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Protection Performance Overview and Validation in Low Strength Areas

The integration of AC connected wind farms into the existing power network has significantly changed the characteristics of the system and adequate small signal wind turbine models will be required to assess system stability considering the existence of difference converter technologies. While the small signal behaviour of Type 4 turbine has been extensively studied, the small signal impedance of doubly-fed induction generator (DFIG) based Type 3 turbine has not been well understood. The purpose of this study is to develop small signal admittance model of Type 3 turbine under different control modes and operating points. In this report the admittances of Type 3 turbine are then compared to the Type 4 turbine to highlight the main differences between the two. The small-signal admittances of both turbine types from the analytical models are verified against the measurements from time-domain models.

This report concentrates on the development of small-signal LCC converter and LCC HVDC system models. The development of the analytical impedance model intends to provide further insight into the impact of circuit and control structure/parameters on system impedance, and similarly highlight the factors that need to be considered when an LCC HVDC connection is defining its frequency-dependent impedance accurately ahead of a network scale small-signal interaction study being performed. The developed impedance models can then be used for assessing stability and interactions between different converters (e.g., MMC, LCC, wind farm, etc.).