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so I'm currently working on an MPPT project using Asynchronous Buck Converter with the design :

Capacitor Input : 470uF/100V Capacitor Output : 1000uF/100V Inductor : 65uH fsw : 39khz current : 30A

My solar panel specification:

Voc : 22,11V Isc : 2,97A Vmp : 18V Imp : 2,78A

I'm using 3 solar panels and connect them in parallel to because my battery is 12V VRLA 20Ah, I have 2 and connecting them in parallel, too.

According to the theory of PV Characteristics, Solar Panels only giving a maximum power at 18V.

PV Curve

Then, I measured the irradiance of sun using solar power meter, the result is around 850-950 W/m2 which is good

SPM

But my solar panels won't produce high current and high voltage to near VMP. The voltage is always drop and the current will never be produced as expected from the specification.

So, whenever my mppt algorithm increase the PWM, the voltage will decrease but the current increases. What I know according to the PV curve, the voltage will remain the same or also increase with pwm & current increase (This situation happen when we are on Left Of MPP Curve).

I Can't get that Vmp 18V with high current, the voltage is always drop when mppt increasing PWM.

Take a look at my arduino serial monitor here,
VI: Voltage Input, VO: Voltage output, CI: Current Input, CO: Current Output From VOC 21V, drop to 17.8V then ended up to 14V

SolaFirstIteration End

Last night, my relay didn't cut off the connection between my buck converter and solar panel, so it was like current flow from battery to the solar panels. From my previous testing, the solar panels was giving a nice vmp around 17-18V whenever the mppt algorithm increase the pwm to achieve the maximum of current can be drawn to achieve the MPP. But now, the vmp is too low when mppt increase the pwm and never get that mpp again. 

But I don't see any burn side on my solar panels. 

Also i have checked the voc was 21V at that time, and isc was 4.9A. But on my buck converter, i only can drawn 3.8 A at maximum 97% of my duty cycle and the voltage only around 14.3-15V. Why is this happend? The current is to far from the isc and never reach the vmp 18v...

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  • \$\begingroup\$ Adding an actual question is highly desirable. Any ideas you may have on why may help. \$\endgroup\$
    – Russell McMahon ♦
    Commented Apr 21 at 2:22
  • \$\begingroup\$ How is the MPPT implemented / controlled? Why does it work on your panel? \$\endgroup\$
    – Russell McMahon ♦
    Commented Apr 21 at 2:24
  • \$\begingroup\$ I Can't get that Vmp 18V with high current, the voltage is always drop when mppt increasing PWM \$\endgroup\$
    – tabun
    Commented Apr 21 at 2:42
  • \$\begingroup\$ @tabun Obviously the voltage of the panel is going to drop when you increase the duty cycle of the PWM - your drawing more current from the panel and that is how buck converters work. For a fixed output voltage, the output current will keep increasing with increasing PWM, until it starts to fall. That's the MPP. \$\endgroup\$
    – MOSFET
    Commented Apr 21 at 3:11
  • \$\begingroup\$ Sorry I forget to mention that last night, my relay didn't cut off the connection between my buck converter and solar panel, so it was like current flow from battery to the solar panels. From my previous testing, the solar panels was giving a nice vmp around 17-18V whenever the mppt algorithm increase the pwm to achieve the maximum of current can be drawn to achieve the MPP. But now, the vmp is too low when mppt increase the pwm and never get that mpp again. \$\endgroup\$
    – tabun
    Commented Apr 21 at 3:48

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