The　appropriate　control　strategy,　which　takes　the　unbalanced　grid　connected　voltage　and　unbalanced　compensation　current　into　account,　is　needed　to　keep　the　DC　side　voltage　of　each　phase　H　bridge　constant　in　star　connection　cascaded　H-bridge　multilevel　static　var　generator　(SVG).　The　common　method　is　to　add　the　zero　sequence　voltage　to　the　SVG.　Considering　the　unbalanced　grid　voltage　or　unbalanced　compensation　current,　the　requirements　for　the　normal　operation　of　the　SVG　were　analyzed　based　on　the　zero　sequence　voltage　component　superposition　method.　The　relationship　of　the　grid　voltage　unbalance　degree,　compensating　current　unbalance　degree　and　the　rated　voltage　was　analyzed.　The　compensation　characteristic　of　the　negative　sequence　current　was　deduced　with　the　certain　grid　voltage.　The　influence　of　grid　voltage　variation　on　the　output　voltage　was　also　considered　with　the　certain　compensating　current.　Finally,　the　correctness　of　the　relevant　theoretical　analysis　was　verified　by　simulation　and　experiment.　These　quantitative　analyses　have　directive　significance　for　the　application　and　selection　of　the　star　connection　cascaded　H-bridge　multilevel　SVG.　©　2018　Chin.　Soc.　for　Elec.　Eng.