Study On Analysis And Countermeasures Of Subsynchronous Oscillation Caused By HVDC

In China, it is a prominent characteristic that energy bases and load centers isreversely distributed. Long distance and large capacity power transmission, asynchronousinterconnection of regional power grid, as well as optimal allocation of energy resources,all of them need the support of high power HVDC transmission technology. However,with the increasing number of newly HVDC projects in China, the structure of grid isbecoming more and more complex, the stability problems caused by HVDC emerge, andthe problem of subsynchronous oscillation which threatens the safe and stable operationof power system is one of them. Therefore, there are very important theoretical andpractical value to research the SSO problem caused by HVDC and its countermeasures. At first, the paper researches the mechanism of SSO caused by traditional hybridAC/DC system, and builds the linear mathematical model of each elements of the hybridsystem. The model has great versatility and is adapted to the analysis of SSO. Take asimple HVDC system as an example, the paper analyzes the damping characteristic ofthe system by the eigenvalue method, and studies the regular pattern of the influence ofoperation parameters to eigenvalues. It lays the groundwork for the SSO study ofmultimachine system and design of damping controller. After that, the paper researches the multimachine and multimodel SSO problem.Based on the Guizhou grid, it makes UIF and stability analysis for the machines ofGuizhou-Guangdong II HVDC system. And it makes a equivalent system which takesPannan plant as the main study object based on the screening results by UIF methed. Itanalyzes different mode dampings of the plant under different operation conditions. The paper takes SEDC as the countermeasures to deal with the SSO problem inPannan plant. It states the mechanism of SEDC, and analyzes the damping characteristicof the system with SEDC. The research proves that SEDC can increase the damping inmode frequency, and there exists the damping conservation phenomenon. Thus, the paperproposes to optimize the magnification of SEDC by GASA algorithm. Besides, it makestheoretical analysis and simulations to veriy the influence of excitation system (with PSS)caused by SEDC. Finally, in order to test the mitigation effect of SEDC physical device in practicalproject, the paper builds the RTDS model of Guizhou grid, and inserts SEDC device andABB excitation device in closed loop. The effectiveness and stability of the simulationplatform are proved by the stability test. And the output signal of SEDC throughexcitation system is also tested. SEDC has favorable mitigation effect to SSO problemsinspired by different types of faults.