Discrete Wavelet Transform for Islanding Detection of Photovoltaic Distributed Generators

The electric power system is changing, and units that previously only consumed power have begun to inject it into the grid. Photovoltaic generation has grown in recent years and is currently the most widely used source of distributed generation in Brazil. One of the main concerns when connecting a distributed generator (DG) to the grid is unintentional islanding, which occurs when a portion of the grid containing DG and loads remains electrified, but electrically isolated from the rest of the grid. In this case, the DG power supply is not supervised by the grid and can lead to many problems, concerning security and operation. This work proposes a methodology that uses Discrete Wavelet Transform (DWT) for islanding detection, analyzing the voltage signal at the point of common coupling between the utility, DG and loads. A real scenario was used to develop and test the proposed method. For the studied case, the algorithm responded correctly in 100 % of the practical cases evaluated, with detection time between 0.06 s and 0.2 s.