Fault currents of doubly-fed induction generator under symmetrical fault condition

摘要

In wind power systems, the fault ride-through capability of doubly-fed induction generators (DFIGs) has become a focus of study. The analysis and computation of fault currents are of great significance for implementing DFIG fault ride-through. This paper systematically analyses dynamic responses of DFIG stator and rotor currents when three-phase short circuit occurs at stator terminals. A new approach, in which the DFIG under fault condition is equivalent to a rotor excited induction machine running in a steady-state and a squirrel-cage induction machine subjected to a three-phase short circuit, is proposed to gain the fault currents mathematical expressions. The two equivalent machines represent the particular solution and the general solution of DFIG differential equations in physical meaning, respectively. Moreover, the method of space vector analysis is introduced to achieve analytical expressions of the fault currents. The maximum rotor and stator short circuit currents, as well as the times when they appear, are demonstrated. Main components of the short circuit currents and their relations are presented. Finally, simulations on a 2 MW DFIG system are carried out, and prove to be in close agreement with results from mathematical analysis.