Control and Power Management of Hybrid Energy Storage Systems

The increasing integration of renewable energy sources and the electrification of transportation have significantly raised the demand for efficient and reliable energy storage systems. Among the various technologies available, Lithium-ion Battery Energy Storage Systems (BESS) have become the most widely adopted solution due to their high energy density and maturity. However, BESS alone faces several challenges when subjected to applications that involve rapid power fluctuations, high-frequency cycling, and frequent charge/discharge events. These operational conditions accelerate battery aging, reduce cycle life, and increase the levelized cost of storage over time. This limitation has motivated the development of alternative system architectures, which aim to offload the high-frequency and transient power demands from the battery to a complementary storage device.
A promising approach to overcome these limitations is the use of Hybrid Energy Storage Systems (HESS), which combine complementary storage technologies, typically a high-energy BESS with a high-power storage element such as a Supercapacitor Energy Storage System (SCES) or a Flywheel Energy Storage System (FESS). ... mehrThe HESS configuration enables the power demand to be split: slow, energy-intensive components are allocated to the battery, while the auxiliary storage handles fast transients and high ramp-rate events. This decoupling not only enhances the performance and responsiveness of the storage system but also mitigates the aging mechanisms of the battery by reducing the stress caused by rapid power variations.
While the HESS architecture offers clear advantages over standalone battery systems, its effective operation requires sophisticated control and power management strategies. The fundamental challenge lies in dynamically coordinating two or more storage components with vastly different characteristics, such as response time, energy capacity, efficiency, and degradation behaviour, under highly variable power demands. Ensuring that each component operates within its safe limits, while jointly fulfilling system-level performance objectives (e.g., minimizing losses, extending lifespan, and maintaining power quality), requires real-time, intelligent control and management systems.
In particular, the power-splitting strategy between the BESS and the auxiliary storage must not only respond to the instantaneous power profile but also consider long-term state variables, such as the State of Charge (SoC) of each unit and the battery's ramp rate limitations. Traditional rule-based or low-pass filter methods often fail to provide adequate flexibility or adaptability under dynamic conditions. Therefore, control of HESS is not just technically challenging; it is essential for unlocking the full potential of hybrid storage systems.
This thesis addresses these challenges by proposing advanced control and estimation strategies for hybrid energy storage systems. In particular, it explores methods for effective power management, accurate SoC estimation, and mitigation of battery aging under dynamic operating conditions. The work examines how HESSs can be controlled more effectively and demonstrates that carefully managing the various storage components can enhance the system's efficiency and longevity. The findings help to better understand how HESS behaves in practice and provide useful guidance for designing hybrid storage systems that perform effectively in real-world applications.