In　order　to　solve　the　problems　of　poor　load　adjustment　ability　and　narrow　output　current　range　in　traditional　hysteretic　current　control,　a　fixed-ripple　control　strategy　based　on　three-phase　combined　DC-DC　Buck　driver　was　proposed,　which　used　the　third-generation　semiconductor　GaN　device　to　increase　the　power　density　of　the　driver.　The　operating　characteristics　of　three-phase　combined　Buck　driver　and　its　fixed-ripple　control　strategy　were　analyzed　in　detail,　the　driver　operating　in　continuous　conduction　mode　(CCM)　and　discontinuous　conduction　mode　(DCM)　were　unified　mathematical　modeling,　small　signal　model　and　corresponding　control　equations　were　deduced,　and　the　key　parameters　of　the　circuit　were　designed.　Finally,　a　1.　8　kW　distributed　multiple-phase　combined　Buck　experimental　prototype　and　a　single　Buck　driver　used　GaN　switching　device　were　built.　Computer　simulation　and　experimental　results　show　that:　The　maximum　efficiency　of　the　prototype　can　achieve　99.　54%　at　the　output　power　of　600　W;　On　and　off　time　of　the　switching　tube　can　be　adjusted　by　using　the　proposed　control　strategy　adaptively,　which　improves　the　dynamic　performance;　10%　~　100%　wide-range　dimming　and　the　fixed-ripple　control　of　inductor　current　are　realized　in　CCM　and　DCM;　The　constant　current　dimming　accuracy　is　improved　by　controlling　the　average　value　of　the　inductor　current　directly,　which　is　less　than　1%　.　©　2023　Editorial　Department　of　Electric　Machines　and　Control.　All　rights　reserved.