Low Voltage Crossing Technology Of Permanent Magnet Direct Drive Wind Power System Based On Improved Auto-disturbance Rejection Control

With the continuous development of energy technologies around the world,wind power generation systems have become the most important part of new energy power generation in recent years.Its increasing share of power generation in the power grid has attracted more and more attention around the world.Each country has issued the operating standards in case of grid fault.When a grid fault causes a voltage drop,the power generation system will not be disconnected from the grid,and provides reactive power support to the grid to support voltage recovery during the voltage sag until the grid fault is eliminated.Direct drive permanent magnet synchronous power generation system is a representative power generation system in today's wind power generation,which is widely used in the wind power generation industry.For the nonlinear,strong coupling,multivariable complex system of wind power generation,combined with the uncontrollable,time-varying,and random characteristics of wind energy,it makes it difficult for traditional PID control to achieve the desired control quality.Therefore,according to the permanent magnet synchronous power generation system,this paper designs a new type of control technology that does not rely on models and has strong anti-interference ability to solve the control problems encountered in low voltage ride-through of wind power systems.The main research work is as follows:1)Starting from the basic structure of the permanent magnet wind power generation system,it focuses on the five modules of wind turbines,synchronous generators,AD / DC converters,DC / DC converters,and DC / AC converters,and details the mathematical models of each module.Then,the principle of maximum wind energy tracking of wind power is analyzed in depth,and the variable pitch control algorithm is used to control the wind turbine to change with the change of wind speed,so that the system runs at the optimal blade tip speed ratio and the maximum wind energy utilization coefficient.Finally,the motor is mainly explained that the control strategy of the transformer on the grid side.The motor side adopts the zero d-axis current control strategy,and the grid side adopts the voltage and current double closed-loop decoupling control.2)Based on the structure of permanent magnet wind power generation system,the low voltage ride-through technology of permanent magnet power generation system is analyzed.Firstly,the types and characteristics of grid voltage sags are described.This paper focuses on three-phase voltage symmetrical fault.Then the various influences of power grid voltage drop on permanent magnet wind power generation system are analyzed,and it can be seen through the matlab simulation model waveform that the wind power will not rise smoothly due to the unsuccessful grid connection,which will cause the grid-side converter to overshoot.In order to solve the problem of over-current when the grid voltage drops,this paper studies a reactive power compensation strategy based on feed-forward control of the grid to realize the charging distribution of active and reactive current.The control strategy can achieve the purpose of restraining the impulse current from the output side of the transformer.Meanwhile,in order to solve the problem of bus over-voltage,this paper outlines the existing Crowbar circuit protection schemes based on energy-consuming and energy-storage types and the low-voltage ride-through control methods of Crowbar circuits.3)Aiming at the fault condition of the symmetrical power grid,when the grid voltage drops deeply,the low voltage ride-through control strategy based on ADRC control and optimized ADRC control is proposed to overcome the shortcomings of traditional PI regulation in suppressing bus voltage spikes.Firstly,the control mathematical model of ADRC is analyzed.Combining with the mathematical model of the grid-connected transformer of the permanent magnet wind power generation system to establish a disturbance immunity paradigm model,and the principle of each part of the paradigm is analyzed.Then based on these principles,an ADRC control method is designed.In order to optimize the parameter setting problem,an optimized ADRC control low voltage ride-through control method is designed.Finally,a model of a permanent magnet synchronous wind power generation system was built in matlab,using PI control,ADRC control,and optimized ADRC control.Through simulation results,the three control strategies were compared to suppress the differences in bus voltage spikes.Using the control strategy based on ADRC and optimized ADRC to obtain the ideal suppression result.