| Wind power has become the common choice of countries around the world to deal with energy crisis and will be promoted vigorously because of its inexhaustble, flexible investment,short construction period, as well as good environmental benefit. But the randomness and intermittent characteristics of wind power generation which is affected by wind speed causes all sorts of power quality problems which seriously restrict the development of wind power technology. At the same time, some abnormal situation from the grid also bring huge impact to the stable operation of the wind turbines. Studying on the structure and control methods of power interface which as the key device of energy conversion and grid control in the wind power generation system, and making it friendly complement with the main power grid have important academic significance and practical value.Nowadays the permanent magnet direct drive wind power system inserts power grid in the form of parallel connection. This access method has poor regulation of power quality.Besides, its ability about low voltage through needs to be improved. To solve these problems,hybrid series-parallel access for wind power generation is proposed in this paper. Its topology,operationa principle, mathematical model are researched in detail. On these basis, at first, the functions of hybrid power interface in the grid connected and fault mode are designed, and the control idea of parallel connection is improved, in order to determine respective control targets for the series and parallel interface. Secondly, according to the theory of generalized harmonic, the voltage and current comprehensive detection algorithm and the parallel interface instruction current synthesis operation of series-parallel power interface based on Park transformation. The simulation results verify the correctness of dq0 algorithm in three-phase current detection, which as a steppingstone to the next step for control method to the hybrid interface. For the designed functions of series-parallel power interface under two operation modes of wind power grid-connected and fault, the traditional parallel access interface of master-slave control mode is improved. Then Research on the output control strategy of series-parallel power interface based on variable ring width and constant frequency of hysteresis current control, and the improved dc-side capacitor voltage control strategy. Again, according to network operational characteristics of wind power system andcon trol target of hybrid interface, comparing the two-level hysteresis and three-level hysteresis in their respective working principles and switching characteristic, a self-adaptive three-level hysteresis control strategy is proposed about the hybrid series-parallel interface.DC link voltage stability is implemented by using double closed loop control strategy of outer voltage loop and inner electric current loop. Finally, the simulation model of series-parallel power interface with wind power generation system is builded on the Matlab/Simulink software platform. With this basis, the system simulation analysis are made under different operation modes.The theory analysis and the results show, using the hybrid series-parallel access and its' gird power interface, with the adaptive current control based on three-level hysteresis, make the hybrid series-parallel power interface realize grid-connection, track the maximum power point, and have superior ability of low voltage ride through. |
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