Modeling of Second-Life Batteries for Use in a CERTS Microgrid

A second-life battery is an electric vehicle battery pack that has reached an end-of-life condition for its vehicular use, yet retains enough performance to be re-purposed for another application. One promising application of a second-life battery is stationary energy storage within a CERTS microgrid. This paper investigates the modeling of multiple paralleled traction battery packs within a CERTS microgrid, examining the impacts of elevated internal pack impedance on microgrid system operation. Impedance spectroscopy and hybrid-pulse power characterization are used to model vehicular Li-ion cells under a range of conditions that include second-life aging. The ac bus dynamics of the microgrid model are validated experimentally. Second-life battery models are incorporated into two CERTS microgrid architectures and system-level effects of changing the battery impedance are explored. Simulation results indicate that the modeled EV second-life batteries deliver promising performance characteristics in both CERTS microgrid architectures that were investigated.