To　analyze　the　permanent　magnet　synchronous　generator　(PMSG)　fault　characteristics,　a　simplified　model　of　grid-side　converter　and　external　characteristics　model　of　controller　with　chopper　are　proposed.　Grid-side　converter　is　an　electric　energy　balance　system　under　controlling　action,　its　complex　structure　is　ignored　and　the　function　and　external　characteristics　are　retained　only.　To　reveal　the　PMSG　short-circuit　current　is　to　analyze　the　three-phase　current　response　under　the　action　of　turbine　terminal　voltage　sag.　A　comparison　with　detailed　model　indicates　that　when　chopper　circuit　does　not　operate,　the　value　of　PMSG　current　is　determined　by　its　output　power　and　the　degree　of　voltage　sag;　besides　50　Hz　component,　there　are　components　whose　frequencies　are　related　to　the　control　parameters;　the　fault　current　firstly　increases　gradually　and　then　decreases　to　a　steady　value;　with　the　increasing　voltage　sag　degree,　the　maximum　fault　current　gets　greater　and　the　corresponding　period　and　transient　decay　time　become　longer;　when　chopper　circuit　operates,　the　fault　current　is　just　the　maximum　converter　current.　©　2015,　Editorial　Office　of　Journal　of　Xi＇an　Jiaotong　University.　All　right　reserved.