Power and Energy Management of Battery Energy Storage Systems for Grid Integration

Battery energy storage system (BESS) plays a critical role in grid applications, where it can perform services such as mitigation of the intermittency of renewable energy, grid frequency regulation, peak shaving, and grid voltage support/var compensation. To interface the BESS to the grid, Modular Multilevel Converters (MMC) are being widely considered, particularly for medium and high voltage applications. This dissertation develops power strategies and energy requirements for a BESS-MMC. The work starts from developing battery models for grid applications to system-level operation, including BESS and the electric grid. A novel methodology to estimate the parameters of the equivalent circuit model (ECM) for lithium-ion battery cells focusing on their use in grid applications is developed. Parameter dependencies on the state of charge (SoC) and temperature are included in the proposed methodology and correlated through polynomial regression. Accelerated degradation tests are performed to obtain the parameter variation as the battery ages. The obtained information is helpful to design components in the BESS-MMC, controller parameters, SoC, and State of Health (SoH) estimation. The dissertation also investigates the precise capacitor energy requirements for various operations of BESS-MMC, which include arm/phase power transfer. Further, the relation between the controller design and the submodule’s capacitor sizing in terms of its energy requirements is also explored. Design guidelines for the module level voltage control to attenuate battery ripple and a detailed analysis of the capacitor energy requirement in each operating mode are presented. Aiming to improve the BESS-MMC resiliency by maintaining it connected to the electrical grid, faulty scenarios involving asymmetric grid voltage conditions and an asymmetric power available in each phase and arm are considered. Several power and SoC balancing techniques with defined active power limits to avoid battery overuse are proposed and verified through C-HIL results. The use of BESS-MMC as an interlinking converter (IC) between AC and DC microgrids in a hybrid microgrid environment is explored. This avoids the connection of battery modules into either DC or AC microgrid and provides complete decoupled operation between grids. Control strategies, as well as possible power management strategies, are proposed and verified through C-HIL results.