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The application of lithium‐ion batteries especially for electric vehicles has been limited by the factors of safety, lifetime, charging time, and cost. One of the principal limitations is that the performance of Li‐ion batteries drops intensely in a cold environment. Cold environment dramatically reduces the available capacity of the batteries and increases its internal impedance at the same time. Therefore, the estimation of state‐of‐health is of great importance in battery performance evaluation and lifetime prediction. Furthermore, the heating methods need to be developed to ensure that batteries work in abnormal temperature conditions. This paper conducts a comprehensive review specifically on the poor performance of lithium‐ion cells under severe conditions. The content contains three sections. First, a comprehensive study on the aging mechanisms of lithium‐ion batteries at cold temperatures is undertaken. Second, the estimation methods of the health state of the batteries are conducted, which is vital to understand the fundamentals and quantify the performance and aging effects for lithium‐ion batteries. Third, the heating methods are classified and studied in detail to reduce the degradation mechanism and promote the performance of lithium‐ion batteries under sub‐zero conditions. [ABSTRACT FROM AUTHOR]

Abstract The reliability assessment of battery packs is an important topic in the reliability design of electric vehicles. To improve the accuracy of the reliability analysis, a modified reliability model for lithium-ion battery packs is developed that couples multiphysics models, degradation models, and a multistate system reliability model. For the degradation models, a stochastic capacity degradation model and a dynamic response impedance (DRI) model are established based on experimental data: a) the stochastic capacity degradation characteristics of cells are investigated, and b) the dynamic response characteristics of the impedance with degradation and changing temperature are studied. It is found that Weibull distribution is slightly more appropriate than normal distribution when the temperature is 25 °C, then reversed with increasing temperature. The algorithm for distribution selection is proposed to describing this concept drift phenomenon. Then, the influence of DRI on the thermal performance is analyzed. Finally, reliability assessment of battery pack and several calculation examples are implemented for comparative analysis. The results show that the fading rate of cells in battery pack are accelerated when DRI is incorporated. Thus, multiphysics-based system reliability model with considering the stochastic capacity degradation and DRI enables more scientific and accurate reliability evaluation of battery pack. Highlights • A modified reliability model for lithium-ion battery packs is developed. • A stochastic degradation model with normal and Weibull distribution is established. • A temperature and capacity dependent dynamic response impedance model is established. • The effect of dynamic response impedance on reliability of battery pack is analyzed. • The simulation results show the fading rate of cells in battery pack are accelerated. [ABSTRACT FROM AUTHOR]

To reduce the internal resistance of battery cells or electrolyte leakage, stacked type battery packs are typically assembled and are tightly compressed by fixture structures such as endplates. Endplates must have enough rigidity to uniformly compress a battery stack, especially for large-formatted battery stacks. The present study proposes a computational approach to analyze and predict the bending deformation of endplates of stacked type battery packs. Computational result agrees well with the actual measurement of bending deformation in a flow battery stack. Analyzing the stress distribution of endplates, nine stiffener models are considered to minimize the bending deformation by reinforcing the endplates. It is found that the endplate with three vertical stiffeners is the most effective design. Additionally, response surface method (RSM) is conducted to find the optimal value of design parameters for the stiffeners. [ABSTRACT FROM AUTHOR]

Summary: State evaluation of battery pack is essential for battery management but laborious when dealing with massive information of cells within the pack. A graphical model for evaluating the status of series‐connected Li‐ion battery pack is established to release the burden. The model is founded by a 2D diagram, with the electric quantity "E" and the capacity "Q" as its axes, therefore called by the "E‐Q diagram." The new graphical diagram presents the dynamics of cell variations in a linear way, thereby benefiting the design and management of battery pack, including (1) quantifying the cell variations by region, (2) illustrating the evolution of cell variations during aging, (3) guiding the estimation of pack states considering algorithm error in cell states, and (4) solving the balancing problem. The experimental results conform to the theoretical analysis, indicating that the E‐Q diagram will be pervasively applied in the design and management of series‐connected battery pack. Moreover, the E‐Q diagram is suitable for education on the basics of a battery pack, because it is a graphical model. Novelty statements: This paper builds a novel graphical model for evaluating the status of series‐connected battery pack. The model can vividly present the cell variations of a battery pack in 2D diagram, named the E‐Q diagram. Error propagation from the cell state estimation to that of the pack and strategies for cell balancing are clearly interpreted by the graphical model. [ABSTRACT FROM AUTHOR]

Abstract Cell variations always undermine the efficiency of energy utilization of battery pack. How does the temperature non-uniformity affect the status of cell variations remains unclear. This paper investigates the underlying mechanisms of the status change of cell variations caused by temperature non-uniformity in a battery pack. First, the status of cell variations has been defined using a graphical model, in which each cell has a coordinate of (capacity, electric quantity). Second, the status transformation caused by temperature non-uniformity has been clarified. Dynamics that describes the thermal-electrochemical effect on the movement of the coordinate for individual cells are firstly established by transformation functions. The movement of the cell locations in the graphical model can vividly interpret the evolution of cell variations caused by temperature non-uniformity with the help of the built transformation functions. Modelling analysis points out that 5 °C increase in the maximum temperature difference among the battery pack can lead to 1.5%–2% capacity loss of the battery pack, therefore the capacity loss caused by cell variations due to temperature non-uniformity should be considered in battery system design. The methodology can be further used to analyze the status change of cell variations in a battery pack caused by all kinds of temperature non-uniformities, benefiting the design of battery management system with high efficiency of energy utilization. Graphical abstract The evolution of cell variations within a lithium-ion battery pack caused by temperature non-uniformity. Image Highlights • The cell variations in battery pack caused by temperature non-uniformity is graphically shown. • The cell variations are defined by a graphical model named the E-Q Diagram. • Thermal-electro coupled dynamic functions are built to interpret the cell variation evolution. • 5 °C increase in temperature difference can lead to 1.5%–2% capacity loss of the battery pack. • The methodology can guide cleaner production of battery system with higher energy efficiency. [ABSTRACT FROM AUTHOR]

This study proposes a novel hybrid energy storage system (HESS) composed of a battery pack and a superconducting magnetic energy storage (SMES) for electric vehicle. Typically, the SMES has a higher power density and lower energy density than other energy storage devices, while battery has higher energy density. Thus, the overall HESS performance can be increased in power and energy density by combining SMES and batteries. The proposed HESS is designed based on bidirectional Z‐source inverter (ZSI). Compared to other SMES/battery‐based HESS topologies that are two stage designs (including DC/DC and AC/DC converters), in this topology, SMES and battery can be incorporated into the Z‐source network which results in lower cost and improved HESS performance. Furthermore, the battery converter has been eliminated due to the buck/boost feature of the ZSI. The fuzzy control method and filters are used to distribute power between the SMES and battery. This study also describes the proposed HESS performance principles and its operation in different modes. [ABSTRACT FROM AUTHOR]

Abstract In this paper, a most significant bits (MSBs) prediction strategy for the design of successive approximation register (SAR) analog-to-digital converter (ADC) in battery pack voltage detection is proposed to reduce conversion time without losing accuracy. The strategy takes advantage of the battery pack voltages characteristics where there is a strong correlation among neighboring cell voltage values. By generating the MSBs with the quantization results of the battery pack in the previous loop, the ADC just needs to convert the remaining least significant bits (LSBs). This paper analyzes the relationship between saved time and five parameters: reading frequency (f), cell number of battery pack (N), cell number (CN) for MSB-prediction, standard deviation (σ), change rate of digital number (K), which can give a feasible prediction on saved working time in any conditions. With this strategy, in a f = 50 kHz, N = 10, CN = 8, σ = 10 system, up to 27.83% A/D conversion time can be saved in charging state, and 27.89% A/D conversion time can be saved in discharging state. [ABSTRACT FROM AUTHOR]

This paper proposes a new novel battery cooling system for hydrogen fueled HEVs that achieves more efficient cooling and driving, which increases vehicle driving range and enhances vehicle safety by maintaining the batteries at optimum operating conditions. The proposed system offers a novel use of the vehicle fuel and a novel cooling plate design. The cooling plate design is optimized in terms of battery's temperature uniformity and battery's maximum temperature. The optimum performance of the design is then investigated through a 600 s high intensity discharging and charging cycle of 4C. The results show that when hydrogen is at a temperature of 10 °C and has an inlet velocity of 0.01 m/s, the maximum temperature is maintained at lower than 30.5 °C. The lowest difference through the battery obtained by the proposed system is less than 7 °C. The performance of the proposed system is compared with the performance of liquid, air and evaporative cooling based systems. The comparison shows that the proposed system is able to perform better than liquid, air and evaporative cooling based cooling systems. The performance of the proposed cooling system demonstrates the advantage of integrating the hybrid vehicle fuel system with the battery cooling system. [ABSTRACT FROM AUTHOR]

Micro-short circuit (MSC) of a lithium-ion battery cell is a potential safety hazard for battery packs. How to identify the cell with MSC in the latent phase before a thermal runaway becomes a difficult problem to solve. We propose a diagnosis method to detect the MSC according to the remaining charging capacity (RCC) variations between cells. When the charging cell voltage curve (CCVC) of the first fully charged cell is regarded as the benchmark, the RCC of each cell can be obtained by the CCVC transformation based on the uniform CCVC hypothesis. The accuracy of the RCC estimation method is validated under constant current and constant power charging experiments. The leakage current of the MSC cell can be obtained by the increase of the RCC after each charge, and it can be converted into the MSC resistance. We set up the battery pack system model with the MSC fault in Simulink ® to verify the effectiveness of the method when the battery pack is charged up to different charge cutoff voltages. Through a series of experiments with external resistors, the adaptability of the MSC diagnosis method is further validated for the aged cell, multi-stage charging, and constant power charging. [ABSTRACT FROM AUTHOR]

Summary: By year 2020, due to enormous growth of production of electric vehicles, it is estimated that approximately 250 000 tons of battery must be disposed or recycled. Till date, the technology to recycle this much amount of batteries in a single year does not exist. Nor, do the methods for recycling are standardized and regulated because of differences in configurations of battery packs. This article conducts a systematic review on research of recycling methods for battery pack used in various stages such as from the dismantling/ disassembly of the battery pack, the detection of the residual energy of the battery, and the recycling/recovery of materials from the battery. The review summarizes basically the 2 main aspects of recycling of battery pack: the mechanical procedure and the chemical recycling. The work describes the existing recycling technology in these 2 aspects and identifies the important research problems in the process of recycling of battery pack such as (1) complexity of dismantling process of battery pack; (2) diversity of connectors used in battery pack; (3) safety of dismantling of battery pack; (4) instability of chemical materials in battery; (5) the chaos of the recycling market; and (6) emerging battery dismantling technologies. One important direction suggested is the automation of battery pack disassembly, which is a main factor towards formulation of generic framework for recycling of battery pack in an efficient manner. Based on these gaps, the present work also proposes a framework for the recycling of battery pack by combining the semi‐automation mechanical procedure of battery pack and enhanced chemical recycling of battery for recovery of vital materials. Future work for authors is to work on establishing and validation of proposed framework. The advantages of the proposed framework are compared with that obtained from the existing framework. The proposed framework when used shall result in efficient and effective recycling of battery module and promote greener environment. [ABSTRACT FROM AUTHOR]

Complex environments and variable working conditions lead to irreversible attenuation of battery pack capacity in electric vehicles (EVs). Online capacity estimation is of great significance for battery pack management and maintenance. This work proposes a state-of-health (SOH) attenuation model considering driving mileage and seasonal temperature for battery health estimation. Firstly, a variable forgetting factor recursive least square (VFFRLS) algorithm is proposed for battery model parameter identification. It adaptively adjusts the forgetting factor according to current fluctuations. Then, an extended Kalman-particle filter (EPF) algorithm is proposed for online capacity estimation. In addition, a battery pack SOH attenuation model is constructed considering seasonal temperature and driving mileage. Finally, the performance of the proposed model and algorithm is verified with nine months of actual vehicle data. The experimental results show that the proposed parameter identification and capacity estimation algorithm can accurately estimate the model parameters and capacity. The average capacity of the battery module decreases with the total mileage. The compensation of monthly driving mileage and ambient temperature factors effectively improves the accuracy of SOH model. • A SOH attenuation model considering temperature and mileage is proposed for EVs. • A variable forgetting factor RLS is proposed for battery parameter identification. • Multidimensional equation of state is constructed for capacity estimation with EPF. • Nine month real vehicle data are used to validate the proposed algorithm and model. [ABSTRACT FROM AUTHOR]

With the rapid development of lithium-ion battery technology in the electric vehicle (EV) industry, the lifetime of the battery cell increases substantially; however, the reliability of the battery pack is still inadequate. Because of the complexity of the battery pack, a reliability design method for a lithium-ion battery pack considering the thermal disequilibrium is proposed in this paper based on cell redundancy. Based on this method, a three-dimensional electric-thermal-flow-coupled model, a stochastic degradation model of cells under field dynamic conditions and a multi-state system reliability model of a battery pack are established. The relationships between the multi-physics coupling model, the degradation model and the system reliability model are first constructed to analyze the reliability of the battery pack and followed by analysis examples with different redundancy strategies. By comparing the reliability of battery packs of different redundant cell numbers and configurations, several conclusions for the redundancy strategy are obtained. More notably, the reliability does not monotonically increase with the number of redundant cells for the thermal disequilibrium effects. In this work, the reliability of a 6 × 5 parallel-series configuration is the optimal system structure. In addition, the effect of the cell arrangement and cooling conditions are investigated. [ABSTRACT FROM AUTHOR]

State-of-charge (SOC) inconsistency impacts the power, durability and safety of the battery pack. Therefore, it is necessary to measure the SOC inconsistency of the battery pack with good accuracy. We explore a novel method for modeling and estimating the SOC inconsistency of lithium-ion (Li-ion) battery pack with low computation effort. In this method, a second-order RC model is selected as the cell mean model (CMM) to represent the overall performance of the battery pack. A hypothetical Rint model is employed as the cell difference model (CDM) to evaluate the SOC difference. The parameters of mean-difference model (MDM) are identified with particle swarm optimization (PSO). Subsequently, the mean SOC and the cell SOC differences are estimated by using extended Kalman filter (EKF). Finally, we conduct an experiment on a small Li-ion battery pack with twelve cells connected in series. The results show that the evaluated SOC difference is capable of tracking the changing of actual value after a quick convergence. [ABSTRACT FROM AUTHOR]

The state-of-charge (SOC) estimation approaches based on the pack model can hardly provide precise estimation due to cell difference, while the approaches based on each cell cost high computation resource, which are not suitable for real-time application. The estimation error can be further enlarged without considering balancing current. The SOC estimation approach of the battery pack considering balancing current is proposed, which dynamically searches for the cell with maximum or minimum voltage, and it only needs to calculate the selected cell in every estimation cycle. Compared to the approaches based on the pack model or each single cell, this approach can achieve precise pack SOC and cost less calculation time and resource. It has been verified with ten series-connected 200 Ah Li(NiCoMn)O2 batteries. The SOC estimation error is limited to 0.3% during the charging process, and a reduction of 2.5% is achieved compared to an error of 2.8% based on the pack model. A reduction of 1% is achieved compared to an error of 1.5% based on the pack model during the discharging process. Compared to an error of 1.7% without considering balancing current, a reduction of 1.4% is achieved during the charging process. [ABSTRACT FROM PUBLISHER]

Series battery equalisation can improve battery charge and discharge reliability and extend battery life. Inductor-based battery equalisation schemes have the advantages of simple topologies and control strategies. According to the energy transfer pathway, inductor-based battery equalisation schemes can be divided into cell-to-cell and cell-to-pack equalisation schemes. The control strategies of the cell-to-cell schemes are simple; the inductor can only transfer energy between the neighbouring cells, so the equalisation speed is low. The cell-to-pack schemes are able to accomplish energy transfer between the cells and pack by charging and discharging the inductors. The equalisation speed is high, but the control strategies may be complex. In this paper, different equalisation topologies are reviewed, then a unified control strategy which is applicable to all of the inductor-based equalisation topologies is proposed. The equalisation speeds and efficiencies of these different schemes, including the newly-proposed unified control strategy, are analysed and compared. Based on the theoretical analysis, simulations, and experimental verifications, it is concluded that this unified control strategy can perform the battery equalisation process quickly and efficiently. [ABSTRACT FROM AUTHOR]

State-of-the-art researches on the modelling of lithium-ion batteries for electric vehicle have been conducted based on the physics and empirical-based models to estimate their states. However, less attention has been paid to evaluating the mechanical strength of the batteries when the battery pack is subjected to sudden external impact or crash. The present work, therefore, proposes a simulation-based probabilistic framework that combines artificial neural network and a moment-based uncertainty evaluation technique utilising the finite element model of a lithium-ion battery to evaluate its mechanical strength. The study was based on the following inputs: displacement, temperature and strain rate of the battery, and their uncertainties when the battery is subjected to sudden impact. The artificial neural network outperforms other well-known modelling methods, such as the radial basis function neural network and polynomial regression, for the global mechanical strength modelling, and the probability distribution obtained from the proposed uncertainty evaluation procedure is shown to be accurate. Further analysis employing the framework reveals that the mean mechanical strength of the battery decreases with increasing temperature, but increases with increasing displacement and strain rate. It was also found that the displacement and temperature have similarly high influence on the mechanical strength of the battery compared to the strain rate. The proposed framework and presented findings can help battery manufacturers improve the road safety of electric vehicles. [ABSTRACT FROM AUTHOR]

A battery pack is the main energy storage element, and directly affects the performance of an electric vehicle. Battery thermal management system research and its development for a modern electric vehicle is required. This paper selects the forced air cooling of battery pack as the research object, and uses simulation methods to research the heat dissipation performance with different structures of battery packs. The results indicate that according to the four types of transient state conditions, the rising temperature of both battery packs are significantly higher than the temperature difference, the maximum temperature rise and temperature difference of a horizontal battery pack are lower than a longitudinal battery pack. When an electric vehicle begins to decrease speed, the curves of temperature rising and temperature difference increase. This shows the internal heat is continuously rising, so even in a electric vehicle beginning to decrease speed, the fan must work. The reference basis for choosing battery pack type and an analysis of heat flow field characteristics, including fan run-time control, are offered. [ABSTRACT FROM AUTHOR]

In this paper, the development of a three-dimensional (3D) lithium titanium oxide (LTO) pouch cell is presented to first better comprehend its thermal behavior within electrified vehicle applications, but also to propose a strong modeling base for future thermal management system. Current 3D-thermal models are based on electrochemical reactions which are in need for elaborated meshing effort and long computational time. There lacks a fast electro-thermal model which can capture voltage, current and thermal distribution variation during the whole process. The proposed thermal model is a reduce-effort temperature simulation approach involving a 0D-electrical model accommodating a 3D-thermal model to exclude electrochemical processes. The thermal model is based on heat-transfer theory and its temperature distribution prediction incorporates internal conduction and heat generation effect as well as convection. In addition, experimental tests are conducted to validate the model. Results show that both the heat dissipation rate and surface temperature uniformity data are in agreement with simulation results, which satisfies the application requirements for electrified vehicles. Additionally, a LTO battery pack sizing and modeling is also designed, applied and displays a non-uniformity of the cells under driving operation. Ultimately, the model will serve as a basis for the future development of a thermal strategy for LTO cells that operate in a large temperature range, which is a strong contribution to the existing body of scientific literature. [ABSTRACT FROM AUTHOR]

As one single cell cannot meet power and driving range requirement in an electric vehicle, the battery packs with hundreds of single cells connected in parallel and series should be constructed. The most significant difference between a single cell and a battery pack is cell variation. Not only does cell variation affect pack energy density and power density, but also it causes early degradation of battery and potential safety issues. The cell variation effects on battery packs are studied, which are of great significant to battery pack screening and management scheme. In this study, the description for the consistency characteristics of battery packs was first proposed and a pack model with 96 cells connected in series was established. A set of parameters are introduced to study the cell variation and their impacts on battery packs are analyzed through the battery pack capacity loss simulation and experiments. Meanwhile, the capacity loss composition of the battery pack is obtained and verified by the temperature variation experiment. The results from this research can demonstrate that the temperature, self-discharge rate and coulombic efficiency are the major affecting parameters of cell variation and indicate the dissipative cell equalization is sufficient for the battery pack. [ABSTRACT FROM AUTHOR]

This paper presents a numerical model used for analyzing heat propagation as a safety feature in a custom-made battery pack. The pack uses a novel technology consisting of an internal short circuit device implanted in a cell to trigger thermal runaway. The goal of the study is to investigate the importance of wrapping cylindrical battery cells (18650 type) in a thermally and electrically insulating mica sleeve, to fix the cells in a thermally conductive aluminum heat sink. By modeling the full-scale pack using a 2D model and coupling the thermal model with an electrochemical model, good agreement with a 3D model and experimental data was found (less than 6%). The 2D modeling approach also reduces the computation time considerably (from 11 h to 25 min) compared to using a 3D model. The results showed that the air trapped between the cell and the boreholes of the heat sink provides a good insulation which reduces the temperature of the adjacent cells during thermal runaway. At the same time, a highly conductive matrix dissipates the heat throughout its thermal mass, reducing the temperature even further. It was found that for designing a safe battery pack which mitigates thermal runaway propagation, a combination of small insulating layers wrapped around the cells, and a conductive heat sink is beneficial. [ABSTRACT FROM AUTHOR]

This paper presents a method for an online real-time electrochemical impedance spectroscopy (EIS) measurement of batteries using closed-loop control of power converter. Unlike the previously proposed method which allows the measurement of the ac impedance for a single frequency, the presented method in this paper allows for obtaining the EIS for a spectrum of frequencies by using the information included in a single perturbation cycle, or a few cycles of perturbation to obtain a more accurate EIS with a very wide frequency range. This will result in faster EIS measurement for a spectrum of frequencies and under the same battery operating conditions. The presented method utilizes closed-loop control operation for the EIS measurement functionality, which allows for better control of the output voltage and for upgrading the concept to be able to achieve no added perturbation ripple at the output of the system. The presented online real-time EIS measurement method utilizes a power converter with closed-loop control in order to create an output voltage step-function perturbation at a given frequency to generate battery voltage and current responses. By applying Fourier analysis to these responses, an EIS can be obtained for a range of frequencies equal or higher than the perturbation frequency of the step function. In addition, this paper presents a method to eliminate the added perturbation ripple when two or more power converters are used. The theoretical basis and experimental prototype results are provided to illustrate and validate the presented method. [ABSTRACT FROM PUBLISHER]

Serially connected batteries present a cell-to-cell variation in their electrochemical behavior that tends to increase over the lifetime. The decision for the best circular economy option for aged or defective battery packs – i.e., repair, remanufacturing, or recycling – requires comprehensive testing, analysis, and an according data basis. Remanufacturing of battery packs refers to the replacement of individual (sub-)modules or cells which are defective or show a diverging aging behavior to the rest of the battery units. A detection algorithm is required to decide if a significant inhomogeneity in a serial connection of batteries is present. For this reason, virtual battery packs are built based on the measurement of 12 individual batteries of the same type. Cell-to-cell variations are determined at the begin of life and a novel representation for the quantitative and qualitative analysis is given. This work extracts impedance-based features of different serial battery pack configurations through a novel comparative analysis approach. The features are extracted from Bode and Nyquist plots and the real and imaginary parts of the impedance itself. The detectability is analyzed depending on the number of cells and the underlying effects are discussed. A detailed sensitivity analysis is carried out for the most promising features, in which the influence of the cell-to-cell variations, the aging condition, and the aging mechanism are analyzed. The feature that shows the highest sensitivity, the so called low-frequency minimum, is able to detect single outliers within a high number of serially connected cells. [Display omitted] • Detection of inhomogeneities in serially connected lithium-ion batteries. • Novel representation of cell-to-cell variations for analysis of Nyquist plots. • Comprehensive analysis of multiple features for the detection of inhomogeneities. • Sensitivity analysis of the studied features concerning the detection accuracy. [ABSTRACT FROM AUTHOR]

The thermal safety of lithium-ion (Li-ion) batteries is of great importance for their further development and application. The accurate evaluation of the thermal safety boundary has always been the key issue. Due to the coupling effect of the internal, external, and randomness factors, the risk probability is difficult to evaluate using existing deterministic analyses. Therefore, a safety risk assessment method for the thermal abuse of Li-ion battery packs is proposed, and an improved bisection-method-based analysis algorithm for the thermal safety boundary is established. Moreover, a multiphysics model is developed considering an equivalent circuit, thermal abuse, and a fluid dynamics model. Furthermore, stochastic models of the battery parameters and loading are constructed to describe the randomness. The temperature and power stress–strength interference models are integrated to evaluate the thermal safety risk of the battery pack. Then, the models are validated by the temperature and analyzing the stochastic parameters. Finally, several case studies are implemented, including the analyses of thermal safety boundary, effect of stochastic parameters, safety risk probability, and thermal runaway propagation in different scenarios. The results denote that the effect of internal resistance dispersion is dominant and that the risk probability will increase with degradation. • A novel risk probability evaluation method for battery pack is proposed. • The proposed method considers the multiphysics and randomness for the first time. • The improved bisection method-based algorithm can improve the efficiency of analysis. • The effect of stochastic parameters on the thermal safety boundary is analyzed. • The thermal safety risk probability of new and degraded battery pack is evaluated. [ABSTRACT FROM AUTHOR]

• Diverging channel design cooling plate with oblique fins is newly proposed. • Thermal unbalance of the battery module is improved using the proposed design. • Cell-to-cell temperature difference in the pack cooling is decreased by 19.07%. • The pumping power to satisfy the temperature conditions is decreased by 67.8%. In this study, the thermal and hydraulic performances of a battery thermal management system are investigated in terms of the design of the cooling plate. A diverging channel with oblique fins (DCOF) cooling plate is newly proposed to overcome the limitations of the conventional straight channel cooling plate. The diverging design is applied to control the coolant velocity and heat transfer area, with oblique fins inserted to enhance the heat transfer efficiency. A simulation model of the battery and cooling system is developed and experimentally validated. When the DCOF design is applied to the battery module, the temperature uniformity is improved in terms of the temperature difference and standard deviation. As the investigation is extended from the module to the battery pack, the temperature difference and temperature standard deviation in the battery module are improved by 19.07% and 27.14%, respectively. Considering the power consumption of the cooling system, as the thermal performance of the DCOF design and baseline design is maintained, the power consumption of the coolant pump of the DCOF design is significantly reduced by 67.8%. [ABSTRACT FROM AUTHOR]

In a battery pack, cell-to-cell chemical variation, or the variation in operating conditions, can possibly lead to current imbalance which can accelerate pack ageing. In this paper, the Pseudo-Two-Dimensional(P2D) porous electrode model is extended to a battery pack layout, to predict the overall behaviour and the cell-to-cell variation under constant voltage charging and discharging. The algorithm used in this model offers the flexibility in extending the layout to any number of cells in a pack, which can be of different capacities, chemical characteristics and physical dimensions. The coupled electro-thermal effects such as differential cell ageing, temperature variation, porosity change and their effects on the performance of the pack, can be predicted using this modelling algorithm. The pack charging voltage is found to have an impact on the performance as well as the SEI layer growth. Numerical studies are conducted by keeping the cells at different thermal conditions and the results show the necessity to increase the heat transfer coefficient to cool the pack, compared to single cell. The results show that the thermal imbalance has more impact than the change in inter-connecting resistance on the split current distribution, which accelerates the irreversible porous filling and ageing. [ABSTRACT FROM AUTHOR]

In this study, a three dimensional (3D) modeling has been built for a lithium ion battery pack using the field synergy principle to obtain a better thermal distribution. In the model, the thermal behavior of the battery pack was studied by reducing the maximum temperature, improving the temperature uniformity and considering the difference between the maximum and maximum temperature of the battery pack. The method is further verified by simulation results based on different environmental temperatures and discharge rates. The thermal behavior model demonstrates that the design and cooling policy of the battery pack is crucial for optimizing the air-outlet patterns of electric vehicle power cabins. [ABSTRACT FROM AUTHOR]

As a key factor for the safety of electric vehicles, electric vehicles are focused on battery pack stability rather than vehicle dynamics. The stability of battery pack depends on the performance of suspensions and battery supporting system. Automobile suspensions can reduce the bumps and vibrations that come from road unevenness. Its purposes are to prevent the shock and vibration from transferring to the body, and reduce the vibration of the battery pack. To improve the performance of suspension systems of the electric vehicle and the stability of battery pack, the paper proposes a study on the interaction of electric vehicle roll and battery pack stability. 9-DOF vehicle vibration and roll model was established based on analysis of movement of the battery pack. Then simulation model was established to check the result to get the reasonable suspension stiffness by using Matlab/Simulink. The results show that the stiffness of the suspension is increased by configuring a high performance shock absorber and a short spring. Although it will inhibit roll, simply increasing the hardness of the shock absorber and the spring will cause a lot of negative effects. [ABSTRACT FROM AUTHOR]

Modern applications of lithium-ion batteries such as smartphones, hybrid & electric vehicles and grid scale electricity storage demand long lifetime and high performance which typically makes them the limiting factor in a system. Understanding the state-of-health during operation is important in order to optimise for long term durability and performance. However, this requires accurate in-operando diagnostic techniques that are cost effective and practical. We present a novel diagnosis method based upon differential thermal voltammetry demonstrated on a battery pack made from commercial lithium-ion cells where one cell was deliberately aged prior to experiment. The cells were in parallel whilst being thermally managed with forced air convection. We show for the first time, a diagnosis method capable of quantitatively determining the state-of-health of four cells simultaneously by only using temperature and voltage readings for both charge and discharge. Measurements are achieved using low-cost thermocouples and a single voltage measurement at a frequency of 1 Hz, demonstrating the feasibility of implementing this approach on real world battery management systems. The technique could be particularly useful under charge when constant current or constant power is common, this therefore should be of significant interest to all lithium-ion battery users. [ABSTRACT FROM AUTHOR]

This paper established the three degree of freedom mathematical model, based on the two degree of freedom linear model with two wheel steering. Then the dynamics differential equation is obtained. With a step input of the front wheel, observing and analyzing the yaw rate response and the side slip angle response in the whole process based on MATLAB/Simulink. Finally, by changing the position of the battery pack to transform the location of the gravity center of the whole vehicle, analyzing the impact on the electric vehicle's steering characteristic while the location of battery pack changed. [ABSTRACT FROM AUTHOR]

Thermal management system is of critical importance for a Li-ion battery pack, as high performance and long battery pack life can be simultaneously achieved when operated within a narrow range of temperature around the room temperature. An efficient thermal management system is required to keep the battery temperature in this range, despite widely varying operating conditions. A novel liquid coolant based thermal management system, for 18,650 battery pack has been introduced herein. This system is designed to be compact and economical without compromising safety. A coupled three-dimensional (3D) electrochemical thermal model is constructed for the proposed Li-ion battery pack. The model is used to evaluate the effects of different operating conditions like coolant flow-rate and discharge current on the pack temperature. Contact resistance is found to have the strongest impact on the thermal performance of the pack. From the numerical solution, a simple and novel temperature correlation of predicting the temperatures of all the individual cells given the temperature measurement of one cell is devised and validated with experimental results. Such coefficients have great potential of reducing the sensor requirement and complexity in a large Li-ion battery pack, typical of an electric vehicle. [ABSTRACT FROM AUTHOR]

Vehicle battery systems are usually designed with a high number of cells connected in parallel to meet the stringent requirements of power and energy. The self-balancing characteristic of parallel cells allows a battery management system (BMS) to approximate the cells as one equivalent cell with a single state of health (SoH) value, estimated either as capacity fade (SoH E ) or resistance increase (SoH P ). A single SoH value is however not applicable if the initial SoH of each cell is different, which can occur when cell properties change due to inconsistent manufacturing processes or in-homogeneous operating environments. As such this work quantifies the convergence of SoH E and SoH P due to initial differences in cell SoH and examines the convergence factors. Four 3 Ah 18650 cells connected in parallel at 25 °C are aged by charging and discharging for 500 cycles. For an initial SoH E difference of 40% and SoH P difference of 45%, SoH E converge to 10% and SoH P to 30% by the end of the experiment. From this, a strong linear correlation between ΔSoH E and ΔSoH P is also observed. The results therefore imply that a BMS should consider a calibration strategy to accurately estimate the SoH of parallel cells until convergence is reached. [ABSTRACT FROM AUTHOR]

Incremental capacity analysis (ICA) is a widely used technique for lithium-ion battery state-of-health (SOH) evaluation. The effectiveness and robustness of ICA for single cell diagnostics have been reported in many published work. In this study, we extend the ICA based SOH monitoring approach from single cells to battery modules, which consist of battery cells with various aging conditions. In order to achieve on-board implementation, an IC peak tracking approach based on the ICA principles is proposed. Analytical, numerical and experimental results are presented to demonstrate the utility of the IC peak tracking framework on multi-cell battery SOH monitoring and the effects of cell non-uniformity on the proposed method. Results show that the methods developed for single cell capacity estimation can also be used for a module or pack that has parallel-connected cells. [ABSTRACT FROM AUTHOR]

This paper offers novel insights to the design and implementation of an innovative state-of-charge (SOC) estimator for the lithium-ion (Li-Ion) series battery pack. The most interesting feature of this approach is that it can utilize information from each filtered terminal voltage of the Li-Ion cells connected in series for SOC estimation of the battery pack. Without actual sensing each discharging/charging current (DCC) applied to the Li-Ion cells, it is possible to extract each DCC estimation from the corresponding filtered terminal voltages with an equivalent electrical circuit model (EECM) identification of all Li-Ion cells in the battery pack. There are two advantages to SOC estimation of the battery pack with this approach. First, the proposal can be implemented simply and effectively, reducing the computational steps required for SOC estimation. By reducing computational steps, the proposal is expected to be more cost-effective. Second, the approach guarantees an improved SOC performance, even if the battery pack results in inevitable cell-to-cell variation among Li-Ion cells. Accordingly, there are fewer differences to previously estimated DCCs among Li-Ion cells. Specifically, all values from the estimated DCCs are properly compensated for by simultaneous parameter modification according to each cell's electrochemical characteristics. Experimental results clearly demonstrate that our DCC sensorless SOC estimator provides robust SOC performance for the battery pack. This approach considered an experimental battery pack (12S1P) connected in series using 2.6 Ah LiCoO2 cells produced by Samsung SDI. [ABSTRACT FROM AUTHOR]

A battery pack is produced by connecting the cells in series and/or in parallel to provide the necessary power for electric vehicles (EVs). Those parameters affecting cost and reliability of the EVs, including cycle life, capacity, durability and warranty are highly dependent on the thermal management system. In this work, computational fluid dynamic analysis is performed to investigate the air cooling system for a 38,120 cell battery pack. The battery pack contained 24 pieces of 38,120 cells, copper bus bars, intake and exhaust plenum and holding plates with venting holes. Heat generated by the cell during charging is measured using an accelerating rate calorimeter. Thermal performances of the battery pack were analyzed with various mass flow rates of cooling air using steady state simulation. The correlation between Nu number and Re number were deduced from the numerical modeling results and compared with literature. Additionally, an experimental testing of the battery pack at different charging rates is conducted to validate the correlation. This method provides a simple way to estimate thermal performance of the battery pack when the battery pack is large and full transient simulation is not viable. [ABSTRACT FROM AUTHOR]

Due to the importance of examining the temperature of battery packs (BYP), a study on the temperature of a lithium-ion BYP with 9 cylindrical cells is performed in this article. The BYP is filled with phase change material (PCM) to better temperature uniformity on the battery cells. The batteries and the PCM pack are placed in an air channel with two inlets. At the inlets, 4 arc blades are supposed to guide the airflow to enhance the uniformity of cooling in the BYP. By changing the horizontal and vertical distance (VD) of the batteries inside the pack, this study is carried out in 2500 s for the charging and discharging times of the batteries (1.5C rate). The thermal analysis is done on the batteries using COMSOL software. The results show that an increment in the horizontal distance (HD) of batteries has less effect on battery temperature (T-BT) and PCM phase change compared to their VD. By enhancing the horizontal and VDs of the batteries, the value of the PCM phase change during the maximum T-BT is higher. The heat transfer coefficient (HTCT) between the PCM and the air is also decreased by increasing the distance between the batteries. The T-BTs is not significantly impacted by changing the distance between them. • Study thermal management of a lithium-ion BYP with 9 cylindrical cells is performed. • BYP is filled with PCM to better temperature uniformity on the battery cells. • T-BTs is not significantly impacted by changing the distance between them. • HTCT between the PCM and air is also decreased by increasing the distance. [ABSTRACT FROM AUTHOR]

In this paper, a 3D battery pack (B-PK) containing 16 battery cells (BCL) with aligned and non-aligned arrangements is simulated. The batteries are 18,650 lithium-ion cylindrical ones. The B-PK is placed in a square air duct. Air enters from the top of the B-PK and exits from the bottom of the batteries. This study is performed by changing the inlet air velocity (V-AR) to the B-PK from 0.03 to 0.09 m/s for three charging and discharging cycles within 2000 s. The findings revealed that extending the duration and charging and discharging of the B-PK up to the third cycle increased the temperature of B-PK. The effect of V-AR changes is more pronounced in the second and especially the third cycles of battery charging process. The maximum (T-MX) and average (T-AV) temperatures of the B-PK as well as the temperature of air leaving the B-PK are all reduced when the V-AR is increased. The central batteries of the B-PK have a high temperature, whereas the batteries at the B-PK corners have a low temperature, according to an analysis of BCLs. Using an aligned arrangement of batteries in the pack reduces the T-AV of B-PK compared to the non-aligned arrangement of batteries. • A 3D battery pack containing 16 lithium-ion cylindrical battery cells is simulated. • Effect of inlet air velocity for three charging and discharging cycles are assessed. • Temperature of B-PK rises by extending its charging/discharging up to third cycle. • The maximum temperature of battery pack reduces by boosting the inlet air velocity. • Aligned batteries entails a lower battery temperature than non-aligned arrangement. [ABSTRACT FROM AUTHOR]

This paper proposes two condition-based opportunistic maintenance policies with two-phase inspections for continuously degraded systems with real-time monitoring and periodic inspections, respectively. The degradation of the components and the system is modeled by a Gamma process. Existing literature finds the optimal maintenance strategies by monitoring the performance of all components in a multi-component system. However, it maybe unrealistic and costly to perform inspections on all components for certain systems. Hence, this study considers a two-phase inspection method, that is, the system-level inspection is conducted first, and then the decision for component-level inspection is made based on the system performance. Maintenance is performed to the component when its degradation reaches the preventive maintenance (PM) threshold or the corrective maintenance (CM) threshold at a component-level inspection. Whenever a maintenance action is implemented, the other components whose degradation exceeds an opportunistic maintenance (OM) threshold will be repaired. Then the long-run expected cost for two-component systems and multi-component systems are derived based on the semi-regenerative properties and simulation method. The combination of the system-level inspection interval, OM, PM and CM thresholds is determined to minimize the long-run expected cost. Finally, this study applies the proposed maintenance policies to the battery pack systems in electrical vehicles. • Propose two CBM policies with two-phase inspections. • Derive the long-run expected cost for two-unit systems based on semi-regenerative process. • Construct the optimization model for multi-unit systems via MC simulation method. • Apply the proposed policies to the battery pack system in EVs. [ABSTRACT FROM AUTHOR]

The numerical and transient behavior of a battery pack (BA-PK) consisting of three battery cells positioned within an air duct is investigated in this work. The BA-PK was connected to a solar system. The inside of the BA-PK is filled with phase change material. The air within the duct moved at a speed of 0.001–0.003 m/s around the BA-PK. The investigation was carried out by altering the dimensions of the BA-PK using COMSOL software. The finite element approach is used to solve the equations. The results of this research indicated that the battery temperature (Tbatt) drops gradually until the surrounding area is filled with molten PCM, but that once the PCM around the battery is entirely frozen, the Tbatt drops abruptly. The use of a larger BA-PK increases the temperature of the exhaust air out of the duct, but reduces the percentage of solid PCM. The Tbatt, as well as the maximum Tbatt and average TPCM within the compartment, are reduced by using a smaller BA-PK. In addition to increasing the quantity of solid PCM, increasing the speed lowers the temperatures of the batteries and PCM, as well as the temperature of the exhaust air. • Numerical and transient behavior of a battery pack positioned within an air. • Battery pack is filled with phase change material and was connected to solar system. • The use of a larger battery pack increases the temperature of the exhaust air. • Increasing the speed lowers the temperatures of batteries, PCM and exhaust air. [ABSTRACT FROM AUTHOR]

This study proposes a hybrid kernel function relevance vector machine (HKRVM) optimized model for battery prognostics and health management. To monitor battery state of health (SOH), two ageing features (AFs) are extracted from the incremental capacity curve to quantify capacity degradation. To further predict remaining useful life (RUL), the AFs are treated with the BOXCOX transformation to enhance the linearity between AFs and cycles. Then, a metabolic extreme learning machine is developed to successionally predict the degradation trends of AFs quickly and accurately. The HKRVM is proposed to capture the underlying relationship between AFs and capacity. To determine the optimal weights and kernel parameters in HKRVM, the biological evolution in the genetic algorithm (GA) is integrated into the grey wolf optimizer (GWO) to further improve the population diversity and optimization performance of the basic GWO. Furthermore, 23 benchmark functions are employed to illustrate the effectiveness of the genetic grey wolf optimizer (GGWO). Finally, the extracted and predicted AFs are fed into the optimized HKRVM for validation. For four battery packs, the mean error of estimated SOH is 2.7773% and the predicted RUL is 21.3333 cycles, which is better than the Gauss process regression, support vector regression, and some particle-filter-based methods. • Two AFs from battery cells are extended to battery packs for aging evaluation. • BOXCOX transformation is utilized to enhance the linearity between AFs and cycles. • A MELM is proposed to predicted the AFs successionally. • An HKRVM is developed for synchronous SOH estimation and RUL prediction. • A GGWO is proposed to determine the optimal weight and kernel parameters of HKRVM. [ABSTRACT FROM AUTHOR]

In this investigation, a systematic surrogate-based optimization design framework for a battery pack is presented. An air-cooling battery pack equipped on electric vehicles is first designed. Finite element analysis (FEA) results of the baseline design show that global maximum stresses under x-axis and y-axis transient acceleration shock condition are both above the tensile limit of material. Selecting the panel and beam thickness of battery pack as design variables, with global maximum stress constraints in shock cases, a multi-objective optimization problem is implemented using metamodel technique and multi-objective particle-swarm-optimization (MOPSO) algorithm to simultaneously minimize the total mass and maximize the restrained basic frequency. It is found that 2nd order polynomial response surface (PRS), 3rd order PRS and radial basis function (RBF) are the most accurate and appropriate metamodels for restrained basic frequency, global maximum stresses under x-axis and y-axis shock conditions respectively. Results demonstrate that all the optimal solutions in Pareto Frontier have heavier weight and lower frequency compared with baseline design due to the restriction of global maximum stress response. Finally, two optimal schemes, "Knee Point" and "lightest weight", satisfied both of the stress constraint conditions, show great consistency with FEA results and can be selected as alternative improved schemes. [ABSTRACT FROM AUTHOR]

Variations in cell properties are unavoidable and can be caused by manufacturing tolerances and usage conditions. As a result of this, cells connected in series may have different voltages and states of charge that limit the energy and power capability of the complete battery pack. Methods of removing this energy imbalance have been extensively reported within literature. However, there has been little discussion around the effect that such variation has when cells are connected electrically in parallel. This work aims to explore the impact of connecting cells, with varied properties, in parallel and the issues regarding energy imbalance and battery management that may arise. This has been achieved through analysing experimental data and a validated model. The main results from this study highlight that significant differences in current flow can occur between cells within a parallel stack that will affect how the cells age and the temperature distribution within the battery assembly. [ABSTRACT FROM AUTHOR]

• Opportunity and bus garage charging schemes for battery electric buses. • Operating model for charging buses along the whole daily service. • System cost minimization via number of chargers, battery size and charging schemes. • Optimization algorithms to define the start time of electric charging operation. • Model applicability and charging performance tested through numerical instances. This paper analyzes the new operations induced by the energy range limitation in battery electric bus (BEB) systems to ensure the service provision along the whole day. An operating model has been developed to estimate the number of resources to be deployed (extra vehicles and charging facilities) for two charging schemes: charging at bus garage facility and opportunity charging at on-street chargers. Firstly, the model calculates the entrance and exit time of buses in service assuming an unlimited battery capacity, caused by demand and headway variations in different time periods along day. Then, based on the previous results, the model estimates the moment when vehicles will run out of energy and proposes a charging schedule as well as new vehicle movements between chargers, bus garage and routes to maintain the targeted headway. Consequently, the model is able to calculate the number of resources needed and the total cost for a given route and battery size, allowing cost and performance comparison to diesel and hybrid powertrains. The estimated results in two bus routes in Barcelona indicate that the purchasing cost of BEB vehicles (670,000 euros/veh for articulated, 500,000Euros/veh for standard vehicles, both depreciated over a lifetime of 15 years), battery packs (231 Euro/kWh purchased, depreciated over a lifetime of 10 years), as well as the investment in chargers, are still high to clearly justify their cost-competitiveness against diesel or hybrid counterparts. Nevertheless, if the acquisition cost of both vehicles and battery pack are only reduced by 9%, the BEB technology may present cost savings for transit agencies. It only happens if the fleet size is as large as the corresponding to diesel and hybrid technologies. Opportunity charging is resulted to be more cost- efficient than charging at bus garage for small battery packs, routes with acceptable time headway adherence and, specially, when fast chargers are located very close to terminal stops. Nevertheless, when the real bus route design and operation do not fulfill these standards, charging scheme at bus garage is preferable. [ABSTRACT FROM AUTHOR]

Battery cell capacity loss is extensively studied so as to extend battery life in varied applications from portable consumer electronics to energy storage devices. Battery packs are constructed especially in energy storage devices to provide sufficient voltage and capacity. However, engineering practice indicates that battery packs always fade more critically than cells. We investigate the evolution of battery pack capacity loss by analyzing cell aging mechanisms using the “Electric quantity – Capacity Scatter Diagram (ECSD)” from a system point of view. The results show that cell capacity loss is not the sole contributor to pack capacity loss. The loss of lithium inventory variation at anodes between cells plays a significant role in pack capacity evolution. Therefore, we suggest more attention could be paid to the loss of lithium inventory at anodes in order to mitigate pack capacity degradation. [ABSTRACT FROM AUTHOR]

This paper presents the modeling of a 50 A h battery pack composed of 56 cells, taking into account real battery performance conditions imposed by the BMS control. The modeling procedure starts with a detailed analysis of experimental charge and discharge SOC tests. Results from these tests are used to obtain the battery model parameters at a realistic performance range (20–80% SOC). The model topology aims to better describe the finite charge contained in a battery pack. The model has been validated at three different SOC values in order to verify the model response at real battery pack operation conditions. The validation tests show that the battery pack model is able to simulate the real battery response with excellent accuracy in the range tested. The proposed modeling procedure is fully applicable to any Li-ion battery pack, regardless of the number of series or parallel cells or its rated capacity. [ABSTRACT FROM AUTHOR]

Battery technology is an enabling technology for electric vehicles (EVs), and improving its safety and reliability while reducing its cost will benefit its application to EVs. In this paper, a method on the design and analysis of lithium-ion (Li-ion) battery pack from the reliability perspective is presented. The analysis is based on the degradation of the battery pack, which is related to the cells configuration in the battery pack and the state of health (SoH) of all the Li-ion cells in the pack. Universal Generating Function (UGF) technique is used for reliability analysis. As adding new battery cells to the battery pack in the production process can improve its reliability but it also increases cost, tradeoff between the number of the redundant battery cells, the configuration of the redundant cells and their reliability is investigated in this work. [ABSTRACT FROM AUTHOR]

This paper describes a cooling strategy development method for an air cooled battery pack with lithium-ion pouch cells used in a hybrid electric vehicle (HEV). The challenges associated with the temperature uniformity across the battery pack, the temperature uniformity within each individual lithium-ion pouch cell, and the cooling efficiency of the battery pack are addressed. Initially, a three-dimensional battery pack thermal model developed based on simplified electrode theory is correlated to physical test data. An analytical design of experiments (DOE) approach using Optimal Latin-hypercube technique is then developed by incorporating a DOE design model, the correlated battery pack thermal model, and a morphing model. Analytical DOE studies are performed to examine the effects of cooling strategies including geometries of the cooling duct, cooling channel, cooling plate, and corrugation on battery pack thermal behavior and to identify the design concept of an air cooled battery pack to maximize its durability and its driving range. [ABSTRACT FROM AUTHOR]

Thermal management is a routine but crucial strategy to ensure thermal stability and long-term durability of the lithium-ion batteries. An air-flow-integrated thermal management system is designed in the present study to dissipate heat generation and uniformize the distribution of temperature in the lithium-ion batteries. The system contains of two types of air ducts with independent intake channels and fans. One is to cool the batteries through the regular channel, and the other minimizes the heat accumulations in the middle pack of batteries through jet cooling. A three-dimensional anisotropic heat transfer model is developed to describe the thermal behavior of the lithium-ion batteries with the integration of heat generation theory, and validated through both simulations and experiments. Moreover, the simulations and experiments show that the maximum temperature can be decreased to 33.1 °C through the new thermal management system in comparison with 42.3 °C through the traditional ones, and temperature uniformity of the lithium-ion battery packs is enhanced, significantly. [ABSTRACT FROM AUTHOR]

The present paper documents a comprehensive study on the ground impact of lithium-ion battery packs in electric vehicles. With the purpose of developing generic methodology, a hypothetic global finite element model is adopted. The force–displacement response of indentation process simulated by the global FE model is cross-validated with the earlier analytical solutions. The punching process after the armor plate perforation, the ensuing crack propagation of the armor plate as well as the local deformation modes of individual battery cells are clearly predicted by the global modeling. A parametric study is carried out, and a few underlying rules are revealed, providing important clues on the design of protective structure of battery packs against ground impact. In the next step, detailed FE models at the level of a single battery cell and shell casing are developed and simulations are performed using boundaries and loading conditions taken from the global solution. In the detailed modeling the failure of individual components is taken into account, which is an important indicator of electric short circuit of a battery cell and possible thermal runaway. The damage modes and the deformation tolerances of components in the battery cell under various loading conditions are observed and compared. [ABSTRACT FROM AUTHOR]

In this work, a novel acausal and reconfigurable battery pack model is presented. The model structure adopted for the battery cell is based on an equivalent circuit representation. The circuit elements are modified to take account of both hysteresis and diffusion limitation. The latter is known to be a nonlinear function of large operating currents or long operating times. It is shown that the integration of a current dependent time constant within the cell model better emulates the solid diffusional dynamics of lithium intercalation into the active material under large electrical loads. The advantages of an acausal modeling approach, when scaling-up individual cell models into a complete battery system are also presented. Particular consideration is given to emulating the impact of cell to cell variations on pack performance. Using statistical analysis of battery tests, cell model parameter variations are characterized and quantified. The cell and scaled-up pack model are parameterized for a number of commercially available cell formats, energy capacities and chemistries. The new models are validated using transient, real-world, electrical data measured from an electric vehicle (EV) operating within an urban environment. [ABSTRACT FROM AUTHOR]

To address the problem of DC bus voltage surge caused by load demand fluctuation in an off-grid microgrid, here, an adaptive energy optimization method based on a hybrid energy-storage system to maintain the stability of DC bus voltage is presented. The adaptive energy optimization method consists of three parts: the average filtering algorithm, extracting fluctuating power in demand load; the supercapacitor terminal voltage control, keeping the terminal voltage of the supercapacitor near reference; and the battery pack balance control, adjusting the charge/discharge to balance the state of charge for battery packs. In this proposed method, after extracting the fluctuating power by the low-pass filter when the demand load fluctuates, the battery packs release the power to offset the low-frequency fluctuation load and the supercapacitor to instantaneously compensate the high-frequency fluctuation power, to prolong the service life of batteries and maintain the stability of DC bus voltage. The effectiveness of the proposed adaptive energy optimization method is validated and is confirmed to maintain the stable operation of the off-grid microgrid, extend the cycle life of batteries in off-grid microgrid simulations and experiments. [ABSTRACT FROM AUTHOR]