A study on the dynamic SOC compensation of an ultracapacitor module for the hybrid energy storage system

There have been a number of methods proposed for accurate state of charge (SOC) estimation of a battery as an important role of the battery management system (BMS). However, adequate test data of batteries and BMS development costs must be taken into consideration before application in actual vehicles. In addition, different algorithms need to be adopted according to the type of energy storage device and system configuration. For a mild-HEV hybrid energy storage device that uses the ultracapacitor module and the VRLA battery, the small capacitance of ultracapacitor module makes accurate SOC difficult. Accordingly, this paper introduces a dynamic SOC estimation algorithm capable of SOC compensation of the ultracapacitor module even when there is current input and output. A cycle profile that simulates the operating conditions of a mild-HEV was applied to a vehicle simulator to verify the effectiveness of the proposed algorithm based on testing.