Topology and Efficiency Analysis of Utility-Scale Battery Energy Storage Systems

Energy storage is an important flexibility measure to stabilize and secure the electrical energy supply system. Lithium-ion battery energy systems (BESS) are, owing to their characteristics, uniquely poised to support and augment the functioning of the energy supply system. It is crucial to identify and analyze the factors which play a role in their efficient and effective operation. This paper identifies and analyses three such major factors application scenarios, power electronics with power distribution strategies, and battery parameters which influence the efficiency of a BESS. The applications analyzed are primary control reserve and peak shaving. Two Power electronics topologies and their load distribution strategies are presented, with their influence on the conversion efficiency being evaluated subsequently. Two commercial lithium-ion technologies a Lithium Iron Phosphate cathode/Graphite anode cell and a Lithium Nickel Manganese Cobalt Oxide cathode/Graphite anode cell are also simulated for two states of health (SOH). The aged cells are considered to possess a capacity equal to 80% of original nominal capacity and a cell resistance twice that of the new cells. It is found that the system conversion efficiency can be greatly improved in applications with low active chargebased and high temporal utilization ratios by deploying a suitable power electronics topology and load distribution strategy. For applications with high active charge-based and low temporal utilization ratios, the battery resistance and the serial-parallel combination play an important role.