I have measured the I-V curve of a solar module and I got the following curves
Why the I-V is at this form?
What are the possibilities of being at this form?
is this curve for a practical experimental test.or based on a mathematical model. it it is for a practical module how did you vary the load on the module.
It is a practical experimental
The load is varied by putting a 1ohm resistor and using a PWM with different duty ratios
as I usually measure the IV curve, I start without any load (R=0) to start the curve at short circuit point then vary the rheostat till open circuit voltage.
there is another why using a capacitor.
may be you should start with 0ohm ? and what is the increment of Duty ratio?
If you upload the circuit diagram of your system may be I can help more
What circuit do You use for filtring PWM?
There are pulses of current (0-Isc) and voltage (Voc-0) present.
May be this I(V)-curve is time response on varying Duty-ratio
I am using BUCK converter ( inductors + capacitor + mosfets ) with 1 ohm load
And I change the duty cycle of the PWM from 0 to 100%
You need to calculete frequencie dependence for Your LCR circuit. I guess there are resonance for some garmonics of Your PWM.
What PWM do You use ? Step-Up, Step-Down or SEPIC? I gues Step-Down is not suitable for this task.
And were are voltage and current detectors located?
Draw whole schematic and mark R, L, C pars.
The frequecy of the PWM is 31KHz
I am using synchronous buck converter with 0.1uH inductor and 4700UF capacitor
with 1ohm resistor
The required current is 6 AMP and 25 volt
Here is my interpretation of Your mesurement shematic with my Solar Battery model. I gues You control V(bat) and I(Ri) on Solar Battery side. This PWM converter model is without any Feedback control. I use 100uF instead 4700uF to decrease evaluation time. Any surprise are absent.
The most interesting thing here is the current of PV module is reducing with its voltage.
The possible causes could be:
1. measurement method, that means the measurement is not accurate. The PV curve looks ok. So most likely, there is some errors in measurement.
2. Temperature, for a given PV system and operation voltage, the higher temperature, the higher current can be generated
3. solar flux, is the sunshine or some kind of simulator constant?
Another thing to note is you cannot get the short circuit current using your existing setup.
Basically, what the converter do is converting the load resistance R in to R/D^2 like a transformer, D is the duty ratio. For example, when D=0.8, the equivaleltagent resistance saw by your PV module is 1/0.8^2= 1.5ohms. As a results, the PV module will operate at 4.4V, 3A (roughly).
Hence, by adjusting D, you can have the resistant range (1, infinite). Note the equivalent resistance cannot be smaller than 1, that is why you cannot get the short circuit current in your attached curve.
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