Research On Subsynchronous Oscillation Of Doubly-fed Wind Power Generation System

Nowadays,with the rapid development of wind power generation technology,some transmission problems have emerged.The wind power production base in China is far from the power load center,so it is necessary to adopt the transmission mode of long distance and long transmission lines.In order to reduce the voltage loss of transmission line,increase the transmission power of transmission line and improve the stability of power system,the series capacitor compensator is usually used on the transmission line.The interaction between the installed capacitors and the wind power generation control equipment can easily lead to the sub-synchronous oscillation of the system.This paper focuses on the sub-synchronous control interaction caused by the series compensated external infinite bus system in the doubly-fed wind power generation system.Sub-Synchronous Control interaction(SSCI)is discussed and studied.The linear mathematical model of each module is established for the state equation of each module of doubly-fed wind power generation system based on Lyapunov’s first law.In order to modify and extend the model,the characteristics of each module and the connection between the modules are taken into account.Based on this,the small disturbance stability analysis model of doubly-fed wind power generation system is built by using Matlab/Simulink platform.The eigenvalue analysis method is used to calculate the eigenvalues of the state coefficient matrix of the small disturbance stability analysis model,and the oscillation modes of the system are analyzed.The participating factors of each state variable in the SSCI oscillation mode are analyzed.The inducements of SSCI are mainly series compensation and rotor side converter parameters.The time domain simulation model of doubly-fed wind power generation system is established on PSCAD/EMTDC platform.The damping ratio is obtained by changing the series compensation degree and the rotor side converter parameters respectively.The results show that the series compensation is increased,the integral parameter of outer loop of rotor side converter is increased,and the proportional parameter of inner loop is increased.Reducing the integral parameters of the inner loop will aggravate the SSCI.At the same time,the simulation analysis of a method to suppress SSCI by controlling the injection of reverse subsynchronous current into the output of DFIG by controlling the additional power electronic device.