Active Equalization Method Research Articles

Active Equalization for Lithium-Iron Battery Pack Based on Reduced-Order Solving Strategy for the Hanoi Tower Problem

In order to address the energy imbalance issue of a series-connected lithium-iron battery pack, this paper proposes an active equalization method based on a reduced-order solving strategy for the Hanoi Tower problem. The proposed scheme utilizes a combined structure of a switching-network circuit and a bidirectional Cuk converter and leverages an ultracapacitor cell as the energy-transfer carrier. Simulation and comparison demonstrate that the exchange of unbalanced energy within the battery pack can be achieved. The proposed approach can effectively achieve various balancing modes such as cell-to-cell, cell-to-string, string-to-cell, and string-to-string with a relatively fast balancing speed.

Multi-Cell-to-Multi-Cell active equalization method based on k-means clustering and battery pack SOC estimation

In this paper, a MC2MC (Multi-Cell-to-Multi-Cell) battery pack active equalization scheme based on reconfigurable circuits and Buck-Boost converters is proposed and validated for the problem of inconsistent single cell power in battery packs. This scheme can simultaneously equalize multiple non-adjacent cells in a single equalization process, improving the equalization time efficiency. Then, based on the relationship between duty cycle and voltage difference, the MC2MC battery pack active equalization control strategy based on adaptive duty cycle is designed. In addition, a k-means based clustering algorithm is used to cluster and reorganize batteries with different charges, and the SOC (State of charge) estimation algorithm of the battery pack is improved and introduced into the equalization control among multiple batteries. Finally, AC2AC (Any-Cell-to-any -Cell), MC2MC, and MC2MC simulations considering the SOC estimation of the battery pack are validated and analyzed for the unbalanced battery packs under MATLAB/Simulink environment, respectively. On the basis of verifying the accuracy of the simulation process, the effectiveness of the MC2MC equalization control method considering the SOC estimation of the battery pack is verified through the comparative analysis of four aspects, namely, equalization time, computational workload, resultant variance, and energy efficiency.

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 Active Equalization Method of Battery Pack Based on Event-Triggered Consensus Algorithm

In this paper, a control strategy of a cell-based multi-agent system is proposed to solve the problem of inconsistency of series lithium-ion battery packs. The bidirectional Cuk converter is utilized as an equalizing circuit serving for balancing adjacent cells in a pack. A SOC-based consensus control with a time-triggered mechanism (TTM) is proposed. In order to reduce the actuator updates, the control method is ameliorated by altering TTM to an event-triggered mechanism (ETM). Adjustable balancing currents are designed in both TTM and ETM methods for the acceleration of the equalization process. The cases in dynamic environments under externally imposed charging/discharging currents by adopting TTM and ETM methods are investigated in detail. By comparison, the simulations and hardware-in-the-loop (HIL) experiments with a Typhoon real-time simulator are illustrated to show that, both in standby or external charging/discharging conditions, the proposed ETM algorithms are superior to TTM’s in terms of equalization time and adaptability to the external environment.

Design of Lithium Battery Management System of Hydrogen Emergency Vehicle

The hydrogen emergency power supply vehicle is mainly powered by a pure lithium battery power supply. Therefore, the reliable operation of the power supply and the analysis of charging characteristics play an important role. A battery management system for emergency vehicle power supply is designed in this paper. Through the battery management system, battery information collection, battery information analysis, and control management are carried out to realize the reliable operation of the power supply. The battery management system adopts the active equalization method for balance management, which improves the balance efficiency, improves the health status of the power supply, and extends the life of the power battery pack.

An active equalization method for series-parallel battery pack based on an inductor

The equalization topologies based on inductive energy storage have high equalization accuracy and perfect functionality, but often have more complex structure and control method. To overcome this problem, an active equalization method based on an inductor is proposed for the series-parallel battery pack. The energy storage device responsible for energy transfer requires only one inductor and the topology is simple and low cost. Combining diodes and MOSFETs to form a switching array reduces the cost of the equalization topology while increasing the fault tolerance of the control signal and making equalization control simpler. First, the working principle and parameter design process of the topology are described, and the control strategy adapted to it is proposed on this basis. Second, based on the simulation models, the variation law of the efficiency and speed of the proposed equalization method influenced by inductance and switching frequency is analyzed, and by comparing the new equalization method with similar methods, it is verified that the new equalization method is simple in structure, low in cost, and convenient in control. Final, by building an experimental platform for “four-series and two-parallel” battery pack, the effectiveness of the new equalization method is verified.

An Active Equalization Method Based on an Inductor and a Capacitor for Series Battery Pack

Combining the characteristics of the high precision of inductive energy storage equalization and the fast speed of capacitive energy storage equalization, an active equalization method is proposed for a series battery pack based on an inductor and capacitor. The energy storage devices responsible for energy transfer have only one inductor and one capacitor. First, we propose the topology, analyze the working principle, and elaborate on its parameter design process. Second, an adaptive equalization control strategy matching the topology is designed. Third, based on the simulation models, the speed and efficiency characteristics of the new equalization method are verified, and the significant cost and volume advantages and the simple control characteristics are analyzed in detail. Finally, an experimental platform was built for a four-cell series battery pack to verify the effectiveness of the new equalization method for the battery pack charging and discharging process. The voltage difference is less than 80 mV.

An active equalization method for redundant battery based on deep reinforcement learning

Battery equalization is essential in the battery management system. In this paper, an active equalization method based on redundant battery is proposed. The equalization circuit consists of a battery string composed of multiple batteries connected in series and a redundant battery. During the discharging process, one cell in the string is selected by the switch controller to be paralleled with redundant cells for equalization purposes. On this basis, an optimal switch control strategy based on deep reinforcement learning (DRL) is proposed, which takes into account the battery's state of charge (SOC), state of health (SOH), and current distribution during parallel connection. The proposed optimal switching control strategy can achieve equalization with the least number of switching times. Simulation shows that, compared with the greedy algorithm and the rule algorithm, the strategy proposed in this paper can reduce the SOC inconsistency of the battery string to less than 1% with the minimum number of switching times.

Active Equalization of Lithium-Ion Battery Based on Reconfigurable Topology

The equalization technique is a key technique in the secondary utilization of retired batteries. In this paper, a double-layer equalization method is proposed, which combines the reconfigurable topology with the converter active equalization method. The inner layer uses the reconfigurable topology to have a balanced set of battery cells. Thanks to isolating the lowest SOC (state of charge) cell in the battery group, the energy transfer loss among cells is avoided. In addition, this topology can reduce cost and control complexity and the number of components. In the outer layer, a Buck–Boost converter is added for each battery group, and the outputs of the converters are connected in series. The output voltage of the converter varies as the SOC of the group varies while the total output voltage is stable. In order to validate the proposed method, an equalization circuit consisting of 12 battery cells is built on Matlab/Simulink. Simulation results show that the proposed method can effectively balance the battery pack and maintain a stable output voltage. Compared to the conventional active equalization method, the proposed method has significantly improved the equalization efficiency.

Efficient and Fast Active Equalization Method for Retired Battery Pack Using Wide Voltage Range Bidirectional Converter and DBSCAN Clustering Algorithm

This article presents an efficient and fast echelon battery equalization method based on wide voltage range bidirectional converter combined with <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DBSCAN (density-based spatial clustering of applications with noise)</i> clustering control strategy. Thanks to the wide voltage range and bidirectional buck-boost characteristics of the four-switch bidirectional converter, the battery energy can be reasonably redistributed between the battery and the super capacitor. The converter operating in synchronous rectification mode can not only achieve bidirectional energy flow in a wide voltage range, but also has a high energy conversion efficiency. The <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DBSCAN</i> clustering algorithm is used to divide all battery cells into groups, and each group may contain one or more adjacent and nonadjacent battery cells. First, the nonadjacent single cells are balanced and integrated into adjacent group with the closest voltage. Then, the groups with different voltages are balanced by group-to-group, thereby realizing rapid balance of the entire battery pack. In order to verify the effectiveness of the proposed method, simulations and experimental verification were carried out. The experimental results show that, comparing with traditional battery balancing methods, the proposed method achieves shorter balancing time and higher balancing efficiency.

A Novel Active Equalization Method for Series-Connected Battery Packs Based on Clustering Analysis With Genetic Algorithm

Battery pack performance is the main concern for electric vehicles and energy storage systems. However, charge imbalance is inevitable due to inconsistent manufacturing techniques and environmental conditions. Charge imbalance reduces the power performance and available energy of battery packs. Hence, it is necessary to perform battery equalization. This article proposes an active equalization circuit and a novel equalization strategy to achieve energy redistribution. A bidirectional equalization topology consisting of a forward transformer and switch matrix is proposed first. Then, an innovative equalization strategy based on clustering analysis and genetic algorithm (GA) is developed. Clustering analysis is introduced to identify the target cells to be balanced. To further increase the speed of the equalization process, GA is employed to optimize the classification results. Finally, a series of experiments were conducted to confirm the effectiveness of the proposed topology and the strategy. Both the simulation and experimental results validate that the proposed equalization strategy not only improves the inconsistency but also increases the equalization speed. In practical battery pack experiments, the pack capacity is improved by 16.84% after equalization, and the equalization time is decreased by 23.8% using the proposed method.

An Active Equalization Method for Lithium-ion Batteries Based on Flyback Transformer and Variable Step Size Generalized Predictive Control

The inconsistency in large-scale battery pack significantly degrades the performance of electric vehicles. In order to diminish the inconsistency, the study designs an active equalization method comprising of equalizer and equalization strategy for lithium-ion batteries. A bidirectional flyback transformer equalizer (BFTE) is designed and analyzed. The BFTE is controlled by a pulse width modulation (PWM) controller to output designated balancing currents. Under the purpose of shortening equalization time and reducing energy consumption during the equalization process, this paper proposes an equalization strategy based on variable step size generalized predictive control (VSSGPC). The VSSGPC is improved on the generalized predictive control (GPC) by introducing the Step Size Factor. The VSSGPC surmounts the local limitation of GPC by expanding the control and output horizons to the global equalization process without increasing computation owing to the Step Size Factor. The experiment results in static operating condition indicate that the equalization time and energy consumption are reduced by 8.3% and 16.5%, respectively. Further validation in CC-CV and EUDC operating conditions verifies the performance of the equalizer and rationality of the VSSGPC strategy.

An any-cell(s)-to-cell(s) equalization method with a single magnetic component for Lithium-ion battery pack

This paper develops a bi-directional active equalization method using an inductor with multiple balancing paths. The new method allows the energy to transfer directly from any cell(s) to any cell(s) which can increase the equalization speed, reduce the energy conversion times and efficiently prevent the batteries from overcharging or undercharging. We adopt the bi-directional switches of low conduction loss for high equalization efficiency. To further improve the battery equalization system performance, the impact factors of the average balancing current which is the main measurement index of the balancing speed are first specifically discussed and the efficiency is also evaluated. The experiments with a four-20Ah Lithium-ion battery string are conducted and the results demonstrate that the developed approach has achieved a good overall performance of equalization.

A Layered Bidirectional Active Equalization Method for Retired Power Lithium-Ion Batteries for Energy Storage Applications

The power from lithium-ion batteries can be retired from electric vehicles (EVs) and can be used for energy storage applications when the residual capacity is up to 70% of their initial capacity. The retired batteries have characteristics of serious inconsistency. In order to solve this problem, a layered bidirectional active equalization topology is proposed in this paper. Specifically, a bridge-type equalization topology based on an inductor is adopted in the bottom layer, and the distributed equalization topological structure based on the bidirectional BUCK-BOOST circuit is adopted in the top layer. State of charge (SOC) is used as the equalization target variable, and the bottom layer equalization algorithm based on a “partition” idea and route optimization is proposed. The static equalization experiments and charge equalization experiments are performed by the 12 retired batteries selected from an electric sanitation vehicle. The results show that the proposed equalization method can reduce the SOC difference between retired batteries and can effectively improve the inconsistency of the retired battery pack with a faster equalization speed.

An Active Direct Cell-to-Cell Balancing Circuit in Continuous Current Mode for Series Connected Batteries

Bi-directional cell-to-cell balancing circuits can well prevent voltage imbalance of batteries that are connected in series. However, it is a challenge to achieve high equalization speed and equalization efficiency with low complex circuit structure. In order to overcome this challenge, it is proposed that a direct bi-directional cell-to-cell active equalization method that works in continuous current mode (CCM) is used. The proposed balancing circuit allows energy to transfer directly from the source cell to the target cell in one step, which guarantees high balancing speed and efficiency. The experiments in which six-20 Ah lithium-ion batteries are connected in series have been carried out, and the results show that the balancing circuit achieves a good comprehensive performance of equalization in efficiency, speed, and circuit complexity.

Active Battery Equalization Method Based on Redundant Battery for Electric Vehicles

In this paper, an active equalization method based on redundant battery is proposed. A redundant battery is added to a battery pack consisting of several series batteries. According to the capacity and SOC (state-of-charge) of series batteries in the battery pack, one of these batteries is in parallel with the redundant battery in a certain time period. On the one hand, the energy is transferred between the redundant battery and the equalized batteries. On the other hand, during the charging or discharging process, the redundant battery acts as a power source, which reduces the current of the equalized battery. By adjusting the length of time that redundant battery and series batteries are connected in parallel, the purpose of battery equalization will be achieved. The balance current is limited only by the maximum charge–discharge ratio of the batteries. As long as the sum of the difference of series batteries capacity is less than the redundant battery capacity, the balance of all batteries can be achieved. Compared with other active equalization methods, the energy storage element (redundant battery) is used to be the main component of the equalization circuit in this method. It not only has the advantages of simple equalization circuit and large equalization current, but also has higher energy density of battery pack. In this paper, the equalization circuit is given, and the equalization strategy with accurate battery parameters and uncertain battery parameters is proposed. The experimental results also verify the correctness of the theoretical analysis and modeling.

A novel active equalization method for lithium-ion batteries in electric vehicles

Abstract Cell inconsistency is inevitable due to manufacturing constraint. Therefore, cell equalization is essentially required. In this paper, we propose a novel active equalization method based on the remaining capacity of cells which is feasible for lithium-ion battery packs in electric vehicles (EVs). The cell models are established based on a combined electrochemical model of lithium-ion batteries. The remaining capacity and state-of-charge (SOC) of cells are observed at the beginning of equalization. The particle filter (PF) method is employed to estimate the cell SOCs during equalization in order to eliminate the drift noise of the current sensor. The first high-SOC cell discharge (FHCD) and first low-SOC cell charge (FLCC) equalization algorithms are proposed and compared with 1% and 3% SOC bounds, respectively. The validation experiment results have shown that the proposed algorithm is suitable for equalization of lithium-ion batteries in EVs.

A Multi-winding Transformer Cell-to-Cell Active Equalization Method for Lithium-Ion Batteries with Reduced Number of Driving Circuits

The bidirectional cell-to-cell equalization methods perform well to prevent the series-connected batteries from overcharging and undercharging. However, it remains a challenge to achieve fast equalization and high equalization efficiency with low complexity. To address the issue, we propose a new bidirectional cell-to-cell active equalization method using a multiwinding transformer. The new method allows the energy to transfer directly from the highest voltage cell to the lowest one by fly-back operation or forward operation which gives a short balancing path and guarantees a fast equalization speed. We adopt the bidirectional switches of low conduction loss for high equalization efficiency. Since the bidirectional switches are turned on or off simultaneously, a common driving circuit for the bidirectional switch has been designed to reduce the number of the driving circuits by half. The experiments with a six 50-Ah Lithium-ion battery strings are conducted and the results have demonstrated that our new approach has achieved a good overall performance of equalization in terms of speed, efficiency, and complexity of the circuit.

Research on Active Equalization of Lithium Battery via SOC

This paper presents an active equalization method for lithium battery via SOC. The high accuracy of SOC is promised by extended Kalman filter algorithm (EKF) based on the adaptive parameters equivalent-circuit model at all SOC region. Then a small size, low loss resonant soft-switching active equalization circuit is presented. That circuit combined with SOC do precisely balance the battery pack during charge and discharge processes, which can effectively improve the battery pack’s using life.