The energy consumption of urban rail transit in China has become a growing concern due to its continuous expansion. In recent years, the ground-based energy storage systems have been widely implemented in urban rail transit to absorb regenerative braking energy, resulting in significant energy savings. However, the current bidirectional DC/DC converter used in these systems utilizes Si IGBT (Silicon Insulated Gate Bipolar Transistor) as the switching device, leading to large converter volumes and masses due to its low switching frequency. In certain substations with limited installation space, the excessive volume of the converter becomes a critical factor restricting the power level of the energy storage system. To address this issue, the research investigates the characteristics of the full SiC converter by replacing the Si IGBT switching device with SiC MOSFET. Additionally, a converter efficiency optimization control strategy is proposed based on the relationship between converter loss and operating power. The strategy involves adjusting the number of bridge arms and can enhance the efficiency of the system.