For solving the phenomenon of DC bias due to UHVDC transmission

a method for identifying key sites in the transmission-end power grid based on complex network theory under DC bias conditions is proposed. PSCAD is used to set up the autotransformer model and conduct the DC bias simulation study of transformer. In order to control the DC bias existing in the substations in Jiuquan area

the simulation model is set up based on the structure parameters of actual grid so to identify and control the critical site which is subjected to the large influence of the bias current. The concept of node entropy and line entropy is defined of which its size reflects whether the node current and line current distribution in the governed area is uniform

and the DC bias control standard is specified so to judge whether the control effect is qualified. The simulation results show that after identifying and managing the key sites

the node entropy and line entropy have decreased significantly and the total bias current in the area has been effectively suppressed.