Analysis And Monitoring Of Sub-synchronous Oscillation Caused By Grid Integration Of Double Fed Wind Farm Via Series Compensate Capacitor

In recent years,the wind power which is a kind of sustainable and clean energy has developed rapidly in our country,because of special Chinese geographic condition,the majority of important wind farms are far from the load center,the long distance wind power transmission is imperative.The series capacitor compensation is a mature and economic technique in power system which can achieve the long distance and large capacity transmission,it has been widely used in wind power transmission.However,the sub-synchronous oscillation problem occurs when the double fed induction generators connect to the power grid via series compensate capacitor.The wind farm sub-synchronous oscillation is a phenomenon that the electrical system and wind turbine exchange energy significantly at one or more oscillation frequency,it caused oscillation of voltage,current and output power,and it's also a threat of wind turbine and power system stability,it's of theoretical and practical significance to study sub-synchronous oscillation caused by grid integration of double fed wind farm via series compensate capacitor.The mathematical model of double fed induction generator and series compensated transmission lines is established firstly,then introduce the mathematical model and control strategy of rotor side converter and grid side converter in detail,and deduce the main impacting factors of sub-synchronous oscillation occurs in wind farm.Then build the model of grid integration of double fed wind farm with series compensation transmission lines in the simulation platform of real time digital simulation(RTDS),studying the characteristic of sub-synchronous oscillation by changing the wind speed,series compensation level,the number of the DFIGs and the control parameters of rotor side converter and grid-side converter,finally getting the regularity of sub-synchronous when working conditions and operation parameters changed.Then summarizing the sub-synchronous heft by using Fourier spectrum analysis the voltage,current and power in point of common coupling.The composite criterion is formed according to the direction of sub-synchronous power and relationship between the sub-synchronous voltage and rated voltage,the main sub-synchronous oscillation source in the wind farm can be identified effectively;The starting criterion and action criterion of the protection device are established according to the level of the sub-synchronous heft in the line current,then finishing to develop the sub-synchronous oscillation protection prototype.At last,test experiment of the prototype is completed by the relay protection meter,experimental results show that the SSP-522 sub-synchronous oscillation monitoring device has the advantage of accurate calculation,reasonable logic and quick action,the device achieves the predetermined goal.