Abstract-The modular structure and the many other advantages of the Modular Multilevel Converter makes it an attractive converter for Battery Energy Storage Systems, allowing the battery units to be distributed throughout the convert, connected in each submodule. However, such an arrangement results in large oscillating components in the battery current, which is harmful to battery performance and lifetime. In most literature this is solved using DC-DC converters as active interfaces between battery and submodule. This paper investigates a passive filter arrangement as an alternative solution to the DC-DC converters. Where the batteries are interfaced with the submodules using a passive filter that suppresses the fundamental component and control technique that injects circulating current to suppress second harmonic component. It is concluded that this passive technique could be an attractive solution especially where high reliability is of concern.

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