| With the rapid development of the global economy,the demand for energy is increasing.Environmental problems have become increasingly prominent,and it is imminent to develop clean energy.As a kind of renewable energy with abundant reserves,wind energy will develop rapidly.Wind power generation will become a kind of power generation mode with great potential and large-scale application.However,the interaction between large-scale wind farms and series-compensated networks will cause sub-synchronous oscillation.In this paper,studying the sub-synchronous oscillation phenomena in doubly fed induction generator(DFIG)-based wind farms interconnected with series compensated networks based on the Nyquist stability criterion,and put forward a kind of damping control strategy.Firstly,this paper describes and analyzes the mechanism of the sub-synchronous oscillation in DFIG-based wind farms interconnected with series compensated networks.Introducing the analysis method of sub-synchronous oscillation.Summarizing the suppression method of sub-synchronous oscillation.Then,introducing the structure of DFIG-based wind farms connected with series compensated transmission network.Dividing the system into six parts,which are wind turbine,shaft system,induction motor,converter control strategy,direct current capacitance and transmission line,building the corresponding mathematical models.The control systems of the rotor-side converter and grid-side converter of the DFIG are described briefly.After that,for the wind-thermal-bundled power transmitted by series-compensated network system,the corresponding system impedance model of the research system is established.Analyzing the influence of wind speed,degree of series compensation and PI ratio coefficient of the current control loop of the rotor-side converter on the system sub-synchronous oscillation with the Nyquist stability criterion.Building the simulation model of the study system based on Matlab/Simulink in order to verify the theory.In addition,the time domain simulation is applied to study the influence of wind power and thermal power output ratio on system sub-synchronous oscillation.Finally,based on the current control loop of the rotor side converter,the design principle of the suppression measures is expounded.And the damping control strategy is put forward,that is,the q-axis damping controller and the d-axis damping controller which are added to the current control loop of the rotor side converter.The damping controllers are added to the simulation model to verify the effectiveness of the suppression.Besides,the influence of damping controller’s gain coefficient on the suppression effect is also studied. |
