Maximum Power Point Tracking

entuty

Hi all,....
I have a project about MPPT. And this is the first time I work with solar cell, so I have some problems.Can anyone of U give me some reference document about it?????
Thanks 4 Ur help so much!!!!!!!!!!!!!

niel

Re: Maximum Power Point Tracking

more specifically about what, the solar cells or the mppt? there's plenty out there on solar cells, but the mppt is specialized electronics.

entuty

Re: Maximum Power Point Tracking

Thanks 4 reply! I want the reference about MPPT. Can U help me????

BB.

Re: Maximum Power Point Tracking

Here is a MPPT FAQ on our host's (NAWS) website.

Are you looking for MPPT information to see what kind/brand/model charge controller (or Grid Tied Inverter) you want to purchase...

Or, to figure out how to design and build your own controller?

Over the years, there have been many "algorithms" for MPPT... The simple ones--just take something like 80% of the open circuit voltage and set the controller's electronics to Vmp=0.8*Voc (of solar panel/string)...

Others "sweep" the current up and down a little bit every 5-15 minutes and try to maximize Pmp=Vmp*Imp

And I am sure their are other algorithms out there too (Solar Guppy designs MPPT controllers and worked hard to optimize his controller designs). Obviously--SG makes a good living off of his experience / Intellectual Property -- and is probably available for consulting...

The more specific you ask your question--probably the better answer you will receive.

-Bill

icarus

Re: Maximum Power Point Tracking

This is completely off topic,, but on a rainy spring day,,,

Can we (collectively) please try to refrain from writing (and replying) in textese?

As a personal observation,,there are those of us of a certain generation for whom the collapse (no pun intended) of the written language is sad. I know that it is easier 4u to write that way,,, it makes for inelegant communication,, IMHO. For those who appreciate wordsmiths and good writing and indeed do write well, it seems silly to have to write and speak with all the alacrity of a 16 year old girl,,,OMG,,Ya know!

The vast majority of people on this forum think and write pretty well,,, and are pretty good with their use of the language. It is an art form that we have the potential to lose.

Tony.

PS I confess that I am a bit of a curmudgeon, but even I lapse into it now and again,,,LOL.

BB.

Re: Maximum Power Point Tracking

I believe Entuty is from Vietnam... So--to speak in "text slang" in a non-native language--Better than I could probably do in my native English (not that I would try to type slang).

In the end, trying to help people from all over the world with vastly different backgrounds--I try not to be too easy to offend (or take offense)...

With text/BBS posts--the lack of body language/verbal cues (let along cultural differences) makes jokes/suggestions difficult to interpret--I try to read everything in the best light.

-Bill

icarus

Re: Maximum Power Point Tracking

Bill,

I didn't mean to offend,,, and I don't think I did. It is just one of my little bug-a-boos that it seems that (collectively) we are losing the ability to write well. I think that texting, twittering, even e-mail has brought into the vernacular a lower level of writing.

I am reminding of my late father, complaining about the cheapening of the language with the introduction (as a matter of policy) of spellings like "lite" into the newspaper world. I recall mentioning at the time that I didn't think it made any difference.

Strange how,, in spite of our best intentions we become our parents as we get older.

Tony

By the way Bill, you write as clearly, concisely and with good thought as anyone here. Sorry if any offense was taken by anyone.

lorelec

Re: Maximum Power Point Tracking

Bill mentioned the two most popular methods of operating a PV at its MPP. The simplest (called "constant voltage and current") is to manually find the MPP through trial-and-error, and it usually ends up being between 70-80% of the Voc. This works because the ratio of Vmp/Voc is nearly constant, even with fluctuations in temperature and light. The trick is determining what the value of the constant is (again, usually between .70 and .80).

The second, called "perturb and observe," is probably the most popular real-time tracking algorithm because it's also relatively easy to implement and is pretty accurate. At set intervals, the controller samples the power output of the panel, adjusts the voltage at the panel up and/or down slightly, and then samples the power output again. Based on the difference in those two measurements (which are repeated over and over), the controller can determine at what voltage the MPP lies.

Other more obscure methods include using a small "pilot cell" with characteristics similar to the PV array. The pilot cell sits alongside the PV array and is used along with an algorithm to determine the MPP. This method is advantageous because it allows uninterrupted output from the main PV array. Most algorithms by their nature are disruptive, so if the disruption can applied to something other than the main array, there is a slight increase in output (over time) from the main array.

"Incremental conductance" necessitates the use of slightly more complex math. The idea behind this algorithm is that a change in power at the MPP divided by a correpsonding change in voltage equals zero. (dP/dV=0). If the value is greater or less than zero, then the controller knows that it is not operating at the MPP and readjusts so that the result once again equals zero.

Other methods, such as finding the capacitance of the p-n junction of the solar cell (which, through calculations involving the conductance of the cell, will reveal the MPP), are thoretically possible to implement, but applying them can be difficult.

The most popular two function pretty well. "Constant voltage and current" is about 91% accurate at tracking the MPP. "Perturb and observe" is around 98% accurate. Applying any algorithm is usually not as simple as it may first appear. There are usually a lot of subtleties involved in getting things to work the way you want them to.

Marc

BB.

Re: Maximum Power Point Tracking

Tony,

I know you did not intend any offense--Just as I did not intend any offense in my (I had hoped, friendly) reply :roll: but now end up having to explain anyway .

It is just the issue that we have hundreds of folks (and the new poster here) who don't know any of us other than our on-line persona (which--for me is just as nerdy in real life ).

To a degree--I try to PM a nice nice message to a person to avoid the public discussions (or one sentence in an otherwise on-topic post)--which still usually ends up with one (or more of us) sounding like we are backpedaling on a completely off-thread topic (but still important in the world of communication and how we present ourselves).

Oh well--back to the topic at hand--whatever that was

-Bill "the never cool" guy

BB.

Re: Maximum Power Point Tracking

lorelec wrote: »

"Incremental conductance" necessitates the use of slightly more complex math. The idea behind this algorithm is that a change in power at the MPP divided by a correpsonding change in voltage equals zero. (dP/dV=0). If the value is greater or less than zero, then the controller knows that it is not operating at the MPP and readjusts so that the result once again equals zero.

Thank you Marc. :cool:

I always enjoy learning how things work (although--I probably will never design a charge controller at this point in my life).

In the end--I can see how getting "too cute" with various algorithms can end up causing other issues in the real world (unmatched strings, stability, how to address cloud/weather changes, start-up and shut down, etc.).

-Bill

entuty

Re: Maximum Power Point Tracking

I don't know what is the mistake that I've made. But I didn't means to do it. May be I'm not good at English and there's the difference between our native language. Anyway, I sorry!

icarus

Re: Maximum Power Point Tracking

Entuty,

Not your mistake my good man,,, but mine. My apologies,

Tony

Bill,, you are right yet again,, and I am contrite!

entuty

Re: Maximum Power Point Tracking

@ ICARUS
Ok. It's over, everything will be better after mistakes . I hope it's our relationship. I don't have the experience in this field. In fact, this is the first time I work with solar cell and MPPT. So I really need Ur help!

entuty

Re: Maximum Power Point Tracking

@ BB:
I'm learnning to design and build my own controller.

BB.

Re: Maximum Power Point Tracking

Entuty,

What Tony was referring to was your use of:

anyone of U give me -> anyone of "you" provide me...

Thanks 4 Ur help -> Thanks "for your" help...

To the "ear" of somebody in the US (or Canada--as in Tony's case -- "eh?" -- a joke about how Canadians always seem to add "eh?" to the end of spoken sentences instead of a "?" question mark )--your English seems to be very good--but uses "slang" that is very commonly used here by teenagers text messaging with cell phones.

Many "older" folks like Tony (or, in the US--typically people from the North Eastern US) tend to "channel" their long dead English teachers as they get older and start correcting "others" use of the language.

The idiom you (Entuty) are using tends to make you "sound young" and should be avoided in "business writing"... It will help you project an older--more business like persona in your future personal communications (at least until old codgers/coots like Tony and I die out and the world is taken over by you young whipper-snappers ).

Here, of course, this is not business--but everyone here tries to be so helpful--that they will often attempt to help posters in other areas too (whether asked for or not--:roll:).

Believe me--Tony has nothing but good intentions towards you with his comment.

Regarding your controller design... You might look up a some electrical simulation models for solar cells/panels and try running some computer simulations... Solar cells--tend to look like a current source and by the several methods talked about earlier--you are looking for the optimum operating point on the I/V/Power curve (change in slope inflection or first derivative (Calculus) per Lorelec/Marc's suggested procedure).

Of course, the only way to find the slope is to push the operating point of your buck mode (typically) power supply operating point up and down a little bit--and see the results.

Take care and have fun Entuty!
-Bill

entuty

Re: Maximum Power Point Tracking

@BB:
Ok. Now I understand. I'm sorry! I will learn from my mistake.

icarus

Re: Maximum Power Point Tracking

Bill,,,

There are a thousand ways I am offended by your previous post!

Where to start,,,, I guess given the nature of the previous I'll just let it go eh!

Tony

(Tongue planted firmly in cheek,,,lol)

lorelec

Re: Maximum Power Point Tracking

I have to agree with Tony, that the "dumbing down" of language is regrettable. Of course, the "true" English language was corrupted long ago, according to the British. I think we are once again stuck in a period of transition. Those who were raised and educated without the assistance of computers, cell phones, and other gadgets were taught that a well-educated person uses proper grammar and syntax. And although the attitude probably isn't always justified, I think that the way a person writes can say a lot about them. Becoming accustomed to a shorthand version of English and constantly relying on things like spell checkers can also lead to trouble down the road when a person is expected to use proper grammar. I'm sure that linguistics will someday soon embrace "4U" and "ur" -- so we should probably just grin and bear it. I don't think we can be too critical of people who learn English as a second language, though. The structure of a foreign language is hard enough to grasp. Learning how the language is traditionally used is even more difficult. If anything, Entuty's use of these shorthand words shows just how deeply they have already become entrenched in our language. Someone who learns English through popular culture and media will no doubt pick them up and use them.

Marc

entuty

Re: Maximum Power Point Tracking

I'm sorry! I joint in this forum to improve my knowledge of solar cell and English. But I don't know much about your culture. So it caused my mistake. I swear it'll be never repeated.

niel

Re: Maximum Power Point Tracking

guys,
how well we use the english language is irrelevant here as none of us are professors of the language and all of us have made mistakes in it. the point is he is from another country, with english not being the prime language there, and he is doing his best to understand and to be understood about the subject of mppt. complaints about shorthanding the language are noted and should be put to rest unless you do not understand what is being said or asked. try to help him on the subject matter he asked about.

BB.

Re: Maximum Power Point Tracking

Entuty,

We all learn from our mistakes--probably more than we learn from our successes. No need to be sorry at all.

Regarding MPPT... You will need to pick what parameters you will be using for the the MPPT function...

My initial guesses:

1. Hold Vmp steady by adjusting input current. Vmp is, mostly affected by solar panel temperature (once there is a minimum useful amount of sunlight). So, Vmp will probably have a time constant of minutes (amount of sun, wind, etc.).

2. Imp will, more or less, be porportional to the amount of sunlight at any particular point in time. So--your processor will simply be changing the current / PWM duty cycle to "hold" Vmp.

3. Every so often, you will perturbe the current setting to check that Vmp is correct (Pmp is a maximum).

4. Then there is the whole output stage of your charger--Once the battery has been "bulk charged" (roughly to 80-90% of its capacity), you will be controlling the PWM duty cycle to reduce the output current/voltage (depending which charging stage you are in--absorb or float, etc.).

5. Suggest that the power for the Switcher from the solar panels--you don't want to waste valuable battery power to power the switching power supply if there is not enough power from the solar panels to even run the switcher in the first place (dawn, dusk, cloudy/dark weather).

-Bill

Solar Guppy

Re: Maximum Power Point Tracking

Here is a thesis written by Hannes Knopf in 1999 ... its what I used as the inital understanding of what Mppt is and the characterization of solar panels and power harvest ( It's referenced in my patents )

Mppt Thesis Hannes Knopf 1999

niel

Re: Maximum Power Point Tracking

is there another link to that pdf as this is hanging up on me after roughly 300kb+?

icarus

Re: Maximum Power Point Tracking

Mods,

How 'bout you either remove my offending posts and the replies or maybe move them to their own thread. I don't know if it is a relevant discussion,, but it certainly has the capacity to confuse those who are asking technical quesions.

Tony

Sorry for starting the fire!

Solar Guppy

Re: Maximum Power Point Tracking

niel wrote: »

is there another link to that pdf as this is hanging up on me after roughly 300kb+?

Try right clicking on the link and do a save as ... I couldn't find any places on the net for it so I uploaded to my site for downloads

I've noticed browsers and pdf's can do all sorts of odd things

niel

Re: Maximum Power Point Tracking

sg,
that got it successfully. thanks.

tony,
you can delete any of your own posts should you wish to.

lorelec

Re: Maximum Power Point Tracking

Entuty,

You didn't do anything wrong, and have nothing to be sorry about. I don't think the comments about language were aimed directly at you, but just were just opinions that obviously have been simmering for a while .

If you need help on any MPPT specifics, just let us know. We'll be happy to help the best we can.

Marc

entuty

Re: Maximum Power Point Tracking

@Solar Guppy:
Your post is very helpful to me. It's really what I need. Thanks you so much.

RCinFLA

Re: Maximum Power Point Tracking

In very simplified terms, a MPPT controller is a buck switcher that takes the product of voltage and current to make the feedback adjustment on the buck switcher.

Your PC uses a buck switcher power supply that only uses the output dc voltage as feedback adjustment on the switcher.

Start by understanding how a buck switcher works. Most buck switcher I.C controllers on the market also have a current limiter feedback input. These are normally used to prevent damage to the buck switcher power supply from overload but with a little creativity can be used to create a MPPT controller. You will need an analog multiplier circuit to create the product of Iout * Vout.

lorelec

Re: Maximum Power Point Tracking

MPPT-based controllers can be of pretty much any topology, not just buck. Buck is among the most efficient, and doesn't have the duty cycle limitations that a topology like boost has. It also tends to be appropriate for the application -- taking a higher voltage from the array and converting it to a lower voltage for the batteries.

PC power supplies are off-line supplies, so they must have some form of isolation. For this reason, you won't see them using a non-isolated topology. They're usually flyback or some type of forward converter, using a transformer for the required isolation. These types of supplies, besides being more difficult to design, also tend to be less efficient.

It's possible to design an MPPT controller using only analog circuitry. Analog Devices makes a simple-to-use multiplier IC (the AD633, I think) that can calculate your power if fed divided-down representations of voltage and current. You would need to differentiate the result (adding a slight change in phase angle), and compare it with a true-time measurement to determine if you were above or below the MPP, and adjust the duty cycle accordingly.

Marc

_OS_

Re: Maximum Power Point Tracking

Here is a link to an article in Electronic Design:
http://electronicdesign.com/Articles/Print.cfm?AD=1&ArticleID=6262