Reduced-Order Models of Squirrel-Cage Induction Generators for Fixed-Speed Wind Turbines Under Unbalanced Grid Conditions

This paper develops a study of reduced-order models for squirrel-cage induction generators used in the fixed-speed wind turbines. The squirrel-cage of these generators must be modeled with a double-cage for accuracy purposes. These proposed reduced-order models are valid for unbalanced grid conditions (unsymmetrical faults), which require flux and current decomposition into positive- and negative-sequences. Three reduced-order models are obtained: R2 model, where the derivative of the positive- and negative-sequences of the stator fluxes are neglected (the usual approach in the literature); R1 model, where the derivative of the negative-sequence of the rotor fluxes are also neglected (proposed model); and R0 model, where all the stator and rotor fluxes are neglected (steady-state electrical model). The analytical models are validated with simulations carried out in the MATLAB and with experimental tests. The results show that R1 model (proposed model) shows a good performance (similar to the full-order model) under unbalanced conditions.