Hi Ian,

Please supply us the flow chart for more info.

Here is the flow chart algorithm.

Sorry if it was not clear, here I have reattached the flowchart.

Thanks again
Regards
Ian

Hi David

I tried to solve that problem. Can you please take a look at this program now.

Thanks
Ian

Hi Ian,

I don't think you are going about this the right way,

I had A long play with your code and could not get it to function correctly.

I think the best way of doing this would be to step through the program with A counter and an equals to op on each line,
so the program reads the input makes A change and rereads the input to see if it is better or worse, then if worse change the other way the the same amout and check. If both ways are worse then the setting was correct so leave it there or adjust in the direction that makes it better.

One other question is why do you move zero to duity when the
value is above 90 why not let it go to 100% but no more.

Hi Jaun,

Can you give me an aid in this because I cannot figure out how to make it work properly.

Thanks

Ian

Hi Ian,
The way I see it a MPPT is no more than a buck converter. Lets say you have a 17V 5A solar array with a power output of 85W at full sunlight. You have a 12V battery that has to charge via a charging circuit capable of giving the maximum power to the battery. E.g. a flat battery of 10.5V charging at the max current the solar panel can deliver, yields 10.5V * 5A = 52.5W that's 85W - 52.5W = 32.5W wasted power. Since you cant change the charging current to the battery directly you will have to bring the solar voltage down to increase the charging current to the battery. Your charging voltage should however be at least 1V above the battery voltage to allow maximum current flow. Thus to charge a 12V battery from flat(10.5V) to full(13.5V) is 11.5V to 14.5V. This is your allowable voltage span to play around with to obtain maximum power transfer to the battery. A flat battery will draw maximum amount of current (in limits). Thus increasing the charging voltage decreases the current(in limits). The power obtained from the V and I will govern the duty cycle. Obviously as your battery charges to its rated voltage the current will decrease accordingly until you can no longer adjust to get the maximum power. The battery has fully charged when there is little or no more current draw from the circuit. The pic has a set point for the minimum current draw an will shutdown if this value is reached.

Which brings me to my point in the beginning that a MPPT charger is very much like a buck converter.
I have attached a pdf that the describes different ways of controlling the power.

HI MGP,

Firstly thanks a lot for your help. Regarding the modified MPPT. This program will keep on incrementing the PWM output as as soon as the value from the adc is increased and similarly when it is reduced will keep decreasing to zero.

If a certain voltage and current are settled the duty cycle will keep increasing or decreasing.

Thanks again
Ian

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Hi Juan,

Regrading the techniques used for MPPT I have already looked at various methods.In my circuit the aim of the MPPT is not depending on battery charging only, but supplying other converters. Thus my aim is to keep the voltage across the PV terminal to 15 Volts since during my test I found that my panels are at there MPPT at approx 15Volts were the open circuit voltage is 20 Volts.

So in my circuit the circuit will be working as a Buck instead of boost

Thanks
Ian

Ian

Sorry of not being clear in my describtion. In my project I am going to use approximately 9 panels and the connection will be groups of 3 in series and than in parallel with each other. This will result in an output voltage of 60 Volts O/C so it is not possible to use such above voltage regulators. Now to track for maximum power the output must be controlled to 45V (ie: 15 Volts across each panel).

Regarding the MPPT I was trying to use the Perturb and observe algorithm.The program you have send me the (better version for MPPT) is that following the latter algorithm?

Thanks

Yes you are right. But that program as soon as the current or voltage increase it will keep increasing till the saturation value of 99 and this will not find a steady value of duty cycle to get the MPPT. I am right ? This will work if the adc values will keep oscillating i am not sure but in the real situation I think that the values will keep oscillation about some value. I am going to put it on the PIC and make some test with your program.

Thanks
Ian

OK np MGP, Thanks for your help.Is it possible to show the values of current and voltage and power on a display and how you can show the decimal point?