The Research On Control Of Wind Turbine Based On Doubly-fed Induction Generator

Because of the gradual depletion of fossil energy resources and the increasingly serious issue of environmental pollution, it has become the inevitable choice to develop renewable energy represented by wind energy and solar energy for the sustainable development of human society. Among many renewable power generation methods, wind power generation is one of the methods which are the most mature and suitable for large-scale development. In the field of wind power generation, the variable-speed-constant-frequency (VSCF) wind turbines based on the doubly-fed induction generator (DFIG) is the most popular kind. In this thesis, the researches about the control technology of the DFIG under different operating conditions are carried out, and some innovative fruits are achieved.The international and domestic development status and trends of wind power generation industry are survey. The structure and characteristics of several kinds of VSCF wind turbines are introduced. Main control technologies about wind turbine based on DFIG are summarized.The VSCF operation principle of the DFIG is introduced.The model of the DFIG in the stationary and synchronous reference frame is described, and the model of the DFIG in the positive and negative sequence synchronous reference frames under unbalanced grid voltage is derived, which is the theoretical basis for the research. A hardware experimental platform is developed in the lab, which provides experimental basis for the research.Because the DFIG is a multi-variable strong coupling system, in order to achieve the best control effect, the relative gain array (RGA) methodology is introduced to choose the most suitable input-output control pairs, and sliding mode variable structure control is introduced to improve the robustness of system. It is specifically manifested in the following aspects:A novel single loop direct voltage control scheme using integral variable structure control is proposed to synchronize the DFIG to the grid. The RGA methodology is used to analysis the degrees of relevance among the variables of the DFIG and develop direct control relationship between rotor voltage and stator voltage, which eliminates the control loop of rotor current. The parametric uncertainty and external disturbances are adequately considered in the design procedure of the controller, which improves the robustness of the system. Both simulation and experimental results show that the proposed control scheme effectively achieves the grid synchronization control of DFIG,and it has satisfied robustness against parametric errors and external disturbances.A grid synchronization control scheme of DFIG under unbalanced grid voltage is firstly proposed. The grid synchronization controller is divided into main controller and auxiliary controller. The main controller is used to control the positive sequence stator voltage to follow the positive sequence grid voltage, while the auxiliary controller is used to control the negative sequence stator voltage to follow the negative sequence grid voltage. Both simulation and experimental results show that the proposed control scheme effectively controls the stator voltage of the DFIG to follow unbalanced grid voltage accurately.An integral variable structure direct torque control scheme of DFIG with constant switching frequency is proposed by combining integral variable structure control with space vector modulation. The torque and reactive power of DFIG are directly controlled by the rotor voltage, which eliminates the control loop of rotor current. The parametric errors are adequately considered in the design procedure of controller, which improves the robustness of the system. The constant switching frequency avoids the inherent current distortion problem in traditional direct torque control. Both simulation and experimental results show that the torque and reactive power of the DFIG can be effectively controlled by the proposed control scheme, and the parametric robustness and generated power quality are satisfied.A direct torque control scheme of DFIG under unbalanced grid voltage is proposed to independently control the torque and reactive power, and simultaneous eliminate torque and power pulsations caused by unbalanced grid voltage. The RGA methodology is used to develop the direct control relationships among the positive and negative sequence rotor voltage and the positive and negative sequence torque and reactive power, based on which positive and negative sequence controllers are designed, respectively. Comparing to existing control schemes under unbalanced grid voltage, the proposed control scheme eliminates the measurement, coordinate transformation and symmetrical component extraction of rotor current, which simplified the controller. Simulation and experimental results shows that the proposed scheme effectively eliminates torque and power pulsations caused by unbalanced grid voltage.This work was supported by the National Natural Science Foundation of China under Grant 60534040 and the National High Technology Research and Development of China under Project 863 Program 2007AA05Z244. All the proposed control schmes are validated on the hardware experimental platform, which establishes basic for further industrialization and provides experience for the engineering applications and extensions of modern control theory.