Large voltage fluctuations are observed in the high-voltage DC bus of high-power traction rectifier units, which negatively impact the power supply quality and system stability. To address the requirements of voltage fluctuation suppression and wide-range load regulation in intermediate DC/DC converter systems, a model predictive control (MPC) strategy based on the trust-region dogleg method was proposed. The triple-active-bridge (TAB) converter was selected as the research object. Firstly, the working principle and port coupling mechanism of the TAB converter were introduced. Secondly, a prediction model was established, and a cost function was formulated. To address the difficulty of solving the cost function online, the trust-region dogleg method was employed to minimize the cost function. Finally, experimental validation was conducted on a laboratory prototype. The results indicate that compared with traditional proportional-integral control, the voltage fluctuations of the TAB converter are effectively suppressed, while the dynamic performance and load regulation capability of the system are significantly enhanced. Additionally, port decoupling is achieved.