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Topic: Wind turbine charge controller prototype/shield (Read 10556 times) previous topic - next topic

@rockwallaby ... some of our other guys are working on a scada system. But they have been a little slow. I found a pre-written php web based scada system.. actually there are a couple of them that I found.  But one of them is pretty much written up in french, which loses me.  It is our intention to do the same kind of scada work you are talking about as another component of the project.   :-) 

#31
Jan 02, 2013, 04:42 am Last Edit: Jan 02, 2013, 05:00 am by rockwallaby Reason: 1
Hi mgshightech,

That sounds interesting, about what you say regarding SCADA systems.
I have worked with industrial SCADA systems for many years, programming them to work with industrial PLC's.

Funny you mention that it is written up in French, as I am just on a French website checking out some things to do with motorcycling for when I head back there in June this year for some months. You could use something like Google translate to help maybe?

What I have been working on over the past months is something that appears like a SCADA system, but to work with small micro-controllers like Arduino's.
There is still much for me to do in regards to developing it to how I intend, and yes, progress has been slow for me as well.

There are two basic approaches I have used;
One is where the Arduino is the server, serving up data to the client, I do this using json formatted data. It is nice and efficient.
Second is where I have the Arduino push up data in json format to my SQL database on my hosted site. Then the host server simply pulls data out of the SQL database and gives it to the client when requested.

The second approach is where I am moving toward as it allows for better through put of data if there are many clients connected.
The Wiznet ethernet for Arduino can only support four simultaneous connections according to the data-sheet.
By having the Arduino push data up to a hosted site gets around this problem and allows for many other possibilities.

The Arduino essentially is the component which gathers sensor data and provides any needed output control, such as PID loop controllers and so forth.
The client side (browser) is mostly made up in javascript and I currently use Backbone.js as my framework to keep things as neat as possible.

Another active member on this forum, Graynomad, is developing a very nice piece of hardware and the software to go with it that might also interest you.
It is called ArdweeNet and it is designed with networking in mind, using RS-485. What Rob is developing I believe slots quite nicely into this area of control.
Maybe Rob might come in at some point if he is interested to do so.

I would be interested to learn more about what you have found in terms of that php based SCADA system if you get a chance.

Regards,
Paul

PeterH


He asked why a wind turbine requires mppt while a solar panel doesn't. The answer is this.


The Wikipedia article about MPPT is wrong, then? You ought to correct that.
I only provide help via the forum - please do not contact me for private consultancy.

I wouldn't be so bold as to assert that the wikipedia article is wrong.  It is only in special cases that other methods are just as good. If you are aware of the special cases, you can take advantage of them to your benefit. If you are unaware, then mppt away.

sorry I haven't been around .... flu ... I have been quite miserable and am still sick.

@rockwallaby ... I thought I named those packages for you. Somehow I don't see th post here, so I am going to repost them. (at least it seems that way to me) the package names are stantor (french)  and seer_2 or s.e.e.r. 2  (english) both available on sourceforge. I would try the seer2 package first.  Just look them up on sourceforge.  I'll be back around as soon as my body is ready for it.






look here:   http://www.wholesalesolar.com/products.folder/module-folder/Eopply/EP125M72-190.html 

you will see that the these curves show that the maximum power voltage doesn't change much as the sunshine level drops.  The wikipedia article shows curves with a more dramatic alteration, but all the curves I have seen for market panels look like this.  (above) So, what you do is you figure you're going to lose a volt IR in transmission, and that if your remaining (max power point) voltage at max sun is around 6-8% too high for the battery, you will not  lose much power because that is within the range where you will only lose around 3% of your power. You'll lose that much power by forcing it through a transistor.  So, then your panels output voltage can drop as much as 12-14% and you will still be within range to only lose 3% of your power. The stats of panels show that the output voltage won't drop more than that.  There are things helping you by the way. When it gets cold and your panels output more voltage, your batteries require more because their internal resistance rises. When it gets hot and your panels output less, your battery requires less. When your panels output current drops and the voltage drops a little as well, guess what, the battery doesn't ask as much voltage because it's internal resistance is causing a smaller IR drop because of the smaller current.  .. So we are going to do tests to verify this stuff, so stick around if you are waiting for the test results.

So if you pick just the right voltage of panels for your condition, you can happily charge with relays and get as much as any other method.  Unfortunately, only maybe 20% of panels lie in the proper voltage range. The rest are going to require fussing.  There are multiple things that drag you out of this ideal zone.  If you are covering more distance, you may consider using  relay charging with 18/35/70 volt panels to offset the IR loss of the cable, or, you can go high voltage/mppt.  Relay charging with 19/37/72 volt panels would only make sense if you were charging a long ways away from your panels, and for panels in the low voltage range like 14/28/56 volts... well, if you want them to reliably approximate maximum power, you are going to have to series/overvolt and mppt.  Consider the 14 volt panel you lose a volt in IR losses, now you're at 13, and you can only trickle charge. If you put a blocking diode in there, you are dead. In my opinion, forget the blocking diodes, just have your controller turn the panels off at night.  Relays suck power for their coils, but only 1-2 watts for 60-120 amps of current capability. That is a lot less than losses in 60 amps of blocking diode. (like 20-30 watts)

Also, I don't think mppt controllers are generally designed to boost ... assume they can only buck and supply them with extra voltage.

I'm going to try and use relay charging. We'll place the panels close to the charging station and use 2 guage cable.  I have an mppt controller, so I'm going to make a comparison and cough up real data. 

Chagrin

If you put a blocking diode in there, you are dead. In my opinion, forget the blocking diodes, just have your controller turn the panels off at night.  Relays suck power for their coils, but only 1-2 watts for 60-120 amps of current capability. That is a lot less than losses in 60 amps of blocking diode. (like 20-30 watts)


Take another look at Tim Nolan's project to see how he uses mosfets for the blocking. More generally, he really does a great job of explaining his circuit and the various sections of it.

I agree with you on dropping the buck/boost for simplicity. Assuming the panel/turbine and batteries are matched well the batteries won't care too much if you overvolt them a little so long as you keep the current within bounds (or is that saying the same thing?). An enduser can always pop on an external module for buck/boost anyway.

#36
Jan 15, 2013, 01:16 am Last Edit: Jan 15, 2013, 06:57 pm by mgshightech Reason: 1
What we are going to do is define a module interface that can accomodate multiple types of charging. And I think the first modules to be designed will not use buck/boost. Later on we may move to design some buck/boost options.

I looked at Tim's use of a fet to block reverse current. For small charging currents at low voltages, this could genuinely be an efficiency boost over using a diode.  I'm not sure why he needs an extra fet for that job, but it's probably some confusion about the nature of mosfets that is causing me that.  I looked at the specs of his transistors.  One of the issues I have discovered is that VDS for mosfets is temperature dependent and apparently tends to rise with temperature.  The specs I looked at for his transistors did not show VDS figures for differing temperatures. Actually it just showed single RDS ratings that I assume you are supposed to use to figure your VDS.  so I doubt that the specs are telling the whole story.  

Nevertheless, I'll make half an apology to those paying attention for shooting down mosfets. for 12, maybe 24 volt charging, it looks like it is not particularly hard to keep transistor voltage drop below 0.4 volts. However, for higher voltage charging, it appears that RDS has to rise because the transistors have to be different higher voltage models, and it could easily become difficult to beat a blocking diode with a mosfet when doing 48 volt charging at high current.  Another reason for not apologising though is that if Tim is right, and you need an extra set of fets to act as current blocking, then that doubles your voltage loss. (ouch) Relays can simply be turned off. They don't need any reverse current blocking.

So I started a writeup describing some module interface definitions. This writeup is not finished, and is open to discussion.  It is here:  http://egrouphub.com/wiki/index.php/Charger_Modules   I'll be looking over Tims design for clues as to how the interfaces may need adjustments, but I think I have most of the necessary details right so far.

OK, so here is how I am picturing the deal. Everyone who writes a significant piece of code or designs a significant module up front will have rights to everyone elses designs who also participates in this fashion. When that is done, and we have reasonable solutions for a fair set of modules, we may wish to close it off for newcomers. However, We will publish the interface definitions and make them publicly available so that we don't become a hindrance to the technology. Ultimately, the goal is not just to make money, but to cut down the cost of solar power systems. This is extremely important for humanities future.    We will examine the locations of the people who are originally involved in the engineering and try to make tentative global dividing lines as to marketing territories that give people the space nearest to them.    There should be a lot of new, unconquered turf down this alley because the market has not yet properly responded to the drop in the cost of solar panels, so there should be a lot of options for doing new, related projects.

:-)


short discussion of the values of two-pole power systems

http://egrouphub.com/wiki/index.php/DC_Power_Distribution#The_multi-voltage_problem

#39
Jan 15, 2013, 08:32 pm Last Edit: Jan 17, 2013, 04:23 am by mgshightech Reason: 1
OK, I got the picture with the mosfet reverse conduction. I was a little confused because of my experience with vlsi design where mosfets are symmetric.  Looks like power mosfets are not symmetric, and include a reverse conduction "body diode", so they can't block any current in reverse.  So he places the mosfet in in reverse so that it can block in reverse and then turns it on at the same time he turns on the other mosfet.   This obviously forces a double voltage drop. In his case, both drops together are probably under 0.6 volts.

RDS for power mosfets from the IR datasheet:

small transistors size of Tim nolan's  (to-220)

v            RDS          MaxI
60         .028          30
100       .077          17
200       .18            10.5
250       .28             7.9

Larger TO-3P

V           RDS           MaxI
60         .014          62
100       .055          41
200       .085          23
250       .14            18

the IRFIP150  (100 volt .055  41 amps) is around $3 a piece
You can see that as soon as we jump out of the 60 volt transistor range, the voltage loss rises rapidly. For the IRFIP150, it is quadruple the loss of the 60 volt version.  Just passing 40 amps through it will cause an over 2 volt drop and  incur the transistors maximum power dissipation of close to 100 watts. To get this loss under control we will have to have 4 of the things. ($12)  That will only drop the voltage drop to 0.5 volts which doesn't beat a diode. And that is only a 40 amp charger ... (whewsh)  To get the same efficiency for 60 amps (a reasonable size charger) ... 6 transistors..... $18  + heatsink + silicone padding/screws  (probably reducible for large quantity orders).  A 40 amp relay is $5. A 60 amp relay is $5 (I got them for $4).  A 120 amp relay is $12 at aliexpress.com .. .. and the relay solves the reverse blocking problem for free, and without voltage loss. So you can see that if your panels match your batteries, relays have the clear advantage for higher voltage charging.  Their problem is that they don't pwm well.

Panels have open circuit voltages considerably higher (like 20% higher) than their maximum power voltage, so charging a 48 volt bank will require an open circuit voltage of 75 volts to do pwm and something closer to 150 or 200 to do mppt.  You need some spare voltage on the transistors for protection against inductance, etc.  On the other hand, the battery helps to give you that spare voltage. To do mppt for a system that can accept panels during the day and rectified 120vac at night, you need the 250 volt transistors.  Just 10 amps per transistor will incur 1.4 volts of loss .. 80 amps ... 8 transistors, probably $25 + heatsink bla bla bla, and if you want to block, use a diode or a relay cause your transistors are imposing a lot of loss.  To get your transistor loss down to diode level, you have to triple your transistor count ... (24 transistors) .... ouch.  Oh woops ... I forgot something... to get the 80 amps out, you may only need 40 amps in for mppt, That sounds like it could halve the transistor count, but it really doesn't because the 40 amps will be bunched up into half of the duty cycle, making it 80 amps and causing the full voltage drop half the time. As the voltage drops down, the duty cycle rises, causing the same voltage drop, but for more time.  So there is some efficiency advantage at higher voltages because the voltage drop is smaller compared to the total voltage. It shows up in less loss because of a shorter duty cycle.


Obviously, to move a lot of power at 12 volts, we are talking about really high currents, like 100s of amps (400 for a 5 kw system). So you can see how the 12 volt solution works great for a small system, but the low RDS doesn't save you if you want to move much power. To move 200 amps for 2.4 kw, you have to have 10 60 volt transistors at 20 amps each, incurring a 0.28 volt loss which doubles to 20 and 0.56 for a reverse voltage blocking system. So that's about 5% power loss.  To do it with relays, we are talking 4 relays at $5 each, free blocking and no appreciable loss.  Now if we put the four relays into a 3 module system. first module does 100 amps, second and third do 50 each.  The controller detects the current flow of each module, and for multi-stage charging, it simply turns off the modules it doesn't want to run in stead of pwm-ing it.   Only thing remaining is to match the panels to the batteries, and you'll still be ahead if your panels have an extra 0.5 to 0.7 volts.

A 24 volt system may still be able to use 60 volt transistors. This creates a competency window for transistors. We can basically cut the percentage power losses of the 12 volt system in four, or only cut them in two and halve our transistor count.  Unfortunately, we can't mppt up to very high voltages this way, but simple pwm power losses will be relatively low.

So it appears that transistor/mppt charging is only competent
a:with small, low power systems
b:systems where we want to raise the voltage to avoid distance IR losses
c:when panels of the proper voltage are more expensive, demanding use of higher voltage, cheaper panels
d:when we are too clueless to match our panels to our batteries
e:maybe 24 volt systems that use low resistance transistors and don't mppt up to over 50 volts.

and it seems to me that d: is probably the most common of these conditions


If anything I am suggesting itches anyone, yeah, just please let me know.   :-)

This project has attracted a group of its own.  Go here to find the people in cooperation:

http://groups.yahoo.com/group/charge-controller/


Ironchef

Are you still working on this project? I have built a wind generator and was interested in what others have done to control it with an arduino.

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