Cut-in/out Control Strategies for Doubly Fed Induction Generator Driven by Variable-speed Wind Turbine
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Several cut-in control strategies for doubly fed induction generator (DFIG)-based variable-speed constant-frequency (VSCF) wind power generation are studied in the paper. The stator voltage open loop control-based cut-in control strategy is easy to be tuned, but the control precision of the no-load stator voltages cannot be guaranteed. In another control strategy with stator voltage RMS close loop control, the control precision is improved, however, the disadvantages in stator voltage symmetry and in no-load stator voltage waving are still not improved very well. The control strategy with stator voltage space vector close loop control not only can guarantee the control precision of the stator voltages, but also can eliminate the stator voltage waving at slip frequency, when a specific controller is adopted. For the voltage space vector close loop control-based strategy, based on the proportional-plus-integral (PI)-based control scheme, a new control scheme composed of an adaptive resonant controller and a PI controller is proposed in the paper, by which the stator voltage waving is almost elimited, and a very well control performance is achieved for stator voltages, naturally, the softly cut-in control is realized. The results of simulation and experiments have validated the theoretical analysis and the designs of the cut-in/out control strategies.