There are mainly two methods with respect to multi-port modeling for electromechanical-electromagnetic transient hybrid simulation. One method is based on the multi-port Norton equivalents and couples the ports directly through circuits(namely the coupled model). The other decouples the ports at the electromagnetic side and couples them at the electromechanical side instead(namely the decoupled model). The mathematical models of the two models are derived. With the electromechanical side calculation taken into account by the formulation of the equivalent voltage for the decoupled model

the consistency of the two models in steady state is proved. Given the controlling characteristics of high voltage direct current(HVDC)transmission system

the expanded nodal admittance matrices of both the coupled and decoupled model are achieved. The transient characteristics of the two models are compared and analyzed with reference to the characteristics of their nodal admittance matrices. Theoretical and simulation results show that when disturbance and fault occur at the electromagnetic side

for the simulation of the commutation failure phenomenon of local direct current transmission system

the two models are basically consistent; while the decoupled model is less adaptive for the simulation of the commutation failure phenomenon of non-fault HVDC line caused by the fault HVDC line in the multi-infeed HVDC system. The two models should be reasonably chosen during modeling.