Transient stability margin assessment of AC/DC hybrid system with commutation failure involved

Abstract The commutation failure of Line Commutated Converter-High Voltage Direct Current (LCC-HVDC) caused by AC fault has an increasingly serious impact on the transient stability of AC/DC hybrid system. This paper presents a novel transient stability margin assessment approach based on energy function, where generators adopt 6th order electromechanical model and DC system adopts electromagnetic model. First, the network structure-preserving model of AC/DC hybrid system is established, and its energy function is deduced. Next, the energy function of post-fault system is approximately calculated by trapezoidal integral path, and energy function based transient stability criteria are put forward to determine whether the post-fault system is stable or not. Then, Bisection Method (BM) is employed to obtain Critical Clearing Time (CCT) quickly and effectively where CCT can be adopted as index of stability margin. Finally, the New England-39 bus system integrated with LCC-HVDC is used as test system to investigate the effectiveness of the proposed transient stability margin assessment approach.