Research On Subsynchronous Oscillation Analysis And Suppression Strategy Of Wind Power Integrated System

Subsynchronous oscillation is a continuous divergent oscillation caused by LC resonance in the circuit or rapid regulation of power electronic devices,which is one of the common problems in the field of power system stability analysis.Early research focused on the thermal power integrated system.In recent years,new energy has been widely exploited and utilized,especially the conversion and utilization of wind energy has become a research hotspot all over the world.Large-scale wind power integration is an important direction for the future development of China’s power grid.However,due to the different mechanism of wind power generation and the power electronic equipment used in integrated system,it may lead to amplified subsynchronous harmonics,which easily causes subsynchronous oscillation in wind power integrated system.In recent years,subsynchronous oscillation caused by wind turbine interconnection has occurred successively in many regions of China.Therefore,it is of great significance to analyze the causes and influencing factors of subsynchronous oscillation in wind power integrated system.Firstly,the equivalent model of wind farm connected by series compensated transmission lines is established,and the control strategy of doubly fed induction generator is analyzed.Then a time-domain test model of wind power integrated system for studying subsynchronous oscillation is constructed in PSCAD,which provides a research object for the analysis of subsynchronous oscillation.Secondly,the linearization of wind turbine converter is carried out by small signal analysis method.Based on the traditional impedance analysis method,the influence of wind turbine converter is considered.The criteria for determining the equivalent resistance of the wind power integrated system to be negative are proposed when the wind turbine converter is considered.And the influence of slip proportional and series compensation degree on the equivalent impedance is analyzed..According to the relationship between equivalent impedance and frequency,the conditions and influencing factors of subsynchronous oscillation are obtained.When the equivalent resistance of the system is negative and the system resonates,the electrical parameters will diverge,leading to the occurrence of subsynchronous oscillation.Then,in PSCAD,the effects of series compensation capacitor,wind speed and proportional control coefficient of wind turbine converter on the stability of wind power integrated system are analyzed.By comparing the electrical output of wind farm,it is concluded that the decrease of series compensation capacitance and wind speed increase the risk of subsynchronous oscillation.The increase of the proportional control coefficient of the wind turbine converter will also lead to the subsynchronous oscillation of the system.Finally,based on the suppression principle based on inverse current injection and the control structure of bypass damping filter,a bypass current compensation method is proposed to suppress the subsynchronous oscillation of wind power integrated system.This method does not need the FACTS device as the injection current source,reduces the interference of external current and harmonics,simplifies the control structure of the suppression system,and ensures the safe and economic operation of the power system.The validity of the method is verified by simulation.