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As Type-3 wind turbine (WT) has already become a typical type of highly penetrated power sources in modern power systems, characterizing its properties during grid fault is a basic requirement for system analysis. However, many significant factors have not been considered in the existing analytical methods and results, such as various switching of internal control and protection circuits in low voltage ride through (LVRT) solutions. In this paper, performance of Type-3 WT during LVRT is first illustrated and summarized as the sequential switching characteristic in multi time scales, viz., instant control, ac control, dc voltage control, and rotor speed control time scales. Thus, for magnitude drops in stator voltage, a mathematical model is proposed to understand this characteristic and fault current analysis's features. Then, an analytical method, based on the operational inductance, is proposed so that fault current components, with the sequential switching considered, can be depicted with a unified and simple analytical expression. By identifying magnitude of symmetrical current, the transient and steady-state equivalent circuits of Type-3 WT are proposed to estimate momentary current and electrical power approximately. Finally, analytical results are verified by comparisons with real-time simulation results of a detailed 1.5 MW WT model in RT-LAB. [ABSTRACT FROM AUTHOR]

The transient responses and stability followed by grid faults of the modern power systems experience diverse changes and have created concerns, especially for those dominated by doubly fed induction generator (DFIG) based wind turbines (WTs), since the transient characteristics of the DFIG-based WT are totally different from those of a synchronous generator (SG). To physically understand the transient response and theoretically analyze the transient stability of DFIG-based WT, this paper proposes a magnitude/phase dynamical model with synthetical consideration on the controllers in the rotor speed control timescale (around seconds). The proposed model physically explains the relationship between the imbalanced active power as well as the output active/reactive powers themselves and the DFIG-based WT's internal voltage vector, whose form is similar to that of the SG. By comparing with the SG, the distinctive transient phase characteristics of the DFIG-based WT are illustrated. An additional phase limitation is found, exceeding which the operation point does not exist. Based on the proposed model, the transient stability of a simple DFIG-based WT-dominated system is theoretically analyzed, and a new instability phenomenon different from that in an SG-dominated system is identified. Furthermore, some key factors influencing the transient stability are discussed. [ABSTRACT FROM AUTHOR]