Three-port　dc-dc　converters　(TPCs)　integrate　renewable　energy　systems,　energy　storage　systems,　and　loads,　which　have　the　characteristics　of　high　integration　and　high　reliability.　This　paper　proposes　a　high-gain　TPC　(HGTPC)　with　soft-switching　for　renewable　energy　system　applications.　In　various　operating　modes　of　the　proposed　converter,　all　switches　can　achieve　zero　voltage　switching　(ZVS)　turn-on　and　all　diodes　can　achieve　zero　current　switching　(ZCS)　turn-off,　which　can　effectively　improve　the　efficiency　of　the　converter.　In　addition,　the　coupled　inductor　achieves　zero　dc　bias,　which　can　reduce　the　magnetic　size　and　core　loss.　The　working　principle,　performance　analysis,　efficiency　analysis,　parameter　design,　energy　management　and　control　and　of　the　proposed　converter　are　presented.　A　300-W　experimental　prototype　with　a　45-V　photovoltaic　(PV)　voltage,　a　90-V　battery　voltage,　and　a　380-V　load　voltage　is　built　to　verify　the　feasibility　and　correctness　of　the　converter.　　©　1986-2012　IEEE.