This　paper　proposes　a　new　modular　multilevel　AC/AC　converter　using　high-frequency　(HF)　transformer,　which　has　the　advantages　of　modular　design,　easy　expansion,　high　power　density,　no　circulation　current,　good　output　voltage　waveform　quality　and　low　cost.　This　converter　has　broad　application　prospects　in　the　fields　of　high-voltage　and　high-power　wind　power　generation,　fractional　frequency　power　transmission　(FFTS)　and　power　electronic　transformer.　The　proposed　converter　topology　can　connect　two　three-phase　AC　systems　with　different　frequencies　and　amplitudes　directly.　By　introducing　HF　transformer,　the　direct　series　connection　of　input　and　output　modules　can　be　realized　simultaneously,　and　the　expensive　industrial　frequency　transformer　with　large　volume　and　weight　can　be　removed.　In　order　to　achieve　HF　electrical　isolation,　the　HF　inversion　of　the　output　pulse　is　carried　out　at　the　inverter　side　to　realize　the　HF　output　of　the　fundamental　wave.　After　passing　the　HF　transformer,　the　pulse　is　restored　to　the　low-frequency　output　wave　by　the　cycloconverter.　Aiming　at　the　problem　of　freewheeling　of　HF　link,　the　method　of　common　state　conduction　is　introduced,　which　can　effectively　reduce　the　switching　loss.　The　modulation　scheme,　control　strategy　and　typical　parameter　design　are　developed.　Furthermore,　the　feasibility　of　the　proposed　converter　is　verified　by　simulation　results.　©　2013　IEEE.