基于MMC-HVDC的海上风电柔直系统频率波动抑制技术

Frequency Fluctuation Suppression Technology of Offshore Wind Power Generation Plants Based on MMC-HVDC Transmission

海上风电柔直系统发生故障等暂态过程时,系统频率波动会影响健全风电场的正常运行,严重时将引起大规模风机脱网。为此,分析了海上风电系统交流电压频率动态与电压d轴、q轴分量的关系,进而提出一种频率波动抑制方案,在换流站控制器中引入频率环对系统母线电压的频率波动进行控制。考虑到风电系统不同位置频率动态的差异性,提出一种海上风电系统频率协同优化控制方案,利用风电机组的无功输出能力对风机汇集点处的频率波动问题进行进一步优化控制。最后,在MATLAB/Simulink中搭建基于模块化多电平换流器高压直流输电(modular multilevel converter based high voltage direct current transmission,MMC-HVDC)送出的海上风力发电系统仿真模型。研究结果表明:在系统故障与运行工况突变的情况下,频率协同优化控制方案可将风电系统母线电压与风机汇集点处电压的频率波动抑制到无控制时的30%以下。所提方案有效地实现了对风电柔直系统暂态情况下的频率波动抑制。

The frequency fluctuation of the offshore wind power generation system based on MMC-HVDC will affect the normal operation of the healthy wind plants when fault occurs or in other transient conditions.In serious cases,large-scale off-grid wind turbines may take place.For this reason,we analyze the relationship between frequency and d-axis and q-axis of the AC voltage in offshore wind power system,and propose a frequency control scheme.A frequency loop is introduced into the offshore converter controller to stabilize the frequency of the bus voltage.Considering the distinctions of frequency in different locations,a scheme of frequency cooperative optimization control is proposed to further optimize the frequency fluctuation at the wind turbine collector substations.Finally,a simulation model of offshore wind power plants based on MMC-HVDC was built on the MATLAB/Simulink.The research results show that,with cooperative optimization control,the frequency fluctuation in wind power system bus voltage and wind turbine collector substations can be reduced to less than 30%of that without control in conditions of system fault and abrupt change of operation.The proposed method can be adopted to effectively suppress the frequency fluctuation of wind power generation system based on MMC-HVDC in transient conditions.