Extensive　solutions　have　been　proposed　to　damp　LCL　resonance,　where　active　damping　(AD)　schemes　based　on　a　single　filter　variable　feedback　have　been　shown　to　be　effective　and　flexible.　This　paper　presents　a　study　of　such　AD　techniques,　where　a　virtual　impedance　model　is　unified　for　four　commonly　used　inner　loop　feedback　state　variable　and　a　unified　analysis　method　is　proposed.　Consequently,　the　quantitative　relationship　between　controller　parameter　and　actual　resonant　frequency　is　revealed,　which　is　meaningful　for　control　system　design.　Finally,　the　effectiveness　and　accuracy　of　the　proposed　method　are　verified　by　system　bode　diagram　design　results.　©　2021　IEEE.