摘要
输电线路中使用串联电容补偿,可减少输电损耗,增加传输容量,提升经济效益。而当采用了串补的输电系统中的汽轮发电机组受到扰动时,就会因机网耦合而彼此互激,发生次同步谐振。大功率半导体技术的发展大大推进了柔性输电的进步,FACTS设备在电力系统各方面研究中得到了广泛的应用,在抑制次同步振荡上也不例外
本文首先介绍了次同步振荡的主要研究内容,并对汽轮发电机轴系的模型进行了详细分析,阐述了SSDC一般设计思路和本文中所采用的设计过程。然后分别研究了采用TCSC和SVC抑制次同步振荡。
针对TCSC常规控制无法阻尼系统次同步振荡的问题,分别采用分模态控制方法和改进模态控制方法在TCSC开环控制上附加次同步阻尼控制器。基于IEEE次同步第一测试模型进行了电气阻尼分析和时域仿真分析,而且考虑了TCSC安装位置的影响。而对电力系统中常用TCSC配合固定电容进行补偿的问题,对二者不同配比设计控制器,并分析了附加次同步阻尼控制器之后的电气阻尼。PSCAD/EMTDC中的暂态仿真验证了电气阻尼分析的结果。
SVC在电力系统中得到了广泛的应用,然而SVC的开环控制和闭环自动电压调节无法有效阻尼系统次同步振荡,因而文中基于分模态控制方法设计了附加次同步阻尼控制器。分析了SVC开环控制上附加该控制器之后的电气阻尼,并研究了将所设计的SVC移动到其他位置和容量变化时的电气阻尼,最后采用时域仿真验证了所设计的次同步阻尼控制器的有效性。
Series capacitors compensation is widely used in transmission lines to cut down losses, enhance the transmission capability and thus promote economic benefits. However, disturbance in power systems with series capacitors compensated in transmission lines would raise the danger of subsynchronous resonance (SSR). Development in power electronics advances flexible AC transmission systems (FACTS) greatly, which contributes the widely use of FACTS device in all fields of power systems research, and damping of subsynchronous oscillation (SSO) is no exception.
A brief introduction is made to the main content of SSO research in this paper firstly, along with detailed analysis of the modeling of a turbogenerator shaft system. After a summarily presentation of principles of FACTS for SSO mitigation, a procedure of designing Supplementary Subsynchronous Damping Controller(SSDC) applied in this thesis is given. Then it comes to the main part of the paper:research on damping of SSO using Thyristor Controlled Series Capacitor (TCSC) and Static Var compensator (SVC).
Given the fact that it's almost impossible to suppress SSO for TCSC with conventional control methodologies, a SSDC is designed, adopting sub-modal control method and modified modal control method separately. The effectiveness of the controller is validated using modified IEEE SSR first benchmark model by means of electrical damping analysis and time domain simulation, taken the location of TCSC into consideration. Knowing that TCSC is always used together with fixed capacitor, so according to different ratio of TCSC/fixed capacitor, different controller parameters are given, and then the electrical damping is evaluated for benchmark model with TCSC and its SSDC. Finally time domain simulation in PSCAD/EMTDC is employed to verify the results of electrical damping analysis, that is the SSDC can mitigate SSO successfully.
Static Var compensator (SVC) is widely used in power systems for its strong ability of voltage control and reactive power support but comparatively low cost, however neither SVC open-loop control nor closed-loop with automatic voltage regulator (AVR) is proved to be effective to mitigate SSO. Based on the idea of sub-modal control, a SSDC is designed to solve the SSO problem. The electrical damping of SVC with the designed SSDC is obtained, using the test signal method, the electrical damping when the location of SVC and rated capacity changes is also acquired. At last, the effectiveness of the SSDC is verified by time domain simulation carried out in PSCAD/EMTDC.
引文
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