Research On The Low Voltage Ride Through Technology For Offshore Wind Farm Grid Connection System Based On VSC-HVDV

Currently, the construction of large scale wind farms has been transforming from the land to the sea. The offshore wind power has already developed into the main potential source of wind power. Due to the favourable characteristics of good grid connection, D-PMSG has been increasingly applied to offshore wind farm. Because of the offshore wind farm uses the VSC-HVDC transmission technology to transfer power to the grid, the dynamic response speed and fault response characteristics of the offshore wind farm with VSC-HVDC transmission are different from the AC transmission system, therefore, the research on the low voltage ride through technology of D-PMSG in the offshore wind farm which is composed of VSC-HVDC has certain engineering application significance.The mathematical model of D-PMSG and VSC-HVDC is established in this paper. An advanced control strategy of the converter station has been put forward based on offshore wind farm which is composed of D-PMSG through the connection between the grid and VSC-HVDC transmission technology. The sea convert station adopts double loop feedback linearization and decoupling control while the shore station adopts double closed loop vector. The simulation model of offshore wind plant through VSC-HVDC grid connected system testifies the validity of the established model and the improved control strategy.This paper analyzes the influence of the wind farm and the grid bus at the grid and the grid connected to the wind farm on the VSC-HVDC grid connected system. For a wind farm and dot bus fault, on D-PMSG unit take Paralleled DC chopper circuit and the grid side converter operation in reactive power priority control mode, to maintain the DC bus power system stability, and for wind farm and network bus provide reactive power support; Based on the hybrid Crowbar circuit system, the technology scheme of the coordinated control strategy for the grid connected system of offshore wind farm and the hybrid Crowbar circuit system is proposed. Simulation results show that the coordination of the control strategy and the blend of crowbar circuit can reduce unbalanced power of the system, restrain the fluctuation of DC bus voltage and maintain the stability of DC bus voltage and thus, provide reactive power to the recovery of voltage on the grid. Finally, the simulation results show that the proposed scheme improves the capability of the low voltage ride on the offshore wind farm through VSC-HVDC grid-connected system.