PV I-V CHARACTERISTIC TESTER
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Measuring the IV characteristics is of high importance since it can be considered as a quality and performance certificate for each PV generator. The most precise and inexpensive measuring method is represented in capacitor charging by the PV generator. Using the equivalent circuit of the PV generator with a capacitor as load and applying transient analysis on the circuit, we obtain the capacitor charging voltage and current as a function of time, as well as their differentials as a function of short circuit current and capacitor size. The figure below is the Electronic circuit of the project The power electronic circuit of this device consists of capacitors, resistors, special resistors and switches as shown in the figure below the capacitors is chosen up to measure a cell have a rated 22 open circuit voltage and 3.5 short-circuit current and from equation in chapter 3 we use 14 mF capacitors bank consist of 5 capacitors The switches here can be relays or transistors of ordinary switches (pushbutton)RL is 10 K and that to protect the capacitors from the reverse current Rshunt is an special resistor its convert the current which follow in it to mV in constant ratioThe sequence of measuring:Before of all we must close switch 3 to rest the capacitors form any charge they may contain then we open switch 3 and close switch 1 to start the charging of capacitors in time constant determined by the capacitors and during this operation we measure the open circuit voltage after we reduce it by constant factor using potentiometer by the inputs leg of the pic to the ADC then in 8 bit though the parallel port to the software.When the capacitor become fully charged we short the cell using switch 2 to measure the short circuit current using Rshunt which convert the amperes in mile volts to transfer it through the PIC and parallel port as the voltage transferred.Also we need form this circuit the radiation and the temperature of the cell and the ambient.To measure the temperatures we use a sensor (LM355) and cable to enter the data to the software directly as the following equation:Tamb=25V/ 2.982To measure the radiation we make an equivalent sensor consists of thin film cell with an adapter consists of two terminals and a resistor 100 1 wattWe test this cell by comparing its reading in volts to the reading of solar meter and we find that the relation is liner in this equation:G= 227.6V- 69.62After all the inputs received to the Computer the C# program will do all the calculations fill factor , efficiency, Vmpp, Impp, Isc, Voc, Pmax, Radiation, Tamb and Tcell.