The　three-phase　dual　active　bridge　(3p-DAB)　converter　is　a　promising　topology　for　high　power　dc-dc　conversion　due　to　advantages　of　bidirectional　power　flow,　inherent　soft　switching　capability,　and　reduced　filter　volume.　This　paper　presents　comprehensive　analysis　of　the　duty　cycle　control　(DCC)　for　optimizing　the　performance　of　3p-DAB.　Based　on　DCC,　an　optimized　modulation　strategy　is　proposed　to　minimize　the　conduction　losses　of　3p-DAB　in　the　whole　load　range.　The　proposed　modulation　strategy　extends　the　soft　switching　range　of　3p-DAB　with　large　voltage　variations　simultaneously.　It　is　established　through　loss　analysis　that　the　proposed　modulation　strategy　boosts　the　efficiency　of　3p-DAB,　especially　at　low　loads.　When　the　duty　cycles　change　fast　as　a　result　of　the　abrupt　changed　transmission　power,　the　transformer　currents　can　become　unbalanced,　leading　to　the　magnetic　bias　and　oscillations　in　dc　currents.　This　paper　further　proposes　a　fast　transient　current　control　(FTCC)　method　for　3p-DAB　with　variable　duty　cycles.　The　FTCC　enables　the　converter　to　transfer　from　one　steady　state　to　another　within　about　one　third　switching　period,　hence　balances　the　transformer　currents　rapidly　and　avoids　oscillations　in　dc　currents.　Finally,　experimental　results　verify　the　outstanding　performance　of　the　proposed　modulation　strategy　and　FTCC　method.　IEEE