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- เผยแพร่เมื่อ 11 มิ.ย. 2024
- A few years ago, I built a crude DIY grid-tie inverter. Its performance however, wasn't good enough, so I decided to have another go at it.
Here's a link to the circuit diagram/code for this project: akiotv.nl/warehouse_data/grid...
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Perhaps I'm stating the obvious, but of course this inverter is meant for demonstration/educational purposes. If you need to deploy an inverter for production use, just get an off the shelf unit that meets all the grid code requirements of your region. Hope you enjoy the video :)
great video and hard work .if u add dc to dc converter as boost one to 320v dc so u can regulate pwm to control the power by measuring the output power that deliveried to grid .the dc to dc input can vary as solar or wind input change so pwm can comensatet that to what the adjusted max power.
u can buy one for example input rate 12v, to 35v after that thake the important components like ferrite trans and mosfet but before check its frequency then reprogram arduino to deliver the sam freq to guarantee the core not saturate.by adding some probe current and volte of output u can produce your pwm duty cycle .
Regarding your high side voltage and current, you can use a current transformer to get the current and a small rectifier with a voltage divider for the voltage. I've implemented the CTs myself in an ESP32 project but have yet to tackle the high side voltage sensing.
First of all, thanks for pointing out my comment on your previous grid-tie inverter video!
I really love the improvements you made, I actually build something simular with the same H-bridge module a while back. I did manage to push 50W into the grid, but unfortunatly I eventually blew up the H-bridge (ordered new a few diffrent new one's with faster slew rates that I want to run at 30 kHz). I think My mistake was that I plugged in the grid before plugging in the DC side, causing the H-bridge to function as a rectifier and blowing the mosfets diodes because of the huge inrush current filling the capacitors. When I get mine working again, I will start experimenting with the possibilty for it to work as a charger too, pulling power from the grid and pushing into the battery, this should be possible without any aditional hardware.
I will keep you updated.
Btw, my question still remains: Did you check the output current waveform on a scope? Since you measured a power factor of 0.95, it should be pretty smooth, but i'm still curious!
Ah yes, I blew up one of these things too. The reason I blew up mine is that the BTS7960 chips that it uses have the low side switch on by default. So if both half bridge devices are enabled, and both PWM signals are low, the low sides are turned on, creating a short circuit through the ground rail. This happens all the time during PWM and is no problem then, but if it happens for a longer time you're done. My mistake was that I programmed the arduino to go into standby mode upon detecting a problem, but then I forgot to add some code to disable the EN signals to the bridge, leaving the bridge with both low sides on with the AC side hooked up.
My thing seems to have no problem with the DC power being off, as long as the inverter is in standby mode and the H-bridge switches all disabled. Would it be possible that your microcontroller enabled the bridge (for instance because it was also powered from a laptop or something) without the DC connected? That could create essentially the same condition I had.
I put the scope across the shunt resistor on the low voltage side on the transformer to see the current. Forgot to include it in the video, but it looks reasonably smooth, although less smooth than the voltage. I think I'm going to put a picture of it in the folder that has the schematics and stuff.
BTW About the battery charging, if it's a simple lead acid battery you might be able to cheat your way into doing this by just using the diodes as a rectifier. You'd just hook up the H bridge to a tap on the transformer that has a slightly higher voltage than the battery and it'll charge passively with the bridge turned off. You could use a simple relay to select the right tap on the transformer, connecting a lower voltage one for sending power onto the grid, and selecting the higher voltage one for automatically charging the battery. It's pretty rough and you'll have no control over charging speed etc. but it'll work, my old school lead acid battery charger is also nothing more than a transformer and a rectifier. (which is in that thing actually a *single diode* haha)
@@AKIOTV I think you're right about the way I blew up my H-bridge. I had the enable pins driven high before the battery was connected and the correct pwm signals where applied. Won't make that mistake again.
Yes please do put a picture of the current waveform in the zip. My current waveform looked very rough, I was expirimenting with many different inductor values and even wound my own on different core types, problem is finding one that has enough inductance, and doesn't saturate up to about 15A
As for the charging part, I have to say I first though of doing it exactly the same way you described, but this would indeed require a perfectly matched transformer winding/tab + the power factor and efficiency would be horrible as a rectifier only draws current at the peaks of the sine wave. Then I found out how victron inverter/chargers work!
It's nicely explained in this video: th-cam.com/video/UPfUn5ki7OM/w-d-xo.html
Basically it's working like a buck converter in inverter mode, and like a boost converter in charging mode. The pwm duty cycle is always following the grid waveform, but is controlled in such a way that it aims just over the grid voltage in inverter mode, and just under in charging mode, causing the current to flow the other way.
In this simple simulation you can see how this works with a simplified half bridge version:
www.falstad.com/circuit/circuitjs.html?ctz=CQAgjCAMB0l3BWK0BsB2AnADgEwI5gMw6SFZYSGEhIAs1CApgLRhgBQAZiISliDhy0Q9HAKE9qYaEhgduvfoQRjRPFTzHTZ0DgHcRxAeUNihkKOwDmpkWBS3atfhcjsANrZwn8Zk69hICGlCSBJiQgxIBDgUFAQ0SwM1b341Kgc3G18eLGEcpxcknj5xYUVjF3YAJR5IYVSBND8isRi4Gk6AtBR2ACcQHv5GrBQG-2QOAGMaDDEyfLnKqGR4OAwNza3tjBBmFF0cTebCWjQ4c8zAjgrz8f47spW3MGaQUfuQDDAWlcSHIoBJAANQA9u4AC4AQysjHYADcBJA0vYkcMJK4RBYwJigewDCQUQ41LRUW5kkYKiSyfjJA4fmkjAzimpmSlkcUKo0KsoxG4qUzvLYsLj2ABJOqfLkTYL886zX6PRoQbHsAAeXzOAiWbDi2ro4H4AHE+gBLAAmAB0AM5TUEAO3tjCmEMYVutEL6UPt1s4oL6AFtGH11YMwLtThAohGnCJDSAAOqm+3m5NWAD0elNfUYNpz1tNHu9UzhBiGyyV-lD4f4rDEGAQEGYu2EYH4AAVQXpgzbOO4u9be31QQGbQAjKEQ119ACeNohoJtVjN7r0AAtGPabQAKCdT4Nz63w8HQ2E2gBUNvNAFcITOpvf3IwAJQ2gB8S5XNuPkJhucH1rbgAQteUwANY2gGoLmi+1YEAIwgNg4OCJK2HZdj2vr9noAGcMOo7WsuFrzou1p7tOh7rpuO7kQe34nn+F5Xre96Pi+NoADyfsRR4MWeAHAaCoIejaACy0GwQMhJPNJzIBNMdLgEKGTgCguKwFG0DfGAtD4DiaBoMoGC8KsQTWIp9gWCpryZJYGo4mh2LGYa1CthAYr2tO9pQu4eaMAWRb2iWtKycpJlyaGpLCKwYDUHw0VsBYDTCB58LBtONoAMJrlCfSwn0NoAA5mkFpqFU+7Cggh4ArLQkAbOAFgHMIFhmOU7BkO8IAAGIQLIjUWKwIAACIsVlbHsEAA
@@nielsdaemen That is a much more proper way of doing the charging thing. It would be quite elegant if you could implement that with merely a software change.
I've added the image to the folder. It's not a perfect waveform, but I'd say it's all right. I suspect the current waveform is more dependent on accurate synchronization than on the filter itself.
@@AKIOTV That current waveform looks quite alright indeed!
Another thing that infuences the current waveform is if the grid waveform isn't actually a nice sine wave. Where I live, the grid waveform always has a huge flat top, so when the inverter tries to output a nice sine wave, it will deliver a bug current spike at the peaks because the difference between the inverter output and the grid is larger.
@@nielsdaemen True
It would be nice to see the arduino replaced with discrete circuitry instead. You don't need to generate your own sine wave when the grid is providing one to you - I _believe_ a phase-locked loop is the correct tool for this job.
You could make it fully analog, but that eliminates a lot of flexibility in the design. Pretty much all grid-tie inverters on the market also use microcontrollers to do the job. The PLL can be implemented in the firmware of the controller. In fact, the method I use could be seen as a basic variant of PLL.
I do like the idea though, there's a certain elegance to a fully analog design so I might just try it in the future.
@@AKIOTV It's the elegance you mentioned that gets me. I'm a programmer by trade, so seeing something solved in code almost always leaves a "so what?" Impression in my mind, but a circuit crafted to achieve the same job is mondo cool. One might even describe it as "rad".
Nice work, good design and great future improvements.
I wonder if a toroidal transformer would improve efficiency? You can get sensors that plug into the main switchboard that measure these things - I guess the time they take to detect and report power, direction, voltage is pretty important?
A toroidal transformer may help. Not entirely sure, perhaps I'll give it a go. The most ideal solution for mains voltage/current monitoring would be a similar device to the cheap power meter I use now, except one that has some interface to connect to the arduino.
@@AKIOTV Yes, thought and inquired about this a lot - I want to measure power and direction so I can control both charging and the a grid tie inverter to minimise the power drawn frin or sent to the grid. I've been told I need a quadrature detector.I'll see what I can find on aliexpress. I'll post back when I find something suitable.
Have you given any thought to isolating the grid side with a relay/breaker to let the inverter run unsynchronized on outage with the ability to continue monitoring the grid side, resynchronize to its phase when it's restored, and re-couple only once phases are in sync?
This is possible, and in some cases it's done, but I don't intend to use this as a backup power system. I have another non grid-tie inverter (which is significantly more powerful) that can power my stuff during an outage.