Control strategy for direct-drive wind power system under asymmetric grid voltage sag

In view of problems of DC side overvoltage, grid-connected current distortion and grid-connected power fluctuation existed in grid-connected operation of direct-drive wind power system under asymmetric grid voltage sag, superconducting magnetic energy storage was connected in parallel at DC side of grid-connected converter. Meanwhile, positive and negative sequence current control to suppress the grid-connected power fluctuation was used to improve control strategy for grid side converter based on analysis of mathematical model of the grid side converter under asymmetric grid voltage sag, so as to stabilize DC side voltage, improve grid-connected current quality and suppress grid-connected power fluctuation. The simulation result verifies correctness and effectiveness of the control strategy.