Research On Control Of Variable Speed Constant Frequency Doubly Fed Wind Power Generator

Due to the crisis of energy and the environmental pollution, clean and renewable energy resources are attracting more and more interesting, especially wind energy. With the great development in manufacture of power electronic converter and its application technology, the variable speed wind turbine with doubly-fed induction generator(DFlG) has turned into mainstream machine in the field of exploring wind energy in the world now, it only deal with the slip power of DFIG and can flexibly join wind turbine to power system, It is important to study the technology, operation characteristics, safety and stability in an electric power system with the type wind turbine. In this dissertation, the AC excitation control law is studied for wind energy generation system with DFIG.At presence, the control scheme of DFIG is to control the grid side converter and machine side converter independently; it can not obtain the good dynamic performance because of separating physical relation between the DFIG and converter. To avoid the defection, the unified model is founded, which consider the DFIG, grid side converter and machine converter as the all and the one, and take their affection each other into account. Base on the unified model of DFIG system, the power characteristic is analyzed in detail, and make sure the active and reactive power limit of DFIG system. To compare the energy efficiency with other types wind turbine, the loss including the converter and DFIG is analyzed too.Because the control law of DFIG which based on the simply dynamic model has not good dynamic performance, and anti-jamming ability, multi-variable nonlinear control law is studied. The inverse system theory is used to design the decoupled control of active and reactive power of DFIG system. With the pseudo linear system obtained by state feedback, the internal model control is developed to construct the decoupled control system to increase the robustness. The control system is modeled on MATLAB/SIMULIND, and the simulation shows its availability and good performance. According to special state of DFIG, the simply law based on inverse system theory is studied too.A 160kW VSCF wind energy generation system with DFIG and back to back PWM converter is designed and established, which consists of a laboratory emulation of wind turbine, DFIG system, the control system of wind generation system and a virtual instrumental system based on Labview. Systematic experimental study of VSCF generation operation has been carried out on this laboratory platform, such as DFIG output active and reactive power decoupled control, grid-connection control, the maxim wind power capture operation and control law of DFIG system based on inverse system theory. The experimental results testify the validity of the strategy proposed by this dissertation.The behavior of DFIG system during and after grid fault such as symmetrical fault, single-line-to-ground fault, two-line-to-ground fault, and line-to-line fault is investigated combined with the analytic and simulation analysis. Based on the deeply understanding of the DFIG system transient under grid fault, a dynamic model with separated positive and negative sequence is developed, and proposed a novel control of DFIG system under the grid fault, which controlled the rotor voltage to counteract the effect of the harmful components in the stator flux, at the same time the stator side resistance is used to weaken the harmful stator flux field. The validity work has been done by system simulations.