lompilomp wrote: ↑Sat Aug 27, 2022 9:09 pm
Those are the high frequency transformers, most high frequency inverters like this work this way:
1. low voltage dc is pulsed into these transformers at very high frequency with a bunch of low-ish voltage MOSFETS. This allows a lot of power to be put through the transformers without requiring a huge iron core. For comparison imagine the size and weight of the transformer you'd need to push 1000w continuously. Probably the size of the entire inverter.
2. The output of the transformers is rectified, possibly by discrete diodes that look like MOSFETS, or in lower power applications could be normal diodes. The thing is at this point, the voltage is around ~170vdc (for 110v inverters) and around ~340vdc for 220v inverters. Note that the dc voltage is higher than the AC voltage because AC voltage is rms, which is a sort of average, but the peak voltage of the sine wave is the DC voltage you're seeing here.
Now the good thing about these high voltages is that to get the 1000w rating, at 120v its only 8-9a going through here, so not as beefy components required in the HV section.
3. In an off-grid inverter you'd have a large-ish capacitor bank to hold the HV and stabilize it, but in a grid tie inverter its not as neccessary because there's no surges and most noise will be supressed later in the circuit.
4. Once you have your HVDC, it goes into an H-bridge, which is always in sets of 4. This is a similar concept to reversing relays, basically they are used to switch the high voltage in a certain way that they can reverse it, so you can get AC from it. Those are the IXFH44N50P transistors you see. They are 500v rated.
5. An SPWM signal is fed into the transistors, to make the output as close to a sine wave as possible. Though it needs a lot of filtering to get rid of all the switching noise.
6. Output of the transistors goes into an LC filter, which is an inductor in series with the output, and a (low capacity) capacitor after the inductor to neutral. This turns the rather noisy sine wave into a basically perfect sine wave (depending on how good the filtering is). Then it just goes out into the utility, and of course there's a lot of microcontrollers in the way, making sure it isn't overheating, outputting when theres no grid, overpowered, or the grid voltage is too high. For example, if the grid voltage is 110v, the inverter will push power in, so it might go up to 110.1v or w/e. If your grid is too weak and your grid-tie inverter is too powerful, it may raise the voltage above acceptable range and a PROPER inverter would realize and either shut down or reduce output. Now with a 1000w inverter I doubt this scenario would happen, although its entirely doable.
But yeah most likely the only difference between the two is the windings of the LV-HV transformers, I'd assume that the higher voltage one has 2x the turns but with thinner wire on the primary side. Secondary is probably the same.
Thats basically the issue with inverters, there's no one-size-fits-all when it comes to voltage ranges. IMO, the higher the voltage the better, because there's less losses the higher you go. That's why you have these solar gridtie inverters that can do 70kw that are smaller lighter and cheaper than 12kw low voltage inverters. But of course thats a different topic b/c going off-grid with high voltage is rather complicated due to having so many batteries in series, and of course the entry cost because you need a large number of solar panels in series to even get started.
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