Research On Technologies Of Low Voltage Ride Through For Grid-connected Direct-driven Permanent Magnet Wind Power Systems

With the rapid development of wind power,the proportion of wind power in the power grid is higher and higher,and the impact of wind power on the power grid is increasing.In this situation,the power grid for wind power grid technology has higher requirements.As one of the key technologies of wind power integration,low voltage ride through has become the research focus of wind power grid connected technology.In this paper,the operating characteristics of permanent magnet direct drive wind power generation system are studied,and the corresponding low voltage ride through scheme is proposed according to the dynamic response of the system in the voltage sag of the grid.Firstly,this paper introduces the development background of wind power generation,and the research significance of the low voltage ride through and the domestic and foreign research status quo.Analyzing each part of permanent magnet direct drive wind turbine system model,and the complex model of the three-phase static coordinate system is transformed into a simplified model of the synchronous rotating coordinate system.Vector control technology is used to realize decoupling control.Secondly,The dynamic response of permanent magnet direct drive wind power generation system under voltage sag is analyzed.From the view of increasing hardware circuit,comparison of several existing crowbar circuit,and focus on the DC side crowbar circuit.The DC side of the crowbar circuit switching strategy is analyzed.The selection principle of energy resistance crowbar circuit is discussed.Simulation results verify the validity of the DC side crowbar circuit applied to low voltage ride through.Finally,from the point of improved control strategy,a low voltage ride through scheme based on power feedback control pseudo maximum power tracking is proposed,and control strategy is improved,which uses maximum power tracking control loop to realize low voltage ride through.The low voltage ride through scheme of grid side converter operating in STATCOM mode is studied.The control strategy of grid side converter by switching from unity power factor mode to static reactive power compensation mode is analyzed.When the grid voltage drops,the grid side converter provides reactive power to the grid to achieve low voltage ride through.