Improved Hybrid Technique for Anti-Islanding Protection of Grid Connected Photovoltaic Systems

Abstract

The whole world faces a huge challenge to avoid theenergy crisis. The diminishing deposits of non-renewable energy resources such as natural gas, coal, are added to this worry. It is thus obviously that an alternative stable energy source is needed to be developed. The immediate need will be to avoid the problems caused by consumptionof the oil and natural gas, but in the long term the need will be to develop means that can replace fossil fuels. The hugeindustrializationandpopulation growth, demand regularly an increased amount of the electrical energy.The interest toward the distributed generation (DG) systems is increased year after year. Distributed generations including renewable energy such aswind turbinesand photovoltaic arrays (solar energy). The technology of photovoltaic gained a great importance nowadays through the high development of such a technology. Islanding is a phenomenon in which the DG system and some of the local loads are disconnected from the grid. Ifthe generation remains operative and this condition is not detected, the isolated DG system will stay supplying the local loads with power. The islanding situation is undesirable as it may cause severe damage to the DG itself or the local loads connected in case of unsynchronized reclose of the grid because of phase difference between the DG and the grid voltage, also it is potentially dangerous for the maintenance personnel. So, a distributed generator should be disconnected within a maximum time delay of two seconds after loss of the grid [1]. To achieve this goal, each DG should be equipped with an islanding detection device, which is also called anti-islanding devices. The thesis introduces a hybrid islanding detection algorithm based on sequentially combining two techniques (a passive method based on monitoring rate of change of frequency(ROCOF)and active method (active frequency drift AFD) in order to overcome the disadvantages of applying only passive techniques or active techniques. The proposed techniques were tested and simulated on the islanding and possible non-islanding conditions such as normal operation, sudden load change, switching a capacitor bank and found to be highly effective in islanding detection. Keywords: Distributed generators, Islanding, ROCOF, ROCOV, Photovoltaic, AFD, Hybrid islanding detection technique and ROCOF relay.