| 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 compensated 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(GSC),internal control and so on.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.Firstly,a single-DFIG equivalent model is established.Based on the complex torque analysis method,the mechanism of single-machine synchronous resonance is clarified,and then the double-machine equivalent model is established to further clarify the mechanism of double-machine synchronous resonance.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 were 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 DFIG side suppression measure,which is to add damping control on the stator side.The basic structure of the controller was designed,and the appropriate feedback signal was selected.The validity of the controller was verified by a typical electromagnetic transient simulation system.In the case that the wind field is at the same wind speed,different wind speed and different installed capacity,the suppression effect of the suppression measures on the subsynchronous resonance is studied by modifying different proportions of DFIGs. |
