| For the moment, direct-current transmission has gotten comprehensive application in our country, and at a few decades, for the future, direct-current transmission will have more extensive potential application. But, the interaction of HVDC system and generator sets shafting quality piece, which may create a type of shape complicated electric stabilization problem, i.e. subsynchronous oscillication. In this paper, the problem of subsynchronous oscillication (SSO) of HVDC is studied systematically, and the control for subsynchronous oscillation damping is investigated. The main works are recapitutaed as follows:1. Briefly generalize and summarize the method of analysis for subsynchronous oscillaition in electric power system, and the method of monitor and control for subsynchronous oscillation.2. The analytical method is used to analyse subsynchronous oscillation in HVDC system, the stimulating conditions of subsynchronous oscillation are revealed, which lay the solid foundation for subsynchronous oscillation in HVDC system further analysis and control.3. Establishing the small-perturbance system model for the study of subsynchronous oscillation in HVDC system, including the generator shaft system model, electromagnetism loop model, excitation system model, AC/DC network transiet model and DC control system model.4. Using the eigenvalue method and complex torque coefficient method, a detailed anlysis of subsynchronous damping for HVDC system and AC/DC hybrid system are performed. The impacts of the DC power level, the firing delay angle in converting station, parameter setting of HVDC rectifier control system and impedance value of AC line on the subsynchronous damping also are discussed.5. A supplemental subsynchronous damping controller (SSDC) for HVDC system is designed with using output feedback linear optimal control theory, time domain simulations using PSCAD/EMTDC show that the designed damping controller can effectively damp the subsynchronous oscillation of HVDC system.
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