Modelling and Evaluation of Valve-Regulated Lead-Acid Batteries

Ander Tenno

Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Department of Automation and Systems Technology for public examination and debate in Auditorium AS1 at Helsinki University of Technology (Espoo, Finland) on the 3^rd of December, 2004, at 12 o'clock noon.

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Abstract

The thesis deals with modelling of valve-regulated lead-acid (VRLA) batteries to answer the two biggest questions of 'will they work' and 'when will they need to be replaced' without resorting to full discharge. Despite the strong efforts undertaken by numerous researchers in search of simple and reliable indicators of the state-of-health (SOH) of a battery they were never found. Originally, it was expected that resistance, conductance and impedance measurements could be such indicators, but they have turned out to be unreliable.

This dissertation attempts to solve the problem by proposing a complex approach utilising fast calculation model for electrochemical processes to predict the behaviour of VRLA batteries under charge-discharge conditions and applying this model to a fast analysis of backup batteries in uninterruptible power supply (UPS) systems and detection of weak batteries in telecommunication networks.

This model can predict the behaviour of VRLA batteries in full range of charge-discharge processes, including deep discharge and overcharge of batteries, using direct current, voltage and temperature measurements. The SOH of batteries can be detected by this method in terms of natural electrochemical processes.

This thesis consists of an overview and of the following 8 publications:

1. Tenno A., Tenno R. and Suntio T., 2001. Charge-discharge behaviour of VRLA batteries: model calibration and application for state estimation and failure detection. Journal of Power Sources 103, number 1, pages 42-53.
2. Tenno A., Tenno R. and Suntio T., 2001. Soft-sensor approach in characterization of VRLA batteries. In: Proceedings of the 23rd International Telecommunications Energy Conference (INTELEC 2001). Edinburgh, Scotland, 14-18 October 2001, pages 554-562.
3. Tenno A., 2002. Software for evaluation of VRLA batteries. In: Proceedings of the Second IASTED International Conference on Power and Energy Systems (EuroPES 2002). Crete, Greece, 25-28 June 2002, pages 461-466.
4. Tenno A., Tenno R. and Suntio T., 2002. Fast model for monitoring of backup batteries in telecommunications networks. In: Proceedings of the 6th IASTED International Conference on Power and Energy Systems (PES 2002). Marina Del Rey, California, USA, 13-15 May 2002, pages 458-463.
5. Tenno A., Tenno R. and Suntio T., 2002. Battery impedance and its relation to battery characteristics. In: Proceedings of the 24th International Telecommunications Energy Conference (INTELEC 2002). Montreal, Québec, Canada, 29 September - 3 October, 2002, pages 176-183.
6. Tenno A., Tenno R. and Suntio T., 2002. Evaluation of VRLA battery under overcharging: model for battery testing. Journal of Power Sources 111, number 1, pages 65-82.
7. Suntio T., Tenno A. and Tenno R., 2003. Impedance characterization of VRLA batteries. In: Proceedings of the 9th Power Quality Conference, pages 325-330.
8. Tenno A., Tenno R. and Suntio T., 2004. A method for battery impedance analysis. Journal of The Electrochemical Society 151, number 6, pages A806-A824.

Keywords: batteries, VRLA, lead acid, modelling, identification

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© 2004 Helsinki University of Technology