Research On Converter In Direct-driven Permanent Magnet Grid-connected Wind Power Generation System

Wind power generation is a sort of reproducible clean energy sources, it can cause notable benefit for human being in environment, economy and society. With the development of economy in our nation, the demand for energy sources is growing. The development of wind energy is one of the main ways to solve energy demand. High-power grid-connected wind power generation is the main way of utilizing wind power energy efficiently at present. Its functions are to convert changing wind energy into mechanical energy, then transform mechanical energy to electric energy and transport to power network. Because the wind power generator units with overdrive gear box, which has low efficiency at fixed speed and constant frequency, mechanism spoilage and much noises, can not meet the requirements of the times, the direct driven grid-connected wind power generation technology, which can track the maximal wind power point at the rated speed, become one of research hot points of wind power generation technologies. Based on above, this dissertation researches direct-driven grid-connected conversion circuit and its best control pattern.At first, this dissertation introduces the current situation and prospects of wind power generation development briefly, and analyzes the ways of wind power generation in detail and concludes the advantages of direct-driven type wind power generation system. Then the various topologys of conversion circuits and their advantages and disadvantages are discussed, and the direct-driven permanent magnet synchronous grid-connected wind power generation system is analyzed in detail. Based on comparing a variety of conversion circuits and considering the level of existing power switching devices, this dissertation proposes topological structure of conversion circuit with a combination of a three-phase uncontrollable rectifier, three paralleled Boost choppers circuits and two paralleled SPWM inverters, which is suitable for the direct-driven grid-connected requirements, and presents the mathematical model of direct-driven permanent magnet grid-connected wind power generation system. Secondly, the structure of main circuit is explained and the principle of each part in converter circuit is analyzed. For tach of Boost choppers, the working principle of three parallel boost choppers and optimal control method are investigated in detail. For tach of inverters, this dissertation elaborates detailedly the working principle of two paralleled SPWM inverters and two control approaches called as direct current control, indirect current control used in inverters, and compares their advantages and disadvantages as well as abilities to restrain circulating currents and harmonics. Furthermore the available control method in inverters is suggested. Finally by reference of the existing converter mathematical model and calculation data, the conversion circuits controlled by direct current are simulated and analyzed with the environment of MATLAB7.0/simulink. From viewpoint of system security and credibility, this dissertation studies the potential problems in wind power generation system. The simulation results indicate that the direct-current control method has advantage not only in dynamic response, anti-disturbs, but also in restraining circulating currents and harmonics which is often founded in paralleled inverter. It is concluded that the direct-current control method is the best one for implementation of conversion scheme proposed in this dissertation. Sum up, the inverter circuits and their control method used in grid-connected wind power generation system have well theoretical value and practical significance, and is worth continuing in-depth study and wide application.