Analysis And Control Of Sub-synchronous Oscillation Of Complex HVDC/AC Power System

With the development of technology of electro electric, more and more HVDC systems are build in our country. The south power grids has became a "six AC and three HVDC large power transmission system". The TianGuan,GuiGuang and SanGuang HVDC systems are put into operation one and after. GuiGuang II and YunGuang HVDC systems are in building now. as a comparison to the AC transmission system, the HVDC systems have advantages of non synchronous connection,no current of capacitor,small amount of line loss and huge transmission ability, so it was widely used in long distance or benthal power transmission and asynchronous systems connection applications. Many power grids used HVDC\AC transmission system. The form of HVDC\AC power transmission become a developing trends in our country. But the operation of the HVDC systems will make the system's character of nonlinear more complex. If there are any disturbances in the HVDC or AC systems, the interaction of the two systems may make them performance worse or even unstable. Sub-synchronous oscillation is a serious stability problem that can exist in such power system described above. It not only can induce power oscillation in the system, but also can cause shaft fatigue and possible damage or failure of the generator involved. So it is important to analysis the characters of SSO and take some measure to damped it.This dissertation devotes itself mainly to the research on sub-synchronous oscillation in complex HVDC\AC power system and to provide resolve schemes of SSO in engineering application. In this dissertation, the stability analysis and control strategy studies on the Sub-synchronous oscillation are systematically and thoroughly investigated. It consists following parts:The first part of this dissertation summarized the pervious SSO analysis methods, and then developed transient torque time simulation method, combine with Fourier analysis method to calculate the oscillation modes. Developed the electric damping coefficient simulation method by fixed frequencies calculating, avoid the interactions of different harmonics induced by the inverter.In the second part, the system identify method is introduced to analyze the characters of sub-synchronous oscillation in complex power systems, it's developed the Prony method to fit for the study of SSO problem, get the reduced-order linear opened-loop model of the complex hybrid HVDC/AC transmission systems, and use transient torque simulation method to validate it.In the third part, it provided a accessible way to design the SSDC in complex power system using the pole assignment method and the Prony identify results.In the fourth part, with the reduced-order linear opened-loop model of the system get byProny identification method, using H_∞Robust Control theory, a SSDC was designed.Simulation results show that this damping controller can work efficiently when the system operation condition varied.The fifth part of the dissertation concentrates on the design of the HVDC damping controller based on Fuzzy immune control algorithm and complex torque coefficient theory. With this controller design strategy, SSDC was very convenient to realize in application. PSCAD/EMTDC Simulation results show that this controller can adjust it's parameter to adapt the different oscillation situations.