Doubly Fed Induction Generator Field Oriented Vector Control Strategy Study

Wind power has become a more and more important renewable power as the supply structure of power keep changing. The global installed wind power capacity increases dramatically in recent years with doubly-fed-induction-generator-based wind turbines being a large portion of the total installed capacity. Grid connected DFIG-based wind turbines control is a research focus and this paper deal with the analysis, modeling and control of DFIG. The study will focus on the vector control strategies of variable speed variable frequency DFIG.Start with DFIG-based wind power system relative concepts and theory, chapter two studies the model of grid connected DFIG-based wind power system and gives a brief introduction to vector control relative knowledge. Grid-side-converter (GSC) control relative grid-filter model and dc-link model have been presented. I-form equivalent circuit and model of DFIG also been introduced as a preparation for vector control of rotor-side-converter (RSC). Also, concepts or methods like space vector, field orientation, and phase-locked-loop-based synchronization have been study in this chapter. The introduction of internal-model-control (IMC) and "active damping" makes a good preparation for the design of controller.With models, concepts and theories of DFIG-based wind power system, chapter two goes further to study the control strategies of the system operation. Grid-voltage-oriented (GVO) vector control (VC) of GSC has been studied with the gird-filter model and dc-link model presented in previous chapter. To enhance the disturbance rejection ability of the dc-link voltage control, a load current feed-forward-compensation has been introduced. Start with current control strategy, torque control and reactive power control, stator-voltage-oriented (SVO) RSC VC strategy has been studied. Also, to enhance the disturbance rejection ability of SVO VC, a new model which taking the dynamic of stator current into consideration has been studied. An improved SVO VC is presented in the last of this chapter.Grid disturbance or grid fault has strong impact to the operation of grid connected DFIG and the DFIG-based wind power system needs to operate under strict constrains of modern grid code. Start with the grid code and analysis of grid fault, protection and ride through control of grid connected DFIG has been studied. Improved synchronization method and ride through control of DFIG when grid disturbance presents, has been studied. To improve the current control ability of both GSC and RSC, a vector-based-hysteresis-current-regulator (VBHCR) is been introduced and studied. The performance of control with VBHCR is also been investigated.At last, DFIG-based wind power system operation experiment has been carried out to examine the performance of the proposed control strategies. Experiment result from operation experiment platform with a permanent magnet synchronous motor (PMSM)-DFIG drive chain has been presented to prove the validity of the proposed control strategies.