Research On Symmetrical Fault Transient Analysis And Low Voltage Rid Through Of Doubly-fed Wind Power System

As we all know,one of the main reasons for the environmental crisis is the abuse of traditional fossil fuels in recent years.The main trend today is the development of renewable energy.Renewable energy is a major feature of wind energy.At present,the development of wind power is an important part of the development of new energy.The growing scale of wind power makes it impossible to ignore the interplay between the grid and wind turbines.At present,the main wind turbine in the market is doubly-fed wind generator.This is due to its high efficiency of energy conversion and small capacity of the field converter and other advantages.Therefore,when the grid voltage drops,the dynamic change of doubly-fed wind turbine is worth studying.At the same time,the safe crossing and the stable operation of the grid are worth studying.The main research content of this paper is as follows:This paper firstly describes the development trend and general situation of wind power in the world today,and the principle and reason of low voltage crossing are discussed.At the same time,the control strategy and power generation principle of the doubly-fed fan are studied.The mathematical model of the doubly-fed motor in three phase stationary and two phase rotating coordinate systems is analyzed.The principle and control strategy of crowbar circuit applied to the rotor side of DFIG under the three-phase symmetric fault state are analyzed.Firstly,based on the dynamic characteristics of the magnetic flux chain and the equivalent impedance under the condition of symmetric sags,the common error of attenuation constant analysis is corrected.The equivalent circuit diagram of the doubly-fed generator is obtained based on the space vector method.The study of rotor current dynamic response is based on pry bar circuit access and known flux changes.Due to the pry bar circuit,the wind power system needs a lot of reactive power.Then,according to a series of mathematical derivation and analysis,the relationship between slip and reactive power demand is obtained.Slip can be suppressed due to the rapid change of pitch Angle.Thus,the fan with backward voltage drop will have lower demand for reactive power,which effectively reduces the reactive power provided by the power grid.Therefore,the application of variable pitch strategy is beneficial to the restoration and reconstruction of power grid voltage.Finally,simulation software is used to verify the effectiveness of the proposed scheme.In addition to adding the hardware protection mentioned above to the rotor side,adrc can also be applied.Firstly,the deficiency of PID control strategy widely used in wind power system is described.Then,the principle of adrc and the components of adrc are explained and the mathematical model is established.Since the total disturbance is estimated by the extended state observer and compensated to the system at the same time,adrc improves the fault crossing ability of the wind power system.Finally,the simulation results show that the adrc strategy has better system dynamic performance and stronger robust performance thanthe typical PID control.The undulating current of the rotor side is suppressed and the fault crossing ability is improved.