Three-phase　PWM　inverters　function　as　energy　converters　and　grid-connected　power　generators　in　renewable　energy　generation　systems,　and　its　dynamic　and　stability　characteristics　affect　the　security　and　reliability　of　the　entire　generator　sets　and　even　the　connected　grid.　The　three-phase　PWM　inverters　based　on　the　VSG　(Virtual　Synchronous　Generator)　technology,　which　is　referred　to　as　the　Static　synchronous　generator　(SSG)　in　this　article,　possess　the　operation　characteristics　of　Rotational　Synchronous　Generator　(RSG),　and　thus　enables　a　compatible　connection　of　the　new　energy　to　the　conventional　power　grid.　This　paper　analyzes　the　inherent　unity　of　SSG　and　RSG　by　the　mathematical　model　and　physical　mechanisms,　and　applies　the　concept,　tools　and　methods　of　the　stability　analysis　in　RSG　to　the　SSG　system.　The　equivalent　inertia,　damping　and　synchronizing　coefficients　are　introduced　for　the　dynamic　analysis　of　SSG　and　the　small-disturbance　stability　is　analyzed　accordingly.