A two-stage AC/DC SST based on modular multilevel converter

This paper proposes the use of the modular multilevel converter (MMC) in ac-dc conversion using medium frequency transformers in a two-stage topology with unidirectional switches. The medium frequency link provided by each module of the MMC is used to supply the windings of the transformer. A full-bridge rectifier connected to the dc side supplies the secondary side as the power flow is controlled by the phase-shift angle between the primary and secondary voltages. The resulting topology is fault tolerant since a short-circuit in the dc side causes low additional stress in the semiconductors. The basic description and some simulation results are presented in order to valid the proposal.