Battery Pack Model Research Articles

An Acausal Li-Ion Battery Pack Model for Automotive Applications

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.

Novel evaluation method of fuel consumption and emission for heavy-duty hybrid electric vehicles

This paper is a continuation of a previous paper titled “A novel way to calculate energy efficiency for rechargeable batteries” published on Journal of Power Sources/2012 describing a new method to calculate energy efficiency for rechargeable batteries. The present paper further describes the application of energy efficiency model on the evaluation of fuel consumption and emission for the heavy-duty hybrid electric vehicles (HD-HEVs). A more accurate calculation method of net energy change for power battery pack is proposed based on energy efficiency model of power battery pack. A more simplified and accurate correction method of fuel consumption and emission is also presented based on equivalent mileage. The fuel consumption and emission on chassis dynamometer are measured in the HD-HEVs. The experiment results show that relative errors of fuel consumption and emission between equivalent mileage correction results and linear regression correction results are less than 3%, which verifies accuracy and validates the proposed evaluation method for HD-HEVs fuel consumption and emission.

Transient modeling and validation of lithium ion battery pack with air cooled thermal management system for electric vehicles

A transient numerical model of a lithium ion battery (LiB) pack with air cooled thermal management system is developed and validated for electric vehicle applications. In the battery model, the open circuit voltage and the internal resistance map based on experiments are used. The Butler-Volmer equation is directly considered for activation voltage loss estimation. The heat generation of cells and the heat transfer from cells are also calculated to estimate temperature distribution. Validations are conducted by comparison between experimental results at the cell level and the pack level. After validations, the effects of module arrangement in a battery pack are studied with different ambient temperature conditions. The configuration that more LiB cells are placed near the air flow inlet is more effective to reduce the temperature deviation between modules.

Analysis on the capacity degradation mechanism of a series lithium-ion power battery pack based on inconsistency of capacity

The lithium-ion battery has been widely used as an energy source. Charge rate, discharge rate, and operating temperature are very important factors for the capacity degradations of power batteries and battery packs. Firstly, in this paper we make use of an accelerated life test and a statistical analysis method to establish the capacity accelerated degradation model under three constant stress parameters according to the degradation data, which are charge rate, discharge rate, and operating temperature, and then we propose a capacity degradation model according to the current residual capacity of a Li-ion cell under dynamic stress parameters. Secondly, we analyze the charge and discharge process of a series power battery pack and interpret the correlation between the capacity degradations of the battery pack and its charge/discharge rate. According to this cycling condition, we establish a capacity degradation model of a series power battery pack under inconsistent capacity of cells, and analyze the degradation mechanism with capacity variance and operating temperature difference. The comparative analysis of test results shows that the inconsistent operating temperatures of cells in the series power battery pack are the main cause of its degradation; when the difference between inconsistent temperatures is narrowed by 5 °C, the cycle life can be improved by more than 50%. Therefore, it effectively improves the cycle life of the series battery pack to reasonably assemble the batteries according to their capacities and to narrow the differences in operating temperature among cells.

Accurate battery pack modeling for automotive applications

This paper describes an advanced battery pack modeling method for automotive applications. In contrast to the common approach of aggregating hundreds of battery cell models in series and parallel for battery pack representation, a simple yet accurate electrical analogue battery model with constant parameters is used to represent the whole battery pack. The modeling process involves only the external characteristics of the battery pack, thus detailed knowledge of the physical construction of the battery pack or the physical parameters of the battery cells are avoided. Battery experimental tests include an independent pulse charging/discharging cycle test and several performance estimates acquired from the anticipated battery application. This modeling approach is achieved by anticipating the bandwidth of the battery application and then optimizing the bandwidth of the battery pack model with this knowledge. The reported work enables a fast dynamic battery pack simulation with a new level of high fidelity. Although the scope of this work does not include temperature and lifetime effects, it is shown that the form of the model and the parameter extraction procedure can encompass these important improvements. This approach was experimentally verified on a 360 V, 21.3 kWh lithium-ion battery pack operated in a plug-in hybrid electric vehicle.

Dynamic electrothermal battery pack modelling and simulation of pack imbalance

In this paper, we present a battery pack model and simulation methodology in order to study some of the operation characteristics of different battery pack configurations, under different temperatures, different initial state of charge (SoC), and different current profiles. During battery pack operation, there can exist significant pack imbalances caused by non-uniform temperature distributions, state of health differences, and manufacturing differences. To study the imbalance that occurs in a pack, we derive an efficient analytical dynamic battery single cell model with scheduled parameters that is used inside a larger pack model. Since the pack model is made up of individual battery cells, pack imbalances can be studied. It is shown that the battery pack model and simulation methodology developed may be extended to support any topology and pack sizing.

Multiphysical Lithium-Based Battery Model for Use in State-of-Charge Determination

This paper presents a multiphysical battery pack model, along with a procedure to identify its parameters and its application to state-of-charge (SOC) determination using an extended Kalman filter (EKF). The model enables the reproduction of the electric and thermal behaviors of batteries with high accuracy. A methodology is proposed to identify the parameters of the model and optimize them. The model is experimentally validated with measurements run on high-energy-density ThunderSky cells. A comparison of measurements and model results shows that the electrical model error is below 1.6% and that the error of the thermal model is below 2.5%. The model is used as an EKF basis to reliably estimate the battery SOC. The results are also experimentally verified through measurements showing that the proposed model performs better than other simpler models and determination methods.

An Improved Lead–Acid Battery Pack Model for Use in Power Simulations of Electric Vehicles

A new model for a lead-acid battery pack is proposed for use in power simulations of electric vehicles. A linear approximation using a constant voltage drop has been used to model the charge-transfer resistance of the battery pack, and an exponential voltage-recovery equation has been used to model the transient capacitance effects following a period of discharge. The new model is easy to implement with simple calculations and easily acquired parameters, combining speed of implementation with accuracy. The new model was found to have a peak error of 3.1% in drive cycle tests, thus comparing favorably to existing models of similar complexity. An initial assessment of the model's suitability for use with a lithium-ion battery pack was also performed, finding a peak error of 5%.

Identifying and Accommodating Cell Variations for Commercial Li-ion Battery Pack Modeling

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Origins and accommodation of cell variations in Li-ion battery pack modeling

Rechargeable battery industry will see significant growth in the use of battery systems for portable devices and power electronics, renewable energy storage, power systems for transportation, and telecom backup power applications. Despite such promising market sentiment, the battery system management remains as a challenging issue to be resolved in order to provide a safe and reliable power and energy storage system. Here we report advancement in the battery management approach by providing a solution to analyze battery performance variations in a lot of batteries produced from the same manufacturing process. A lot of 100 Li-ion cells were analyzed in order to quantify the inherent cell variations associated with cell manufacturing process and test protocol. Both statistical and electrochemical analyses were used to characterize and quantify the capacity variations among the cells along with other parameters that can be readily derived from the test results. Information extracted from a minimal testing of the cells in the lot and more intensive characterizations on a few cells including one as the nominal sample cell allows the establishment of a single cell model (SCM), based on a generic equivalent circuit, with high accuracy in predicting cell performance. The analyses also permit a carefully crafted logic development of how to separate the origins that cause the cell variations in performance. Such separation of the attributes enable a proper tuning of the cell parameters in the model, which allows the accommodation of cell variations in a battery pack model to handle most of the imbalance issues. A careful validation of the SCM to predict performance of any arbitrary cell in the lot with high accuracy was demonstrated. Copyright © 2009 John Wiley & Sons, Ltd.

Estimation of Internal States of Power Lithium-ion Batteries Used on Electric Vehicles by Dual Extended Kalman Filter

For the development of electric vehicles, power lithium-ion battery is an option of assistant power source for such kind of vehicles. An equivalent physical model of the power lithium-ion battery pack is founded which is then described in a discrete state-space form. The principle of how to use Kalman filtering to estimate the internal states including state of charge and state of health independently is introduced, and based on this, how to estimate state of charge and State of health synchronously by using dual extended Kalman filtering is proposed. A corresponding experiment is designed in which the data such as current and voltage are acquired to test the algorithm, and the testing results show that internal state estimation of battery by the method of dual extended Kalman filtering is effective and results in a relatively hiyh estimation accuracy, thus well reflecting the actual internal state of the battery pack.

Design and experiment of electric bus

Performance and reliability experiments on BJD-6100EV electric buses, jointly developed by Beijing Institute of Technology and Beijing Public Transport Company, are introduced. Output power model of battery pack is established and maximum output power is analyzed. A permanent magnetic direct current (PMDC) motor with enhanced windings is developed for the bus. Torque-speed characteristics of the motor are modeled and performance of electric bus is analyzed. Computational method of the range of electric bus is proposed and discussed. Experiments show that electric bus can realize design requirements. Computational methods are verified with the help of field test. It is expected that design and computation method will provide helpful reference to development of electric vehicles.