Three-phase　power　factor　correction　(PFC)　converters　capable　of　step-down　voltage　are　attractive　in　lower　components　voltage　stress,　and　optimal　design　of　following　dc-dc　stage,　which　is　an　alternative　for　next-generation　datacenter　power　conversion.　An　improved　three-phase　step-down　PFC　converter　(swiss　rectifier)　based　on　harmonic-current-injection　(HCI)　concept　is　proposed.　It　improves　input　current　quality　by　eliminating　switching　dead　zone　of　HCI　network　and　avoids　short　circuit　fault　from　hardware　level.　According　to　one-cycle　control　(OCC),　a　novel　nonlinear　control　strategy　(termed　as　closed-loop　OCC)　is　presented,　which　reduces　the　impact　of　dc　inductor　current　ripple　on　input　current.　The　principles　of　the　improved　swiss　rectifier　and　closed-loop　OCC　are　analyzed　in　detail,　verified　by　simulation　and　on　an　80　kHz,　300　V/2　kW　prototype　with　digital　controller.　At　rated　condition,　input　current　THD　©　2017　CPSS.