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This work investigates the effect of alternating current partial discharge (AC PD) byproducts on the dielectric frequency response (DFR) of oil-paper insulation comprising of a small cavity, in the frequency range of 1.0 mHz to 1.0 kHz. The investigations were done by utilizing experimental results in combination with a Finite Element Method (FEM) model. The results presented in this paper show that ageing by-products in the cavity (PD stressed volume) alone will not result into the change in DFR of oil-paper insulation. According to simulation results, the significant change in the DFR results is mainly caused by PD by-products (positive and negative charges, and electrons) which tend to conduct or diffuse into the bulk of oil-paper insulation. The change in a dissipation factor curve due to PD by-products was observed to occur mainly in the middle and low frequency regions. The results indicate that the dissipation factor curves in the middle and low frequency regions depend on the level of PD by-products in oil and paper, respectively. [ABSTRACT FROM AUTHOR]

As striking lightning impulse waveforms in power transformers are quite different from the standard lightning impulse waveform (SLIW) used in the withstand voltage tests, it is essential to identify the breakdown characteristics of oil-impregnated paper (OIP) under non-SLIW and to quantitatively compare them with those under SLIW. On that basis, the impulse insulation levels of power transformers can be rationally determined and then the insulation specifications can be evaluated to maintain high equipment reliability. In this paper, with damped alternating oscillation waveform as a representative basis, the breakdown characteristics of oil-impregnated paper were experimentally obtained by changing the frequency and damping rate of the applied voltage. All experiments were conducted using a column-column electrode model. In addition to the 50% breakdown voltages (U50), Minimum breakdown voltage Umin and V-t characteristics under different circumstances, the influence of various parameters on breakdown characteristics and the possible reasons were discussed. After comparing waveforms and corresponding results, the specific relationship between waveform parameters and U50 were expressed as a single equation. As a result, the breakdown voltage was 1.106 to 1.435 times higher than that under SLIW depending on frequency and damping rate. The steepness of the wave peak and the duration of high voltage around wave crests are considered to be two important factors affecting the breakdown voltage. An effective way was proposed to predict U50 of oil-impregnated paper as a reference for insulation specifications irrespective of wave shape. These results support the rationalization of insulation for actual lightning impulse waveforms in the power transformers. [ABSTRACT FROM AUTHOR]

Partial discharge (PD) characteristics of hexadecane were studied in a needle-plane electrode geometry under AC field with a tungsten needle of 20 μm tip radius. PD experiments were conducted on samples containing known concentrations of oil/paper degradation compounds. Partial discharge inception voltage (PDIV), streamer repetition rates, and phase resolved PD (PRPD) patterns were acquired. Ionization potentials (IP) and electron affinities (EA) of hexadecane and a selection of additives were calculated with density functional theory (DFT) and correlated to PD characteristics. IP did not have a significant effect on the number of streamers initiated as most additives had higher IP relative to hexadecane. The presence of electronegative oxygen changes substantially the PD characteristics and, for most additives, increases the number of positive and negative streamers initiated. The greatest changes in PD characteristics, a reduced number of negative streamers, was observed for compounds with large electron capture cross section, even those with negative EA. [ABSTRACT FROM AUTHOR]

Solid insulation materials need to be robust in terms of both mechanical and electrical performance for application in a high-voltage superconducting apparatus. It is known that creepage discharge characteristics of solid insulation materials are inferior to their electrical breakdown characteristics with penetration. Therefore, electrical breakdown accidents in a superconducting apparatus could occur as a form of creepage discharge rather than electrical breakdown with penetration. In this study, we conduct dielectric experiments on the penetration and creepage discharge characteristics of epoxy resin and polypropylene laminated paper under cryogenic temperature by using three kinds of electrode systems. The first is for creepage discharge experiments along the surfaces of solid insulation materials in liquid nitrogen. The second is for creepage discharge experiments across the interface between two different solid insulation materialsmaking contact in liquid nitrogen. The third is for experiments of electrical breakdown with penetration on solid insulation materials in liquid nitrogen. Dielectric experiments are conducted with an absolute pressure of 0.1 MPa under alternating current and lightning impulse voltages. Experimental results for electrical breakdown characteristics of solid insulation materials with penetration are compared with the creepage discharge characteristics on the surface and interfaces between solid insulation materials. Moreover, the criteria for electric field intensities at creepage discharge voltages in various conditions are deduced as empirical formulas. [ABSTRACT FROM AUTHOR]

This paper develops a statistics-based approach for analysis of transmission outage data. The method is applied to the Western Electricity Coordinating Council (WECC) transmission inventory and outage data collected and submitted by member utilities to the North American Electric Reliability Corporation's (NERC) Transmission Availability Data System (TADS). The developed model considers the random nature of Alternating Current (AC) circuit outages and introduces fourteen inventory attributes of the AC circuits as explanatory variables for the outage frequency. The main goal of the paper is to investigate statistical relationships between the number of automatic outages on AC circuits and AC circuit inventory attributes based on the TADS data from 2013–2018, which has proven to be sufficient in obtaining statistically valid results. Concepts associated with the statistical validation of performance indices are discussed with emphasis placed on analysis of distinct types of explanatory variables such as voltage class, mileage, number of terminals, circuits per structure, terrain, elevation, etc. [ABSTRACT FROM AUTHOR]

When an alternating voltage is applied to a dielectric material, dipoles in the material try to align in the direction of the applied voltages and polarization process starts. For multi-dielectric media especially in which a liquid interface is involved, such as oilpaper insulation, interfacial polarization is predominantly active among all polarization processes. This interfacial polarization is a very slow process and is effective in lower frequency range. This interfacial polarization reflects the inherent condition of the oilpaper insulation. Due to this reason, frequency domain spectroscopy is performed in lower frequency range to assess the condition of oil-paper insulation. So, the time required for frequency response measurement using conventional frequency domain spectroscopy is quite long. Considering the aforesaid facts, a different procedure has been taken here to measure the dielectric response in a significantly lesser time keeping the entire frequency range of conventional frequency domain spectroscopy. Instead of using pure sinusoidal excitation voltages over wide frequency range, dielectric response current has been measured using excitation having time growing frequency sweep (TGFS) signal. For this purpose, test samples that emulate the oil-paper insulation of real-life transformer have been prepared in the laboratory. The moisture contents of the test samples have been kept different to investigate the reliability of the proposed method. A setup has been made in the laboratory to measure dielectric response currents using the both excitations. In order to investigate the applicability of the proposed method, experiment has also been performed on actual transformers. It has been observed that the use of excitation signal having time growing frequency sweep provides almost similar information regarding insulation condition as obtained by the use of conventional sinusoidal excitation voltages. Hence, the proposed method is capable of reduction in time in FDS nearly by an amount of 85%. [ABSTRACT FROM PUBLISHER]

In classical gun and satellite launching systems, noise, flame, and hazardous gasses occur during the explosion of gunpowder, and it is possible to change the muzzle velocity of projectile only during the production phase. In addition, negative aspects of classical guns include the storage of munitions, their decay in time, high amount of their mass, and their high cost. In this paper, “A New Electromagnetic Coilgun” is designed to allow acceleration of a ferromagnetic projectile with the help of instantaneous alternate current applied on four sequential stator coils without using any mechanical boosters. programmable interface controllers microcontroller software and Delphi software were used to obtain the data from optic systems placed at the beginning of stator coils for gradual velocity measurement of the projectile, to process the same, and to perform triggering checks. Furthermore, such Delphi-based software allowed to improve the muzzle velocity by changing the triggering time for coils and, thus, to optimize the system. This paper is distinguished from other studies in the literature in terms of the software used and the design of accelerating coil. Data communication was ensured through the serial port of the PC during the launching process. The study examined the effects of variables such as the voltage applied on coils, number of turns of the coil, and the number of capacitors on the maximum muzzle velocity that may be obtained through the launcher and these were discussed in detail in the scope of the paper. [ABSTRACT FROM AUTHOR]

This paper widens the application of a testing protocol for overhead line insulators introduced by TERNA. Testing results relevant to three groups of Room Temperature Vulcanized pre-coated cap-and-pin insulators removed from High Voltage Alternate Current and Extra-High Voltage Alternate Current Italian lines after different years of service are reported and statistically processed; the third group is treated here for the first time and new results for the other two groups are included. Among the various tests prescribed in the protocol, focus is on the Quick Flashover test, with the aim to examine and compare the flashover voltages of all three groups as a function of service time. The dependence of flashover voltage on electric field is also analyzed and a model correlating flashover voltage with field and time is proposed for the first time. It is confirmed that the flashover voltages provided by the Quick Flashover test can be considered as a diagnostic property of Room Temperature Vulcanized insulators, as they drop with the ageing time and the electric field. [ABSTRACT FROM AUTHOR]

The insulation performance of an oil-immersed power transformer against lightning surges is verified by applying a lightning impulse (LI) voltage alone. However, the surge voltage generated at the transformer terminal in an actual system is superimposed over the ac operating voltage. Particularly for UHV- and 500 kV-class, where the ratio of ac operating voltage to the LI withstand voltage is high, the insulation characteristics for this LI and ac superimposed voltage are crucial factors to study the insulation design. Accordingly, this paper reviewed the research results of insulation characteristics of transformers for the superimposed voltage. Subsequently, these results were evaluated from perspectives of an insulation coordination and transformer insulation test. The insulation elements of transformers covered were the turn-to-turn and section-to-section insulation, for which the LI test is key for insulation design. As a result, for the section-to-section insulation for a shell-type transformer and the turn-to-turn insulation, the breakdown (BD) voltage for the superimposed voltage remained unchanged from the result when the LI was applied alone. Conversely, for the section-to-section insulation of a continuous disk winding for a coretype transformer, the BD voltage attributable to the superimposed voltage declined by about 10% to 20% from that when the LI was applied alone if the oil-impregnated paper component ratio compared to the oil-gap length was low. This is because the oil gap was primarily responsible for the BD and flaws were generated there when the ac voltage was applied. On the other hand, when this ratio was increased, the oil-impregnated paper part was primarily responsible for BD and the decline in BD voltage could be suppressed. For the section-to-section insulation for the interleaved disk winding, the BD voltage attributable to the superimposed voltage remained constant from that when the LI was applied alone. This is because the BD was determined by the LI partial discharge inception at the turn-to-turn part of the section-to-section insulation, where the superimposed voltage made little impact on BD. Based on the above, the LI test is considered adequate to verify the insulation performance of the section-to-section insulation for a shell-type transformer and for an interleaved disk winding and the turn-to-turn insulation against surge overvoltage. Conversely, for the section-to-section structure of a continuous disk winding, the influence of the ac voltage must be taken into account. These results are key findings for rationalizing transformers while maintaining their insulation reliability. [ABSTRACT FROM AUTHOR]

Permanent magnet (PM) materials are nowadays widely used in the electrical machine manufacturing industry. The eddy-current loss models of PMs used in electrical machines are frequently discussed in research papers. In magnetic steel materials we have, in addition to eddy-current losses, there are hysteresis losses when alternating current or a rotating flux travels through the material. Should a similar phenomenon be also taken into account in calculating the losses of PMs? Every now and then, authors seem to assume that some significant hysteresis losses are present in rotating machine PMs. This paper studies the mechanisms of possible hysteresis losses in PMs and their role in PMs when used in rotating electrical machines. [ABSTRACT FROM PUBLISHER]

In the paper by Jin et al. (IEEE Trans. Ind. Electron., vol. 62, no. 3, pp. 1363–1371, Mar. 2015), the authors present an expansion of Ohm's law in the nonsinusoidal ac circuit, based on which a distinct instruction for analyzing and designing nonsinusoidal circuit including ac/dc link circuit is provided. This paper is very interesting and a good work. However, some equations and expressions may be improved. In this paper, they are discussed and modified. [ABSTRACT FROM AUTHOR]

The integration of the dynamic line rating (DLR) of overhead transmission lines (OTLs) in power systems security constrained unit commitment (SCUC) potentially enhances the overall system security as well as its technical/economic performances. This paper proposes a scalable and computationally efficient approach aimed at integrating the DLR in SCUC problem. The paper analyzes the case of the SCUC with AC load flow constraints. The AC-optimal power flow (AC-OPF) is linearized and incorporated into the problem. The proposed multi-period formulation takes into account a realistic model to represent the different terms appearing in the Heat-Balance Equation (HBE) of the OTL conductors. In order to include the HBE in the OPF, a relaxation is proposed for the heat gain associated to resistive losses while the inclusion of linear approximations are investigated for both convection and radiation heat losses. A decomposition process relying on the Benders decomposition is used in order to breakdown the problem and incorporate a set of contingencies representing both generators and line outages. The effects of different linearization, as well as time step discretization of HBE, are investigated. The scalability of the proposed method is verified using IEEE 118-bus test system. [ABSTRACT FROM AUTHOR]

Future power systems will contain more converter-based generation, among which are the voltage-source converter–high-voltage direct-current (VSC-HVDC)-connected offshore wind power plants (WPP). Their interaction with the onshore system influences power system dynamics in the transient stability timeframe. The respective protection and control methods which cause this interaction must be taken into account in grid-integration studies performed today. This paper gives insight into the effect of typically required fault ridethrough (FRT) and post-FRT measures of VSC-HVDC-connected offshore WPPs on the combined ac and HVDC system dynamics. Several important sensitivities are addressed, among which are: 1) FRT implementation, 2) the postfault active power-recovery rates, 3) the ac network dynamic characteristics, and 4) the HVDC topology. The analysis is first performed as a proof of concept on a small benchmark system, and subsequently generalized to a realistic dynamic model of the future Northwestern European power system. The results of this paper can be used as a reference for understanding the effects of large-scale VSC-HVDC-connected offshore WPPs on the stability of the onshore interconnected power systems. [ABSTRACT FROM AUTHOR]

In this paper, we propose a novel ac/dc bridgeless and contactless energy transmission system. The coreless planar transformer and magnetic dipole moment are applied to transmit electrical energy in a noncontact method. In addition, the input ac current of the proposed converter has effective power factor correction. Simultaneously, the primary-side switches have zero-voltage switching, and the secondary-side diodes have zero-current switching. Thus, the power quality and efficiency of the proposed system can be upgraded. Furthermore, the proposed system can increase the transmission distance with the voltage multiplier receiver connected at the rear of the secondary-side coreless planar transformer. Power transmission and circuit operation are described in this paper. Finally, a prototype system is constructed, and its validity has been confirmed with experimental and practical measurements. [ABSTRACT FROM AUTHOR]

With the increasing use of sensors and wireless communication systems, predictive maintenance is acquiring more and more importance to assess the condition of in-service equipment. Predictive maintenance presents promising cost savings, as it allows minimizing unscheduled power systems faults, which can have very costly and catastrophic consequences. Early stage detection of power system failure requires acquiring, monitoring, and periodically analyzing the condition of the elements involved, such as high-voltage power connectors, since they are critical devices which are often located in key points of power systems. This paper proposes a low-cost online system to determine the contact resistance of high-voltage direct current (dc) and alternating current (ac) power connectors, to determine their health condition in order to apply a predictive maintenance plan. The contact resistance is considered as a reliable indicator of the connector’s health condition. However, it cannot be directly measured, and the applied strategy differs between dc and ac power systems. The experimental results show a maximum uncertainty of 4.5%, thus proving the accuracy and feasibility of the approach presented in this paper, since the proposed limit of acceptable resistance increase is 20%. This approach can also be applied to many other power systems’ elements. [ABSTRACT FROM AUTHOR]

A single-stage TRIAC (TRIode for alternating current switch) dimmable LED (light emitting diode) driver using a buck converter fed through a capacitor input rectifier provides many advantages such as small-scale implementation, low output current ripple, and stable dimming operation. This circuit topology, however, has a serious issue: A large inrush current to the smoothing capacitor. To solve this issue, this paper focuses on a bleeder circuit in the TRIAC dimmable LED driver. This paper presents the mechanism of the large inrush current issue and its relationship to a conventional bleeder circuit. Moreover, this paper proposes a turn-off delay controlled bleeder circuit. The proposed bleeder circuit is analyzed by using its discrete-time state-space model in order to set proper circuit parameters for inrush current reduction. Experimental results demonstrate the inrush current reduction by the proposed method, which leads to a 37% reduction of maximum input current, as well as proper dimming operation and low output current ripple. The proposed method achieves further small-scale implementation, which enhances the advantages of the intended main circuit topology. [ABSTRACT FROM AUTHOR]

We report in this paper the design and fabrication of single-chip alternating current-LEDs (AC-LEDs) by monolithically integrating, for the first time, high-breakdown Schottky barrier diodes (SBDs) and micro-LED arrays using III-nitride LED epi-wafers of standard specs for volume production. A technique of cyclic mixed-etching has been introduced to restore the surface of inductively coupled-plasma (ICP) etching processed gallium nitride to device quality for fabricating high-breakdown Schottky junctions. Proof-of-concept single-chip AC-LED devices and a prototype driver-free white AC-LED lamp were demonstrated, showing high-efficiency LED emission, high chip area utilization efficiency, low power loss of the on-chip SBD bridge rectifier, and good luminous efficacy of the prototype AC-LED lamp. This paper paves the way toward mass-producing reliable and low-cost driver-free AC-LED lamps for solid-state lighting with existing LED manufacturing infrastructures. [ABSTRACT FROM AUTHOR]

In this paper, we proposed and verified the feasibility of a unique wireless power transfer structure called a rail transformer to drive multiple low-power devices such as electronic shelf label (ESL) devices. The rail transformer is composed of a rectangular, circular-shaped transmitting yoke and two transmitting coils to provide wireless power. Multiple receiving yokes coupled with receiving coils are installed across the elongated edge of the transmitting yoke. It can be driven by low-frequency ac power at 50/60 Hz. In our prototype, the transmitting yoke is 900 mm long and 15 mm wide. We obtained the minimal induced wireless power, and the voltage was $\sim 61$ mW and 3.5 V, which is sufficient to drive a typical ESL device. By designing a nonuniform gap thickness between the transmitting and the receiving yokes at the specific locations, we improved the uniformity of the induced power for multiple ESL devices. [ABSTRACT FROM AUTHOR]

This paper provides a theoretical and experimental discussion on ac-inductors design for a modular multilevel triple-star bridge-cells (TSBC) converter, or shortly a TSBC converter. This converter requires multiple ac inductors for controlling nine cluster currents. This paper proposes three three-legged, six-winding, “interzigzag” inductors for the TSBC converter. Since each leg of the individual inductor has two windings, the three inductors have 18 windings in total. The wire leads are zigzagged among the three inductors. This unique structure of the “interzigzag” windings leads to the following feature: Both three-phase supply and motor currents produce no magnetic flux in each of the nine legs. This feature makes each inductor smaller in size and lighter in weight. A specially-designed downscaled motor-drive system rated at 400 V and 15 kW is constructed and tested to confirm the validity of a design of the proposed inductors, as well as to verify transient motor-drive performance during four-quadrant operation. [ABSTRACT FROM AUTHOR]

Travelling wave (TW) fault location has been widely utilized for high-voltage alternating current (HVAC) transmission lines, which is proven to have a higher accuracy than conventionalpower frequency data based fault location. However, as known, the performance of travelling wave-based fault location (TWFL) principles is often challenged by several factors including fault location, fault initial angle, fault resistance as well as frequency dependency of HVAC transmission lines. In this context, this paper proposes a novel off-line TW fault location principle for transposed HVAC transmission lines to address the robustness against those uncertain factors. Firstly, the frequency-dependent characteristic of HVAC transmission lines is analyzed. Then upon that, a novel TW fault location principle is proposed, which consists of two important components: i) arrival time detection of TW and ii) accurate frequency calculation of TW. Eventually, simulations are carried out on a 500 kV AC transmission system using PSCAD/EMTDC to validate the effectiveness of the proposed method and itsrobustness against different fault types, resistances, locations, initial angles and noises. [ABSTRACT FROM AUTHOR]

Reactive power planning has always been a key research area in power distribution engineering; technically and economically. However, the problem needs to be revisited to consider several aspects of modern distribution systems, such as a high penetration level of renewable resources with intermittent nature; the microgrid concept and the possibility of system operation in grid-connected or isolated single microgrid mode, or isolated multiple microgrids; and probabilistic or hourly load profile. Motivated by these needs and considering all these aspects, this paper presents a generalized approach for probabilistic optimal reactive power planning in modern distribution systems. A new index is defined to probabilistically assess the success of microgrids in terms of real and reactive power adequacy and voltage limit constraints. Afterward, the reactive power planning is performed to reduce the annual energy losses of the grid-connected system and increase the defined microgrid success index. The problem formulation and solution algorithms are presented in this paper. The well-known PG&E 69-bus distribution system is selected as a test case, and through several sensitivity studies, the effect of optimization coefficients on the design and the robustness of the algorithm are investigated. A cost–benefit case study is also presented to determine the optimum total size of distributed reactive sources for the system under study. [ABSTRACT FROM PUBLISHER]

This paper presents a comprehensive analysis of the limitations and the key dynamics of closed-loop active power control systems for voltage-source converter (VSC) HVDC, regarding stability, performance, and robustness. Detailed dynamic models are derived and the controllability and robustness issues for VSC active power control are identified. Limitations imposed by ac system strength, converter operating point, and current control design on the stability and performance of the two leading active power control principles are addressed, using frequency-response analysis and time-domain simulations. The dynamic interactions between the active power control design and the dc voltage droop control are examined. The simulations are performed using average-value VSC models and a high-fidelity modular multilevel converter model. Impacts of the active power control design on dynamic behaviors of multiterminal dc (MTDC) systems are investigated using a four-terminal model. This paper provides a systematic study on the key stability and performance issues associated with the active power control. Furthermore, the methodology offers a framework for the analysis of more complex active power and dc voltage droop controllers for future MTDC systems. [ABSTRACT FROM AUTHOR]

This paper presents analytical closed-form expressions that uncover the contributions of nodal active- and reactive-power injections to the active- and reactive-power flows on transmission lines in an AC electrical network. Paying due homage to current- and voltage-divider laws that are similar in spirit, we baptize these as the power divider laws. Derived from a circuit-theoretic examination of AC power-flow expressions, the constitution of the power divider laws reflects the topology and voltage profile of the network. We demonstrate the utility of the power divider laws to the analysis of power networks by highlighting applications to transmission-network allocation, transmission-loss allocation, and identifying feasible injections while respecting line active-power flow set points. [ABSTRACT FROM PUBLISHER]

This paper presents a new method for measuring grounding resistances, which is based on the measured net charge drained by the grounding system when excited by an impulse generator. The circuit property used by the method is briefly described, alongside with the method itself. An advantage of this method with respect to the traditional ones is that it is not affected by the self and mutual reactances present in the grounding system and in the measuring wires. Moreover, the proposed method does not require the measurement of surface potentials, which are prone to interference due to soil non-homogeneities, buried conductive bodies, and stray currents. This paper presents experimental results from the method using lumped components and using actual grounding systems. The results show that the method provides consistent and accurate values of grounding resistances. [ABSTRACT FROM AUTHOR]

High-resolution multiplying digital-to-analog converters (MDACs) are often used as digitally controlled ac voltage dividers in precise instruments and measurement systems. Proper application of these converters requires knowledge of their parameters, especially amplitude and phase errors, which are usually not specified by MDAC manufacturers. This paper presents the results of investigations of voltage amplitude ratio errors and phase errors, as well as the time stability of voltage ratio and phase shift of selected commercial 16- and 18-bit MDACs. These parameters were measured with a dedicated high-resolution sampling system. The amplitude ratio and phase errors were determined as a function of the MDAC digital input word. Phase errors were also determined as a function of frequency. [ABSTRACT FROM AUTHOR]

This paper examines the small-signal stability of an integrated multiterminal dc (MTDC)/ac power system. The examination is based on a closed-loop multi-input multi-output interconnected model of the MTDC/ac power system, which comprises an MTDC subsystem and an ac subsystem. The focus of the examination is the condition of open-loop modal coupling when an open-loop oscillation mode of the MTDC subsystem is close to an open-loop oscillation mode of the ac subsystem on the complex plane. Analysis in the paper indicates that when the open-loop modal coupling happens, the multivariable ac–dc dynamic interactions between the MTDC and ac subsystems degrade the small-signal stability of the MTDC/ac power system. Estimation on the degree of stability degradation is derived. Hence, the paper reveals the mechanism about why the integration of the MTDC network may bring about the small-signal instability risk. In addition, a method of open-loop modal analysis to detect the risk is proposed. Example multimachine power systems with an MTDC network are presented to validate the analysis and conclusions made in the paper. Application of the proposed open-loop modal coupling analysis for parameter tuning of converter control systems of the MTDC network is demonstrated. [ABSTRACT FROM AUTHOR]

In this paper, the active differential-mode (DM) electromagnetic interference (EMI) filter topology for ac/dc converters is first briefly investigated. The active DM EMI filter model was developed based on the models of filter components including a current transformer, a high-pass filter, an operational amplifier, and a class AB amplifier. The system model including the active filter, ac/dc converter, and line impedance stabilization networks (LISNs) are explored. With the developed system model, the loop gain and insertion gain of the active filter are derived. Based on the loop gain, the stability of the active filter is investigated and the compensation is applied to achieve stability and good EMI reduction. Both simulations and experiments are conducted to validate the developed technique. [ABSTRACT FROM AUTHOR]

In a hybrid ac/dc grid, the ac-side unbalance voltage introduces adverse effects on dc grids and interfacing converters (IFC) (active power oscillations, dc-link voltage oscillations, and IFC peak current increase at the same average power production). For parallel IFCs, these adverse effects can be easily aggregated. In this paper, two new control strategies are proposed for parallel IFCs to improve both ac and dc subgrids power quality. The proposed control strategies focus on canceling active power oscillations of parallel IFCs that provide oscillation-free dc link and sharing collective peak current of parallel IFCs. In the first proposed control strategy, IFCs’ power coefficients are controlled by solving a set of nonlinear equations, and this method is called as coefficient-based strategy, whereas, in the second proposed control strategy, peak currents of IFCs are controlled directly through the derived relationship of IFCs' peak currents under zero power oscillation in this paper, and this method is named as peak current based strategy. This peak current based strategy features much simplified calculation and could be easy to implement. To achieve control objectives, thorough study on parallel IFCs' peak currents is conducted. Based on the study, it is shown that the collective peak current of all IFCs is a constant under zero total active power oscillation, and therefore, keeping all IFCs' peak currents in the same phase and in-phase with collective peak current optimizes the utilization range of parallel IFCs. The numerical examples and experimental results are provided to verify the validity of the proposed control strategies under different operating conditions. [ABSTRACT FROM AUTHOR]

This paper presents a novel digital control strategy for the islanding mode operation of a power electronics-based energy management system (EMS). Thanks to the use of a high-performance repetitive controller combined with active damping, the EMS is capable of supplying a high-quality sinusoidal voltage to critical loads when the ac grid is not available. The proposed control scheme is analyzed and implemented in a field-programmable gate array-based control platform; it achieves a very low output voltage total harmonic distortion and holds a large stability margin for a wide range of load conditions. Analysis and simulations demonstrate the superiority of the proposed controller versus open-loop control. Laboratory experiments with linear and nonlinear loads validate the model used for the simulations that demonstrate the excellent performance of the new control strategy. [ABSTRACT FROM AUTHOR]

This paper presents a single-phase ac power supply circuit that based on modified voltage-fed quasi-Z-source inverter topology; it suits to the light or the heavy load and is fit for the resistive, inductive, or capacitive load. The topology, operating principle, voltage gain, control method, and its realization by DSP are described in this paper. The feasibility and rationality of the system is verified by the simulation and experimental results. [ABSTRACT FROM PUBLISHER]

The stacked switched capacitor (SSC) energy buffer is a recently proposed architecture for buffering energy between single-phase alternating and direct current. When used with film capacitors, it can increase the life of grid-interfaced power converters by eliminating limited-life electrolytic capacitors while maintaining comparable energy density. This paper introduces an enhanced version of the bipolar SSC energy buffer that achieves higher effective energy density and round-trip efficiency while maintaining the same bus voltage ripple ratio as the original design. Furthermore, the enhanced buffer uses fewer capacitors and switches than the original design. The enhancement in performance is achieved by modifying the control and switching patterns of the buffer switches. A prototype enhanced SSC energy buffer, designed for a 320-V bus and a 135-W load, has been built and tested. The design methodology and experimental results for the enhanced SSC energy buffer are presented and compared with the original design. This paper also presents a comparison of unipolar and bipolar SSC energy buffers. It is shown that, although bipolar designs are superior in terms of effective energy density at low ripple ratios, unipolar designs can outperform bipolar designs at high ripple ratios. [ABSTRACT FROM PUBLISHER]

The Center Solenoid Model Coil (CSMC) is a pre-research project of CFETR, and its task is to design and manufacture the CS superconducting model coil to gain wider experience in solving the related technical problems existing in design and construction of CFETR CS coils. The expected achievement is to charge the CSMC up to the operation current of 47.65 kA and the maximum magnetic field to 12 T with a swift rump rate of 1.5 T/s without quench. Quench detection by voltage measurements is likely to be the fastest available technical solution to avoid coil's damage caused by quench, but the voltage detection is a real challenge due to large noise induced by the power supply in alternating current operation. The pick-up sensors, comprising the co-wound wire (CWW) and the co-wound tape (CWT), are used in the CSMC quench detection system for noise compensation and suppression. To accurately compensate all related induced voltage in the multi-pulse coil system, the foremost task is to estimate the static inductance matrix between the CSMC and its pick-up sensors. In this paper, a numerical model is developed for inductance calculation and analysis. Moreover, several numerical simulations with this design model to evaluate the maximum inductive noises and quench detection signals by CWW and CWT have been conducted for the case of the worst test scenarios. [ABSTRACT FROM AUTHOR]

High accuracy is required from devices operating in the measuring and protection systems of transmission lines during the transformation of signals. Their immunity to external fields is very important because it has a direct influence on the proper functioning of the protection system. In this paper, the electromagnetic current-to-voltage transducers, with coils designed and manufactured using a multilayer high-density interconnect printed-circuit board technology, are presented. The analysis of the influence of the external magnetic field caused by other devices on the proper functioning of the current-to-voltage transducer has been presented. The analysis of the electromagnetic-field distributions has been carried out using the 3-D field-circuit method based on the finite-element numerical method. The magnetic-field distributions and the induced secondary voltages for several different applications have been presented. The results have been compared with tests of real-life models. [ABSTRACT FROM AUTHOR]

A fully digital, nonlinear, wide-bandwidth current controller for dc–ac and dc–dc voltage source converters is presented in this paper. Exploiting oversampling, the controller mimics an analog hysteresis current controller, but it does not employ analog comparators, digital-to-analog converters, or any other analog signal pre- or postprocessing circuitry. Indeed, it fully virtualizes the hysteresis controller's operation and, based only on a nonlinear, efficient current error processing algorithm, drives the power converter at almost constant switching frequency. Overall, it offers the same excellent dynamic performance of the analog hysteresis controller and, at the same time, solves most of the related problems. Because the current error sample processing algorithm is inherently parallel in structure, the controller is suited for VHDL synthesis and field-programmable gate-array implementation, which guarantees flexibility and low cost, together with minimum computation and signal conversion delays. Its intended application areas include active filters, uninterruptible power supplies, microgrid distributed energy resource controllers, laboratory battery testers, and welding machines. [ABSTRACT FROM PUBLISHER]

A fault protection and location method for ungrounded dc traction power systems is presented in this paper. Many dc traction power systems have an ungrounded power circuit to increase the leakage path resistance. Although ungrounded systems can continue operating with a single ground contact, unlike solid- or low-resistance grounded systems, because of the very low fault current, a second ground fault in another pole will result in a line-to-line fault that could cause significant system damage. However, it is difficult to detect the first ground contact due to the low ground current and even harder to locate because it can be seen by many detectors in the network. The proposed scheme in this paper uses a probe unit to detect and locate the first single ground fault in ungrounded traction power systems. The probe unit applies probe voltage to detect the fault and, once the fault is detected, analyzes the response to dc or swept-frequency ac probe voltage to locate the fault. The proposed concepts have been verified with computer simulations and hardware experiments and demonstrated a successful performance. [ABSTRACT FROM PUBLISHER]

Faults on the alternating current (AC) transmission lines could cause commutation failures of nearby line-commutated converter-based high-voltage direct-current (LCC-HVDC) systems, which in turn, may challenge the fault detection of AC systems. To address this issue, this paper proposes a fast fault detection method based on instantaneous active power and fault variation component to alleviate the impacts of commutation failures and reactive power compensation while mitigating the dead zone problem. Upon that, an integral-based differential protection algorithm is presented to enhance reliability. Simulations are carried out on a real hybrid AC/DC system in North China with different fault locations and resistances to verify the effectiveness of the proposed method. Finally, we further validate the proposed method by leveraging on-site recorded fault data. [ABSTRACT FROM AUTHOR]

In this paper, a new control system to regulate the reactive power supplied by a variable-speed wind energy conversion system (WECS), based on an induction generator fed by a matrix converter (MC), is presented. The control system discussed in this paper is based on an input current observer, implemented using an estimation of the modulation matrix, and a nonlinear control loop that regulates the displacement angle at the MC input. The reactive power capability of the proposed system is also investigated. The work presented in this paper demonstrates that, for the proposed WECS, the maximum reactive power supplied to the grid is about 40% of the nominal value. Experimental results obtained from an experimental prototype are presented in this paper. The performance of the system using a wind turbine emulator and typical wind profiles is discussed in this paper. [ABSTRACT FROM AUTHOR]

Hybrid gas-liquid electrical discharge has been investigated in recent years as an innovative technology for contaminated water treatment. A high-voltage pulsed-power supply is commonly needed for the generation of electrical discharges. This paper aims, in lieu of cost effectiveness, to evaluate the degradation efficiency of electrical discharges with an alternating-current (ac) power since it is generally cheaper than a pulsed one. An ac power supply with a fixed voltage of 13 kV and a fixed frequency of 60 Hz is therefore adopted in this paper for the inactivation of aquatic microorganism. The energies required for one log order of reduction of E. coli, S. aureus, and Yeast were 23,34, and 31 J/ml, respectively. The energy efficiencies achieved with an ac power in this paper are comparable with other studies that achieved with a pulsed-power. [ABSTRACT FROM AUTHOR]

This paper analyzes carrier-signal voltage injection zero-sequence current-based sensorless control techniques for delta-connected three-phase ac machines. The analysis will focus on rotor position estimation (tracking of rotor-position-dependent saliencies), but the method applies equally well to flux position estimation (tracking of flux-dependent saliencies). The paper first develops a theoretical model and then provides analysis of relevant implementation aspects, such as selection of carrier-signal frequency and voltage magnitude, measurement of the zero-sequence carrier-signal current, measurement and compensation of saturation-induced saliencies, and the signal processing needed for position/flux angle estimation. A similar implementation to that proposed in this paper, and with practically the same performance in terms of accuracy and estimation bandwidth, can be obtained for the case of wye-connected machines using the zero-sequence carrier-signal voltage, as shown in IEEE Trans. Ind. Appl., vol. 41, no. 6 pp. 1637-1646, Nov./Dec. 2005. [ABSTRACT FROM AUTHOR]

This paper analyzes the performances of different carrier phase-shifting pulse width modulation (PWM) techniques to be used with a multilevel cascaded H-bridge converter in case of unbalanced operational conditions. In fact, in many practical applications, the ideal condition of equal dc voltages and equal reference signals for each H-bridge cannot be achieved. In such conditions, the conventional carrier phase-shifting PWM technique loses its harmonic canceling capabilities and then the multilevel ac voltage harmonic quality is deeply affected. To overcome this limit of the original technique, different variations have been proposed. All of them still rely on the carrier phase-shifting concept and propose to use a different value of the shifting angle for each carrier (unlike the original technique) whenever unbalanced operational conditions occur. In this paper, the three main solutions proposed over the last years to extend the capabilities of the carrier phase-shifting PWM technique are compared. The analysis is focused on a three-cell cascaded H-bridge converter. Simulation and experimental results are presented. [ABSTRACT FROM PUBLISHER]

This paper jointly addresses two major challenges in power system operations: 1) dealing with non-convexity in the power flow equations, and 2) systematically capturing uncertainty in renewable power availability and in active and reactive power consumption at load buses. To overcome these challenges, this paper proposes a two-stage adaptive robust optimization model for the multi-period AC optimal power flow problem (AC-OPF) with detailed modeling considerations, such as reactive capability curves of conventional and renewable generators and transmission constraints. This paper then applies strong second-order cone programming (SOCP)-based convex relaxations of AC-OPF combined with the use of an alternating direction method to identify worst-case uncertainty realizations, and also presents a speed-up technique based on screening transmission line constraints. Extensive computational experiments show that the solution method is efficient and that the robust AC OPF model has significant advantages both from the economic and reliability standpoints as compared to a deterministic AC-OPF model. [ABSTRACT FROM PUBLISHER]

Conventional single-phase power-factor-correction (PFC) rectifiers with active power decoupling capability typically require more than three active switches in their circuits. By exploring the concept of power-buffer cell, a new single-stage PFC rectifier with two active switches, one inductor and one small power-buffering capacitor is reported in this paper. The proposed converter can achieve high-power factor, wide output voltage range, and power decoupling function without using electrolytic capacitor. Additionally, an automatic power decoupling control scheme that is simple and easy to implement is proposed in this paper. The operating principle, control method, and design considerations of the proposed rectifier are also provided. A 100-W prototype with ac input voltage of 110 Vrms and a regulated dc output voltage ranging from 30 to 100 V has been successfully designed and practically tested. The experimental results show that with only a 15 μF power-buffering film capacitor, the proposed converter can achieve an input power factor of over 0.98, peak efficiency of 93.9%, and output voltage ripple of less than 3%, at 100-W output power. [ABSTRACT FROM PUBLISHER]

In this paper, we study the computational modeling of electromagnetically induced heating in magnetic fluid hyperthermia. Owing to the Brownian rotation and Neel relaxation of induced magnetic moments, ferrofluids can generate heat when exposed to an alternating current magnetic field. To destroy all tumors cells while preventing deleterious physiological responses, input parameters such as the frequency and intensity of magnetic fields and the complex susceptibility of ferrofluids should be determined precisely. In this paper, a solution to Maxwell’s equation for a model of a tumor and its neighboring tissues are coupled as input to Penne’s bioheat equation. Both sets of equations are solved using the finite element analysis method with perfectly matched layers for isothermal boundary conditions in COMSOL. We use a bilayered spherical model with blood perfusion and metabolism to simulate the temperature distribution in tumor regions during hyperthermia therapy. Power density due to electromagnetic field simulation serves as input to the bioheat transfer equation and determines the heat generated by the ferrofluids. The obtained results indicate that tumor regions are heated without adversely affecting healthy regions. [ABSTRACT FROM AUTHOR]

Roebel cables made of high temperature superconducting (HTS) coated conductors can carry high currents with a compact design and reduced ac losses. Therefore, they are good candidates for manufacturing coils for HTS applications such as motors and generators. In this paper, we present the experimental dc and ac characterization of several coils assembled from a 5-m-long Roebel cable built at Karlsruhe Institute of Technology, which differ in the number of turns and turn-to-turn spacing. Our experiments, which are supported by finite-element-method calculations, show that a more tightly wound Roebel coil, despite having a lower critical (and therefore operating) current, can produce a higher magnetic field than a loosely wound one. For a given magnetic field produced at the coil's center, all the coils have similar ac losses, with the exception of the most loosely wound one, which has much higher losses due to the relatively large current needed to produce the desired field. The experiments presented in this paper are carried out on the geometry of pancake coils made of Roebel cables, but they are exemplary of a more general strategy, based on coupling experiments and numerical simulations, that can be used to optimize the coil design, with respect to different parameters, such as tape quantity, size, or ac loss, the relative importance of which is dictated by the specific application. [ABSTRACT FROM PUBLISHER]

This paper presents a new functionality for high-power battery chargers by incorporating an impedance measurement algorithm. The measurement of battery impedance can be performed by the battery charger to provide an accurate equivalent model for battery management purposes. In this paper, an extended control capability of the onboard battery charger for electric vehicles is used to measure the online impedance of the battery. The impedance of the battery is measured by the following: 1) injecting ac current ripple on top of the dc charging current; 2) transforming voltage and current signals using a virtual \alpha-\beta stationary coordinate system, a d-q rotating coordinate system, and two filtering systems; 3) calculating ripple voltage and current values; and 4) calculating the angle and magnitude of the impedance. The contributions of this paper are the use of the d-q transformation to attain the battery impedance, theta, and its ripple power, as well as providing a controller design procedure which has impedance measurement capability. The online impedance information can be utilized for diverse applications such as the following: 1) a theta control for sinusoidal current charging; 2) the quantifying of reactive current and voltage; 3) ascertaining the state of charge; 4) determining the state of health; and 5) finding the optimized charging current. Therefore, the benefit of this method is that it can be deployed in already existing high-power chargers regardless of battery chemistry. Validations of the proposed approach were made by comparing measurement values by using a battery charger and a commercial frequency response analyzer. [ABSTRACT FROM AUTHOR]

Soft-switching ac-link universal power converters, also called partial resonant converters and ac-link buck–boost converters, have received noticeable attention during the last few years. In these converters, each of the inputs and outputs can be dc, single-phase ac, or multiphase ac; therefore, they can be used for dc–dc, dc–ac, ac–dc, or ac–ac power conversion systems. The soft-switching ac-link universal power converters are compact, reliable, and expected to offer longer lifetime compared with the other types of converters. However, they require more switches, which make the control process more involved. The sparse ac-link buck–boost converters were proposed to partially solve this problem. The sparse configuration reduces the number of switches from 24 to 20 in a three-phase ac–ac configuration. This paper proposes a modified configuration, which further reduces the number of switches without changing the principles of operation. This converter, which is named ultrasparse ac-link buck–boost converter, reduces the number of switches from 24 to 16, in a three-phase ac-to-ac case, and from 20 to 10, in a dc-to-three-phase-ac configuration. The proposed converter is applicable to systems with unidirectional flow of power, such as PV and wind power generation systems. This converter is expected to offer higher reliability compared with the original converter and higher reliability and efficiency compared with the sparse configuration. Another important feature of this configuration is that it can be fabricated by insulated-gate bipolar transistor modules, which are more compact and more cost effective compared with discrete devices. This paper presents the principles of the operation of this configuration and compares the efficiency, the failure rate, and the current rating of the switches in the ultrasparse, sparse, and original configurations. Moreover, it evaluates the performance of the proposed converter through simulation and experiment. [ABSTRACT FROM AUTHOR]

Printed circuit board (PCB) windings are convenient for many applications given their ease of manufacture, high repeatability, and low profile. In many cases, the use of multistranded litz wires is appropriate due to the rated power, frequency range, and efficiency constraints. This paper proposes a manufacturing technique and a semianalytical loss model for PCB windings using planar litz structure to obtain a similar ac loss reduction to that of conventional windings of round wires with litz structure. Different coil prototypes have been tested in several configurations to validate the proposal. [ABSTRACT FROM AUTHOR]

This paper develops a robust tool for handling ac side stability issues occurring in $LCL$-filter-based grid-connected converters. $LCL$ filters give advantages in cost and dynamic as smaller inductors employed compared with $L$ filters for the same required damping of the switching harmonics. Nevertheless, the additional poles introduced by the $LC$ part induce resonance in the system leading to stability problems. To deal with this stability issue, a new damping method based on the generalized circle criterion is proposed in this paper. The large signal nature of the applied theory allows obtaining high damping efficiency and robustness under large variations of the grid impedance. A theoretical analysis and the experimental results are presented to show the effectiveness of the proposed compensating method. [ABSTRACT FROM PUBLISHER]

The ac resistance of power cable conductors is an important parameter for accurately estimating the ampacity of power cable and optimally designing power cable. Although international standard IEC-60287 has recommended a simplified formula for calculating the ac resistance, it is not capable of taking into account the effect of stranded conductor parameters, such as the direction and the length of lay, on the ac resistance because the stranded conductor is simplified as a solid conductor. In this paper, the method which has been used for analyzing the ac resistance of aluminum-conductor steel-reinforced overhead power lines is applied to single-core power cable conductors. Basically, the magnetic fluxes around each layer of the stranded wires are divided into circular magnetic fluxes and longitudinal magnetic fluxes, and thus each layer is equivalent to a circuit with resistor and inductor in series. Then, the ac resistance of single-core power cable conductors is calculated from the paralleled equivalent circuits representing all layers. A case study of 800 mm \(^{2}\) single-core power cable is given to investigate the effect of the parameters of the stranded wires on the ac resistance. Results show that the ac resistance for bidirectional stranding of copper wires is a few percentage points higher than that for unidirectional stranding. Such difference will be significant in the optimization of cable design as even a slight decrease in ac resistance can save considerable copper in large-scale industrial application. [ABSTRACT FROM AUTHOR]

This paper proposes an effective charging-torque elimination method for six-phase integrated on-board electric vehicle (EV) chargers. The integrated EV charger is derived from the power inverter, motor windings, sensors, and microchips, which can significantly reduce the system cost and volume. In fact, the charging electromagnetic torque is inevitable to produce, since the alternating currents flow through the motor windings. This is due to the motor windings serving as the filtering inductors of the rectifier for the on-board charger. In order to keep the vehicle standstill during the charging process, a universal expression of charging torque is derived and analyzed, which is according to magnetic co-energy approach. All possible charging torque elimination positions are presented with a numerical method. Moreover, the unity power factor and zero sequence current control are executed during the EV charging process. Finally, the proposed charging torque elimination method is verified by both simulation and experimentation. The results prove the validity of the proposed charging-torque elimination method for six-phase permanent magnet synchronous machine. [ABSTRACT FROM AUTHOR]