Control of bidirectional DC/DC converters in reconfigurable, modular battery systems

Abstract

Bidirectional power systems such as renewable energy systems and DC micro grids employ battery cells for energy storage and a DC bus for loads and power sources. This paper presents a control approach to interconnect reconfigurable modules that serve as an interface between battery cells and the DC bus. The modules are composed of series or parallel output sub-module converters that have single or multiple battery cells connected at their input port. The proposed control approach achieves DC bus voltage regulation and output voltage sharing among sub-module power converters under bidirectional power flow, and can be used for an arbitrary number of converters in either series or parallel configuration. The control strategy performs continuous cell balancing by actively distributing power differentially among sub-module converters according to the relative state-of-charge and capacities of the battery cells. A reconfigurable module composed of two series or parallel output 480 W, 27–37 V dual-active bridge sub-module converters, and twelve 25 Ah Li-ion NMC battery cells is used to demonstrate DC bus voltage regulation and cell balancing in hardware experiments.