Asymmetric Fault Ride Through Research Of Wind Power Based On The Large Capacity Of SMES

With the deterioration of the global energy shortage,wind power is heading for a single large scale and increasing installed capacity.For large capacity grid connected wind turbine,because of the current limitation of power component,the traditional three-phase bridge type two level grid inverter can’t meet the demand any more.However the high rates of grid asymmetric fault make it important to research on asymmetric fault ride through of large capacity wind turbine.Firstly,in this paper the large capacity Superconducting Magnetic Energy Storage,SMES,is introduced to apply to circuit topology of grid connected MW level direct-drive permanent magnet synchronous wind turbine,D–PMSG.And the working principle of large capacity SMES is analyzed specially.At the same time,D-PMSG mathematical model,the wind turbine side converter mathematical model and the grid side multiple grid connected converter mathematical model are established.Secondly,the symmetrical components method is introduced and the traditional grid inverter power model is derived under the asymmetrical fault.The positive and negative sequence current control of grid side converter which is based on traditional power model is also introduced in this paper.Then the power expression of the zero sequence current is deduced,and the zero sequence current power expression is combined with traditional power model.The improved grid side converter power model which containing the zero sequence current and the corresponding control algorithm are obtained.For chopper control,the power correction link is added based on the traditional voltage loop current inner loop to adjust chopper charging and discharging dynamically during grid fault.The wind turbine side converter control adopts power external loop current inner loop control method,and reference power value is given according to the MPPT principle of permanent magnet direct-drive wind generators.Finally,simulation model of the large capacity of superconducting magnetic energy storage applied in MW level direct-drive permanent magnet synchronous wind turbine is built in the MATLAB/Simulink.Through the single-phase grid voltage drop in different range,the traditional control algorithm and the improved control algorithm which contains zero sequence current are compared to get the advantages and disadvantages respectively.The correctness and effectiveness of the improved control algorithm is verified.Comparing dc side with chopper and without chopper under single-phase grid voltage drop and two-phase drop,significant inhibition effect to grid current rise during the period of fault of superconducting energy storage is verified.The wind turbine’s grid side output negative sequence current and 2 times fluctuant active power are both eliminated under different grid fault conditions.