Research On Control Strategy Of DFIG-based Wind Power Generation Systems Adapted To Complicated Grid Conditions

Doubly Fed Induction Generator(DFIG)has become the main motor type adopted in wind power generation for its property advantages such as the variable-speed and constant-frequency characteristics and flexible control strategy.Considering the network condition and grid-connected requirements of wind power generation,the support and operations control research focus of DFIG has turned from under ideal network condition to under non-ideal network condition.The research of the fault ride-through operation and control of the DFIG under generalized unbalanced and distorted grid voltage conditions has received a lot of attention.This paper focuses on the adaptive operation and control strategy of DFIG under unbalanced and distorted grid voltage conditions in the ?? reference frame.Firstly,after a comprehensive analysis of the background and research status of the subject,this dissertation analyzes the components and working principle of the DFIG.The working principle of the vector control based on grid voltage orientation was analyzed.The principle of the symmetrical component method was introduced.The mathematical model of the DFIG wind power system under unbalanced and distorted grid voltage conditions was analyzed in detail in the ?? reference frame.The fluctuant components of DFIG stator output active and reactive power and electromagnetic torque was analyzed in the ?? reference frame when faced unbalanced and distorted grid voltage conditions.The related fluctuant power components of grid side converter was analyzed as well.Secondly,the calculation methods of the grid voltage unbalance degree and harmonic distortion rate was introduced.The influence on the output performance of DFIG wind power system caused by unbalanced and distorted grid voltage conditions when the conventional vector control strategy is taken was researched through MATLAB/Simulink simulation.Based on the above analysis,a kind of extraction method for the positive and negative sequence and fifth order harmonic and seventh order harmonic component of relevant electromagnetic quantities was designed when faced unbalanced and distorted grid voltage conditions in this paper.The propotional odd multiple frequency Resonant(P-odd-MFR)controller was taken to control the positive and negative sequence and fifth order harmonic and seventh order harmonic component of the rotor current and grid side converter current.The rotor current reference instructions that suppressed the fluctuant components of DFIG stator output active and reactive power and electromagnetic torque was calculated based on analysis of DFIG stator output active and reactive power and electromagnetic torque fluctuant components.Meanwhile,the rotor current reference instructions that suppressed the negative sequence and harmonic fluctuation of the rotor current and stator current of DFIG was calculated as well. Moreover,The grid side converter current reference instructions that suppressed the fluctuant components of DFIG wind power system total output active and reactive power and DC bus voltage was calculated based on analysis of DFIG wind power system total output active and reactive power and DC bus voltage fluctuant components.Meanwhile,the grid side converter current reference instructions that suppressed the negative sequence and harmonic fluctuation of the total current of DFIG wind power system was calculated as well.At last,The feasibility and effectiveness of the adaptive control strategy proposed of DFIG under unbalanced and distorted grid voltage conditions was proved through MATLAB/Simulink simulation.