Study On Voltage Stability Of D-PMSG Grid-connected System Based On The Bifurcation Theory

With a large number of wind farms incorporated into the power network, wind power is more and more influence on power network. In recent years, the scale of wind farms in China continues to increase, and a lot of electrical and electronic equipment have been invested, but it also led to a variety of problems, especially voltage stability and other related issues largely restrict the development of wind power system. In this paper,the voltage stability of wind power system is analyzed from the motor side and grid side respectively based on the bifurcation theory.Firstly, the voltage stability of the direct-drive permanent magnet synchronous motor is analyzed. Based on the circuit theory and coordinate transform. The mathematic model of D-PMSG is obtained. Then the chaotic model is got after affine transformation and time scale transformation. The voltage oscillation characteristics of D-PMSG are analyzed by using phase trajectory, time domain diagram and bifurcation diagram. And using time domain simulation method to analyze its output voltage stability combined with PSCAD/EMTDC.Secondly, analyze the bifurcation of 3 node model of wind power system by setting single parameter. The MATCONT software is used to discuss the voltage stability from the perspective of reactive power disturbance. 'The results show that there exists HOPF bifurcation and saddle node bifurcation point. The existence of bifurcation points seriously affects the voltage stability of the system. In order to delay or cancel these unstable bifurcation points,the original system is introduced in the washout-filter assisted SVC bifurcation control method, then the simulation results of the improved system are compared with the former ones, which shows that this method can effectively delay the bifurcation and improve the voltage stability of the system.This study is helpful to better understand nonlinear dynamics of DPMSG,and is valuable to parameter design for guaranteeing stable operation of this system.