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Design of a State of Charge (SOC) Estimation Block for a Battery Management System (BMS).
Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering. RWTH Aachen University, Germany.. (ISEA (Institute for Power Electronics and Electrical Drives) RWTH Aachen)
2013 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesisAlternative title
Entwicklung eines Ladezustand Block für Battery Management System (BMS) (German)
Abstract [en]

Battery Management System (BMS) is an essential part in battery powered applications where large battery packs are in use. BMS ensures protection, controlling, supervision and accurate state estimation of battery pack to provide efficient energy management. However the particular application determines the accuracy and requirements of BMS where it has to implement; in electric vehicles (EVs) accuracy cannot be compromised. The software part of BMS estimates the states of the battery pack and takes the best possible decision.

In EVs one of the key tasks of BMS’s software part is to provide the actual state of charge (SOC), which represents a crucial parameter to be determined, especially in lithium iron phosphate (LiFePO4) batteries, due to the presence of the high hysteresis behavior in the open circuit voltage than other kind of lithium batteries. This hysteresis phenomena appears with two different voltage curves during the charging and discharging process. The value of the voltage that the battery is going to assume during the off-loading operation depends on several factors, such as temperature, loop direction and ageing.

In this research work, hybrid method is implemented in which advantages of several methods are achieved by implementing one technique combined with another. In this work SOC is calculated from coulomb counting method and in order to correct the error of SOC, an hysteresis model is developed and used due to presence of hysteresis effect in LiFePO4 batteries. An hysteresis model of the open circuit voltage (OCV) for a LiFePO4 cell is developed and implemented in MATLAB/Simulink© in order to reproduce the voltage response of the battery when no current from the cell is required (no load condition). Then the difference of estimated voltage and measured voltage is taken in order to correct the error of SOC calculated from coulomb counting or current integration method. To develop the hysteresis model which can reproduce the same voltage behavior, lot of experiments have been carried out practically in order to see the hysteresis voltage response and to see that how voltage curve change with the variation of temperature, ageing and loop direction. At the end model is validated with different driving profiles at different ambient temperatures.

Place, publisher, year, edition, pages
2013. , 85 p.
Keyword [en]
LiFePO4 battery, hysteresis model, state of charge, open circuit voltage, empirical modeling, Lithium-ion battery, OCV hysteresis, hysteresis loop, hybrid electric vehicle, battery management system, SOC estimation, battery hysteresis
National Category
Control Engineering
URN: urn:nbn:se:kau:diva-30717OAI: diva2:680114
External cooperation
ISEA (Institute for Power Electronics and Electrical Drives) RWTH Aachen University
Subject / course
Electrical Engineering
2013-11-29, ISEA-RWTH Aachen University Bibliothek, Jaegerstr.17-19, D-52066, Aachen, Germany, Aachen, 11:00 (English)
Available from: 2014-01-08 Created: 2013-12-17 Last updated: 2014-01-09Bibliographically approved

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