A novel multiobjective charging optimization method of power lithium‐ion batteries based on charging time and temperature rise

Power lithium‐ion batteries have been widely utilized in energy storage system and electric vehicles, because these batteries are characterized by high energy density and power density, long cycle life, and low self‐discharge rate. However, battery charging always takes a long time, and the high current rate inevitably causes great temperature rises, which is the bottleneck for practical applications. This paper presents a multiobjective charging optimization strategy for power lithium‐ion battery multistage charging. The Pareto front is obtained using multiobjective particle swarm optimization (MOPSO) method, and the optimal solution is selected using technique for order of preference by similarity to ideal solution (TOPSIS) method. This strategy aims to achieve fast charging with a relatively low temperature rise. The MOPSO algorithm searches the potential feasible solutions that satisfy two objectives, and the TOPSIS method determines the optimal solution. The one‐order resistor‐capacitor (RC) equivalent circuit model is utilized to describe the model parameter variation with different current rates and state of charges (SOCs) as well as temperature rises during charging. And battery temperature variations are estimated using thermal model. Then a PSO‐based multiobjective optimization method for power lithium‐ion battery multistage charging is proposed to balance charging speed and temperature rise, and the best charging stage currents are obtained using the TOPSIS method. Finally, the optimal results are experimentally verified with a power lithium‐ion battery, and fast charging is achieved within 1534 s with a 4.1°C temperature rise.     

Control strategy of a fuel-cell power module for electric forklift

Fuel cell-battery hybrid systems for the powertrain, which have the advantage of emission-free power generation and adapt to material transport and emission reduction, are investigated. Based on the characteristics of the fuel cell system and the characteristics of the electric forklift truck powertrain system, this work defines the design principle of the control strategy to improve overall performance and economy. A simulation platform for fuel cell and electric vehicles has been established. The optimal performance of the fuel cell stack and the battery capacity were defined for the specific application. An energy control strategy was defined for different operating cycles and operating conditions. Model validation involved comparing simulation results with experimental data obtained during VDI60 test protocol. The main parameters that influence the forklift performance were defined and evaluated, such as energy loss, fuel cell operating conditions and different battery charging cycles. The optimal size of the fuel cell stack of 11 kW and the battery of 10 Ah was determined for the specific load profile with the proposed control strategy. The results obtained in this work forms the basis for an in-depth study of the energy management of fuel cell battery drive trains for forklift trucks.     

Preheating strategy of variable-frequency pulse for lithium battery in cold weather

Aiming to the issue of charging difficulty and capacity fading for lithium-ion battery at low temperature, this study proposes a preheating strategy using variable-frequency pulse. The innovation of this paper is to propose the thermo-electric coupling model based on the electrochemical impedance spectroscopy of battery at different temperatures, integrated with variable frequency changing for pulse method to develop an effective inner pre-heating strategy. Meanwhile, the evaluating method of impact of this strategy on capacity fading of battery has also been proposed to examine its effectiveness, to find the optimal strategy. First, temperature rise model and the thermo-electric coupling model at different temperatures according to the equivalent circuit model of battery are presented. Further, optimal heating frequency of current pulse at different temperatures is calculated according to the changing of internal impedance. The results show that the optimal variable-frequency pulse pre-heating strategy can heat the lithium-ion battery from −20°C to 5°C in 1000 seconds. Meanwhile, it brings less damage to the battery health and improves the performance of battery in cold weather based on the views of power consumption, capacity attenuation, and internal impedance changes.     

Aging model development based on multidisciplinary parameters for lithium-ion batteries

In this paper, a method composed of state of health (SOH) testing experiments and artificial intelligence simulation is proposed to carry out the study on the change of battery characteristic during its operation and generate mathematical models for the prediction of aging behaviour of battery. An experiment comprising of multidisciplinary parameters-based SOH detection is conducted to study the battery aging characteristics from several aspects (ie, electrochemistry, electric, thermal behaviour and mechanics). In total, 200 sets of data (corresponding 200 charging/discharging cycles) are collected from the experiment. The data obtained from the first 150 cycles are employed in generation of the models. The result of sensitivity analysis based on the obtained genetic programming models shows that it is better to apply voltage value at the end of charging step, charging time and cycle number to predict the operational performance of the battery. The average predicted accuracy of model (without stress) is 94.52%, whereas the average predicted accuracy of model (with stress effect) is 99.42%. The proposed models could be useful for defining the optimised charging strategy, fault diagnosis and spent batteries disposal strategies.     

基于实时内阻测试的锂电池自适应电流充电策略

为降低电动汽车锂离子电池的充电损耗,提出了一种基于实时内阻测试的锂电池自适应电流充电策略。针对该充电策略中电池的实时内阻测试和最优电流集的求解问题,提出了一种电化学阻抗谱(EIS)检测法和随机进化算法。通过在MATLAB/Simulink中进行仿真实验,验证了算法的可行性。在不改变充电时间的情况下,文章所提出的充电策略比传统的恒流充电方法的减损效果更加显著。     

Heterogeneous aging of large-scale flexible lithium-ion batteries based on micro-heterostructures and simulation

To meet application demands of electric vehicles, cathode materials of batteries have to overcome the life limitation and performance attenuation caused by crack propagation on the surface of electrode particles. With the increase of size and power of batteries, the voltage gradient generated by metal foil current collectors with high conductivity cannot be neglected. This study reconstructed a porous microstructure based on images of surface morphologies of lithium manganese oxide particles collected by a field emission-scanning electron microscope. Based on this, a multi-scale and multi-physics simulation model coupling electro-chemo-thermo-mechanical behaviours was developed to predict heterogeneous mechanical stress and capacity loss of a large-scale flexible lithium-ion battery. The results arising from use of the model show that: (1) Lithium in electrode particles cannot be diffused in time under a high-charge and discharge rate, and the capacity loss of the battery is directly proportional to the stress generated on the electrode particles. Capacity loss at discharge rate of 10C is 46% higher than that at the rate of 1C and corresponding stress in the microstructure increases by 16%. (2) In the design of the battery layout adopted in this study, utilization rates of electrodes and temperature fields are highly heterogeneous at the higher rate. Mechanical stress near the tab is 8% higher than that at the bottom edge, and it is speculated that the rate of aging of the tab is 35% higher. (3) Mechanical stress during lithium extraction in the cathode during charge is less than half of that during discharge. Attributed to small influences of material activity and excellent performance of lithium titanate oxide in the anode, capacity loss during charge is only 2%. (4) During discharge, stress in the contact region of between particles is the largest, resulting in the decrease of the activity and the low lithium-ion concentration. This leads to cracks during cyclic charging and discharging, which further decreases the activity of the materials. (5) Heterogeneity in the distribution of lithium-ion concentration with different sizes of particles significantly rises with the rate. The model built in this research couples the analysis of temperature field of a battery cell and stress field of the microstructure, which is conducive to understanding mechanisms underlying performance attenuation of the large-scale flexible lithium-ion battery under high-rate use.     

Effect of charge rate on capacity degradation of LiFePO4 power battery at low temperature

Limited by the current power battery technology, electric vehicles show extremely poor duration performance and potential risk at low temperature, which is mainly caused by poor charging performance of lithium-ion batteries. To explore the impact of charging process on cycle degradation at low temperatures, a cycle aging experimental scheme with different charging C-rate (0.3C and 0.5C) under −10°C and −20°C was designed for the commercial LiFePO₄ battery. The experimental batteries showed severe degradation after a few of cycles. The phenomenon of reduced internal resistance and up-shift of the charging curve was found during the early cycle stages (0th-20th cycle). The influence of low-temperature cycle on battery was analyzed by the increment capacity analysis (ICA); the fast decreasing intensity of ①*II showed sharp loss of lithium ions. Those lithium ions mainly transformed into lithium plating and built up dendrites instead of reintercalating into the anode crystal structure, causing the further degradation of capacity and ohmic resistance. Degradation law was obtained by curve regression analysis in the end.     

NCR18650A电池的充放电温度特性与管理

采用实验测试与数值仿真的方法对NCR18650A三元锂电池组在1 ~ 3 C放电和1.6 C充电过程的温升特性进行测试,同时验证所建立电池产热模型的准确性。结果显示,实验测试结果与电池产热模型仿真结果之间的相对误差在合理范围内,满足工程应用需求。电池组在自然冷却的情况下,仅在1 C放电状态下符合其最佳工作区间42.5 ~ 45.0℃的要求,3 C放电倍率下最高温度为89.4℃。提出并建立基于热电致冷主动热管理模型,将热电致冷组件设置在电池组上方,致冷功率为50 W时可有效控制电池组3 C放电过程的温度,在最佳工作区间实现电池单体温差小于5℃,抑制电池组的热失效并实现良好的均温性。     

Review of research on heat generation characteristics during charging and discharging of lithium ion batteries

电动车辆的性能和成本很大程度上取决于动力电池组的性能和使用寿命,而电池组的性能和使用寿命又受到电池单体产热的影响。研究锂离子电池充放电过程中的产热特性及影响因素,对锂电池的开发及使用具有指导意义。本文从环境温度、充放电倍率、电池材料、荷电状态和老化程度五个方面入手,综述了各因素对锂离子电池产热的影响。     

Passive thermal management of the lithium‐ion battery unit for a solar racing car

In this study, a three‐dimensional numerical model is developed to investigate the thermal and electrical characteristics of 18 650 lithium‐ion battery cells that are used in the solar racing car of Dokuz Eylül University, i.e., SOLARIS. The Newman, Tiedemann, Gu, and Kim (NTGK) battery model of ANSYS Fluent software is implemented to resolve the coupled multiphysics problem. In the analysis, only the discharging period of the battery is considered. Before going through parametric studies under variable weather conditions, time‐wise variations of the cell temperature and the battery voltage are evaluated both experimentally and numerically under two different ambient conditions of 0°C and 25°C. Comparative results revealed that reasonable predictions are achieved with the current battery model, and the difference between the predicted battery surface temperature and experimental data is less than 1°C. Following the model validation, the battery performance is numerically examined by applying the battery model to a real race procedure of SOLARIS. Phase change materials (PCMs) with different amounts and melting temperatures are implemented around the batteries, and transient analyses are conducted under real weather conditions. The current study aims to keep the battery temperature of a solar racing car above a certain limit to prevent the overcooling and maintain higher charging capacity. Implementation of PCM with a melting temperature of 26°C yields 3.15% of capacity increment, and such a performance improvement corresponds to 15.51 Wh of extra energy that can be extracted from an individual battery.     

Performance analysis of a micro-combined heating and power system with PEM fuel cell as a prime mover for a typical household in North China

Proton exchange membrane (PEM) fuel cells produce a large amount of waste heat while generating electricity through electrochemical reactions, making them suitable for driving combined heating and power (CHP) systems. According to the hourly thermal and electric loads in a typical North China household, a 2-kW PEM fuel cell-based micro-CHP system with a lithium-ion battery energy storage system is proposed in this paper. The thermal and economic performances of the micro-CHP system with a lithium-ion battery (CHPWB) and a CHP system without a lithium-ion battery (CHPWOB) are comparatively analyzed by developing a thermal and economic performance analysis model on the MATLAB/Simulink platform. The thermal-load-following strategy is adopted during the design and simulation process. The results indicate that the storage capacity of the lithium-ion battery decreases by 6.6% after one cycle. The lithium-ion battery can be charged by the fuel cell stack during off-peak hours or using commercial electricity, and the charging cycle of the system is one week long. The average total efficiency of the CHPWB system can reach 81.24% with considering the energy loss in each conversion process, which is 11.02% higher than that of the CHPWOB system. The daily hydrogen consumption of the CHPWB system can be reduced by 14.47% compared with the CHPWOB system under the same operating conditions, and the average daily costs can be reduced by 8.4% and 9.5% when the lifespan is 10 and 15 years, respectively.     

储能系统协同常规机组调峰控制策略研究

大规模风电并网会引起电力系统调峰能力不足,造成火电机组频繁启停或弃风。文章利用电池储能充放电灵活、可补充常规机组调峰能力不足的特性,提出了AGC机组、NON-AGC机组与储能系统间的协调控制策略。该策略引入了改进调度时间级,实现储能与常规机组时间协调配合;以AGC机组与NON-AGC机组的协调机制为基础,建立了AGC机组向NON-AGC机组与电池储能的转移功率模型。根据前一时刻机组的输出功率,计算出机组的调节余量实现电池储能参与系统调峰。实际系统算例分析结果表明,所提控制策略的可行性和有效性。     

Numerical analysis of an energy storage system based on a metal hydride hydrogen tank and a lithium-ion battery pack for a plug-in fuel cell electric scooter

This work investigates on the performance of a hybrid energy storage system made of a metal hydride tank for hydrogen storage and a lithium-ion battery pack, specifically conceived to replace the conventional battery pack in a plug-in fuel cell electric scooter. The concept behind this solution is to take advantage of the endothermic hydrogen desorption in metal hydrides to provide cooling to the battery pack during operation.The analysis is conducted numerically by means of a finite element model developed in order to assess the thermal management capabilities of the proposed solution under realistic operating conditions.The results show that the hybrid energy storage system is effectively capable of passively controlling the temperature of the battery pack, while enhancing at the same time the on-board storage energy density. The maximum temperature rise experienced by the battery pack is around 12 °C when the thermal management is provided by the hydrogen desorption in metal hydrides, against a value above 30 °C obtained for the same case without thermal management. Moreover, the hybrid energy storage system provides the 16% of the total mass of hydrogen requested by the fuel cell stack during operation, which corresponds to a significant enhancement of the hydrogen storage capability on-board of the vehicle.     

Research on the heat dissipation performance of lithium‐ion cell with different operating conditions

This paper aims to research the thermal power of lithium‐ion cell with different operating conditions. A 55‐Ah lithium‐ion cell is selected as the research object. Experiment and simulation are chosen as the methods to research the temperature distribution and thermal power of the cell under different conditions. Combining with the thermal power of cells, this paper also researches the heat dissipation performance of battery pack under different operation conditions. The results indicated that average thermal power of a 55‐Ah lithium‐ion cell decreases along with the increase of ambient temperature and the decrease of state of charge and charge and discharge rates. The results achieved through simulation and experiment are consistent, so simulation could be used to research the temperature distribution of cell during charge and discharge. As considering the longitudinal battery pack with steady analysis, high temperature area is in the centre, and the temperature of air inlet is relatively low. The airflow mostly passes the top of battery pack but not through both sides. As considering the longitudinal battery pack with transient analysis, the temperature rise of battery pack is evidently higher than the inner temperature difference by studying three operating conditions (sustained deceleration, sustained acceleration and pulsed discharge). The curves of temperature rise and inner temperature difference rise along with sustained acceleration of the electric vehicle; therefore, even if the electric vehicle begins to decelerate, the fan must still work until the temperature of battery pack decreases. Then, the references are given for researching thermal characteristic during charge and discharge of the cell and the heat dissipation analysis of battery pack. Copyright © 2017 John Wiley & Sons, Ltd.     

Research on optimal operation control based on the equivalent model of VRFB system

全钒电池的建模和运行参数是影响电池性能的重要因素,现有的等效电路模型往往由于缺乏和流体力学模型的耦合,无法研究流量对全钒液流电池性能和效率的影响,因而在实际项目应用中不够完善;另外纯粹的流体力学模型对于电池本身的电气特性过于简化,无法充分反映全钒液流电池系统的特性。因此本文利用钒电池基本原理和等效损耗建立了等效电路模型,根据机械损耗和钒电池结构参数,建立钒电池流体力学模型,根据搭建的钒电池系统等效模型分析电池运行参数对电池性能的影响规律。仿真分析表明,充放电期间的最优流量是关于荷电状态的函数,根据该现象利用流量随着荷电状态SOC的变化进行分段控制。通过仿真分析,根据SOC变化而分段控制流量的优化运行策略可以有效地提高钒电池效率。     

Air cooling strategy of power battery based on minimum energy consumption

针对目前电动汽车动力电池风冷散热能耗高、散热滞后的问题,提出一种基于最小能耗的动力电池风冷控制策略,根据车载导航系统预报的工况信息预测动力电池的未来温升,在满足动力电池散热需求的前提下以风机能耗最少为目标,运用分段式动态规划算法确定风机在未来路段的开启时机与最优风速。以添加了坡度信息的ARB02、HWFET和UDDSHDV的组合工况为测试工况,对动力电池未来温升的精度进行了硬件在环试验,得出实际路况试验温度与预报工况试验温度的最大差值为0.3℃,最大偏差率为0.7%。与其他两种控制策略进行了Fluent仿真对比,结果表明基于最小能耗控制策略下动力电池的最高温度为39.87℃,最大温差为1.1℃;风机能耗是全程开启型控制策略的77.2%,是温度开关型控制策略的53.7%。该策略能有效控制动力电池的温度且风机能耗最小。     

光伏系统中蓄电池充电过程的建模与仿真

蓄电池的充放电管理一直是其控制器的关键.为提高光伏系统中蓄电池的充电效率,延长蓄电池使用寿命,采用脉宽调制的三段式充电策略(快速充电、脉冲式恒压充电及浮充电),利用MATLAB/Simulink软件平台对整个系统进行建模并仿真,为光伏系统中蓄电池的充放电管理提供了参考与依据.仿真结果验证了系统仿真模型的可用性和通用价值以及蓄电池控制策略的可行性和合理性,并表明在此蓄电池管理策略下可提高蓄电池充电效率,延长其使用寿命.     

A review of novel thermal management systems for batteries

In the recent years, significant developments in the electric batteries have made them one of the most promising storage technologies for electrical energy. Among the various rechargeable batteries that are developed, lithium ion batteries stand out due to their capability of storing more energy per unit mass, low discharge rate, low weight, and lack of a memory effect. The advantages that batteries offer have promoted the development of the electric and hybrid electric vehicles. However, during charging and discharging processes, batteries generate heat. If this heat is not removed quickly, the battery temperature will rise, resulting in safety concerns and performance degradation. Thermal management systems are developed to maintain the temperature of the battery within the optimum operation range. This review paper focuses on novel battery thermal management systems (BTMSs). Air, liquid, phase change material, and pool‐based BTMSs are considered. Air‐based thermal management systems are discussed first. Liquid cooling systems and phase change‐based systems are discussed subsequently, and then the recently proposed evaporating pool‐based thermal management system is considered.     

Active cell balancing of lithium-ion battery pack based on average state of charge

Differences in the environment and parameters of lithium-ion battery (LiB) cells may lead the residual capacity between the battery cells to be inconsistent, and the battery cells may be damaged due to overcharging or overdischarging. In this study, an active balancing method for charging and discharging of LiB pack based on average state of charge (SOC) is proposed. Two different active balancing strategies are developed according to the different charging and discharging states of LiB pack. When the LiB pack is charging, charging balance strategy is performed, wherein the battery cells whose SOC is higher than the average SOC of the LiB pack are balanced to increase the charging capacity of the entire LiB pack. When the LiB pack is discharging or static standing, discharging balance strategy is performed, wherein the batter cells whose SOC is lower than the average SOC of the LiB pack are balanced to increase the discharging capacity of the entire LiB pack. The experimental results show that the proposed active balancing method can reduce the inconsistency of residual energy between the battery cells and improve the charging and discharging capacity of the LiB pack.     

Research and characterization of pulse charging strategy for lithium-ion traction battery

动力电池充电策略对提高电动汽车性能和使用寿命起着至关重要的作用。针对一种三元材料体系18650圆柱形电池进行脉冲充电策略研究,将其与标准恒流恒压充电策略进行综合比对,全面客观地分析脉冲充电策略关键参数对动力电池电性能的影响,并系统地评估了脉冲充电策略对电池寿命的影响。在循环寿命研究方面,采用电化学交流阻抗欧谱（EIS）分析不同循环周数和SOC下的交流阻抗,采用X射线断层扫描（CT）无损分析技术对循环500周后电池结构进行表征分析,揭示了带负脉冲充电策略对电池循环性能和结构影响的关系。