In my SPV system I am connecting a MPPT system to extract maximum power from the SPV system by changing the duty cycle of the buck converter. I think the model is working properly with 3 ohm (load) resistance, but whenever the resistance changes (say, 30 ohm) the power drown by the resistance (load) reduces. Can you suggest me the possible error of my model?
First find the maximum resistance offered by solar PV cell/panel under low illumination & find minimum resistance offered by PV panel at full illumination. Or select the load value equal to the Voc/Isc of the panel.
It will work propery. As the attached file is in matlab advanced version, i could not open. I have matlab 2010a
Maximum power drawn by a load resistance R is V2/4R where V is the source voltage . As you have increased the load resistance from 3 to 30 ohms, maximum power drawn by it reduces if V remains same. Check whether your converter is tracking voltage corresponding to maximum power.
the role of the buck converter is to match the load resistance to the resistance offered by the solar PV cell/panel. when you increase the load the converter is not able to track the MPPT. i need a simulink file to look at :) i have many work in the subject you can download from my page. Also message me for any help needed thanks ayman
MPPTs are not magic! In practice they will work over a comparatively limited range of impedances. Let me explain. Buck converters work by allowing the generator to drive a load of lower impedance - but there is a limit. As the impedance of the load reduces, the currents in the convertor circuits increase, by a large amount. As you know, the power lost in a circuit varies as the square of the current, so reducing the impedance by ten times increases the current by ten times and the MPPT power loss by 100 times. At this point it is probably absorbing more energy than the PV system is generating. A boost convertor enables a generator to drive a higher impedance load than the generator, with the same limitations. As the impedance ratio increases, the power lost in the MPPT increases very rapidly, and the MPPT ceases to be effective.
In your case, you have a buck convertor, and this will drive loads of lower impedance than the PV system. Clearly a 30 ohm load is too much for it! To match a 30 ohm load it looks like you need to convert the PV voltage up, not down, and a buck convertor won't do that. If you want to drive loads of arbitrary impedance then use some sort of buck-boost convertor; but remember, the range of impedances they work over is not that large. 10:1 is a realistic figure for a real world convertor.
If you have to drive a 30 ohm load, reconfigure your PV system so that it can drive a 40 ohm load without the MPPT, then add the MPPT. If you want it to drive both a 30 ohm load AND a 3 ohm load, then accept that the reduced efficiency you get at either extreme may mean the MPPT simply isn't doing very much.
Good luck with your research!
- Badges
- Science topic