| HVDC transmission technology is more and more widely applied in the power grid in our country, and large capacity and long-distance HVDC plays an important role in west east power transmission project. At present, there are multiple DC transmission lines which are runing in the southern power grid, with the ac power lines, it forms a typical AC/DC parallel transmission mode. In this kind of transmission mode, the system damping may be different from pure AC transmission mode in some typical conditions, therefore it is necessary to further study. In this paper, In view of the central point of busbar short circuit, DC line fault closure, AC/DC parallel switch to DC under typical working conditions such as asynchronous operation has carried on the detailed modeling and simulation. Compared the small signal stability analysis with time-domain simulation results, and then the paper analysis for the characteristics of the damping of the typical operating conditions change. Firstly, in order to improve the system damping in typical operating conditions, this paper uses the field datum collected by synchronized PMU, then obtains the system low frequency oscillation identification information and weak damping unit through the Prony, and applies technology of fuzzy clustering to get homology fleet; Secondly, in view of the oscillation in the area and interval oscillation mode respectively take different damping strategies. The strategy in theory can be applied to online control damping when occurring low-frequency oscillation. The simulation results proved the effectiveness of the method in this paper.
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