Contents I. INTRODUCTION
Doubly Fed Induction Generator (DFIG) wind power system has become the mainstream of wind power market in recent years [1]. The advantage of DFIG wind power system is that it only needs a power converter with the power rate about one third of the generated power. However, as the stator of DFIG is directly connected to the grid, previous researches by the predecessors show that the performances of DFIG wind power system are deteriorated under distorted grid voltage conditions, such as voltage dips [2], asymmetry [3] and harmonics [4] of the grid voltage. Wind farms are often located on end of transmission lines or remote area where the grid is weak and may have lower order harmonics (mostly negative 5th and positive 7th order). The lower order harmonics of the grid voltage causes stator harmonic current [5], which may cause the DFIG wind power system fail to meet in the grid codes [6]. Besides, it may cause voltage fluctuation on the DC-bus of rotor side converter and reduce the reliability and the life time of the converter. The stator harmonic current will also brings fluctuation of the electronic torque, reduce the life time of the mechanical system, and affect the efficiency of the generator [7] [8].
