Research On Subsynchronous Damping Effect Of VSC-HVDC

As the development of the economics, large-scale and long-distance AC transmission and DC power transmission became the new features of the power system. For a long time, long-distance compensated transmission lines and HVDC power system are the two main factors which lead to the subsynchronous oscillations of the power system. To solve this problem, lots of researches had been carried out and the corresponding solutions were proposed. However, in the last decades, a new generation of HVDC transmission technology, voltage source converter based HVDC(VSC-HVDC), has been developed rapidly in the world. There were literatures point out that VSC-HVDC could damp power system oscillaions. It is worthwhile to furtherly invesigate that if VSC-HVDC could be a new approach to the subsynchronous oscillation damping. Hence, it is necessary to study the damping effects of VSC-HVDC to its adjacent generation units’subsynchronous oscillation.Firstly, the widely used complex torque coefficient method and its time-domain solution are deeply analyzed. The applicabilty of complex torque coefficient method and its time domain solution in multiply generator systems are disscussed. Then a verification of the previous disscussion based on the IEEE second benchmark model is shown.Secondly, a simulation model is established based on PSCAD/EMTDC simulation platform, which illustrates a generator unit transmits power though series compensated lines and VSC-HVDC. Based on complex torque coefficient method, the impact on subsynchronous damping characteristics is carefully analyzed where VSC-HVDC is under different operation mode and control strategies.At last, based on Prony recognition algorithm, the transfer function of state variables in a complicated AC-DC systems is obtained. In order to effectively suppress the subsynchronous oscillation of generators, an auxiliary damping controller of VSC-HVDC based on phase compensation method is proposed.