Development of electric vehicle battery capacity estimation using neuro-fuzzy systems

by Wu, Kwok-Chiu

(Uncorrected OCR) Abstract of thesis entitled

Development of Electric Vehicle Battery Capacity Estimation Using Neuro-Fuzzy Systems

Submitted by

WUKwokChiu

for the Degree of Master of Philosophy at The University of Hong Kong

in September 2003

The growing concern with environmental protection and energy conservation has

encouraged the development of electric vehicle (BV) technologies, including battery charging methods and propulsion technologies. Ideally, EV batteries should use state of available capacity (SOAC) indicators instead of state-of-charge (SOC) indicators, but EV batteries are highly nonlinear, and this characteristic makes SOAC estimation difficult.

The objective of this study was to develop EV battery capacity estimation using neuro-fuzzy systems. The study adopted two main approaches: firstly, to develop battery capacity estimation for lead-acid battery using neural network (NN); and secondly, to develop battery capacity estimation for lead-acid battery, nickel metal hydride (Ni-MH) battery and lithium-ion (Li-Ion) battery using adaptive neuro-fuzzy inference system

(ANFIS).

The first approach involved usmg neural network (NN) to elucidate the relationship between the SOAC and the terminal voltage, discharge current, battery

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surface temperature and discharged capacity. This enabled the SOAC to be estimated by mapping between the inputs and the output ofNN.

The second approach exploited the adaptive neuro-fuzzy inference system (ANFIS). In this approach, the discharged and regenerative capacity distribution was used to describe the discharge current profile in EV s. The capacity distribution and the battery surface temperature were selected as the inputs of the ANFIS while the output of the ANFIS was the SOAC. Consequently, the SOAC could be estimated by mapping between the inputs and the output of this ANFIS. For further improvement, the system inputs were modified and the results were given.

Experiments using the battery testing and evaluation system were performed to test the lead-acid battery, the Ni-MH battery and the Li-Ion battery. Various discharge current profiles at different battery surface temperatures were designed in order to replicate the battery operating conditions in EV s. Experimental data used for the development and verification of the proposed approaches were recorded, and comparisons between the estimated SOAC from the proposed approaches and recorded SOAC from the experimental data were made.

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