DC Charging Research Articles

High Power Density Z-Source Resonant Wireless Charger With Line Frequency Sinusoidal Charging

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.

Spin and Charge Pumping by a Steady or Pulse-Current-Driven Magnetic Domain Wall: A Self-Consistent Multiscale Time-Dependent Quantum-Classical Hybrid Approach

We introduce a multiscale framework which combines time-dependent nonequilibrium Green function (TD-NEGF) algorithms, scaling linearly in the number of time steps and describing quantum-mechanically conduction electrons in the presence of time-dependent fields of arbitrary strength or frequency, with classical time evolution of localized magnetic moments described by the Landau-Lifshitz-Gilbert (LLG) equation. The TD-NEGF+LLG framework can be applied to a variety of problems where current-driven spin torque induces dynamics of magnetic moments as the key resource for next generation spintronics. Using magnetic domain wall (DW) as an example, we predict that its motion will pump time-dependent spin and charge currents (on the top of unpolarized DC charge current injected through normal metal leads to drive the DW motion). The conversion of AC components of spin current, whose amplitude increases (decreases) as the DW approaches (distances from) the normal metal lead, into AC voltage via the inverse spin Hall effect offers a tool to precisely track the DW position along magnetic nanowire. We also quantify the DW transient inertial displacement due to its acceleration and deceleration by pulse current and the entailed spin and charge pumping. Finally, TD-NEGF+LLG as a nonperturbative (i.e., numerically exact) framework allows us to establish the limits of validity of the so-called spin-motive force (SMF) theory for pumped charge current by time-dependent magnetic textures---the perturbative analytical formula of SMF theory becomes inapplicable for large frequencies (but unrealistic in magnetic system) and, more importantly, for increasing noncollinearity when the angles between neighboring magnetic moments exceed $\simeq 10^\circ$.

Vacuum-dressed cavity magnetotransport of a two-dimensional electron gas

We present a theory predicting how the linear magnetotransport of a two-dimensional electron gas is modified by a passive electromagnetic cavity resonator where no real photons are injected nor created. For a cavity photon mode with in-plane linear polarization, the dc bulk magnetoresistivity of the 2D electron gas is anisotropic. In the regime of high filling factors of the Landau levels, the envelope of the Shubnikov-de Haas oscillations is profoundly modified and the resistivity can be increased or reduced depending on the system parameters. In the limit of low magnetic fields, the resistivity along the cavity-mode polarization direction is enhanced in the ultrastrong light-matter coupling regime. Our work shows the crucial role of virtual polariton excitations in controlling the dc charge transport properties of cavity-embedded systems.

Ion Dynamics in Ionic-Liquid-Based Li-Ion Electrolytes Investigated by Neutron Scattering and Dielectric Spectroscopy.

A detailed understanding of the diffusion mechanisms of ions in pure and doped ionic liquids remains an important aspect in the design of new ionic-liquid electrolytes for energy storage. To gain more insight into the widely used imidazolium-based ionic liquids, the relationship between viscosity, ionic conductivity, diffusion coefficients, and reorientational dynamics in the ionic liquid 3-methyl-1-methylimidazolium bis(trifluoromethanesulfonyl)imide (DMIM-TFSI) with and without lithium bis(trifluoromethanesulfonyl)imide (Li-TFSI) was examined. The diffusion coefficients for the DMIM+ cation and the role of ion aggregates were investigated by using the quasielastic neutron scattering (QENS) and neutron spin echo techniques. Two diffusion mechanisms are observed for the DMIM+ cation with and without Li-TFSI, that is, translational and local. The data additionally suggest that Li+ ion transport along with ion aggregates, known as the vehicle mechanism, may play a significant role in the ion diffusion process. These dielectric-spectroscopy investigations in a broad temperature and frequency range reveal a typical α-β-relaxation scenario. The α relaxation mirrors the glassy freezing of the dipolar ions, and the β relaxation exhibits the signatures of a Johari-Goldstein relaxation. In contrast to the translational mode detected by neutron scattering, arising from the decoupled faster motion of the DMIM+ ions, the α relaxation is well coupled to the dc charge transport, that is, the average translational motion of all three ion species in the material. The local diffusion process detected by QENS is only weakly dependent on temperature and viscosity and can be ascribed to the typical fast dynamics of glass-forming liquids.

Feature Extraction Method for DC Charging Signal of Electric Vehicle

The high-power DC charging of electric vehicle charging stations leads to a large amount of ripple and unsteady waves in the power grid, which seriously affects power quality. The existing algorithms cannot accurately identify the signal characteristics of the fundamental wave, ripple, and the unsteady wave, and it is urgent to develop a comprehensive signal feature extraction method. Aiming at the time-varying characteristics of fundamental and non-steady-state waves in DC charging signals, the layered parameters of wavelet transform are modified, a multi-resolution method is established, and the fundamental and unsteady wave signals are identified and separated. Based on the amplitude-frequency and phase-frequency characteristics of DC charging signal, Fourier transform (FFT) is used to identify the amplitude and frequency of each sub-ripple, and a signal feature recognition method based on Fourier/wavelet transform is proposed to extract the signal characteristics of the DC charging process. The experimental results show that the signal feature recognition method based on Fourier/wavelet transform can identify the DC charging signal characteristics of electric vehicle with high accuracy, and can separate the unsteady state signal from the steady state signal.

Non-equilibrium charge and spin transport in superconducting-ferromagnetic-superconducting point contacts.

The conventional Josephson effect may be modified by introducing spin-active scattering in the interface layer of the junction. Here, we discuss a Josephson junction consisting of two s-wave superconducting leads coupled over a classical spin that precesses with the Larmor frequency due to an external magnetic field. This magnetically active interface results in a time-dependent boundary condition with different tunnelling amplitudes for spin-up and -down quasi-particles and where the precession produces spin-flip scattering processes. As a result, the Andreev states develop sidebands and a non-equilibrium population that depend on the details of the spin precession. The Andreev states carry a steady-state Josephson charge current and a time-dependent spin current, whose current-phase relations could be used to characterize the precessing spin. The spin current is supported by spin-triplet correlations induced by the spin precession and creates a feedback effect on the classical spin in the form of a torque that shifts the precession frequency. By applying a bias voltage, the Josephson frequency adds another complexity to the situation and may create resonances together with the Larmor frequency. These Shapiro resonances manifest as torques and, under suitable conditions, are able to reverse the direction of the classical spin in sub-nanosecond time. Another characteristic feature is the subharmonic gap structure in the DC charge current displaying an even-odd effect attributable to precession-assisted multiple Andreev reflections.This article is part of the theme issue 'Andreev bound states'.

Modeling, Design, Control, and Implementation of a Modified Z-Source Integrated PV/Grid/EV DC Charger/Inverter

Solar energy has been the most popular source of renewable energy for residential and semicommercial applications. Fluctuations of solar energy harvested due to atmospheric conditions can be mitigated through energy storage systems (ESS). Solar energy can also be used to charge electric vehicle batteries to reduce the dependence on the grid. One of the requirements for a converter for such applications is to have a reduced number of conversion stages and provide isolation. The Z-source inverter (ZSI) topology is able to remove multiple stages and achieve voltage boost and dc–ac power conversion in a single stage. The use of passive components also presents an opportunity to integrate ESS into them. This paper presents modeling, design, and operation of a modified ZSI integrated with a split primary isolated battery charger for dc charging of electric vehicle batteries. Simulation and experimental results have been presented for the proof of concept of the operation of the proposed converter.

Tailoring charge transport in epoxy based composite under temperature gradient using K2Ti6O13 and asbestine whiskers

The solid-gas interface flashover performance of insulators under dc is influenced to a considerable extent by the residual charge effect. The investigation of the charge origin and charge transport in dielectric materials is a significant topic. In this work, the Al2O3-filled epoxy resin composite was manufactured as the basic dielectric composite. To investigate the charge transport behavior and restrain the charge injection under the temperature gradient, asbestine and K2Ti6O13 whiskers were doped into the basic matrix and post type model insulators were prepared. Experimental results demonstrate that the introduction of K2Ti6O13 whiskers can effectively restrain heat propagation due to its excellent thermal barrier property, which can restrain the charge transport under temperature gradient to some extent. The charge injection level increases for insulator doped with asbestine whisker, which is due to the introduction of large amounts of shallow traps with trap level density ranging from 0.75–0.91 eV. This work is helpful to understand DC charge transport behavior under temperature gradient and provides important significance in design of a suitable insulator inside HVDC GIL.

A technological review on electric vehicle DC charging stations using photovoltaic sources

Within the next few years, Electrified vehicles are destined to become the essential component of the transport field. Consequently, the charging infrastructure should be developed in the same time. Among this substructure, Charging stations photovoltaic-assisted are attracting a substantial interest due to increased environmental awareness, cost reduction and rise in efficiency of the PV modules. The intention of this paper is to review the technological status of Photovoltaic–Electric vehicle (PV-EV) charging stations during the last decade. The PV-EV charging station is divided into two categories, which are PV-grid and PV-standalone charging systems. From a practical point view, the distinction between the two architectures is the bidirectional inverter, which is added to link the station to the smart grid. The technological infrastructure includes the common hardware components of every station, namely: PV array, dc-dc converter provided with MPPT control, energy storage unit, bidirectional dc charger and inverter. We investigate, compare and evaluate many valuable researches that contain the design and control of PV-EV charging system. Additionally, this concise overview reports the studies that include charging standards, the power converters topologies that focus on the adoption of Vehicle-to grid technology and the control for both PV–grid and PV standalone DC charging systems.

Compensating the effect of residual dipole energy on dielectric response for effective diagnosis of power transformer insulation

Analysis of relaxation current is a widely accepted method for diagnosis of power transformer insulation. The accuracy of such diagnostic tool is dependent on insulation model parameters which are formulated using relaxation current. This implies that the accuracy and hence the reliability of existing insulation diagnosis methods indirectly depends on the accuracy of the recorded polarisation depolarisation current. Sometimes during field measurement relaxation current measurement equipment fails to record proper current, even after application of dc charging voltage. As per utilities, this primarily happens due to improper/loose connections (this cannot be avoided entirely due to the involvement of human factors) and such situation is usually followed by checking and rectifying improper connection. The analysis presented in this study shows that the polarisation current recorded immediately after rectifying the correction is inaccurate and leads to the erroneous diagnosis. Furthermore, it is observed that in these cases, the measured and calculated (using insulation model) values of performance parameters like dissipation factor, polarisation index, and paper-moisture differ by a large extent. This work is aimed at removing the effect of this residual dipole energy introduced during the improper connection phase.

A High-Gain Reflex-Based Bidirectional DC Charger with Efficient Energy Recycling for Low-Voltage Battery Charging-Discharging Power Control

This study proposes a high-gain reflex-charging-based bidirectional DC charger (RC-BDC) to enhance the battery charging efficiency of light electric vehicles (LEV) in a DC-microgrid. The proposed charger topology consists of an unregulated level converter (ULC) and a two-phase interleaved buck-boost charge-pump converter (IBCPC), which together provide low ripple and high voltage conversion ratio. As the high-gain RC-BDC charges, the LEV’s battery with reflex charging currents, high battery charging efficiency, and prolonged battery life cycles are achieved. This is possible due to the recovering of negative pulse energy of reflex charging currents to reduce charge dissipations within LEV’s batteries. Derivations of the operating principles of the high-gain RC-BDC, analyses of its topology, and the closed-loop control designs were presented. Simulations and experiments were implemented with battery voltage of 48 V and DC-bus voltage of 400 V for a 500 W prototype. The results verify the feasibility of the proposed concept and were compared with the typical constant-current/constant-voltage (CC/CV) charger. The comparison shows that the proposed high gain RC-BDC improves battery charging speed and reduces the battery thermal deterioration effect by about 12.7% and 25%, respectively.

Cyclotron resonance of the magnetic ratchet effect and second harmonic generation in bilayer graphene

We model the magnetic ratchet effect in bilayer graphene in which a dc electric current is produced by an ac electric field of frequency $\omega$ in the presence of a steady in-plane magnetic field and inversion-symmetry breaking. In bilayer graphene, the ratchet effect is tunable by an external metallic gate which breaks inversion symmetry. For zero in-plane magnetic field, we show that trigonal warping and inversion-symmetry breaking are able to produce a large dc valley current, but not a non-zero total dc charge current. For the magnetic ratchet in a tilted magnetic field, the perpendicular field component induces cyclotron motion with frequency $\omega_c$ and we find that the dc current displays cyclotron resonance at $\omega_c = \omega$, although this peak in the current is actually smaller than its value at $\omega_c = 0$. Second harmonic generation, however, is greatly enhanced by resonances at $\omega_c = \omega$ and $\omega_c = 2\omega$ for which the current is generally much larger than at $\omega_c = 0$.

Features of Charging–Discharging of Supercapacitors

We present the results of experimental investigations of supercapacitors produced by Panasonic using several methods, namely, measurements of temporal dependences of charging–discharging currents, cyclic dc charging, and cyclic voltammetry. The values of the internal resistance, static and dynamic capacitance, as well as their dependences on the bias voltage of the capacitors, have been determined. Measurements have shown that the initial stage of relaxation of current is well approximated by the exponential time dependence, and then transition to a powerlike dependence occurs. This well-known effect is explained on the basis of the allowance for specific transport properties of a porous fractal-type medium. These processes are adequately described by the fractional-differential model of anomalous diffusion. A weak dependence of relaxation curves on the voltage at low values of the latter ( 3 V) is explained by the appearance of new percolation paths blocked at low charging voltages due to the presence of high-potential barriers. The internal resistance and the static capacitance have been determined by measuring the voltage across the supercapacitor in the mode of dc charging. These parameters have been shown to depend on the voltage applied to the capacitor. The dependence of the dynamic capacitance on the voltage has been determined using cyclic voltammetry. It has been shown that the capacitance depends not only on the voltage, but also on the prehistory of charging and discharging of the capacitor. Comparison of the experimental results and the published data on the models and equivalent circuits with passive R, L, and C elements allows one to conclude that such models and equivalent circuits can be applied only when explaining a limited number of phenomena, in particular, behavior at small relaxation times.

Study on Ripple Characteristics of Uncontrolled Rectifier Circuit

The ripple in DC charging is a basic indicator of the voltage quality, which is related to the filter capacitor and external load. In this paper, the single-phase bridge rectifier circuit is used as the research object. It analyzes the generation process of ripple voltage and derives the expression of ripple voltage. And the effects of filter capacitor C, voltage U and external load R on the ripple coefficient are simulated and analyzed, as well as the spectrum distribution characteristics of the ripple.

Design and Development of Three Levels Universal Electric Vehicle Charger Based on Integration of VOC and SPWM Techniques

In order to successfully launch Electric vehicles (EVs) over the actual world, EVs battery chargers have a crucial role to predict the charging time. This work presents the design process of a universal EV charger, The proposed charger is able of providing a controllable and constant charging voltage for a various EVs, which is composed of three levels of charging, 650 V/100 A DC for bus or lorry, single-phase 120 V/16 A AC for motorcycle, and three-phase 240 V/60 A for saloon car battery charging. The output voltage ranges are 40 V–60 V, 400 V–500 V, or 500 V–600 V. The power system of this work consists of two converters; First one, is for the three-phase pulse-width modulated (PWM) of a bridge rectifier with an output of 850 V DC unregulated voltage, while the second converter is for the three-phase DC–DC converter. To satisfy the voltage control and the isolation between Grid To Vehicle (G2V), a three-phase transformer has been exploited within the DC/DC converter. The primary output circuit achieved the charge levels one and two, while the whole circuit output can charge level three or the DC charge. For efficient and secure battery charging, voltageoriented control (VOC) technique is proposed. The unity power factor for the PWM-based rectifier and SPWM are designed and evaluated using MATLAB/Simulink block sets. The total harmonic distortion (THD) for the input current is less than 5%, while the overall simulation-based efficiency is more than 97%. A prototype and simulation results validate that the proposed EV charger is robust, accurate, and applicable.

Variability of FinFET AC parameters: A physics‐based insight

AbstractThis paper presents a fully physics‐based variability analysis of single‐fin double‐gate Metal Oxide Semiconductor FET (MOSFET) AC parameters, without resorting to any approximated quasi‐static analysis based on the variations of the DC drain current or charge. Variations of the AC parameters have been investigated as a function of all the relevant geometrical and physical parameters, with emphasis on the ones affecting the device parasitics, especially important for high‐frequency analog applications. A numerically efficient Green's function technique is applied to reduce the simulation time to a few percent of the time required for standard Monte Carlo–based variability analysis. The Green's function approach especially allows for a deep insight into the so‐called local variability source, highlighting the regions of the device where physical variations most significantly affect the output AC performances and opening the way for possible structure optimization. Although presently implemented in a 2D in‐house software, the technique can be easily exported to standard 3D Technology Computer‐Aided Design (TCAD) tools, eg, for tri‐gate FinFET analysis.

Anisotropy of transport in bulk Rashba metals

The recent experimental discovery of three-dimensional (3D) materials hosting a strong Rashba spin-orbit coupling calls for the theoretical investigation of their transport properties. Here we study the zero temperature dc conductivity of a 3D Rashba metal in the presence of static diluted impurities. We show that, at variance with the two-dimensional case, in 3D systems spin-orbit coupling affects dc charge transport in all density regimes. We find in particular that the effect of spin-orbit interaction strongly depends on the direction of the current, and we show that this yields strongly anisotropic transport characteristics. In the dominant spin-orbit coupling regime where only the lowest band is occupied, the SO-induced conductivity anisotropy is governed entirely by the anomalous component of the renormalized current. We propose that measurements of the conductivity anisotropy in bulk Rashba metals may give a direct experimental assessment of the spin-orbit strength.

RANCANG BANGUN SISTEM PENGISIAN DAYA PADA MOBIL LISTRIK SOLAR CELL

System design to solar cell electric car batteries can be done in a way to recharge a car battery when it is in use and after use, where the batteries are fully charged at a voltage of ± 55 Volts and discharged state at a voltage ± 47 Volt. Tools that are used to recharge are Solar Cell and Charger Accu 48 Volt DC. Solar Cell is an electronic device that can convert solar energywhich is inexhaustibleinto DC voltage. Accu Charger 48 Volt DC is a tool used as an alternative when the Solar Cell is not enough in recharging the batteries of car after being used. Accu 48 Volt DC Charger is a charger that is directly connected to the sources of electricity of 220 Volt AC voltage which has been lowered by using transformers and stabilized by using a voltage stabilizer circuit. Keywords: Solar Cell, Charger Accu, Accu.

Breakdown Characteristics of Ferroelectric Glass-Ceramic Dielectric for Pulsed Power Applications

Breakdown characteristics of ferroelectric glass-ceramic capacitors in the PbO-SrO-Na2O-Nb2O5-SiO2 system were studied, including under dc charging and pulse charging. Results revealed that capacitance before and after charging was with no significant alternation. Relationship between dielectric constant and electric field was also explored. Meanwhile, a peculiar phenomenon was found that the breakdown strength of glass-ceramic dielectric under pulse charging was much lower than that under dc charging, which is of considerable discrepancy to common theory. Possible explanations were summarized afterward.

A High-Efficiency Isolated-Type Three-Port Bidirectional DC/DC Converter for Photovoltaic Systems

This paper proposes a novel high-efficiency isolated three-port bidirectional DC/DC device for photovoltaic (PV) systems. The device contains a high step-up converter for PV modules to supply power to the DC bus, and a bidirectional charge/discharge control circuit for the battery with an improved boost-flyback converter. When the PV modules supply sufficient energy, their output can be stepped up and energy supply to the DC bus and charging of the battery can be achieved simultaneously. However, when the energy supplied is insufficient, the battery provides energy to the DC bus. When the proposed converter is operated in the step-down mode, the DC-blocking capacitor on the high-voltage side is used to reduce the voltage on the transformer and achieve high step-down performance. Moreover, to improve the overall efficiency of the system, the energy stored in the leakage inductance is recycled and supplied to the DC-blocking capacitor during operation in the step-up mode. Finally, to verify the feasibility and practicability of the proposed devices, a 500 W three-port bidirectional DC/DC devices was implemented. The highest efficiencies achieved for operation in different modes were as follows: high step-up mode for the PV modules, 95.2%; battery step-up mode, 94.2%; and step-down mode, 97.6%.