Study On The Influence Of SVC On Voltage Stability Of Power System

In recent decades, many incidents of large-scale blackouts have happened at home and abroad, which has a huge impact on people’s production and life. Most of these accidents are caused by the uneven distribution of reactive power or the shortage of reactive power. The lack of reactive power will lead to voltage dropping directly, and the power quality of power system will be affected greatly. SVC(Static Var Compensator) is a kind of dynamic reactive power compensation devices and it is widely used in power system. In terms of voltage stability problems, the studies of issue about SVC to power system voltage stability are a hot topic at present. In this paper, the problem is carried out research from the static and dynamic aspects.Firstly, this paper introduces the study background of power system voltage stability,and then describes the working principle with control strategy of three kinds SVC in detail, which are the thyristor controlled reactor(TCR), thyristor switched capacitor(TSC) and thyristor controlled reactor-thyristor switched capacitor(TCR-TSC).Secondly, the impact of SVC on static voltage stability of the power system is studied. This paper makes a detailed derivation, which is about the application of the characteristic structure analysis in WSCC including SVC. Based on characteristic structure analysis method, a simulation is made about WSCC-3 machine 9-bus system by using power system analysis software(PSAT), which is developed at the University of Waterloo. Simulation results can be seen not only the method’s effectiveness of static voltage stability, but also illustrate the key position of SVC in voltage stability.Thirdly, this paper improves the traditional PI voltage control method of TCR-TSC type SVC. An AGC module and a susceptance regulator module are added in order to achieve automatic continuous control of the regulator gain. The traditional PI voltage control method and the improved PI voltage control method are applied to a specific transfer function. When a step response occurs suddenly, the result shows that the speed is more quickly and the overshoot is smaller on the improved method. Then a simple system with SVC is set up in MATLAB, and the improved PI voltage control method is applied in this system. Simulation results demonstrate the effectiveness of this method.Finally, the impact of SVC on dynamic voltage stability of the power system is studied. Based on improved PI control method, a dual-load system is set up and did simulation experiments by MATLAB in this paper. When the horizontal and vertical fault occur in the system,a study is made about the impact of the device to the power system voltage stability by the change of system parameters. Simulation results show that SVC can reduce the lasting time of various faults and improve the dynamic voltage stability of power system greatly.