Transient Stability Analysis Of The Two-Area With AC/DC Paralleled Interconnected Power System

As one of the most important forms in China’s current and future transmission grid,AC/DC hybrid transmission mode can organically combine the advantages of AC and DC systems,but the cross-regional coupling characteristics of AC and DC in space make the interaction between AC and DC systems more closely,thus making the stability characteristics of AC/DC hybrid systems more complicated.After the system is disturbed,one of the main stability problems faced by AC/DC hybrid systems is the rotor angle instability problem.Therefore,it is important to reveal the transient rotor angle instability mechanism and the subsequent emergency control strategy of the hybrid system after it has been disturbed,and the main research contents of this paper are as follows.The LCC-HVDC system reaction process of DC continuous commutation failure triggered by AC fault at the receiving end is studied.Firstly,based on the basic structure and control mode of the LCC-HVDC system,the normal commutation failure process of the LCC-HVDC system is summarized.Secondly,the accuracy of the LCC-HVDC system electromechanicalelectromagnetic transient hybrid simulation results is confirmed.Finally,a large-scale extended IEEE39 node electromechanical-electromagnetic hybrid simulation model is built in ADPSS to analyze the key factors causing the continuous commutation failure of the LCC-HVDC system.The transient rotor angle stability characteristic that belongs to a parallel AC/DC transmission system in two regions after the occurrence of DC commutation failure is studied.Firstly,the rotor equation of motion is improved,and the transient rotor angle stability margin index of the hybrid system is determined based on the extended equal area criterion,for the mechanism analysis of the influence on the rotor angle stability of the hybrid system.Secondly,the effects of the operating conditions of the hybrid system,the ratio of DC transmission power,and the inertia time constant of the system at the sending and receiving ends on the transient rotor angle stability of the AC/DC parallel system in two regions are analyzed.Finally,the model is built and simulated in ADPSS to verify the correctness of the proposed conclusions.The emergency control measures of the hybrid system after DC blocking are analyzed.Firstly,the transient rotor angle instability mechanism of the hybrid system and the effectiveness for the machine cutting strategy after DC blocking are analyzed,from the perspective of energy through the equivalent rotor angle characteristic curve of the hybrid system.Secondly,the transient stability characteristics of the hybrid system are explored under different amount of machine cutting,and based on the extended equal area criterion,a coordinated control strategy with the minimum machine cutting is proposed,and the effectiveness of the strategy is verified by simulation.Finally,the influence of the DC transmission power ratio under different working conditions on the amount for machine cutting of the hybrid system after DC blocking is analyzed by simulation.