Stability and power quality considerations for energy augmentation of BESS projects

This paper observes potential stability and power quality conditions that may emerge during energy augmentation of Battery Energy Storage Systems (BESS). The term “energy augmentation” describes methods used to maintain contracted energy capacity of BESS projects over the lifetime of the project as battery health degrades. Some BESS vendors may achieve this purely through DC side modifications such as replacement or addition of batteries. However, for logistical reasons, some vendors may choose to augment the project on both the AC and DC sides by delivering integrated systems with additional transformers, converters, and batteries. These additional AC side components change the physical impedance characteristics of the project, which may create new interactions between the project and the system that were not observed in prior study processes. Both positive-sequence phasor domain and electromagnetic transient (EMT) time-domain methods are shown to be inadequate or time consuming to apply to a large number of cases, which makes them inappropriate to assess performance sensitivity to changing designs. The paper addresses these modelling challenges through application of frequency-domain analytical methods to screen for sufficient design margin to maintain desired stability and power quality across the evolving project and system impedance conditions.