Research On Modeling And Simulation Of Vscf Doubly-fed Wind Power Generation

The exploitation and utilization of renewable energy is inevitable choice for solving energy and environment issue because of gradual exhaustion of the fossil fuel and serious environment pollution. Wind energy, as a kind of renewable energy, has a promising future of being developed in the globe. Wind power has already become a new energy generation technology which is worth of exploiting in scale and an expecting future in commerce. Because of the compensation and sustentation from large power grid, grid-connected wind power has become the main technology in wind power generation. Meanwhile, doubly-fed induction generator (DFIG) has become the most widely applied wind turbine in variable speed constant frequency (VSCF) wind power generation, since it presents many advantages such as variable speed running, the decoupled control of active and reactive power, and the small rotate difference power.This dissertation takes the VSCF doubly-fed wind power generation as the research object, and focuses on its operation principle analysis, control strategy realization, modeling and simulation of system, etc. The main contents include as follows:1. Based on the research of mechanical power extracted from the wind, transfer and maximum power point tracking (MPPT) control algorithm, simulation model of the wind turbine drive train is built. Besides, the dissertation writes three S-Function procedures of three different wind circumstances with MATLAB/Simulink to simulate wind circumstances in the simulation of wind power generation system.2. The operation principle of DFIG and its steady model are produced. The machine model in three-phase stationary reference frame is derived, and based on this, the model in d-q synchronous rotating reference frame which is applied in industry is derived. Stator-flux orientation control strategy of DFIG generation operation is analyzed with MPPT algorithm and P-Q decoupled idea. Based on deep analysis of DFIG generation operation, it transforms the machine model into the state-equation that can reflect its control idea, and establishes models for electric and mechanical parameters of DFIG with S-Function. Then the two S-Functions are combined into a generation operation machine simulation model, which is took part in the wind power generation control model built with stator-flux orientation control strategy.3. The dissertation introduces two grid-connected means which are no-load and load connected grid. It analyzes no-load connected grid control strategy for DFIG model in d-q synchronous rotating reference frame with stator-flux orientation control strategy, and derives another machine model different from the one in generation operation. Then transforming the no-load DFIG model into the state-equation, and built S-Function model. Finally, no-load operation model is built. Two separately subsystems and the wind turbine train must be joined into a whole model. Then the dissertation emulates the model in three different wind circumstances, and analyzed the simulation results which include machine electric parameters, power flow, decoupled control, MPPT, etc. These conclusions validate theories and reliability of the system.4. The running principle of the grid side converter is introduced. Then the DFIG model in module invariability d-q synchronous rotating reference frame of grid side converter is derived, and the power grid voltage orientation control strategy of DFIG is analyzed. Space vector pulse width modulation (SVPWM) algorithm which makes use of DC voltage better is studied. S-Function model of SVPWM algorithm is built instead of traditional switch blocks built for removing dead zone and reliable simulation results are deserved. Grid side converter mathematical model is established with MATLAB/Simulink and the whole grid side converter control model based on power grid voltage orientation control strategy is accordingly erect. Rectifier and converter which constitute two circumstances of grid side converter are emulated, and the right outcomes are also deserved.This dissertation analyzes VSCF doubly-fed wind power generation system deeply, and establishes S-Function models based on state-equation for some key parts. The whole model and its conclusions are useful, which are the base for my subsequent research work on wind power generation.