im trying to built a supply for a load of 8-10V, using solar cells (the total output of solar cells is 3.2V). in general, i need to built a boost converter and MPPT.

Hi emerson

i did a project a while ago, it was a boost maximum power point tracker to charge 12 volt batteries from 6 volt solar panels.
i will look for the schematic and the code and post them up so you can use. it will be similar to your project.

it used a Microchip Picaxe 8m for the tracking and regulation. It was coded in BASIC.

Ill post it up shortly, the schematic was drawn in switchercad III/LTSpice.

Your system should have a configuration similar to this. You will need to create the software to regulate the input voltage at 3.2 volt and not let the output exceed 12 volts.

For the MCU, you could use an Atmel attiny13 or a microchip picaxe8. They are both happy with 3volts.

Hi tony,

tanx again 4ur help.

can i order directly the picaxe8 starter pack? hope it does have everything in the pack.

want to use an LP2950 as voltage regulator.

can u plz help me with te code, plzz because i am really clueless.

abt the PWM, i think the frequency of the signal should be high enough (ard 75-100KHz) to be able to boost the voltage to 12v !!!
hw abt the regulation of the input voltage at 3.2V???

im asking hw are we going to always get the Maximum power point, hw are we going to know that we are at the max current and max voltage?

for the output voltage, we cant exceed 12V, bt is it gonna be possible to use a load of 8,9, 10 V for eg.?

tanx again 4ur help, looking fwd to hear from u.

emerson

can i order directly the picaxe8 starter pack? hope it does have everything in the pack.

Yes the Picaxe 8 starter pack is great and has everything to get you started.

want to use an LP2950 as voltage regulator.

Yes that would work perfectly.

can u plz help me with te code, plzz because i am really clueless.

The code is in BASIC, and is very easy to learn, ill post up a code example of a project my friend did. You code would be very similar to this.

abt the PWM, i think the frequency of the signal should be high enough (ard 75-100KHz) to be able to boost the voltage to 12v !!!

Yes the picaxe can run at 8MHz and will easily produce a PWM with high enough frequency. It can produce a PWM signal 8bit resolution at 31.382KHz.

hw abt the regulation of the input voltage at 3.2V???

A typical solar cell has a Voc of 0.55 volts and a maximum power point of 0.35-0.45 volts. by regulating the output of each cell to 0.4 volts, that is 0.4 x 8 = 3.2volts, we can have sufficient regulation at the MPP. This provides us with voltage regulation on the MPP rather than POWER regulation, Although this method is not as efficient, it will still be sufficient for this project.

im asking hw are we going to always get the Maximum power point, hw are we going to know that we are at the max current and max voltage?

We know we are at, or near, the MPP because we are regulating the input voltage at 0.4 volts which in theory is very close to the actual MPP. If you want to find the 'true' MPP, you will need to measure the current coming out of the solar cell as well as the voltage. This is much more complicated, and only provides about 5-10% more tracking efficiency because with heat, and insolation changes, the actual MPP doesn't fluctuate to far. A 5-10% increasing in tracking efficieny will only probably provide 1-2% more power, so its probably better to first start of with voltage regulation around the MPP rather than power regulation.

for the output voltage, we cant exceed 12V, bt is it gonna be possible to use a load of 8,9, 10 V for eg.?

You output voltage can be regulated to not exceed 12V by decreasing the duty cycle on the PWM. However, the actual output voltage will depend on the load resistance and total power of the solar array. The output voltage can be found buy the P=(V^2)/R relationship. Basically, the more current your load draws (the lower its internal resistance), then the more your output voltage drops.

Thanks.

hi tony,

can u plz help to draw an algorithm diagram of the program, ?? i am a bit confuse

tanx.

ok ill do this tonight. Ill upload it soon .

Tanx. If ican have it 2day hummm.. . ....it wil save mylife.nway tanx n lookin fwd 2hear 4m u.would like 2 ask wat parameter do u think itcan influence da system durin da test n evaluation process. Tanx again 4ur help n lookin fwd 2hear 4m u. ...... .......2day(crossin my fingers ...lol)

hi tony the characteristic of da cell is 0.5v/4w,meanin da current is 8A .i design for the boost an inductor of 4.5 mh,use a IRF7201 as transistor,a 1N5817 for a diode,a cap of 68uf.wat do u think abt it? Do u think ht can work? Dat curent of 8A, is it gona ok for the micro controllor? Plz let me knw. Waitin 4ur reply.Tanx.

Your program will go like this:



This will hold your input at the maximum power point, ie, 3.2volts, and also, not let you output exceed 12volts.
If there is no load on the output the intput voltage will rise to Voc (open circuit).

For your component values, they will depend on your PWM frequency as well. What is the PWM frequency you are going to use?

I think using a PWM frequency of 20-40KHz would be a good value because you want small components to minimize the size the size of the circuit. Also switching losses at this frequency wont be too bad.

hi tony

i think the higher the frequency is, the more current ur inductor delivers, the more voltage you can get at the output. so i remember i did a boost converter before, and just to get 5V output i used a frequency of 25KHZ and also the transistor that i used could delivered 1A. so my concern is also the output current of the cell which is between 4-8A, im a bit confused.

tanx solar one for ur reply

tanx

emerson

The higher your duty cycle, the more current you will pull from your solar panel thus causing a voltage drop.
You need to make sure that when you increase they duty cycle, the input voltage wont fall below 3.2volts.
If the input voltage begins to drop below 3.2volts you need to decrease the duty cycle.

Remember, the higher the duty cycle, the larger the load, thus causing a larger voltage drop on the solar panel.

When you have more sunlight, your panel will be able to produce more current, therefore you will be able to increase the duty further, thus resulting in a higher voltage, or current, on the output. Your output voltage will fluctuate with load conditions.

hey tony,

still alive, learning the basic programming. i think i will need help man, however i wil try to write something for this weekend and will show you. tanx man.

hey man, programming is killin me, plzzzz help me out. someone is dying.

tanx already 4ur help

hey tony
to get used to the microcontroller picaxe 08M, i decided to firstly implement the TEST program which is given in "getting started document", i connected the USB cable in one of hte usb port of my PC, but when i run it, it just says " error hardware not found on COM3 ", i dt know. i even followed the instruction to change the port, but nothing,

pls help urgent

im stressing like crazy coz i need my project to get going , and the basic code is driving me crazy

plzzzzzzz help

PS : i attached the error message to the mail, plz help me guys, dt know wats wrong.

tanx

Hi,
are you using a USB or a serial port?

Hey tony,

im using a USB cable AXE027U.

I would like also to know how to set up the pwm at a certain frequency! i have also a concern . my cell output is 0.55V, using 8 cells i will have an input voltage of 4.5V. we are using a 3V voltage regulator to supply the micro controller chip.i bought the starter pack , and they say we should supply the chiop with a 3 AA batteries of 1.5V each, which is 4.5V. so do we still need a 3V voltage regulator??

tanx.

hi tony

im dying, im so clueless in programing, plz help me with the code, plzz man.

still havent solved that problem of "picaxe test", still not working. it stressed me a lot.

plzz help me man,

really need ur help.