Dynamic Model of Battery Charging

In smart grid environment, batteries charged from grids during off peak hours (specially late night) for use either in electric vehicles or as emergency power source play an important role as Distributed Energy Resources (DERs) at the demand side. It is important to estimate the support available from such a resource for energy management during a contingency. In this paper, a dynamic (time varying) model of charging with constant current has been developed for lead acid batteries. This model provides a means to compute analytically the open circuit voltage (OCV) at a given time and the corresponding state of charge (SOC). A few sets of data obtained from practical tests of different sizes of batteries have been used to determine model parameters. The model is then applied to another battery and the output compared with its available test data for validation. As lead acid batteries are very common and affordable these have been used in this work. However, the methodology reported in this paper can always be extended to develop similar models for Nickel Metal Hydride (NiMH) or Lithium ion (Li-ion) batteries. Therefore, this paper presents a generic model that can be used for other, newer battery types.