Query: Battery pack

title: A Sensor Fault Diagnosis Method for a Lithium Ion Battery Pack in Electric Vehicles
abstract: In electric vehicles, a battery management system highly relies on the measured current, voltage, and temperature to accurately estimate state of charge (SOC) and state of health. Thus, the normal operation of current, voltage, and temperature sensors is of great importance to protect batteries from running outside their safe operating area. In this paper, a simple and effective model based sensor fault diagnosis scheme is developed to detect and isolate the fault of a current or voltage sensor for a series connected lithium ion battery pack. The difference between the true SOC and estimated SOC of each cell in the pack is defined as a residual to determine the occurrence of the fault. The true SOC is calculated by the coulomb counting method and the estimated SOC is obtained by the recursive least squares and unscented Kalman filter joint estimation method. In addition, the difference between the capacity used in SOC estimation and the estimated capacity based on the ratio of the accumulated charge to the SOC difference at two nonadjacent sampling times can also be defined as a residual for fault diagnosis. The temperature sensor which is assumed to be fault free is used to distinguish the fault of a current or voltage sensor from the fault of a battery cell. Then, the faulty current or voltage sensor can be isolated by comparing the residual and the predefined threshold of each cell in the pack. The experimental and simulation results validate the effectiveness of the proposed sensor fault diagnosis scheme.

title: Thermal management of Li ion battery pack with the application of flexible form stable composite phase change materials
abstract: A method for thermal management of Li ion battery pack with the application of various flexible form stable composite phase change materials (CPCMs) is proposed, and investigated both numerically and experimentally. Flexible CPCMs embedded in battery pack lower the thermal contact resistance, thereby improving the thermal control performance. Experimental results show that with the application of flexible CPCMs, the battery temperature drops by 18 degC at 10 C discharge rate. In addition, flexible CPCM has better thermal control performance than the case of conventional CPCMs. This allows Li ion battery pack to safely work for an extended period of time without exceeding upper temperature limits. The thermal control performance is observed to vary considerably with three factors: the phase change temperature of flexible CPCMs, working condition, and the ambient temperature. One flexible CPCM with phase change temperature of 33 degC is found to be optimal for small power levels and low ambient temperatures. Another flexible CPCM with 47 degC of phase change temperature is suitable for high power levels, short term high heat fluxes, and high ambient temperatures. The numerical results are in reasonable accordance with experimental ones.

title: Energy and environmental assessment of a traction lithium ion battery pack for plug in hybrid electric vehicles
abstract: Traction batteries are a key factor in the environmental sustainability of electric mobility and, therefore, it is necessary to evaluate their environmental performance to allow a comprehensive sustainability assessment of electric mobility. This article presents an environmental assessment of a lithium ion traction battery for plug in hybrid electric vehicles, characterized by a composite cathode material of lithium manganese oxide (LiMn2O4) and lithium nickel manganese cobalt oxide Li(NixCoyMn1 x y)O2. Composite cathode material is an emerging technology that promises to combine the merits of several active materials into a hybrid electrode to optimize performance and reduce costs. In this study, the environmental assessment of one battery pack (with a nominal capacity of 11.4 kWh able to be used for about 140,000 km of driving) is carried out by using the Life Cycle Assessment methodology consistent with ISO 14040. The system boundaries are the battery production, the operation phase and recycling at the end of life, including the recovery of various material fractions. The composite cathode technology examined besides a good compromise between the higher and the lower performance of NMC and LMO cathodes, can present good environmental performances. The results of the analysis show that the manufacturing phase is relevant to all assessed impact categories (contribution higher than 60% With regard to electricity losses due to battery efficiency and battery transport, the contribution to the use phase impact of battery efficiency is larger than that of battery transport. Recycling the battery pack contributes less than 11% to all of the assessed impact categories, with the exception of freshwater ecotoxicity (60% of the life cycle impact) The environmental credits related to the recovery of valuable materials (e.g. cobalt and nickel sulphates) and other metal fractions (e.g. aluminium and steel) are particularly relevant to impact categories such as marine eutrophication, human toxicity and abiotic resource depletion. The main innovations of this article are that (1) it presents the first bill of materials of a lithium ion battery cell for plug in hybrid electric vehicles with a composite cathode active material; (2) it describes one of the first applications of the life cycle assessment to a lithium ion battery pack for plug in hybrid electric vehicles with a composite cathode active material with the aim of identifying the "hot spots" of this technology and providing useful information to battery manufacturers on potentially improving its environmental sustainability; (3) it evaluates the impacts associated with the use phase based on primary data about the battery pack's lifetime, in terms of kilometres driven; and (4) it models the end of life phase of the battery components through processes specifically created for or adapted to the case study.

title: A surrogate thermal modeling and parametric optimization of battery pack with air cooling for EVs
abstract: The battery packs in electric vehicles usually operate at high current discharge rates which leads to the higher heat generation. This may have safety issues and negative impact on the battery performance over the period. Existing researches focused more on the configurations and design of battery cells/modules arrangements to reduce the maximum temperature rise of the battery pack. However, temperature differences are more important and difficult to manage. It is also known that smaller the size of the battery pack, higher the space can be saved. This article proposes a comprehensive methodology to design an efficient air cooling system, which is hybrid of system volume and cooling performance. The proposed methodology comprises of the four steps: the design of air cooling battery, setup of the computational fluid dynamics codes, design of experiments (DoE) evaluation and selection of surrogate models. These models are then optimized using the multi objective optimization approach for the selection of optimum scheme for air cooling battery module. The optimization results show that the optimized air cooling battery module has higher thermal performance. The proposed methodology will be useful for industrial battery pack design process to reduce maximum temperature, temperature difference and the volume of battery pack.

title: Model based insulation fault diagnosis for lithium ion battery pack in electric vehicles
abstract: The condition monitoring and fault diagnosis of the lithium ion battery system are crucial issues for electric vehicles. The shocks, blows, twists, and vibrations during the electric vehicle driving process may cause the insulation fault. In order to ensure the safety of the drivers and passengers, a real time monitor to detect the insulation state between the high voltage and ground is required. However, the conventional battery management system only provides very simple and coarse grained measurements to detect the insulation resistance. In this work, a model based insulation fault diagnosis method is proposed. Firstly, the equivalent circuit model for insulation fault diagnosis is established using a high fidelity cell model. Then, the recursive least squares method is employed to identify the model parameters. Considering the system nonlinear properties, measurement noise and unknown disturbance, the Kalman filter based state observer is designed for joint estimation of both the battery voltage and state of charge using the identified battery model. Finally, the positive and negative virtual insulation resistance are quantitatively assessed based on the prediction results of the state observer. Experiments under different loading profiles are performed to verify the proposed method.

title: Design of the structure of battery pack in parallel air cooled battery thermal management system for cooling efficiency improvement
abstract: In this paper, the cell spacing distribution of the battery pack in the parallel air cooled BTMS is designed to improve the cooling efficiency of the system. The flow resistance network model is used to calculate the airflow rates in the cooling channels. A modification factor is introduced to reduce the error of the model. The effectiveness of the model is verified by the computational fluid dynamics (CFD) calculation, and the CFD method is validated by the experimental air cooled system with aluminum blocks. Combining with the improved flow resistance network model, an optimization strategy is adopted to optimize the battery cell spacings for the homogenization of the airflow rates among the cooling channels. Then an adjustment coefficient is introduced to adjust the airflow rates in the cooling channels for more uniform cell temperatures. The results of typical numerical cases indicate that the cooling efficiency of the BTMS is improved remarkably after the cell spacing optimization using the developed strategy. Compared to the original BTMS, the maximum temperature of the battery pack for the optimized BTMS is reduced by about 4.0 K, and the maximum cell temperature difference is reduced by more than 69% for various inlet airflow rates. Compared to the optimized BTMS in previous study, the maximum cell temperature difference for the present optimized BTMS is reduced by more than 25% for various inlet airflow rates.

title: Three dimensional thermal modeling of Li ion battery cell and 50 V Li ion battery pack cooled by mini channel cold plate
abstract: In this work, three dimensional (3D) thermal modeling of a single Li ion battery cell and a 50 V Li ion battery pack composed of 14 prismatic batteries is performed. Equivalent circuit model is used for subscale electrochemical modeling. The heat generated by electrical resistance and electrochemistry reactions is then solved in the cell domain which resolves the heat transfer in battery and battery pack. The modeling provides highly resolved temporal 3D insight into thermal and battery dynamics under fast discharging and abusive condition. It is found that with low coolant velocity, the cell temperature easily exceeds 40 degC, and temperature non uniformity exceeds the limit value of 5 degC under 5C discharging condition; and under external shorting condition, temperature rises fast and reaches the 80 degC point quickly which can further trigger thermal runaway. On the other hand, with adequate coolant flow rate, the cell temperature and temperature gradients are effectively limited to tolerable level under both 5C discharging and external shorting conditions. Thus, coolant rate needs to be carefully designed to prevent high temperature and localized high temperature spot in Li ion battery. The modeling method used in this study can be applied to general Li ion battery and Li ion battery pack designing.

title: Thermal performance investigation of an air cooled lithium ion battery pack considering the inconsistency of battery cells
abstract: A lithium ion battery pack is the power source of an electric vehicle, and its temperature rise is one of the main concerns. Existing research mainly focused on the design of cooling systems, and always used computational fluid dynamics to analyze the thermal behavior of batteries, regardless of the individual differences of batteries. In this paper, the heat dissipation performance of air cooled battery packs considering the different thermal performance of different batteries was studied. A more realistic thermal model of the battery pack at 1C discharge rate was obtained through equivalent calculation and experimental verification. The results showed that the temperature of batteries with different thermal performance rose faster and the temperature difference was larger. At the same time, the thermal performance of the battery can be improved by placing the outlet and inlet on the same side. The thermal performance was more sensitive to the inlet exhaust height than to the outlet exhaust height. The research results can provide a basis for exploring the design method of battery packs with better heat dissipation performance, lower energy consumption, and a smaller volume.

title: Minimization of thermal non uniformity in lithium ion battery pack cooled by channeled liquid flow
abstract: In this work we conduct a numerical study with the aim of analyzing the effectiveness of cooling channels to reduce thermal non uniformity in lithium ion battery packs of electric vehicles. Particular approaches toward zero or near zero thermal non uniformity in lithium ion battery packs are proposed and their performance and viability are evaluated through numerical simulations. Battery packs cooled by liquid flowing in serpentine channels are used to illustrate the proposed approaches. A thermal model, which has been extensively tested, is applied to a battery module of 71 18650 type NMC (nickel manganese cobalt) batteries. In particular, among several approaches, two of them show considerable promise in improving the pack thermal uniformity, namely: (a) shortened flow paths by using multiple serpentine channels, and (b) increasing contact areas between the batteries and the serpentine channel along the flow path in the streamwise direction. The results of the numerical simulation indicate that these two particular approaches can reduce the thermal non uniformity of the battery module under 5C discharge operations to values lower than 2.2 K and 0.7 K, respectively. The description, functional feasibility and effectiveness of these approaches are extensively covered in the present work.

title: A Novel Dynamic Performance Analysis and Evaluation Model of Series Parallel Connected Battery Pack for Electric Vehicles
abstract: Due to the low voltage and small capacity of a Li ion battery cell, large numbers of cells are connected to construct a battery pack to satisfy the voltage and capacity requirement of the power system of an electric vehicle. Focusing on parallel and series connection mode of battery packs, the main contributions include the following. First, in order to increase the utilization rate of cells and enhance the performance of the battery pack, a method that makes the battery pack achieve their maximum initial capacity has been proposed. Second, a dynamic modeling and analysis method for the battery pack based on the equivalent circuit model has also been proposed. The results show that the battery pack in parallel and then in series has a better performance on charge/discharge capacity, efficiency, and utilization rate of cells. Third, the performance analysis and evaluation platform of the battery pack has been built, and the battery pack test results of different groups supported the conclusion of the simulation. The battery packs in parallel and then in series can achieve superior performance and greatly increase capacity and energy utilization.