inverter with PWM control, then the current must be controlled to match the (filtered ) voltage with no phase error, such that the net power dissipation in your inverter is never exceeded. Do you have this control?
Do you have ;
Suitable margins for component specs. with a design spec?
If you have a transformerless inverter with PWM control, then the current must be controlled to match the (filtered ) voltage with no phase error, such that the net power dissipation in your inverter is never exceeded. Do you have this control?
Do you have ;
Suitable margins for component specs. with a design spec?
I used a flyback topology for the inverter, and included all the circuits in these list. And for my test I added an Isolation transformer in between my AC line and my inverter. I tried again another test and I take the isolation transformer out, its kinda risky but there is no over current that happens. I think it is my isolation transformer that causes the problem. or does unecessary noises in sinewave be from a transformer?
Nice chat, unfortunately without substantial information about the inverter circuit and control method.
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As a first step, basic information about the topology is needed. If it's like below, overcurrent may be easily produced by SCR trigger or commutation problems.
Where do you observe overcurrent? In the flyback output or at the grid interface?
Nice chat, unfortunately without substantial information about the inverter circuit and control method.
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As a first step, basic information about the topology is needed. If it's like below, overcurrent may be easily produced by SCR trigger or commutation problems.
I had observed it at the grid interface.. what do you think is the possible cause? does it has something to do with my output sine wave and the electric utility sine wave?.. and if the overcurrent happens at the flyback output? possible cause is the SCR trigger? or is there any other that could be the source of overcurrent?
To monitor it properly, I think you need to track current through a low-ohm resistor at every moment in the cycle. When we hook up a plain resistive load, current travels in the expected direction through it during a positive or negative waveform. Your equipment must cause the opposite to happen. Current must always flow in the opposite direction.
This means that your waveform must always be greater amplitude than the grid, and it must be the same polarity, positive or negative.
And for my test I added an Isolation transformer in between my AC line and my inverter. I tried again another test and I take the isolation transformer out, its kinda risky but there is no over current that happens.
Your zero crossings must coincide with the grid's zero crossings. You must avoid allowing your circuitry to introduce a power factor error. However there may be something internal to your circuitry (or in the isolation transformer) that introduces a delay/ advance of your waveform.
You can correct it by adjusting your switching times, earlier or later.
To monitor waveforms properly, you need an oscilloscope.
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