| Due to the reversed distribution of natural resources and load centers in China, Ultra high voltage AC transmission system (UHVAC) and ultra high voltage DC transmission system (UHVDC) have been used in order to realize the large capacity and long distance power transmission. As a major methods of enhancing the transmission capacity of AC transmission system, series compensation have been widely used. However, it may cause subsynchronous oscillation (SSO) and will threaten the stability of large thermal power unit and even the whole power system. With the increasing of wind power, photovoltaic (PV) power and other new energy generation connected to power system, the problem of subsynchronous oscillation becomes more complicated. In this paper, the following research has been carried out on the problem of power system subsynchronous oscillation with large-scale new energy:The operation principle and operation characteristics of doubly fed induction generator (DFIG) are elaborated. wind turbine model, shaft model, induction generator model, converter and its’ control system model and wind turbine control system model in the full range of wind speed are established. Meanwhile, per-unit equations of all components of DFIG are given, which lay the foundation of the following study of SSO.Aimed at SSO problem in power system where DFIG wind farm connected to grid through series compensated transmission lines, the small signal analysis model and the time domain simulation model which are suitable for studying the SSO problem are established in software MATLAB and PSCAD respectively. By using eigenvalue analysis and time domain simulation, SSO characteristics of research system are described, and the effects of wind speed, series compensation degrees, PI parameters of the rotor side converter (RSC), PI parameters of the grid side converter (GSC), and line resistance on SSO are studied. The frequency domain results are also verified by time-domain simulation method.For SSO problem in power system where the bundled wind power generator and thermal generator connected to grid through series compensated transmission lines, the simulation models which are suitable for studying the SSO problem are established in software PSCAD. The SSO characteristics of research system are analyzed using time and frequency domain method. Meanwhile, the effects of wind power penetration level, wind speed, location of wind farm on thermal generation SSO problem are studied.In order to study SSO problem in power system where the bundled PV generation and thermal generator connected to grid through series compensated transmission lines, the modified model which contains grid-connected PV generation are established in software PSCAD based on IEEE SSR first benchmark model, complex torque coefficient method and time domain simulation method are used to analyze the effects of PV on SSO characteristics of research system. The active and reactive type additional damping controller and mixed additional damping controller are designed based on multi-channel structure are designed. Meanwhile, The influence of gird-connection PV capacities and types of additional damping controller on suppressing SSO are also analyzed. |
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