This　paper　compares　the　popular　control　methods　for　two　dominant　types　of　active　power　filters　(APFs).　With　the　equivalent　transformation　of　their　control　diagrams,　the　recently　proposed　current-source　control　method　for　series　active　power　fdter　(SAPF)　is　revealed　to　have　the　same　control　structure　as　the　traditional　voltage-source　control　method　therefore　have　same　compensation　performances.　Similarly,　two　kinds　of　popular　control　methods　for　parallel　active　power　filter　(PAPF)　are　also　compared　and　found　to　have　the　similar　control　structure.　The　recently　proposed　PAPF　control　scheme　without　harmonics　detection　is　revealed　as　a　reduced　version　of　the　traditional　control　scheme　with　harmonics　detection.　Therefore　both　have　same　basic　control　principles　regarding　load　current　harmonics　compensation.　A　general　expression　of　the　control　methods　for　PAPF　is　then　proposed　in　the　form　of　both　a　control　diagram　and　a　set　of　equations　based　on　current　detection.　With　a　particular　set　of　filter　gains　of　the　three　detected　currents,　each　particular　control　scheme　can　be　specifically　identified　and　described　by　the　general　expression.　Subsequently　the　64　possible　sets　of　filter　gains　are　examined　by　the　proposed　necessary　conditions　to　locate　practically　valid　control　schemes.　Finally　4　valid　control　schemes　come　out　and　among　which　some　are　schemes　that　have　never　been　reported　before.　With　the　comprehensive　comparison　of　the　control　methods　and　the　proposed　general　expression　in　this　paper,　the　essential　relationships　of　the　control　methods　are　revealed,　some　misinterpretations　from　previous　publications　are　clarified,　and　some　new　control　schemes　are　obtained.　copy;　2008　IEEE.