Balanced Topology Research Articles

A novel active cell balancing topology for serially connected Li-ion cells in the battery pack for electric vehicle applications

In a Battery Management System (BMS), cell balancing plays an essential role in mitigating inconsistencies of state of charge (SoCs) in lithium-ion (Li-ion) cells in a battery stack. If the cells are not properly balanced, the weakest Li-ion cell will always be the one limiting the usable capacity of battery pack. Different cell balancing strategies have been proposed to balance the non-uniform SoC of cells in serially connected string. However, balancing efficiency and slow SoC convergence remain key issues in cell balancing methods. Aiming to alleviate these challenges, in this paper, a hybrid duty cycle balancing (H-DCB) technique is proposed, which combines the duty cycle balancing (DCB) and cell-to-pack (CTP) balancing methods. The integration of an H-bridge circuit is introduced to bypass the selected cells and enhance the controlling as well as monitoring of individual cell. Subsequently, a DC–DC converter is utilized to perform CTP balancing in the H-DCB topology, efficiently transferring energy from the selected cell to/from the battery pack, resulting in a reduction in balancing time. To verify the effectiveness of the proposed method, the battery pack of 96 series-connected cells evenly distributed in ten modules is designed in MATLAB/Simulink software for both charging and discharging operation, and the results show that the proposed H-DCB method has a faster equalization speed 6.0 h as compared to the conventional DCB method 9.2 h during charging phase. Additionally, a pack of four Li-ion cells connected in series is used in the experiment setup for the validation of the proposed H-DCB method during discharging operation. The results of the hardware experiment indicate that the SoC convergence is achieved at ~ 400 s.

The controllability and structural controllability of Laplacian dynamics

In this paper, classic controllability and structural controllability under two protocols are investigated. For classic controllability, the multiplicity of eigenvalue zero of general Laplacian matrix L ∗ is shown to be determined by the sum of the numbers of zero circles, identical nodes and opposite pairs; however, it is always simple for the Laplacian L with diagonal entries in absolute form. For a fixed structurally balanced topology, the controllable subspace is proved to be invariant even if the antagonistic weights are selected differently under the corresponding protocol with L. For a graph expanded from a star graph rooted from a single leader, the dimension of controllable subspace is two under the protocol associated with L ∗ . In addition, the system is structurally controllable under both protocols if and only if the topology without unaccessible nodes is connected. As a reinforcing case of structural controllability, strong structural controllability requires the system to be controllable for any choice of weights. The connection between parent nodes and child nodes affects strong structural controllability because it determines the linear relationship of the control information from parent nodes. This discovery is a major factor in establishing the sufficient conditions on strong structural controllability for multi-agent systems under both protocols, rather than for complex networks, about latter results are already abundant. Finally, we present a sufficient and necessary condition to identify the strong structural controllability. Moreover, a method to construct a strongly structurally controllable graph is proposed.

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.

Single Line-to-Ground Fault Type Multilevel Classification in Distribution Network Using Realistic Recorded Waveform.

The further identification of fault types for single line-to-ground faults (SLGFs) in distribution networks is conducive to determining the cause of grounding faults and formulating targeted measures for hidden danger treatment and fault prevention. For the six types of SLGFs generated in the actual power grid, this paper deeply studies their fault characteristics. Firstly, the classification criterion of fault transition resistance is derived by the generation mechanism of fault zero sequence voltage (ZSV). At the same time, by comparing and analyzing the same and different characteristics between faults, three criteria for fault classification are obtained. Based on the above four criteria, a multilevel and multicriteria fault classification method is proposed to judge six types of SLGFs. Then, the proposed method is verified by various fault state simulations of the distribution network model with a balanced topology and unbalanced topology. The engineering application of the method is demonstrated by the verification of actual power grid data. Finally, noise and data loss interference test results show the robustness of the method.

Research on equalization scheme of lithium-ion battery packs based on consistency control strategy

In order to address the inconsistency problem of series-connected lithium-ion battery groups in practice, a two-level balanced topology based on bidirectional Sepic-Zeta circuit is designed in this article. Two-level equalization topology uses bidirectional Sepic-Zeta circuits both within and between groups, which can achieve the equilibrium between any cells in a battery group and between any battery groups. With the state of charge (SOC) of the battery as the equalization variable, and the equalization control strategy is designed based on the consistency controller and PI controller to achieve fast and efficient equalization by dynamic adjustment of equalization current, and to efficiently decrease the inconsistency of the equalized battery packs. The experiments are conducted by Matlab/Simulink platform. According to the experimental results it can be obtained that compared with the topology based on single Cuk equalizer, the topology based on single Sepic-Zeta equalizer and the adjacent topology based on Sepic-Zeta equalizer, the proposed topology shortens the equilibrium time by about 51.57 %, 51.43 % and 42.24 %, respectively. Under the same operating conditions, the equalization control strategy designed in this article shortens the equilibrium time by about 29.4 % and 11.19 % compared to the conventional fixed-threshold method and the Fuzzy Logic Control (FLC) algorithm, respectively, and also achieves better results in the equalization efficiency and consistency problem, which effectively verifies the feasibility of the equalization scheme in this article.

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.

An Intermodular Active Balancing Topology for Efficient Operation of High Voltage Battery Packs in Li-Ion Based Energy Storage Systems: Switched (Flying) DC/DC Converter

To meet the load voltage and power requirements for various specific needs, a typical lithium–ion battery (LIB) pack consists of different parallel and series combinations of individual cells in modules, which can go as high as tens of series and parallel connections in each module, reaching hundreds and even thousands of cells at high voltage (HV) levels. The inhomogeneity among the cells and modules results in voltage imbalances during operation and reduces the overall system efficiency. In this work, a robust and flexible active balancing topology is presented. It can not only mitigate the charge imbalance within a module, i.e., intramodular equalization, but also help to balance the state of charge (SoC) level of the modules in a high voltage pack, i.e., intermodular equalization, which is an often-overlooked topic. The proposed concept was proven by experimental verification on parallel and series configurations of cells in realistically sized modules and practical battery management system (BMS) hardware, when the LIB was both idle and under load.

A Novel Voltage Balance Topology With High Efficiency and Low Current Stress for MVdc Interface of Distributed PV

The input independent output series DC/DC converter has one stage of power conversion, which has low cost and high efficiency. However, shadow occlusion, dust coverage, and manufacturing differences will cause power mismatch of the photovoltaic (PV) panels, which in turn causes the unbalanced output voltage. In order to avoid device damage and power degradation caused by unbalanced voltage, a novel topology based on multi-winding transformer is proposed. By multiplexing the switches of each sub-module (SM), this topology can transmit the mismatched power among all the SMs and balance the output voltages. In the traditional method, the mismatched power can only be transferred between adjacent SMs. When the power mismatched SMs are far away, differential power will go through many SMs to reach the target one, causing unnecessary power losses. In the proposed topology, mismatched power can be directly transferred to the target SM, Therefore, it has higher efficiency. Moreover, all the switches have zero voltage switching (ZVS), which further improves the efficiency. 1/3 of the switches in proposed topology have lower current stress than the traditional topology. The hardware cost can be reduced. Finally, the proposed topology is verified by simulation and experiment of 1kW.

Route Optimization Equalization Scheme Based on Graph Theory for Liquid Metal Battery Strings

In order to solve the inconsistency problem of series connected liquid metal battery (LMB) strings, a route optimization equalization scheme is proposed in this article. In terms of balancing topology, a modular double-layer cell-to-cell balancing topology based on inductor and flyback multi-winding transformer is designed, which can transfer energy between any two batteries within or among modules. For control strategy, an equalization strategy based on graph theory and ant colony optimization (ACO) is proposed, which has been compared with the traditional maximum/minimum equalization control strategy. The static condition simulation results show that compared with traditional equalization strategy, the balancing speed of the route optimization control strategy is improved by 88.62%, and the balancing efficiency is increased by 19.43%. Moreover, the inconsistency problem of the battery strings can be significantly improved under both static and dynamic conditions. Therefore, by improving the balancing effect, the proposed scheme can not only effectively avoid overcharging or discharging problems, but also increase the consistency, available capacity and service life of liquid metal battery strings.

Cascade Active Balance Charging of Electric Vehicle Power Battery Based on Model Prediction Control

As a bi-directional converter, the Buck-Boost converter, which has the advantages of simple structure and taking the SOC of the battery as the balance variable, is adopted as the balance topology in this paper. In view of the shortcomings of traditional balance topology, which can only balance two adjacent batteries, resulting in a long balance time and insufficient balance accuracy, a cascade active balance charging topology that can balance in intra-group and inter-group situations simultaneously is proposed. At the same time, the fuzzy control algorithm and model predictive control are used as the balance control strategies, respectively, to control whether the MOSFET is on or off in the balance topology circuit. The duty cycle is dynamically adjusted to the size of the balance current to achieve the balance of the battery pack. The results show that the cascade Buck-Boost balance topology based on model prediction control can accurately control the balancing current and improve the accuracy and speed of the balance, and it is more suitable for the actual working process.

A Broadband SiGe HBT Cascode Power Amplifier Achieving Watt-Level Peak Output Power With 38.6% PAE and 90.9% Large-Signal Fractional Bandwidth

This brief presents a broadband SiGe power amplifier that achieves 30.1 dBm peak <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{P}_{SAT}$ </tex-math></inline-formula> , 38.6% peak power-added efficiency (PAE), 90.9% large-signal fractional bandwidth (FBW) and a 3 dB bandwidth from 5.4 to 13.8 GHz. A balanced topology with two-stage, four-way combing is utilized to achieve watt-level output power and high-power efficiency in a wide range of operating frequency. Power stage is optimized and simulated from the perspective of high output power. At the output stage, a 90° coupler and two transformers are co-optimized for broadband output power combining as well as power matching. This balanced PA is implemented in a 0.13- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\boldsymbol {\mu }\text{m}$ </tex-math></inline-formula> SiGe BiCMOS process with a chip area (with pads) of 2.31 mm2.

A Highly Linear Ka-Band GaN-on-Si Active Balanced Mixer for Radar Applications

A highly linear active mixer in Gallium Nitride on Silicon (GaN-on-Si) monolithic microwave integrated circuit (MMIC) technology, operating in Ka-band for radar applications is introduced. It exhibits a local oscillator (LO) balanced topology of gate-pumped mixers based on high-electron mobility transistors (HEMT) and operates in down-conversion mode. Its design principles and the theoretical foundation of its linearity features resulting from both the high power handling capability of GaN-on-Si HEMTs and the corresponding high applied LO level are presented. An extensive characterization based on excitation of a prototype by broadband continuous wave signals and frequency modulated continuous wave signals validates both the analytical treatment of its linearity and the design of the prototype of the mixer. In the 35–40 GHz operating band, this prototype exhibits a state-of-the-art input referred third order intercept point that reaches 39.1 dBm, and a maximum input referred second order intercept point of 39.4 dBm, with a corresponding conversion gain of −5.2 dB, and LO level of 24 dBm.

Balanced Control System Based on Bidirectional Flyback DC Converter

The inconsistency of the battery pack will cause the “barrel effect“ when the battery pack is working. The battery with lower power will first reach the discharge cut-off condition, resulting in the battery pack not being fully discharged, reducing the battery utilization rate. This paper uses the state of charge (SOC) as an equilibrium variable and the forgetting factor recursive least square–extended Kalman filter (FFRLS-EKF) method to estimate the SOC. Using a balanced topology based on a bidirectional impact direct current (DC) converter, the energy transfer can occur between any battery and only between batteries that need to be balanced, increasing energy utilization and the effect of equalization. The equalization system is simulated under various conditions, which proves the effectiveness of the equalization control system.

A fast and energy-efficient nonnegative least square-based optimal active battery balancing control strategy for electric vehicle applications

In an electric vehicle, a battery pack with many series-connected cells suffers from charge imbalances caused by manufacturing and varying operating conditions. The battery balancing system overcomes the cell imbalance while providing the required capacity maximization, prolonging the battery life, and safe operation. Various balancing topologies and control algorithms have been developed based on the difference in energy transfer methods. Among these, the passive balancing method is to convert the energy of the highly charged cell into heat. The active balancing method transfers the excessive energy of the high-charged cell to the low-charged cell through an electronic circuit. This type of balancing has high conversion efficiency compared to passive balancing and provides a noticeable improvement in increasing the useable capacity of the battery pack, thus increasing the range of the EVs. In this study, an optimal balancing control strategy for the active cell-to-pack balancing system has been developed. A unidirectional common flyback as a DC-DC converter has been used as a balancing circuit for transferring the excessive energy of the cells to the battery pack. The proposed optimal control algorithm eliminates the imbalances among battery packs in the minimum balancing time that ensures maximizing energy efficiency.

Energy-efficient system and charge balancing topology for electric vehicle application

Demand for electric vehicles (EVs) are increased because of flexible, easy to handle, and more powerful energy storage (ES) systems. In electric vehicles, the driving motor would run by energy storage systems. It is necessary to recognize energy storage technologies' battery lifetime, power density, temperature tolerance, and flexible electrochemical behavior. Supercapacitor’s have increased attention due to their exclusive structures such as high capacitance, working efficiency, temperature tolerance, and eco-friendly nature. Additionally, hybrid energy storage systems significantly influence advanced electric vehicles applicable power utilization. A battery management system (BMS) requires a reliable and highly efficient power source from the storage technology for electric vehicles applications. Electrochemical energy storage systems are affected by overcharge/over-discharge, temperature or cell unbalancing. The key factor in a battery management system is cell balancing between cells in a string that prolongs the energy storage device’s lifecycle and performance. This paper highlights a comprehensive study and evaluations focusing on different types of batteries, Supercapacitor’s, and balancing circuits applicable in BMS on electric vehicles and renewable energy storage systems. This rigorous study presents different electrochemical batteries chemistry, anode, cathodes, electrolyte, charging and discharging lifecycle, advantages, and disadvantages. For the Supercapacitor, different types of electrode materials, electrolyte interface, energy storage function, and available Supercapacitor’s capacitance in the market, cell, and module voltage are presented. Also, this study shows the different types of cell balancing circuit’s components number, control complicity, voltage and current stress, overall balancing circuit efficiency, power loss, circuit size and cost, advantages and disadvantages. This manuscript highlights all the insights that will lead to choosing the required and appropriate battery, Supercapacitor or blanching circuit for future applications on electric vehicles systems.

A 400-μW IoT Low-IF Voltage-Mode Receiver Front-End With Charge-Sharing Complex Filter

This work reports on a low-intermediate frequency (IF) voltage-mode receiver front-end for Internet-of-Things (IoT) applications. Design and noise analysis of an unbalanced gate-boosted common-gate low-noise amplifier (LNA) is presented, showing 50% lower power dissipation compared with the conventional balanced topology. Improved linearity is achieved thanks to channel-selection, consisting of two complex poles centered at 2 MHz IF. The first complex pole is embedded in the passive down-conversion mixer for improved frequency selectivity in front of the baseband voltage amplifier. Built in a 28-nm CMOS process, the proposed front-end occupies an active area of 0.175 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , it is supplied with 1 V and consumes only 400 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{W}$ </tex-math></inline-formula> , while showing a minimum noise figure (NF) of 6.8 dB and an out-of-band (OOB) IIP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> of −0.35 dBm. The performance meets Bluetooth low-energy (BLE) requirements and is competitive with other sub-mW receivers.

Flyback Converter Using a D-Mode GaN HEMT Synchronous Rectifier

The flyback converter with its active cell balancing topology for charging lithium-based batteries in Electrical Vehicles (EV) have been adopted recently into the industry. Electrical Vehicle battery charging requires high current operation in continuous current mode and hence, the power loss on the Schottky diode rectifier on the secondary side determines the power conversion efficiency. The depletion mode (D-mode) GaN HEMT synchronous rectifier proposed in this paper has been used to replace the Schottky diode on the secondary side of the flyback converter in order to improve the power conversion efficiency. This synchronous rectifier regulates the forward voltage drop of an external switch to about 100 mV per ampere of current flow with no concern to threshold voltage. The first challenge of converting the D-mode GaN HEMT as a synchronous rectifier is that the normally-on device must be off when the primary side inductor of the flyback converter is initially charging the magnetic energy. That is, the rectifier must behave as the normally-off device during its initialization stage. The second challenge is that the D-mode GaN HEMT must switch off as soon as the secondary current becomes zero. The third challenge is posing a fast recovery feature to reduce the drain-source voltage rise on the primary side switch, which suffices to be the main reason as to why the D-mode GaN HEMT is used instead of MOS devices. The proposed depletion mode GaN HEMT synchronous rectifier is verified to be able to overcome all challenges and in result becomes a candidate for the synchronous rectifier.

Consensus of nonlinear multiagent systems with uncertain disturbance under stochastic switching topologies

In this paper, we investigate the mean square consensus problem of leader‐following nonlinear multiagent systems which suffer from white noise disturbance under randomly switching interaction topologies. The control protocol of each agent is designed based on its local information from its neighbors and the leader. Using matrix inequality theory and stochastic stability theory, a sufficient condition is presented to guarantee the mean square consensus. Moreover, two special cases: balanced topologies switching randomly and random connection failures are considered. Finally, two corresponding numerical simulations are provided to demonstrate the theoretical results.

Continuous-Mode Hybrid Asymmetrical Load- Modulated Balanced Amplifier With Three-Way Modulation and Multi-Band Reconfigurability

This article introduces a novel high-order load modulation power amplifier (PA) architecture, i.e., continuous-mode hybrid asymmetric load modulated balanced amplifier (H-ALMBA). The two sub-amplifiers (BA1 and BA2) of the balanced topology in an LMBA are set as peaking amplifiers with different thresholds when cooperating with the control amplifier (CA) as the carrier, forming a hybrid load modulation behavior between Doherty and ALMBA. Compared to standard LMBA, the proposed H-ALMBA has a three-way load modulation with CA, BA1 and BA2 through proper amplitude control and phase alignment. Thus, this new mode offers extended power back-off range and enhanced back-off efficiency without suffering from difficulty and complexity in wideband design as imposed on three-way Doherty PAs. Based on comprehensive theoretical derivation and analysis, the proposed H-ALMBA is designed and implemented using commercial GaN transistors and wideband quadrature couplers. Moreover, the continuous-mode matching is applied to the carrier amplifier achieving a maximized wideband efficiency at power back-off. This is the first time that continuous mode and ALMBA have been used in combination, and very satisfactory results have been achieved, exhibiting the highest 10-dB OBO drain efficiency (DE) ever reported for wideband load-modulation PAs. The developed prototype experimentally demonstrates wide bandwidth from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.7 - 3.0$ </tex-math></inline-formula> GHz. The measurement exhibits an efficiency of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$63 - 81\%$ </tex-math></inline-formula> at peak output power, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$51 - 62\%$ </tex-math></inline-formula> for 5-dB OBO, and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$50 - 66\%$ </tex-math></inline-formula> for 10-dB OBO within the design bandwidth. When stimulated by a 20-MHz long term evolution (LTE) signal with 10.5-dB peak to average power ratio (PAPR), a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$50 - 55\%$ </tex-math></inline-formula> average efficiency is measured over the entire bandwidth at an average output power around 32 dBm.

Balanced Six-Port Reflectometer With Nonmatched Power Detectors

In this article, a six-port reflectometer is proposed, which utilizes nonmatched power detectors. In the presented solution, the signals reflected from power detectors are efficiently used to obtain a signal flow required for correct measurements. As a consequence, impedance matching networks for power detectors are no longer needed. Simultaneously, due to its balanced topology, the developed six-port exhibits advantageous measurement conditions and theoretically ideal matching at both its input and measurement ports. To experimentally validate the proposed concept, a six-port reflectometer operating at 2.4 GHz is designed, manufactured, and utilized in reflection coefficient measurements. The obtained results are consistent with the values measured using a commercial vector network analyzer. For additional verification, the impact of power detectors’ asymmetry is investigated theoretically and experimentally.