Phase Trajectory Analysis And Control Model Studies For AC-DC Transmission System With Wind Power Integration

Nowadays,there is an energy crisis all over the world.Because of the high efficiency and cleanliness of wind power and the maturity of power generation technology,it is widely loved by power grids in various countries.However,the fluctuation of wind power make the transient stability of the system more difficult to predict.What’s more,the analysis of power system transient stability is complex when a large number of HVDC transmission systems connected to the grid.Phase trajectory analysis method is a real-time method to judge the transient stability of the system based on the power angle and angular velocity trajectory of the generator,and it provides a new idea for the transient analysis of DC transmission system with wind power integration.In this paper,phase trajectory analysis method is used to analyze the transient stability and a kind of control method of DC transmission system with wind power integration is proposed.The main work of this paper is as follows.(1)A simplified analysis model of DC transmission system with wind power integration is proposed in this paper.Then the expanding equal area rule is used to analyze the transient stability of this model.Finally,the conclusion is drawn that under certain conditions,the transient power angle stability of the system can be improved by the connection of DC system and DFIG.(2)In this paper,a new method for judging transient stability of AC/DC hybrid system based on phase trajectory is proposed.This method improves the traditional criterion of phase trajectory stability,so that it can be applied to transient identification of AC/DC hybrid system.Finally,it is concluded that under certain conditions,with the increase of DC transmission power,the boundary of the system security region will move outward in parallel.(3)A transient preventive control method for DC transmission system with wind power integration is proposed in this paper.This method adopts the strategy of priority adjustment of DC transmission power,and it not only guarantees the transient stability of the system,but also greatly improves the economy of the control strategy.The validity of the proposed method are verified in the 2DC system and a real power system in China.