Abstract: Modular multi-level DC converters have received extensive attention from industry and academia with the rapid development of large-capacity medium-voltage DC power distribution technology. However, achieving highly reliable auxiliary power supply is one of the key technical bottlenecks to realize the application of DC converters in medium-voltage DC power distribution scenarios. To this end, this paper proposes a highly reliable self-powered system architecture for modular multi-level medium-voltage DC converters. The architecture realizes the medium-voltage direct power supply of the central controller and sub-modules, so that no additional low-voltage DC power supply is required, and the system startup speed is greatly improved. Based on this architecture design, the auxiliary power supply of the sub-module controller and the bypass switch for modular multi-level medium-voltage DC converters have achieved three times redundancy, which improves the fault-tolerant operation capability of the system. A voltage balancing method of sub-module capacitors based on the autonomous control of auxiliary power supply in the pre-charging stage is proposed, which ensures the reliable pre-charging of the modular multi-level DC converter. Finally, the feasibility of the proposed auxiliary power supply system architecture is verified by experiments.