Study On Decentralized Coordinated Control Scheme Of Small-disturbance Stability Of Interconnected Power Systems

Nowadays the development trends of our grid are West-to-east power transmission, mutual supply between South and North thus forming a large interconnected power system, which is decided by the primary energy distribution and economic development in our country. With the scale of power system becomes larger and larger, higher demands for the reliability and stability of power system are put forward. However, with the rapid growth of power load as well as the weakness of present network configuration, some dynamic stability problems would take place, among which low frequency oscillation is just one of the most important issues. In this thesis, studies on the small signal stability research in low frequency oscillation are done by eigenvalue analysis methods. The main work is as follows:(1) The effects of small disturbance stability results caused by Canay model and model parameters are studied by eigen-analysis. Based on electrical equations, the linearized model of synchronous machine is established. With the Phillips-Heffron six-coefficient model and twelve-coefficient model including damper windings considered, an equivalent simplification method is proposed. Then Canay model is presented, compared with traditional model, and the conclusion is that: The traditional model is not appropriate for analyzing the small disturbance problem especially when the synchronous machine is under light load. As a conclusion, Canay model should be used in the analysis of small disturbance problems.(2) Based on EMD and Prony algorithm for identifying modal parameters of sub-synchronous torsional oscillation (SSTO), a novel method for extracting SSTO signal by EMD and re-sampling is presented in this paper; then model parameters of SSTO are obtained by Prony algorithm; finally, the Prony analysis based on a plant measured data is taken to demonstrate that this method can effectively improve the accuracy of SSTO modal parameters.(3) A decentralized coordinated control strategy about LFO is discussed, which contains equivalent modal control,inverse system compensation and multi-band theory. Firstly the equivalent modal control idea is used for realizing controlled modals and lasted modals; then the inverse system compensator is proposed to compensate for the actuator dynamic characteristics, with the combination of blend multi-band idea in additional excitation control and additional governor control, and in this way, lower-frequency band modals are controlled by the governor system as actuator and higher-frequency band modals are controlled by the excitation system as actuator, so LFO modals can achieve decentralized coordinated control effect. Finally the validity of this control strategy is demonstrated by the calculated results of the 4 machines 2 areas system.