Interlinking modular multilevel converter of hybrid AC-DC distribution system with integrated battery energy storage

Installing the battery energy storage in the interlinking converter of hybrid AD-DC grid can effectively reduce the exchanged energy of hybrid grid and therefore reduce the losses. Being different from the two-level or three-level interlinking converter for low voltage grid application, this paper proposes an interlinking modular multilevel converter (MMC) with integrated battery energy storage for hybrid AC-DC distribution system, where multiple independent batteries are connected to the sub-modules of MMC, respectively. The proposed system can manage the power flow of AC and DC distribution systems and the integrated multiple battery stacks. The circulating current of MMC can help regulate the status of batteries. The injected grid current and external dc currents can be used to control the variables of hybrid grid. This paper analyzes the operational principle of MMC with common dc link voltage and independent sub-module voltages and then proposes the control methods of interlinking MMC. Finally, a scaled down experimental prototype has been built to verify the proposed system.