LiFePO4 Battery Pack Research Articles

Optimization of air-cooling technology for LiFePO4 battery pack based on deep learning

The forced air-cooling system is applied extensively in the battery thermal management system (BTMS) to ensure temperature uniformity because of the simple structure and low cost. In this paper, a BTMS of LiFePO4 cuboid battery module with adding different additional airflow outputs in typical U-type cooling system is designed to optimize temperature uniformity. Because the features of these additional airflow outputs, including positions, numbers and areas of them, influence the temperature of battery pack simultaneously, a nine-layer fully connected deep network AI model is built to find the relationship between temperature of pack and these features of additional airflow outputs in BTMS. The temperatures of batteries with different additional airflow outputs are simulated by a three-dimensional computational fluid dynamics (CFD) model. Comparing with the CFD simulation results, the AI model's mean absolute errors of maximum temperature and temperature differences are 0.046% and 0.99%, respectively. An optimal BTMS air-cooling design is found as a U-type structure adding three 4 mm additional airflow outputs with gaps of 40 mm, 120 mm, 10 mm, and 48 mm after comparison of 765,846 BTMS structures. The maximum temperature is decreased by 6.22 K, while the temperature difference is reduced by 40.36% compared to original design.

Investigation on battery thermal management system combining phase changed material and liquid cooling considering non-uniform heat generation of battery

In order to keep the working temperature of lithium-ion battery in desired range under harsh conditions, a novel coupled thermal management with phase changed material (PCM) and liquid pipe was proposed and numerically investigated for prismatic LiFePO4 battery pack. The verified non-uniform heat generation model of the battery was employed to simulate the real temperature distribution on battery surface. The effects of coolant velocity, pipe position and ambient temperature on cooling performance of coupled system were analyzed. Cycle test under harsh conditions was conducted to evaluate the thermal performance of the system. Simulation results showed that the coupled system exhibited good cooling performance even at ambient temperature of 45 °C, which suppressed the maximum temperature and temperature difference of battery pack to 47.6 °C and 4.5 °C, respectively. In addition, the system removed the heat stored in PCM and improved the liquid fraction of PCM effectively, especially in the area close to the electrode tabs. In cycles, properly reducing the coolant velocity during charge was feasible in saving power consumption of liquid cooling while keeping the cooling capacity. These results might be helpful for the application of PCM and liquid cooling in battery thermal management system for better cooling performance and lower power consumption under harsh conditions.

Research on diagnosing micro-short circuit of LiFePO4 battery pack

Research on diagnosing micro-short circuit of LiFePO4 battery pack

Active battery balancing system for electric vehicles based on cell charger

Cell imbalance can cause negative effects such as early stopping of the battery charging and discharging process which can reduce its capacity. In the previous active balancing research, the energy used for the balancing process was taken from the cell or battery pack, resulting in drop of electric vehicle driving range. In this paper, a cell charger based battery balancing system is proposed with a reduction in the number of switches. The use of a cell charger aims to increase the usable energy of the battery pack, since the energy used for the balancing process is taken directly from the grid. The use of fewer switches aims to reduce the cost and space used on the battery management system (BMS) hardware. The charger used for the balancing process has a maximum current of 3 A and a maximum voltage of 3.65 V while the number of switches used is n+5 for n batteries. A 15S1P 200 Ah LiFePO4 battery pack consists of 15 cells used for testing purpose. The test results show that the time needed to equalize the 15 cell battery voltage reaches 6 hours from the difference between the highest and lowest battery cell voltages of 145.1 mV to 15.1 mV.

Investigation on liquid cold plate thermal management system with heat pipes for LiFePO4 battery pack in electric vehicles

An appropriate battery thermal management system is essential for electric vehicles to keep an optimal working temperature range with minimal temperature difference, and meanwhile to ensure the battery is more efficient and safe. In this paper, the liquid cold plate thermal management system with heat pipes is proposed to investigate the thermal characteristic of LiFePO4 battery pack during various discharge rate operations. A three-dimensional numerical model based on standard k-ε turbulent model is developed to realize the visible analysis of fluid flow and heat transfer for the proposed thermal management system. The 50 Ah battery module is used in the experiment to validate the cooling effects of proposed thermal management system relied on heat pipes, and its performance is compared with liquid cold plate without heat pipes. Furthermore, the cooling performance of the cold plate with heat pipes could be further improved through the orthogonal experiment design, the maximum temperature of battery cell and temperature difference of battery module could be dropped by 6.95% and 11.08%, as compared with the original design. What’s more, the channel height of cold plate with heat pipes has the greatest effect on the maximum temperature of battery cells and temperature difference of battery modules.

Determination of the load capability for a lithium-ion battery pack using two time-scale filtering

Accurate determination of the continuous and instantaneous load capability is important for safety, durability, and energy deployment of lithium-ion batteries. It is also a crucial challenge for the battery-management-system to determine the load capability of a pack due to inevitable differences among in-pack cells. To overcome these challenges, a flexible battery equivalent-circuit-model is first developed without prior knowledge of in-pack cells’ capacity and internal resistance. Then, a method for determining the load capability of a pack is proposed based on a two time-scale filter using a combination of recursive-least-square-method and Kalman-filter. Distinguished from traditional model-based state-of-charge estimation strategies, only the terminal voltages and currents are used to estimate the open-circuit-voltages of each cell. The temperature and hysteresis effects are compensated to improve estimation accuracy. To reduce the computational complexity, a two time-scale scheme is designed to monitor the state-of-charge and model parameters of in-pack cells, which are further used to determine the peak power of the battery pack. Experiments and simulations conducted on LiFePO4 battery pack are employed to verify the performance of the proposed approach under dynamic operating currents and temperatures. The results indicate that the proposed approach is suitable for determining the load capability of a battery pack.

A Coolant Circulation Cooling System Combining Aluminum Plates and Copper Rods for Li-Ion Battery Pack

The spontaneous combustion of electric vehicles occurs frequently, and the main reason is the thermal runaway of a lithium-ion battery. In order to prevent the heat that is produced in the use of a lithium-ion battery out of control, this study proposed a coolant circulation cooling system, that is, the heat generated by the lithium-ion battery is transferred to heat sinks through aluminum plates and copper rods, and then dissipated through the coolant. Based on a CALB-LB5F73 LiFePO4 battery pack, experiments with the coolant circulation cooling system were conducted to study the temperature rise characteristics at different ambient temperatures. The temperature of the battery pack was still close to the upper limit of permitted temperature when the ambient temperature reached 313 K. Further improvement, increasing the diameter of copper rod of the system was proposed to enhance heat dissipation and simulations with this scheme were completed. The findings show that the cooling system can clearly reduce the temperature of a lithium-ion battery pack and control the temperature within the safe temperature range.

Variable fractional order - A comprehensive evaluation indicator of lithium-ion batteries

This paper presents a novel indicator that captures frequency characteristics of variable fractional order in terms of the electrochemical impedance spectroscopy (EIS), which is adept at evaluating the performance of lithium-ion (Li-ion) batteries comprehensively. This model-free indicator is extracted geometrically from the capacitive resistance arc in EIS acquired off-line or on-line. Particularly, in order to acquire EIS on-line and allow for the practical applications of the proposed indicator, the fractional order impulse response time-invariant principle is applied to the digital implementation of EIS by using short-term and linear I/O data. A series of experiments on LiFePO4 cells and battery packs validate that the discussed indicator is closely related to state of charge (SOC), aging degree and discharge rate, which is presented as a comprehensive embodiment for states and performance of Li-ion batteries.

A novel heat pipe assisted separation type battery thermal management system based on phase change material

In this paper, a heat pipe assisted separation type battery thermal management system (BTMS) using porous metal foam saturated with phase change material is developed to balance the temperature in a LiFePO4 battery pack. The produced heat is first transmitted to the heat management module through heat pipes, and then is absorbed by the phase change material. An additional fan is used to enhance heat dissipation when the battery temperature exceeds the setting value. Since the filling of the phase change material and other materials inside the battery pack is not required, the proposed BTMS is safe and easy for maintenance. The performance of the BTMS is experimentally investigated using a Lab-scale battery pack with constant current discharge rates of 1C, 3C, 4C, 5C, as well as different discharge-charge cycles. The results show that the proposed system offers a more suitable temperature and can better reduce the temperature imbalance within the battery pack than other methods. Especially, under the long-time operation conditions, the reliability and performance of the proposed BTMS can be greatly improved. These results are expected to provide insights into the design and optimization of BTMS.

A Fast Charging Balancing Circuit for LiFePO4 Battery

In this paper, a fast charging balancing circuit for LiFePO4 battery is proposed to address the voltage imbalanced problem of a lithium battery string. During the lithium battery string charging process, the occurrence of voltage imbalance will activate the fast balancing mechanism. The proposed balancing circuit is composed of a bi-directional converter and the switch network. The purpose of bi-directional is that the energy can be delivered to the lowest voltage cell for charging mode. On the other hand, the energy stored in the magnetizing inductors of the transformer can be charged back to the higher voltage cell in recycling mode. This novel scheme includes the following features: (1) The odd-numbered and even-numbered cells in the string with the maximum differential voltage will be chosen for balancing process directly. In this topology, there is no need to store and deliver the energy through any intermediate or the extra storing components. That is, the energy loss can be saved to improve the efficiency, and the fast balancing technique can be achieved. (2) There is only one converter to complete the energy transfer for voltage balancing process. The concept makes the circuit structure much simpler. (3) The structure has bi-directional power flow and good electrical isolation features. (4) A single chip controller is applied to measure the voltage of each cell to achieve the fast balancing process effectively. At the end of the paper, the practical test of the proposed balancing method on LiFePO4 battery pack (28.8 V/2.5 Ah) is verified and implemented by the experimental results.

A low-complexity state of charge estimation method for series-connected lithium-ion battery pack used in electric vehicles

Practical and accurate state of charge estimation for battery pack is a challenging task due to the inconsistency among in-pack cells. In this paper, we propose a low-complexity state of charge estimation method for series-connected battery pack. Firstly, to reduce computation cost, the capacity and state of charge calculations of battery pack are effectively simplified based on the probability theory. Secondly, we propose a selection method for the representative cells, which is validated by the simulation under Dynamic Stress Test. Subsequently, the state of charge of each representative cell is estimated by the recursive least squares-adaptive extend Kalman filter algorithm successively. Finally, the aging experiments for LiNCM and LiFePO4 battery packs are carried out to validate the feasibility of the simplified method, and the complexity of the three estimation methods is compared. Experimental results indicate that the capacity of battery pack depends only on the representative cells at different cycles, and the proposed “representative cell” method can estimate the state of charge of battery pack with high accuracy and low complexity. The mean absolute errors and root mean square errors for state of charge estimation are less than 3% under Urban Dynamometer Driving Schedule test at different cycles.

Experimental and numerical study of employing Potassium poly acrylate hydrogel for thermal management of 500 Wh cylindrical LiFePO4 battery pack

One of the main challenges of employing lithium-ion batteries specially in large-scale applications is overheating due to the heat generation. In this work, the effect of using Potassium Polyacrylate, a superabsorbent hydrogel, on decrease in the maximum temperature inside a 500 Wh industrial pack consisting of 38,120 cells is studied. Experiments are performed for 1C and 2C discharge current rates. Due to experimental limitations, results for discharging battery pack at 3C rate are obtained by numerical simulation. Heat source term in simulation part of work is obtained based on the experimental data for different discharge rates. It was found that inserting hydrogel inside the battery pack leads to 3.9 °C, 7.5 °C and 10.9 °C decreases in the maximum temperature for 1C, 2C and 3C discharge rates, respectively. In addition, results revealed that the decreases in the temperature of the battery pack is considerably influenced by full filling of hydrogel at points near the edges. Moreover, the effect of distance variation between cells on the temperature distribution of the battery pack is numerically studied. The results demonstrated a significant advantage to employ hydrogel for controlling battery pack temperature compared to increasing distance between cells. Finally, to compare the effect of different parameters on the maximum temperature of battery pack, the sensitivity analysis was performed. Results showed that cell density and specific heat capacity play significant role on the pack thermal behavior.

Vanadium redox flow batteries application to electric buses propulsion: Performance analysis of hybrid energy storage system

Abstract This paper presents a comparison between different battery energy storage systems (ESS) suitable for an urban electric bus. The investigation starts from a daily energy consumption analysis of a bus route in term of batteries state of charge (SOC). Specifically, three different ESS configurations are modelled basing on experimental data: LiFePO4 battery pack, LiFePO4 battery coupled with PEM fuel cell stack and a hybrid battery system composed by LiFePO4 and vanadium redox flow batteries (VRFBs). Moreover, authors provide an evaluation about the battery life through the application of the rainflow-counting algorithm on the yearly SOC trends of each system. As result, the proposed analysis highlights the favorable effect on the ESS due to the introduction of VRFB in the system. The improvements are found both on the net daily operating hours (one hour longer than the conventional case) and on the life expectancy of the LiFePO4 battery (over 9 years, with a gain factor of 5). The obtained results can be considered as a starting point for a wider study focused both on the ESS sizing and on the routes planning of a city buses fleet.

A Reformatory Model Incorporating PNGV Battery and Three-Terminal-Switch Models to Design and Implement Feedback Compensations of LiFePO4 Battery Chargers

This study developed and implemented a LiFePO4 battery pack (LBP) rapid charger. Using the three-terminal switch and partnership for a new generation of vehicles (PNGV) battery models, this study could obtain a small-signal system matrix to derive transfer functions and further analyze frequency responses for the charge voltage and current loops; therefore, both voltage and current feedback controllers could be designed to fulfill the constant-voltage (CV) and constant-current (CC) charges. To address practical applications, the proposed equivalent model also considered the wire resistance-inductance of the power cable. According to the derived high-order transfer function, the pole-zero break frequency in the Bode plot was observed that approximated the practical measurement; therefore, the pole-zero compensation could be accomplished for both charge loop requirements. Moreover, the design features for implementing the CV and CC charges are presented in detail herein, and the current overshoot during the start-up phase could be mitigated using the method of zero break frequency shifting and a novel proportional shifting proportional-integral control. The LBP parameter estimations, model construction processes, and frequency response analyses are also presented. The feedback compensation design based on the proposed model was validated through simulations and experiments. The results were determined to be in excellent agreement with theoretical derivations.

Capacity Estimation of Serial Lithium-ion Battery Pack Using Dynamic Time Warping Algorithm

The existence of the consistency degradation of the battery pack hinders the accurate estimation of pack capacity and cell capacity in the battery pack. The paper focuses on the capacity estimation of cells in the serial battery pack. The shape invariance of the charging voltage curve is discussed and used as the theoretical foundation of cell capacity difference identification. The matching relationship between two voltage curves is obtained based on the dynamic time warping algorithm. Then the capacity difference identification algorithm to calculate the capacity difference between the two cells is proposed. Based on the algorithm, a three-step capacity estimation method is established. The proposed method can only use the previous charging curve of one cell in the pack and the current charging data of the battery pack to rapidly estimate the capacity of each cell in the battery pack. A 16 serial LiFePO 4 battery pack is employed to verify the method. The result shows the estimation error of cell capacities is less than 3% rated capacity. With this method, the cell capacities in the pack can be rapidly and accurately estimated, providing a foundation for the consistency analysis and equalization of the battery pack.

Available power prediction limited by multiple constraints for LiFePO4 batteries based on central difference Kalman filter

The available power of vehicle-mounted batteries needs to be real-time predicted to accommodate prospective driving demands of overtaking, gradient climbing, constant-speed cruising, and regenerative braking. Generally, battery power capabilities are limited by multiple constraints, for example, terminal voltage, current, state-of-charge (SoC), and State-of-Energy (SoE). This paper constructs SoC and SoE estimators resorting to the square-root central difference Kalman filter (SR-CDKF) and an equivalent circuit model with online updated parameters. In addition, a battery thermal evolution model is formulated, whereby the ordinarily ignored temperature constraint is taken into account. Based on above achievements, a battery power prediction scheme conforming to multiple constraints is realized. Finally, experimental verifications are conducted on a LiFePO4 battery pack subject to consecutive Federal Urban Driving Schedule profiles. The SR-CDKF-based SoC and SoE estimators give accurate results under different conditions. In contrast to the conventional PNGV-HPPC method, the proposed method behaves with more reliability and robustness at different time horizons, temperatures, and aging levels. The assessment results justify the effectiveness of the battery modeling and algorithm utilization efforts.

Experimental investigation and thermal modelling of a series connected LiFePO4 battery pack

The present paper reports the results from modelling and experimentation with a lithium-ion battery pack operating at room temperature and under varying discharge rates. The variation in the internal resistance of the cell with change in the temperature is investigated experimentally. The prismatic Li-ion battery pack is discharged at 1C, 2C, 3C and 4C and significant parameters, such as pack voltage, temperature, and state of charge, are obtained. This is accomplished by connecting three LiFePO4 20 A h capacity prismatic batteries in series and applying 18 thermocouples at various locations on the surface of all three cells. The results show that there is a significant increase in battery surface temperature with an increase in discharge rate. The highest average surface temperature of the battery pack (56.5 °C) is observed experimentally at a 4C discharge rate, and the lowest (30.7 °C) at 1C based on modelling. Similarly, the maximum total heat generation (59.2 kJ) is observed at 4C experimentally and the minimum (37.5 °C) at 1C from modelling. A comparison of the modelling results with the experimentally determined temperature, voltage and heat generation shows good agreement. Also, the internal resistance of the cell is observed to increase as the state of charge decreases, and to decrease with increasing cell temperature.

Characteristic research on lithium iron phosphate battery of power type

In this paper, it is the research topic focus on the electrical characteristics analysis of lithium phosphate iron (LiFePO4) batteries pack of power type. LiFePO4 battery of power type has performance advantages such as high capacity, lower toxicity and pollution, operation at high temperature environment and many cycling times in charging and discharge and so on. The charging and discharging characteristics for LiFePO4 batteries of power type pack have been verified and discussed by the actual experiment. Base on the 12V10AH LiFePO4 battery was proceeding on charging and discharging test with over high current value and which investigate the parameters such as the internal resistance, the related charge and discharge characteristics of LiFePO4 battery pack, the actual value of internal voltage and internal resistance of the battery pack and by polynomial mathmatic model to approach the accury of inner resistance on discharging mode.

Experimental study of a passive thermal management system using copper foam-paraffin composite for lithium ion batteries

A passive thermal management system using copper metal foam saturated with phase change materials is designed for LiFePO4 battery pack. Copper metal foam is aimed to enhance low thermal conductivity of PCM and improve temperature uniformity of the battery pack. The thermal efficiency of the system is experimentally investigated and compared with two dissipation patterns of air cooling and pure PCM. The results show that the dissipation pattern of the foam-PCM composite can significantly reduce the battery’s surface temperature compared with the other two patterns. Moreover, the foam-PCM composite can bring the battery pack a better temperature uniformity, especially during the higher discharge rate.

A Novel Active Online State of Charge Based Balancing Approach for Lithium-Ion Battery Packs during Fast Charging Process in Electric Vehicles

Abstract: Non-uniformity of Lithium-ion cells in a battery pack is inevitable and has become the bottleneck to the pack capacity, especially in the fast charging process. Therefore, a balancing approach is essentially required. This paper proposes an active online cell balancing approach in a fast charging process using the state of charge (SOC) as balancing criterion. The goal of this approach is to complete pack balancing within the limited charging time. An adaptive extended Kalman filter (AEKF) is applied to estimate the pack cell SOC during the charging process to obtain accurate results under modeling errors and measurement noises. To implement the proposed AEKF, only one additional current sensor is required to obtain the current of each cell required for the SOC estimation. An experimental platform is established to verify the effectiveness of the proposed approach. The results show that the proposed balancing approach with the SOC as a balancing criterion can overcome the challenges of non-uniformity and flat voltage plateau and charge more capacity into a LiFePO4 battery pack than those with the terminal voltage as a balancing criterion in the fast charging process.