Possessing　the　capability　to　handle　high　voltage,　the　bidirectional　input-series-output-series　(ISOS)　modular　dc-dc　converter　is　suitable　for　use　in　dc　grids.　Regarding　topology　selection　of　the　constituent　modules,　the　open-loop　controlled　series-resonant　dual　active　bridge　(SR-DAB)　converter　exhibits　superior　efficiency　performance　and　the　advantage　of　simple　control.　However,　it　has　no　regulation　capability.　Aimed　to　reap　the　advantages　of　SR-DAB　and　achieve　flexible　control,　this　article　presents　a　hybrid　ISOS　converter　composed　of　SR-DAB　and　nonresonant　phase-shift　controlled　dual　active　bridge　(PS-DAB)　modules.　The　SR-DAB　modules　process　most　of　the　power　to　ensure　high-efficiency　conversion,　whereas　the　PS-DAB　is　responsible　for　flexible　control.　At　the　output　stage　of　the　ISOS　system,　embedded　nonisolated　resonant　dual　active　half-bridge　(NR-DAHB)　converters　are　integrated　between　every　two　adjacent　modules　without　adding　any　switches.　The　transformer　property　of　the　open-loop　controlled　SR-DAB　and　NR-DAHB　circuits　facilitates　natural　voltage　sharing　at　both　the　input　and　output　sides.　The　hardware　experiment　has　been　conducted　to　verify　the　operating　principles　and　performance　of　the　proposed　ISOS　system.　©　1982-2012　IEEE.