Principle of Directional Fault Discrimination in the AC Grid Integration System of Doubly Fed Wind Turbine Generator in the Near Zone

In the context of the development of new power systems, the growing proportion of new energy sources in the power system has significantly increased. The high level of power electronic integration has greatly transformed the transmission characteristics of power, and it exhibits operational and fault characteristics distinct from traditional power systems. When a fault occurs in the near-zone transmission lines of a doubly fed wind turbine generator AC grid integration system, the complex characteristics of the system make it difficult for traditional directional elements to determine the fault direction. The paper analyzes the fault characteristics of the near-zone transmission lines in a doubly fed wind turbine generator AC grid integration system. Then, a calculation method for the electromagnetic transient analysis of the temporal and frequency components of the equivalent sequence impedance of the back-end system is proposed, utilizing the differences between measured voltages, currents, and those of the AC boundary elements. Finally, a new directional fault discrimination principle is proposed based on the differences in the fluctuation coefficients of the temporal and frequency components of the equivalent sequence impedance within a predefined time window for forward and reverse faults. The performance of the proposed method is validated through extensive simulations. The simulation results indicate that compared to the conventional voltage polarization direction element, the proposed direction element in this paper can accurately identify the fault direction in the grid-connected system of the doubly-fed wind turbine, with higher reliability and sensitivity.