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240    CHAPTER 7 Strategies for Fault Detection and Diagnosis




                         such as currents, voltages, energy at the inverter outputs, and number of peaks pre-
                         sent on the IeV curve that can indicate the normal and the faulty operations. Other
                         methodologies for supervision of PV systems are based on the parameterization of
                         metadata and the quality control of PV power output data [40]. Moreover, remote
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                         supervision and fault detection on OPC -based monitoring of PV systems [41]
                         was carried out by using indicators of voltage and current as key parameters of
                         the supervision algorithm [42,43].



                         5. MODELING AND SIMULATION OF PHOTOVOLTAIC
                            SYSTEMS
                         As it has been described in the previous section, the simulation of the PV system
                         behavior is the key for most supervision and diagnostic methods in automatic fault
                         detection of PV systems. The simulation results give information about the expected
                         evolution of main electrical output parameters of the PV system or try to reproduce
                         the IeV characteristic of PV modules and arrays in real conditions of work. There-
                         fore, these simulations are also useful for forecasting the energy produced by PV
                         systems.
                            The comparison of the results obtained in the simulations with the real measured
                         data obtained from the monitoring system allows the identification of malfunctions
                         in the PV system and the diagnostic of the most probable fault. For this purpose, it is
                         necessary to work with accurate models of the main GCPVS components such as PV
                         modules and inverters. Nowadays, a wide variety of software tools are available for
                         the simulation of PV systems [44]. These tools present different degrees of
                         complexity depending on the specific tasks that each tool has been developed for.
                         However, the accuracy of the simulation results depends primarily on the models
                         used. Some of the most used models in simulation of PV systems as well as several
                         software environments that can be used in the simulations of these models are intro-
                         duced in this section.

                         5.1 MODELING SOLAR CELLS, PHOTOVOLTAIC MODULES,
                             AND ARRAYS
                         One of the most used solar cell models is the one-diode model also known
                         as the five-parameter model. This model includes a combination of a photo-
                         generated controlled current source I PH , a diode, described by the single-
                         exponential Shockley equation [45], and a shunt resistance R sh and a series
                         resistance R s modeling the power losses. The equivalent circuit for this model is
                         given in Fig. 7.4.



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                          OPC is an interoperability standard for the secure and reliable exchange of data. It is platform inde-
                         pendent and ensures the seamless flow of information among multiple kinds of devices.
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