LCL　filter　is　widely　used　in　grid　connected　converters　for　good　harmonic　mitigation　performance.　However,　resonance　poles　of　LCL　filter　challenge　the　system　stability,　especially　in　digital　controlled　system.　Various　active　damping　approaches　have　been　proposed　to　solve　the　resonance　issue,　where　the　capacitor　current　based　active　damping　control　is　an　attractive　option.　In　this　paper,　system　stability　with　capacitor　current　based　active　damping　control　is　analyzed　with　the　consideration　of　digital　control　delay.　A　design　principle　for　the　active　damping　compensator　is　proposed　in　this　paper,　where　maximum　stability　margin　can　be　reached　for　active　damping　loop.　It　is　shown　that　capacitor　current　feedback　control　with　negative　proportion　gain,　instead　of　positive　gain,　presents　much　better　performance　with　considerable　control　delay.　Simulative　and　experimental　results　validate　the　proposed　control　method.　©　2020　IEEE.