| Summary: | 碩士 === 聖約翰科技大學 === 電機工程系碩士班 === 97 === An integrated islanding detection method for use with grid-connected distributed generator (DG) is proposed in this thesis. The proposed integrated islanding detection method contains passive islanding detection method and active islanding detection method. The passive islanding detection method is based on two indices: the rate of change of frequency (ROCOF) and rate of change of voltage (ROCOV). The detection system monitors the terminal voltage at the grid-interconnected point, and operates when the value of ROCOF or ROCOV exceeds a setting and duration exceeds a time delay setting. When DG is grid-interconnected, the ROCOF and ROCOV are lower than the threshold values. In contrast, as an islanding occurs, the ROCOF or ROCOV would become much higher than the threshold values.
The active islanding detection method is based on correlation factor calculation. The method obtains voltage fluctuation through the high impedance load switching on the grid periodically. The correlation factor between the periodic perturbed signal and the fluctuant voltage is then used as an islanding detection index. When DG is connected to the grid, the correlation factor is lower than a threshold value. In contrast, as an islanding occurs, the correlation factor would become much higher than the threshold value.
The proposed integrated islanding detection method monitors the terminal voltage at the grid-interconnected point, and operates when the value of ROCOF or ROCOV exceeds a higher setting and duration exceeds a time delay setting. If the value of ROCOF or ROCOV exceeds a lower setting, the active islanding detection method will started. Then the correlation factor will be calculated to determine the operation state of DG.
Experiments are discussed which demonstrate the principles of the technique. Test results are presented which show that the integrated islanding detection method is reliable, economical and easy for implementation.
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