In this paper is analyzed is the passive technique of the voltage Harmonic Distortion (HD) for the protection and distribution of PV systems connected to the utility grid. We have made the measurement of the HD voltage in the PCC and the measured value is compared with a certain threshold if this threshold is exceeded inverter will be disconnected. During normal operation, the voltage at the PCC is the grid voltage, so distortion in most cases can be considered as negligible. However, when islanding condition happens, the current harmonics produced by the inverter are transmitted to the load and presents higher impedance than the grid. The interaction of the harmonic currents and the grid impedance generates voltage harmonics which can be measured. Therefore, the voltage HD variations beyond a certain threshold can be used to detect islanding. The technique in question is analyzed based on the non-detection area and based on the possibility of degradation of the output power quality, which is a known weak point of this method. The analysis focuses on the worst case of detecting when the energy produced by the photovoltaic system is the same energy that takes the load when there is no change to the parameters at the common point of connection to the utility grid. Results are obtained by monitoring a grid connected to the photovoltaic system with a power of 3.9 kWp installed on a flat roof of a laboratory building of FECE in Pristina. Simulations for the respective topology were made with Matlab Simulink.
Słowa kluczowe: photovoltaic module, utility grid, islanding detection, passive methods, voltage total harmonic distortion
W artykule analizowany jest system fotowoltaiczny podłączony do sieci z pasywnym układem poprawy zawartości harmonicznych. W układzie moerzona jest zawartość harmonicznych I układ jest odłączany gdy ta wartość przekroczy dopuszczalny poziom. Jednocześnie przekraczanie zawartości harmonicznych może być sygnałem zjawiska wyspowania.
Keywords: system fotowoltaiczny, efekt wyspowania, zawartość harmonicznych
The problem of islanding of photovoltaic systems interconnected with utility grid has been the main challenge in implementing distributed generation of electricity. Islanding is a condition in which a portion of the utility system, which contains both load and operating generation. The distributed generation of electricity is an option that is being considered seriously around the world, especially in countries where the centralized power generation system is very old and causes large environmental pollution. Distributed generation, as defined by Karlsson is “…an electrical power generation source connected directly to the distribution grid or on the customer side of the meter". One of the main problems encountered in distributed generation is the possible formation of isolation conditions (areas called the island) that can continue to work normally even if the electrical grid is disconnected. For applications without detection and correction, it is better to combine more methods for detection of islanding detection based on other work processes [1, 2]. This unity power factor condition combined with passive parameters of parallel RLC load and frequency is considered the worst case for islanding detection when the active power of load matches to the output power of distributed generation [3, 4]. Is describes an anti-islanding control technique for use in utilityinterconnected photovoltaic systems. The technique can be used to prevent islanding in any distributed generation resource that uses a static inverter as the interface device . The ability to protect from the creation of islanding circumstances is an important request for distributed generation. It is necessary to detect when the system works under insulation conditions and disconnect from the network as soon as possible . Detecting the islanding is important for all DG systems. In the last decade, many algorithms have been developed for such detect [...]
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