Active Balancing System Research Articles

Hierarchical Structure-Based Wireless Active Balancing System for Power Batteries

Hierarchical Structure-Based Wireless Active Balancing System for Power Batteries

Active balancing system in battery management system for Lithium-ion battery

The existing battery management systems perform many functions, such as simply monitoring the battery's voltage, current, and temperature for the most basic and compensating energy imbalances between battery cells for the most advanced systems. In this last example, the function balancing helps protect the battery from obtaining a better lifespan. However, these systems with such functions remain complex because they involve techniques specific to power electronics and energy conversion. The number of components, implementation complexity, and cost increased. The work presented in this paper fits directly into this context. The main objective is to provide a solution to the problem of battery management and careful pack cell balancing. The proposed system aims to balance the battery pack cells based on the intermediate state of charge by charging or discharging the imbalanced cell. The implementation of the proposed control strategy was for a battery pack composed of five cells under MATLAB/Simulink.

Balancing resistor-based online electrochemical impedance spectroscopy in battery systems: opportunities and limitations

Active dissipative balancing systems are essential in battery systems, particularly for compensating the leakage current differences in battery cells. This study focuses on using balancing resistors to stimulate battery cells for impedance measurement. The value of impedance spectroscopy for in-depth battery cell diagnostics, such as temperature or aging, is currently being demonstrated and recognized by vehicle manufacturers, chip producers, and academia. Our research systematically explores the feasibility of using existing balancing resistors in battery management systems and identifies potential limitations. Here we propose a formula to minimize hardware requirements through signal processing techniques. A quadrupling of the sampling rate, number of averaging values, or the size of the fast Fourier transform is equivalent, concerning the signal-to-noise ratio, to increasing the analog resolution by one bit or reducing the input filter bandwidth by a quarter.

A novel methodology to study and compare active energy-balance architectures with dynamic equalization for second-life battery applications

The continuous growth of the electric vehicles market and the increasing environmental awareness impose to search for innovative solutions to reuse the exhausted vehicle batteries in different applications. One of the main problems of second-life batteries is the very high mismatch among their cell capacities which reduces the overall battery performance. The mismatch effect can be overcome by using dynamic equalization. This technique aims to keep balanced as much as possible the State of Charge of the cells during the battery operation, i.e. in both the charge and discharge phases. In order to do this, the dynamic equalization approach requires a high-current active energy balancing system able to move a quantity of charge among the battery cells much higher than the active balancing circuits sometimes used in first-life batteries. The use of a high equalization current increases the design complexity of the balance system.A methodology to study and compare the main balance system topologies suitable for second-life batteries with dynamic equalization approach is presented in this work. The Adjacent Cell-to-Cell, Direct Cell-to-Cell, Cell-to-Pack, and Pack-to-Cell active balance topologies are analyzed considering the case study of a second-life battery composed of 10 series-connected cells with capacity values uniformly distributed around±15% of the nominal value.The investigation proves that the Direct Cell-to-Cell topology has the best performance. This balancing topology improves the usable battery capacity of around 16% with respect to the case in which no dynamic equalization is applied if a DC/DC converter with a power efficiency of only 70% is used. Finally, the results show that the Adjacent Cell-to-Cell performance is strongly affected by the position of the cell mismatches in the battery.

Comparative Analysis and Evaluation of the Different Active Cell Balancing Topologies in Lithium Ions Batteries

Series connected batteries must have their cells balanced whenever charging and discharging to extend battery lifespans, assure safe operation, and increase battery pack useful capacity. It also causes charge imbalance issues, which will result in battery cell damage and battery life loss. Several charge/discharge equalization circuits have been suggested however, presently there has been no work regarding the comparison and evaluation of the speed and efficiencies in both modes. In this study, cell balancing on dc-to-dc buck-boost converter and interleaved flyback converter topologies operating in discontinuous current mode are analyzed, designed, and implemented. A simulation model of the converter-based topologies of an active cell balancing system is proposed and designed along with a power loss analysis, efficiencies, and control technique. With the purpose of establishing an energy storage application, the system’s cells are grouped into 8 series cells for SOC balancing and 2 series cells for voltage balancing circuit design. Power loss analysis is performed to analyze the efficiency of these two converter topologies to identify which system performs better. In SOC balancing in charging mode, the buck-boost and interleaved flyback converters’ power efficiencies are 85.596% and 65.1521% respectively and during voltage balancing 93.9078% and 73.1506% respectively.

Design of an Active Balancing System for Rotating Orbital Devices

This paper presents the design of an active balancing system for rotating orbital devices, motivated by recent space applications for spacecraft endowed with rotating payloads. The main motivation behind this work is the Copernicus Imaging Microwave Radiometry mission, which will feature a large rotating microwave radiometer to provide observations of sea-surface temperature, sea-ice concentration, and sea-surface salinity. Due to the presence of highly uncertain inertial asymmetries in the rotating device, potentially large internal forces and torques can appear at interface between the spacecraft and the rotor, which can cause a significant degradation of the system performance and can even affect its stability. To counteract such unbalance effects, an active balancing system made of a suitable set of actuated movable masses and sensors is developed in this work. Exploiting the time-periodic nature of the underlying dynamics, a harmonic controller has been designed to command the positions of the actuated masses in such a way that the effects of rotor unbalance are significantly reduced. After extensive numerical simulations, accounting for both parametric uncertainties and exogenous disturbances in the model, a dedicated breadboard has been developed and experimental validation of the control law has been carried out.

Aging Determination of Series-Connected Lithium-Ion Cells Independent of Module Design

In this work, a battery consisting of eight commercial NMC/graphite cells connected in series was cycled to 60% of its initial capacity. During the test, special care was taken to ensure that the results were not influenced by either the module assembly or the module design. For this purpose, the cells were virtually connected in a laboratory environment with the help of the test device as if they were operated together in a battery. Extrinsic influences that affect cell aging were thus reduced to a minimum. Differential Voltage Analysis (DVA), Electrochemical Impedance Spectrum (EIS), and relaxation measurements were performed to analyze the aging behavior of each cell. The results show that despite a theoretically perfect module design, Cell-to-Cell Variations (CtCV) occurred during aging. The shifting Depth of Discharge (DoD) values among the cells further amplify CtCV. Lithium plating was also observed in the faster aging cells after cyclic aging, suggesting that this aging effect contributes significantly to the development of CtCV. After the aging test, the battery was equipped with an active balancing system that maximizes capacity utilization. More important, the balancing charges which are calculated iteratively within the used balancing algorithm show a strong correlation to the pure capacity losses and thus provide a new way to determine the capacity values of each cell individually without disassembling the battery.

Modeling and Attitude Control of Spacecraft With an Unbalanced Rotating Device

This letter addresses the problem of controlling the attitude of spacecraft endowed with a rotating device, motivated by recent space applications which will make use of large rotating payloads. Due to the presence of uncertain and potentially large inertial asymmetries in the rotating device, an internal force and a torque can appear at interface between the spacecraft and the rotor, causing performance degradation and even affecting the system stability. To counteract such unbalance effects, active balancing systems, using movable masses mounted on the rotating device, are being considered in the literature. During the balancing phase, it is important for the attitude control system to maintain a stable configuration. After deriving a suitable control-oriented model of the multi-body spacecraft, we propose using a coordinate-free attitude controller that ensures safe balancing operations and desirable pointing performance.

A novel charging and active balancing system based on wireless power transfer for Lithium-ion battery pack

Lithium-ion batteries are widely used in applications that require tightness, such as underwater unmanned vehicles and mine-searching robots. The traditional wired charging and balancing for battery pack is not suitable for the required tightness and safety of battery pack. Therefore, this paper proposes a novel charging and active balancing system based on wireless power transfer (WPT) for lithium-ion battery packs. This system only uses a set of energy-transmitting and energy-receiving coils, to wirelessly transfer the energy required for both battery pack charging and single battery balancing. The charging and balancing power is adjusted according to the voltage level of the primary side of the DC/DC converter. The switching matrix functions acts as a switch to connect either the battery pack or any single battery in the pack to be balanced. In addition, a multiobjective optimal balancing strategy based on a genetic algorithm (GA) is proposed to optimize the pack available capacity and the balancing time of the pack. The experimental results show that the proposed system achieves the dual functions of wireless pack charging and wireless battery balancing. In addition, compared with the traditional state of charge (SOC) consistency balancing strategy, the proposed balancing strategy simultaneously increases the pack available capacity by 7.9 %, and the pack maximum difference in SOC is only 2.19 %.

Automatic active balancing of rotating systems using real-time controlled magnetorheological fluids

A major source of vibration in rotating systems is dynamic excitations due to an unbalanced mass. While the principle of balancing rotors is already state of the art, systems varying the mass distribution during operation are rare. A promising approach for balancing is the targeted displacement of magnetic fluids controlled by magnetic fields, which is the subject of this work. Until today only a few concepts have been developed that use magnetic fluids manipulated by a magnetic field for balancing. While achieving satisfying results in balancing, the proposed systems are rather complex for example due to the use of slip rings, and depend on continuous feeding of electric energy to maintain the balanced state. In this contribution an advantageous design is presented to reduce cost and complexity of active real-time balancing systems. The proposed design requires only one stationary coil to selectively move the magnetic fluid in situ and to achieve the state of mass balance. With the support of a model-based approach and multiphysics simulations, the system behavior is analyzed, optimized and finally validated by experimental investigations.

Adaptive Balancing Control of Cell Voltage in the Charging/Discharging Mode for Battery Energy Storage Systems

To improve the balancing time of battery energy storage systems with “cells decoupled and converters serial-connected,” a new cell voltage adaptive balancing control method in both charging and discharging modes is proposed in this study. The overall system architecture and basic operating principle of the active balancing system with “cells decoupled and converters serial-connected” are presented first. Then, by dynamically regulating the balancing acceleration coefficient of each cell according to the cell voltage deviation, the adaptive balancing control of cell voltage in charging and discharging modes is analyzed. An experimental prototype consisting of six smart cells is developed, and experiments in charging and discharging modes were carried out. The experiment results demonstrate that compared with the balancing process with a static acceleration coefficient, the proposed adaptive balancing control of cell voltage shows significant improvement in balancing speed and smaller cell voltage discrepancy.

A remaining charging electric quantity based pack available capacity optimization method considering aging inconsistency

Regarding battery packs in electric vehicles (EVs), the variations in the electric quantity and capacity of a pack due to aging inevitably affects its available capacity and performance. Thus, it is necessary to optimize the available capacity of the battery pack. Focusing on this problem, this paper proposes a novel concept of the remaining charging electric quantity (RCQ) to describe the battery state while considering aging. Then, a dual adaptive dual extended Kalman filter (Dual-ADEKF) algorithm is utilized to identify the model parameters and RCQ of each cell under working conditions. Furthermore, the actual RCQ of the battery pack after constant current charging is predicted while considering the aging caused capacity degradation and the increase in the DC internal resistance. To maximize the available capacity, a bidirectional active balancing system is used to adjust the electric quantity distribution in the pack to ensure that the RCQ of each cell is consistent; the available capacity of the pack is then determined by the battery with the lowest actual RCQ. The results show that the available capacity estimation of aged batteries while considering the influence of capacity degeneration and the DC internal resistance is effectively achieved. To test a battery pack with an initial capacity and an electric quantity inconsistency caused by aging, a federal urban driving schedule (FUDS) test is performed. The electric quantity to be balanced of each cell is calculated according to the RCQ estimation results with the target of maximizing the available capacity of the pack. It is verified that the available capacity of the pack increases by 11.7% compared to that before equalization, while the maximum electric quantity variation between cells is improved, decreasing from 20% to 2.6%. • A novel concept of remaining charging electric quantity(RCQ) to describe the battery aging state is proposed. • Battery internal resistance increase and capacity loss caused by aging are the major factors of RCQ degradation. • Model parameters and RCQ for aged batteries in pack are identified online using a Dual-ADEKF algorithm. • Actual RCQ consistency can ensure the maximum pack available capacity for aged battery pack.

Performance of Passive and Active Balancing Systems of Lithium Batteries in Onerous Mine Environment

To use lithium-iron-phosphate battery packs in the supply systems of any electric mining equipment and/or machines, the required conditions of work safety must be met. This applies in particular to coal mines endangered by fire and/or explosion. To meet the spark-safety conditions, the cells (together with the battery management system—BMS) must be isolated from the influence of the environment, and therefore placed in special fire-tight housings. This significantly degrades the heat dissipation, thus affecting the operating conditions of the cell-packs. Therefore, their usage without the so-called BMS is not recommended, as shown in the authors’ preliminary research. In practice, various BMS are used, most often with the so-called passive balancing. However, their application in mines is uncertain, due to the effect of heating under operation. When it comes to active BMS, they usually possess a quite complex structure and hence, are relatively expensive. Therefore, the authors conducted research for two specially developed active and one commercial passive BMS cooperating with selected lithium-iron-phosphate (LiFePO4) batteries when used in a suspended mining vehicle type PCA-1. The tests were carried out under environmental temperatures ranging from +5 °C to +60 °C. The effect of mismatching (12.5% to 37.5% of total cells number) of the cell parameters on the temperature distribution and voltage fading at the terminals of individual cells was checked. As a result of the investigations, the practical usefulness of the developed active BMS was determined, enabling the extension of the lithium-iron-phosphate battery life under onerous mine conditions, for a single recharge, which is a novelty. On the basis of the obtained results, appropriate practical conclusions were formulated.

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 <em>n</em>+5 for <em>n</em> batteries. A 15S1P 200 Ah LiFePO<sub>4</sub> 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.

Evaluation and Comparative Study of Cell Balancing Methods for Lithium-Ion Batteries Used in Electric Vehicles

Vehicle manufacturers positioned electric vehicles (EVs) and hybrid electric vehicles (HEVs) as reliable, safe and environmental friendly alternative to traditional fuel based vehicles. Charging EVs using renewable energy resources reduce greenhouse emissions. The Lithium-ion (Li-ion) batteries used in EVs are susceptible to failure due to voltage imbalance when connected to form a pack. Hence, it requires a proper balancing system categorised into passive and active systems based on the working principle. It is the prerogative of a battery management system (BMS) designer to choose an appropriate system depending on the application. This study compares and evaluates passive balancing system against widely used inductor based active balancing system in order to select an appropriate balancing scheme addressing battery efficiency and balancing speed for E-vehicle segment (E-bike, E-car and E-truck). The balancing systems are implemented using “top-balancing” algorithm which balance the cells voltages near the end of charge for better accuracy and effective balancing. The most important characteristics of the balancing systems such as degree of imbalance, power loss and temperature variation are determined by their influence on battery performance and cost. To enhance the battery life, Matlab-Simscape simulation-based analysis is performed in order to fine tune the cell balancing system for the optimal usage of the battery pack. For the simulation requirements, the battery model parameters are obtained using least-square fitting algorithm on the data obtained through electro chemical impedance spectroscopy (EIS) test. The achieved balancing time of the passive and active cell balancer for fourteen cells were 48 and 20 min for the voltage deviation of 30 mV. Also, the recorded balancing time was 215 and 42 min for the voltage deviation of 200 mV.

Evaluation and Comparative Study of Cell Balancing Methods for Lithium-Ion Batteries Used in Electric Vehicles

Vehicle manufacturers positioned electric vehicles (EVs) and hybrid electric vehicles (HEVs) as reliable, safe and environmental friendly alternative to traditional fuel based vehicles. Charging EVs using renewable energy resources reduce greenhouse emissions. The Lithium-ion (Li-ion) batteries used in EVs are susceptible to failure due to voltage imbalance when connected to form a pack. Hence, it requires a proper balancing system categorised into passive and active systems based on the working principle. It is the prerogative of a battery management system (BMS) designer to choose an appropriate system depending on the application. This study compares and evaluates passive balancing system against widely used inductor based active balancing system in order to select an appropriate balancing scheme addressing battery efficiency and balancing speed for E-vehicle segment (E-bike, E-car and E-truck). The balancing systems are implemented using “top-balancing” algorithm which balance the cells voltages near the end of charge for better accuracy and effective balancing. The most important characteristics of the balancing systems such as degree of imbalance, power loss and temperature variation are determined by their influence on battery performance and cost. To enhance the battery life, Matlab-Simscape simulation-based analysis is performed in order to fine tune the cell balancing system for the optimal usage of the battery pack. For the simulation requirements, the battery model parameters are obtained using least-square fitting algorithm on the data obtained through electro chemical impedance spectroscopy (EIS) test. The achieved balancing time of the passive and active cell balancer for fourteen cells were 48 and 20 min for the voltage deviation of 30 mV. Also, the recorded balancing time was 215 and 42 min for the voltage deviation of 200 mV.

A Consensus Algorithm for Multi-Objective Battery Balancing

Batteries stacks are made of cells in certain series-parallel arrangements. Unfortunately, cell performance degrades over time in terms of capacity, internal resistance, or self-discharge rate. In addition, degradation rates are heterogeneous, leading to cell-to-cell variations. Balancing systems can be used to equalize those differences. Dissipative or non-dissipative systems, so-called passive or active balancing, can be used to equalize either voltage at end-of-charge, or state-of-charge (SOC) at all times. While passive balancing is broadly adopted by industry, active balancing has been mostly studied in academia. Beyond that, an emerging research field is multi-functional balancing, i.e., active balancing systems that pursue additional goals on top of SOC equalization, such as equalization of temperature, power capability, degradation rates, or losses minimization. Regardless of their functionality, balancing circuits are based either on centralized or decentralized control systems. Centralized control entails difficult expandability and single point of failure issues, while decentralized control has severe controllability limitations. As a shift in this paradigm, here we present for the first time a distributed multi-objective control algorithm, based on a multi-agent consensus algorithm. We implement and validate the control in simulations, considering an electro-thermal lithium-ion battery model and an electric vehicle model parameterized with experimental data. Our results show that our novel multi-functional balancing can enhance the performance of batteries with substantial cell-to-cell differences under the most demanding operating conditions, i.e., aggressive driving and DC fast charging (2C). Driving times are extended (>10%), charging times are reduced (>20%), maximum cell temperatures are decreased (>10 °C), temperature differences are lowered (~3 °C rms), and the occurrence of low voltage violations during driving is reduced (>5×), minimizing the need for power derating and enhancing the user experience. The algorithm is effective, scalable, flexible, and requires low implementation and tuning effort, resulting in an ideal candidate for industry adoption.

Optimal control of bidirectional active clamp forward converter with synchronous rectifier based cell-to-external-storage active balancing system

Active cell balancing is a more energy-efficient way of balancing cells in series comparing to passive balancing. To further improve the performance of an active balancing system, an optimal control approach can be applied to optimise the system performance indexes. This paper proposes an optimal controller for the bidirectional active clamp forward converter with synchronous rectifier (ACFC-SR) based cell-to-external-storage active balancing system to concurrently optimise the balancing speed and the energy efficiency. The formulated optimization problem does not require the complicated nonlinear converter efficiency model compared to other optimal controllers that involve efficiency model to reduce energy loss. The flexibility in changing the balancing priority of the balancing time and the converter efficiency is achieved via different weights on the objective function. The effectiveness of the proposed controller is validated experimentally with real cells and the power electronics board.

Design and Performance Analysis of Active and Passive Cell Balancing for Lithium-Ion Batteries

Electric Vehicles (EV) are growing areas of research since the demand for clean transportation is ever-increasing. Batteries form an integral part of EVs. Battery Management systems (BMS) need to support many features, including charge balancing to improve battery life and longevity. Among passive cell balancing and active cell balancing, the latter provides better battery life and efficiency. Among different active and passive cell balancing techniques, popular techniques like Flyback transformer-based active cell balancing and switched capacitor-based active cell balancing are used. These methods are not only easy to implement but also provide good performance. These balancing circuits are integrated with non-ideal RC models of a lithium-ion battery. The bleed resistor-based passive cell balancing took more than 16000 seconds to reach a 0.01V difference for capacitors with 5F capacitance, whereas the switched capacitor design is estimated to take 500 seconds. The multi-winding flyback active cell balancing system reached a 2% difference in SOC in 1800 seconds. There was a visible increase in time taken for balancing the cells using multi-winding active cell balancing as the cell temperature increased. A 2.32% increase in the time taken for balancing the cells was observed when cell temperature increased from 293K to 313K.

ANALYSIS OF BATTERIES ACTIVE BALANCE SCHEMES EFFICIENCY

The paper reviews the existing circuit solutions of devices for balancing electric batteries. The balancing principle on the basis of capacitive and inductive buffer elements has been described. It was shown the features of their work and the basic calculations for each device type. For circuits with transformer topology, the calculated values for determining the balancing current are indicated. Based on the circuit solutions analysis, the efficiency of using solutions based on inductive buffer elements is numerically determined and proved. Powerful batteries for power supply systems are used in the form of stacks, consisting of a series-parallel connection of single cells. During their operation, there is a problem of uneven discharge or charge, to compensate which it is necessary to make voltage levels balancing in the stack batteries. For safely using electrochemical batteries the using of specialized balancing devices is required. The most efficient, from an energy point of view, are active balancing systems. The analysis of the mathematical model of two types (capacitive and inductive) buffer elements operation allowed to give a qualitative assessment of their efficiency. The first, in comparison with inductive - not only have worse energy characteristics, but also do not allow to perform "scaling" of the device without significant complication of the control system. The current amplitude value in circuits with a capacitive buffer element is limited only by the internal parasitic resistances of the circuit elements, therefore, with a relatively large value of imbalance, in circuit elements (including batteries) takes place a significant energy loss in the form of heat which negatively effects on rechargeable battery parameters. The current amplitude value in the circuit based on inductive buffer elements is limited by the inductance value. It can be calculated at the device design stage. In addition, providing the control system with intermittent converter operation allows to reduce switching losses in the circuit power switches and increases the overall operation efficiency. With a large number of batteries (more than three) should be preferred transformer balancing systems, as a special case of inductive topology.