Minimization of current stress on the grid synchronization of doublyfed induction generators for wind power generation

Doubly-fed induction generator (DFIG) is the most common type of generators for wind power generation, because of their high energy yield and the possibility of generating power at variable speeds. For most papers in literature, only the synchronization and power generation of DFIGs, but not the transition between them, are discussed. This paper presents a method to control the transition of DFIGs from synchronization to power generation, in order to minimize the peak current during the transition so as to reduce the impact of synchronization on the power system. In this paper the mathematical model of DFIGs for synchronization, transition, and power generation are firstly described. Then the effects of the time difference between the state transition of the controllers and the closing of the stator side contactors and associated current stresses are investigated. A real-time detection method to determine the optimal time for controller state transition is proposed. Simulation and experimental validations confirm that the current stress is greatly reduced if the time difference is minimized using the proposed method.