With the ongoing advancement of renewable energy, the significance of microgrids has grown substantially. For the Modular Multilevel Converter plate-bridge series microgrid system, which is extensively utilized in microgrid applications, maintaining the stability of the micro-source DC bus voltage is crucial for ensuring its reliable operation. To address the issue of DC voltage fluctuations in the MMC-MG system caused by various factors, this paper proposes a distributed control strategy based on dual-mode switching. Additionally, to enhance the disturbance rejection and robustness of the micro-source DC bus, an improved Linear Active Disturbance Rejection Controller incorporating proportional differential control is introduced. Mathematical models of the microsource system and its associated converters are established, and the dual-mode switching mechanism along with the enhanced LADRC control scheme are meticulously designed. Simulation results demonstrate that the proposed control method not only effectively minimizes overshoot and regulation time of the micro-source DC voltage within the MMC-MG system but also prevents unplanned shutdowns due to insufficient micro-source output, thereby significantly enhancing the overall stability of the system.