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This paper focuses on the enhanced control and improved fault-ride-through capability of a doubly fed induction generator (DFIG)-based wind turbine system under both unbalanced and distorted grid voltage conditions. A more integrated mathematical model of DFIG is first set up with both the negative-sequence and the low-order harmonic grid voltages considered. Based on the developed model, the instantaneous active/reactive powers and electromagnetic toque are redefined in detail. Besides, four alternative control targets and their corresponding rotor current references are calculated and assigned. A novel current controller, consisting of a conventional PI regulator and a dual-frequency resonant (DFR) compensator, tuned at twice and six times the grid frequency, named PI-DFR controller, is designed to regulate the fundamental and the fifth- and seventh-order harmonic components simultaneously. Experiment studies verify the correctness of the developed model and the effectiveness of the suggested control strategies in improving the fault-ride-through capability of a DFIG system under such adverse grid conditions.
Date of Publication: Sept. 2012