Interaction paths analysis and stability-enhancing methods for LCC-HVDC system with weak receiving-end grid

•The critical interaction paths between LCC and AC grid is extracted and analyzed, which is beneficial for the system operator to comprehend coupling relations among the key electrical and control quantities.•The extinction angle (EA) is an important node in phase interaction path, so the influences of two EA coefficients on system stability are investigated.•The damping characteristics of each coupling branch in phase path are revealed and corresponding explanations in physical term are given, which is helpful for the engineer to understand the instability mechanism intuitively.•Based on the above discoveries, two corresponding methods that have the equivalent effects on modifying these coefficients are proposed. The proposed methods extend the approach to improve the stability of LCC-HVDC system and thus reduce the burden of parameter tuning. The stability problem becomes more prominent when line-commuted converter based high voltage direct current (LCC-HVDC) system is connected to weak receiving AC network. Although the impacts of controller parameters on the stability of LCC-HVDC system have been well studied, the interaction mechanism between LCC and weak AC network has not been totally understood and revealed. As a result, the proposal of corresponding solutions is restricted. To remedy such insufficiency, firstly, the sketchy interaction paths between LCC and AC network are extracted and analyzed in this paper based on the motion equation model. The results reveal that the phase interaction path provides negative damping and is the main contributor to the instability. Moreover, since the extinction angle (EA) is the critical node in phase path, the impacts of two coefficients of EA on the system stability are analyzed, namely phase tracking error (PTE)-EA coefficient kδγ and firing angle order (FAO)-EA coefficient kαoγ. The theoretical analysis shows that increasing kδγ or decreasing kαoγ will strengthen the system damping. Next, the comprehensive physical explanations for the above discoveries are presented. Then, two methods that have the same effects on modifying these coefficients are proposed to enhanced the system stability. Finally, the effectiveness of these two methods is verified by the simulations in PSCAD/EMTDC.