# Investigation of Failures during Commissioning and Operation in Photovoltaic Power Systems
## 2 Materials and Methods  
In this study, a grid-connected solar power plant modeled in the MATLAB Simulink program and its electrical faults are examined. In [12], a fault is described as, \"an abnormal condition that may cause a reduction in, or loss of, the capability of a functional unit to perform a required function\". Recent years have seen a significant increase in the research area of fault classification and detection since defects in PV power plants may affect their capacity to generate electricity [13]. Examining the most frequent failures in PV power plants is one of the most crucial steps to understanding the causes of failures and their effects. Faults can be analyzed in this context under two categories: AC side faults and DC side faults. AC side faults may arise due to problems with the power grid or inverter. There are more DC side faults than AC side faults. These include faults in the junction box, bypass diode, cell, open circuit, short circuit, arc fault, and ground fault [1]. The classification of electrical faults in photovoltaic plants is shown in Figure 1 in order to increase understanding and to make physical follow-up of the fault incidence zones easier. The classification is as follows:  
In the case of faults occurring on the AC side, the power of the entire system may be cut off, or, as a result of the fault, only the photovoltaic system may be disconnected from the AC side and a grid outage may occur [14; 15; 16]. Inverter faults: In case of a fault in the inverters, the AC output power decreases or goes completely to zero while the DC power remains constant [17]. Grid faults: Grid faults include damage to components in substations, power transmission lines, and even other power plants connected to the grid, and faults such as short circuits, open circuits, and overloads. Grid faults directly affect the grid connection of photovoltaic power plants. Grid faults may disrupt the synchronization situation or cause the photovoltaic power plant to be disconnected from the grid due to low voltage [17; 18]. Ground faults: A ground fault occurs when there is contact between the line conductors and ground potential. A ground fault occurs between the positive or negative conductor and the ground on the DC side, while it occurs between the phase conductors and the ground on the AC side [8; 19]. Line-line short-circuit faults: A short circuit that occurs between two points at different voltage levels or different phase voltages is called a line-line short-circuit fault. A line-line short-circuit fault occurs between the positive and negative conductor on the DC side and occurs between the phase conductors on the AC side. In photovoltaic power plants, line-to-line short-circuit faults may occur on the AC side as a result of damage to the cable insulation due to corrosion, physical impact, or animals, and on the DC side, short circuits in photovoltaic arrays may occur within the arrays or between two arrays [20; 21]. Arc faults: Damage to cable insulation and improper connections at connection points are the main causes of arc faults [21; 22]. Open-circuit faults: An open-circuit fault is a situation where the continuity of the conductor is interrupted at a certain point. This may occur due to external factors or over time due to improper and loose connections at the connection points [4; 9; 23]. Mismatch faults: Incompatibilities in photovoltaic modules occur when a cell or a group of cells differs from other cells [23; 24; 25]. Photovoltaic cell/panel/module/array faults: Photovoltaic cell/panel/module/array faults are named according to the equipment where the fault occurs [26]. Diode faults: The purpose of using diodes in photovoltaic panels is to provide unidirectional current flow. Diode failures are mostly caused by incorrect connection and overheating [19; 20; 27]. The MATLAB Simulink model is shown in Figure 2. In this model, the central inverter is shown on the DC side, and combiner boxes are shown between these central inverters and photovoltaic panels.