In interconnected microgrids, the control method for Soft Open Point (SOP) dynamically switches from PQ to Uf control after fault incidents to preserve system stability. However, this mode switching induces frequency and voltage fluctuations, jeopardizing the operational stability of distributed generations (DGs). This paper presents a seamless mode switching control strategy specifically tailored for SOP-based interconnected microgrids incorporating Electric Vehicle (EV) clusters. We investigate the fluctuations and transient impacts associated with emergency control switching and propose a decentralized Virtual Synchronous Generator (VSG) control strategy for energy storage systems. This strategy factors in the State of Charge (SOC) of batteries to mitigate imbalances between source and load during switching delays. Additionally, we introduce a seamless switching method encompassing collaborative phase angle compensation, control mode transition, and pre-synchronization techniques to minimize transient disturbances. Validation through PSCAD/EMTDC simulations and RT-LAB experiments shows effective suppression of fluctuations and transient impacts, thus enabling seamless mode switching in interconnected microgrids.