Research On Harmonics Of Doubly Fed Wind Power Generator Under Balanced And Unbalanced Network Voltage Conditions

The Variable Speed Constant Frequency (VSCF) doubly-fed wind generation system has gradually been more and more attention due to its low equipment wear and tear, wide operating range, low cost, easy to control and many other advantages. Modeling and control of grid-connected system is an important component of the wind power generation system. This paper discusses the control of the doubly fed wid generation systems and conduct the necessity and validity of the research from the harmonic point of view. The contents of this dissertation are as follows:The dissertation analyzes the operating theory of VSCF doubly-fed wind generation system, establishes the model of wind turbine and analyzes the control strategy of wind turbine to make the system output power maximum under a given wind speed. Based on the stesdy state mathematical model of Doubly Fed Induction Generator (DFIG), the control strategy of rotor-side converter and grid-side converter is designed by using vector control method under balanced grid voltage. In the vector control, active and reactive power can be controlled separately, maximum wind power tracking can be achieved and DC bus voltage remains constant.The control strategy of VSCF doubly-fed wind generation system is discussed. The symmetrical component method is used to study the operating behavior of DFIG under unblanced grid voltage. Based on the mathematical model of DFIG in the negative-and positive-synchronously rotating frames under unblanced grid voltage, the control strategy of rotor-side converter and grid-side converter and coordination cintrol strategy of rotor-side converter and grid-side converter are proposed to eliminate the second harmonic and negative sequence component.The above theoretical analysis and control strategy are implemented in MATLAB/Simulink. The simulation results show that harmonic and negative sequence components can be eliminated by through the improvement of the control strategy under unblanced grid voltage and the uninterrupted operation of the system capacity is improved.