diy solar

diy solar

99.5% Efficient Inverter Design

I like the out of the out-of-the box thinking! It'll be interesting to see what the EE guys like @BiduleOhm make of it.

I think I get the concept, but the 150V (13 batteries in series) didn't make sense to me as 170V is the peak V for 120Vrms (for a true sine wave).

The circuit operates so efficiently because the switching frequency is incredibly low; the setup creates three isolated islands of batteries, one with nine 12V batteries, the next with three 12V batteries, and the last with a single 12V battery. In a solar setup, this means three separate MPPTs. For the H-bridge switching between the nine batteries in series, that’s four state changes in 1/60 second. For the island with three batteries in series, you have sixteen state changes in the same timeframe and fifty-two for the final H-bridge. In a standard inverter, MOSFETs are switching at 100kHz or more. You will need MOSFETs rated for their respective batteries: 40V for the single battery H-bridge, 60V for the three batteries, and for the nine battery H-bridge, 150V.
Click to expand...

It also seems you'd want the most number of batteries in parallel at the lowest voltages to provide the maximum current draw and how would you charge those batteries at the same time as discharging like a standard MPPT/inverter setup? Probably nothing insurmountable there and possibly there are more efficiency gains to be had?
 
I already thought about making a transformer-less inverter but with just a high voltage battery and some PWMed FETs to make the sinus.

This approach is different tho, it's similar in the way there's just a battery and a H bridge but instead of using PWM he uses multiples rails voltages with multiple bridges to make the sinus. It'll improve the efficiency of course because you don't switch the FETs at a high frequency but the two big downsides are the complexity and a lower quality sine wave.

But, the thing is, I'm not sure we're talking about an inverter here. The article is very blurry because on one side it talks about PV panels to battery power losses reduction and MPPT, and about 120 V AC and THD on the other side... So unless it's a MPPT SCC + an inverter in the same package (highly doubt that) it's either one or the other and the article is just crappy. From the images I think it's an inverter so nothing to do with panels and MPPT, but can't be sure.

Also, you can make an inverter with FETs switching as low as 20 kHz (you can actually go far lower and still have a very nice sinus but then you start to get in the audible domain...) which is really low in the frequencies world (actually, even 100 kHz is relatively low for mosfets). If you combine that with multiple FETs banks you enable/disable dynamically you can still have a really high efficency without the complexity of having multiple isolated voltages rails and mutiples H bridges.

Also, the typical inverters (and SCC) don't have the best efficiency they can have because low Rdson low Ciss FETs are expensive so a compromise is often made. I was actually thinking of experimenting with a cheap chinese inverter and replacing the FETs by better ones (and maybe improving a few other things while I'm here) to see if it's worthwhile or not ;)
 
Cal said:
The problem with lower switching frequency is the transformer and inductors are significantly larger. That's usually not cost effective.
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I think the concept doesn't use magnetics.

He is directly converting battery voltage into mains AC.

Like I said in my post, no galvanic isolation. This would be illegal in China.
 
Cal said:
Perhaps you want to rethink your opinion.

Take a look at the photo again.
Click to expand...
That tiny transformer is part of the control electronics. Unless this is only a 10W inverter he is not passing the AC line current through that.

I hate websites like this that make fantastic claims, but are light on details.

Can you do what he claims? Yes.

Is it a good idea? Considering the peak voltage potential that is going to be developed across those batteries (170VDC)? I wouldn't do it. How are you going to charge the cells?
 
Absolutely, he's using magnetics.

He'll provide a schematic if you ask.
 
Cal said:
Absolutely, he's using magnetics.

He'll provide a schematic if you ask.
Click to expand...
60 Hz Power Transformers have at best 96% efficiency and this is with the highest quality ($$$) toroidal transformers. Lower cost power transformers are lucky to hit 90%.

Please explain how he is getting 99.5% efficiency passing AC power through a power transformer?
 
BiduleOhm said:
complexity and a lower quality sine wave.
Click to expand...
You could PWM modulate the smallest voltage stage at higher frequency/resolution to get high quality sine wave.

IIRC multi-level inverters are nothing new in really high power installations. Typical range might be 1MW and up
 
It appears this is not a conventional inverter where we're starting with a 13V battery. Perhaps he's using 4 36V batteries? If the H-bridge configures them in series then you have 144Vdc. You don't need a transformer. I would be surprised if there are no inductors though.

He states the inverter doesn't work well with lower power factors. That's probably because just one battery must provide all the power. Microwaves typically have PF = 0.7, which rules out microwaves as a load.
 
To quote from the web page.

"What's more, there are no big filter inductors, no transformers, and the associated core losses, etc..."

This is such a bad idea.
 
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HaldorEE said:
To quote from the web page.

"What's more, there are no big filter inductors, no transformers, and the associated core losses, etc..."

This is such a bad idea.
Click to expand...
Having a 170v string of non-isolated batteries is no big deal on professional setup.

AFAIK pretty common to have ~350v battery on a large UPS. But that is not really average DIY project.
Or like they say: "Just keep your dick in a vise."
 
MattiFin said:
Having a 170v string of non-isolated batteries is no big deal on professional setup.

AFAIK pretty common to have ~350v battery on a large UPS. But that is not really average DIY project.
Or like they say: "Just keep your dick in a vise."
Click to expand...
At least right now this is a DIY project. And how are you going to charge the cells?
 
The islands are not all the same capacity so you can't just charge them in series.

Will you need isolated chargers for each battery? What happens to your efficiency going through isolated DC to DC chargers?

Making this work is one thing. Making it practical and safe is something very different.
 
HaldorEE said:
The islands are not all the same capacity so you can't just charge them in series.

Will you need isolated chargers for each battery? What happens to your efficiency going through isolated DC to DC chargers?

Making this work is one thing. Making it practical and safe is something very different.
Click to expand...

My first impression is that is trades one problem for 3 problems (or more).
 
I read through the instructible and here are my thoughts:
  • It is not really practical for the typical home DIY, I would add more solar panels rather than add the complexity and complications of this design to get that ~5% to ~10% extra power.
  • However, it is a very clever design. I like the out-of-box thinking. This type of out-of-box thinking is where the breakthrough changes in technology come from.
  • As @BiduleOhm points out, there are similarities between this and some of the new solid state inverters that are coming out.
  • At this point, it is more a proof of concept. There seem to be a lot of tweaks that would need to go into a final product.
  • An interesting aspect of the concept is that you can use SW to make substantial changes to the frequency, voltage and wave-form of the output.
  • It requires a separate charge controller for each battery bank. (This does not demand, but certainly implies a separate solar array for each bank. It would take a special charger design to use the same array for all 3 banks)
  • Special care must be taken to balance match capacity of each battery bank to the needs. (And the associated chargers and Solar arrays for each bank)
  • Some of the gains of the design are probably going to be lost in the extra chargers and potential over-paneling on one or two of the banks.
  • It might be a good concept for a grid scale storage system where getting that last bit of efficiency is important and the batteries, chargers and arrays are can be tuned/designed to optimize for the concept.
  • There is nothing inherently unsafe in the concept but care would need to be taken to ensure the design of the concept is safe.
  • It does not use magnetics/transformers in the power conversion but:
    • The instructible does discuss putting an inductor on the AC Output to limit surge current. (It did not sound like that has been
      done in the prototype.)
    • I suspect the small transformer shown in the picture is for creating power for the control electronics.....but that is a guess on my part.
 
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