Research On The Stability And Control Of AC/DC Power System Subjected To A Severe Disturbance

With China’s national energy strategies, the Chinese national power grid has become a interconnected AC/DC power system. At current state, the link between the North and Mid China has become a weak point, and face severe stability problems. When there is a fault occurring in Sichuan power grid, the North-Mid intertie suffers great power fluctuations. In order to solve this problem and propose a corresponding control strategy, this paper analyzes the many aspect of this stability problem.Through comprehensive system stability calculations, this paper analyzes the stability characteristics of Sichuan power gird, where the fault had occurred. After that, this paper thoroughly studies the dynamic process of UHVAC itertie power surge via energy flow and oscillation analyses. This has lead to a conclusion which is suitable for general situation, that when the disturbance is severe enough, the power curve of the intertie will display a unique "two peak" feature, and that feature is determined by the functional relashionship between power, voltage and rotor angle. This paper propose a HVDC control strategy to enhance system stability, which uses the stability information the "two peak" curve contains as start/stop criterion The effectiveness of this control strategy has been verified.In order to weaken the coupling effect between the Sichuan power grid and UHVAC intertie, this paper analyzes the impact of manipulating the generation distribution of Sichuan power grid. Conclusions have been made, that when the thermal power generation move closer to the main grid, disturbances occured in Sichuan power grid have less effect on the UHVAC intertie. The contributing factors are,1. the change of generation distribution caused change in inertia distribution of the system, thus weakens the matching effects of main oscillation modes;2. the added voltage support via thermo power generation(closer to the main grid than hydroelectric power) means less low voltage load release. This paper gives suggestions on how to regulate thermo power generation in Sichuan power grid when the stability of the system is the main concern. The effect has been verified via computer simulation.