Abstract: Electromagnetic transient simulation can accurately simulate the dynamic characteristics of AC/DC power system under asymmetric faults. In order to reduce the amount of simulating calculation and improve the simulation efficiency， it is necessary to simplify the large-scale power system. A dynamic equivalent method for three-sequence network applied to electromagnetic transient simulation of AC/DC system is proposed. On the basis of dynamic reduction technique for the physical equivalence， this method improves the standard equivalent structures of low-voltage networks， takes into account the negative sequence and zero sequence currents under asymmetric short-circuit faults， adopts a practical engineering method of parameter aggregation of equivalent generators and selection of controller models， makes the impedance of each sequence network of the trunk grid equal before and after the simplification， and gets better simulation accuracy of the equivalent system under asymmetric faults. This equivalent method does not produce negative resistance branches in the simplification process， and avoids the emergence of equivalent transformers with negative resistance or reactance. Thus， the equivalent system can be directly used in electromagnetic transient simulation. Finally， the corresponding equivalent software is developed and applied to the equivalence of East China Power Grid. Simulation results verify the effectiveness of the proposed method.

Key words: large-scale AC/DC power system, electromagnetic transient, dynamic equivalence, three-sequence network, asymmetric faults