Study On The Interaction Between Uhv Ac And Dc Power System

As China power grid speeding up UHV transmission construction, China boasts the highest voltage level and power transmission market all around the world, With the thorough implementation of strategy like'Nation wide Inter connection, West-to-East Power Transmission, South-and-North Power Exchange', in the near future, UHV electrical power pool including AC and DC covered the whole nation will come into being.It is such a massive AC and DC power system that the complexity and difficulty of operation is unprecedented in the world, which may results in critical technical problems such as stability of UHV grid, maximum power transmission of the UHV transmission line and interaction between AC and DC systems etc.. Only by analyzing and studying problems mentioned above, the reliability of power transmission can be ensured and stable operation of AC and DC systems can be realized. In this paper, the transmission capacity of UHV system and interaction between AC and DC systems are studied by using power system simulation software BPA and PSCAD where the actual planning data of 2020 are adopted. With UHV AC and DC system connecting to original system, it is significant to give prospective analysis and judgment for planning, design, control and operation of the system in order to ensure the safe and stable operation of the new system.This project firstly expounds the requirement and the development of UHV grid in China. The mathematical model used for calculating the transmission capacity as well as for analyzing the mechanism of DC and AC system is given and various stability constraints influenced the transmission capacity are discussed. By using UHV data from actual provincial planning , calculated and analyed the stability . it is concluded that stability constraints is the main reason for limitation of transmission capacity. So the solutions are put forward in the light of the actual situation. Then probe into the problem of subsynchronous oscillation. The reason for subsynchronous oscillation caused by HVDC system is explained. And the simulation model for subsynchronous oscillation under this condition is established. During time domain simulation the phenomena of subsynchronous oscillation occurred. Subsequently analyzed the characteristics of subsynchronous oscillation occurred in AC and DC system.Finally,detailed analysis for interaction mechanism of UHVDC system under great disturbance is given. To study the influence of fault of AC and DC transmission line on the system, the simulation results show that the target grid is strong enough. It is said that when fault occurred on AC system near DC inverter , the system is able to operate safely; and when lock fault occurred on unipolar or bipolar, the receiving end only need to reduce appropriate reactive power without other measures to maintain system stability.