| As the distribution of electric power and load is unbalanced in China, long-distance, high-capacity transmission mode is widespread. In order to increase transmission capacity, the direct-current transmission technology and the series capacitor compensation technology have gotten comprehensive application in our country. However the application of the direct-current transmission technology and the series capacitor compensation technology can both cause the subsynchronous oscillation (SSO) which may lead to turbine-generator shaft failure.In this thesis, subsynchronous oscillation of ac/dc power systems is focused and the mechanism of subsynchronous oscillation caused by HVDC is analyzed in detail. For the subsynchronous oscillation modeling of Yimin power plant, the impact of shaft parameters upon torsional frequencies is studied based on sensitivity analysis method. Then the eigenvalue analysis method is utilized to analyze the impact of HVDC control system parameters on the real part of the SSO mode eigenvalue.Considering that the damping effect of SSDC equipped in HVDC system is not so good when the systems suffer from small disturbances, the scheme to use supplementary excitation damping controller (SEDC) and supplementary subsynchronous damping controller (SSDC) to damp the SSO in AC/DC system is proposed. The feasibility of the scheme is analyzed based on the principle of SEDC and SSDC. Finally frequency-domain analysis time-domain simulation verified the conclusion.On basis of the above AC/DC systems, the principle and the structure of SSDC is discussed and based on phase compensation principle supplementary subsynchronous damping controller (SSDC) is designed. Then the effectiveness of the designed controller is verified by time-domain simulation method. |
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