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Topic: Wind turbine charge controller prototype/shield (Read 9 times) previous topic - next topic

rockwallaby

#25
Jan 01, 2013, 01:58 am Last Edit: Jan 01, 2013, 05:46 am by rockwallaby Reason: 1
From reply #12 mgshigtech informs us
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I am an  EE as well as a software engineer

I am making the assumption EE generally stands for electronics engineer, so you are an electronics and software engineer, is this correct?

In your lengthy reply # 23 you state
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....transistors just eat voltage.
The only thing they are good for is controlling the current draw rate.

I hope you had learnt that transistors are current devices and that they don't eat voltage.
In the context we are talking about I think you mean to say that transistors dissipate power, and that you are eluding to their possible in-efficiency in such a circuit, is this correct?

In your long reply #23 you assert the following
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A wind turbine needs mppt where a pv array doesn't

I wonder how you arrive at such conclusions?

You go on to write the following
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There is one more issue that you didn't notice here, and forgot to mention

Who is it that you are referring to when you say 'you'?
And is it not presumptuous to say that whoever you is, actually forgot to mention something else?

Rather, would it not be better to have said something along the lines of 'Oh, and I thought of another issue and also something else to add as well'

Then
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If this is how we are doing it, then we are just DIYers, not open source.

So, I am again assuming reading this that you think DIYers and open source are mutually exclusive and that there is not point to being a DIYer?
When you read back what you have written, I wonder if you see the level of your opinionated views?

It appears to me you have a dislike for transistors, for 12 volt systems and even to some extent the thoughts and designs of others.
Again it appears to me you make a lot of assertions but very little to explain in relevant detail any explanation to provide further understanding.
Though you state a liking for class D (audio) amplifiers several times.

I could continue...

It seems being an electronics and software engineer today is something quite different from how I became one.
I will apologise here now in advance if mgshightech feels offended in anyway by what I write, but I simply write in response to what I notice.

On a more positive note, I do notice some hint that mgshightech does have a keenness in wanting to engage in developing systems, though I am unsure in what specific direction that interest is at present, as he/she talks about arcing relays to radiation showers from Russia.

I wish to be able to communicate in a discussion where there is an openness, a mutual respect of the interests of others.
A nurturing of a pot of like minded people who do want to be 'DIYers' and who do embrace open source concepts.
Hopefully what I write may provide him/her (mgshightech) with a little prod to think about these things.

I may elect to bow out of this thread as unfortunately for me it has lost relevance.

Paul

mgshightech

@rockwallaby

a transistor turned all the way on, which is what we do with pwm and/or mppt can be considered a concoction of resistors and diode drops.  The voltage coming out the business end of it will be lower than the voltage going in.  So, you are welcome to word that by saying that they dissipate power. It makes little difference to me.  High current, hot mosfets turned all the way on will tend to have a d-s drop of 1-2 volts. Of course, you can add more transistors in parallel to partially counteract this problem at a cost.  That's what the datasheets say, and it isn't a lot different for bipolars.  Well, losing voltage can push you away from maximum power point and cost you additional optimizational losses, so, for a a 30 volt panel for example can comfortably charge a 24 volt battery quite optimally.  If, however, we subtract 1.5 volts from the 30 because of transistor losses, 28.5 volts remain.  This will still comfortably charge a 24 volt battery, but if we then account for IR drops, we may be cut down to 27.5 or 27 volts. To charge a 24 volt battery up to its top at the 20 hour rate requires very close to 28.2 volts, so the 27.5 is 0.7 volts shy. The panel has to make up for that by reducing its current flow in order to push the voltage up higher. So, we lose both voltage and current.  We can choose the panels that output a couple of extra volts.  Of course, that can be done, again at a cost. So a system of multiple relays does not have much of any d-s drop, but they don't pwm very well. So the obvious solution to that problem is to have charging module options that use multiple pv arrays, turning them on separately so as to provide differing current flows for different charge stages.   This is a good idea anyways for relay systems as relays tend to have current limits of around 60-120 amps. So, even in a 48 volt system, we are talking about 3-5 percent power loss, which for a 5 kw system amounts to  around 200 watts, which can cost $300 or so to replace.

OK, so in truth, the relay strategy is not optimal for all designs. It sucks for long distance cable runs because you have to provide battery voltage at battery current wheras mppt systems can raise the voltage and have smaller IR loss.  So other strategies need to be cared for in a flexible system.  Also, if you know a good way to cut the voltage drop across transistors down to 0.2 volts or something, then of course, I would be very interested.  So, yes, for 12 volt systems, mppt or pwm  could easily (not necessarily) cost 10-15 percent of the power up front. For 48 volt systems, this is of course less of a concern.  I am shooting for 48 volt (dual 24 volt poles) but a flexible system will allow for people to choose their favorite charging system.


Hmmm. regarding the question mark of being ee/cs.  I guess I have been in enough degree contests to prefer to avoid that route because what we need more than to compete is to get along somehow.  But let's just say that I'm pretty sure one of the driving forces behind arduino is open source strategy.  So, when DIYers show up. This is of course beautiful.  It will be more beautiful if we can work as a group to accomplish a public project. There should be plenty of people around to work on that.  I can get our guys together and try to hit up kickstarter for public funding for a public project, but I'm reticent for a few reasons (that may melt away).   So, one way or another, it is our intention to accomplish some strategic technological additions to the open source community that are designed to help re-balance the social flow.  If you prefer for society to never evolve or improve, I suppose that is your right.

So, I'm going to tell you this because I guess I have to, but the reason why all the other stuff got into the talk is because I am a systems theorist who has spent some decades examining the current social structure.  There is a pathway to overcoming some of its current weaknesses that lies down the lines of the concept of balance.  Everything is connected to everything in the real world, and small deeds can have large results.  ... or they can peter out and be forgotten in the infinity of time.  (butterfly effect) So, I didn't want to get too deep into that kind of stuff because this isn't that kind of forum. Nevertheless, systems and complexity theory have a great deal to say about what we aught to be focusing on.   So I have hoped for people to see the potential advantage of providing a top class solution to the dc power distribution problem .. open source.  Of course, if people don't care about that, then I hope that they care about something else in relationship to the development of a top class mppt/charge controller architecture.

Let's see ... 1938, Otto Hahn discovers two kinds of fission, thorium   http://en.wikipedia.org/wiki/Thorium_fuel_cycle  and uranium.  Thorium is far far safer to fission than uranium, but you can't make bombs with it.  So, I am going to try to respect the topic of the forum and not drag you any deeper into that.  There is enough info. in the wiki page for anyone who is curious, except that I don't think it mentions chinas development of thorium fission reactors.   OK, so what it boils down to is that I have a big picture in my head. I realize that some people don't like big pictures.  I'm not accusing you of that. Feel free to make your own choice.

The arcs in relays as they open/close are of course definitely on topic.  Arcs destroy relay contacts and can render charge control dysfunctional, potentially even dangerous. So if we want to use the relay option for cases where it is optimal, then we have to study this issue out. 

I don't know just what sort of people are here. As my nameplate says, I am a noob on this site.  I must decline to further discuss egrouphub in detail on this site because it is not on topic, and I wish to respect arduino.cc as I wouldn't be thrilled if people got too far off of topic on our site either.   

Thank you for your comments. I hope others feel more positive about it.   :-)


So, in case anyone is noticing, I have been on this project for some several months already.  I have examined the curves, data of parts, etc. found a lot of ideal electronic parts and created some strategies, but I don't expect to out-think the arduino community by myself as that would of course be ridiculous.  :-)

And class d amplifiers just save 1/2 to 3/4 of the power that is spent by other amplifier classes.  This is a big deal if you are paying for all of your power up front.  They can be powered directly by dc power sources, saving us the expense of the power supply and the energy it wastes humming at 60 hz all day, and the space it takes up and the shipping weight.  So it's just another way of reducing system cost, but It is also not directly on topic. I just pointed out that if we can reduce the cost of multiple parts of a power system, we can cut the entire system cost by as much as approx. 50%, which is huge.  The price of solar power dropping is huge. It's huge again if we can use it more efficiently (i.e. use less of it).  And there are a lot of ways to do that that are improvements over what solar installers are currently setting up.  (yes, I have discussed with solar installers and have a good idea as to what they are currently doing.)  I'm not asking anyone to get involved in that kind of stuff right now, just trying to paint the picture a little wider in an attempt to help people to feel more motivated.   :-)  Looks like it backfired and got smoke all over my face.  I'm reminding myself of Ronald Weasly and his wand.  LOL.

OK, it has been a pleasure.


mgshightech




Khalid

Okay,
Now you tell what you want from us.. :smiley-mr-green: I am also a guy like you to work collaboratively ]:D..

mgshightech

@ Khalid   U R awesome dude.  :-)  I think "We got work to do"  Hopefully some others agree on that.

BTW I failed to answer one of the questions. He asked why a wind turbine requires mppt while a solar panel doesn't. The answer is this. If a wind turbine is trying to charge a battery, the turbine will be spinning at different speeds. Both dc and ac motors produce different voltages at different speeds.  The higher the speed, the higher the voltage. OK, so as long as the output voltage of a turbine is below the battery voltage, there is no charging because the battery is pushing harder at the electrons than the wind turbine.  In fact, the system will most likely require some kind of diode to prevent the battery from dumping current into the wind turbine. .. Not what we had in mind...   OK, so the rpm rises, the voltage rises the voltage reaches battery voltage and a tiny bit of current starts to flow. The voltage rises to around 2 volts more and a ton of current starts to flow. (btw I was keeping track of the wind turbine generation faq on alt.energy.renewable around 1995) .. So a ton of current starts to flow and it acts as a barrier to the increase of the wind turbines speed because the wind turbine can't produce the energy demanded by the current flow.  So it slows down (or refuses to speed up).  Well, when the turbine is spinning slowly, the force on the blades may rise a little, allowing for more current, but the energy output of the turbine will be proportional to force (torque) multiplied by angular speed.  So, now that the turbine is blocked at a particular rpm from spinning faster, it can't collect the energy that is available because the speed can't rise.  The solution to this problem is mppt.  The mppt algorithm watches the current flow/voltage in tandem and scans the current/voltage dimension for the combination which produces the most power.  When that optimum in power is produced at a voltage (respective turbine speed) above the battery voltage, the algorithm buck-converts the higher voltage down to battery voltage with higher current and presto ..... more power     :-)

Now, let's talk about the solar panel.  The solar panel is basically an arrangement of P-N junctions.  They convert light into current. Basically, a 2 electron volt photon is incident onto the panel and it jumps an electron over a two volt junction gap producing 2 electron volts of available power.  If more 2 ev photons are incident on the panel, then more electrons jump the 2 ev junction gap, but they are still only at 2 volts potential because that is all the energy available in the 2 ev photons.  We arrange a bunch of these in series, to raise the voltage up to something that can match our batteries.  Now, what happens when more sunshine hits the panel is that because of quantum mechanics above, the voltage output from the panel doesn't really change (not much anyways). In stead, the panel becomes capable of sourcing more current.

Now, not all photons are red 2-ev photons, so this makes the dynamic a little more complex.  If we raise the voltage required to charge the battery, what happens is that the 2 ev photons are close to being the weakest of the bunch.  There are also infrared photons, but the panels will not be designed to receive them because receiving them means shrinking the junction gap voltage and hence the cell voltage, and hence the cell power. ok, if we raise the voltage demanded of the panel, The red  2 ev photons will discover that the voltage on the junction has risen above 2 volts and they can no longer push the electron over the gap, so we lose current. However, there are higher voltage photons in the mix. Visible light contains half the energy of sunlight, and the panels are tuned to be most receptive to particular photon energies. So, what happens as we demand more voltage from the panel is that the higher energy photons can still jump the gap.  Visible light is a concoction of photons between 2 and 4 electron volts.  The cells are probably not particularly sensitive to 4 ev photons (blue) because they just can't engineer the silicon to be optimally receptive to all photon energies. Next, keep in mind, that if a 4 ev photon is incident on the panel, it can jump only one electron over the gap which is operating at around 2 ev. This means that the extra 2 ev in the photon are wasted.

So the designers of the panel are caught in a conundrum of shrinking the gap and receiving the IR photons, but wasting the extra energy of the higher energy photons and the alternative of raising the gap energy to receive the full  power of the higher energy photons, but excluding the use of the lower energy photons.  So you can see why pvs have efficiency problems.  Recent attempts to produce panels that can split the energy of a single high energy photon into two and jump two electrons across the gap have been successful. However, these cells/panels are not ready for production and may never be.

So the way this boils down is that panels produce only slightly more current if short circuited (like maybe 25% more) then at voltage ranges from small up to their designated maximum power point, their output current is nearly constant and it begins to drop off as we demand more voltage from the panel than it can produce. So there is this sweet spot of about +- 6% of the panels output voltage where it produces very close to its maximum power. If we demand voltage below that, then we waste voltage. If we demand higher voltage, then the panels current sharply drops off. It's better to demand lower voltage than higher voltage because if you raise the voltage required of the panel as much as even 15% above its maximum power point, you will discover that it outputs very little power. Most of the photons incident on the panel will be unable to make electrons jump the gap.  

Once again, the photon energies in sunlight are pretty much the same no matter how much light you are getting, so the panels output voltage pretty much stays the same. It just becomes more current-capable.

So, if we charge a 24 volt battery with a 30-31 volt panel in a relay configuration, the panel and the battery are closely matched.  MPPT is useless because there is no spare voltage to dc-convert down, and PWM is bad because the pwm transistors will absorb the last volt or so, causing a mismatch between the panel and the battery.  So, if we use a 35-37 volt panel in stead, then MPPT is slightly useful (get us maybe 5-7% advantage). PWM is perfect for the 35 volt panel, but becomes wasteful for the 37 volt panel.  So, the next thing we do is we say ... we hate line losses and purchasing a lot of copper, so we raise the panel voltage up a lot higher by putting them in series.  Then, MPPT really shines because it transforms the extra voltage into extra current.  Basically, MPPT controllers can be considered to be dc-dc converters. PWM and Relays do not do this.  So the answer is ... if you are running power a long distance (say a couple hundred feet) then you want an mppt controller, and the more distance you run, the more voltage you want the mppt controller to accept. Midnite solars highest voltage mppt controller accepts 250 volts and dc-dc converts it down to battery voltage.  Now, when matching panels to the mppt controller, you have to consider the panels open circuit voltage which will be some 10-20% higher than its maximum power voltage.  Failing to do this could cause a failure when the controller turns the current flow off and the panel output voltage rises to its peak.  We will basically risk crashing through the dc-dc converter transistors.  So, what this means is that for the 250 volt controller, you want to run a maximum power voltage of around 180-190 volts.. so you choose your panels to do this.

BTW, crashing through the mppt converter transistors is a high risk for wind power because the voltage output is so drastically variable.  So, if you are using wind and MPPT, then you are wise to include a voltage clipping stage that will cut the voltage down to MPPT maximum if it goes higher.  


mgshightech

also, nother btw, working as a team does not mean that we have to do what we don't want to do.  We can combine our efforts into a larger project by making only small adjustments in what we do.  I.e.  suppose we want to do a 12 volt charge controller or a 12/24 volt charge controller of a particular type. You can still do exactly that. Only thing required to hook this into a larger project is to comply with a group defined standard for module/system interfacing. That's it.  Now what we created becomes part of a configurable, flexible system. People can use our charge control module, or they can use someone elses charge control module, and all we had to design was just one module and leave the rest of the work to someone else.  Someone else can worry about the control panel code, the vt100 interfacing library, the OOP classes and subclasses that drive the modules etc.  (I already have a vt100 library on another platform that can create guis on a vt100 panel)   let's see ... nother small issue ... if we don't want to go through the expense of adding a vt100 panel to a cheap controller, we can run a vt100 emulator on a computer and spare the panel.  :-)

OK, maybe I am pesky. I guess I am just really excited about this project.

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