Battery Pack Model Research Articles

A Practical and Comprehensive Evaluation Method for Series-Connected Battery Pack Models

Accurate and computationally efficient series-connected battery pack models (PMs) in new energy vehicles are extremely important for battery management. Based on a system of indexes of accuracy, adaptability, and computational complexity, this article presents a practical and comprehensive evaluation method for series-connected battery PMs, which is crucial for model selection and model-based algorithm development. Seventeen battery PMs, based on four series-connected battery pack structure models and three battery cell models, are introduced and discussed in detail. Experiments are designed and carried out to collect realistic battery test data for parameter identification and model comparisons. The estimation accuracy and computational complexity of different battery PMs are compared. Both the merits and demerits of each battery PM are thoroughly analyzed and discussed. The practical comprehensive evaluation results provide useful insights that will enable industry and academia to design more advanced battery management systems for battery packs.

Efficient battery thermal management system design to ensure fast charging in extreme cold conditions

In extreme cold conditions, there are negative consequences on battery life due to extremely slower rate of chemical reactions, resulting in lower charging rates. Therefore, an efficient battery thermal management system is required to ensure temperature optimization is low which may also result in charging. In best of authors understanding, there is hardly any research being carried out in this direction. In this paper, an Intelligent Optimization framework combined with computational fluid dynamics (CFD) shall be proposed to optimize the heating method accuracy so as to maintain the uniform and desired temperature across the battery for ensuring smooth and quick charging. Battery pack model shall be designed in CFD platform and the thermal analysis shall be carried for given set of conditions (such as constant heat source, air flow rate, air temperature). Based on the obtained set of analysis samples, a model shall be formulated illustrating relationship between the minimum temperature output and the inputs (air flow rate, air temperature, etc.). The minimum temperature output shall be maximized using NSGA II so as to determine the optimum set of input conditions (air flow rate, air temperature, etc.). The battery pack simulation revealed that thermal system utilizing a liquid medium is more effective than air medium. Future research directions shall be discussed in the end.

Estimation of SOC Inconsistencies in Lithium-ion Battery Packs Based on Battery Pack Modeling and Clustering Algorithm

Estimation of SOC Inconsistencies in Lithium-ion Battery Packs Based on Battery Pack Modeling and Clustering Algorithm

Incremental Capacity Curve Peak Points-Based Regression Analysis for the State-of-Health Prediction of a Retired LiNiCoAlO2 Series/Parallel Configured Battery Pack

To recycle retired series/parallel battery packs, it is necessary to know their state-of-health (SOH) correctly. Unfortunately, voltage imbalances between the cells occur repeatedly during discharging/charging. The voltage ranges for the discharge/charge of a retired series/parallel battery pack are reduced owing to the voltage imbalances between the cells. To determine the accurate SOH of a retired series/parallel battery pack, it is necessary to calculate the total discharge capacity using fully discharging/charging tests. However, a fully discharging/charging test is impossible owing to the reduced voltage range. The SOH of a retired series/parallel battery pack with a voltage imbalance should be estimated within the reduced discharging/charging voltage range. This paper presents a regression analysis of the peak point in the incremental capacity (IC) curve from the fresh state to a 100-cycle aging state. Moreover, the SOH of the considered retired series/parallel battery pack was estimated using a regression analysis model. The error in the SOHs of the retired series/parallel battery pack and linear regression analysis model was within 1%, and hence a good accuracy is achieved.

Numerical analysis of the influence of mechanical stress on the battery pack’s housing of an electric vehicle

In this paper is presented a crash simulation analysis of the battery pack in order to increase the stiffness when the electric vehicle is involved in traffic accidents. In the first part is presented the state of the art, highlighting the advantages of using electric vehicles. The second part of the study presents the steps required to create the crash analysis of the battery pack. The CAD design of the assembly model is generated using advanced modelling techniques for two simulations battery pack models: the first model has a basic shape geometry and the second model has a shock absorber mounted on the external faces to reduce the crash impact. The crash analysis of the battery pack is determined for three velocity cases: 7 m/s, 14 m/s and 21 m/s. The final part of the paper presents the simulation results and different advantages of the battery pack geometry with the shock absorber.

Transient Temperature Distributions on Lithium-Ion Polymer SLI Battery

Lithium-ion polymer batteries currently are the most popular vehicle onboard electric energy storage systems ranging from the 12 V/24 V starting, lighting, and ignition (SLI) battery to the high-voltage traction battery pack in hybrid and electric vehicles. The operating temperature has a significant impact on the performance, safety, and cycle lifetime of lithium-ion batteries. It is essential to quantify the heat generation and temperature distribution of a battery cell, module, and pack during different operating conditions. In this paper, the transient temperature distributions across a battery module consisting of four series-connected lithium-ion polymer battery cells are measured under various charging and discharging currents. A battery thermal model, correlated with the experimental data, is built in the module-level in the ANSYS/Fluent platform. This validated module thermal model is then extended to a pack thermal model which contains four parallel-connected modules. The temperature distributions on the battery pack model are simulated under 40 A, 60 A, and 80 A constant discharge currents. An air-cool thermal management system is integrated with the battery pack model to ensure the operating temperature and temperature gradient within the optimal range. This paper could provide thermal management design guideline for the lithium-ion polymer battery pack.

A model-based state-of-charge estimation method for series-connected lithium-ion battery pack considering fast-varying cell temperature

Accurately estimating the state-of-charge (SOC) of lithium-ion batteries under complicated temperature conditions is crucial in all-climate battery management systems. This paper proposes a model-based SOC estimation method for series-connected battery pack with time-varying cell temperature. Systematic battery experiments are conducted to investigate the influences of changing temperature on both cell characteristics and cell-to-cell inconsistencies. A normalized open-circuit voltage (OCV) model is developed and applied in cell Thevenin model to describe the temperature-dependent OCV-SOC characteristic. The battery pack SOC is analyzed considering the effect of passive balance control. Then, a lumped parameter battery pack model is established by connecting cell models in series. To reduce computational complexity, a dual time-scale parameter identification framework is proposed which is supported by an online filtering process of selecting variable reference cell (VRC). An adaptive co-estimator is presented to update pack parameters in dual time-scale using an optimized recursive least squares algorithm, and to estimate the battery pack SOC using an extended Kalman filter. Experimental verifications are conducted under time-varying environmental temperature ranging from −40 °C to 40 °C. Results indicate the established model can well describe the dynamic behavior of battery pack, and the proposed method can estimate the battery pack SOC with considerably high precision.

An equivalent circuit model analysis for the lithium-ion battery pack in pure electric vehicles

According to the demand of vehicle lithium-ion battery pack, the splice equivalent circuit model is constructed. First, a joint experiment of intermittent discharge and hybrid power pulse characterization, basis of the requirements of parameter identification for the model, is designed to identify the parameters. Study shows that it can identify the parameters. Second, the splice equivalent circuit model of vehicle lithium-ion battery pack is simulated by MATLAB/Simulink, which shows the model is feasible to describe the vehicle lithium-ion battery pack. The simulation error of ohmic internal resistance R0 should be less than 0.05 mΩ. Study suggests that the vehicle lithium-ion battery pack has a stable discharge period within the state-of-charge range of [20%, 80%]. However, when stage of charge is below 20%, vehicle lithium-ion battery pack is no longer stable and the parameters of the splice equivalent circuit model change dramatically.

Innovative Modeling Approach for Li-Ion Battery Packs Considering Intrinsic Cell Unbalances and Packaging Elements

In this paper, an innovative modeling approach for Li-ion battery packs is proposed by considering intrinsic cell unbalances and packaging elements. The proposed modeling method shows that the accurate battery pack model can be achieved if the overall influences of intrinsic cell unbalances and packaging elements are taken account. Concurrently, the proposed method takes a practical model structure, resulting in the reduction of computational burden in a battery management system. Furthermore, because the proposed method utilizes cell information without a manufactured battery pack, it can be helpful to design optimal battery packs. The proposed method is verified through simulation and experimental results of the Li-ion battery pack along with the battery cycler. In three test profiles, the mean absolute percentage errors and root mean square errors of the proposed pack model do not exceed 0.5% and 0.07 V, respectively.

Optimization of Acceleration Motion Trajectory of SHEV Based on Radau Pseudospectral Method

Abstract In order to improve the acceleration response of hybrid tracked vehicles, this paper applies Radau pseudospectral method to solve the trajectory optimization problem of vehicle acceleration. The mathematical model of engine-generator, battery pack and electric motor is established, and the optimal control problem of vehicle acceleration time is constructed. The problem equation of state has strong nonlinearity. Therefore, the problem is transformed into a nonlinear programming problem by Radau pseudospectral method, and the numerical solution is carried out. The rotational speed and torque trajectory curves of the engine-generator set and the motor are obtained. The simulation results show that Radau pseudospectral method can optimize the working curve of various components of hybrid vehicles and improve response speed.

Battery energy storage system modeling: A combined comprehensive approach

Abstract Battery pack modeling is essential to improve the understanding of large battery energy storage systems, whether for transportation or grid storage. It is an extremely complex task as packs could be composed of thousands of cells that are not identical and will not degrade homogeneously. This paper presents a new approach toward battery pack modeling by combining several previously published models into a comprehensive framework. This work describes how the sub-models are connected, their basic principles, what adjustments were necessary, and what new parameters needed to be introduced. Overall, this paper introduces an open modular framework for future work on, among others, the impact of cell-to-cell variations, inhomogeneous degradation, SOC and SOH tracking, balancing and performance forecast.

Hybrid characterization procedure of Li-ion battery packs for wide frequency range dynamics applications

This paper presents a hybrid characterization procedure of battery packs capable of reproducing their behavior under different dynamic operation conditions. During the experimental procedure, both time and frequency tests are performed. These tests have been carried out on a commercial battery pack, instead of a single cell, in order to include packaging effects as well as performance of battery pack devices in real electrical applications. As a result of this procedure the battery pack model has been experimentally validated for four cases based on real electrified transportation and grid applications. Additionally, the model response has been compared with the widely used Partnership for a New Generation of Vehicles (PNGV) model. The validation tests show that the proposed battery pack model reproduces the dynamic battery response with better accuracy than the PNGV for all analyzed cases.

The parameter identification method study of the splice equivalent circuit model for the aerial lithium-ion battery pack

According to the special condition expression of the aerial lithium-ion battery pack, a novel targeted equivalent model (Splice–Equivalent Circuit Model) is proposed and constructed. The Splice–Equivalent Circuit Model achieves the accurate mathematical expression of the special operating conditions and the working process for the lithium-ion battery pack, which is realized by using the equivalent simulation of different internal effects in the charging and discharging process of the battery pack. The theoretical study and analysis of the working principle is investigated to express the working characteristics of the aerial lithium-ion battery pack together with the experimental analysis. Then, the equivalent circuit model of the aerial lithium-ion battery pack is carried out on the composite construction methods. The experimental studies are carried out in order to identify the parameters of the improved Splice–Equivalent Circuit Model, obtaining respectable identification results of battery equivalent model parameters.

Assessing the potential of an electric vehicle hybrid battery system comprising solid-state lithium metal polymer high energy and lithium-ion high power batteries

In this work the characterization and application of a prototype solid-state lithium metal battery for an electric vehicle application is addressed. This mid-temperature battery is operated at a temperature of 80 °C. In an innovative approach, this high energy technology is integrated into a hybrid battery system, where it is supported by a highest power lithium-titanate technology. Three hybrid battery system configurations are systematically derived for a high class vehicle with different performance requirements. On the basis of an overall vehicle simulation model, comprising a thermal model of the lithium metal polymer battery pack, the performance of the system is evaluated under regular and extreme driving conditions. The results indicate that battery hybridization makes a reasonable utilization of the lithium metal polymer battery in an electric vehicle possible. The power capability of the overall battery system in discharge as well as charge direction is significantly increased. Moreover, the system allows for a wider utilization of overall battery system's energy, resulting in an increase of drivable distance. Furthermore, additional functionalities of the hybrid battery system are discussed, such as warm-up procedure, low temperature performance enhancement and redundancy.

Mathematical model for thermal behavior of lithium ion battery pack under overcharge

An overcharge model of lithium ion battery pack was built by coupling the electrochemical model with thermal abuse model. The pack consists of three fully-charged batteries, each of which has a capacity of 10 Ah, using Li[Ni1/3Co1/3Mn1/3]O2 as the positive electrode. The three batteries in the pack were juxtaposed, and only the middle one was overcharged. The influences of current, convection coefficient and gap between batteries on the thermal runaway propagation were studied. The results of temperature and voltage obtained from the models were validated experimentally, and they were agreed well with the experimental data with the relative error within 6%. The results showed that the onset temperature of thermal runaway of the charged battery increased with an increase in the current, while the temperatures for the other two decreased. The temperature rate of the charged battery changed little when the convection coefficient was greater than 40 W/m2 K. The clamp of lithium ion battery pack had an important effect on the thermal runaway propagation. The occurrence of thermal runaway propagation was depended on whether there was the existence of clamp when the battery gap exceeded 5 mm.

Parametric study of forced air cooling strategy for lithium-ion battery pack with staggered arrangement

Battery thermal management is critical for the success of all electric vehicles due to the effects of extreme temperature on performance, reliability and lifespan of batteries. In this study, the three-dimensional model of a stagger-arranged battery pack was developed to investigate the effects of cooling channel size and air supply strategy on the thermal behavior of battery pack. The thermal resistance model of single irregular air passage was used to validate the numerical scheme. It was found that the appropriate cooling channel size of 1 mm for 18650 lithium-ion battery was achieved based on the three key parameters, namely, the maximum temperature, the space utilization and the energy efficiency factor. The numerical results illustrate that the best cooling performance can be achieved when airflow inlet and outlet are located on the top of battery pack. The cooling energy efficiency β decreases markedly with the increase of battery numbers along horizontal direction. As the ratio of the length of batteries along horizontal direction to battery diameter equals to 36.10, the lowest value of β is still acceptable. The analysis indicates that packing more battery along flow direction is an appropriate solution in terms of battery power density and cooling requirement.

A novel approach of battery pack state of health estimation using artificial intelligence optimization algorithm

An accurate battery pack state of health (SOH) estimation is important to characterize the dynamic responses of battery pack and ensure the battery work with safety and reliability. However, the different performances in battery discharge/charge characteristics and working conditions in battery pack make the battery pack SOH estimation difficult. In this paper, the battery pack SOH is defined as the change of battery pack maximum energy storage. It contains all the cells' information including battery capacity, the relationship between state of charge (SOC) and open circuit voltage (OCV), and battery inconsistency. To predict the battery pack SOH, the method of particle swarm optimization-genetic algorithm is applied in battery pack model parameters identification. Based on the results, a particle filter is employed in battery SOC and OCV estimation to avoid the noise influence occurring in battery terminal voltage measurement and current drift. Moreover, a recursive least square method is used to update cells' capacity. Finally, the proposed method is verified by the profiles of New European Driving Cycle and dynamic test profiles. The experimental results indicate that the proposed method can estimate the battery states with high accuracy for actual operation. In addition, the factors affecting the change of SOH is analyzed.

A phenomenological force model of Li-ion battery packs for enhanced performance and health management

A 1-D phenomenological force model of a Li-ion battery pack is proposed to enhance the control performance of Li-ion battery cells in pack conditions for efficient performance and health management. The force model accounts for multiple swelling sources under the operational environment of electric vehicles to predict swelling-induced forces in pack conditions, i.e. mechanically constrained. The proposed force model not only incorporates structural nonlinearities due to Li-ion intercalation swelling, but also separates the overall range of states of charge into three ranges to account for phase transitions. Moreover, an approach to study cell-to-cell variations in pack conditions is proposed with serial and parallel combinations of linear and nonlinear stiffness, which account for battery cells and other components in the battery pack. The model is shown not only to accurately estimate the reaction force caused by swelling as a function of the state of charge, battery temperature and environmental temperature, but also to account for cell-to-cell variations due to temperature variations, SOC differences, and local degradation in a wide range of operational conditions of electric vehicles. Considering that the force model of Li-ion battery packs can account for many possible situations in actual operation, the proposed approach and model offer potential utility for the enhancement of current battery management systems and power management strategies.

Streamline three-dimensional thermal model of a lithium titanate pouch cell battery in extreme temperature conditions with module simulation

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.

A phenomenological force model of Li-ion battery packs for enhanced performance and health management

A 1-D phenomenological force model of a Li-ion battery pack is proposed to enhance the control performance of Li-ion battery cells in pack conditions for efficient performance and health management. The force model accounts for multiple swelling sources under the operational environment of electric vehicles to predict swelling-induced forces in pack conditions, i.e. mechanically constrained. The proposed force model not only incorporates structural nonlinearities due to Li-ion intercalation swelling, but also separates the overall range of states of charge into three ranges to account for phase transitions. Moreover, an approach to study cell-to-cell variations in pack conditions is proposed with serial and parallel combinations of linear and nonlinear stiffness, which account for battery cells and other components in the battery pack. The model is shown not only to accurately estimate the reaction force caused by swelling as a function of the state of charge, battery temperature and environmental temperature, but also to account for cell-to-cell variations due to temperature variations, SOC differences, and local degradation in a wide range of operational conditions of electric vehicles. Considering that the force model of Li-ion battery packs can account for many possible situations in actual operation, the proposed approach and model offer potential utility for the enhancement of current battery management systems and power management strategies.