217 research outputs found
Lithium-ion battery thermal-electrochemical model-based state estimation using orthogonal collocation and a modified extended Kalman filter
This paper investigates the state estimation of a high-fidelity spatially
resolved thermal- electrochemical lithium-ion battery model commonly referred
to as the pseudo two-dimensional model. The partial-differential algebraic
equations (PDAEs) constituting the model are spatially discretised using
Chebyshev orthogonal collocation enabling fast and accurate simulations up to
high C-rates. This implementation of the pseudo-2D model is then used in
combination with an extended Kalman filter algorithm for differential-algebraic
equations to estimate the states of the model. The state estimation algorithm
is able to rapidly recover the model states from current, voltage and
temperature measurements. Results show that the error on the state estimate
falls below 1 % in less than 200 s despite a 30 % error on battery initial
state-of-charge and additive measurement noise with 10 mV and 0.5 K standard
deviations.Comment: Submitted to the Journal of Power Source
Identifiability of generalised Randles circuit models
The Randles circuit (including a parallel resistor and capacitor in series
with another resistor) and its generalised topology have widely been employed
in electrochemical energy storage systems such as batteries, fuel cells and
supercapacitors, also in biomedical engineering, for example, to model the
electrode-tissue interface in electroencephalography and baroreceptor dynamics.
This paper studies identifiability of generalised Randles circuit models, that
is, whether the model parameters can be estimated uniquely from the
input-output data. It is shown that generalised Randles circuit models are
structurally locally identifiable. The condition that makes the model structure
globally identifiable is then discussed. Finally, the estimation accuracy is
evaluated through extensive simulations
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Radially resolved measurement of stator heat transfer in a rotor-stator disc system
This paper describes a new experimental method for measuring stator heat transfer in a rotor–stator disc system using an electrical heater array. The system is partially blocked at the periphery, with radial outflow of rotor-pumped air from an inlet at stator centre. The aim is to improve thermal performance prediction for air-cooled disc type electrical machines. Local Nusselt numbers were measured for 0.63e5 for all gap ratios. Increased Nusselt numbers at the periphery are observed for all Reθ and G because of the ingress of ambient air along the stator due to the rotor pumping effect
Detection and Isolation of Small Faults in Lithium-Ion Batteries via the Asymptotic Local Approach
This contribution presents a diagnosis scheme for batteries to detect and
isolate internal faults in the form of small parameter changes. This scheme is
based on an electrochemical reduced-order model of the battery, which allows
the inclusion of physically meaningful faults that might affect the battery
performance. The sensitivity properties of the model are analyzed. The model is
then used to compute residuals based on an unscented Kalman filter. Primary
residuals and a limiting covariance matrix are obtained thanks to the local
approach, allowing for fault detection and isolation by chi-squared statistical
tests. Results show that faults resulting in limited 0.15% capacity and 0.004%
power fade can be effectively detected by the local approach. The algorithm is
also able to correctly isolate faults related with sensitive parameters,
whereas parameters with low sensitivity or linearly correlated are more
difficult to precise.Comment: 8 pages, 2 figures, 3 tables, conferenc
Constrained optimal control of monotone systems with applications to battery fast-charging
Enabling fast charging for lithium ion batteries is critical to accelerating
the green energy transition. As such, there has been significant interest in
tailored fast-charging protocols computed from the solutions of constrained
optimal control problems. Here, we derive necessity conditions for a fast
charging protocol based upon monotone control systems theory
A parametric open circuit voltage model for lithium ion batteries
The financial support of EPSRC UK and Jaguar Land Rover Ltd is gratefully acknowledged.We present an open circuit voltage (OCV) model for lithium ion (Li-ion) cells, which can be parameterized by measurements of the OCV of positive and negative electrode half-cells and a full cell. No prior knowledge of physical parameters related to particular cell chemistries is required. The OCV of the full cell is calculated from two electrode sub-models, which are comprised of additive terms that represent the phase transitions of the active electrode materials. The model structure is flexible and can be applied to any Li-ion cell chemistry. The model can account for temperature dependence and voltage hysteresis of the OCV. Fitting the model to OCV data recorded from a Li-ion cell at 0°C, 10°C, 20°C, 30°C and 40°C yielded high accuracies with errors (RMS) of less than 5 mV. The model can be used to maintain the accuracy of dynamic Li-ion cell models in battery management systems by accounting for the effects of capacity fade on the OCV. Moreover, the model provides a means to separate the cell's OCV into its constituent electrode potentials, which allows the electrodes’ capacities to be tracked separately over time, providing an insight into prevalent degradation mechanisms acting on the individual electrodes.Publisher PDFPeer reviewe
Minimally invasive insertion of reference electrodes into commercial lithium-ion pouch cells
The authors gratefully acknowledge the financial support of EPSRC UK and Jaguar Land Rover Ltd for this work.Two procedures to introduce a lithium metal reference electrode into commercially manufactured lithium-ion pouch cells (Kokam SLPB 533459H4) are described and compared. By introducing a stable reference potential, the individual behavior of the positive and negative electrodes can be studied in operando under normal cycling. Unmodified cells and half-cells made from harvested electrode material were cycled under identical conditions to the modified cells to compare capacity degradation during cycling and thus validate each modification procedure for degradation testing. A configuration that did not affect the performance of the cell over 20 cycles was successfully developed.Publisher PDFPeer reviewe
Breakdown Resistance Analysis of Traction Motor Winding Insulation under Thermal Ageing
Stator inter-turn faults are among the most important electric motor failures as they progress fast and lead to catastrophic motor breakdowns. Inter-turn faults are caused due to the windings’ insulation degradation. The main stress which deteriorates the insulation is the thermal one. Proper understanding of how this stress influences the electrical properties of insulation over time may lead to reliable prognosis and estimation of the motor’s remaining useful life. In transport applications where reliability and safety come first it is a critical issue. In this paper, extensive experimental testing and statistical analysis of thin film insulation for traction motor windings has been performed under fixed thermal stress. The results indicate that for high thermal stress the electrical properties of the insulation material present a non-monotonic behavior thus proving the well-known and established Arrhenius law inadequate for modelling this type of problems and estimating the remaining useful life of thin film insulation materials
The Impact of Thermal Degradation on Properties of Electrical Machine Winding Insulation Material
Inter-turn stator short circuits can develop quickly leading to serious damage of an electric machine. However, degradation mechanisms of winding insulation material are not yet fully understood. Therefore, the main contribution of this article is analysis of the impact of thermal ageing on the electrical properties of the thin film winding insulation. The insulation samples have been aged thermally at 200–275 °C and for 100–1600 hours. After ageing, impedance spectroscopy measurements were undertaken on the samples and equivalent circuit model (ECM) parameters fitted for each measurement. This allows the impact of thermal ageing on ECM parameters to be analysed, giving insight into the changes of the electrical properties of the insulation. Finally, high voltage was applied to the samples aiming to identify the breakdown voltage characteristics of the insulation material
Nonlinear electrochemical impedance spectroscopy for lithium-ion battery model parameterization
In this work we analyse the local nonlinear electrochemical impedance
spectroscopy (NLEIS) response of a lithium-ion battery and estimate model
parameters from measured NLEIS data. The analysis assumes a single-particle
model including nonlinear diffusion of lithium within the electrode particles
and asymmetric charge transfer kinetics at their surface. Based on this model
and assuming a moderately-small excitation amplitude, we systematically derive
analytical formulae for the impedances up to the second harmonic response,
allowing the meaningful interpretation of each contribution in terms of
physical processes and nonlinearities in the model. The implications of this
for parameterization are explored, including structural identifiability
analysis and parameter estimation using maximum likelihood, with both synthetic
and experimentally measured impedance data. Accurate fits to impedance data are
possible, however inconsistencies in the fitted diffusion timescales suggest
that a nonlinear diffusion model may not be appropriate for the cells
considered. Model validation is also demonstrated by predicting time-domain
voltage response using the parameterized model and this is shown to have
excellent agreement with measured voltage time-series data (11.1 mV RMSE).Comment: 40 pages (excluding supplementary material). Submitted to the Journal
of the Electrochemical Societ
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