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Cascaded Isolated DC-DC Converters (IDCs) is a popular topology for battery energy storage system in data center application with the advantage of galvanic isolation, higher efficiency and independent control capability. However, the absence of normal operation under unbalance conditions among battery modules is a big issue. To this end, considering the voltage-power relationship and limited voltage gain of IDC, a distributed multimode control is proposed in this paper. Each IDC can be switched flexibly between multiple operation modes to extend the range of system optimization operation. Individual power regulation and autonomous distribution of output voltage are achieved without real-time communication under the proposed control strategy. Meanwhile, boundary operation conditions are analyzed in detail. Furthermore, a parameter design procedure for cascaded IDCs based battery energy storage system is also proposed considering the upper/lower gain limits of IDCs and three kinds of boundary operation conditions. In this way, modular design is achieved and the operation efficiency and robustness are improved. A simulation system and a down-scaled experimental system is constructed to verify the effectiveness of the proposed control strategy.

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