The　grid-connected　inverter　is　a　key　device　in　the　renewable　energy　power　generation　system　and　large-scale　energy　storage　system,　which　the　operational　stability　and　reliability　are　the　basis　for　the　efficient　and　safe　application　of　electrical　energy.　A　real-time　fault　diagnosis　method　of　a　three-phase　for　grid-connected　application　combining　a　mixed　logic　dynamic　(MLD)　model　and　finitecontrol　set　model　predictive　control　(FCS-MPC)　is　proposed.　This　paper　not　only　realizes　the　open　circuit　fault　diagnosis　and　location　of　the　switching　devices　in　the　main　power　circuit,　but　also　discusses　the　threshold　issues　and　post-fault　operations.　The　advantage　of　the　proposed　method　is　that　it　directly　uses　the　control　data　and　measurement　signals　of　the　controller　without　extra　sensors　and　calculation,　which　will　shorter　the　fault　diagnosis　time　and　occupy　less　calculation　resource　of　the　main　processor.　Simulation　results　illustrate　the　quickness　of　the　fault　identification　and　accurate　position　with　robustness　to　the　interference　of　the　diagnosis　method.　Finally,　the　effectiveness　of　the　diagnosis　method　was　verified　by　a　1500　W　experimental　prototype　in　a　laboratory.