Research On A Medium Range Frequency Oscillation In The Sending Power System With The Interconnection Of DFIG System

Recently,as the gradual depletion of fossil and the growing problem of environment pollution,new energy power generation technology has developed rapidly.Large-scale new energy power generation brings clean power,but also causes a series of new wide band oscillation problems.Among them,sub/supersynchronous oscillations<100Hz)and high range frequency oscillations(>1000Hz)have been widely concerned,and medium range frequency oscillations(100-1000Hz)are rarely reported.So it is necessary to study the frequency stability of sendingpower system with the interconnection of DFIG system.The main work is as follows:(1)The muti-frequency response of single device under sub/supersynchronous and medium range perturbations is studied.Firstly,the DFIG system are divided into controlled asynchronous machine system(CAMS)and grid side converter system(GSCS)based on the response route of subsynchronous disturbance signal(SDS).Secondly.frequency responses of each component of the two subsystem are qualitatively derived and analyzed,then muti-frequnecy response of the whole DFIG system which injected into grid is obtained,and its muti-frequency response character is revealed.Finally,the conclusion of theoretical analysis are verified based on the simulations in PSCAD.(2)The mechanism and impact factor analysis of a medium range frequency oscillation in the sendingpower system with the interconnection of DFIG system is studied.Firstly,the concerned system in DIgSILENT software are introduced with the phenomenon of medium range oscillation were introduced.Second,the impedance model of the concerned system was established and the frequency characteristic of the system impedance under the above parameters was analyzed;thus,the mechanism of medium range frequency oscillation is revealed.Meanwhile,the result of Nyquist curve of the system are plotted and it verified the above result.Finally,the influence factors of the oscillation are analyzed preliminarily with simulations,and the major influence factors were determined.(3)The suppression measures of the above medium range frequency oscillation is studied.Specifically,the measures can be taken in control system and primary side of system.In control system,supplementary damping controller or low pass filter can be equipped to suppress the oscillation;in primary side of system,high pass filter can be parallelled into the bus to suppress the oscillation.Finally,effectiveness of the above three measures are verified through simulation.