Analysis and implementation of an enhanced modular multilevel DC/DC converter for super capacitor energy storage system

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.