Modular multilevel converter (MMC) with partial battery energy storage system (BESS) integration is the critical equipment in the medium-voltage (MV) side of data centers, which not only enhances the power reliability, but also enables real-time power scheduling for data centers and grids. However, the modular structure somehow complicates its auxiliary power supply (APS) and communication architecture. In this paper, a centralized APS (CAPS) with information communication function is designed. The proposed CAPS utilizes a current-transformer (CT)-based H-bridge to power all the submodules (SMs) of MMC, meanwhile the digital signal “1” and “0” are encoded into the shape of the CT current, so that the information can be broadcast to all the SMs synchronously. As an example, the proposed CAPS is utilized to broadcast a synchronization signal to all SMs, which facilitates accurate measurement and synchronized conversion of SM capacitor and battery voltages, thereby helping achieve efficient balancing control of SM voltages. The proposed CAPS is verified in the experimental prototype.