I. Introduction
The random fluctuating character of wind energy causes the generation output of a wind power plant is neither continuous nor controllable. From a power system perspective, the wind farm integrated to power system is a random disturbance source. The integration of wind farms can result in voltage variations outside the regulation limits, as well as violations on flicker and other power quality standards. Besides, it can change the line's transmission power and the distribution of the former load flow. With the rapid increasing capacity of wind power in the power system, the analysis of the impact of its integration to the power system[1]–[2] has great significance for the influence is becoming more widespread.