Connected Battery Cells Research Articles

A Two-Stage Module Based Cell-to-Cell Active Balancing Circuit for Series Connected Lithium-Ion Battery Packs

This paper addresses a two-stage module based cell-to-cell active equalization topology based on a modified buck-boost converter for series connected Lithium-ion battery packs. In the proposed topology, initially module based equalizing currents are controlled. Subsequently, cell-based equalizers are controlled in parallel within each battery module. The proposed topology significantly reduces the balancing time by transferring higher balancing current from a strong cell to the weakest cell in a module directly. With the proposed topology's modularized design, reduces voltage stress on long strings of switches, resulting in improved performance with fewer components. The operating principle, control strategy and design constraints are analyzed in detail. The MATLAB/Simulink platform is utilized to demonstrate the feasibility of the proposed technique for balancing the energy in series connected battery cells. To reduce the complexity of the control approach, the digital control is implemented using an FPGA control board. Further, a laboratory prototype is developed to show the feasibility and operability of the proposed topology.

A Novel Electric Vehicle Battery Management System Using an Artificial Neural Network-Based Adaptive Droop Control Theory

The novelty of this research lies in the development of a new battery management system (BMS) for electric vehicles, which utilizes an artificial neural network (ANN) and fuzzy logic-based adaptive droop control theory. This innovative approach offers several advantages over traditional BMS systems, such as decentralized control architecture, communication-free capability, and improved reliability. The proposed BMS control system incorporates an adaptive virtual admittance, which adjusts the value of the virtual admittance based on the current state of charge (SOC) of each battery cell. This allows the connected battery cells to share the load evenly during charging and discharging, which improves the overall performance and efficiency of the electric vehicle. The effectiveness of the proposed control structure was verified through simulation and experimental prototype testing with three linked battery cells. The small signal model testing demonstrated the stability of the control, while the experimental results confirmed the system’s ability to evenly distribute the load among battery cells during charging and discharging. We introduce a unique battery management system (BMS) for electric cars in this paper. Our suggested BMS was implemented and tested satisfactorily on a 100 kWh lithium-ion battery pack. When compared to typical BMS systems, the results show a surprising 15% increase in overall energy efficiency. Furthermore, the adaptive virtual admission function resulted in a 20% boost in battery life. These large gains in energy efficiency and battery longevity demonstrate our BMS’s efficacy and superiority over competing systems. Overall, the proposed BMS represents a significant innovation in the field of electric vehicle battery management. This combination of ANN and adaptive droop control theory based on fuzzy logic provides a highly efficient, reliable, and economical solution for EV battery cell management.

A Switch-Reduced Multicell-to-Multicell Battery Equalizer Based on Full-Bridge Bipolar-Resonant LC Converter

Many battery equalizers have been proposed to achieve voltage consistency between series connected battery cells. Among them, the multicell-to-multicell (MC2MC) equalizers, which can directly transfer energy from consecutive more-charged cells to less-charged cells, can enable fast balancing and a high efficiency. However, due to the limitations of the equalizers, it is not possible to achieve fast equalization and reduce the size of the circuit at the same time. Therefore, a MC2MC equalizer based on a full-bridge bipolar-resonant LC Converter (FBBRLCC) is proposed in this paper, which not only implements MC2MC equalization, but also greatly reduces the circuit size by reducing the number of switches by nearly half. A mathematical model and simulation comparison with conventional equalizers are used to illustrate the high-speed equalization performance of the proposed equalizer and excellent balancing efficiency. An experimental prototype for eight cells is built to verify the performance of the proposed FBBRLCC equalizer and the balancing efficiencies in different operating modes are from 85.19% to 88.77% with the average power from 1.888 W to 14.227 W.

An Enhanced Multicell-to-Multicell Battery Equalizer Based on Bipolar-Resonant LC Converter

In a battery management system (BMS), battery equalizer is used to achieve voltage consistency between series connected battery cells. Recently, serious inconsistency has been founded to exist in retired batteries, and traditional equalizers are slow or inefficient to handle the situation. The multicell-to-multicell (MC2MC) topology, which can directly transfer energy from consecutive strong cells to consecutive weak cells, is promising to solve the problem, but its performance is limited by the existing converter. Therefore, this paper proposes an enhanced MC2MC equalizer based on a novel bipolar-resonant LC converter (BRLCC), which supports flexible and efficient operation modes with stable balancing power, can greatly improve the balancing speed without much sacrificing the efficiency. Mathematical analysis and comparison with typical equalizers are provided to illustrate its high balancing speed and good efficiency. An experimental prototype for 8 cells is built, and the balancing powers under different operation modes are from 1.426 W to 12.559 W with balancing efficiencies from 84.84% to 91.68%.

A novel power state evaluation method for the lithium battery packs based on the improved external measurable parameter coupling model

Abstract The power state evaluation plays a decisive influence on the safety implication of the lithium battery packs, and there is no effective online evaluation method so far due to the imbalance phenomenon among the internal connected battery cells, which cannot be abstained by the advancement of the materials and techniques. A novel power state mathematical evaluation method is proposed in this paper by investigating the improved external parameter coupling treatment, in which the mutual relationship description is conducted by the parameter information feature decomposition together with the Bayesian sequential decision algorithm. The complicated power state evaluation model with the coupling relationship decomposition is constructed by investigating the non-convex optimization treatment under complex working conditions for the lithium battery packs. The evidence combination is realized by introducing the information fusion strategy, according to which the multi criteria decision is realized by using the evidence theory. As can be seen from the experimental results, the voltage difference is within 10 mV in both of the first and the second phases, which increases rapidly in the third phase and reaches a maximum of 120 mV. Meanwhile, its power state evaluation accuracy is 95.00% and has a good output voltage tracking effect in the complex working conditions. The power state evaluation can be realized effectively by the proposed model constructing method, which is suitable for the complex battery cell combination structures and environmental influences, protecting the reliable and hierarchical working state monitoring and management of the lithium battery packs. It provides safety protection and energy management basis for the reliable power supply in the cleaner production of the power lithium battery packs.

A Novel Battery Management System Using the Duality of the Adaptive Droop Control Theory

This paper proposes a new battery management system (BMS) for a series string of battery cells. The proposed control structure is based on the duality of the adaptive droop control theory used in dc micro-grid connected sources. An adaptive virtual admittance is used in this paper similar to the virtual resistance control structure used with dc micro-grid connected sources. The virtual admittance value is adjusted according to the associated state of charge for every connected battery cell. The presented BMS control structure yields higher reliability compared to the conventional ones due to its decentralization features and its communication-less ability. Thus, balanced power-sharing is realized among the connected battery cells during charging/discharging conditions. The stability of the proposed control is analyzed using the small signal model. The proposed BMS control structure is validated using simulation results and an experimental prototype for three connected battery cells.

Control and Analysis of a Modular Bridge for Battery Cell Voltage Balancing

A new distributed control scheme and charge flow analysis is presented for voltage balancing of series connected battery cells using nondissipative modular power electronics. Each modular bridge is connected across two battery cells using a high frequency transformer and an asymmetrical half-bridge. This results in using one switch and one diode per battery cell. Intrabridge charge transfer equalizes the voltage of two battery cells within a module using coupled transformer windings. Each modular bridge is connected to adjacent bridges by connecting transformer windings within each module. This allows interbridge charge transfer and the balancing of pairs of battery cells, both within adjacent bridge modules and modules more removed. The proposed controller uses a distributed control strategy whereby the control of each modular bridge monitors its own battery cell voltages and also those of adjacent bridges, thus reducing the number of feedback sensors. Detailed analysis is presented that quantifies the flow of charge between a number of series connected battery cells ( $ N$ battery cells). A per-unit design methodology is used to illustrate the system charge flow characteristics. Simulations, design guidelines and experimental results are presented to validate the proposed method.

A novel safety anticipation estimation method for the aerial lithium-ion battery pack based on the real-time detection and filtering

Abstract Lithium-ion battery packs have become increasingly important for power supply applications, in which the state of charge estimation and output voltage tracking should be very critical for the safety protection. A novel real-time estimation method is proposed by using the improved extended Kalman filtering algorithm together with the two-order resistance and capacitance circuit network battery model, aiming to solve its security protection issues. Experimental results show that this method can track the voltage signals effectively along with the real-time state estimation in the discharging and charging maintenance operation processes. The battery cell voltage detection accuracy is found to be 1.00 mV and the pack voltage measurement error is less than 20.00 mV. Meanwhile, the state of charge value can be estimated with a great accuracy of 2.00%, in which the state of balance parameter is considered for the internal connected battery cells. The developed experimental associated battery management system can be used for the working state monitoring in the aerial power supply application of the lithium-ion battery pack.

Power optimisation of electric coaster

Sustainability is the capacity to endure and ensure that the advanced technology for electric vehicles (EVs) remain diverse and productive over time. The power optimisation of the battery pack has been maintained by enhancing the lifespan of the battery with keeping the battery temperature 35-40°C and cell's state-of-charge (SOC) balance with the variation 2-5%. A ZigBee wireless battery management system (WBMS) has been developed from this study to control the evaporative cooling battery thermal management system for the optimum range of battery temperature both in charging/adverse discharging. The WBMS allows the vehicle to utilise the maximum energy available from the battery for a given drive cycle whilst maintaining pack SOC balance within the range of optimal functionality. The WBMS multistage charge balancing system offering more effective and efficient responses to several numbers of series connected battery cells. The balancing results for two cells and 16 cells are improved by 15.12% and 25.3% respectively.

Wireless Battery Management System of Electric Transport

Electric vehicles (EVs) are being developed and considered as the future transportation to reduce emission of toxic gas, cost and weight. The battery pack is one of the main crucial parts of the electric vehicle. The power optimization of the battery pack has been maintained by developing a two phase evaporative thermal management system which operation has been controlled by using a wireless battery management system. A large number of individual cells in a battery pack have many wire terminations that are liable for safety failure. To reduce the wiring problem, a wireless battery management system based on ZigBee communication protocol and point-to-point wireless topology has been presented. Microcontrollers and wireless modules are employed to process the information from several sensors (voltage, temperature and SOC) and transmit to the display devices respectively. The WBMS multistage charge balancing system offering more effective and efficient responses for several numbers of series connected battery cells. The concept of double tier switched capacitor converter and resonant switched capacitor converter is used for reducing the charge balancing time of the cells. The balancing result for 2 cells and 16 cells are improved by 15.12% and 25.3% respectively. The balancing results are poised to become better when the battery cells are increased.

Active Balancing of Li-Ion Battery Cells Using Transformer as Energy Carrier

A circuit for balancing Li-ion battery cells is proposed. This circuit requires one small transformer and N + 3 bilateral switches to equalize the charging states of N serially connected battery cells. The transformer works as an energy carrier, and the switches select two unbalanced cells that require an energy transfer from one to the other cell. The circuit was tested for a 12-cell Li-ion battery under static, cyclic, and dynamic charging/discharging conditions. Under static condition, the power-transfer efficiency was measured as 80.4% at a balancing power of 0.78 W; two 4400-mA·h battery cells at a state of charge $(\text{SOC}) = 70$ and 80% were equalized after 78 min. The results of cyclic and dynamic charging/discharging conditions show that the circuit is appropriate for balancing the Li-ion battery cells for vehicles and energy storage systems.

Equalisation strategy for serially connected LiFePO 4 battery cells

Owing to different temperature gradients, charge/discharge rates, and coulomb efficiencies, various releasable capacities of each cell have significant impacts on a pack capacity. Therefore, the equalisation system is an essential part in a battery pack, especially for a high-power application such as electric vehicle. In this study, the authors first review several traditional equalisation strategies. Subsequently, a new equalisation strategy (ES) based on the real `state' of a battery is proposed. They further establish the destination state-of-charge versus open-circuit voltage (SOC-OCV) cluster which is the target of the ES. Moreover, not only each SOC in serially connected battery cells, but also the SOC error according to the destination SOC-OCV cluster can be estimated. To avoid over-equalisation, the SOC error caused by the dispersion of OCVs is taken into account during the calculation of equalisation SOCs. A battery pack with five lithium iron phosphate cells in series is employed to verify the method, and results show that the capacity of battery pack is increased by 11% with equalisation.

A New Modularized Balancing Circuit for Series Connected Battery cells

The series connected battery cells are mainly used in high voltage battery pack application. However parameter inequality of each battery cell makes battery voltage imbalance problem. In this paper, a new balancing circuit utilizing converter scheme for the series connected battery cells is proposed. Proposed circuit offers easy control and fast equalization time. Moreover the circuit can be used in a practical application because it has high modularity and can operate during the charging/discharging cycle. To show its superiorness and effectiveness, the principle of proposed circuit is explained with computer simulation and experiment is carried out using lithium-ion battery.

An Adaptive Backward Control Battery Equalization System for Serially Connected Lithium-ion Battery Packs

This paper presents an adaptive controller for a battery equalization system (BES) for serially connected Li-ion battery packs. The proposed equalization scheme consists of software and hardware parts to implement an adaptive neuro-fuzzy algorithm. The proposed combined software and hardware implementation of the adaptive neuro-fuzzy algorithm provides an offline learning ability to track the dynamic reactions on battery packs and a high-speed response for equalizing currents in the individual cell equalizers (ICEs). The output currents driving pulsewidth-modulated (PWM) signals are generated from the proposed hardware analog controllers. A feedback line is utilized to observe these output currents for the training process. The adaptive neuro-fuzzy algorithm is implemented in the main processor to provide adaptive parameters for the hardware. The proposed BES has an adaptability and tracking ability to deal with dynamic reactions of serially connected battery cells. The hardware controllers are implemented in a 0.13- μm CMOS technology with a supply voltage of 2.5 V. The results demonstrate that the proposed scheme has the ability to learn from previous stages and to provide a precise model of the battery cell voltages and currents. The proposed system achieved learning accuracy error of 1.8 × e -5 .

Charge balancing of serially connected lithium-ion battery cells in electric vehicles

Active charge balancing is a commonly used method to increase the usable energy of a battery stack with serially connected battery cells with different cell capacities. In this article an active charge balancing method with a multiple winding transformer DC/DC converter is described. The advantage of active charge balancing is shown using a prototype with twelve serially connected Lithium ion battery cells. Moreover, the influence of the cell capacity variance and the influence of the balancing current on the discharging energy is investigated.

A Current Equalization Method for Serially Connected Battery Cells Using a Single Power Converter for Each Cell

This paper presents a method to control the current of each battery cell in a serially connected battery stack according to each cell capacity. With this method, the performance of a battery stack can be increased significantly. In a second life concept, battery cells with different capacities and even battery cells with different chemistries can be connected together. Moreover, if one or more battery cells become inoperative, then the battery stack can still be used in the limp-home operation mode. The required power converter structure and the calculation of the individual cell currents are presented, and a simulation for two different power converters during discharging and charging is performed. A current equalization prototype is used to validate the simulation results and to show the performance on a real battery stack with 12 serially connected cells. Finally, the influence of the equalization currents and the capacity variance in the battery stack on the discharging energy are investigated.

A New Equalization Scheme for Series Connected Battery Cells

In this paper a new equalization scheme for series connected battery cells or monoblocks is presented which provides both charge and discharge equalization. The equalization scheme described in this paper provides support for the battery operation even with damaged cells, ensures a uniform battery cell voltage fall, thus protecting cells from reverse polarization, and maximizes the energy delivered by the battery (Fig. 2). An evaluation Battery Management System (BMS) was developed in the laboratory, utilizing the proposed equalization scheme, and the experimental results verify the theoretical ones.