The Voltage Stability Research Of Grid-connected Wind Power System Based On Hopf Bifurcation Theory

Since the output power of wind farm is unstable and random, voltage stability problemhas become the bottleneck of interconnecting wind farm with power grid. It has importanttheoretical and actual value that bifurcation theory is applied to analyze the voltage stabilityof wind power system. The main achievements involve the following aspects:1. The dynamic equivalent model of wind farm is built based on the constant speedconstant frequency wind generator. The injected active power and reactive power of windfarm are chosen as the control parameters, and the dynamic bifurcation curve of the voltage atthe access point of wind farm is obtained, as well as the bifurcation boundary of stable power.The analysis indicates that wind power systems exist complicated bifurcation phenomena aswind turbines injecting power varies, and it is possible that hopf bifurcation occurs beforelimit point in the power system. Therefore it is biased towards optimism that the stabilitymargin is usually estimated by static power limit point. Concerning the algorithm, this papernot only combines the continuation method with direct method, but also successfullyintroduces the critical eigenvalue method to multiparameter bifurcation analysis. As a resultthe hopf bifurcation point can be more succinctly tracked and quickly calculated.2. Based on the single machine infinite bus system including wind farm, the variation ofwind farm injecting active power is chosen as the control parameter, and contrastive analysisabout hopf bifurcation phenomena in wind systerm is conducted in three differentcircumstances that without compensation device, applying SVC and applying STATCOM ataccess poin where wind farm is connected with infinite system. The research showes that inthe condition without compensation device, the voltage amplitude falls and the frequencyoscillation varies widely when the system operating point approaches hopf bifurcation point.By applying SVC and STATCOM it can effectively reduce the system voltage oscillation,restrain hopf bifurcation phenomena and to some extent increase the system stable operationregion. Further theoretical analysis and digital simulation show that the dynamic performanceof STATCOM is superior to SVC, and STATCOM is able to more effectively and timelyretrain system voltage fluctuation in the case of hopf bifurcation happening.