Analysis Of Wind Power System Stability Concering OLTC Regulation

With the increasing scale of wind power grid, the impact of power system dynamic behavior is increasingly obvious. In power system which contains DFIG, the on load tap changer is an important means to regulate the voltage. When adjusting the OLTC taps, the change of mechanical properties may lead the voltage instability and influence the power system. In this paper, using the typical three nodes system, the impact of regulation characteristics of OLTC is studied when the DIFG parallels in the grid basing on the bifurcation theory.In this thesis, the bifurcation of voltage has been taken to study when the reactive power increases based on DIFG model. The research shows when the OLTC is regulated, voltage will happen ordinary static bifurcation, saddle node bifurcation and Hopf bifurcation. Research results show when use the across span method to regulate the OLTC, the voltage will occur dynamic instability and lead power system instability. And with the method of continuous span adjustment, the power system than across span adjustment has higher stability. In the selection of OLTC time constant, the smaller the time constant will be more conducive to the stability of the system, and large time constant is a certain influence on the stability of the system.At the same time, this paper also studies the stability of power system including the OLTC when SVC is joined. Through the supplementary equations, the SVC will be introduced to the mathematical model. After join the SVC compensation, in terms of span adjustment and the time constant of the selection, system stability margin will be improved. And due to the join of SVC, the instability mode of power system may change. When the SVC is joined, the stability of power system will raise when using the method of continuous span adjustment. And when using the t method of across span adjustment, the dynamic instability may change to the static instability. And under the different OLTC time constant, the join of SVC is conducive to the recover of power system. But the compensation of SVC cannot be completely eliminated the disadvantage due to the improper way of regulating method. So the choose the proper methods according to the practical situation is the first way to maintain power system stability.