Two harmonic analysis of short circuit current in wind farm

Abstract

With the increase of capacity and the improvement of economy, doubly-fed induction generator (DFIG) is gradually becoming the most widely used wind power generator in the world. DFIG has different characteristics of transient operation from the synchronous generator and its short-circuit current is affected by the converter control mode, thus when there is a voltage sags occurs, the short-circuit current of the wind farm may contain a certain amount of two harmonic. Power transformer is one of the most important power equipment in power system and the normal or not of transformer protection determines the safe and stable operation of power system. At present, the main protection of transformer is longitudinal differential protection. In order to correctly identify the inrush current, it is usually equipped with two harmonic braking measures to ensure the reliable operation of differential protection. Therefore, when the transformer failure occurs in wind farm, the protection may refuse to operate due to the reason that the short-circuit current contains a certain amount of two harmonic. Focused on the large-scale application of DFIG and the lack of the short-circuit current harmonic characteristics analysis, this work is devoted to the study of two harmonic characteristics and their influence on transformer protection when the grid voltage occurs in a non-depth drop. Through the analysis of the short-circuit current, harmonic components under different control modes of converter research the characteristics and production mechanism of the two harmonic currents of the doubly-fed wind power generator. This also lays a solid foundation for the improvement of transformer protection. Finally, the correctness of the analysis is verified by the experiments of short-circuit and time-domain simulation.