Even harmonic current disturbing method for islanding detection in the distributed power generation systems

Islanding protection is necessary for the distributed generation (DG) systems, but it is difficult for some traditional methods such as frequency or phase variation methods to detect the islanding effect when the power generated by the DG systems matches with the demand power of the local load. The islanding detection capabilities about different disturbing signals are analyzed and even harmonic current disturbing signal suiting to multi-inverter DG system is available in this paper. Combining with a zero-crossing frequency detector, the positive feedback loop with even harmonic current disturbance is introduced to detect the islanding phenomenon. Output current reference in the grid-connected inverter is affected by a minute disturbance signal in general. Once the islanding occurs, the positive feedback of disturbance current makes the voltage frequency at the point of common coupling go beyond a preset threshold value. It is easy to design the software program, less to inject the current harmonics into the grid, quick to detect the islanding effect, equal to form the multi-inverter system. Simulation and experimental results verify that the method is effective and reliable.