| ower system in case of low-voltage fault,this paper summarizes and analyzes the existing typical low-voltage Wind power generation is one of the most promising green power generation technologies in the application of new energy.With the increasing proportion of wind power in the world and the increasing installed capacity of wind power in China,even though the rapid development of power generation technology makes the cost of wind power drop significantly,the serious low-voltage ride through phenomenon after the wind power grid connection of units and the chain disconnection phenomenon of high-voltage fault caused by low-voltage after the repair of fan fault become more and more serious.Therefore,in order to make the operation of wind turbine and power grid more stable and reduce the economic loss,the following study deals with low / high pressure infiltration technology for permanent magnet wind turbines:First of all,understand the current wind power energy situation and the development trend and existing problems of wind turbine,and introduce the operation mode and unit type of wind power system.Starting from the topology of converter,according to the development trend and current situation of direct drive wind power,the basic technical criteria and requirements of voltage ride through and the latest progress of basic research on low / high voltage ride through by experts and scholars at home and abroad are briefly summarized.Then,the topological structure and operation principle of each unit of the permanent magnet direct drive wind power system are analyzed to facilitate the design and construction of the mathematical structure model of the wind turbine in this system,as well as the mathematical structure model of the main wind power generation modules such as the corresponding connected permanent magnet synchronous generator and the power electronic device Dual PWM converter under the equivalent coordinate transformation.Secondly,due to the different structure and function control characteristics of the two sides of the converter,this paper studies and analyzes the corresponding double closed-loop structure power control strategy of the converter side and the grid side under the stable state of the wind turbine.In addition,the influence of voltage surge is analyzed.Starting from the relationship of power variation under high voltage,a high-voltage through technical scheme of double unloading circuit which can reduce the DC side voltage according to the magnitude of voltage surge during fault is proposed.At the same time,when the grid side converter can not use its own compensation reactive power,it is connected with static synchronous compensator(STATCOM)to compensate certain inductive reactive power to the grid.According to the requirements of hvrt grid connection criterion,the technical strategy is analyzed and verified by Matlab / Simulink simulation software.Finally,based on the transient characteristics of the direct drive wind power system in case of low-voltage fault,several typical low-voltage ride through technologies are summarized and analyzed.Aiming at the shortcomings and advantages of various technologies,an improved LVRT technology scheme with hierarchical control is proposed,in which the DC variable resistance unloading circuit will select the right one in real time according to the degree of voltage drop According to the unloading resistance value,and using the simulation Matlab / Simulink software experiment simulation and analysis,effectively verify the superior performance of the control scheme coordination and complementarity. |
