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This paper studies the driving of white light emitting diodes (LEDs) from very low voltages in the 1.2 to 2 V range. The proposed idea is based on replacing the standard Schottky diode used in conventional converter topologies (i.e., buck, buck–boost, and boost) with an LED while shortcutting the output of the converter. In this configuration, the LED works both as the load and the rectifier diode of the converter, hence switching the LED at high frequencies (>100 kHz). Moreover, a thorough analytical study is carried out for the two topologies proposed in this paper, emphasizing in particular their static analysis and the obtaining of the boundaries between the different conduction modes. Finally, the idea is experimentally validated by means of the boost converter variation (i.e., the DL//S ac-LED driver). The DL//S ac-LED driver was also compared with a dc–dc boost converter, showing a better luminous efficacy while disposing of the Schottky diode and the output capacitor. The analysis was carried out when connected to a Li-ion battery using a simple control and integrated circuit for its development. [ABSTRACT FROM AUTHOR]

This paper proposes data transmission method between primary and secondary of the flyback converter without additional communication circuit while simultaneously transferring power. In some application such as a battery charger, the data exchanges between the primary and secondary sides are necessary. In the conventional system, an additional line or wireless communication modules is used for data exchanges, thereby increasing the system and connector size. The proposed system, in comparison, does not use additional signal transceiver but instead exchanges data by simply alternating operation mode of the flyback converter, thus adding communication function while not increasing the volume of the terminal and overall system. The waveform of transformer voltage is used to count the number of resonant pulses, which is used for decoding and encoding the data packet. Bidirectional communication between primary and secondary sides is possible while power is transferred to the output using an appropriate communication protocol. This paper proposes data transmission method for both single output and the multioutput cases. Also, both half-duplex and full-duplex communication using the proposed method is explained. The experimental results are presented to verify the performance of the proposed communication method. [ABSTRACT FROM AUTHOR]

A plug-in hybrid electric vehicle (PHEV) uses an internal combustion engine to extend its cruising range, and to produce the electric power needed to be supplied to its electric motor when the charge level of the vehicle's battery becomes low and reaches a predetermined state of charge (SOC). This paper provides a better solution by replacing the internal combustion engine of a PHEV with a small-size photovoltaic (PV) module located on the roof of the PHEV, and a micro wind turbine located in front of the PHEV, behind the condenser of the air conditioning system. Thus, this study proposes a novel battery/PV/wind hybrid power source to be utilized in PHEVs. The power source equipped with vehicle-to-grid (V2G) technology is composed of a 19.2-kWh Lithium (Li)-ion battery used as the main energy storage device, and a PV module and a wind energy conversion system. A prototype of the battery/PV/wind hybrid power source has been constructed and utilized in a PHEV. Experimental verifications are presented that demonstrate utilizing the PV module and micro wind turbine adds 19.6 km to the cruising range of a PHEV with the weight of 1880 kg during two sunny days, and provides higher power efficiency (91.2%) and speed (121 km/h). Highly accurate dc-link voltage regulation and producing an appropriate three-phase stator current for the traction motor by using pulse width modulation technique are the other contributions of this paper. [ABSTRACT FROM AUTHOR]

This paper devises an innovative mesoscale electrothermal model for Li-ion batteries. This model manipulates the mesoscale calculation grid in finite element analysis as independent small cell sandwiches and establishes a lumped equivalent circuit model for each cell sandwich. Then, such electrical models are arranged in parallel to form a multilayer equivalent circuit to simulate electrical characteristics of a whole battery, through capturing the current and terminal voltage of each constituent cell sandwich. This modeling idea overcomes the entrenched disadvantage of heat generation models with lumped parameters, i.e., the unavailability of heat generation distribution inside a battery. Besides the current and terminal voltage, the temperature and state of charge dependent open-circuit voltage and entropy coefficient are incorporated into a Newman's heat generation model to estimate the heat generated in the calculation grid. The battery temperature distribution is eventually derived by solving the heat conduction equation with thermal conductivity as a function of the battery temperature. We leverage the developed electrothermal model to track the temperature evolution of an 18 650 Li-ion battery at different ambient temperatures and discharge rates, for the first time. Experimental results demonstrate that the electrothermal model can precisely emulate the battery thermal dynamics with an average error of 0.72 °C. Moreover, a comparative study shows that the proposed model outperforms common resistance-based thermal models that do not consider the heat generation distribution and the interdependence between the battery temperature and thermal conductivity. [ABSTRACT FROM AUTHOR]

This paper proposes a highly effective voltage cell equalization method for lithium-ion (Li-ion) battery management systems (BMSs) for several applications, such as nearly zero energy buildings, microgrids, and electric vehicles. The concept of the suggested method is the proper control of the charging current of each cell of a battery stack through the suitable regulation of the gate source of each cell's parallel-connected mosfet. Thus, the mosfet can act as a controllable current source for providing the proper equalization current according to the specific needs of each battery cell. The correct voltage level of the gate-source of each mosfet is determined by a cell equalization controller through the comparison of the performance of each cell of a battery stack with the healthier cell, which is detected by an aging estimation algorithm based on the evaluation of the internal resistor and the capacity fade of each cell. Therefore, smoother and faster cell equalization is achieved compared to the conventional dissipative method. The practicality and the high effectiveness of the proposed cell equalization technique have been experimentally validated. Several experimental results are presented to demonstrate the operational improvements of the proposed cell equalization technique against the conventional one. [ABSTRACT FROM AUTHOR]

Lithium iron phosphate battery packs are widely employed for energy storage in electrified vehicles and power grids. However, their flat voltage curves rendering the weakly observable state of charge are a critical stumbling block for charge equalization management. This paper focuses on the real-time active balancing of series-connected lithium iron phosphate batteries. In the absence of accurate in situ state information in the voltage plateau, a balancing current ratio (BCR) based algorithm is proposed for battery balancing. Then, BCR-based and voltage-based algorithms are fused, responsible for the balancing task within and beyond the voltage plateau, respectively. The balancing process is formulated as a batch-based run-to-run control problem, as the first time in the research area of battery management. The control algorithm acts in two timescales, including timewise control within each batch run and batchwise control at the end of each batch. Hardware-in-the-loop experiments demonstrate that the proposed balancing algorithm is able to release 97.1% of the theoretical capacity and can improve the capacity utilization by 5.7% from its benchmarking algorithm. Furthermore, the proposed algorithm can be coded in C language with the binary code in 118 328 bytes only and, thus, is readily implementable in real time. [ABSTRACT FROM AUTHOR]

In this paper, a battery balancing circuit is proposed for the series-connected lithium-ion battery cells based on the principle of synchronous rectification. The proposed balancing circuit, also referred to as an equalizer, mainly includes a buck–boost converter (BBC), a multiport half-bridge converter (MHBC), and a driving circuit. The MHBC is coupled with a multiwinding transformer. Compared with the conventional congeneric methods, the number of transformer windings is almost reduced by half, leading to a more compact size and lower cost. Moreover, the secondary mosfets of the MHBC are synchronously driven by the primary half-bridge converter (HBC) without the need of additional isolated mosfet gate drivers and power supplies, dramatically reducing the circuit cost and complexity. In addition, the proposed equalizer can realize the module-to-multi-cell (M2MC) equalization under severe imbalance conditions to improve the balancing speed, and work at the any-cell-to-any-cell (AC2AC) self-balancing mode under slight imbalance conditions to improve the balancing efficiency and effectiveness, which achieves a good trade-off between balancing speed and effectiveness. The expressions of the equalization current and efficiency are derived and verified by experimental results. The proposed equalizer is experimentally evaluated for a string with 12 series-connected lithium-ion cells. [ABSTRACT FROM AUTHOR]

In electric vehicles, a battery management system highly relies on the measured current, voltage, and temperature to accurately estimate state of charge (SOC) and state of health. Thus, the normal operation of current, voltage, and temperature sensors is of great importance to protect batteries from running outside their safe operating area. In this paper, a simple and effective model-based sensor fault diagnosis scheme is developed to detect and isolate the fault of a current or voltage sensor for a series-connected lithium-ion battery pack. The difference between the true SOC and estimated SOC of each cell in the pack is defined as a residual to determine the occurrence of the fault. The true SOC is calculated by the coulomb counting method and the estimated SOC is obtained by the recursive least squares and unscented Kalman filter joint estimation method. In addition, the difference between the capacity used in SOC estimation and the estimated capacity based on the ratio of the accumulated charge to the SOC difference at two nonadjacent sampling times can also be defined as a residual for fault diagnosis. The temperature sensor which is assumed to be fault-free is used to distinguish the fault of a current or voltage sensor from the fault of a battery cell. Then, the faulty current or voltage sensor can be isolated by comparing the residual and the predefined threshold of each cell in the pack. The experimental and simulation results validate the effectiveness of the proposed sensor fault diagnosis scheme. [ABSTRACT FROM AUTHOR]

This paper proposes a battery simulator (BS) based on a Z-source rectifier (ZSR), with the intention of emulating the discharge or charge characteristic of an actual lithium-polymer battery with high voltage and large capacity. The proposed BS is used for power testing for battery applications. The battery model, combined with a Shepherd model and a Thevenin model, is adopted to freely change the properties and specifications of the battery and to replicate the dynamic behavior of the battery, which is discretized to utilize the digital controller of the BS. The closed-loop voltage controller at the dc side of the ZSR is designed to emulate the rapid dynamic characteristics of the battery based on small-signal methods, considering the influence of the components of the impedance network. In this paper, battery voltage control algorithm (BVCA) is also utilized to minimize the voltage stress across switches while controlling two dc-side voltages within a wide range of output voltages. Simulation and experimental results are provided to verify the BS of the new feature and the proposed control method. [ABSTRACT FROM AUTHOR]

With the rapid proliferation of cloud computing, the energy cost of datacenters and the impact of reactive power on the grid have become major concerns. This paper presents two energy management control schemes for distributed uninterruptible power supply (UPS) architectures utilizing lithium-ion ultracapacitors (LIC) for improved system efficiency and reactive power mitigation. One scheme is proposed for low-power servers with an internal dc bus, while another is proposed for medium-to-high-power server racks with an in-rack dc bus. The LIC and the dc bus interface with a bidirectional dc–dc converter, which allows the power supply unit to run in the optimal operating region for the improved system efficiency and power factor. The server-level UPS architecture is experimentally tested using a 200-kHz, bidirectional, multiphase dc–dc converter with hysteretic current-mode control, while achieving 33% reactive power mitigation. Based on the SciNet datacenter in Toronto, ON, Canada, a rack-level distributed UPS architecture is built in MATLAB, and system-level simulations indicate a 37% reduction in the reactive power. [ABSTRACT FROM AUTHOR]

Online State of Charge (SoC) and State of Health (SoH) estimations are essential for efficient, safe, and reliable operation of Lithium ion batteries. Based on the first-order equivalent-circuit model (ECM), a multi-scale extended Kalman filter is adopted in this paper to estimate ECM parameters and battery SoC using dual time scales. The nature of the battery excitations significantly influences the estimation performance. When the input–output data, i.e., the input current and output voltage, is insufficiently rich in frequency content, the estimation performance is poor. Thus, the excitation current should be optimized for the accurate estimation of parameters and states. A Cramer–Rao bound analysis is conducted considering voltage noise, current amplitude, and current frequency, which shows the loss of accuracy in multi-parameter estimation (estimating all states and parameters) when compared to single-parameter estimation (estimating only one parameter/state). However, it also shows that the loss of accuracy can be significantly reduced when the excitation current is carefully chosen to satisfy certain criteria. Both simulation and experimental results verify the analysis results and show that a current profile with optimal frequency components achieves the best estimation performance, thereby, providing guidelines for designing battery current profiles for improved SoC and SoH estimation performance. [ABSTRACT FROM AUTHOR]

The prognosis and health management of lithium-ion batteries are extremely important issues for operating performance as well as the cost of energy storage systems in vehicular applications. This is achieved through the estimation of the state-of-health and the prediction of remaining useful life (RUL). This paper presents a lithium battery prognosis model considering the battery-aging conditions. The proposed model is developed based on the Rao-Blackwellization particle filter, which is able to estimate the posterior values of the aging indicators, i.e., capacity and resistance, and to predict the RUL. The particularity of the proposed model is that it considers the aging conditions of batteries as inputs of the prognosis model. In order to validate the proposed method, experiments have been carried out under different aging conditions for three types of lithium-ion batteries. The proposed model performances have been evaluated. A comparison against the particle filter prognosis model is presented. Results highlight the effectiveness of the proposed technique to predict the RUL for different cases: initial conditions, types of lithium-ion batteries, and aging conditions. The RUL prediction using the proposed prognosis model presents a maximum relative error of 6.64%, which is low compared to 14.3% when a simple particle filter prognosis model is used. [ABSTRACT FROM AUTHOR]

The accurate state of charge (SOC) estimation plays a significant role in charge/discharge control, balance control, and safe management of lithium-ion batteries (LIBs). However, due to the model mismatch issues, either from battery inconsistency or battery dynamic characteristics difference, the accuracy of the model-based SOC estimation method is usually unsatisfactory. To solve this problem, a joint moving horizon estimation (joint-MHE) approach that can simultaneously estimate the model parameter and state is proposed here. In this paper, the circuit-equivalent battery model is first constructed by parameterizing the circuit parameters as polynomial function of SOC. Then, by the sensitivity analysis, the update parameters are selected and added to the state-space model as additional states. Finally, the joint-MHE strategy is conducted for the simultaneous parameter and SOC estimation. To investigate the performance of the proposed method thoroughly, three model mismatch conditions are considered, including battery inconsistency, battery dynamic characteristics difference, and the combination of both. The results demonstrate that the joint-MHE approach is an effective way to solve the model mismatch problem. Moreover, compared to joint extended Kalman filtering, the proposed approach can offer a more reliable, robust, and accurate SOC estimation of LIBs under various model mismatch conditions. [ABSTRACT FROM AUTHOR]

This paper outlines a battery charging strategy to reduce charging losses in a lithium-ion battery for electric vehicles. The proposed charging strategy utilizes an adaptive current profile based on variations of the battery internal resistance as a function of the state of charge and the charge rate. To address the problem of finding the optimal current set for the proposed strategy, an evolutionary algorithm, which is a type of stochastic approach, is applied. A strategy for selecting the optimal number of charging intervals is also presented to reach a compromise between loss reduction and computational burden. Experimental results obtained using 34-Ah lithium-nickel-manganese-cobalt-oxide battery cells have proved that the proposed charging strategy decreases the charging loss of the battery cell by 40.1% compared with a conventional constant-current charging strategy. Furthermore, a 3.3-kW on-board charger prototype has been built to investigate the total loss reduction in an electric vehicle charging system that includes a 12-kWh battery pack. The proposed adaptive-current charging strategy reduces the total charging losses including both battery loss and charger loss of electric vehicles by 7.2%, 11.2%, and 21.2% in charging systems with power ratings of 3.3 kW, 6.6 kW, and 13.2 kW, respectively. These improvements can have the same effect as increasing the charger efficiency from a minimum of 0.50% to a maximum of 3.72% in our analysis range of 3.3–52.8 kW. [ABSTRACT FROM AUTHOR]

Lifetime of energy storage systems is a key factor that is extremely influenced by the operating conditions. For this reason, lithium-ion batteries (LiBs) and supercapacitors (SCs) were subjected to accelerated aging tests in several previous research in order analyze their lifespan. Lithium-ion capacitors (LiCs), which fall in between LiBs and SCs, are still considered as a novel technology. Their behavior during accelerated aging tests is not yet well studied in the literature. This paper focuses on studying the degradation of their properties during floating aging. Eighteen samples were tested under three different voltage values and two different temperatures over 12 months. Cells that were discharged to the minimum voltage showed a severe capacitance decrease that was much higher than the one of fully charged cells. The best storage voltage of LiCs was found to be 3 V, which is equivalent to a half charging state. The hybrid structure of LiCs was found to be the major cause of this change in behavior during aging at different voltages. Mechanisms that affect the electrodes and the internal composition of the cells in the diverse conditions were analyzed and predicted. [ABSTRACT FROM AUTHOR]

Voltages of series-connected batteries gradually become imbalanced due to nonuniformity in terms of not only battery characteristics but also self-discharge rate that is significantly dependent on temperature. In large-scale energy storage systems, a large temperature gradient is very likely because of its huge geometry, and therefore, equalizers capable of relatively large equalization currents would be necessary to eliminate voltage imbalance originating from uneven temperature distribution. A two-switch string-to-battery voltage equalizer using a half-bridge converter with multistacked current doublers (MSCDs) is proposed for series-connected batteries in this paper. The proposed equalizer is capable of providing relatively large equalization currents without increasing ripple currents thanks to the interleaved operation of the MSCDs. Fundamental operational analysis for a discontinuous conduction mode, in which currents in the equalizer can be limited to desired levels without feedback control, is performed. The experimental results of equalization tests performed for four supercapacitor modules and lithium-ion batteries connected in series demonstrated the equalization performance of the proposed equalizer. [ABSTRACT FROM AUTHOR]

Wireless charger for electric vehicles (EVs) is an offline application and it needs power factor correction (PFC) function, which usually consists of a front-end boost PFC and a cascaded dc–dc converter. Z-source resonant converter (ZSRC), a single-stage solution with low cost and high efficiency, was proposed for EV wireless charger lately. The Z-source capacitors in the ZSRC are designed to absorb the double-line frequency ripple in this single-phase application. Sinusoidal charging, which allows the double-line frequency ripple propagate to the output, is another solution aiming at reducing the bulky capacitors. Recently, a comparison of low-frequency (120 Hz) sinusoidal charging and dc charging shows a negligible impact on Li-ion batteries’ performance. Therefore, the ZSRC's capacitor, the biggest component, can be reduced dramatically from millifarad to several microfarads with a sinusoidal charging technique, which features the ZSRC high power density. Also, it keeps the Z-source's benefit of boost ability and being immune to shoot-through problems. In this paper, the sinusoidal charging behavior for the ZSRC is modeled, and a control scheme that has both PFC function and load regulation for sinusoidal charging is proposed. This control scheme can pass IEC61000-3-2 Class A criterion. Experimental results based on a 1-kW prototype with 20 cm air gap between the primary and secondary side are presented to illustrate the proposed control scheme. [ABSTRACT FROM AUTHOR]

Accurate battery power capability prediction can contribute to reliable and sufficient utilization of the battery to absorb or deliver a certain amount of power within its safe operating area. The power capability of a battery is a finite quantity that is limited by the electrochemical reaction properties occurring inside the battery. Note that the instantaneous available power of the battery is strongly related to the surface lithium concentration of solid particles in battery electrodes, but their relationship has not been explored sufficiently yet. This paper proposes a novel method for battery instantaneous available power prediction using a practical physical limit (i.e., lithium concentration limit) rather than the limits of macroscopically observed variables, such as the cell terminal voltage and current, thus providing a direct insight into electrochemical processes inside batteries. The surface lithium concentration of the solid particle is derived from a simplified battery electrochemical model, and a relationship between battery instantaneous available power and surface lithium concentration is quantified for the power capability prediction. Promising results with small forecast errors can be achieved for battery charging and discharging at different cell aging levels and ambient temperatures, which highlights the superior accuracy and robustness of the proposed method. [ABSTRACT FROM AUTHOR]

This paper presents a method for evaluating the performance of duty cycle balancing schemes and conventional energy redistribution active balancing schemes using a common linear programming framework. The framework is used to calculate the maximum usable capacity of a battery pack composed of cells of varying capacity coupled to a balancing circuit of a specified type and size. In the duty cycle balancing case, the effect of cell redundancy for packs with dc and ac outputs is explored. In the energy redistribution case, the balancing performance of different circuit topologies with varying ratings is evaluated. An experimental validation of the numerical prediction for the duty cycle balancing method is conducted for a pack of 12 cells, where the duty cycle of each cell is controlled using a full-bridge circuit. In all cases, the numerical and experimental results show an agreement in usable capacity to within 1%. The experimental results indicate that for a duty cycle balanced pack constructed from cells with an extreme capacity range (where variation between cells is as large as the average cell capacity), the inclusion of two redundant cells in a 12 cell pack enables the extraction of 95% more capacity than in the case of no redundancy. [ABSTRACT FROM AUTHOR]

Effective battery voltage regulation is fundamental to extend battery lifetime and to avoid overvoltage. However, the design of this regulation is complicated due to the wide battery impedance range, which, when dealing with universal chargers, is dependent not only on the operating point but also on the battery type and size. This paper first shows how the voltage response becomes highly variable when designing the controller as described in the literature. Then, it proposes to emulate virtual impedance in parallel with the battery, making it possible to achieve a voltage control which is independent of battery characteristics. Experimental results are carried out for a new lithium-ion battery with 25 mΩ impedance and an overused lead-acid battery with 400 mΩ impedance. For this large impedance variation, the results evidence the problems of the conventional control and validate the superior performance of the proposed control. [ABSTRACT FROM AUTHOR]

This paper presents a sinusoidal ripple current charging algorithm based on embedded impedance measurements. Existing battery charging strategies typically do not take into account the electrochemical properties of batteries, because these factors are difficult to obtain during charging operation. Factors of concern include lithium plating, growth of a solid electrolyte interphase, limited exchange current, and slow diffusion rates. It is beneficial to utilize these parameters during charging operation, because the charging current can adapt to the time-varying characteristics of a battery. Consequently, battery life cycle, charging speed, and charging efficiency all improve. In this paper, rigorous analysis of electrochemical characteristics is performed and a method for minimization of variations of charge transfer impedance is explained based on a sinusoidal ripple current charging algorithm. To obtain the optimal ripple current frequency, ac impedance analysis based on the dq transformation method is proposed. As a result, this method improved charging efficiency and reduced lithium plating by activation polarization. Simulation and experimental results using a 14.6-V LiFeMgPO4 battery are used to validate and demonstrate the performance of the proposed control scheme. Based on the proposed control scheme, the charging time and efficiency of the Li-ion battery are improved by 5.1% and 5.6%, respectively. [ABSTRACT FROM AUTHOR]

Among the various cell balancing circuits for series-connected batteries, the bidirectional cell-to-cell balancing structure using two switches per cell shows good balancing ability. However, an increase in the number of switches leads to an increase in both cost and size. To reduce the number of switches, this paper proposes a new cell-to-cell balancing circuit with a center-cell concentration structure. The proposed circuit collects the charges of an overcharged cell into the center cell, and then the collected charges are redistributed to the other cells. The proposed circuit has a unidirectional balancing structure with single switch per cell. However, it can achieve competitive balancing ability when compared with the bidirectional structure. In this paper, the operational principles of the proposed circuit are analyzed, and a comparison between the conventional and proposed circuits is shown. To verify the validity of the proposed circuit, experiments with 15.5-Ah batteries are carried out, and the experimental results demonstrate the improved cell balancing ability although a single switch is used per cell. [ABSTRACT FROM AUTHOR]

Conventional implementations of fully integrated, battery-connected, switched-capacitor voltage regulators (SCVRs) require either thick-oxide mosfets or stacked thin-oxide mosfets as power switches to sustain the voltage stress induced by a nominal 3.7-V Li-ion battery voltage. These approaches, however, exacerbate power loss, thus unable to achieve good power efficiency. Therefore, this paper proposes a solution to overcome the breakdown issue while improving the power efficiency by using only nonstacked, thin-oxide mosfets. This is realized by using a three-state, low-voltage-stress SCVR with a cross-phase-switching technique to decrease the output impedance and increase the total equivalent capacitance in a multiphase configuration. A prototype 3:1 SCVR is implemented fully on-chip in a standard 130-nm CMOS process. The chip is capable of delivering a maximum load current of 45 mA with an input voltage range from 3.2 to 4 V. Measurement results show 78–80% efficiency over a range of output power 4–28 mW, and a power density up to 38 mW/nF. The measured output ripple is 30–50 mV over a load range of 11–45 mA, and the measured voltage droop is 69 mV with 200-ns settling time under a 13-mA load step. [ABSTRACT FROM AUTHOR]

This paper presents a hierarchical balancing algorithm for use in large-scale reconfigurable ac battery packs. Using a decentralized battery management system, the pack is organized in control layers with each layer controller responsible for a small number of slave controllers, thereby significantly reducing communication and centralized processing requirements. The hierarchical balancing algorithm uses all available voltage steps in the pack ensuring a high-quality sinusoidal output voltage while balancing the objects of different layers. Balancing priority can be swapped dynamically between layers according to the maximum state of charge (SoC) variation between the objects of each layer while also ensuring that the output voltage reference is always met even when a cell failure occurs, as long as there are an adequate number of cells available in the pack. An experimental demonstration of the proposed balancing algorithm is presented using an ac battery pack comprising 144 20-Ah lithium–titanate cells. Cell balancing to within 2 mV of the cell open-circuit voltage is achieved between cells with 20% initial SoC variation and 5% capacity difference. [ABSTRACT FROM PUBLISHER]

The integration of energy storage systems (ESSs) in contemporary applications highly depends on the performance of these devices. Supplying high power for a reasonable period of time is one of their main targets in several applications like backup systems and transport technologies. For this purpose, lithium-ion capacitors (LICs) would demonstrate better suitability than conventional ESSs for applications requiring a small installation space and a long lifetime. They are known for their energy density greater than that of supercapacitors and their power density greater than that of lithium-ion batteries. This paper explains the electrochemical processes that interfere in the storage of energy inside an LIC. The analysis of these phenomena was the tool for assessing the nonlinear capacitance evolution of the LIC with respect to its voltage. Several measurement techniques in the frequency and time domains were elaborated and compared in order to assess this nonlinear behavior of the LIC. Some of the measurement protocols contained constant voltage phases that had a significant effect on the variation of the capacitance. The novelty of this study concerns the introduction of a new measurement protocol that takes into account the particular characteristics of LICs. Their unique behavior is explained for the first time based on a physicochemical analysis. [ABSTRACT FROM PUBLISHER]

The technique of wireless power transfer (WPT) via magnetic coupling resonance provides a way to transfer power wirelessly to cardiac pacemakers from external source. For wireless charging system to be used in clinical environment, this paper gives priority consideration to three technical difficulties, i.e., implantation, efficiency, and safety. The LCC-C compensation topology for pacemaker wireless charger is presented, where only one secondary side resonance capacitor needs to be implanted, and resonance compensation parameters are derived. The compensation network can make the WPT system operate at stable resonance and high efficiency. The prototype of the wireless charging system for implantable cardiac pacemaker is developed, where a thin flexible receiving unit was designed to effectively shield eddy currents in the pacemaker shell. The experiments of wireless charging through pork tissues reveal that 3.072-W power can be received from a 3.919-W power source at 300 kHz, reaching a rather high WPT efficiency of 78.4%, such that the charging is fast, i.e., the 1050 mA·h, 4.2-V Li-ion battery voltage increases from 3.98 (80% residual capacity) to 4.2 V within only 27 min, and only 3.3 °C maximum temperature rise of the pork is in safe limits. The feasibility and safety of the charging system were further evaluated by simulations of specific absorption rate and temperature rise in human tissues and electromagnetic fields in the pacemaker case. [ABSTRACT FROM AUTHOR]

A cell voltage equalizer circuit for future plug-in hybrid electric vehicles (PHEV) or renewable energy storage is proposed in this paper. This topology has fewer passive components compared to the conventional topologies found in the literature, and therefore, it could reduce implementation complexity. This circuit is based on a time shared flyback converter, and any number of series connected cells in a string could be used without any apparent issues ensuring good modular architecture. Each cell in a module shares a single converter during its allocated time slot allocated by a low-power microcontroller. In addition, dynamic allocation of time slots is possible to achieve a faster cell balancing, and the circuit dynamically distributes depleted charge among the cells in a regenerative fashion. The operating principles and design procedures of the proposed topology have been presented in the paper. The prototype of a four-cell lithium-ion battery balancer circuit with the proposed topology has been constructed, and the test results have been included. [ABSTRACT FROM AUTHOR]

This paper proposes a hierarchical active balancing architecture for the series-connected lithium-ion batteries. The key point of the architecture is that by grouping the battery string into different packs and introducing the top layer, the coupled influence among the cells in different packs is eliminated, which reduces the required balancing time and the energy loss. The repeated charging and discharging problem is avoided, which is beneficial for increasing the state-of-health. Moreover, the proposed architecture can lower the current rating of the balancing circuits, which helps decrease the required cost and improve the system efficiency. On the basis of the architecture, a balancing control using the state-of-charge of each cell is proposed to achieve the balance for all the cells. Furthermore, to deliver the energy from one pack to any other pack bidirectionally, a multidirectional multiport converter along with the current control method is proposed to serve as the top layer. This converter is different from the conventional three-port converter as it can achieve the arbitrary current flow direction control for any number of ports. The experimental results based on 24 series-connected 200-Ah lithium-ion batteries verified the benefits of the proposed architecture and the balancing circuits. After balancing, 4.1% of the total energy of the battery string is saved. Compared to the conventional adjacent cell-to-cell architecture, the proposed architecture can decrease the balancing time and the energy loss during the balancing process by 27.6% and 44.0%, respectively. In addition, the current rating and the cost of the balancing circuits in the proposed architecture is only 37.5% and 11.5% of that in other references. [ABSTRACT FROM AUTHOR]

Electric-drive vehicles, including hybrid, plug-in hybrid, and electric vehicles, require a high-voltage (HV) battery pack for propulsion and a low-voltage (LV) dc bus for auxiliary loads. This paper presents an architecture that uses modular dc–dc bypass converters to perform active battery cell balancing and to supply current to auxiliary loads, eliminating the need for a separate HV-to-LV high step-down dc–dc converter. The modular architecture, which achieves continuous balancing of all cells, can be used with an arbitrary number of cells in series, requires no control communication between converters, and naturally shares the auxiliary load current according to the relative state-of-charge (SOC) and capacities of the battery cells. Design and control details are provided for LV low-power dual active bridge (DAB) power converters serving as the bypass converter modules. Furthermore, current sharing is examined and worst-case SOC and current deviations are derived for mismatches in cell capacities, SOCs, and parasitic resistances. Experimental results are presented for a system consisting of 21 series 25 Ah Panasonic lithium-ion NMC battery cells and 21 DAB bypass converters, with combined outputs rated to supply a 650-W auxiliary load. [ABSTRACT FROM PUBLISHER]

In lithium-ion battery system for hybrid electric vehicle, charge equalizer is essential to enhance the battery life cycle and safety. However, for a large number of battery cells, a conventional equalizer has the difficulty of individual cell balancing and the implementation size problem as well as the cost. Moreover, it shows high voltage stress of electrical elements in the equalization converter due to the high voltage of battery pack. To improve these drawbacks, this paper proposes a modularized two-stage charge equalizer with cell selection switches. The proposed circuit employs the two-stage dc-dc converter to reduce the voltage stress of equalization converter. Contrary to conventional method, the proposed equalizer can achieve the individual cell balancing only through the cell selection switches. With the two-stage converter and the cell selection switches, the proposed equalizer leads to the great size reduction with lower cost which brings advancement of individual cell balancing in a large number of battery cells. In this paper, a prototype for 88 lithium-ion battery cells is optimally designed and implemented. Experimental results are presented to verify that the proposed equalization method has a good cell balancing performance showing the low voltage stress and small size with the lower cost. [ABSTRACT FROM AUTHOR]

This paper describes the design and performance of a 6-kW, full-bridge, bidirectional isolated dc-dc converter using a 20-kHz transformer for a 53.2-V, 2-kWh lithium-ion (Li-ion) battery energy storage system. The dc voltage at the high-voltage side is controlled from 305 to 355 V, as the battery voltage at the low-voltage side (LVS) varies from 50 to 59 V. The maximal efficiency of the dc-dc converter is measured to be 96.0% during battery charging, and 96.9% during battery discharging. Moreover, this paper analyzes the effect of unavoidable dc-bias currents on the magnetic-flux saturation of the transformer. Finally, it provides the dc-dc converter loss breakdown with more focus on the LVS converter. [ABSTRACT FROM AUTHOR]

One important test for the formation and grading of a lithium-ion battery is to confirm the performance of the battery while discharging it down to zero volts. In this paper, a novel soft-switching charge/discharge converter with the zero voltage discharge function is proposed. The proposed converter is able to discharge a battery until its voltage reaches zero volts. The phase-shift full-bridge method is used to charge the battery and the current-fed push–pull method with bidirectional switches is used for the discharge. Zero voltage switching (ZVS) of the switches is achieved at turn-on during the charge operation. ZVS turn-on and zero current switching turn-off of the switches are achieved during the discharge operation. The charge/discharge controllers are designed taking into account the internal impedance of the battery. The performance of the system is verified by the experiments using lithium-ion batteries. [ABSTRACT FROM AUTHOR]

This paper presents a control strategy for the power flow management of a wayside energy storage system based on a supercapacitor technology installed in a tramway network. The control is based on the management in real time of voltage levels at catenary point connections in order to optimize the energy flow among the running tramcars and substations with the goals of improving the energy saving and reducing the voltage drops in the supply network. The suggested control algorithm was experimentally validated using a laboratory-scale model to verify the effectiveness of the strategy. A lithium-ion capacitor module with 72 series-connected laminated cells of the JSR Micro ULTIMO type was used. Thus, an emulation of a real tramway network in the city of Naples (ANM) was implemented to evaluate the potential impact in terms of costs/benefits of the next installation on the ANM network. [ABSTRACT FROM AUTHOR]

State-of-charge (SOC) estimation is an important aspect for modern battery management system. Dynamic and closed loop model-based methods such as extended Kalman filter (EKF) have been extensively used in SOC estimation. However, the EKF suffers from drawbacks such as Jacobian matrix derivation and linearization accuracy. In this paper, a new SOC estimation method based on square root unscented Kalman filter using spherical transform (Sqrt-UKFST) with unit hyper sphere is proposed. The Sqrt-UKFST does not require the linearization for nonlinear model and uses fewer sigma points with spherical transform, which reduces the computational requirement of traditional unscented transform. The square root characteristics improve the numerical properties of state covariance. The proposed method has been experimentally validated. The results are compared with existing SOC estimation methods such as Coulomb counting, portable fuel gauge, and EKF. The proposed method has an absolute root mean square error (RMSE) of 1.42% and an absolute maximum error of 4.96%. These errors are lower than the other three methods. When compared with EKF, it represents 37% and 44% improvement in RMSE and maximum error respectively. Furthermore, the Sqrt-UKFST is less sensitive to parameter variation than EKF and it requires 32% less computational requirement than the regular UKF. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A single charge equalizer using the multi-winding transformer (SCEMT) is useful for the precise and fast equalization. Since this type of equalizer requires voltage sensing circuits for each battery cell, the size and cost of the overall equalizer system increase. In this paper, a novel switching method, which does not require voltage sensing circuits, is proposed for the SCEMT. However, due to the problems related to the implementation of multiwinding in a single transformer, the SCEMT is definitely difficult to apply to long series-connected lithium-ion battery string. In order to overcome these drawbacks, a novel module charge equalizer based on the configuration of the SCEMT is developed. Unlike the conventional module charge equalizer using additional components, the proposed novel module charge equalizer utilizes the magnetizing energy of the multiwinding transformer for the equalization among modules. Therefore, proposed module charge equalizer does not suffer from the size, cost, and loss related to the modularization. The validity of the proposed module charge equalizer is verified through experimental results. [ABSTRACT FROM AUTHOR]

The paper suggests an energy management control strategy of wayside Li-ion capacitor (LiC) based energy storage for light railway vehicles (LRV). The installation of wayside supercapacitor (SC) storage devices, as widely recognized, allows the recovery of the braking energy for increasing the system efficiency as well as a better pantograph voltage profile. A new type of SC, LiC, interfaced with dc-interleaved converter has been presented. This technology has an energy density comparable to batteries and power density much higher than the batteries. The authors propose a control strategy based on the maximum kinetic energy recovery throughout braking operations of the running vehicles. The stored energy comes back to the vehicles during the accelerations. The strategy stays on the knowledge of the state of charge of LiC device and the actual vehicle speeds. In particular, the control algorithm evaluates, in real time, the actual value of LiC voltage and current references on the basis of the vehicles inertial forces and acceleration estimations, taking into account the power losses of the system. Experimental tests made on electromechanical simulator, equipped with a 136-V, 30.5-F LiC module, fully confirm the validity of the suggested control. Finally, experimental characterization of LiC module has been achieved. [ABSTRACT FROM AUTHOR]

This paper proposes a practical capacity fading model for Li-ion cells based on real operating conditions in electric vehicles (EVs). Numerous LiFePO4 cells have been cycled with a current profile containing regenerative braking to determine the capacity fading rate. The cells have been cycled at different temperatures with different initial state of charges, depth of discharges, or C-rates. From the experiments, an empirical model is constructed, which is capable of modeling the capacity fading in EV battery cells under most operating conditions. The capacity fading model can be used to estimate the state of health of EV battery cells, and simple ways to optimize the battery lifetime are proposed. [ABSTRACT FROM AUTHOR]

In the lithium-ion battery systems for electric vehicles (EVs), a battery management system (BMS) is essential for enhancing the battery's life cycle and safety. As a result, a BMS is required to realize both the effective cell monitoring and balancing. Moreover, individual cell balancing and monitoring circuit with a smaller size are required in a large number of battery cells. To meet these requirements, a modularized charge equalizer using the monitoring integrated circuit (IC) is proposed for EV battery strings. The proposed scheme exhibits efficient charge equalization with simple control of the monitoring IC. In the proposed equalizer, the battery string is modularized into a master module and multiple slave modules. A central equalization converter in the master module is shared by all of the battery cells through the module and cell switches in the slave module, instead of a dedicated charge equalizer for each of the cells. Individual charge equalization can be controlled by the cell monitoring IC in the slave module. With this configuration, the battery monitoring and balancing can be effectively merged into one controller. Moreover, the individual charge equalizer can be effectively implemented without affecting the size or cost based on the numbers of cells. In this paper, a prototype for 88 lithium-ion battery cells is optimally designed and implemented. Experimental results verify that the proposed method exhibits outstanding balancing performance with simple operation methods. [ABSTRACT FROM AUTHOR]

This paper describes the comparison and parameterization process of dynamic battery models for cell and system simulation. Three commonly used equivalent circuit battery models are parameterized using a numeric optimization method and basic electrical tests with a lithium-ion polymer battery cell. The maximum model performance is investigated, and the parameterized models are compared regarding the parameterization effort and the model accuracy. For the model with the best tradeoff between the parametrization effort and the model accuracy, a reasonable simplification of the parameterization process is presented. This model is parameterized with the simplified parameterization process and, finally, validated by using a current profile obtained from an electric vehicle simulation performing a real-life driving cycle. [ABSTRACT FROM AUTHOR]

Design of a battery-ultracapacitor semiactive hybrid for powering pulsed current loads is presented in this paper. The semiactive hybrid energy source consists of an ultracapacitor assisted Li-Ion battery, connected to the load via a dc–dc converter. The system is controlled such that the battery is supplying a near-constant current to satisfy the average load demand while the ultracapacitor supplies the dynamic component of the load current. The control algorithm is based on a well-known capacitance-emulating approach. As a result, a high-energy battery can be used despite the high-power load demand spikes. In addition, the battery-load voltage matching is not required and the control algorithm does not require load current sensing. It is shown that the proposed system performance is equivalent to the performance of a passive hybrid, employing a very high nonfeasible capacitance. Moreover, it is revealed that the battery current is independent of the capacitor size, which affects the load voltage ripple only. Extended simulation and experimental results are presented to demonstrate the feasibility of the approach. [ABSTRACT FROM AUTHOR]

In this paper, a new cell-to-cell charge equalization converter using a multiwinding transformer is proposed. The proposed scheme achieves the direct cell-to-cell charge transportation by buck-boost and flyback operation. In this operation, the adjacent two cells share either a current path or a tap of multiwinding transformer. Therefore, the number of windings ia cut in half in comparison to the number of batteries, resulting in a small circuit size. To verify the operation of the proposed charge equalization converter, an experiment with a lithium-ion battery stack is performed. [ABSTRACT FROM AUTHOR]

Differences in electrochemical characteristics among Li-ion batteries result in erroneous state-of-charge (SOC)/capacity estimation and state-of-health (SOH) prediction when using the existing dual extended Kalman filter (DEKF) algorithm. This paper presents a complementary cooperation algorithm based on DEKF combined with pattern recognition as an application Hamming neural network to the identification of suitable battery model parameters for improved SOC/capacity estimation and SOH prediction. Two kinds of pattern such as discharging/charging voltage pattern (DCVP) and capacity pattern (CP) were measured, together with the battery parameters, as representative patterns. Through statistical analysis, the Hamming network is applied for identification of the representative DCVP and CP that most closely matche that of the arbitrary battery to be measured. The model parameters of the representative battery are then applied for SOC/capacity estimation and SOH prediction of the arbitrary battery using the DEKF. This avoids the need for repeated parameter measurement. [ABSTRACT FROM AUTHOR]

Differences in electrochemical characteristics among Li-ion cells inevitably result in state-of-charge (SOC) imbalance when the existing voltage balancing technique is used. This paper presents a new approach based on a screening process for improved voltage/SOC balancing of a Li-ion series battery pack. Two kinds of screening processes, capacity screening and resistance screening, are implemented in an orderly manner. The capacity screening process matches open-circuit voltage (OCV)-SOC relation for achievement of voltage/SOC balancing. In the resistance screening process, pulse-type discharging/charging currents are applied to various SOC points to select the cells with similar voltage variance. Through two screening processes, the cells that have similar electrochemical characteristics are finally selected, and can be used for stable configuration of a Li-ion series battery pack. The proposed screening process has been validated by extensive experimental results and SOC estimation results based on extended Kalman filter. [ABSTRACT FROM AUTHOR]

This paper analyzes two different architectures for a hybrid power source comprising a polymer electrolyte membrane fuel cell and a Li ion battery. The hybrid power source feeds the propulsion motor of an all-electrical aircraft, the Boeing Fuel Cell Demonstrator. Unregulated and regulated hybrid power architectures are examined. The regulation is achieved by means of a controllable series boost converter (SBC) connected in series with the fuel cell. Both architectures have been simulated, implemented, and tested in the Boeing Fuel Cell Demonstrator airplane. [ABSTRACT FROM AUTHOR]

A recent paper by Wang et al. [ibid., vol. 33, no. 10, pp. 8449–8460, Oct. 2018] proposes a state of a charge-dependent polynomial equivalent circuit model for lithium batteries. The model consists of an inductor, a Warburg element, a constant phase element (CPE), and two resistors. The authors quote the impedance equation of a Warburg element, where τ is the diffusion time constant, ϕ varies between 0 and 1, and RW is the Warburg resistance. This equation is wrong; in a Nyquist plot, the angle in a Warburg element is fixed to 45° at high frequencies, corresponding to ϕ = 0.5. Such behavior is a result of diffusion through a semi-infinite medium. The frequency band where it is observed is called the Warburg region. The correct form of the impedance equation of a Warburg element is provided. [ABSTRACT FROM AUTHOR]