A state-space model for integration of battery energy storage systems in bulk power grids

Applications of Battery Energy Storage Systems (BESS) in the power grids will be expanded in the coming years due to factors such as decreasing costs of such systems. In a modern power network, BESS systems can be optimally controlled for peak-load shaving and other ancillary services such as volt-var control, system balancing and loss reduction. However, all these “system-level” controls will depend on the capability of each individual BESS to independently control the active and reactive power injection/absorption at its connected bus, and to maintain the voltage of the DC link between its AC/DC and DC/DC converters. As a result, understanding the behavior and control requirements for the operation of the BESS is necessary. In this paper, an active AC/DC rectifier and a bidirectional DC/DC converter have been modeled and analyzed for charging and discharging of the batteries in a BESS system. The models used in these analyses have been developed based on an integrated state-space equation set for the converters and the battery. This type of modeling is proper for demonstration of the effects of massively integrated storage systems in the bulk power grids.