| In the field of new energy,wind energy is a kind of green and renewable energy.With the rapid development of wind power generation in China,the installed capacity of large scale wind power collection area has been equivalent to that of conventional thermal power plants.Since many large wind farms are located in remote areas and far away from the load area,series compensation devices are needed to increase transmission capacity of the upper transmission lines.Double Fed Induction Generator(DFIG)has become the main power type of many wind farms in China.Its operation control mode and converter structure often cause subsynchronous resonance(SSR)problem.This paper first took the power system of a large wind farms integration area in northern China as a case,analyzed the subsynchronous resonance phenomenon caused by series compensated transmission lines transporting large scale wind power and the recorded data.The generation conditions and characteristics of subsynchronous resonance in wind power series compensatied transmission system were summarized,including electrical variable waveform,frequency,system damping,series compensation capacitance,reactive power compensation device,Generator type response and load impact.Secondly,according to the research needs,a detailed mathematical model of doubly fed induction generator was established,including shafting,induction generator,Rotor Side Converter(RSC),grid side converter(Grid Side Converter,RSC),internal control and so on.At the same time,the wind speed model was set up,and the maximum power tracking control was adopted.Then,based on the actual power grid in the case area,the equivalent system model was established on the matlab/simulink simulation platform,and the equivalent model of the DFIG was connected.Because of the large number of wind turbines in this area,under certain conditions,a single large capacity DFIG was used to equivalently the whole wind field.Through the small signal stability analysis method,combined with the state equation of the wind power series compensation system,this part analyzed the affecting factors of all the state variables under the oscillation mode,and determined the type of subsynchronous oscillation.Then,the simplified circuit of the single-DFIG series compensated system and the multi machine series compensated system were derived,and the mechanism of the sub synchronous phenomenon of wind power were identified,which is the induction generator effect(Inducton Generator Effect)of DFIG control.In addition,based on the equivalent model simulation and eigenvalue method,the influence of wind speed,the number of grid-connected DFIG,and the current tracking ratio of rotor side converter on the subsynchronous resonance was analyzed qualitatively.Finally,this paper summarized subsynchronous resonance suppression method,characteristic and influence factors of combining the case area of subsynchronous resonance phenomenon,proposed a centralized suppression measure,namely the Grid-Side Damper(GSD).The basic structure of the GSD was designed,and the appropriate feedback signal was selected.The validity of the GSD was verified by a typical electromagnetic transient simulation system.The GSD was then simulated and tested under various disturbances. |
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