This paper deals with a novel power conversion system for integrating different Battery Energy Storage Systems (BESSs) in electric power systems. It consists of a suitable combination of a three-phase three-level Neutral-Point-Clamped converter (NPC) and two Dual Half Bridge converters (DHBs): the former represents the interface between the AC grid and the DC-link, while each DHB connects a BESS to one side of the DC-link. The proposed configuration enables a suitable BESS management in terms of power and voltage regulation, especially the possibility of operating with different DC-link voltages in accordance with different BESS requirements. This goal is achieved through suitable DHB and NPC control systems, together with a novel Multilevel Space Vector Modulation (MSVM), which enables a decoupled control of AC power and DC-link voltages. Simulation results show the effectiveness and the potentiality of the proposed power conversion system, which are also corroborated by some experimental results.