A Novel Scheme for Isolated Modular Converter Based Lithium-ion Battery Energy Storage System

The isolated modular converter (IMC) based energy storage system (ESS) is a kind of bidirectional power system. This article introduces a new scheme for backup power supply applications, which consists of the hybrid cascaded topology of IMC and the distributed control strategy of Lithium- ion series battery packs. The IMC is used as the power exchange interface between DC-bus and battery packs, which is a two-stage power electronic circuit. The first stage is input-series-output- parallel connection (ISOP) circuit based on isolated bidirectional DC-DC sub-modules. The second stage is H-bridge. The function of H-bridge is to adjust the output voltage in positive and negative range. By cascading the ISOP sub-modules and H- bridge circuit, the IMC device is formed. The control method in this paper includes DC-bus connection control method and SOC equalization of Lithium-ion battery packs control method. Benefiting with hybrid cascaded topology and control strategy, ESS can provide stable voltage or current to DC-bus and realize SOC equalization of battery packs. This paper realizes the design of lkW isolated bidirectional DC-DC with 93% peak efficiency. The theoretical peak efficiency of a 12kW hybrid cascaded IMC based on 5 series lkW isolated DC-DC sub-modules is 97%. Due to the distributed control strategy, the energy of Lithium-ion battery packs is fully utilized and the total energy utilization of ESS will be greatly improved.