风火打捆经直流送出系统的次同步振荡问题研究

During the transmission of massive wind-thermal-bundled power via HVDC transmission system, the sub-synchronous oscillation (SSO) in thermal and wind power system might be induced, and then the secure and stable operation of massive wind power base and transmission system is influenced. The key problems about equivalent method of wind farm, interaction forms between wind turbines and thermal generators, and the applicability of SSDC in wind-thermal-bundled system, are not effectively resolved. Projects of the transmission of massive wind-thermal-bundled power via HVDC transmission system will be launched in the future, and SSO has become an urgent problem in the secure operation of grid..The rational equivalent of wind farm is conducted in this project. The equivalent model applying for the study of SSO in wind farm is built, and the converter is equivalent to controlled source in order to improve calculation efficiency. The mechanism of SSO in wind-thermal-bundled power system is revealed. The key factors that impacts SSO, including proportion of wind power and thermal power, DC power level, and fire angle of converter, are researched. Based on the sub-synchronous damping controller (SSDC) used to damp SSO in thermal generator and the fact that torsional natural frequency of wind turbine generator is lower than that of thermal generator, the function of SSDC is expanded. For improving the ability of defending SSO, the three-layer defense system consisting of SSDC, STACOM in wind farm and interlock tripping plan is proposed. At last, the achievement of this project is verified by Ha-zheng UHVDC project.

大规模风电与火电打捆经高压直流输电送出时，可能会诱发风、火电系统的次同步振荡问题，影响风/火电基地与外送系统的安全稳定运行。风电场等值方法、风/火电机组相互作用形式、SSDC对风火打捆系统的适用性等关键问题，现有研究均未有效解决。未来风火打捆经直流外送工程将逐步启动，次同步振荡已成为我国电网安全稳定运行亟待解决的重要问题。.本项目拟对风电场进行合理等值，建立适用于研究次同步振荡的等值模型，并采用受控源对换流器进行等效以提高计算效率；揭示风火打捆条件下次同步振荡机理，研究风火比例、直流功率、换流器触发角等关键因素对次同步振荡的影响；基于抑制火电机组次同步振荡问题的SSDC，根据风机轴系自然扭振频率比火电机组低的特点，扩展SSDC的功能，并提出由SSDC、风电场STATCOM和联锁切机预案组成的三层防御体系，提高风火打捆系统抵御次同步振荡的能力；最后，通过哈郑直流工程验证本项目成果的准确性。

风火打捆经高压直流输电（HVDC）送出是大规模风电外送的重要输电形式，但可能引起次同步振荡问题（SSO），影响系统的稳定运行。项目主要以双馈风电场（DFIG）为研究对象，研究了DFIG与火电机组打捆经HVDC送出系统的的建模方法、次同步振荡发生机理及抑制措施。具体内容如下：. 针对传统方法建立多源系统的状态空间模型难度较大的问题，提出一种图形化建模方法。该方法基于由基本元件构成的图形化模型库（状态空间形式），可以直观地构建复杂系统状态空间模型。相对于传统方法，图形化建模方法具有独立性强、灵活性高、可视性好和扩展性强的优点。.分析了DFIG并网次同步振荡的发生机理，提出一种基于自抗扰控制（ADRC）的DFIG转子侧换流器抑制策略。ADRC通过采用扩张状态观测器对系统次同步扰动进行实时估计与反馈补偿，实现多运行工况下的SSO抑制。结果表明，ADRC抑制策略更适用于出力随机波动、扰动因素较强的风力发电系统，可以有效抑制DFIG与固定串补之间的次同步控制相互作用。. 分析了DFIG与HVDC之间的次同步交互作用。基于图形化建模方法，建立了系统的小信号模型，并验证了模型的正确性。特征值分析和参与因子分析表明，DFIG和HVDC两个系统之间的交互作用并不明显；系统稳定裕度较大，发生SSO的风险较小。. 基于特征值法和时域仿真法，研究了DFIG接入对火电机组与HVDC之间SSTI的影响，分析了直流附加宽带通式次同步阻尼控制器（SSDC）抑制风火打捆经HVDC系统次同步振荡的有效性。结果表明，DFIG接入后火电机组轴系各振荡模态的模态阻尼有所提高，宽带通式SSDC仍具有抑制效果。