Battery systems are affected by many factors, the most important one is the cells unbalancing. Without the balancing system, the individual cell voltages will differ over time, battery pack capacity will decrease quickly. That will result in the fail of the total battery system. Thus cell balancing acts an important role on the battery life preserving. Different cell balancing methodologies have been proposed for battery pack. This paper presents a review and comparisons between the different proposed balancing topologies for battery string based on MATLAB/Simulink® simulation. The comparison carried out according to circuit design, balancing simulation, practical implementations, application, balancing speed, complexity, cost, size, balancing system efficiency, voltage/current stress … etc.

/pdf/passive-and-active-battery-balancing-comparison-based-on-1m6gyrcy7n.pdf

Passive and active battery balancing comparison based on MATLAB simulation

In conventional equalizers, the facts of bulky size and high cost are widespread. Particularly, the zero-switching loss and zero-voltage gap (ZVG) between cells are difficult to implement due to the high-frequency hard switching and the voltage drop across power devices. To overcome these difficulties, a direct cell-to-cell battery equalizer based on quasi-resonant LC converter (QRLCC) and boost dc-dc converter (BDDC) is proposed. The QRLCC is employed to gain zero-current switching, leading to a reduction of power losses. The BDDC is employed to enhance the equalization voltage gap for large balancing current and ZVG between cells. Moreover, through controlling the duty cycle of the BDDC, the topology can online adaptively regulate the equalization current according to the voltage difference, which not only effectively prevents overequalization but also abridges the overall balancing time. Instead of a dedicated equalizer for each cell, only one balancing converter is employed and shared by all cells, reducing the size and implementation cost. Simulation and experimental results show the proposed scheme exhibits outstanding balancing performance, and the energy conversion efficiency is higher than 98%. The validity of the proposed equalizer is further verified by a quantitative and systematic comparison with the existing active balancing methods.

/pdf/a-cell-to-cell-battery-equalizer-with-zero-current-switching-3jgtj99ttg.pdf

A Cell-to-Cell Battery Equalizer With Zero-Current Switching and Zero-Voltage Gap Based on Quasi-Resonant LC Converter and Boost Converter

Battery packs with a large number of battery cells are becoming more and more widely adopted in electronic systems, such as robotics, renewable energy systems, energy storage in smart grids, and electronic vehicles. Therefore, a well-designed battery pack is essential for battery applications. In the literature, the majority of research in battery pack design focuses on battery management system, safety circuit, and cell-balancing strategies. Recently, the reconfigurable battery pack design has gained increasing attentions as a promising solution to solve the problems existing in the conventional battery packs and associated battery management systems, such as low energy efficiency, short pack lifespan, safety issues, and low reliability. One of the most prominent features of reconfigurable battery packs is that the battery cell topology can be dynamically reconfigured in the real-time fashion based on the current condition (in terms of the state of charge and the state of health) of battery cells. So far, there are several reconfigurable battery schemes having been proposed and validated in the literature, all sharing the advantage of cell topology reconfiguration that ensures balanced cell states during charging and discharging, meanwhile providing strong fault tolerance ability. This survey is undertaken with the intent of identifying the state-of-the-art technologies of reconfigurable battery as well as providing review on related technologies and insight on future research in this emerging area.

/pdf/reconfigurable-battery-techniques-and-systems-a-survey-2c61a524jo.pdf

Reconfigurable Battery Techniques and Systems: A Survey

The development of electric vehicle (EV) technologies, its applications, energy managements and storage systems are the most important sectors to the automotive industries on their environmental and global economic issues. The electrochemical batteries have a great market in EVs for their long-run and short-run energy storage profiles. Thus, to enhance the battery lifecycle and its performance over the charge and discharge periods, the perfect charge equalization of the long string battery pack is compulsory. The development of new charge equalization controller (CEC) and intensifying the features of existing CECs are now great deal in the field of high-tech storage systems towards the advancement of the sustainable EV technologies. This paper presents the EV technologies with their drive train architectures in different configurations and designs. A study on batteries regarding their formation, properties, energy management systems, advantages and disadvantages are also conducted in the review. A comprehensive review of the different type of CECs for EV applications is highlighted. From the rigorous review, it is concluded that a good equalization controller should have high equalization speed, high efficiency, small volume, simple wiring and execution, low cost and good extensibility. It is observed that the existing CECs have a good contribution to run the EV systems safely and efficiently with their balancing capabilities. However, they still have some problems to achieve all properties for efficient equalization towards the enhancement of battery performance and life. Consequently, a comparison on the salient feature characteristics among the CECs are explained on their topologies, types and execution times, difficulties in control, efficiencies, cost, components, merits and demerits to develop sustainable battery energy storage systems. All the highlighted insights of this review will hopefully lead to increasing efforts towards the development of the advanced CEC for the future high-tech battery energy storage systems in the vehicle applications.

Battery charge equalization controller in electric vehicle applications: A review

A series of switched-capacitor (SC) cell balancing circuits is proposed for rechargeable energy storage devices like battery and supercapacitor strings in this paper. Taking a basic SC-based cell balancing unit as an equivalent resistor, the behavioral models of the proposed cell balancing circuits are developed to evaluate their balancing performance. Comparing with existing SC-based cell balancing circuits, the main advantage of the proposed circuits is that their balancing speed is independent of both of the number of battery cells and initial mismatch distribution of cell voltages. In order to improve the operation performance of SC-based cell balancing circuits in the respect of minimizing the equivalent resistance, optimizing methodologies of circuit parameters are introduced by referring the concepts of slow switching limit and fast switching limit as well as inductive switching limit of SC power converters. Simulation and experimental results are provided to verify the feasibility of the proposed cell balancing circuits.

Topology, Modeling, and Design of Switched-Capacitor-Based Cell Balancing Systems and Their Balancing Exploration

Voltage balancing between series-connected cells of rechargeable lithium-ion batteries is important for battery life, autonomy, and safety. Active balancing is the designated choice for applications that are sensitive to energy losses and maximized autonomy. First, a well-known next-to-next balancing technique is presented and its design and operating limitations are analyzed. Then, the paper focuses on an evolution of the converter's architecture offering better performances while being more compact, requiring fewer and smaller filtering needs and still, being simple to implement. The experimental results of the balancing operation of a pack of eight cells connected in series show demonstrative and satisfactory results.

An Optimized Topology for Next-to-Next Balancing of Series-Connected Lithium-ion Cells

Voltage balancing between series-connected cells of rechargeable lithium-ion batteries is important for battery life, autonomy and security. Active balancing is the designated choice for applications that are sensitive to energy losses. A well-known next-to-next balancing technique is presented and its design and operating limitations are analyzed. This paper then presents a new technique for next-to-next balancing that improves on the conventional technique by offering better performances while being simpler to implement. Experimental results show an important reduction of the size of the magnetic coupler while maintaining efficiency at a level above 90%.

Optimized structure for next-to-next balancing of series-connected lithium-ion cells

Energy storage systems are critical elements in electric vehicle (EV) and hybrid electric vehicle (HEV) applications. In these systems, lithium-ion batteries are preferred for their outstanding characteristics and advantages: high power density, long life cycles and high efficiency. For high voltage applications, batteries cells are connected in series, raising the issue of voltage balancing among cells. This paper presents a new structure of active voltage balancing of Li-ion cells associated in series in battery stack. It is based on the use of micro-converters network. The principle of the charge equalization is to derive energy from an overcharged cell and to transfer it to an undercharged cell no matter whether the battery is currently in charge or in use supplying a load. The highlight of this structure is not only its high efficiency and its ease of implement but moreover, its integration capacity in contrast to state of the art passive and active balancing topologies. A monitoring system is required to perform forced balancing. The results from simulations and experimental test bench validate the feasibility and the interest of the proposed balancing circuitry and operating principle.

Voltage balancing converter network for series-connected battery stack

This paper presents the implementation of a bidirectional multi-level voltage inverter, isolated converter based on a multi-cell architecture for battery charger applications. Dual Active Bridge based DC to DC isolated converter cells are cascaded with H bridges which are then associated in series to implement a multi-level topology able to produce AC waves from DC source and vice versa. The operating principle is provided along with converter main advantages and drawbacks. A special attention is dedicated to the control part. The operation of the multi-level converter is validated with experimental results. A special care is applied to efficiency measurements. Efficiency and power densities are provided to highlight the interest of the converter.

Bidirectional AC to DC Isolated Multi-Cell Converter

Dual Active Bridge converter is selected for the implementation of hybrid integration of isolated low power low voltage SMPS Its architecture, as well as natural ZVS operation and limited amount of passive devices are convincing criteria for this type of application Its design analysis shows outstanding ability to minimize passive elements while offering high efficiency levels, in the range of 90% Details of active and passive device designs are given The experimental results carried out upon the realization of specific CMOS chips and passive devices demonstrate the interest of such conversion structure for SMPS low power low voltage applications

Thanh Hai Phung

Papers

An Optimized Topology for Next-to-Next Balancing of Series-Connected Lithium-ion Cells

Optimized structure for next-to-next balancing of series-connected lithium-ion cells

Voltage balancing converter network for series-connected battery stack

Bidirectional AC to DC Isolated Multi-Cell Converter

Integrated low power low voltage isolated switch mode power supply