Study On Stability Of Doubly-fed Wind Power Generation System Based On Bifurcation Theory

With the expanding scale of wind power industry, the proportion of Wind power generation in renewable energy generation is increasing. Doubly-fed induction generator has good performance, so it has become the mainstream model of wind farm. Doubly-fed induction generator will affect the voltage stability and bring challenge to the safe and stable operation of the system when it connected to power grid. According to system differential dynamics equation, this paper uses bifurcation theory to study the stability of doubly-fed wind power generation system from the perspective of nonlinear dynamics.Firstly, the bifurcation phenomenon in doubly-fed induction generator is studied in this thesis. The indirect vector control strategy is introduced in the doubly-fed induction generator mathematical model of the dq rotating coordinate system. Using the MATCONT to track the power system equilibrium solution manifold and search the instability bifurcation point. Through time domain simulation to verify the bifurcation phenomenon and analyze stability of the system. The study confirms that doubly-fed induction generator under the condition of certain parameters will appear Hopf bifurcation phenomenon which can make the system oscillation and affect the safety and stability of the motor.Secondly,the stability of the LCL inverter is analyzed based on the bifurcation theory. Using the stroboscopic map to establish the discrete iterative model of inverter system. Then to predict the bifurcation point of the system operation, judge bifurcation type and divide stability region according to the change of maximum modulus eigenvalue of Z matrix. The accuracy of the model and stability domain are verified by the time domain simulation. The results show that the unreasonable design of the control parameter can cause the system to appear Hopf bifurcation,which can cause the inverter to occur oscillation instability.Lastly, the voltage stability of power system connected by DFIG is analyzed.Using the MATCONT to simulation the power system equilibrium solution manifold and instability bifurcation point. Based on the matrix eigenvalue of system analysis voltage stability. Through analyzing the voltage time domain simulation waveform verify the system bifurcation phenomenon and recgonize the system voltage instability mode. On the basis of this, SVC is introduced to suppress the system bifurcation point and the effect of SVC parameter on system voltage stability is analyzed. Studies show that the system will appear Hopf bifurcation and saddle node bifurcation, which can make the voltage waveform occurs oscillation and monotonous instability. Setting reasonable parameters of SVC can delay system bifurcation phenomenon,different SVC parameters have different effects on the stability of the system.