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The converter transformer epoxy impregnated paper bushing is a multi-media electrical equipment, and the main materials include the internal conductor, the external conductor, transformer oil, SF6 gas, the air inside internal conductor, the main insulation material epoxy impregnated paper, sheath, and fittings. In actual operating, the converter transformer bushing is undertaken by the harmonic current with large number of high harmonics and the temperature distribution of the epoxy impregnated paper converter transformer bushings under actual current waveform needs to be researched. What's more, the temperature distribution of the epoxy impregnated paper converter transformer bushings is affected by several factors and to provide basis for the optimization of bushings it's necessary to research about the impact of these factors on the temperature distribution of the epoxy impregnated paper converter transformer bushings. In this paper, on the basis of our previous paper [8], the 3-D temperature distribution of the 400 kV epoxy impregnated paper converter transformer bushing under actual current waveform with large number of harmonics has been simulated by using the computational fluid dynamics (CFD) and finite element method (FEM) analysis. The temperature distribution regularity of the 400 kV converter transformer bushing under different influencing factors has been computed and analyzed. The dissipation structure of the bushing has been optimized and the DC steady-state electric field distribution of the 400 kV converter transformer bushing has been obtained considering the temperature gradient in epoxy impregnated paper. [ABSTRACT FROM PUBLISHER]

Frequency Domain Spectroscopy is a popular non-invasive method that is widely used for condition assessment of oil-paper insulation in real-life power transformers. Conventional Frequency Domain Spectroscopy is done using sinusoidal excitation over a wide frequency range. In this work, a different approach has been taken to investigate some more possibilities of Frequency Domain Spectroscopy using non-sinusoidal excitation for a better condition assessment of oil-paper insulation. For that, triangular waveshape was chosen as non-sinusoidal excitations whose slope can be changed to vary the harmonic content and amplitudes of constituent components. Samples with preset moisture contents that emulate the oil-paper insulation of real-life transformer have been prepared in the laboratory for the assessment of insulation condition. For a comparative study, both sinusoidal and triangular excitations having same peak as well as time period are applied to the prepared samples under controlled environmental condition and corresponding dielectric response currents are measured. From the applied voltages and corresponding dielectric response currents, dielectric dissipation factors are calculated and compared. It has been observed that use of nonsinusoidal excitation provides better results than sinusoidal excitation in the estimation of paper moisture content. It has also been observed that among the applied non-sinusoidal excitations, a particular waveform provides more accurate information about the paper moisture content. [ABSTRACT FROM AUTHOR]

This paper presents a novel technique to determine the optimized slope of triangular excitation in frequency domain spectroscopy that can provide better information about condition of oil-paper insulation. In conventional frequency domain spectroscopy, estimation of frictional losses due to the interactions of oscillating dipoles helps in investigating insulation condition. But, different types of dipoles in insulation cannot have similar dielectric relaxation times. Therefore, excitation having multiple frequencies is necessary for the dipoles to undergo more synchronized oscillations. This synchronized oscillation of dipoles reduces the inter-dipolar interactions and provides better information regarding insulation condition. Hence, in this work, triangular excitation is used for frequency domain spectroscopy since its harmonic contents can be varied by changing the slope. The slope of the triangular excitation is optimized to obtain more accurate information about the insulation condition. The optimized triangular excitation for insulation is determined using the proposed equivalent circuit model. To experimentally determine the effectiveness of the model, three test samples having preset moisture content in paper have been prepared in the laboratory. The optimized triangular excitations are then applied to the test samples to estimate their insulation condition. Experimental results show that the use of optimized triangular excitation provides information regarding the condition of oil-paper insulation with greater accuracy. In order to investigate the applicability of the proposed equivalent circuit model, the experiment has also been performed on real-life transformers. [ABSTRACT FROM PUBLISHER]

Frequency domain spectroscopy is a potential tool for non-invasive condition assessment of oil-paper insulation in power equipment. On the other hand, it is well known that the results of frequency domain spectroscopy are affected predominantly by temperature. Moreover, the voltage used for frequency domain spectroscopy is sinusoidal is nature. But the actual insulation system at site is stressed by voltage that may deviate significantly from sinusoid during operation. Considering these two aforesaid facts, in this paper, the response of oil-paper insulation has been studied at different temperatures using both sinusoidal as well as non-sinusoidal excitation. An experimental sample has been prepared in the laboratory that emulates the composite insulation of oil immersed type power transformer at site. The results of frequency response using sinusoidal voltage waveform at different temperature show good agreement with the conventional results that validates the scheme of the experimental setup. Some more information is obtained from the response of non-sinusoidal excitation that could help to get a better interpretation of the actual physical condition of oil-paper composite insulation. [ABSTRACT FROM AUTHOR]

In recent years, there is an increased use of passive filters in both transmission and distribution systems due to the proliferation of power electronic devices. However, the problem of filter design has not been well addressed in the past and one example is the application of high-pass filters in a filter package. Three types of HP filters are widely used to mitigate multiple harmonics, i.e., 2nd HP filter, 3rd HP filter and C-type filter. There is still a lack of research to clearly reveal the characteristics of each filter, which makes it difficult for the designer to select the optimal filter topology under different circumstances. The main goal of this paper is to solve the problem of how to select a proper configuration among three HP filter candidates for a given harmonic problem. Unlike the conventional optimization-based filter studies, this paper investigates three HP filters in an analytical way. As a result, the paper provides a deep insight into the inherent characteristics of the filter and the conclusions drawn in the paper are universal; thus can be used in different applications, ranging from low voltage levels to high voltage levels. The research results lead to a recommended application scope of each HP filter, which is very useful to guide the design of filter packages and help designers to evaluate the design results. [ABSTRACT FROM AUTHOR]

The paper deals with a final experimental validation of three-dimensional Multiconductor Cell Analysis (MCA) developed by the Electric Energy Transmission Laboratory of the University of Padova. This final confirmation comes from the measurement campaign carried out on one of the longest (100 km) HVAC submarine three-core cables: the Sicily-Malta interconnector. The considered frequency measurements range from 0 to 40th harmonic order with both positive and zero sequence supplies. In this overall harmonic interval and with both supplies, the comparison between measurements and MCA results highlights a very good agreement (maximum differences of 10%). These differences are negligible if measurement uncertainties are considered. [ABSTRACT FROM AUTHOR]

Load profile classification is very important in load forecast, planning and management. Although customers are generally grouped by utilities into residential, commercial classes and respective subclasses, there is a lack of systematic framework that can be used to characterize different classes with signatures that are both human-readable and machine-readable. The work presented in this paper attempts to formulate the theoretical framework for customer classification using the annual load profiles. This paper demonstrates how to extract characteristic attributes in frequency domain (CAFD) and use these CAFDs to formulate a hierarchy of load profiles that can be used as the systematic framework for customer load classification. As signatures for customer classes and subclasses, the CAFDs are obtained by using a data mining method called CART (classification and regression tree). The paper presents a load profile classification test to establish the efficacy of the proposed approach which is significant improvement over current practices that provide mostly qualitative labeling. [ABSTRACT FROM AUTHOR]

A high-harmonic traveling-wave tube (HHTWT) is designed, developed, and tested in this paper. This device is configured as a multiplier–amplifier with Q-band input signals and its third harmonic, i.e., D-band output power. The tested result demonstrates that 280 mW at 133.5 GHz is obtained as a result of 200 mW at 44.5-GHz input signal. The simulation and experiment validate that the high-harmonic radiation can be generated and amplified in the HHTWT. The approach described in this paper could find application in exploring high power, wideband tunable terahertz source. This paper is expanded from a conference paper on IVEC 2017. The detail design produce and tested result are added in this paper. The explanation of the simulation and tested results is also presented. [ABSTRACT FROM AUTHOR]

The rising cost of production testing for a system-on-a-chip (SoC) is one of the crucial matters to chip makers, due to long test time and costly automated-test-equipment. This paper proposes a spectral leakage-driven built-in self-test (BIST) scheme to precisely predict the nonlinearity of mixed-signal circuits in the loopback mode, thereby accomplishing cost-effectiveness (compared to previous BIST-based works). A digitally synthesized single-tone sinusoidal stimulus used for conventional harmonic testing is incoherently sampled by a device under test (DUT). The DUT output signal exhibits the correlation between the DUT harmonics and the spectral leakage introduced by the incoherent sampling. The DUT output signal is then fed to another DUT through a loopback path, so that the harmonics of a pair of DUTs are correlated with the spectral leakage on the loopback response; the magnitude of the spectral leakage is considered as a weighting factor on the harmonic magnitude of those DUTs. The correlation is quantitatively modeled as characteristic equations in , and postprocessing predicts the harmonics of the two individual DUTs, by simultaneously solving the characteristic equations using on-chip DSP core available in an SoC. Simulation and hardware measurements validated that this paper can be practically used for production testing by showing less than 0.3 and 0.6 dB of the prediction errors, respectively. [ABSTRACT FROM AUTHOR]

An increasing need for fast and reliable models has led to a continuous development of Fourier-based (FB) analytical modeling. This paper presents an overview of the techniques that are currently available in FB modeling for electric machines. By coupling that overview to the most relevant literature related to the subject, an interesting starting point is provided for anyone who wants to use or improve FB models. The following seven aspects of FB models are discussed in detail: 1) the magnetic potential (scalar or vector potential); 2) the coordinate system and the solution of the partial-differential equations for each magnetic potential and for each coordinate system; 3) the way in which time dependence is accounted for; 4) the implementation of the source terms; 5) the possibilities to account for slotted structures; 6) the modeling of eccentricity; and 7) the post-processing computation of physical quantities, such as flux density, electromotive force, torque, losses, and eddy currents in conductive objects. Furthermore, this paper gives the closed form solution of the Laplace, Poisson, and Helmholtz equations in each coordinate system. In addition, this paper tackles other important features of FB models such as computational time reduction and coupling the machine model to an electric circuit. [ABSTRACT FROM AUTHOR]

Existing non-intrusive load identification methods face with the difficulty of being applied to industrial users whose operation and ON/OFF status are hard to be acquired. Focusing on the above challenge, this paper proposes a non-intrusive identification method of harmonic source loads for industrial users. Utilizing Clarke transform, an equation with respect to voltage and current is formulated to calculate the integrated equivalent impedance, which is then decomposed with the improved complex local mean decomposition (CLMD) and complex fast independent component analysis (C-FastICA) achieving non-intrusive separation of the equivalent impedance signals of individual branches. The separated impedance signals will be used as the basis for load type identification. The proposed method is validated by numerical simulations as well as actual three-phase voltage and current monitoring data. The case study shows that it can effectively identify the types of harmonic source loads while being resistant to noise and impacts of sampling accuracy and diverse load capacities, which obviously demonstrates its practical applicability. [ABSTRACT FROM AUTHOR]

Few of the challenges with development of a single on–board motor for direct–drive electric vehicles include high torque density and low torque ripple. Therefore, in this paper, a 36–slot, 34–pole consequent pole six–phase permanent magnet synchronous machine (PMSM) has been optimized to address the aforementioned challenges for direct–drive application. Existing literature on optimization processes that rely solely on finite element models are restricted to three–phase machines only and also take longer computation time. Therefore, this paper proposes a novel optimization approach based on supervised machine learning for six–phase PMSM. In this approach, a non–conventional extended dual dq–frame model that accounts for higher order space harmonics in inductances and flux linkages has been developed and used for accurate computation of average torque and torque ripple of six–phase PMSM. Using the performance characteristics obtained from the extended dual dq–frame model for a set of initial design candidates, support vector regression algorithm is employed for supervised machine learning and increasing solutions in the design space. Furthermore, pareto front is used for selecting optimal machine models with maximum torque density and reduced torque ripple. Multi–objective trade–offs and comparison of initial and optimized designs based on average torque, torque ripple, efficiency and cost are performed. [ABSTRACT FROM AUTHOR]

The increasing use of induction motors (IMs) with variable frequency drives for industrial process control and automation has necessitated the need to evaluate their energy efficiency in the presence of voltage and current harmonics. As the determination of IM efficiency is becoming mandatory in many countries, there is a need to develop a testing approach that eliminates inaccuracies due to the operator. This paper presents an automated efficiency testing procedure developed to mitigate the adverse effect of varying technical skill and competence levels of testing personnel on efficiency test results. This is a particularly useful development considering the recently proposed IEC/TS 60034-2-3 methodology which specifies identical tests between sinusoidal supply and converter operation. A comparison of several manual and automated efficiency tests on a 55-kW IM highlighted improvements in repeatability, correlation, and temperature variation due to the latter. In addition, the advanced data acquisition and computation capability of the measurement device used in the developed test rig provides an excellent platform to investigate the dynamic operation of IM drives. [ABSTRACT FROM AUTHOR]

In a common dc-link dual-fed open-end winding permanent magnet synchronous motor (OEW-PMSM) topology, it is well known how the additional flow of a zero-sequence current (ZSC) is permitted. The low zero-sequence impedance characteristic of high-speed machines leads to high-intensity and high-frequency ripple of the ZSC. Therefore, there is a necessity to eliminate the zero-sequence-voltage (ZSV) produced by the two voltage source converters that feed the machine. Furthermore, the non-sinusoidal back electromagnetic force (back EMF) causes the circulation of a third harmonic ZSC. An OEW-PMSM high-speed starter-generator fed by a dual-inverter with a single dc-link is considered. Part I of this paper proposes a modulation for the considered topology able to eliminate instantaneously the ZSV produced. In this paper, a detailed analysis of the deadtime (DT) effect on the ZSV has been carried out and a novel hysteresis control for the ZSC using the DT as a control action is presented. The DT produces a ZSV distortion on the zero-axis that can be used to control the third harmonic ZSC flowing due to the non-sinusoidal machine back EMF. [ABSTRACT FROM AUTHOR]

Unavoidably, the controlsystem of any permanent magnet synchronous motor (PMSM) is subjected to perturbations, e.g., motor nonidealities and inverter nonlinearities. To reject these perturbations, a new super-twisting (ST) control variant, called speed adaptive super-twisting (S-AST) control, is proposed in this paper. In the S-AST control, a proportional-integral (PI) and a ST controllers are merged using an adaptive law that is based on the motor speed measurement. This is done to reduce the chattering problems that the standard ST control presents. In addition, a mathematical design for the S-AST control is proposed, where the relationship between the chattering amplitude, the switching frequency and the system perturbations is shown. The main contribution in this paper is the application of the S-AST controller to reduce the total harmonic distortion (THDi) of the PMSM currents. By comparing the S-AST control against PI control, the THDi is reduced from 9.9% to 1.27%, in simulation, and the THDi is reduced from 22.79% to 1.56%, experimentally. These results demonstrate how the S-AST control is an excellent alternative to improve the waveform of the PMSM currents. [ABSTRACT FROM AUTHOR]

A three-section coupled-cavity traveling-wave tube (CC-TWT) has been developed for avionic applications. The design parameters for a TWT operating in ${X}$ -band with a high average power, high power, high efficiency, high duty, wideband, low weight, and rugged structure have been obtained. Data presented show a good agreement between simulation results and prototype test results. The small-signal simulations were done with software developed in house for the evaluation of interaction impedance. The commercial code CST suite was used for the prediction of the dispersion diagram. The large-signal simulations were carried out with the “1-D code, computer program for analysis of CC-TWT,” by Cosmic. This paper explains the theory used for the design and shows the “cold test” and “hot test” results achieved with the prototype. The prototype has been able to deliver more than 1.5-kW average output power in a bandwidth larger than 1 GHz. [ABSTRACT FROM AUTHOR]

This paper presents a research work on the electromagnetic loss modeling and demagnetization analysis for a high-speed permanent magnet machine (HSPMM). The iron loss is estimated by improved modeling considering harmonics and rotational magnetic field effects to achieve high precision; rotor eddy current loss is researched and comprehensively investigated using finite-element method (FEM). The auxiliary slot and PM beveling are also proposed to reduce the rotor eddy current loss for machine at high-speed operation. Temperature-dependent PM demagnetization modeling is utilized in HSPMM FEM analysis to investigate machine performance due to temperature variation, while optimized rotor structures are proposed and comparatively researched by FEM to improve the machine anti-demagnetization capability in harsh conditions. The HSPMM temperature is estimated based on the calculated loss results and machine computational fluid dynamic modeling. Experimental measurements on the prototype machine verify the effectiveness of the machine electromagnetic and thermal modeling in the paper. [ABSTRACT FROM AUTHOR]

This paper presents a broadband poly-harmonic behavioral model for microwave mixers operating in the linear regime. It is extracted from large-signal vector measurements and predicts the response with respect to an arbitrary local oscillator (LO) phase. The model is capable of estimating the performance of the converted signals and the main mixing products for an intermediate frequency that spans within an a priori defined bandwidth. This paper gives a detailed model analytical treatment along with a discussion of its properties and the description of the characterization method. The model validation is achieved by the characterization of a subharmonic mixer implemented in the hybrid technology that operates with a 2.229-GHz LO, an intermediate frequency bandwidth of 732–754 MHz, and a corresponding radio frequency bandwidth of 5.191–5.211 GHz. Independent experimental validation is achieved by an image rejection mixer composed of two nominally identical mixers, individually characterized by the proposed technique. Validation is concluded with experimental data, demonstrating the model’s capability to deal with a phase-modulated LO signal. [ABSTRACT FROM PUBLISHER]

Improvised asymptotic boundary conditions are a sparse but approximate method of solving open boundary problems. Since this method approximates unbounded space as series of isotropic shells, it can be readily implemented in virtually any finite element solver without the need for additional code. A previous paper addressed application of this technique to magnetic problems described with a vector potential formulation. This paper extends the method to electrostatics and related scalar potential formulations. [ABSTRACT FROM AUTHOR]

In a previous paper, we introduced a modified Steinmetz equation to account for dc-bias field effects, which requires only a simple dc permeability measurement to predict total power loss. In this paper, we expanded our investigation to include Finemet nanocrystalline material and found that our modified Steinmetz formalism was effective in predicting dc-bias-related losses for this system as well. In this paper, it was observed that Finemet cores exhibit lower losses than Metglas cores under identical test frequencies and bias fields. In addition, we show that a full characterization of the dc loss component necessitates the consideration of higher order ( $n>1$ ) harmonic components. In order to quantify these higher frequency loss components, a dc–dc converter-based test system was built to intentionally introduce inductor current harmonics by varying the filter capacitance and parasitic inductance of the test system. Both core types were evaluated under fundamental frequencies of 20 to 150 kHz and dc-bias fields of up to 1.3 kA/m, with the inclusion of distorted waveforms obtained by varying filter capacitance. At higher frequencies, the Metglas cores were found to exhibit greater loss fractions associated with the higher order harmonic components. A detailed summary of the measured core loss characteristics for both core types is included and discussed. This paper includes the details of the measurements, the modified Steinmetz relation, and the loss extraction algorithm used for analysis. [ABSTRACT FROM PUBLISHER]

This paper yields a systematic scientific foundation for the evaluation of responsibility of utility and customer to the harmonic distortions at the point of common coupling (PCC). In this regard, this paper proposes a technical process for the evaluation of harmonic distortions. This technical process provides a way to answer some technical questions related to harmonic issues based on the following aim: identifying the dominant side, determining the responsibility of each side to harmonic distortions, determining the influence of the utility on harmonic current distortions at the PCC, and determining the influence of the customer on harmonic voltage distortions at the PCC. This paper deciphers these technical questions in the concrete “relevant factors” for the evaluation of harmonic distortions. These “relevant factors” are systematically classified based on the equivalent circuits of utility and customer side for harmonic studies. In this regard, six well-defined “relevant factors” for the Thevenin equivalent circuit and six analogue “relevant factors” for the Norton equivalent circuit are formulated. Some of these “relevant factors” are proposed, for the first time, in this paper. Furthermore, this paper explains the relations between the “relevant factors” to ascertain their interdependence. In addition, the usefulness of the “relevant factors” to answer the technical questions related to the harmonic issues is illustrated using a calculation example. [ABSTRACT FROM AUTHOR]

The goal of the paper is to develop a hybrid modulation technique to combine space vector modulation (SVM) scheme and synchronous optimal pulsewidth modulation (SOPWM) technique for current source inverter (CSI). SVM provides better dynamic performance, but is unable to produce less total harmonic distortion (THD) on inverter current at low device switching frequency ($< $ 1 kHz). SOPWM provides less THD even at low device switching frequency, however it needs a conversion technique to operate CSI and it needs an additional control technique to improve dynamic performance. Hence to overcome these limitations, this paper develops a single modulation technique called optimal SVM technique that can achieve less THD as well as better dynamic performance. To develop optimal SVM technique, three methods have been proposed in this paper. These three methods do not require an additional conversion technique to operate CSI and they provide less THD even under low device switching frequency of 450 Hz. Experimental results prove that the proposed modulation technique can provide better steady-state performance as well as dynamic performance. [ABSTRACT FROM AUTHOR]

This paper proposes a single-phase ac–dc–ac converter composed of a transformer and two three-leg converters connected in series. The proposed converter allows to supply the load with a voltage with constant amplitude and frequency, and to operate with the grid current with low harmonic distortion and high power factor. In addition, the converter can be used to mitigate fundamental overvoltage and voltage harmonics at the grid. The system model, regions of operation, a power flow analysis, and a method to regulate the dc-link voltages using the voltage vector redundancies are given. In the first version of this paper, two pulsewidth modulation (PWM) techniques (including space vector PWM) and a control system were provided. The proposed topology is compared with two conventional systems in terms of operation range, harmonic distortions, and semiconductor losses. Simulation and experimental results are provided to validate the feasibility of the system. [ABSTRACT FROM AUTHOR]

This paper investigates the contribution of each order inductance harmonic to the torque (both average torque and torque ripple) of multiphase doubly salient synchronous reluctance machines (DS-SRMs). Such machines are similar to switched reluctance machines but supplied with sine wave currents. The investigations in this paper are as follows. First, a general analytical torque model based on Fourier series analysis of inductances has been built for machines with different phase numbers, slot/pole number combinations, and also winding configurations. The instantaneous torque for DS-SRMs with any given phase number can then be accurately predicted. Using such model, contribution of each order inductance harmonic to torque can be investigated separately. It is found that the torque ripple frequency of the DS-SRM only depends on phase number. For example, for an m-phase machine, there will be m $\times $ kth-order torque ripple if mod(mk, 2) = 0, where m is the phase number and k is a natural number. This paper also explains why certain phase numbers inherently produce lower torque ripple than others. The findings in this paper provide a future direction for potential torque ripple reduction methods either from machine design or advanced control. The simulations have been validated by experiments using a six-phase DS-SRMs. [ABSTRACT FROM AUTHOR]

Simulating the interaction of RF-waves with charged particle beams is difficult and computationally expensive, even on present high-end computers. There is a tradeoff between fidelity and complexity/expense of the two primary techniques, particle-in-cell and envelope methods. This paper presents an approach based on the partial decomposition of the Maxwell equations to achieve a fully second-order set of ordinary differential equations (ODEs) describing the interaction. It has the potential for self-consistent inclusion of ac and dc space-charge effects through a solution of evanescent ODEs, effects that are handled poorly, if at all, by existing envelope methods. The resulting technique provides flexibility in adjusting simulation fidelity versus computational costs. The developments presented in this paper establish a mathematical framework for this technique and test its core aspects by demonstrating accurate solution of the ODEs using analytic sources. [ABSTRACT FROM AUTHOR]

Power line harmonic radiation (PLHR) is an artificial electromagnetic pollution source in the near-earth space environment. Up until now, there has been little quantitative research on its formation mechanism. This paper details a model and solver for electromagnetic waves propagation in a stratified anisotropic ionosphere. In our model, these electromagnetic waves are generated by an arbitrary electric dipole source above a nonideal conductive ground. The matrix-exponent method and a full-wave method are combined to analyze the model, avoiding the problem of numerical overflow and swamping in numerical calculations. The computing results obtained from the proposed method and the observed electric field data by using DEMETER satellite are compared and found to be in good agreement. Furthermore, this paper considers the effects on PLHR propagation in the ionosphere due to dipole source frequency, earth’s conductivity, electron density, geographic latitude, and geomagnetic field orientation. Results show that when the frequency increases, the strength of PLHR penetrating into the ionosphere has an increasing tendency. If the harmonic current remains constant, lower ground conductivity and electron density of the ionosphere result in higher radiation power. PLHR propagates along the direction of the geomagnetic field in the ionosphere, and its strength decreases with the increasing geomagnetic inclination at the same height. In addition, the radiation power of less than 1 W may trigger PLHR. [ABSTRACT FROM AUTHOR]

In this paper, an 18-slot/26-pole vernier permanent magnet synchronous machine (VPMSM) with coil pitch of two slot pitches is proposed based on a nine-slot/18-flux-modulation-pole/26-pole VPMSM with concentrated tooth-coil windings. Compared with the original VPMSM, the number of slots is doubled and the phase winding connection is adjusted to reduce the space harmonic content, the phase inductance, and hence, improve the power factor. This paper shows that the proposed VPMSM increases power factor from 0.73 to 0.95 with better torque and flux-weakening capability. Moreover, a series of VPMSMs with high-power factor is proposed from the same design principle and given design guidelines. [ABSTRACT FROM AUTHOR]

In this paper, rotor inter-turn faults in salient-pole synchronous machines are investigated using finite-element analysis. The machine under study is a 22 MVA eight-pole hydropower generator with fractional-slot windings. Simulated faulty cases include 1, 2, 5, 10, and 20 short-circuited turns (out of 58 turns) in one rotor pole. In the electromagnetic analysis, the effect of faults on airgap flux density and radial forces is studied. Furthermore, this paper investigates online detection of inter-turn faults using spectral analysis of stator voltage or current is studied. The amplitude of fault-related harmonics is investigated at various fault severities, as well as at no-load and full-load operations. This paper also discusses the effects of damper bars, an influence of parallel circuits in the stator windings, and influence of the pole pair number. In addition, a comparison between fault-related harmonics in the case of dynamic eccentricity and rotor inter-turn faults is presented. [ABSTRACT FROM AUTHOR]

This article investigates energy storage requirements in the submodules of a class of converters known as hybrid cascaded modular multilvel converters (HC-MMCs). The complexities arising from the usage of different submodule types and their non-conventional arrangement necessitate detailed analysis of submodule capacitor voltage ripples, which are needed for development of guidelines for sizing submodule capacitors. This paper characterizes electric charge variations in the submodule capacitors to derive expressions for capacitor voltage ripples, and to determine the energy storage requirements of the converter. The paper uses detailed electromagnetic transient (EMT) simulations and experimental results on a laboratory-scale MMC setup to verify and validate its findings. [ABSTRACT FROM AUTHOR]

This paper presents a dual active bridge (DAB) converter with reactive power control capability (Q-capability) for a battery energy storage system (BESS) or an electric vehicle (EV) to deliver vehicle-to-home (V2H) and vehicle-to-grid (V2G) services. The DAB topology is preferable for EV charging systems due to its galvanic isolation and bidirectional power flow capabilities. However, this topology increases reactive current peak and loses zero voltage switching (ZVS) operation at light loads if it is not controlled with improved modulation strategies and proper Q control. This paper proposes a mixed modulation method and a reactive power optimization (RPO) algorithm based on power system load flow concepts. Due to the complexities associated with the analytical solution using time domain analysis, this paper develops detailed universal expressions of a DAB converter using the harmonic analysis method. Analytical identification of ZVS boundaries and DSP implementation of the RPO algorithm become easier with these universal expressions. Multiple modes analysis for different operational states is no longer required. Simulation results have been shown for different modulation strategies of the DAB converters. The theoretical analysis of modulation strategies, RPO algorithm and ZVS operation are validated by experimental results on a DAB prototype. Results show that the proposed control strategy reduces the reactive power and provide ZVS operation over a wide ranges of voltages. [ABSTRACT FROM AUTHOR]

The open-end winding permanent magnet synchronous motor (OW-PMSM) with common DC bus configuration provides a path for zero-sequence current (ZSC). Apart from the zero-sequence voltage (ZSV) generated by inverters modulation, ZSC also comes from the third harmonic back-EMF. However, the third harmonic back-EMF contains the position information of the rotor, which can be extracted by an appropriate strategy to achieve position sensorless drive. In order to achieve sensorless drive and ZSC suppression simultaneously, this paper proposes a novel general-integral extended state observer (GI-ESO) based method. The third harmonic back-EMF of the OW-PMSM is estimated and calculated in three-phase stationary coordinate system by GI-ESO. And then, a single-phase phase lock loop observer (SPLL) is exploited to extract the position and speed information of the rotor. Meanwhile, the estimated third harmonic back-EMF is directly fed forward to SPWM as the ZSV reference, then the output voltages of the inverters contains the ZSV that can exactly counteract the third harmonic back-EMF, so as to realize the suppression of ZSC. Compared with the method of combining the fundamental back-EMF detection and proportional resonance (PR) regulator, this method can realize sensorless drive and ZSC suppression at the same time with only one scheme. Benefiting from the use of GI-ESO, the observer bandwidth can be relatively low, which helps suppress noise and extend the speed range of sensorless operation. Moreover, this method has strong robustness against motor parameters. The proposed strategy is validated by experiments. [ABSTRACT FROM AUTHOR]

High Impedance Faults (HIFs) occur by the contact between an energized conductor and a high impedance surface. Due to the low fault current level, HIFs cannot be detected by conventional protection and there is no fully efficient solution to this problem. HIF detection methods often extract metrics using signal processing techniques, such as Fourier Transform, Wavelet Transform, Stockwell Transform, and Mathematical Morphology. However, these techniques are applied under specific conditions, which hinders comparative and critical analyses among them. Therefore, this paper presents a critical review of HIF detection methods based on the aforementioned techniques, and also shows a detailed investigation of the performance of the metrics commonly used with them. To do this efficiently, the authors proposed a set of assessment indices based on the ratio between the metrics’ characteristics and another one based on the repeating of the metrics features. The proposed indices revealed that some of these metrics fail to distinguish HIF from other typical occurrences in power distribution systems, and their performances are negatively affected by the fault location and by the existence of noise in the measurements. Additionally, the results showed a need to specify system conditions in which any HIF detection technique is valid. [ABSTRACT FROM AUTHOR]

This is the second of a two-paper series, in which the field-data-based analytical method proposed in Part I has been extended to determine the amount of harmonic currents absorbed by the shunt harmonic filters of the iron and steel (I&S) plants from the rest of the system. The nonlinear characteristics of the plants and the utility are modeled as harmonic current sources, whereas the linear parts of the proposed extended model consist of passive circuit elements, with the harmonic filter $RLC$ circuit parameters also integrated into the model. This extended method, which can be also used for harmonic contribution assessments, requires sample-by-sample time-synchronized harmonic current measurements inside the plants and at the point of common coupling (PCC). It eliminates the need for harmonic voltage measurements at the expense of the need for inside-plant measurements. It has been verified both by computer simulations and by application on field data. The results have shown that the proposed method is a successful tool to determine the magnitude of harmonic currents that are absorbed by the harmonic filters of I&S plants connected to the PCC, particularly when measured harmonic currents of I&S plants exceed the actual contributions. [ABSTRACT FROM AUTHOR]

Electrical equipment of the floating nuclear power plant operates in a long-term vibration environment. Ground faults occur frequently and are often accompanied by arc, a reliable arc suppression algorithm for the generator stator winding is necessary. In this paper, an active arc suppression method is proposed by connecting a controllable voltage source to the generator neutral point. Through regulating the neutral point voltage to be equal in amplitude and opposite in phase to the fault potential, the fault point voltage can be clamped to a low level to achieve arc suppression. Since the generator's phase potential contains certain harmonic components, the controllable voltage source includes fundamental and third-order harmonic components. To accurately calculate the output voltage, online calculation methods for the fault location, fault potential and grounding capacitance are proposed. The accuracy of the fault location method is verified by simulation and dynamic test. And simulation results based on PSCAD/EMTDC software show that the proposed method can achieve effective arc suppression at different ground fault conditions. [ABSTRACT FROM AUTHOR]

Modern electric grid usages extensive non-linear loads leading to the increased harmonic current injection in the system. This paper proposes a data-driven algorithm based on a sparse decomposition approach with the Overcomplete Hybrid Dictionary (OHD) and provides in-depth mathematical analysis to detect and mitigate harmonics in emerging electric power systems. The sparse decomposition method is widely used in image processing applications with significant advantages to big-data applications. However, its application is not properly addressed in electric grids’ applications despite massive data generation in a smart grid environment. Hence, in this paper, the performance evaluation of a sparse decomposition-based algorithm using a greedy approach is proposed and carried out in a real-time simulation environment for Distribution Static Compensator (DSTATCOM) application for the real-time detection, classification, and mitigation of PQ events to show its suitability and effectiveness. Finally, the experimental results on a small-scale laboratory setup are presented to validate the effectiveness of the proposed sparse-based control algorithm for DSTATCOM in real-time applications. The comparative result shows that the proposed sparse-based method is advantageous for off-line PQ signal processing and capable of real-time detection, classification, and control of the power apparatus for harmonics mitigation. [ABSTRACT FROM AUTHOR]

The use of synchronized measurement technology leads to a more reliable and secure operation of the power system. Phasor calculation is needed for all buses where a phasor measurement unit is installed, and fast and precise estimation is necessary for accurate monitoring, protection and control. The Prony algorithm is one promising method due to its capability to estimate phasor adaptively with changing frequency. The algorithm projects the signal on $L$ exponentially damped sine functions, where $L$ is the order of the Prony. However, the order under different conditions should be adapted automatically to reduce computation time. To adaptively specify the order, the empirical mode decomposition (EMD) method is proposed in this paper to be combined with the Prony and named EMD-Prony. The EMD decomposes a signal into finite single oscillatory modes, representing the number of modes in the signal. EMD is also used as a pre-processing step to filter noise from an input signal of Prony. Therefore, EMD is proposed here as an assistant of Prony in a phasor estimation. Finally, the proposed method is tested on the benchmark signals proposed in the IEEE standard, signals obtained from a simulated power system, and measured data from a real-world power system. [ABSTRACT FROM AUTHOR]

First harmonic analysis (FHA) is arguably the most widely used analytical technique for wireless power transfer (WPT) circuits due to its simplicity. Although FHA can provide closed-form solutions, the existence of rectifier diode forward voltage drop and higher order harmonics, especially the second and third harmonics at variable duty cycle operation, can significantly deteriorate its accuracy. This paper presents an accurate and efficient method called enhanced multiple harmonic analysis (eMHA) for the optimal design and optimal control of WPT systems. The eMHA method considers the nature of nonlinear rectification networks under nonsinusoidal current and reexamines the concept of the equivalent load. As a result, the rectified WPT system is transformed into a series of linear systems with complex load impedances. The steady-state electric quantities can be then explicitly calculated. This enables eMHA to seamlessly work with numerical optimization algorithms to facilitate the automated design and optimization of WPT systems. An example of optimal design and optimal control of a 10 W WPT system is demonstrated. The results obtained by eMHA and FHA are also compared. A prototype of the designed circuit was constructed. The accuracy and effectiveness of eMHA are verified by experimental measurements. This paper is accompanied by a MATLAB-based analytical tool with a graphical user interface demonstrating the effects of circuit variables on electrical quantities and waveforms. [ABSTRACT FROM AUTHOR]

In this part of the paper (Part II), available technical solutions to minimize or prevent wildfires caused by power networks are reviewed in more detail. These methods include fundamental changes to power system equipment, periodic checkups and maintenance, identification of faults via voltage/current waveforms, changes to protection and relaying settings and coordination, and installation of new power system apparatus. The strengths and drawbacks of each method are discussed. The discussion section brainstorms some future possible solutions that smart-grid technologies can enable. The paper concludes that there has neither been enough research in universities nor enough investment by industry to develop viable preventive solutions for wildfires that initiate from the daily operation of electrical power grids. This, in the authors’ opinion, is the crucial time for investment in research and development to tackle the lethal wildfire problem while electric power networks offer “the lowest hanging fruits to pick.” [ABSTRACT FROM AUTHOR]

The main standard for avionic equipment DO-160G defines a set of tests that require compliance before the employment of a device in aircraft. An important test involves the generator voltage and consequential current distortion of the three-phase load in the variable 360–800 Hz frequency grid. The main purpose of this paper is to present and analyze a systematic design methodology for three-phase boost and buck rectifiers in order to meet with the voltage distortion test requirement. For a given voltage harmonic profile, the current harmonic limits that have to be satisfied are translated into equivalent per-harmonic admittances and a profile of maximum rectifier input admittance versus frequency is obtained. The defined profile, due to normalization, is applicable to arbitrary power level with simple shifting by the base admittance governed by the converter nominal power. It is shown that for boost-type rectifiers there is a tradeoff between current controller bandwidth and input inductor size, while for the buck-type rectifiers main limitation lies in the input LC filter design used for differential electromagnetic interference filtering. The experimental results conducted on an SiC three-phase 10 kW VIENNA rectifier are tightly backing up the proposed theoretical analysis. This paper is accompanied by three videos demonstrating experimental measurement of d-axis open-loop duty cycle to inductor current transfer function, loop-gain of d-axis current controller with 3.8 kHz bandwidth and variable grid frequency 360–800 Hz operation of the converter under 0% and 10% input three-phase voltage total harmonic distortion. [ABSTRACT FROM AUTHOR]

Transformations between abc, stationary dq0 ($\alpha \beta 0$) and rotating dq0 reference-frames are used extensively in the analysis and control of three-phase technologies such as machines and inverters. Previous work on deriving the matrices describing these transformations follows one of two approaches. The first approach derives Clarke's matrix by modifying symmetrical components. Park's matrix can be subsequently found from a rotation matrix. The second approach derives Park's matrix using trigonometric projection by interpreting the transformation as a rotation in the plane of the cross-section of a machine. Then, Clarke's matrix can be found trivially using a reference angle of zero in Park's matrix. This paper presents a third approach to deriving the Clarke and Park transformation matrices: a geometric interpretation. The approach exploits properties of the linear transformation using the Cartesian representation. We introduce the locus diagram of a three-phase quantity and show how these diagrams have applications in power quality. We show that, unlike a phasor diagram, a single locus diagram can fully represent a three-phase system with harmonics. [ABSTRACT FROM AUTHOR]

This paper proposes a method to reduce the torque pulsation of the three-phase fractional-slot concentrated-winding (FSCW) interior permanent magnet (IPM) motor by lowering sub-harmonics. The key principle of this method is the selection of an optimized six-layer winding with different numbers of conductors. Firstly, the interaction of stator-rotor magnetomotive force (MMF) which contributes to the torque pulsation is analyzed. Additionally, the relationship between sub-harmonics (1st sub-harmonic and 2nd sub-harmonic) and torque pulsation orders is revealed. Then, different numbers of conductors are adopted in coils to eliminate the 2nd sub-harmonic. Nevertheless, the 1st sub-harmonic increases in the two-layer and four-layer windings. Therefore, the optimized six-layer winding is employed to suppress the 1st sub-harmonic and ensure that the 2nd sub-harmonic is zero. Besides, there are almost no other harmonics except the main harmonic and slot harmonics in the proposed IPM motor. Hence, the torque pulsation can be greatly reduced even under different current angles. Furthermore, the principle for torque pulsation reduction by lowering sub-harmonics is revealed. The effectiveness of the proposed method is verified through the comparisons with finite element analysis and experimental test. [ABSTRACT FROM AUTHOR]

The grid voltage information such as the phase-angle, the frequency, and the amplitude is crucial for the design of synchronization and control of power converters in the micro-grid. The conventional approach to estimate the grid voltage information is accomplished by phase-locked loop (PLL) techniques. Among various existing PLL techniques, filter-based PLLs can provide more accurate estimations even under adverse grid conditions. In this paper, a new single-phase filtering technique based on multiple delayed signal cancellation (MDSC) is proposed for extracting both in-phase and quadrature components of the selected harmonic order of the single-phase grid voltage signal. This MDSC technique can be realized in both the direct-form and the recursive-form. In comparison with existing single-phase cascaded delayed signal cancellation (CDSC) techniques, this MDSC technique utilizes less memory for the extraction of grid voltage fundamental frequency component. The proposed MDSC filter can be applied as a pre-filter to the enhanced PLL (EPLL) for the prompt and accurate estimations of the grid voltage information under adverse grid conditions. Both frequency adaptive and non-adaptive MDSC-based EPLL schemes are proposed in this paper. To validate the effectiveness of the proposed methods, experiments are conducted on the MDSC-based EPLLs and compared with the CDSC-EPLL under various grid voltage disturbances. [ABSTRACT FROM AUTHOR]