Development of Methodologies for Analysis of Positive Feedback Anti-Islanding Protection of Inverter-Based Generators

Abstract

The usage of inverter-based generators connected directly to electric power distribution networks has considerably increased due to the technological advances of fuel cells and photovoltaic cells. In this context, the usage of anti-islanding protection devices at the interconnection point is required by the main technical guides utilized by the utilities. In the case of inverter-based generators, the main devices employed to supply anti-islanding protection are based on the positive feedback concept. These methods use the deviations of voltage frequency and/or magnitude from normal values as positive feedback signals to influence the operation of inverter-based DGs. The essential idea is to destabilize the generator when it is islanded, which facilitates the detection of islanding condition. If the generator is connected to a strong utility system, the destabilizing force of the positive feedback has a negligible impact and the generator can operate without difficulties. On the other hand, when the generator is islanded, the positive feedback can destabilize the generator easily. Such distinctively different generator behaviors facilitate the detection of islanding conditions.However, since the positive feedback scheme is a destabilizing force, the impact of this scheme on the stability of a grid-connected DG system and on other DGs becomes a natural concern when a large number of inverter-based DG is connected to a weak supply system. If the positive feedback gain is too high, the DG system may become unstable even if it is connected to the main supply system. Thus, the objective of this project is to develop several small-signal models to investigate the stability of distribution network with multiple inverter-based generator with positive feedback anti-islanding protection by using modal analysis.