Abstract：In response to the susceptibility of wind storage DC building microgrid systems to external

interference，the DC bus is prone to instability during multi-mode switching and high-power load switching，posing a serious threat to the safe and reliable operation of electrical equipment. A large-signal simplified model of the permanent magnet direct-drive synchronous wind power generation system was established，the theory of mixed potential function was applied，the large-signal stability boundary of the system was calculated ，and the correctness and accuracy of the criterion was verified ，and the error could be controlled within 6%. Finally，through analyzing the criterion，it was concluded that the parameters of the system such as inductance L，capacitance C，and the magnitude of the rectifier PI control parameter Kvp have an important influence on the large-signal stability

boundary. This provided new ideas for improving the operational switching stability and optimizing control

parameters of DC building systems.

      Key words：DC microgrid；mixed potential function theory；large-signal stability analysis