Hierarchical SOC Balancing Controller for Battery Energy Storage System

This article presents a hierarchical state-of-charge (SOC) balancing control method for a battery energy storage system. In the presented system, multiple battery cells are connected in-parallel at the inputs of a single-inductor multiinput single output (SI-MISO) power converter to form a battery module and multiple battery modules are connected in series at the output to form the complete battery system or pack. The presented hierarchical controller is able to control the SOC (achieve SOC balancing) at both the cell level and the module level (between all cells that are effectively connected in series and in-parallel) while simultaneously maintaining bus voltage regulation at the battery system or pack output. This is achieved by using the presented modulation scheme for the duty cycles of the power converter switches. Theoretical analysis and results from a proof-of-concept experimental prototype are presented and discussed in this article in order to evaluate and validate the operation of hierarchical SOC balancing controller and battery system.