To　improve　the　efficiency　of　the　dual　active　bridge　(DAB)　converter　working　in　the　low-　and　medium-power　ranges,　this　article　proposes　a　new　triple-phase　shift　(TPS)　modulation　scheme　based　on　frequency-domain　fundamental　harmonic　analysis　(FDFHA)　with　lower　root　mean　square　(rms)　current　and　wider　zero-voltage　switching　(ZVS)　range.　The　DAB　converter＇s　Fourier　decomposition　expression　under　TPS　is　generated,　and　the　FDFHA　expression　is　created　using　fundamental　harmonic　analysis　(FHA).　With　the　rms　current　as　the　optimization　target,　the　operating　point　with　the　smallest　rms　current　is　found　by　solving　for　it　using　the　extended　global　optimum　condition　(EGOC)　that　applies　to　the　FDFHA　expression.　Based　on　this,　a　control　strategy　with　a　simple　controller　structure　is　established,　which　has　excellent　dynamic　performance.　In　addition,　when　comparing　the　proposed　scheme　to　other　optimized　schemes,　the　results　show　that　the　proposed　scheme　can　drastically　lower　the　rms　current　in　the　low-　and　medium-power　ranges　and　achieve　a　wider　ZVS　range,　notably　in　the　low-power　range　to　enable　all　switches　to　achieve　ZVS.　Finally,　an　experimental　prototype　with　a　peak　efficiency　of　95.95%　was　built　to　verify　the　effectiveness　of　the　proposed　scheme.