Resonant　modular　multilevel　converters　(RMMCs)　have　been　proposed　for　high-voltage　dc-dc　applications.　Using　different　modulation　strategies,　RMMC　operates　in　different　modes　and　achieves　flexible　step　ratio.　To　provide　a　comprehensive　study　of　RMMCs,　this　paper　presents　the　modulation　method　achieving　a　wide　range　of　step　ratio　with　the　ability　of　inherent-balancing.　The　conditions　for　guaranteeing　the　inherent-balancing　ability　are　provided.　The　operation　principle　and　performance　of　the　RMMC　are　presented　in　this　paper,　which　have　been　explored　in　a　case　study.　The　experimental　results　are　obtained　from　a　bench-scale　setup,　which　have　verified　the　theoretical　analysis.