how to design MPPT solar charge controller

[Mithun_K_Das]

I want to know how to design MPPT solar charge controller. Can anyone help for this case?

 

[vimalkhanna]

Kindly read "Microchip AN1211" aplications note for deign of Solar MPPT design ...

 

[ea.arun]

there are many ways to design solar charge controllers.....like you can use specific chips such as national's SM72441 and a charger IC or MPT612 from NXP......or as mentioned in the previous post by vimal you can use micrcontrollers write algorithms for the same purpose.....here are some product docs which might help you.....
**broken link removed**
http://ics.nxp.com/support/documents/pdf/an10936.pdf

 

[vimalkhanna]

Thanks .I shall go thru the complete assembly and then revert/confirm back with my results on the effectiveness of the sun tracking stabilization facility.

 

[Mithun_K_Das]

nice links. Thanks for help. I want to design based on MCU. so I need to know the theme of the system first. Then the process will be easy for me.

---------- Post added at 18:38 ---------- Previous post was at 18:31 ----------

But I need some practical working theme of the system.

 

[vimalkhanna]

Fine step for a system based on MCU..You may like to go for PIC16 F697 against which the system design is based .
The software can be sent seperately.

 

[nicolethomson]

Mr. Vimal Khanna, can i have the software too?

 

[Tahmid]

Fine step for a system based on MCU..You may like to go for PIC16 F697 against which the system design is based .
The software can be sent seperately if you send me your email ID. on vimkha@email.com

From this, I assume that you have done the coding for such a project.
May I know how you determined the maximum power point. What method did you use?
Did you use the "hill climbing" method? At what frequency did you do this? What was the efficiency of the converter? Did you compare against a commercial MPPT charge controller? If yes, what were the results?

 

[Mithun_K_Das]

Yes, I also want to know as Tahmid. Please tell us

 

[enjunear]

Having worked on a team that developed and raced solar powered electric vehicles, lets just say that you can spend a LOT of time tweaking on your own MPPT before it comes close to a commercial unit. The biggest problem is reducing your switching losses. If you want to build one for your own self-esteem, it's a great challenge to undertake. If you want one for highest efficiency and/or power handling, just purchase one. That was what the majority of the race teams determined by 2002 (lots of senior BS.EE and MS.EE students did research projects to make/refine MPPTs... great learning opportunity, but LOTS of time was spent and most didn't beat the mid-grade systems on the market).

 

[Tahmid]

Do you know how the commercial units determine maximum power point? What helps improve their switching losses so much as compared to self-made units? Is it the method of driving the MOSFET and related magnetics and selected frequency?

 

[enjunear]

Do you know how the commercial units determine maximum power point? What helps improve their switching losses so much as compared to self-made units? Is it the method of driving the MOSFET and related magnetics and selected frequency?

The commonly used methods (for the entire body of work that I reviewed) were fixed-step incremental and variable-step incremental conductance, and 3-point perturb and observe. Here's a paper that talks about the three methods. I haven't read it in-depth for content, but a cursory review shows that it covers the main points (as much as I remember, having not done solar stuff in about a decade).

I don't recall which method was the favorite in the commercial world. IIRC, it had more to do with complexity of implementation and resources as far as which vendor used a particular method. Everyone touted their own design/implementation as the best, but comprehensive comparisons of all three flavors were rare to find and difficult to compare objectively. There may be better analyses out there, I just haven't had need to do a literature review on that topic lately.

 

[vimalkhanna]

Easiest is the comparision method followed .
The MPPT designed for self was put on the battery along with a commercial unit starting day at 8.00am and ending 6.00pm.
The currents of both units was monitored for independent battery chargers using a clamp or shunt resistance method with 1mA meter.
The 1hr gap //six reading s prove the peak hill ascending/decending slopes .

 

[Mithun_K_Das]

It is really a complex design for MPPT I think. But how it work when the panel voltage is less than 12V? As I see, most of the controllers use just a buck converter. Then how it can work when the panel voltage is too low? Should we use buck-boost converter at a time?

 

[enjunear]

It is really a complex design for MPPT I think. But how it work when the panel voltage is less than 12V? As I see, most of the controllers use just a buck converter. Then how it can work when the panel voltage is too low? Should we use buck-boost converter at a time?

What you do when the panel voltage reaches 12V is up to you, mostly based on your overall system topology.

Case 1: You have an array/panel that nominally puts out 100V. When it drops down to 12V or less, it's probably very overcast or close to sunset... so you might stick with a more efficient buck-only MPPT and live with not collecting power when the voltage falls below your Vin,min (which would be infrequent).

Case 2: You use an array/panel that is nominally 24V. With that configuration, you'd potentially operate at 12V (or below) more often. In this case, you might increase the complexity and lower the MPPT efficiency (a little) and use a buck/boost topology so you can collect power during the more frequent low-voltage times.

 

[Mithun_K_Das]

In my country as I see, user just use one 12V array which give around 16~20V depending on sunlight. So, if I want to make the controller efficient I have to use both buck-boost converter. But the problem is what should be the output voltage of the converter so that battery get charge at the maximum rate? How can I determine that point. Also for the solar panel, how can I determine the maximum point? For buck-boost should I use Flyback topology ? which is efficient?

 

[vimalkhanna]

For 12VDC supply 16-20VDC is emf of the panels .However , placing a 9--24VDC input window of the buck boost converter sorts out this problem.The general output needs to be 16.3V across which battery charge is accumulated ..Efficiency of converters operating at 350KHz is about 93% + .When the sunset ,cloudy period occurs this voltage falls to 9VDC and near cutoff.At this time the source impedance goes high and has low charging rates .It is inefficient to get charging done now .....better to forget this short period .However , if you want to cater to this also ,,use a 5-12VDC input converter and boost this to 16VDC ....15 mins of extra charge can be got thru this too.

- - - Updated - - -

 

[Mithun_K_Das]

What I really planning to use a Flyback converter of 1:1 ratio. varying the duty cycle only output voltage can be controlled. So if x is the term which is related for current control, and I1 is the first step charging current and I2 is the second step charging current, then the program should be:

   initialize I2 = 0;
   Read I1;
   
   if(I2<I1)
   {
    x++;
    I1=I2;
    }
   else
    {
     x--;
     I1=I2;
     }

 

[Mithun_K_Das]

I got a file here for non-inverting buck-boost converter; I designed as they suggest. https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0CGAQFjAA&url=http%3A%2F%2Fwww.herjulf.se%2Fdownload%2Fbuck-boot-application-note.pdf&ei=tkjST9mYKpDOrQedmJH9Dw&usg=AFQjCNEB5XCZKvNrB64ltj0_LDtLsGlDzQ&sig2=6uGhLr4b7HQr8OId1IxKGg

I kept the operating frequency at 32KHz. Only varying the duty cycle. Here is my PCB: but cannot control the output voltage as they say. It work as they say but after few mins no load current start rising and rising, smoke comes on from the FETs(P55). I'm using L= 15T/18SWG & C=1000uF/63V. Can you say what is the problem? Output voltage is stable, but current varies a lot without any load.

 

[enjunear]

If the FETs are smoking, then they are dissipating a lot of power. Have you checked to see if the FETs are both trying to conduct at the same time? (a crossover timing issue)

BTW, once smoke starts coming out of the FETs, its probably time to replace them. Depending on the failure mode, they may not operate anywhere close to "normal" once they've been overstressed to the point of melting the plastic package.