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The paper develops two computationally efficient models, namely a detailed equivalent model and an average-value model, with provisions for representation of the critical state of converter blocking, for modular multilevel converters with embedded storage. These models are indispensable in the simulation of dc faults. The developed detailed equivalent model provides accuracy that matches electromagnetic transient (EMT) simulations, with much reduced computational burden; the developed average-value model represents the averaged behavior of the converter by neglecting switching transients. Both models are extensively evaluated in the context of an HVDC system against benchmark results form a detailed switching model developed in PSCAD/EMTDC. The results confirm the validity and accuracy of the models for steady state, transient, and faulted operating conditions including when the converter is blocked in response to a dc fault. [ABSTRACT FROM AUTHOR]

This article presents a single stage isolated bidirectional DC–DC converter comprising of LCL-T resonant network for universal electric vehicle (EV) charging. Fixed frequency operation along with phase-shift control enables easier design of passive components, while achieving high efficiency across wide output voltage range. Furthermore, to increase the switching frequency and consequently the power density, gallium nitride (GaN) switches are explored in the proposed solution. In order to facilitate use of commercially available 650 V GaN transistors, a multi-level inverter and a reconfigurable rectifier architecture is utilized along with LCL-T resonant network, accommodating an input voltage of 800 V, generated from an universal three phase ac input supply, and an output voltage ranging from 150 V to 950 V catering to large variation of battery voltages from different vehicle manufacturers. The constant input voltage-to-output current gain property of LCL-T network, along with an efficient phase-shift modulation proposed in this paper enable soft switching of all transistors with minimum circulating currents over constant current (CC), constant power (CP), and constant voltage (CV) modes of battery charging. Experimental results are provided for a single-phase DC–DC converter prototype utilizing 650 V GaN transistors operating from an 800 V DC bus and providing a very wide output voltage from 150 V to 950 V at 6.6 kW maximum power at a constant switching frequency of 500 kHz. The prototype achieves two peak efficiency points of 98.2% and maintains $>$ 97% efficiency across the entire output voltage range at a power density of 120 W/in3 (7.3 kW/L). [ABSTRACT FROM AUTHOR]

A high efficiency and a constant voltage at the output stage are among the major concerns in wireless charging of dynamic electric vehicles. They are usually achieved by additional converters or asymmetric switching which suffer from high cost and hard switching. To overcome these drawbacks, a variable-frequency retuning approach is proposed in this paper with LCL-Series compensation. As opposed to conventional control methods with resonance frequency as target operating frequency, this approach uses a new optimum frequency which enables ZVS. Also, it minimizes the conduction loss of the inverter switches in a wide range of load and coupling coefficients. In addition, it improves the total system efficiency up to 6% together with an increase in the power transfer capability. Using the proposed method, both sides’ currents increases up to 45% depending on the load. To find the optimum frequency in a system without resonant parameter information, an on-line maximum efficiency search method based on Perturb and Observe is employed. Extensive simulation results using PLECS, together with experimental results from a laboratory setup are presented to confirm the effectiveness of the proposed method under varying load and coupling. [ABSTRACT FROM AUTHOR]

With the advancements of the battery energy storage systems (BESSs), reduction of their manufacturing costs and government subsidies, the BESS uptake is likely to increase rapidly in power distribution networks. This paper investigates the effects of residential BESSs on low-voltage (LV) networks using the actual household load profiles equipped with BESS and solar-photovoltaic (PV) systems. The electricity consumption data collected via smart meters (2200 households with PV/BESS, 1950 households with PV only and 1000 households without a PV or a BESS) at different solar-PV penetration levels and network types are used to simulate real network operating scenarios. A real LV distribution network in Australia is analysed in DIgSILENT PowerFactory under different scenarios, such as, customers with and without a solar-PV/BESS, with a solar-PV but without a BESS, and without a solar-PV, by using both the power flow and quasi-dynamic simulation studies under balanced and the unbalanced network loading conditions. According to the study, customers experience large voltage excursions from solar-PV power exports, which could be resolved by the household BESS, provided that the BESS charging is coordinated with the solar-PV production. Moreover, quasi-dynamic simulation shows that the BESS could reduce the violation of the over-voltage limit during the solar peak hours (midday) by lowering the worst-case feeder voltage by 3%. Finally, extreme-event (high solar PV generation scenario) simulation shows that the implementation of the BESS controller to facilitate charging BESS during afternoon solar-PV export may reduce the negative grid impact and will assist to avoid network upgrades. [ABSTRACT FROM AUTHOR]

This paper presents a hybrid load-shift keying (LSK) modulation for a load-insensitive back telemetry system to realize near-constant voltage changes in a primary coil (L1) against a wide range of load variations. The hybrid-LSK-enabled full-wave rectifier enables the sequential combination of open- and short-coil functions for hybrid-LSK modulation in addition to wireless power conversion operation. Load-insensitive L1 voltage changes can be demodulated using the proposed slope- based demodulator, which utilizes the threshold slope of L1 voltage changes over the back data pulse width, enabling robust data recovery regardless of the load conditions. The 0.56-mm2 0.18-μm standard CMOS hybrid-LSK prototype demonstrated that the variation of L1 voltage changes could be minimized to 60 mV under load changes between 50 Ω and 50 kΩ at coil separation distance of 10 mm, achieving 88.2% reduction compared to the conventional short-coil LSK with 510 mV variation. The proposed back telemetry system also achieved a bit error rate (BER) of < 9.1 × 10−10 under load ranges from 50 Ω to 50 kΩ and data rate of 1 Mbps, ensuring reliable back data recovery against load variations. [ABSTRACT FROM AUTHOR]

Lithium-ion batteries have been widely applied in energy conversion sectors, where effective future ageing prediction is crucial to guarantee their safety and performance. Due to the highly nonlinear ageing behaviours, developing a reliable method that could not only consider the knee point effect but also predict the future ageing trajectory with uncertainty quantification poses a formidable task. This paper derives a machine learning solution, based on the migrated Gaussian process regression (GPR), for predicting future battery two-stage ageing trajectory. Specifically, a base model is first offline identified from the easier collected accelerated-speed ageing data, through which the long life ageing information can be effectively learned. With this base model, a migrated mean function is then designed and coupled within the GPR framework for battery ageing predictions. Experimental data from three different batteries are applied for model validation and performance evaluation. Results indicate that the proposed solution leads to effective improvements in prediction accuracy and uncertainty quantification for both cases of training before and after the knee point. This is the first time to couple migration concept within GPR, paving the way to reduce experimental cost and predict battery future two-stage ageing trajectory with only a few (first 30%) data available. [ABSTRACT FROM AUTHOR]

The use of multiple low-power fuel cells (FCs), instead of a high-power one, in the powertrain of a FC-hybrid electric vehicle (FC-HEV) has recently received considerable attention. This is mainly due to the fact that this configuration can lead to higher efficiency, durability, and reliability. However, the added degrees of freedom require an advanced multi-agent energy management strategy (EMS) for an effective power distribution among power sources. This paper puts forward an EMS based on game theory (GT) for a multi-stack FC-HEV with three FCs and a battery pack. GT is a well-approved method for characterizing the interactions in multi-agent systems. Unlike the other strategies, the proposed EMS is equipped with an online identification system to constantly update the time-varying characteristics of the power sources. The performance of the suggested strategy is investigated through two case studies. Firstly, a comparative study with two other EMSs, dynamic programming (offline), and a competent rule-based strategy (online), is conducted to realize the capability of GT. Secondly, to justify the necessity of online system identification, the degradation effect of each power source on the EMS performance is examined. The carried-out studies show that the total cost (hydrogen consumption and degradation) of the proposed strategy is almost 6% better than the rule-based EMS while keeping a reasonable difference with dynamic programming. Moreover, health unawareness of power sources can increase the hydrogen consumption up to 7% in the studied system. [ABSTRACT FROM AUTHOR]

Wireless charging devices for implantable cardiac pacemakers have not been clinically applied. For actual applications, safety assessments of a wireless charging system must be conducted. For systems with a certain power, frequency is one of the important factors that directly affect safety. This paper aims to study the safety evaluation method and optimal operation frequency of a cardiac pacemaker wireless charging system. The wireless power transfer (WPT) model considering the coils’ AC resistance is established, which is more in line with the actual situation. The analytical solution to the current in coupling coils is derived, which reveals the effect of the frequency. The currents used in electromagnetic and thermal simulations are calculated or measured for different charging prototypes. A safety evaluation method that comprehensively considers specific absorption rate (SAR), electric field, efficiency, temperature rise and electromagnetic interference (EMI) is proposed. In particular, the temperature rise is an innovative perspective as it has rarely been studied in previous literatures. The optimal frequency of a 3 W wireless charging system for cardiac pacemaker is determined based on the results of safety evaluation. The theoretical temperature rise reaches the minimum at 203 kHz, and the theoretical energy loss reaches the minimum at 260 kHz. The comfort and safe frequency band is approximately from 150 kHz to 370 kHz based on theoretical and experimental results, and the optimal frequency band from 200 kHz to 300 kHz is recommended. [ABSTRACT FROM AUTHOR]

In this paper, a battery charging and swapping optimization model is established for electric vehicles (EVs) and battery charging/swapping stations (BCSS). The EVs are categorized into private electric vehicles (PrEVs) and electric taxis (ETs), where the charging behaviors of PrEVs are modeled based on the Monte Carlo (MC) method, and the battery swapping (BS) strategies of ETs are optimized by bi-level dynamic game. Moreover, the voltage deviation of the power grid is considered in the load regulation process of ETs. A “path-location” model is established combining with the Floyd algorithm in the simulation and the IEEE 14-Bus system is used to derive the node voltage. Numerical results show that the proposed strategy can simultaneously increase the revenue of BCSS and ETs and reduce the voltage deviation. [ABSTRACT FROM AUTHOR]

Accurate state of energy (SOE) estimation of the battery pack is very important for the electric vehicle's driving range estimation, which is still a very challenging problem under actual vehicle application conditions at present. This paper proposes a method for estimating the SOE of the battery pack based on prediction, taking into account the future voltage and temperature changes of the battery pack. Firstly, a novel definition of the battery pack SOE is proposed, which considers the inconsistency of the battery pack. Secondly, the thermo-electric lumped parameter equivalent circuit model of a single cell in the battery pack is applied. The electrical parameters are identified using the forgetting factor recursive least-squares algorithm, and the extended Kalman filter is used to estimate the SOC of each cell. Finally, the future current, voltage and temperature response of the cell in the battery pack are accurately predicted and iterative calculations are performed to get SOE under the condition that the future output power of the battery pack is predicted by the Markov chain model method. The effectiveness of the proposed method is verified under dynamic conditions at different temperatures. The results show that the above method has high precision and good robustness, and can meet the needs of actual vehicle applications. [ABSTRACT FROM AUTHOR]

This paper considers the co-operation of distributed generators (DGs), battery energy storage systems (BESSs) and voltage regulating devices for integrated peak shaving and voltage regulation in distribution grids through a co-optimization framework, which aims to minimize the operational costs while fulfilling the operational constraints of network and devices. To account for the uncertainties of load demand and generation, we then convert the co-optimization model into a two-stage stochastic program where state-of-charge (SoC) trajectories of BESSs and operation of voltage regulating devices are optimized at the first stage for day-ahead scheduling, while the reactive powers of DGs and BESSs are left at the second stage for potential intra-day scheduling to handle short-term voltage issues. The proposed co-optimization scheme is validated on the IEEE 37-node test feeder and compared with other practices. [ABSTRACT FROM AUTHOR]

This paper investigates a new DC voltage sag compensating scheme by using hybrid energy storage (HES) technology involved with one superconducting magnetic energy storage (SMES) unit and one battery energy storage (BES) unit. Two fault simulations of power supply fluctuation and sensitive load fluctuation are carried out to evaluate the dynamic voltage and power smoothing behaviours. The results obtained show that this HES-based DC voltage sag compensator has the ability to suppress the discharging / charging current overshoots for the BES unit and to enlarge the voltage compensating time for the SMES simultaneously. [ABSTRACT FROM AUTHOR]

This article proposes a novel bidirectional isolated dc–dc converter with high voltage gain and wide input voltage, which can be applied to bidirectional power conversion systems. The proposed topology is composed of a bidirectional buck-boost converter and a forward-flyback converter; it has the advantage of higher voltage gain and has continuous current characteristic of the low-side port in step-up and step-down mode. In addition, the proposed topology also has the function of leakage inductance energy recovery, which can improve the efficiency of the converter, reduce the voltage surges on switches, and have the characteristics of zero voltage switching on certain switches. Finally, this paper implements a 500-W bidirectional dc–dc converter to verify the feasibility of the proposed topology. The low-side voltage of the proposed topology is 24, 48, and 55 V; the maximum efficiency in step-up mode are 94.2%, 95.6% and 96.9%, and the maximum efficiency are 92.6%, 94.2% and 94.5% in the step-down mode, respectively. [ABSTRACT FROM AUTHOR]

Existing centralized equalization methods can only equalize one battery cell at a time, which is the main reason that limits the equalization speed and practicability of such methods. To overcome this limitation, this article proposes an integrated cascaded multiport converter (ICMPC) to optimize the structure and performance of the centralized equalization system. Through the proposed converter, the simultaneous and single-stage energy exchange between multiple unbalanced cells and the battery string can be achieved, so as to effectively improve the equalization speed. Meanwhile, the number of ports of the ICMPC is easy to expand, and the optimized system possesses the advantages of compact structure, high efficiency, and high cost effectiveness compared with conventional methods. As the basic and typical form of the ICMPC, the integrated cascade three-port converter is analyzed as an example in terms of operation principle, parameter design, and zero-voltage switching analysis. Finally, to confirm the theoretical analysis, a laboratory prototype is designed, and a comprehensive comparison is performed. The experimental and comparative results fully prove the practicality and superiority of the proposed ICMPC-based centralized equalization. [ABSTRACT FROM AUTHOR]

This article presents a versatile shunt-based current sensor for battery management applications. It digitizes the current-induced voltage drop across an external shunt resistor with the help of a 2nd-order delta-sigma ($\Delta \Sigma $) ADC, whose summing node is implemented as a low-noise capacitively coupled amplifier. To compensate for the shunt’s finite temperature coefficient (TC), the TC of the ADC on-chip voltage reference can be tuned. As a result, the sensor maintains high accuracy when used with low-cost high TC shunts, such as PCB traces, as well as with more expensive low TC shunts, such as metal-alloy resistors. Optimal gain flatness over temperature is achieved by a two-current room-temperature TC tuning scheme, which exploits the shunt’s self-heating at high current levels. Fabricated in a standard 0.18- $\mu \text{m}$ CMOS process, the current sensor occupies 0.36 mm2 and draws 265 $\mu \text{A}$ from a 1.8-V supply. Over the industrial temperature range (−40 °C to 85 °C) and a ±25-A current range, it achieves the state-of-the-art gain error (±0.25%) with both PCB (1.6 $\text{m}\Omega $) and metal-alloy (2 $\text{m}\Omega $) shunts. With these shunts, it achieves 5.3-mA/4.3-mA (rms) resolution in a 10-kHz bandwidth. [ABSTRACT FROM AUTHOR]

This article presents an efficient and fast echelon battery equalization method based on wide voltage range bidirectional converter combined with DBSCAN (density-based spatial clustering of applications with noise) 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 DBSCAN 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. [ABSTRACT FROM AUTHOR]

The cascaded H-bridge (CHB) multilevel converter is an attractive solution for integrating photovoltaic (PV) generators with the ac grid. However, the power generated in the PV panels may be unequal due to partial shading, temperature change, and dust layer accumulation leading to unequal and unbalanced power between the phases and possible violation of power quality constraints. Fundamental frequency zero-sequence voltage (FFZSV) injection can be applied, but this method can produce overmodulation in conditions with high PV power mismatch. A new FFZSV is proposed in this article assuming a CHB with a battery energy support (BES) to compensate for the effects of unbalanced PV power generation. A barycentric coordinate representation helps to determine the capacity of the BES required. A coordinated control between the PV system and BES is also proposed in the article. Additionally, a novel approach to deliberate FFZSV injection is discussed in this article by which the maximum charge and discharge rate for the BES can be obtained along with balanced current injection into the grid. The effectiveness of the proposed technique is verified in numerical simulations and with experimental results. [ABSTRACT FROM AUTHOR]

Battery energy storage systems (BESS) based on modular multilevel converters (MMCs) allow battery packs to be integrated into the electrical grid in a modular fashion. Inherent to the operation of the MMC, the module's dc-link capacitor voltage experiences oscillations at grid frequency and its harmonics. This article investigates the close relation between this voltage oscillation and the battery current ripple. The precise capacitor energy requirements for various operations of BESS-MMC, which include arm/phase power balancing and state-of-charge balancing are analyzed in this article. Furthermore, this article also explores the relation between the controller design and the submodule's (SMs) capacitor sizing in terms of its energy requirements. Design guidelines for the SM level voltage control to attenuate battery ripple and detailed analysis for the capacitor energy requirement in each operating mode are presented. The control and capacitor sizing design are validated in real-time using embedded microprocessors in a Typhoon-based controller hardware-in-the-loop environment. [ABSTRACT FROM AUTHOR]

The range of electric vehicles (EV), especially those powered by aged battery packs, is partly limited by cell-to-cell imbalance, i.e., the weakest cell determines the performance of the entire battery pack. Active cell balancing can mitigate these differences, but balancing ad hoc discrepancies in voltage or state-of-charge (SoC) does not necessarily result in the best performance in terms of range. This brief employs a distributed feasibility approach to retrieve the maximum range and corresponding balancing currents for a specific scenario. Moreover, using aging data from literature and a real-time applicable model-predictive-controller, a lifetime projection is made on the benefits of active cell balancing, which shows that a significant extension of End-of-Life (EoL) is achieved, i.e., 10% for the considered example. Finally, we show when and why the applied balancing controller, which can effectively balance a battery pack using balancing currents with a maximum $C$ -rate of only 1/ $50C$ , performs better than others in terms of maximizing the range. [ABSTRACT FROM AUTHOR]

Electric vehicle (EV) has been widely used in our life, one of the key technologies is the batteries, power accumulator battery test system (PABTS), which is initiated for evaluating the performance of the EV batteries, has been used in many battery-manufacture companies. The parallel operation of the PABTS forms a dc-microgrid, owing to the low inertia of the dc-link capacitance, the charging and discharging tests of the batteries can easily cause dc-bus voltage fluctuations, which may jeopardize the system stability. To increase the system inertia and achieve good system stability, a fractional-order model-predictive-control (FOMPC) and fractional-order virtual-inertia-control (FOVIC) strategy (namely, FOMPC-FOVIC method) is proposed for the bidirectional grid-connected converter. First, the fractional-order virtual inertial link is used to replace the integral-order virtual inertial link, which significantly improves the system stability. Second, combined with fractional-order model-predictive-control, virtual dc current compensation is proposed to further suppress the dc-bus voltage fluctuations. Finally, the fractional-order discrete state-space equation of the virtual inertial link is derived, and the cost function design and its optimal solution are elaborated. To demonstrate the effectiveness of the proposed FOMPC-FOVIC scheme, experimental results indicate that the proposed method is superior to the existing methods in terms of inertial support and dc-bus voltage regulation. [ABSTRACT FROM AUTHOR]

In the operation of battery energy storage systems (BESSs) based on the cascaded H-bridge (CHB) converters, it is desirable to balance the state of charge (SoC) among the submodules (SMs) within each phase arm. However, there are constraints on the active power distribution among the SMs that intend to balance the SoC. For instance, each SM in a practical system is designed with a specific power rating and can be damaged if it is exceeded. Therefore, a novel rule-based method is proposed in this article to achieve a fast SoC balancing, while respecting the power constraints of the SMs. The proposed method is general and readily applicable to hybrid BESSs, where the SMs are integrated with heterogeneous energy storage. Experimental results are obtained to verify the effectiveness of the proposed algorithm and to compare its performance with respect to existing methods. [ABSTRACT FROM AUTHOR]

Triboelectric nanogenerator (TENG) is a class of ambient mechanical energy harvesters used to augment the battery life of electronic devices such as sensors in implantables, wearables, and internet of things applications. In this work, the fundamentals of pre-biasing (precharging) the TENG at the start of the operation cycle to enhance the percycle extracted energy is presented. The energy gain is mathematically formulated, and the optimum pre-biasing voltage (equivalently charge) is derived by analyzing the energy exchange between the mechanical and the electrical domain over a periodic cycle. Further, a novel energy extraction circuit (EEC) termed as “pre-biased synchronous charge extraction (pSCE)” is introduced to 1) realize synchronous pre-biasing of TENG using the load battery itself and 2) achieve enhanced energy extraction from TENG. Energy output percycle is derived analytically for the pSCE circuit and compared to the state of the art synchronous charge extraction (SCE) circuit. The experimental implementation is performed for the proposed pSCE circuit that shows a 6.65 fold gain over the full wave rectifier (standard EEC) and 1.45 over the SCE circuit for a 5 V battery load. [ABSTRACT FROM AUTHOR]

The state of power (SOP) of lithium-ion batteries plays an essential role in power distribution of electric vehicles and energy storage stations. However, due to the highly nonlinear dynamic behaviors and the parameter errors, accurate and reliable SOP estimation is always difficult. This article develops an optimization strategy to estimate SOP, in which the multiple constraints are simultaneously considered and the nonlinear equivalent circuit model (ECM) is directly adopted. On basis of it, the effects of single parameter uncertainty and multiparameter uncertainty are thoroughly investigated. The results show that compared to the conventional method, the proposed method could provide more reliable SOP estimation during the whole operation range. Moreover, different uncertainty sources have different effects on estimation results, not only the estimate values but also the constraint regions. This is the first time to directly employ the nonlinear form of ECM parameters in the SOP estimation and provide a comprehensive investigation of various uncertainty sources. [ABSTRACT FROM AUTHOR]

An isolated multilevel bidirectional dc–dc converter is presented in this article to interface the low-voltage (LV) battery and the high-voltage (HV) propulsion inverter in electric vehicles. The proposed topology achieves a HV step-up ratio in the motoring mode by reconfiguring two split capacitor half-bridge circuits in series/parallel through the symmetrical modulation of a voltage bidirectional, two quadrant switch. This reconfiguration generates a high-frequency multilevel voltage output at the dc-bus side of the inverter, which reduces the output filter volume. The dc-bus voltage is regulated by the duty cycle modulation of the intermediary switch in the motoring mode, simplifying the sensing and control. During regenerative braking, the converter is operated with phase shift modulation between the HV half bridges and the LV full bridge to regulate the battery voltage. The presented modulation strategies achieve zero voltage switching for the full-bridge devices over a wide load range. A comprehensive analysis of the proposed multilevel converter in motoring and braking modes along with the design constraints and soft switching boundary conditions is presented in this article. Detailed experimental results on a 1.5-kW laboratory prototype are presented to verify the design approach and illustrate the converter performance. [ABSTRACT FROM AUTHOR]

This article proposes a multilevel dc–dc converter topology for fast charging of electric and plug-in hybrid electric vehicles (EVs and PHEVs). The proposed dc–dc converter topology converts the front end ac–dc converter output and provides regulated supply to the EV propulsion battery. The proposed topology consists of full-bridge converter at the primary, while the secondary side consists of voltage doubler rectifier units and combination of diodes and mosfet for reconfiguration of the voltage doubler rectifiers to generate the multilevel voltage. The multilevel voltage at the output helps in reducing the output filter size and increases the power density of the converter. The topology utilizes the resonance between leakage inductor of high frequency transformer, parasitic output capacitors of full-bridge mosfets and voltage doubler capacitors to achieve soft switching (ZVS turn-on) for all the full-bridge devices and soft turn-offfor the rectifier diodes. The load limited ZVS turn on capability of conventional full-bridge topologies is mitigated through the use of resonance between magnetizing inductance of transformer and mosfet output capacitors. The converter is designed for 650 V dc bus input and 200–400 V EV battery output at 100 kW rated charging power. The analysis of the proposed converter in continuous and discontinuous modes of operation, soft switching operation, and the component design guidelines are presented in this article. The proposed converter is validated through detailed PLECS simulation results for 100 kW charging power. Experimental results from laboratory prototype of 500 W power are also presented to validate the design methodology and converter performance. [ABSTRACT FROM AUTHOR]

Designing transactive energy (TE) markets in distribution systems has been a hot topic due to the increased presence of residential prosumers. In the literature, several residential market platforms have been proposed; however, they usually have two main drawbacks: 1) ignoring the effect of single-phase distributed energy resources on the voltage unbalance (VU) in active distribution networks to develop a transactive coordination model that will effectively mitigate the VU and 2) inability in providing a user-friendly strategy for home occupants to adjust the willingness to pay/accept of responsive assets according to their comfort and economic purposes. This article amends the shortcomings by proposing a network-constrained TE model to coordinate residential prosumers with the main goal of satisfying households’ preferences as well as mitigating distribution system problems. The case study is then carried out demonstrating that the proposed TE-concept-based coordination of residential prosumers is aligned with customers’ preferences (comfort and economic purposes) and concerns (plug-in electric vehicle battery life) and could effectively decrease the VU. [ABSTRACT FROM AUTHOR]

For power batteries used in the electric vehicle, accurate state-of-charge (SOC) and state-of-health (SOH) are important. Meanwhile, the current rate in actual working conditions often varies dramatically. However, the influence of current rates on voltage and battery states estimation has been neglected for a long time. To solve this problem, in this article, a hierarchical estimation model considering the current rate is proposed. The fractional-order model is used in the battery modeling, the data-driven method is used to identify parameters, and a multiscale dual extended Kalman filter (DEKF) is used in estimation of battery states. For SOC estimation, the proposed method improves the accuracy by 35.8% and 36.5% compared with traditional DEKF under two conditions. For SOH estimation, the proposed method improves the accuracy by 34.8% and 43.1% under two current conditions. [ABSTRACT FROM AUTHOR]

Accurately estimating the capacity of lithium-ion batteries in electric vehicles (EVs) is critical for making correct management decisions. However, the randomness of the charging voltage range of EVs can lead to missing observations or reduced accuracy of capacity estimation methods. This article proposes an adaptive battery capacity estimation method suitable for arbitrary charging voltage range based on incremental capacity (IC) analysis and data-driven techniques. All charging conditions of EVs are divided into three categories according to the charging voltage range. Three data-driven estimation submethods with sequential application priority are designed for the three charging conditions separately, including back-propagation neural network with IC peak coordinates as input, ensemble learning with local high IC curve as input, and linear regression with ampere-hour coordinate transformation. The method is based on a priori knowledge to select a suitable estimation submethod under different charging conditions, so as to improve the adaptability. Experimental data is collected from eight commercial lithium-ion battery modules for model establishment and verification. Over 250 000 experimental samples at different states of health and random charging ranges show that the method can accurately estimate battery capacity under arbitrary charging conditions, with a maximum error of 2%. [ABSTRACT FROM AUTHOR]

An integrated inductor for a highly compact embedded battery charger is designed in this article. A zero-voltage switching (ZVS) buck converter is the selected topology to achieve high power density. ZVS is achieved by sizing the inductor based on energy balance and introducing the $k$ factor. A novel four-leg magnetic core structure is proposed as the integrated inductor. By introducing a modified parameter $\alpha _{\mathrm{eff}}$ to the improved generalized Steinmetz equation method, the optimal switching frequency for core losses can be found. From the constructed inductor model and semiconductor loss calculation, the design tradeoff and optimization is analyzed. The optimal $f_{\mathrm{sw}}$ is found to be around 2 MHz, which is when the performance factor for the core material peaks. As a proof of concept, a highly compact prototype, featuring stacked printed circuit board solution, with 16.2 × 19.2 × 6 mm $^{3}$ dimension is built. The input voltage ranges from 6 to 12 V, and the converter is capable of delivering up to 10 A at the 4-Voutput. Converter peak efficiency of 96% is achieved, and the inductor design has a power density of 113.6 W/cm $^{3}$. This shows improvement over several state-of-the-art designs. This article is accompanied by a video demonstrating the flux distribution in the magnetic core over the switching period. [ABSTRACT FROM AUTHOR]

Charging infrastructure (CI) is crucial for the widespread adoption of plug-in electric vehicles (PEVs). The optimal portfolio of CI is beneficial for PEV owners, power systems, and policymakers. Therefore, an optimal CI portfolio estimation method is proposed to minimize the grid impacts of PEVs. All possible CI types (residential, workplace, public, and commercial) along with the three commonly used charging levels are considered and seven PEV charging profiles are estimated. Then, an optimization model is developed to determine the optimal portfolio of CI. An index is proposed to compare the performance of the proposed method with other CI portfolios. Various cases are simulated to analyze the performance under diverse conditions such as the presence of renewables and specific policy scenarios. The proposed method can be used by policymakers for making new policies, in new PEV markets, and to incentivize the use of specific CI types, in mature/developing markets. [ABSTRACT FROM AUTHOR]

In the operation of cascaded H-bridge converters and modular multilevel converters with energy storage or renewable power resources, unbalanced active power distribution among the submodules (SMs) is unavoidable. Depending on the operating conditions, there are certain upper and lower limits on the active power that can be processed by a single SM or a subset of SMs. The control system needs to restrict the SM power references to these limits, hence, accurate knowledge of the power limits is important. In existing methods to derive the power limits, the SM capacitor voltages are assumed to have negligible ripples, whereas in practice the ripples can be considerable. This article analyzes the effect of capacitor voltage ripples on the SM active power control limits and highlights the importance of considering the ripple effect. A methodology is proposed to accurately incorporate capacitor voltage ripples in the derivation of SM active power control limits. Simulation and experimental results are provided to evaluate the effectiveness of the proposed methodology. [ABSTRACT FROM AUTHOR]

The rapid development of battery technology has promoted the deployment of electric vehicles (EVs). To ensure the healthy and sustainable development of EVs, it is urgent to solve the problems of battery safety monitoring, residual value assessment, and predictive maintenance, which heavily depends on the accurate state-of-health (SOH) estimation of batteries. However, many published methods are unsuitable for actual vehicle conditions. To this end, a data-driven method based on the random partial charging process and sparse Gaussian process regression (GPR) is proposed in this article. First, the random capacity increment sequences (△Q) at different voltage segments are extracted from the partial charging process. The average value and standard deviation of △Q are used as features to indicate battery health. Second, correlation analysis is conducted for three types of batteries, and high correlations between the features and battery SOH are verified at different temperatures and discharging current rates. Third, by using the proposed features as inputs, sparse GPR models are constructed to estimate the SOH. Compared with other data-driven methods, the sparse GPR has the highest estimation accuracy, and its average maximum absolute errors are only 2.88%, 2.52%, and 1.51% for three different types of batteries, respectively. [ABSTRACT FROM AUTHOR]

Conventional pulse frequency modulation is typically adopted in the reverse LLC converter resulting in a low voltage gain. The output bus voltage may be lower than peak grid voltage, so that the buck-type inverter cannot output 220 Vac and poses series challenge to achieve bidirectional charger operation. A bidirectional synchronous/asynchronous rectifier control is proposed for wide battery voltage applications in the LLC converter. In the forward mode, a simplified model is built to calculate the synchronous rectifier (SR) on-time and achieve high efficiency by using a two-order function. In the reverse mode, the turn-on instants of primary side and secondary side power devices are controlled with a delay angle to obtain high voltage gain and high efficiency. A 6.6-kW silicon carbide bidirectional LLC charger was built. With the proposed SR control, the forward LLC efficiency improves 0.2% compared with the conventional SR method. The reverse LLC voltage gain is up to 1.33 so that the charger can output 220 Vac in the full battery voltage range of 200–500 V. [ABSTRACT FROM AUTHOR]

Dispatching a fleet of distributed energy resources (DERs) in response to wholesale energy market or regional grid signals requires solving a challenging disaggregation problem when the DERs are coupled within a distribution network. This manuscript presents a computationally tractable convex inner approximation for the optimal power flow (OPF) problem that quantifies a feeder’s aggregate DERs hosting capacity and enables a realtime, grid-aware control policy for DERs in radial distribution networks. The inner approximation is derived by considering convex envelopes on the nonlinear terms in the AC power flow equations. The resulting convex formulation is then used to derive provable nodal injection limits, such that any combination of DER dispatches within their respective nodal limits is guaranteed to be AC admissible. These nodal injection limits are then used to construct a realtime, open-loop control policy for dispatching DERs at each location in the network to deliver fast grid services in aggregate. The IEEE-37 distribution network is used to validate the technical results and illustrate use cases. [ABSTRACT FROM AUTHOR]

In conventional electromagnetic energy harvesting systems, a two-port ac–dc rectifier is utilized to process the harvested power. However, it is difficult to achieve voltage regulation and maximum-power-point-tracking (MPPT) simultaneously. To resolve this issue, this article proposes a three-port power-electronic-interface (PEI) dedicated to this application. A battery port is introduced to buffer the redundant energy. A bidirectional dc–dc converter is utilized to tightly regulate the load side voltage. To capture the maximum power for the harvester, a simple MPPT method is proposed for this PEI. The power tracking of ac source can be simplified by dealing with the power of the battery port. The regulations of power and output voltage are fully decoupled with different control degree-of-freedoms. Moreover, when the harvester is in idle mode, the load can be powered by the battery via the bidirectional dc–dc converter independently. A 24-mW rated laboratory prototype, which processes the power flow among a 0.6 V, 100 Hz ac source, a 1.2 V battery, and a 3.3 V constant voltage load is developed and tested. The proposed concept is validated by experimental results. [ABSTRACT FROM AUTHOR]

In this article, a highly efficient battery-balancing circuit with output voltage regulation for mobile applications is proposed and analyzed. The proposed circuit performs a cell-balancing operation for series-connected multiple-battery cells and voltage regulation operation simultaneously without additional power conversion stages. Therefore, it can be integrated into a battery pack with maximized power density and efficiency. These features are essential for recent low-power applications with multiple batteries, such as wireless/smart speakers, drones, and electronic point-of-sale, that require high power density. The operational principle, electrical modeling, and tradeoff relationship between the system power losses and balancing characteristics are derived, and the optimal design candidates of the proposed topology are discussed in terms of Pareto optimization. The effectiveness of the proposed system is verified with a prototype board using GaN switches, and 96.05% efficiency is achieved with a 1.8 V, 0.5 A load. [ABSTRACT FROM AUTHOR]

The boom of electric vehicles (EVs) has urged new designs and applications of power conversion technologies. Power converters, as one of the most critical components in EV battery systems, have seen significant developments in recent years. However, thus far forward design approaches for power converter topologies have been widely adopted, which are based on engineers’ empirical knowledge and instinct. This has been deemed having low design efficiency with high randomness and limited applicability, due to the absence of a systematic guideline. This approach, though widely adopted, can no longer meet the increasingly stringent and diverse needs of today’s research and industry, with the emerging trend of renewable energy sources. Aware of these drawbacks, in this study, we propose a novel reverse design approach through establishing general polynomial relations between the topology and voltage gain of high-step-up converters, which are found to be functions of basic boost converters’ voltage gains. With this newly formed polynomial relation, a generalized approach to devising power converters for various industrial needs can be derived, which is baptized the General Polynomial Reverse Design (GPRD) approach. Three polynomial converters are derived as examples to validate the proposed method, whereby their functionality and performances are verified and tested by prototype experiments, which substantiate the proposed design theory. [ABSTRACT FROM AUTHOR]

In this article, a high-power factor ac–dc conversion system based on bridgeless isolated positive output Luo converter is demonstrated for light electric vehicles charging. Unlike conventional bridgeless Luo converters, the presented topology ensures positive voltage polarity at its output and incorporates a minimum component count over the universal supply voltage range of 85 VRMS to 265 VRMS. Meanwhile, the volume of magnetic components and the charger's cost are reduced by considering a discontinuous inductor current mode (DICM) design. To accomplish desired charging profile of the battery, a simple control incorporating few sensing devices and single gate drive circuitry, is utilized. It is noteworthy that, the single stage bridgeless structure of the presented topology with DICM design considerably reduces conduction and switching losses of the charger. Finally, the presented topology is designed and modeled through MATLAB environment, and its efficacy is tested through a prototype in the laboratory environment. The critical test results at various operating conditions are demonstrated to verify design and control objectives of the charger. A brief comparative analysis with existing solutions, is presented to justify the effectiveness of the presented solution. [ABSTRACT FROM AUTHOR]

The limited voltage gain characteristic of the mainstream dc–dc converter restricts the application in single-stage light electric vehicles’ (LEVs) chargers. Typically, the battery voltage of an LEV is in the range from 24 to 72 V. Thus, while implementing the single-stage LEVs’ chargers, a line- or high-frequency transformer is essentially required. The utilization of transformer, however, compromises the overall cost, size, and efficiency of LEV chargers. Therefore, a transformerless single-stage bridgeless charger topology is presented in this article, aiming to realize a simple, reliable, efficient, and low-cost charger for the LEVs. The presented topology utilizes a switched inductor single ended primary inductance converter (SISEPIC) to achieve a high step-down dc voltage gain. Furthermore, the active power factor correction is incorporated to ensure enhanced power quality (low total harmonics distortion and unity power factor) at the ac supply side during constant current and constant voltage state charging. Additionally, this charger is controlled by employing reduced sensing devices and control complexities. Both simulation and experimental validations are provided to manifest the effectiveness of this SISEPIC charger topology for LEVs. [ABSTRACT FROM AUTHOR]

In this study, image feature extraction techniques based on principal component analysis (PCA) and QR factorization were employed to represent the measured terminal voltage of several batteries in terms of a few dominant features instead of raw data. In previous studies, directly measured terminal voltage was used to create the feature space by inputting raw sampled data to a supervised classifier. This was ineffective because it leads to false alarms owing to data overlap and requires a relatively considerable processing time. However, the proposed methods are useful for building a reduced and distinguishable feature space, where a classifier can quickly process and separate regions with small labeling errors. Therefore, different supervised machine learning classifiers, namely neural networks (NNs), k-nearest neighbors (kNNs), and support vector machines (SVMs), were trained based on the dominant features to distinguish between the safe and failure regions of battery units. Interestingly, the proposed technique requires no knowledge of the model parameters and state of charge (SOC) in the training and testing phases, although the SOC is necessary in the data labeling stage. The results showed that the nonlinear classifiers represented by NNs and kNNs demonstrated slightly better detection performance than the linear SVMs. [ABSTRACT FROM AUTHOR]

The increasing penetration level of photovoltaic (PV) systems in low-voltage networks causes voltage regulation issues. This brief proposes a new voltage regulation strategy utilizing distributed battery energy storage systems (BESSs) while incorporating the inevitable communication delays. The proposed strategy ensures that the voltage regulation burden is appropriately shared among all involved BESSs in the network. The effects of communication delays on the performance of the proposed strategy are analyzed and an admissible delay bound is established. Case studies are conducted to verify the effectiveness of the proposed strategy. [ABSTRACT FROM AUTHOR]

The classic cascaded boost–buck converter has inductors at the input and output ports of the converters, which makes it an ideal interface for bidirectional battery charging applications, where accurate current control and low ripple currents are required. This article proposes a split duty cycle coupled multiphase variant applied to the cascaded boost–buck converter and utilizes coupled inductor features to achieve very lower current ripples at the output, lower power losses, and reduction in magnetic component volume. Moreover, current sharing between each phase is inherently implemented, making it suitable for a high-conversion-ratio bidirectional operation in systematic energy storage applications, where the low-voltage port has very high current. This article covers a split duty cycle converter operation principle using coupled inductors between the input and the multiphase output. Magnetic component design and selection guidelines are presented. The proposed control method and the coupled inductor structure are validated by simulation and experimental results. [ABSTRACT FROM AUTHOR]

This article investigates the evaluation of different charging patterns of multistep constant current-constant voltage (MSCC-CV) for fast charging of a valve regulated lead-acid battery for electric vehicles. In this article, four parameters are sensed and feedback for closed-loop operation, i.e., battery temperature, terminal voltage, state of charge (SOC), and time. The battery current is dynamically adjusted in response to these four parameters for three different charging patterns. The three charging patterns of MSCC-CV by controlling 1) SOC and temperature, 2) the terminal voltage, SOC, and maintained temperature, and 3) the charging time and SOC. Further work is carried out to investigate the effects of charging strategies on battery health. As per the experimental results, it has been demonstrated that charging pattern with four-step by regulating battery terminal voltage, SOC, and maintained temperature shortens the charging time to 3.6 h as compared to conventional constant current-CV with improved battery life and health. [ABSTRACT FROM AUTHOR]

This article presents output voltage sharing among series output connected battery power modules (BPMs) in plug-and-play (PnP) dc microgrids with a wide bus voltage range. The system provides active cell balancing and interfaces cells to the bus voltage through series output connected BPMs. A cell current sensor is utilized to achieve both state-of-charge regulation and output voltage sharing. To improve microgrid modularity, the battery pack behaves as a current source. A current-dependent droop between the individual output voltages and input currents is used to facilitate series output connected voltage sharing with bidirectional power flow, simple control, and smooth transitions between charge and discharge regions. Experimental results are reported for a 3 kWh 1C-rate prototype consisting of two parallel 24 V subsystems, with five series output connected BPMs in each subsystem. Each BPM consists of three battery cells and three 100 W dc–dc converters. [ABSTRACT FROM AUTHOR]

This article presents a dual-frequency (DF) dual-input–dual-output interface based on a reconfigurable switching converter for thermoelectric energy harvesting. The DF operation decouples the rate of energy extraction at the input stage from the rate of energy distribution at the output stage. The interface automatically makes transitions among two energy-harvesting modes and one energy-recycling mode according to the load condition. The low-frequency harvesting together with the high-frequency recycling allows the interface to maintain high efficiency across a broad range of load. A zero-current detection (ZCD) approach based on real-time calculation turns off the power switches instantaneously and accurately to prevent synchronization loss. The interface is fabricated with a 0.13-μm CMOS process. From the measurement results, the input voltage is regulated in the range from 30 to 500 mV with the aid of maximum power point tracking (MPPT) and the output voltage is regulated at 1.2 V. The peak energy harvesting efficiency is 86% with 250-mV input voltage. Higher than 80% efficiency is achieved with 80–500 mV input voltages. The peak energy recycling efficiency is 94% and the power consumption of control circuits is 0.6 μW. [ABSTRACT FROM AUTHOR]

This article presents a method for modifying an electrostatic harvester (EH) to allow autonomous management of its charge. The method involves segmenting a naturally antagonistic (out-of-phase) EH and connecting it with diodes to form an integrated self priming circuit (I-SPC). A model for the I-SPC is presented and shown that an exponential increase in voltage on the EH will occur over 10's of harvesting cycles. Furthermore, the model finds that increasing the segmentation of the EH allows harvesting at lower capacitance change ratios. The model is validated through simulation and experiment. The experiment is performed using a dielectric elastomer EH which consists of eight segments. During experimentation, it is confirmed that an I-SPC charged to 5 V is capable of reaching a voltage of approximately 2600 V after 40 capacitance change cycles. This fast voltage gain highlights the possibilities of self-managed EHs which harvest renewable kinetic energy autonomously to power wireless sensor networks (WSNs). The lack of maintenance associated with these systems will allow cheap WSN powered by renewable energy sources to be implemented in industrial applications. [ABSTRACT FROM AUTHOR]