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Large signal stability means that a system can be a transition to a new stable state without losing synchronism after a large disturbance. The large signal stability problem brought by large capacity electrical loads in ac/dc independent power system is prominent, which seriously affects the dynamic security of the system. In view of modeling characteristics of ac/dc system, a generalized state space average large signal modeling method for the ac/dc independent power system in dq-coordinates is proposed. A large signal model of the ac/dc independent power system is constructed, which includes generators, inverter units, rectifying units, and dc/dc converters. The simulation results indicate that the large signal model constructed in this paper can accurately reflect the dynamic characteristics of the system under large disturbances, such as startup and sudden change in load, which is helpful to understand and improve the dynamic performance of the system under large disturbance. Furthermore, with feasibility and effectiveness, the large signal model provides convenience and possibility for the theoretical analysis of large signal stability of ac/dc independent power systems in the future.