PV educator

Solar PV cells are the smallest unit in a PV panel. These are low power output units and hence in order to produce a reasonable output from them, several cells are connected in series and parallel configurations. In a series and parallel configuration, we use to add a bypass diode that prevents the sinking of a group of cells in case of shading. This blocking diode is always connected across a group of cells because of two reasons. First, no ideal diode exists which means that diodes need to overcome a potential difference to work. Secondly, in a single cell, it is very difficult to forward bias the diode because of very low output voltage levels. 

Figure 1 : Schematic. PV module consists of 5 X 2 cells

Figure 2: Under uniform irradiance condition

Figure 3 : Partial shading on three cells of module 1.

Figure 4. Code for PSPICE

In PSPICE plotting is not based on programming like that in MATLAB. In fact, the plotting is based on the set of variables that can be selected for x and y axis. The problem, however, is that if you want to plot two curves with different ranges of x axis variables.  I spent quite a time on solving this issue. Although I did not reach where I wanted to land, however, i found one solution but first, let me introduce you to the circuit i wanted to simulate.
The figure above shows two PV cells connected in series with each other. The combined output is taken from the node 3 and 5. I want to draw the I-V curves of both the cells as well as their combined output. However, in order to do so if I select the x axis as the voltage V3 the I-V curve for the individual cells is compromised and if I select the x axis as V3-V1 then the I-V curve of combined cells is compromised. To solve this I selected two plots and unsynchronized their x axis as shown in the figure below. To unsyncronize the x axis click on plot > unsynchronize x axis.


The next challenge is to plot them on one plot. 

PSPICE probe window works with a black background as a default colour and it does not allow the user to choose the background colour. However, in order to change these colours, one has to edit the file name "PSPICEEV". This file is not located in PSPICE folder rather it is located in the windows folder. So here is how you can change the background colour in PSPICE probe window.

1. Search for PSPICEEV.ini file in windows folder. [Save a backup]
2. Right click on it and open it in PSPICE. [I tried editing it in notepad but saving it gave me errors.
3. Search for background and foreground and swap their values. (Black to white and white to black]
4. Save the file. 
5. Run the simulation

Shunt and series resistance are important to model a realistic PV module. These resistances demonstrate the non-idealities in a PV module. The series resistance Rs defines the resistance of the material that collects the charge from the PV module. This resistance is small and ideal value is zero. The shunt resistance Rsh defines the defects in the semiconductor and the electron-hole recombination before it reaches the output. The value of this resistance is very high and ideally, it is infinity.
On a current-voltage curve, the shunt resistance lies on a slope near Isc and series resistance on the slope near Voc. To elaborate this further, consider that the series resistance is zero and therefore, the voltage V=Vsh.

Finalterm Spring2017 Solution