Battery Equalization Research Articles

Hierarchical equalization scheme for retired lithium-ion battery packs based on inductor-flyback transformer

Some lithium-ion batteries can be reused after sorting and recombination. Equalization of these batteries during the process of step utilization is an effective way to improve the inconsistency of battery packs and extend their lifespan. This paper proposes a hierarchical equalization topology based on a combination of inductor and transformer, which is divided into intra-group and inter-group battery equalization. The intra-group equalization circuit achieves energy transfer between non-adjacent individual batteries through an improved Buck-Boost circuit. The inter-group equilibrium circuit exchanges energy between any battery subpackages and the entire battery pack using a flyback transformer. An LCD (Inductance-Capacitor-Diode) lossless absorption network is added to the transformer to absorb voltage spikes caused by leakage inductance while achieving soft switch to reduce switch losses. Considering that retired lithium-ion batteries can affect battery capacity and State of Charge (SOC) estimation accuracy due to aging issues, a modified Extended Kalman Filter (EKF) algorithm is proposed to improve battery SOC estimation accuracy. A fuzzy logic controller is introduced into the SOC-based control strategy to improve the equalization efficiency of the battery pack. Finally, to validate the effectiveness of the proposed equalization scheme, a model is built and simulated using MATLAB/Simulink software. The experimental results show that compared with the traditional double-layer inductor equalization scheme using the most value equalization algorithm and fuzzy logic control algorithm respectively, this equalization scheme has a faster equalization speed and higher equalization efficiency.

A New Phase Shift Full Bridge dc/dc Converter With Integrated Intermodule Battery Equalization Circuit (IBEC)

A New Phase Shift Full Bridge dc/dc Converter With Integrated Intermodule Battery Equalization Circuit (IBEC)

A novel multimode constant magnetizing current battery equalizer with few sensors in electric vehicles

A novel multimode constant magnetizing current battery equalizer with few sensors in electric vehicles

Active Methods for the Equalization of a Serially Connected Lithium-Ion Battery Pack: A Review

Traditional fuel vehicles are currently still the main means of transportation when people travel. It brings convenience to their travels, but it also causes energy shortages and environmental pollution. With the development of science and technology and the popularization of green environmental protection, electric vehicles have gradually entered people’s lives, greatly alleviating these problems. As a power supply device for electric vehicles, the performance of batteries directly affects various indicators of vehicles. Due to their long lifespan and high energy density, lithium-ion batteries are now the preferred source of power for electric vehicles. However, due to various factors in the manufacturing and operation of lithium-ion batteries, there are often differences among individual cells. The power balance and performance of a battery pack are closely related. Thus, battery equalization is an important standard for a battery management system to work normally, and it is also one of the various battery management application problems. This paper reviews battery equalization systems and various active equalization circuits and summarizes the working principle and research progress of each active equalization circuit. Then, various active equalization circuits are analyzed and compared, and dynamic equalization for a second-life battery is introduced to enrich this review of equalization technology. Finally, the above contents are summarized and prospected. In order to obtain the best outcomes, different equalization circuits need to be chosen for various situations.

An Integrated Self-Modularized Battery Equalizer and Supercapacitor Charger for Hybrid Electric Vehicle Energy Storage System

An Integrated Self-Modularized Battery Equalizer and Supercapacitor Charger for Hybrid Electric Vehicle Energy Storage System

Active Equalization of Lithium Battery Pack with Adaptive Control based on DC Energy Conversion Circuit

Background:: How to solve the inconsistency of battery pack is a key point to ensure reliable operation of electric vehicles. Battery equalization is an effective measure to address the inconsistency. Passive equalization method has poor efficiency and thermal management problems. Average voltage equalization method is only suitable for situations where there is a significant voltage difference between batteries. The SOC-based equalization method is relatively difficult and may inevitably lead to the accumulation of errors during the process. Objective:: In order to avoid the disadvantages of traditional control methods, a new control method is proposed to improve the accuracy and self-adaptation of active equalization, which is easy to be realized without online calculation. Methods:: Cascaded bidirectional Buck-boost circuit is adopted as the novel equalization topology. Based on fuzzy PID theory, an adaptive digital-analog hybrid control strategy based on fuzzy PID is proposed in this paper. Parameter design of the fuzzy PID controller is carried out. A battery equalization system based on cascaded bidirectional Buck-boost circuit is designed and developed. Experimental verification is conducted on relevant hardware platforms. Results:: An adaptive digital-analog hybrid control strategy based on fuzzy PID is proposed. Compared to passive equalization, this proposed method provides high efficiency. Regarding traditional voltage control, the method improves control reliability and flexibility. Compared to the average voltage equalization method, the approach needs less convergence time. Moreover, the control method is much easier to realize than the SOC-based equalization method. Conclusion:: By using the presented adaptive control based on DC energy conversion circuit, the degree of self-adaptation of the equalization process has been obtained as higher and the inconsistency as smaller.

Current control for a supercapacitor-based battery equalization system

This paper presents a novel supercapacitor-based energy equalization system and discusses a new equalization current control method. The proposed battery equalization system is composed of a bidirectional boost–buck circuit, a switch matrix, and a supercapacitor, which can realize stable electric current transmission between batteries and supercapacitors. The buck or boost mode of the circuit is triggered automatically based on the threshold of the voltage drop between the battery and the supercapacitor. A modified control logic of the metal-oxide-semiconductor field-effect transistor is proposed to improve the efficiency of the circuit, and a model predictive control (MPC) algorithm is designed to track the target current. Simulation results indicate that for a conventional electric current transmitting circuit, the current fluctuates violently under a fixed pulse width modulation duty. In contrast, the proposed supercapacitor-based energy equalization system tracks the target current well under the control of the MPC controller. In a wide operating range, the transmission efficiency of the new energy equalization system with the modified control logic is 13.0% higher than that of the conventional electric current transmitting circuit with the original control logic.

An Active Equalization Method for Cascade Utilization Lithium Battery Pack With Online Measurement of Electrochemical Impedance Spectroscopy

Abstract With the rapid development of new energy vehicles, a large number of lithium batteries have been produced, used and retired. The full utilization and safe use of the whole life cycle of the batteries have become a hot topic in the research field. Compared to brand new batteries, retired power batteries exhibit significant inconsistency and safety risks due to aging, thus necessitating effective battery equalization and safety monitoring methods. In this article, an active equalization method for cascade utilization lithium battery pack with online measurement of electrochemical impedance spectroscopy is proposed to actively equalize the retired battery pack and alleviate the inconsistency of the battery pack. Besides, the electrochemical impedance spectrum of the single battery is measured online without adding additional hardware circuit, so as to realize real-time safety monitoring and solve the safety problem of the battery. Finally, in order to verify the feasibility of the active equalization and electrochemical impedance spectrum monitoring scheme designed in this article, a simulation model is built based on MATLAB-Simulink platform. The simulation results show that the six batteries in the proposed scheme model complete the active equalization in about 710s, 850s and 740s respectively in the balance mode, charge mode and discharge mode, and the electrochemical impedance spectrum in the frequency range of 1-20KHz can be successfully measured.

An Efficient and Compact Equalizer Based on Forward-Flyback Conversion for Large-Scale Energy Storage Systems

An effective battery equalizer is of great significance to eliminate inconsistencies and improve the performance of large-scale battery packs. Nevertheless, the existing balancing circuits have various problems such as slow balancing speed, high cost, bulky size, complex control, etc. Therefore, this paper designs an efficient and compact transformer-based equalizer, which works at forward-flyback conversion. Distinguished from the conventional transformer-based equalizers, the proposed equalizer requires only one MOSFET and one transformer winding equipped with each cell. Two complementary PWM signals can control all MOSFETs used in the proposed equalizer. The equalizer can automatically equalize all cells without the need for additional voltage sensing and demagnetization circuits, reducing the cost and volume. It can directly transfer energy between any two adjacent modules, improving the equalization efficiency and speed. An experimental prototype of eight series-connected cells was set up. The experimental results and systematic comparison with the existing balancing topologies show that the proposed equalizer is appropriate for balancing large-scale energy storage systems. The energy delivery efficiency among cells can be as high as 93.15% over various loading conditions.

Average Model of Switched-Energy-Tank Battery Equalizer for Accelerated Performance Assessment

Average Model of Switched-Energy-Tank Battery Equalizer for Accelerated Performance Assessment

A simple and easy-to-implement battery equalization strategy for photovoltaic-battery energy storage systems

Abstract For renewable energy sources such as photovoltaic (PV), energy storage systems should be prioritized as they smooth the output well. Although lithium-ion battery energy storage systems are favored for their excellent performance, the large number of batteries connected in series and parallel may lead to inconsistent battery packs, which can cause system problems. Therefore, battery equalization techniques should be employed. This article proposes a battery equalization technique suitable for PV battery energy storage systems. In terms of the equalization circuit, we propose an equalization circuit consisting of a switch-selective circuit and a Cuk circuit, which is simple and easy to expand; in terms of the equalization strategy, we adopt a highly robust fuzzy logic control to better adapt to PV battery energy storage systems, we developed a set of control rules suitable for this equalization strategy. We have investigated the principle of the proposed battery equalization technique and verified it experimentally during the battery pack's resting, charging, and discharging. The consistency of the battery pack is significantly improved as a result.

Active balancing circuit for advanced lithium-ion batteries used in photovoltaic application

An approach to the analysis and design of a bidirectional DC power converter for the cell voltage balancing control of a series connected lithium-ion battery string is presented in this paper. The proposed Cell Balancing Circuit (CBC) is designed to transfer the energy from the fully charged battery cell to the weakest one using a switch mode power converter operation. This operation maintains cell batteries at the same State-Of-Charge (SOC) and voltage range. Unlike previous battery balancing circuits, the balancing method uses only one magnetic component, resulting small size system. Simulation and experimental results show that the proposed cell balancing method can not only enhance the bidirectional battery equalization performance, but can also reduce the switching loss during the equalization period. Experiment results are provided to verify the operating principle of the proposed balancing method. Specific conditions of experiments are used to reproduce photovoltaic operations

A multicell-to-multicell battery equalizer with more balancing modes based on half-bridge bipolar-resonant LC converter

A multicell-to-multicell battery equalizer with more balancing modes based on half-bridge bipolar-resonant LC converter

Electric vehicle battery equalization technology applied to vehicle-to-grid

Electric vehicle battery equalization technology applied to vehicle-to-grid

Battery equalization improves efficiency, safety, and lifespan for powering electric vehicles

Cuk circuits combined with a flyback transformer allows batteries in series to be quickly and efficiently equalized.

Design of a bus-based battery equalization with zero-current switching

A novel any cell to any cell equalization circuit topology with small column, low weight, low cost, and high efficiency is proposed for serial-connected batteries, especially suitable for unmanned aerial vehicles, satellites, and other fields with strict requirements on size, weight, reliability, and safety. To solve the problems of high switching losses in equalization circuits and low reliability of complex control schemes. A half-bridge circuit to convert the DC voltage of the battery into AC voltage is employed, and the energy is exchanged autonomously via the bus. At the same time, LC resonant circuit is used to achieve zero-current switching of the MOSFET, thus reduces greatly the switching losses. The working principle is analyzed by theoretical derivation, and the parameters of the circuit are optimized through circuit simulation. Furthermore, experiments which support six cells equalization are carried out to verify the feasibility and advantage of this topology. This equalization uses a bus-type architecture to improve equalization efficiency and topological flexibility making it even more valuable in the industrial and aerospace fields.

A Modularized Voltage Equalizer Based on Phase-Shift Modulation for Series-Connected Battery Strings

The modular design can effectively improve the circuit extensibility and control flexibility of equalizers for long series-connected battery strings. This paper proposes a modular battery equalizer based on phase-shift modulation. The LC resonant converters with synchronous rectification are employed as the automatic cell-level equalizer to realize any-cells-to-any-cells (AC2AC) equalization and soft-switching operation, which enhances the balancing speed and efficiency. Different cell-level equalizers are connected with auxiliary windings. The fast equalization between modules is achieved by adjusting the phase shift of driving signals applying for the cell-level equalizers. A prototype with three modules, each consisting of three series cells, is built and tested. Experimental and comparative results confirm the validity and characteristics of the proposed modular equalizer.

A simple and effective capacitor‐based equalizer for cell‐to‐cell battery equalization

SummaryWe propose an equalizer using two capacitors along with a resistor and a cell access network to address the weakness of low equalization power for the flying‐capacitor based equalizer, which integrates the merits of simplicity and reliability in the application of cell‐to‐cell battery equalization. The equalization process is implemented by alternately charging the capacitors from high state of charge (SoC) cell and discharging the capacitors to low SoC cell, where the capacitors are run in parallel in charging and in series in discharging, and the charging or discharging duration is determined by ξ, the multiple of the time constant of the circuit. A protection is also designed to suppress the peak current occurred when initializing the equalizer due to the zero‐boot voltage of the capacitor. Theoretical analysis shows that the equalization power, which is governed by the lumped resistance of equalization path and ξ, can range from less than 1 W to greater than 6 W. The battery discharging time increases about 5.14% under constant current of 0.5 C in the experimental test. Additional advantage of our equalizer is its operating frequency as low as several Hz, which benefits hardware implementations. The equalizer can attain high equalization power through simple capacitors and a regulating resistor, which is suitable to be used for industrial applications.

Optimal design for efficiency enhanced hierarchical cell-to-cell equalization systems based on centralized model predictive control

Effective topology is particularly significant for enabling high-efficiency hierarchical cell-to-cell (CC) equalization systems for large-scale batteries. This paper proposes an efficiency-enhanced hierarchical battery equalization systems (BESs) by formulating a topology graph-balancing connectivity evaluation method. As a performance evaluation index, connectivity takes both balance time and energy loss into consideration, which can be measured by the second small eigenvalue of the Laplacian matrix of the topology graph. Then, a centralized model predictive control (MPC) balancing strategy is formulated and integrated with hierarchical topologies to tackle optimal residual available energy (RAE) balancing problems. Making use of simulation tests of hierarchical BESs with different configurations, results show that the balancing performance and measured connectivity are consistent, and the balancing connectivity gradually rises and then decreases with an increasing number of module groupings. The optimal hierarchical BES with 96-series cells can achieve a low balancing time of 229 s and an energy loss of 0.67%. The balancing time and energy loss of centralized MPC can be reduced by 80.28% and 34.02%, respectively, relative to decentralized MPC balancing. For practical implementation consideration, dynamic balancing simulation and hardware-in-the-loop (HIL) experiments are conducted, and the experimental results are well matched with the simulation.

The function of the time constant in RC series circuit signal filtering

Battery storage systems are essential components in the realm of renewable energy systems and electric vehicles, providing critical support in managing power supply and demand. However, a prevalent issue within these systems is charge imbalance among individual battery cells, which can lead to suboptimal power efficiency, reduced reliability, and potential safety hazards. Addressing this challenge, researchers have focused on developing battery equalization techniques to ensure uniform charge distribution. Among the various strategies, switched-capacitor-based battery equalizers have emerged as a promising solution due to their cost-effectiveness, compact design, and controllability. This paper delves into the analysis of several switched-capacitor-based battery equalizers, including conventional, two-level, modular, chain structure types I and II, series-parallel, and single switched-capacitor equalizers. The study begins with the formulation of mathematical models that simulate the charge and discharge cycles of these equalizers, providing insights into their operational mechanisms. The goal is to enhance the understanding of switched-capacitor equalizers, paving the way for advancements in battery management systems that optimize performance and extend battery life.