Analysis Of Low Frequency Oscillation In Power System With Wind-Thermal-Bundled Power Transmitted By AC/DC System

Wind-termal-bundled power transmitted by AC/DC system will be an important way for electricity delivery of large energy base in northeast, north and northwest region of China in the future, so it is significant to study the modal mechanism and characteristics of low frequency oscillation in this manner. In this paper, small signal stability of power system with wind-thermal-bundled power transmitted by AC/DC system is studied. The main work of this paper is as follows:(1) Based on PSD-BPA software which is developed by CEPRI (China Electric Power Research Institute), the simulation models suitable for small signal stability analysis of power system with wind-thermal-bundled power transmitted by AC system (take two-area four-machine system and provincial power system as examples) and AC&DC system (take single-machine infinite-bus system as example) are estabilished.(2) Modal characteristics of low frequency oscillation of power system with wind-thermal-bundled power transmitted by AC system are studied. The simulation results show that wind-termal-bundled power transmitted by AC system will not introduce a new low frequency oscillation mode, it mainly affects the modal characteristics of low frequency oscillations by changing the output circumstances of conventional synchronous generators. Wind power penetration level and wind-thermal-bundled power delivery mainly influence damping characteristics of interarea modes, the impact on local modes is much smaller, the PSSs (power system stabilizer) of synchronous generators can improve damping ratio of power system to some extent. The damping ratio of interarea mode become bigger and bigger with the increase of wind power penetration level whether local consumption or interarea consumption. The damping characteristics of interarea modes with local consumption are much better than interarea consumption under the same wind power penetration level.(3) Modal characteristics of low frequency oscillation of power system with wind-thermal-bundled power transmitted by AC&DC system are studied. Dynamic simulations of power system with wind-thermal-bundled power transmitted by AC&DC system are accomplished with wind speed disturbance and system short-circuit fault respectively, the simulation results show that the system is better damping. By altering spining reserve capacity of thermal power (option A) and unit operating condition of thermal power (option B) separately, the proportion of wind power is changed, the simulation results show that:When PSSs are all put into operation, the damping ratio of option A increases first and then decreases with the increase of wind power proportion (small amplitude), the damping ratio of option B increases with the increase of wind power proportion (large amplitude), the damping characteristics of option B are much better than option A under the same wind power proportion. When PSSs are all out of operation, the damping ratio of option A increases with the increase of wind power proportion (large amplitude), the damping ratio of option B increases with the increase of wind power proportion (small amplitude), the damping characteristics of option A are much better than option B under the same wind power proportion. In the same proportion of wind power, the impact of DFIG and PMSG on modal characteristics of low frequency oscillation of power system with wind-thermal-bundled power transmitted by AC&DC system has little difference. When PSSs are all put into operation, the impact of DC allocation ratio on the damping ratio is much smaller. When PSSs are all out of operation, the damping ratio of system increases with the increase of HVDC allocation ratio (large amplitude). HVDC control mode has no effect on the system damping.