Research On Direct Power Control Technology Of Variable Speed Constant Frequency Doubly-Fed Wind Power Generation

With the more and more serious conflict between energy and environment, the strategy of sustainable development becomes very important for the world. In this context, the development and use of renewable energy is one of the most popular topics in the field of power electronics. The wind power is supposed to be the third biggest potential generating energy, following the thermal energy and hydro power. So the wind power becomes more and more attractable. In traditionally, the constant speed constant frequency (CSCF) is most wide used in the wind power system. But the wind-electric energy conversion efficiency of this system is low and the mechanical Components stress of wind turbine bear is very large. The variable speed constant frequency (VSCF) wind energy generation system with doubly fed induction generator (DFIG) becomes the alternative developing direction of the wind power. The direct power control strategy (DPC) for the DFIG system of VSCF is studied in this paper. The primary content and original contributions of this dissertation are as follows:First, the direct power control strategy (DPC) for grid-side rectifier is studied. Base on the model of voltage oriented vector control strategy (VOC), the mathematic model of rectifier for DPC is analyzed and the corresponding control scheme is developed. The estimating equation for instance active and reactive power is derived. The way to achieve the constant switching frequency for DPC is introduced. The simulation models of rectified on Matlab/Simulik environments are established. The simulation results verify the DPC for the system of rectifier.Then, a DPC strategy for the rotor-side converter is studied. The mathematical models of the grid-connection DFIG are established and the control scheme based on classical grid-flux oriented control (FOC) is derived. The DPC strategy using space-vector modulation (DPC-SVM) applied to the DFIG is present and the corresponding mathematic model and DPC scheme are developed. Also, the models of DFIG system with the rotor-side converter on Matlab/Simulink environments are established. With comparing the simulation results of FOC and DPC, the merit of the DPC is discussed.Finally, the control strategies are carried out on the real platform of VSCF wind energy generation system with DFIG. The structure and the way to achieve the control strategy scheme in real experimental platform system are introduced. The comparisons of FOC and DPC are carried out in terms of several different operations. From the experimental results, we can get the conclusion that the proposed DPC strategy applied to DFIG allows to obtain the combination of constant switching-frequency, and 10 times quicker dynamic response than the FOC.