A　self-adaptive　controller　is　proposed　to　operate　inverter　in　both　grid-connected　(GC)　state　and　stand-alone　(SA)　state　and　ensure　seamless　transfer　between　them　without　reconfiguring　the　control　structure.　The　controller　is　mainly　composed　of　phase-locked-loop　(PLL)　and　two　cascaded　control　loops.　The　role　of　PLL　is　not　only　to　estimate　the　frequency　but　also　to　generate　the　reference　of　voltage　loop.　When　the　grid　is　normal,　the　reference　and　the　feedback　value　of　voltage　loop　are　always　equal　and　the　proposed　controller　accurately　regulates　the　grid　current　of　inverter.　When　islanding　occurs,　the　inverter　can　automatically　convert　from　current　control　mode　to　voltage　control　mode　without　critical　islanding　detection.　The　self-adaptive　controller　has　several　advantages.　First,　compared　with　direct　current　control,　it　can　operate　in　both　strong　and　weak　grid　conditions.　Second,　its　dynamic　performance　in　the　GC　state　is　much　better　than　that　of　indirect　current　control.　Third,　when　the　grid　returns　to　normal,　the　pre-synchronization　of　inverter＇s　output　voltage　and　grid　voltage　can　be　achieved　automatically　without　any　extra　control　algorithm.　Finally,　simulation　and　experimental　results　are　provided　to　verify　the　effectiveness　of　proposed　self-adaptive　controller.　©　2013　IEEE.