Abstract: Alternating current (AC) is capable of heating up a lithium-ion battery efficiently before charging at low temperature. Generally, the lower the frequency of the AC current, the higher the heat generation rate. Yet at low frequency, there is a risk of lithium-ion deposition during the half cycle of charging. This study develops a temperature-adaptive, deposition-free AC preheating method. The electrochemical impedance spectroscopies (EIS) of both positive and negative electrodes are measured at different temperatures using a three-electrode lithium-ion cell. The equivalent electric circuit (EEC) models are fitted through the EIS data. The maximum permissible amplitudes of the heating current without incurring lithium deposition at different frequencies are determined at each temperature using the fitted EEC model and the lithium deposition potential. Combining the maximum permissible AC current and the heat generation rate model in the frequency domain, a multistep AC preheating method, in which the amplitude is adjusted according to the cell temperature, is developed. Using this method, the cell can be heated from −20°C to 5°C within 800 s at 100 Hz frequency with the multistep temperature-adaptive amplitude profile.

Abstract: Summary An alternating current (AC) heating method for lithium-ion batteries is proposed in the paper. Effects of current frequency, amplitudes and waveforms on the temperature evolution and battery performance degradation are respectively investigated. First, a thermal model is established to depict the heat generation rate and temperature status, whose parameters are calibrated from the AC impedance measurements under different current amplitudes and considering battery safe operating voltage limits. Further experiments with different current amplitudes, frequencies and waveforms on the 18650 batteries are conducted to validate the effectiveness of the AC heating. The experimental data recorded by appropriate measurement instrument are of great consistence with simulation results from the thermal model. At high frequency, the temperature rises prominently as the current increases, and high frequency serves as a good innovation to reduce the battery degradation. However, efficient temperature rise can be obtained from high impedance at low frequencies. Typically, 600 s is needed to heat up the battery from −24 °C to 7.79 °C with sinusoidal waveform and approximately from −24 °C to 25.6 °C with rectangular pulse waveform at 10A and 30 Hz. The model and experiments presented have shown potential value in battery thermal management studies for electric vehicle (EV)/hybrid electric vehicle (HEV) applications at subzero temperatures. Copyright © 2016 John Wiley & Sons, Ltd.

Abstract: In this study, power system stabiliser (PSS), static VAR compensator (SVC), and thyristor controlled series capacitor (TCSC) controllers are simultaneously used to increase the stability and damping of the oscillations of a multi-machine power system. By SVC, the transferrable power in the steady state can be increased and the voltage profile can be controlled along the line. TCSC can regulate line impedance and therefore, increase the transferred power of the system. PSS is added to excitation system to enhance the damping of electric power system during low frequency oscillations. SVC, TCSC, and PSS can combine with each other for further damping and stability; therefore, their coordination is very important. Then, adaptive velocity update relaxation particle swarm optimisation algorithm is used to optimise the parameters of PSS, SVC, and TCSC simultaneous controllers. The robustness of the proposed algorithm has been tested on 16-machine 68-bus power system.

Abstract: An impedance measurement approach with various current amplitudes is proposed to investigate the impedance behavior of power Lithium-ion battery in the frequency domain Notably, the impedance arc is divided into amplitude-independent response in the high-frequency range and amplitude-dependent response in medium-frequency range A shrinking of semi-circle diameter of the impedance arc at medium-frequency part of measured spectrum is distinctly observed with rising current amplitude Thus, a series of particular experiments are performed to facilitate the interpretation of the phenomenon The possible influencing factors for the battery, including its state of charge, internal pressure, and temperature rise during the high-rate short-time charge/discharge, are illustrated and excluded for analysis, respectively Based on the analysis of Butler-Volmer equation and Arrhenius empirical equation, a formula, which contains temperature and current known to influence the charge-transfer resistance, is derived logically It indicates that the charge-transfer resistance reduces as the current amplitude increases at a fixed temperature, which fundamentally dominates the shrinking of the semi-circle at medium frequencies Therefore, the medium-frequency impedance arc is able to represent the chemical reaction process, even under large current excitation (within a certain range)

Abstract: We measure graphene coplanar waveguides from direct current (DC) to a frequency f = 13.5 GHz and show that the apparent resistance (in the presence of parasitic impedances) has an dependence (where ), but the intrinsic conductivity (without the influence of parasitic impedances) is frequency-independent. Consequently, in our devices the real part of the complex alternating current (AC) conductivity is the same as the DC value and the imaginary part is ~0. The graphene channel is modeled as a parallel resistive–capacitive network with a frequency dependence identical to that of the Drude conductivity with momentum relaxation time ~2.1 ps, highlighting the influence of AC electron transport on the electromagnetic properties of graphene. This can lead to optimized design of high-speed analog field-effect transistors, mixers, frequency doublers, low-noise amplifiers and radiation detectors.

Abstract: © 2016 IOP Publishing Ltd. High-T c superconducting (HTS) flux pumps are capable of injecting flux into a superconducting circuit, which can achieve persistent current operation for HTS magnets. In this paper, we studied the operation of a rectifier-type HTS flux pump. The flux pump employs a transformer to generate high alternating current in its secondary winding, which is connected to an HTS load shorted by an HTS bridge. A high frequency ac field is intermittently applied perpendicular to the bridge, thus, generating flux flow. The dynamic resistance caused by the flux flow 'rectifies' the secondary current, resulting in a direct current in the load. We have found that the final load current can easily be controlled by changing the phase difference between the secondary current and the bridge field. The bridge field of frequency ranging from 10 to 40 Hz and magnitude ranging from 0 to 0.66 T was tested. Flux pumping was observed for field magnitudes of 50 mT or above. We have found that both higher field magnitude and higher field frequency result in a faster pumping speed and a higher final load current. This can be attributed to the influence of dynamic resistance. The dynamic resistance measured in the flux pump is comparable with the theoretical calculation. The experimental results fully support a first order circuit model. The flux pump is much more controllable than the traveling wave flux pumps based on permanent magnets, which makes it promising for practical use.

Abstract: In low-voltage converter-based alternating current (AC) microgrids with resistive distribution lines, the P-V droop with Q-f boost (VPD/FQB) is the most common method for load sharing. However, it cannot achieve the active power sharing proportionally. To overcome this drawback, the conventional P-ω/Q-V droop control is adopted in the low-voltage AC microgrid. As a result, the active power sharing among the distributed generators (DGs) is easily obtained without communication. More importantly, this study clears up the previous misunderstanding that conventional P-ω/Q-V droop control is only applicable to microgrids with highly inductive lines, and lays a foundation for the application of conventional droop control under different line impedances. Moreover, in order to guarantee the accurate reactive power sharing, a guide for designing Q-V droop gains is given, and virtual resistance is adopted to shape the desired output impedance. Finally, the effects of power sharing and transient response are verified through simulations and experiments in converter-based AC Microgrid.

Abstract: An aerosol delivery device is provided that includes at least one housing enclosing a reservoir configured to retain an aerosol precursor composition, and a heating element controllable to activate and vaporize components of the aerosol precursor composition The aerosol delivery device also includes a power source connected to and configured to provide power to an electrical load that includes the heating element, and an induction receiver connected to the power source, the induction receiver including a resonant receiver coupling device in which an alternating current is induced when exposed to an oscillating magnetic field, and a rectifier configured to convert the alternating current to a direct current from which the power source is rechargeable

Abstract: In this paper, a multiple synchronous reference frame (MSRF) analysis framework is developed to determine the positive- and negative-sequence components of all interharmonic and harmonic currents produced by alternating current electric arc furnace (AC EAF) installations, which can be considered as balanced but asymmetrical three-phase, three-wire loads on the power system. The aim of developing the MSRF analysis framework is twofold; deep understanding of the EAF characteristics, and fast and accurate generation of reference signals to the controllers of the advanced technology compensation systems such as active power filters (APFs), synchronous static compensators (STATCOMs), and energy storage systems (ESS), which may successfully compensate interharmonics, harmonics, and flicker. Online characterization of interharmonics and harmonics by MSRF analysis utilizes continuously measured line currents and line voltages on the medium-voltage side of the EAF transformer at a sampling rate of 25.6-kHz per data channel. It has been shown by offline computations that compensation of the sequence components of interharmonics and harmonics of the EAF currents obtained by the proposed framework, reduces the short-term flicker values at the point of common coupling by up to 10-fold. The proposed MSRF analysis framework has been successfully verified by comparing the frequency spectrums of the EAF currents with Fourier analysis results based on one-cycle sliding windows of 10-cycle duration.

Abstract: A power conversion device includes an alternating current rotating machine having a multiple of multi-phase windings, a multiple of power conversion means that convert direct current voltage of a direct current power supply based on a multiple of switching signals and apply voltage to the multiple of multi-phase windings, first current detection means that detects a first bus current, which is current flowing between the power conversion means that applies voltage to one multi-phase windings of the multiple of multi-phase windings and the direct current power supply, and first phase current calculation means that calculates the current flowing through the one multi-phase windings based on the first bus current, wherein the first current detection means detects the first bus current at a timing at which a multiple of voltage vectors based on the multiple of switching signals neighbor or coincide.

Abstract: Large-scale integration of renewable energy resources in the Alternating Current (AC) grids will have a serious impact on power system operation. The development of the Direct Current (DC) is presented as a solution to overcome some of the negative impacts on massive micro-generation deployment. Over 100 years later, from the time when AC was proving superior over DC, the existing AC electric power grids, equipment, and transmission method facing a big challenge from DC. In this paper, what has changed since Edison and Westinghouse public battle are firstly discussed? Then the high voltage DC (HVDC) transmission system is depicted the developmental history and the system׳s structure, and the HVDC applications based on voltage-source converters (VSCs) combined with the renewable generation are introduced, such as onshore, offshore wind, and City Power Supply. Then, those key technologies are represented. Finally, how to build future electricity grid network and VSCs-HVDC may improve the world is explored, and some recommendations are proposed.

Abstract: In the present work, corrosion rates of API grade X65 pipeline steel in sodium chloride solutions with and without alternating currents (AC) at different direct current (DC) potentials were measured using weight loss analysis. The results show that the effect of AC is most pronounced near the open-circuit potential; at more positive potentials, the rates approach those of the ohmic drop/mass transport-limited DC rates. Correspondingly, at negative potentials the rates decrease. Surprisingly, it was found that at all potentials, the AC corrosion rate was equal to the average AC current in the system. The data generated from weight loss experiments were compared with the results from a model for AC corrosion that was developed using a modified Butler-Volmer approach. The model considers the anodic and cathodic Tafel slopes, diffusion limited oxygen transport, interfacial capacitance, and solution resistance. Both experimental and model results showed the importance of the interfacial capacitance on the rate...

Abstract: We present a feedback control scheme for a hybrid bidirectional interlinking converter of an alternating current (AC)/direct current (DC) microgrid. The output voltage and current are measured which allow us to design a suitable control for the power flow. We propose a robust droop control strategy to cater for the uncertain voltage and frequency droop caused by load variations. The proposed droop controller takes into account the unmodeled load dynamics as well as the power switching transients between AC/DC microgrids. A conventional current controller followed by a sliding mode controller (SMC) are able to maintain the power stability in different operating conditions. Simulation results are presented which show performance of the proposed control scheme.

Abstract: A wireless power receiver is disclosed. The wireless power receiver according to an embodiment of the present invention comprises: a resonator for receiving wireless power; a rectifier for converting alternating current power received from the resonator to direct current power and supplying output power to a load; and a control unit for adjusting a resonant frequency of the resonator to directly control the output power of the rectifier supplied to the load.

Abstract: The electrical endurance of an electromagnetic alternating current (ac) contactor can be reflected by the mass loss of its contacts during operations. This paper carries out ac contactor endurance tests in which arcing phase angles (APAs) are fixed. Contact mass losses are measured, and the electrical signals of the contactor circuit are acquired. Thus, the corresponding energies of each break process are computed. This paper investigates the relation of arcing phases, arcing energies, and mass losses of break processes, and concludes that the higher arcing energies cause greater contact mass losses. Then, this paper proposes a breaking strategy that controls the APAs to minimize and balance the contact mass losses of the three phases of an ac contactor. Therefore, the erosion on each contact is reduced and the total operation number can be increased. Compared with random breaking, the novel strategy significantly improves the electrical lifetime of the ac contactors.

Abstract: Potential drop measurements are routinely used in the non-destructive evaluation of component integrity. Potential drop measurements use either direct current (DC) or alternating current (AC), the latter will have superior noise performance due to the ability to perform phase sensitive detection and the reduction of flicker noise. AC measurements are however subject to the skin effect where the current is electromagnetically constricted to the surface of the component. Unfortunately, the skin effect is a function of magnetic permeability, which in ferromagnetic materials is sensitive to a number of parameters including stress and temperature, and consequently in-situ impedance measurements are likely to be unstable. It has been proposed that quasi-DC measurements, which benefit from superior noise performance, but also tend to the skin-effect independent DC measurement, be adopted for in-situ creep measurements for power station components. Unfortunately, the quasi-DC measurement will only tend to the DC distribution and therefore some remnant sensitivity to the skin effect will remain. This paper will present a correction for situations where the remnant sensitivity to the skin effect is not adequately suppressed by using sufficiently low frequency; the application of particular interest being the in-situ monitoring of the creep strain of power station components. The correction uses the measured phase angle to approximate the influence of the skin effect and allow recovery of the DC-asymptotic value of the resistance. The basis of the correction, that potential drop measurements are minimum phase is presented and illustrated on two cases; the creep strain sensor of practical interest and a conducting rod as another common case to illustrate generality. The correction is demonstrated experimentally on a component where the skin effect is manipulated by application of a range of elastic stresses.

Abstract: In this paper, a novel class of hybrid excitation, stator vernier permanent magnet (VPM) machines (HE-VPM) are proposed. The proposed machines are with salient rotor structure, stator located PMs, and concentrated armature windings. Therefore, the superiority of the proposed machine is robust rotor structure, short and non-overlapping end-winding, and easy heat dissipation. Besides, a novel DC-biased sinusoidal current, which contains an alternating current (AC) component and a direct current (DC) component, is applied, with this novel current, a novel hybrid excited VPM machines without additional field windings are obtained. The simulation results shows that the proposed machines exhibit higher torque density, power factor, and efficiency, Also, the constant power operation range is broadened, as the injected DC biased current can weaken or enhance the exciting fields at high/low speed. Finally, a prototype has been designed and under built, and the corresponding experiments will be added later.

Abstract: Carbon nanotube thermophones can create acoustic waves from 1 Hz to 100 kHz. The thermoacoustic effect that allows for this non-vibrating sound source is naturally inefficient. Prior efforts have not explored their true efficiency (i.e., the ratio of the total acoustic power to the electrical input power). All previous works have used the ratio of sound pressure to input electrical power. A method for true power efficiency measurement is shown using a fully anechoic technique. True efficiency data are presented for three different drive signal processing techniques: standard alternating current (AC), direct current added to alternating current (DCAC), and amplitude modulation of an alternating current (AMAC) signal. These signal processing techniques are needed to limit the frequency doubling non-linear effects inherent to carbon nanotube thermophones. Each type of processing affects the true efficiency differently. Using a 72 W(rms) input signal, the measured efficiency ranges were 4.3 × 10(-6) - 319 × 10(-6), 1.7 × 10(-6) - 308 × 10(-6), and 1.2 × 10(-6) - 228 × 10(-6)% for AC, DCAC, and AMAC, respectively. These data were measured in the frequency range of 100 Hz to 10 kHz. In addition, the effects of these processing techniques relative to sound quality are presented in terms of total harmonic distortion.

Abstract: Alternating current (ac) voltammetry provides access to faster electrode kinetics than direct current (dc) methods. However, difficulties in ac and other methods arise when the heterogeneous electron-transfer rate constant (k0) approaches the reversible limit, because the voltammetric characteristics become insensitive to electrode kinetics. Thus, in this near-reversible regime, even small uncertainties associated with bulk concentration (C), diffusion coefficient (D), electrode area (A), and uncompensated resistance (Ru) can lead to significant systematic error in the determination of k0. In this study, we have introduced a kinetically sensitive dual-frequency designer waveform into the Fourier-transformed large-amplitude alternating current (FTAC) voltammetric method that is made up of two sine waves having the same amplitude but with different frequencies (e.g., 37 and 615 Hz) superimposed onto a dc ramp to quantify the close-to-reversible Fc0/+ process (Fc = ferrocene) in two nonhaloaluminate ionic li...

Abstract: We report the experimental evidence of the ac Josephson effect in a transition edge sensor (TES) operating in a frequency domain multiplexer and biased by ac voltage at MHz frequencies. The effect is observed by measuring the non-linear impedance of the sensor. The TES is treated as a weakly linked superconducting system and within the resistively shunted junction model framework. We provide a full theoretical explanation of the results by finding the analytic solution of the non-inertial Langevian equation of the system and calculating the non-linear response of the detector to a large ac bias current in the presence of noise.

Abstract: The invention relates to a gas insulated electrical equipment partial discharge multi-sensor combined monitoring experiment device comprising a power frequency AC power supply system, a gas discharge chamber, at least four artificial insulation defect models and a multi-sensor combined detection system which comprises four parts of a pulse current method sensor detection system, an ultrahigh frequency sensor detection system, a gas chromatography mass spectrometric detection sensor detection system and a fluorescence fiber sensor detection system Partial discharge of an SF6 gas insulated electrical equipment typical defect under different air pressure, different electric field distribution and different gas types of the condition of power frequency alternating current can be simulated, electrical, optical, ultrahigh frequency and gas component multi-source information of partial discharge of equipment is acquired, and effective characteristic quantity of the most mechanism of PD signals with the closest insulation connection can be mined so that a simple and feasible method and experiment platform are provided for the experimental study of construction of a comprehensive and integrated complete SF6 gas insulated electrical equipment insulation state information base

Abstract: Sensorless monitoring technology based on motor current signature analysis is a nonintrusive and economical technique to monitor motor-driven equipment. Sensorless monitoring technology can be applied to a centrifugal pump system. This technology is also based on the motor current signature of centrifugal pump load; however, systematic research regarding motor current signature in overall normal operation points which is the applied basic for sensorless monitoring technology has been rarely performed. As such, we partially examined the motor current signature of a centrifugal pump load by experimental observation, theoretical analysis, and numerical simulation. Results show that stator current is a sinusoidal alternating current that strictly follows sine law associated with the cycle of the fundamental frequency of supply power. The trend of the root mean square and peak–peak of current is the same as flow–shaft power characteristics; hence, this trend could be used as indicator of the pump operational p...

Abstract: An arrangement for interrupting current(10) comprising a first and a second terminal (11,12) being adapted to electrically connect two sections (100,200) of a power system is provided. A voltage control means (4) is controllable in use to inject energy into said loop to force a rapid increase of an alternating current (Io) flowing through said main branch (15) while it is being controlled to open to interrupt amain current (I), and whereby zero cross-over of the current (Isw) through the mechanical main circuit breaker (1) is realized as the amplitude (AIo) of the alternating current (Io) exceeds the amplitude (AI) of the main current. An energy absorbing device (2) is adapted to limit the voltage across said capacitor (31) and across said mechanical breaker (1) when the mechanical breaker is open. Furthermore, the energy absorbing device is adapted to limit the voltage across an inductive element (32) if the voltage across the mechanical breaker breaks down, at or immediately after an opening process, thereby limiting the rate-of-rise and the peak of the current through said loop.The rate-of-rise and the peak of the current through said resonant loopis thereby limited and an improved current interrupting capability is obtained regardless of the type of current to be interrupted. A system and a method for interrupting current are also provided.

Abstract: Disclosed in the present invention is a four-port power electronic transformer based on a hybrid modular multilevel converter (MMCs). The four-port power electronic transformer includes a hybrid MMC, direct current (DC)/DC converters, and an inverter. Each DC/DC converter includes a front stage part, a high frequency transformation part and a back stage part. Compared with an existing power electronic transformer, the present invention has the following characteristics: an MMC module and a front stage of a DC/DC circuit connected to the MMC module jointly complete DC fault ride-through, and the number of adopted devices is small; the MMC module controls a DC voltage and the DC/DC circuit controls power; voltages of one or two capacitors in the module can be controlled independently or simultaneously; and the four-port power electronic transformer has four ports: a high-voltage DC port, a high-voltage alternating current (AC) port, a low-voltage DC port, and a low-voltage AC port, and is applicable to a high-voltage high-power scenario with multiple voltage types and levels, particularly to the energy internet to be used as an energy router and the like.

Abstract: The invention discloses a dual-capacitor module based MMC type multi-port power electronic transformer. The transformer comprises a modular multilevel converter (MMC), a DC/DC converter and an inverter, wherein the MMC has two sub modules; the DC/DC converter comprises a primary part, a high frequency voltage transformation part and a secondary part, wherein the primary part has four kinds of selective topologies. The transformer can be operated on the high voltage direct current side at a low voltage; the transformer has fault ride-through capability, and relatively less devices are used; the module in the MMC and the DC/DC converter are responsible for direct current voltage control and power control respectively; a single capacitor voltage of the module can be controlled independently, or two capacitor voltages of the module can be controlled simultaneously; the transformer is equipped with the four ports, including a high voltage direct current port, a high voltage alternating current port, a low voltage direct current port and a low voltage alternating current port, so that the transformer is suitable for multi-kind high-voltage high-power occasions of multiple voltage levels, and particularly suitable for the energy internet; for example, the transformer can be used as an energy router, and the like.

Abstract: The development of ultra-efficient commercial vehicles and the transition to low-carbon emission propulsion are seen as strategic thrust paths within NASA Aeronautics. A critical enabler to these paths comes in the form of hybrid electric propulsion systems. For megawatt-class systems, the best power system topology for these hybrid electric propulsion systems is debatable. Current proposals within NASA and the Aero community suggest using a combination of alternating current (AC) and direct current (DC) for power generation, transmission, and distribution. This paper proposes an alternative to the current thought model through the use of a primarily high voltage AC power system, supported by the Convergent Aeronautics Solutions (CAS) Project. This system relies heavily on the use of doubly-fed induction machines (DFIMs), which provide high power densities, minimal power conversion, and variable speed operation. The paper presents background on the activity along with the system architecture, development status, and preliminary results.

Abstract: The increasing penetration of renewable generators can be a significant challenge due to the fluctuation of their power generation. Energy storage (ES) units are one solution to improve power supply quality and guarantee system stability. In this paper, a hybrid microgrid is built based on photovoltaic (PV) generator and ES; and coordinated control is proposed and developed to achieve power management in a decentralized manner. This control scheme contains three different droop strategies according to characteristics of PV and ES. First, the modified droop control is proposed for PV, which can take full utilization of renewable energy and avoid regulating output active power frequently. Second, to maintain the direct current (DC) bus voltage stability, a novel droop control incorporating a constant power band is presented for DC-side ES. Third, a cascade droop control is designed for alternating current (AC)-side ES. Thus, the ES lifetime is prolonged. Moreover, interlinking converters (ICs) provide a bridge between AC/DC buses in a hybrid microgrid. The power control of IC is enabled when the AC- or DC-side suffer from active power demand shortage. In particular, if the AC microgrid does not satisfy the reactive power demand, IC then acts as a static synchronous compensator (STATCOM). The effectiveness of the proposed strategies is verified by simulations.

Abstract: The relative polarization behavior of micron and submicron polystyrene particles was investigated under direct current and very low frequency (<1 kHz) alternating current electric fields. Relative polarization of particles with respect to the suspending medium is expressed in terms of the Clausius-Mossotti factor, a parameter of crucial importance in dielectrophoretic-based operations. Particle relative polarization was studied by employing insulator-based dielectrophoretic (iDEP) devices. The effects of particle size, medium conductivity, and frequency (10-1000 Hz) of the applied electric potential on particle response were assessed through experiments and mathematical modeling with COMSOL Multiphysics(®). Particles of different sizes (100-1000 nm diameters) were introduced into iDEP devices fabricated from polydimethylsiloxane (PDMS) and their dielectrophoretic responses under direct and alternating current electric fields were recorded and analyzed in the form of images and videos. The results illustrated that particle polarizability and dielectrophoretic response depend greatly on particle size and the frequency of the electric field. Small particles tend to exhibit positive DEP at higher frequencies (200-1000 Hz), while large particles exhibit negative DEP at lower frequencies (20-200 Hz). These differences in relative polarization can be used for the design of iDEP-based separations and analysis of particle mixtures.