# Investigation of Failures during Commissioning and Operation in Photovoltaic Power Systems
## 4 Discussion  
In this study, electrical faults in photovoltaic power plants are classified, these faults are modeled in the MATLAB Simulink program, and the measurement data are examined on graphics. Although the content of the studies examined from the literature research part of this study to the completion of this study is wide-ranging, some studies are directly related to the computer-based simulation of electrical faults in photovoltaic power plants. Not all studies have examined electrical faults in general terms similar to this study. While in some studies, only one fault is simulated [28; 29; 30], in other studies, more than one fault is simulated [31; 32; 33]. Furthermore, in other studies, no fault simulation output is produced, but the effects of the malfunction are mentioned [5; 34]. In the Simulink model that was created, a phase-to-phase short-circuit fault on the AC side was modeled and the results were observed. In this case, it was observed that when a three-phase short-circuit fault occurs, the AC voltage goes towards zero, but the current value increases excessively, and the waveform is distorted. When the Simulink model created in this study was compared with other studies in the literature, similar results were obtained in the graphics, although the current and voltage values were different because the power plants used in the models had different power values [28; 35; 36]. In the MATLAB Simulink model, it was observed that in open-circuit faults occurring at the inverter and grid output on the AC side, the current decreased to zero and the voltage amplitude and waveform were slightly distorted. When looking at previous studies, it can be seen that the results obtained are similar [8; 37]. In the case of an open-circuit fault on the DC side, it was observed that the DC current decreased to zero, the DC voltage decreased but approached its nominal level in time, and on the AC side, the AC current approached zero and the AC voltage was not affected by the fault. In the previous studies, graphical outputs close to the graphics in this study were obtained [32; 37; 38; 39]. In the photovoltaic power plant model, it was observed that a line-to-ground short-circuit fault on the DC side causes large fluctuations in DC current and voltage. On the AC side, it was observed that the main voltage was not affected, but the current was affected by the fault condition. In contrast to these graphical outputs, in some studies in the literature, measurements were stopped when the short circuit started because the simulation was carried out as if the system protection elements were activated and the circuit was opened after the short circuit fault [4; 38]. In some studies, similar graphs were produced by not interrupting the circuit and continuing the fault condition, as in this study [37; 40]. In the graphs obtained by creating a line-to-line short-circuit fault on the DC side, it is seen that the line-to-line short-circuit fault on the DC side leads the current and voltage to zero. In the graphs created with measurements taken from the AC side, it is seen that a line-to-line short circuit occurring on the DC side does not directly affect the transformer output voltage but does affect the transformer output current [37]. In the model, to create photovoltaic module failure, a line-to-line short-circuit fault is created. However, since the line-to-line short-circuit fault created for the module fault has a different place in the model, different results were obtained from the DC side line-to-line short-circuit fault. These results obtained in the MATLAB Simulink model are similar but different from previous studies. One of the reasons why the same graph cannot be obtained is that different graphic formats are used to show the outputs. In this study, current-time and voltage-time graphs were used, but some studies made explanations about the model through the current-voltage curve [31; 41]. However, the results obtained were still similar to this study [33; 42].