Power　balancing　topology　is　an　effective　solution　to　the　photovoltaic　(PV)　power　mismatch　problem　in　a　medium　voltage　DC　system.　However,　the　existing　power　balancing　topologies　are　all　based　on　a　chain　structure,　in　which　the　mismatched　power　needs　to　be　transferred　through　multiple　power　balancing　units　(PBUs).　In　the　case　of　severe　power　mismatch,　the　accumulated　balancing　power　is　very　large,　resulting　in　increased　system　power　losses　and　current　stress　on　the　switches.　To　solve　this　problem,　a　circular　power　balancing　topology　is　proposed　in　this　paper.　By　connecting　another　PBU　between　the　first　and　last　submodules　(SMs)　of　the　modular　converter,　the　power　balancing　path　becomes　circular.　With　this　new　structure　adopted,　there　are　two　paths　for　power　transfer　between　any　two　SMs.　An　optimization　method　is　also　proposed　to　reduce　the　current　stress　by　half.　Compared　with　an　existing　scheme,　the　proposed　topology　is　able　to　improve　the　power　efficiency.　The　theoretical　analysis　is　verified　by　simulation　and　experiment.　　©　1986-2012　IEEE.