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In order to improve the dynamic performance of modular super capacitor energy storage system, in this paper, a load current feed-forward control strategy based on extended state observer (ESO) is proposed, which enables the system own the feature of “plug-and-play”. An ESO is designed to observe the load current and details on the design of the ESO are provided, including the convergence of the observer and the design principle of the key parameters. Stability of the proposed control strategy is carried out by using root locus. At last, the effectiveness of the proposed strategy is verified by experimental results.

This paper proposes a novel modular multilevel DC/DC converter(MMDDC) used in super capacitor energy storage system(ESS). Unlike the conventional MMDDC, this converter has an ability to overcome the problem associated with over-current in charge mode. Along with that, it also possesses advantage of convenience in pre-charging super capacitors(SCs) from DC link without additional charging circuits. For the sake of adaption in an ESS, a compound control strategy is developed for the proposed MMDDC, which consists of multiple closed loops. By means of this, system current can be restricted to a safe value, and hence system reliability has potential to be improved. The pre-charge of SCs is also achieved, which benefits from employing the proposed MMDDC. Finally, the effectiveness of the proposed converter and control strategy is verified by simulation and experimental results.