Study On Electromagnetic Transient Analysis And Crowbar Topology Of Doubly Fed Wind Turbines

With the rapid development of economy and science, the energy problem has become the major social problems today. For the clean and renewable energy, wind energy, is attracting much attention. Nowadays, with the expending scale of the wind turbines capacity year by year, the wind power penetration is increasing. Doubly fed induction generator (DFIG) is widely used in high-power class wind turbines on account of its advantages of flexible control, less cost and variable speed constant frequency operation. However, The distinct driving scheme makes DFIG sensitive to the grid disturbance, so with the low voltage ride through capability has become the necessary performance for the doubly fed wind turbines. This dissertation studied the electromagnetic transition and low voltage ride through of DFIG-based wind turbines under grid fault. The main contents of the dissertation can be summarized as:Firstly, the mathematic model of the DFIG was built,meanwhile the operating principle and control method of doubly fed induction generator was analyzed. On the basis of the above,2 MW DFIG simulation model was built, the simulation verify the feasibility of the control method.Secondly, The reason why the LVRT problem of DFIG is so complicated and difficult to solve properly roots in the complex electromagnetic transients. Therefore, a deep and comprehensive analysis of the transients would base the associated researches and solutions. Meanwhile, the analysis would also be the key for study on their effects on power grid, especially the calculation of short-circuit currents. To analyze the transients in the high-order complex plants analytically, a novel calculation method based on equivalence and superposition has been creatively proposed and the associated analytical calculation have been accomplished. In the analytical results, not only are the popular calculations with the assumption of the crowbars triggered promptly just upon the voltage dip for simplification covered, the cases with crowbar not triggered and/or triggered in delay, as in engineering practice, are also considered, completing the characteristics analysis and simulation verification of electromagnetic transient process.Thirdly, By adding some low-priced and robust SCR and resistor crowbar circuit to the conventional rotor driving converters, the forced commutation of SCR is realized by using the switching off of the rotor side converter, and then realize the active crowbar function, and then successfully get two active crowbar schemes based on low cost and high reliability SCR devices. The active crowbar circuits are realized by the low-priced SCR elements rather than the normally adopted high-priced and tenuous IGBT elements.Finally, 11kW DFIG experiment platform is built in the laboratory. Then, the vector control, the electromagnetic transient analysis and the crowbar protection circuit of DFIG are verified by experiments. The experimental results verify the correctness and feasibility of the analysis and design in this paper.