Non-isolated DC/DC converters face challenges such as weak stability, poor power quality, and limited fault handling capability in grid interconnection. This paper analyzes the topology and fault blocking principle of a bipolar Π-type DC/DC converter (DC-MMC) with single-phase operation and bi-directional DC fault blocking capability. A double-closed-loop PI control strategy is designed based on single-phase dq decoupling to control the DC component of the bridge arm, the system circulating current, and the power balance between the bridge arms in the converter. However, model predictive controls applicable to DC-MMC often have the problems of complex control, large computation and slow response, etc. Aiming at the strong coupling characteristics of the converter structure, an improved model predictive control strategy based on the principle of step-by-step optimization is proposed to improve the steady-state and transient performance of the converter. Finally, the feasibility and effectiveness of the proposed control strategy are verified using a simulation model built in MATLAB/Simulink.