Research On LVRT Control Strategy Of Direct Drive Permanent Magnet Wind Turbine

In recent years,the wind power industry has developed rapidly,but the volatility and randomness of wind energy will affect the stability of the voltage,and even in severe cases,the bus voltage will collapse.The new grid operating rules require wind turbines to have low voltage ride through capability,while direct drive permanent magnet synchronous wind turbines have higher low voltage ride through capability than doubly fed wind turbines.Therefore,this paper takes the direct-drive permanent magnet synchronous wind turbine as the research object,and deeply analyzes the problems and control strategies encountered in the process of low voltage crossing.The control strategy based on supercapacitor energy storage technology is studied in detail under the condition of various grid faults.The main contents are summarized as follows:(1)The working principle and mathematical model of direct-drive permanent magnet synchronous wind power system are introduced.The simulation experiment is used to analyze the pitch angle control strategy based on the control algorithm and the fault of the unloading resistance control strategy based on the auxiliary hardware technology when the grid voltage depth falls.In view of these problems,the dc side based on ultracapacitor energy storage technology is analyzed,studied and improved.(2)A power balance control strategy based on super capacitor is proposed.Aiming at the problem that the DC side voltage and the grid voltage will be violently fluctuated during the fault recovery based on the supercapacitor energy storage system on the DC side,the strategy is to change the DC side to the power outer loop current inner loop to achieve power smoothing,and the grid side based DC side voltage feedback is used to increase the grid side active output,thereby accelerating the power balance on both sides of the DC side.The simulation experiment by matlab\simulink shows that the proposed improved control strategy can eliminate the violent fluctuation of DC voltage and grid voltage,so as to achieve better and smooth recovery of grid voltage,so as to improve the low voltage ride-through capability of wind power system.(3)The control strategy of the direct-drive permanent magnet synchronous fan under asymmetric fault is improved.By analyzing the mechanism of 2 times power frequency component generated by the grid voltage under asymmetric fault,a new improved control strategy for PMSG based on supercapacitor under asymmetric fault is designed.On the network side,the second-order generalized integrator phase-locked loop is used to replace the single-phase phase-locked loop in the traditional method,and the accurate measurement of the positive and negative sequence fundamental components in the asymmetric fault is realized.The simulation in Matlab/Simulink shows that the control strategy can effectively suppress the network side active and DC side voltage double frequency fluctuations in the case of asymmetric faults,and improve the low voltage ride-through capability of the system under asymmetric faults.Improve the effectiveness of control strategies.