The Research On Voltage Source Converter Based High Voltage Direct Current Considering Wind Power Fluctuation

How to reduce the fluctuation of wind power and increase the penetration rate of wind power is an important issue in recent years.Unstable wind power generation,insufficient trans-regional power transmission capacity,and mismatched construction schedules have greatly reduced the utilization rate of wind power.The Voltage Source Converter based High Voltage Direct Current(VSC-HVDC)can be directly connected to weak systems or passive networks without filtering and non-compliance.Many advantages such as power compensation device,convenient power flow reversal,and decoupling control of active and reactive power,provide technical support for the large-scale grid connection of wind power,but cannot completely eliminate The problem caused by wind power instability,For exemple,grid-connected voltage instability and random power fluctuations.(1)Firstly,based on the composition of the VSC-HVDC system,comprehensively analyze the types of grid-connected converters;then,according to the working principle of the grid-connected converters,rotate the coordinates simultaneously in the abc three-phase static coordinate system and the dq two-axis synchronously.The mathematical model of the converter is established under the department;finally,the system-level control method of the VSC-HVDC system is designed through the control method of the converter,which provides an effective theoretical basis for the control method adopted by the wind power into the VSC-HVDC system.(2)Based on master-slave control,voltage margin control and DC voltage droop control,a joint control strategy suitable for The Voltage Source Converter multi-terminal DC system(VSC-MTDC)is proposed;the characteristic curve of the Voltage Source Converter multi-terminal DC system and the joint control strategy process are analyzed;The Voltage Source Converter of five-terminal flexible DC system as a case,and a simulation model is established.The results show that the proposed control strategy can effectively reduce the fluctuation of wind power and stabilize the DC voltage on the DC side.(3)In view of the problems of DC side voltage instability and DC line failure when wind power is integrated into the VSC-HVDC,considering using superconducting magnetic energy storage(SMES)to stabilize system power fluctuations.A parameter optimization method for superconducting magnetic energy storage is proposed with the smallest cumulative DC power fluctuation,the smallest cumulative DC voltage fluctuation,and the smallest initial inductance of Superconducting magnetic energy storage as the three optimization objectives.The particle swarm algorithm is used to design the optimal parameters of superconducting magnetic energy storage;Take a small wind farm in China as an example,and compare and analyze it under the three conditions of not installing superconducting magnetic energy storage,non-optimal SMES parameters,and optimal SMES parameters.The simulation results show that the SMES configured by the proposed optimal parameter calculation method can effectively suppress the DC side power fluctuation,stabilize the DC voltage,limit the peak fault current,and improve the stability of the system.