中文摘要：

启动控制是双馈式变速恒频风机可靠并网运行的基础，同时柔性直流输电技术作为最具技术经济性的风电场并网方式，其工程应用日益广泛。该文分析了双馈式变速恒频风机的柔性直流并网控制，提出一种基于定子磁链定向和转子电流闭环控制的双馈式风机启动控制，以抑制并网过程中的冲击电流。为实现风电场稳态运行，设计风场侧模块化多电平换流器无源电压跟随控制器，使其在风机并网过程中呈现理想电压源特性；该控制策略无需检测风电场物理量，只在换流器本地即可实现。在PSCAD／EMTDC环境下进行49电平柔性直流风电并网仿真分析，并进行了现场试验，仿真和试验结果验证了所提出的风电场经柔性直流启动及并网控制策略的正确性。

英文摘要：

This paper analyzes the integration of doubly fed induction generator （DFIG）-based variable-speed constant-frequency wind turbine （VSCF） via a voltage source converter-based HVDC transmission system. A detailed algorithm for start-up control of DFIG-based VSCFs, based on stator flux orientation and closed-loop control of rotor current is proposed to depress the overcurrent of DFIG stator during the cut-in transience. Then the control principles of modular multilevel voltage source converter are discussed. For the smooth operation of wind farms composed of DFIG-based VSCFs, a passive network voltage tracing strategy is proposed to control the wind farm modular multilevel converter as an infinite voltage source, which dose not contain any information obtained from wind farm. Simulations of 49-level MMC in the PSCAD/EMTDC environment are presented to validate the effectiveness of proposed control schemes. Field tests results verify the effective performance of discussed system.