Aiming　at　the　problems　of　low　output　voltage　and　poor　power　supply　reliability　of　solar-storage　combined　power　supply　system,　a　non-isolated　high　step-up　three-port　DC-DC　converter　with　multiple　working　modes　is　proposed.　The　three　ports　of　the　converter　share　the　ground,　which　are　respectively　connected　to　the　photovoltaic　power　generation　unit,　the　energy　storage　unit　and　the　load.　The　improved　quadratic　structure　improves　the　voltage　gain　and　reduces　the　stress　of　the　switching　device.　The　converter　has　five　working　modes,　which　can　meet　the　requirements　of　various　operating　conditions　of　the　off-grid　solar-storage　power　generation　systems.　In　addition,　the　converter　has　no　voltage　constraints　between　the　photovoltaic　port　and　the　energy　storage　port,　and　is　suitable　for　more　occasions.　The　working　principle　and　steady-state　characteristics　of　the　converter　in　each　working　mode　were　analyzed　in　detail,　and　the　working　characteristics　were　compared　with　the　existing　similar　converters.　According　to　the　control　requirements　of　the　solar-storage　combined　power　supply　system　and　the　power　flow　of　the　converter　under　different　working　conditions,　the　corresponding　mode　operation　and　switching　control　strategies　were　studied.　Finally,　a　300　W　experimental　prototype　was　built　for　verification.　©　2023　Editorial　Department　of　Electric　Machines　and　Control.　All　rights　reserved.