The development of new energy generation and DC transmission technologies, coupled with the increasing proportion of photovoltaic power generation, necessitates a medium-voltage high-capacity DC-DC converter with wide-range regulation capabilities to connect the photovoltaic output to the DC grid through a DC converter. This paper proposes a resonant modular multilevel converter and its control strategy, which introduces its modulation method and operating principle and investigates the adaptation of input voltage and output power by adjusting the operating frequency of the converter. Additionally, the proposed control method enables soft switching of the devices, reducing power losses. Finally, a simulation on 60kW RMMC that converts 350-410V to 10kV is built to verify the feasibility of the proposed converter and control strategy.