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Observer techniques for estimating the state-of-charge and state-of-health of VRLABs for hybrid electric vehicles

By B S Bhangu, P Bentley, D A Stone and Chris Bingham

Abstract

The paper describes the application of observer-based state-estimation techniques for the real-time prediction of state-of-charge (SoC) and state-of-health (SoH) of lead-acid cells. Specifically, an approach based on the well-known Kalman filter, is employed, to estimate SoC, and the subsequent use of the EKF to accommodate model non-linearities to predict battery SoH. The underlying dynamic behaviour of each cell is based on a generic Randles' equivalent circuit comprising of two-capacitors (bulk and surface) and three resistors, (terminal, transfer and self-discharging). The presented techniques are shown to correct for offset, drift and long-term state divergence-an unfortunate feature of employing stand-alone models and more traditional coulomb-counting techniques. Measurements using real-time road data are used to compare the performance of conventional integration-based methods for estimating SoC, with those predicted from the presented state estimation schemes. Results show that the proposed methodologies are superior with SoC being estimated to be within 1% of measured. Moreover, by accounting for the nonlinearities present within the dynamic cell model, the application of an EKF is shown to provide verifiable indications of SoH of the cell pack

Topics: H600 Electronic and Electrical Engineering
Publisher: Institute of Electronic and Electrical Engineering
Year: 2005
DOI identifier: 10.1109/VPPC.2005.1554646
OAI identifier: oai:eprints.lincoln.ac.uk:2553

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