| In recent years,with the development of clean energy power generation technology,the proportion of new energy power generation technology in the power system has also increased.The reliability and stability of its grid-connected power generation have become more and more important.Direct-drive permanent magnet synchronous generator(D-PMSG)sets has the remarkable characteristics of large single-machine capacity,high efficiency and low cost,and has become the development trend of large-scale onshore and offshore wind power generation.The converter is an important bridge between the D-PMSG wind turbine and the power grid.When the sensor fails and the control strategy is poor,its reliability and stability will be reduced,which will affect the normal operation of the entire system;on the other hand,when the power grid occurs In the event of a fault,the wind turbine is disconnected from the grid,which will cause the grid voltage to collapse again.Therefore,it is necessary to improve the control strategy of the wind power grid-connected system to provide reactive power compensation to the grid to quickly restore the grid voltage,so the low voltage ride-through(LVRT)research of the wind power grid-connected system has Very important significance and practical application prospects.First,it introduces the current situation of wind power generation system,direct drive permanent magnet wind turbine converter technology and control strategy.Aiming at the main problems of direct drive permanent magnet wind power grid-connected system,low voltage ride through requirements and technology,wind energy conversion,transmission The working principle of chain,variable pitch angle and direct-drive permanent magnet wind power generation system is established,and its dynamic mathematical model is established;the topology structure of the NPC type three-level back-to-back converter is analyzed,and its output voltage equation is given;The eccentric load characteristics of wind turbines and the basic principles of maximum wind energy tracking and capture;use Simulink and S-function in MATLAB to build a wind turbine simulation model.Then,aiming at the machine-side and grid-side control strategies of the direct-drive permanent magnet wind power grid-connected system,based on the mathematical model of the system,using model predictive control theory,a finite control set model predictive control(FCS-MPC)is proposed.Strategy combined with the principle of space voltage vector,a converter based on sliding mode observer is constructed to optimize the FCS-MPC strategy,and its simulation model is established;the simulation results show that when the grid voltage drops to different degrees,it is compared with the traditional FCS-MPC Compared with the strategy,the improved FCS-MPC strategy can not only make the system run stably,but also has a strong low voltage ride-through capability,the reliability of the converter is enhanced,and the grid quality of the system is improved;a super capacitor energy storage is proposed.(SC-ESS)and an improved coordinated control strategy,the use of super capacitor energy storage system to achieve the DC side bus voltage to maintain stability;combined with the reactive power compensation requirements of the State Grid,an improved grid-side based on static synchronous compensator(STATCOM)operation mode is proposed The low voltage ride through control strategy enables the system to switch operation in unit power factor and STATCOM mode,and provides reactive power compensation to the grid voltage to assist grid voltage recovery;simulation results show that this control strategy can not only enable direct drive permanent magnet wind power generation The grid-connected system operates reliably,safely and stably,and its system has good low voltage ride through capability and grid quality.Based on the traditional FCS-MPC control strategy,the paper uses the model control theory to construct an FCS-MPC strategy based on current deadbeat.Then,based on the FCS-MPC strategy based on current deadbeat,a power function-based sliding is adopted.A mode observer is used to construct an optimizable FCS-MPC strategy to realize real-time observation of coupling items;on the basis of a super capacitor energy storage system,an optimizable FCS-MPC strategy based on a sliding mode observer is constructed,and finally proposed An improved grid-side low voltage ride through control strategy based on STATCOM operating mode is presented.The simulation results show that this method can make the system operate stably.The observer based on sliding mode control can more accurately estimate the grid voltage,and at the same time,it can reduce the system voltage.In addition,the control strategy can improve the grid quality of the grid-connected system and improve the low voltage ride-through capability of the D-PMSG grid-connected system.It provides new and improved ideas for the stability and safety of D-PMSG grid-connected power generation. |
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