Analytical Study of Grid-Fault Response of Wind Turbine Doubly Fed Induction Generator

Grid-connected wind turbine doubly fed induction generators (DFIGs) are sensitive to dips in supply voltage, so-called "grid faults". Fault ride through systems must be designed to manage the large and potentially dangerous fault currents in both stator and rotor circuits. However, DFIG fault response has been only partially or summarily treated in contemporary literature. This paper presents a detailed analytical analysis of wind turbine DFIG grid-fault response. The physical behavior of the machine is presented through a description of the flux-linkage response and later developed with analytical solutions of the generalized DFIG machine equations operating under fault conditions showing that the frequencies of the decay components of current deviate from pure dc and rotor speed due to magnetic drag effects. The analysis is experimentally verified and evaluated using a 7.5-kW test facility.