Study On Response-based Peak Value Prediction And Suppression About Active Power Fluctuation On Tie-line Of Two-area Interconnected Power System

In order to solve the outstanding contradictions in China’s energy distribution and demand,China has vigorously promoted the transmission of electricity from the west to the east and nationwide interconnection..The long-distance,large-capacity AC/DC project has greatly eased the energy needs of developed regions and strengthened the rational allocation of resources.At the current stage,the problem of " Strong HVDC and Weak AC System" in China is prominent,manifested by the lack of the ability of the AC power grid to withstand DC impact.The AC tie-line connecting the North China and Central China power grids is a typical weak link.The fluctuation of power flow after power grid disturbance threatens the safe and stable operation of the tie-line.Therefore,it is of great significance to study the physical mechanism of tie-line power fluctuations and to prevent the peak power surge of tie-line from threatening the safety of transmission interface.Based on the review of domestic and foreign research results,this paper focuses on the use of PMU/WAMS system to predict and restrain the power fluctuation peak value of the tie-line.(1)Aiming at the problem of power fluctuations of weak tie-lines in interconnect power systems,the second-order system response mechanism of tie-line power fluctuations is deduced by the two-machine system.It turned out that the main factors affecting the peak power fluctuation of tie-line are the damping ratio,the two-area inertia ratio and the unbalanced active power.The key factor to predict the peak value is the acquisition of unbalanced active power.(2)According to the coupling relationship between the rotor frequency of the synchronous machine and the unbalanced active power,this paper proposes a method of using the PMU to obtain the frequency information of the nodes at both ends of the tie-line in real time,quantifying the amount of unbalanced power after disturbance in the system.By treating the two areas as two equivalent synchronous machine,the frequency change rate of the tie-line node is multiplied by the equivalent inertia of each area,and the summed value is used as the predictor of the unbalanced power in the system.Through the real-time prediction of the unbalanced power,the peak value of the active power impact of the tie-line is predicted.Taking the two-machine system as an example,the theoretical basis of the proposed method is verified.Taking the actual power grid of the North China and Central China power grids as an example of actual power grid,the simulation of different faults verifies the feasibility of the application in the actual power grid.After monitoring the magnitude of the unbalanced active power,the peak value of the tie-line active power can be calculated in advance using the damping ratio of the regional oscillation and the unbalanced power obtained.(3)In view of the possibility that the peak power fluctuation of the tie-line may endanger the stability of the interconnected power system,the main influencing factors of using DC emergency power support to suppress the peak value of power fluctuation are studied.For the suppression of the peak value of the tie-line and the reduction of the steady-state value,it is necessary to prioritize and reasonably use the emergency DC power support strategy,and take measures to cut generators and load to ensure the stable operation of the tie-line.Finally,the integrated control strategy of active power of tie-lines is proposed.