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Electromagnetic vibration and noise of driving motor affect the comfort for electric vehicles. Considering low harmonic component and pole design flexibility of double-layer interior permanent magnet (IPM) machines, in this paper, an improved analytical method of no-load air gap flux density for double-layer IPM machines is introduced, and the harmonic spectrum of electromagnetic force is analyzed. A commercial double-layer IPM machine is taken as benchmark, the electromagnetic–structure–sound coupling model is established. The main spatial and temporal order of electromagnetic force for benchmark motor is indicated. Based on this analytical model, a method to minimize the electromagnetic force of specific harmonic component is proposed to reduce electromagnetic vibration and noise, by optimizing parameters of double-layer IPM machine rotor pole without impairing the motor performance. The vibration and noise of the optimized motor under working condition and no-load are compared with the results of the benchmark motor by multi-physics simulation, and validate the proposed optimization approach.

Real-time monitoring of multiple (bio)chemical agents, molecules and gases is in a high demand, particularly for the future internet-of-things (IoTs) and point-of-care tests (POCT), that are connected via the 5G ecosystem. Here, we propose a lightweight, multi-agent (bio)-chemical wireless sensor based on graphene field-effect transistor (GFET) circuits, taking advantage of GFET’s dual functionalities, i.e., frequency modulation and (bio-)chemical sensing. The GFET-based radio-frequency (RF) modulators circuits can convert the continuous wave (CW) monotonic signal to multiple harmonics, with conversion efficiencies sensitively depending on densities of (bio-)chemical agents. Specifically, we exploit a machine learning (ML)-based readout method to extract the concentration levels of the (bio-)chemical dopants from the harmonic spectrum. Further, we show that by increasing the order of GFET circuits and thus the number of detectable harmonics, the neural network performance and the overall readout accuracy can be enhanced. The proposed GFET-based wireless sensor could be ultracompact, ultralow-profile, portable and flexible, thus potentially benefiting a wide range of applications in IoTs, POCTs, and Industry 4.0.

Generally, driven by a specific laser waveform, a single-order harmonic from the atomic harmonic spectrum can be enhanced, caused by the multiple acceleration-recombination processes. However, in t...

Multilevel cascaded H-bridge (CHB) converters are an attractive solution for multiple applications like flexible ac transmission systems and solid-state smart transformers, among others. This article is focused on a CHB working with unbalanced conditions per cell (different cell dc voltages and/or cell voltage references). In this scenario, the phase-shifted pulsewidth modulation (PS-PWM) technique produces a harmonic distortion around twice the carrier frequency and its multiples in the CHB output voltage. In this article, a generalized variable-angle PS-PWM method is presented in order to mitigate this drawback improving the CHB output voltage harmonic spectrum. The proposed method is based on applying a mathematical search algorithm to determine the phase displacement angles to be applied to the PS-PWM technique. Experimental results show how this objective is achieved without introducing any disadvantage in the CHB operation. The method can be applied to CHB with any number of cells.

This article develops a new closed-form analytical solution to the harmonic spectrum of the pulsewidth modulated (PWM) output voltage of the single-phase inverter connected to the dc bus with considerable voltage ripple. The solution is based on a double Fourier series expansion in two variables. As the single-phase inverter forms the basic building block of most converters, the developed expressions can be applied to various topologies. This article first identifies the interactions of a single-frequency sinusoidal modulation signal and the carrier signal with the dc bus voltage harmonics. The dc bus voltage harmonics are constrained in this article to multiples of the inverter output voltage fundamental frequency. The analysis is then extended to include a multifrequency modulation signal. Starting from the general solution, new expressions for the output voltage harmonics of the modular multilevel converter (MMC) are developed. The low-capacitance MMC is chosen in this analysis due to inherent low-frequency voltage oscillations in the converter internal capacitors. The MMC analytical harmonic spectrum can incorporate the effects of the circulating current control and third harmonic injection PWM, by including the second- and third-order harmonic components in the modulation signal, respectively. The MMC analytical harmonic spectrum is benchmarked against the experimental results.

A space-shifted wye–delta winding for fractional-slot concentrated winding (FSCW) is proposed that can simultaneously cancel both sub- and super-order harmonics of its stator MMF. The new winding concept proposes two sets of three-phase windings by doubling the number of stator slots connected in the wye–delta configuration. These two winding sets are shifted in space with respect to each other and are connected in series. The wye–delta configuration eliminates subharmonics and enhances the torque-producing component, whereas their relative shifting angle eliminates the dominant higher order harmonics to provide a cleaner and enhanced MMF spectrum. In FSCW motors, dominant space harmonics other than the torque-producing component give rise to undesirable losses in the magnet and rotor core. The efficacy of the proposed method is demonstrated through its stator MMF, harmonic spectrum, and motor performance using finite-element analysis. The application of the proposed winding to a permanent magnet (PM) machine showed dominant sub- and super-order harmonics cancellation, total harmonic distortion reduction, and magnetic loss reduction along with torque density and power factor improvements. A prototype PM machine is built, and the performance of the proposed concept is verified experimentally.

We study the process of propagation of high harmonics of optical radiation in an active medium of a plasma-based X-ray laser, simultaneously irradiated by an intense optical field of fundamental frequency. It is shown that for moderate plasma dispersion of the active medium at the frequency of the modulating optical field, the energy and relative amplitudes of the harmonics at the output of the medium are determined by their phases at the entrance to the medium, as well as by the time-delay of the harmonics with respect to the modulating field. These dependences are due to interference of high-order harmonics with a set of multi-frequency fields generated by each of the harmonics in the process of coherent scattering in a modulated active medium. The possibilities of using these effects to increase the efficiency of harmonic amplification, to control the harmonic spectrum, and determine the relative phases at the entrance to the medium are discussed on the example of the active medium of hydrogen-like Li2+ ions (with a 13.5 nm wavelength of an inverted transition).

Paralleling of voltage source converters (VSCs) with a limited maximum output power is essential when the power rating of a system must be increased. Interleaving (ILV) of the switching signals for parallel-connected VSCs provides a better harmonic spectrum than hard paralleling (HP), i.e., applying identical signals to all VSCs. This can be particularly beneficial for grid-tied converters, since a smaller LCL filter can be realized. To investigate the performance limitations and the impact of ILV operation on the LCL filter hardware, a comprehensive optimization procedure for LCL filters and intercell transformers (ICTs) for two paralleled VSCs is presented in this paper. In addition, a comparative evaluation of HP and ILV operation of VSCs is carried out. The developed optimization procedure and the hardware benefits of ILV operation were verified through testing on a 260-kW full-scale system. Compared with the commercial state-of-the-art weight-optimized LCL filter for HP, the developed LCL filter for ILV utilizing an integrated ICT reduces the total filter weight by 30% while guaranteeing harmonic standard compliance and meeting thermal requirements.

We theoretically investigate high-order harmonic generation from nanowire in inhomogeneous laser field. By solving the time-dependent Schrödinger equation, the simulated harmonic spectrum exhibits a double-plateau structure. The cutoff of the second plateau is extended and the intensity of the high-order harmonics in the second plateau is increased by about two to three orders of magnitude compared with that from the homogeneous laser field. Moreover, we analyze the influence of the inhomogeneous laser field polarization orientation to the nanowire. It is shown that the intensity of the high-order harmonics in the second plateau can be effectively controlled by varying the inhomogeneity parameter and the laser field polarization orientation to the nanowire. These phenomena are attributed to the time-dependent population of the electron, which has a strong relevance with the intensity of the harmonic.

© 1986-2012 IEEE. In this work, a model predictive control (MPC) strategy based on optimal switching sequence (OSS) concepts is proposed for a grid-connected three-level neutral-point clamped converter. The proposed cascaded-OSS-MPC strategy does not require a weighting factor to balance the dc-link capacitor voltages and optimally controls both the grid currents and the capacitor voltages even during disturbances and large step changes in the references. The resulting MPC strategy allows operating the converter with a predefined harmonic spectrum, fixed switching frequency, and fast and robust dynamic response. Besides, an efficient optimization algorithm is also introduced to reduce the computational burden typically observed in this kind of MPC strategies. Experimental and simulation results are provided to demonstrate the effectiveness and high-quality performance of the proposed strategy.

The generation of high-order harmonics and single attosecond pulses via the asymmetric polarization gating technology has been theoretically investigated. It is shown that when the two circularly polarized laser fields are asymmetric in amplitude and phase, not only can the modulations of the harmonic spectrum be decreased, but also the efficiencies of the harmonics can be enhanced. As a result, a super-continuum with the bandwidth of 85 eV, contributed by the single harmonic emission peak and the near-single short quantum path, can be obtained. Finally, through the Fourier transformation of the selected harmonics on this supercontinuum, a near-single attosecond pulse with a full width at half maximum of 52 as can be obtained.

This paper proposed a modulation strategy for a hybrid converter, composed by a n-cell Flying Capacitor Converter (FCC) and a classical two-level inverter. The balancing of the inner capacitors is done with logical circuits, while current control is performed with the Optimal Switching Sequence MPC. The simulation results show a good dynamic performance and an improvement of the harmonic spectrum is presented, compared to the classic two-level inverter.

This article presents a method for determining losses in high-speed permanent magnet synchronous machines. Methods for determining magnetic losses in permanent magnets are considered, based on the solutions of the system of equations of Maxwell, Helmholtz and the Umov-Poynting theorem. The influence of the penetration of electromagnetic waves into the permanent magnet and the harmonic spectrum on the losses in permanent magnets from eddy currents is considered. The distribution of the field inside the permanent magnet is investigated and the losses in permanent magnets are determined by solving the system of Maxwell's equations and taking into account the nonlinearity and hysteresis. To solve the equations, the finite-difference method and the sweep method are used. Computer simulation of losses in permanent magnets has been carried out. Comparison of the results of determining losses using the numerical modeling of Maxwell's equations by the finite-difference method and three-dimensional modeling in the Comsol Multyphisics software package is made.

The rapidly increasing demand for Distributed Photovoltaic Power (DPVP) generation system transformers and the rise in the construction of solar photovoltaic plants in South Africa, present technical challenges in the latter involving high top-liquid and hotspot temperatures problems during their service lifetime. The winding Eddy current loss harmonic factors recommended by the standards do not take into account the skin effect due to the restricted penetration of electromagnetic fields on the conductors at high harmonic orders, which results in erroneous estimation of these losses as well as high temperature rise. In order to enable optimum estimation of the winding Eddy current losses, it is proposed in this paper a harmonic loss factor that considers the conductor skin effect under harmonic conditions by using the data supplied by the manufacturer for losses under rated conditions. Based on supplied harmonic spectrum, the service losses of a liquid-filled step-up transformer are estimated, top-liquid and hotspot temperature conditions are then realized. Lastly, the capacity of a transformer when supplying the given distorted load current profile is evaluated by using a technique ascribed to as derating. The use of this method is achieved by the computation of the maximum permissible current as a result of increased winding Eddy current loss and other structural losses. The results indicate transformer loading capacity increase to 97.6 % compared to 91.3 % when applying the harmonic factor approach recommended by the standards.

International audience; Quantum-optical spectrometry is a recently developed shot-to-shot photon correlation-based method, namely using a quantum spectrometer (QS), that has been used to reveal the quantum optical nature of intense laser–matter interactions and connect the research domains of quantum optics (QO) and strong laser-field physics (SLFP). The method provides the probability of absorbing photons from a driving laser field towards the generation of a strong laser–field interaction product, such as high-order harmonics. In this case, the harmonic spectrum is reflected in the photon number distribution of the infrared (IR) driving field after its interaction with the high harmonic generation medium. The method was implemented in non-relativistic interactions using high harmonics produced by the interaction of strong laser pulses with atoms and semiconductors. Very recently, it was used for the generation of non-classical light states in intense laser–atom interaction, building the basis for studies of quantum electrodynamics in strong laser-field physics and the development of a new class of non-classical light sources for applications in quantum technology. Here, after a brief introduction of the QS method, we will discuss how the QS can be applied in relativistic laser–plasma interactions and become the driving factor for initiating investigations on relativistic quantum electrodynamics.

The generation of ultrashort attosecond pulse requires both an enhanced high harmonic generation and the spectral-phase control. In the present work, an efficient method is theoretically investigated for extending HHG cutoff energy in Br2 molecule using TDDFT. The effects of molecular orientation and carrier-envelope phase of the laser on the high harmonic spectrum are analyzed. As a result, by the fine modulations of the laser field, the harmonic plateau is enlarged and the position of structure-induced interference minimum shifts. We also provide a physical picture on the intensity dependence of the spectral minima in the harmonic spectra.

In this paper, two control schemes based on finite control set-model predictive control (FCS-MPC) are proposed for a reduced-capacitor multilevel converter, referred to as four level-single flying capacitor (4L-SFC) converter. By using the notion of reconstructing phase voltage levels, natural capacitor voltage balancing can be achieved for the 4L-SFC converter, which is not fulfilled by the PI-based conventional modulation methods. Besides, two proposed strategies present a weighting factor-less approach to achieve fixed switching frequency, lower current distortion, and reduced ripple of capacitor voltages as well as lightening the computational burden. A single-objective cost function based on voltage vector error is defined in both methods to accomplish the reference current tracking. The second proposed method employs modulated model predictive control (M2PC) to guarantee a well-concentrated harmonic spectrum and lower current distortion compared to the first strategy. Simulation studies are conducted to validate and compare the performance of the proposed methods in terms of steady-state and transient-state response.

As renewable energy generation in South Africa continues to take a lion share of the republic’s energy generation, the design of distribution transformers for renewable energy applications has introduced several design and performance challenges that have not previously been taken into consideration during the design stage. Transformers in RE application have failed as a result of challenges associated with harmonics and distortion, distorted load cycle, over-voltages and oil-gassing issues. This study is used to give an analysis of various transformers ranging from 100 kVA to 1500 kVA that have failed within RE plants. In the study, the harmonic spectrum is considered to adequately specify the harmonic loading of the transformers during service. Three results from analytical method, Finite Element Method (FEM) and practical measurements are considered to ascertain the transformer service losses under the supplied harmonic spectrum. The improvement in computational accessibility of designing the transformers in FEM has proven to produce reliable results yielding about 98 % in comparison to measured results. In the end, the study reveals that the use of FEM in the transformer design for RE application has high prediction accuracy, and that these transformers failed on account of the loading exceeding the transformer ratings due to underestimation of the harmonic-induced losses during the design stage.

We report high harmonic generation in the extreme ultraviolet (XUV) region by using two-color laser fields at the wavelengths of 800 nm and 400 nm. With a Ti: sapphire femtosecond laser at a 10 Hz repetition rate efficient high harmonic generation was obtained in an argon gas medium with the IR field (ω) and its second harmonic (2ω) with parallel and perpendicular polarizations. The relative delay between the pulses is controlled via a Michelson interferometer arrangement. In addition to the odd high harmonic spectrum with frequencies (2n+1)ω, where n - integer number, also even spectral components 2nω are obtained, when the fields of the two colors are temporally overlapped and interact with the argon gas. Due to this overlap, the yield of odd harmonics can be increased as well. The calculations of electron trajectories within the semiclassical approach show differences in the action of the fields with parallel and perpendicular polarizations. For the former, there exist broad time intervals for returning electrons, and in the latter case there are only narrow intervals for possible solutions for each of the electron returns to the parent ion for a fixed phase difference between the ω and 2ω fields. By varying the relative delay between the two laser fields it is possible to spectrally enrich and enhance the produced XUV radiation or suppress it. The conclusions of the semi-classical approach were confirmed by calculations of the harmonic intensities within the strong field dipole approximation., Robert A. Welch Foundation, grant No. A1546.

The laser interaction with an electron-positron-ion mixed plasma is studied, from the perspective of the associated high-order harmonic generation. For an idealized mixed plasma which is assumed with a sharp plasma-vacuum interface and uniform density distribution, when it is irradiated by a weakly relativistic laser pulse, well-defined signals at harmonics of the plasma frequency in the harmonic spectrum are observed. These characteristic signals are attributed to the inverse two-plasmon decay of the counterpropagating monochromatic plasma waves which are excited by the energetic electrons and the positron beam accelerated by the laser. Particle-in-cell simulations show the signal at twice the plasma frequency can be observed for a pair density as low as $\sim 10^{-5}$ of the plasma density. In the self-consistent scenario of pair production by an ultraintense laser striking a solid target, particle-in-cell simulations, which account for quantum electrodynamic effects (photon emission and pair production), show that dense (greater than the relativistically-corrected critical density) and hot pair plasmas can be created. The harmonic spectrum shows weak low order harmonics, indicating a high laser absorption due to quantum electrodynamic effects. The characteristic signals at harmonics of the plasma frequency are absent, because broadband plasma waves are excited due to the high plasma inhomogeneity introduced by the interaction. However, the high frequency harmonics are enhanced due to the high-frequency modulations from the direct laser coupling with created pair plasmas., Comment: Accepted in Physical Review E (Phys. Rev. E)

The article considers a simulation model of the operation of a semiconductor converter. It allows to connect a three-phase induction motor to a single-phase electrical network and provide a three-phase symmetrical voltage on the stator winding. The parameters of elements included in the structure of the phase number converter are calculated. Authors have designed a simulation model using The Simulink Matlab software which describing the operation of the phase converter and confirming the theoretical conclusions. Calculation expressions are given for determining the parameters of the smoothing filter, which is included in the structure of the phase converter. The harmonic spectrum of the phase voltage at the output of the converter is analyzed.

The GaN flying capacitor multilevel converter (FCMC) offers a better harmonic spectrum and attains higher voltages with a limited maximum device rating but suffers from high components quantity and cost. In this paper, a Si/GaN hybrid single-phase 5-level flying capacitor multilevel inverter (FCMI) is proposed with a much-reduced component quantity and cost. The proposed hybrid FCMI consists of only two pairs of GaN devices and a pair of line-frequency Si devices, compared with four-pairs eight high-frequency GaN devices in a conventional five-level FCMI. Furthermore, the proposed FCMI has a twice effective voltage. The operation principle and modulated strategy are detailed discussed. Meanwhile, a new current ripple model is introduced to investigate the output performance. A 600V, 5-level hybrid Si/GaN converter prototype is designed and built. The experimental results confirm the validity and effectiveness of the presented converter and current ripple model.

The ceiling fan motors have been most outlooked motors from an efficiency point of view. However, with an increasing number of such motors in residential and commercial sectors, the need for efficient ceiling fans has arisen. The design of the outer rotor single-phase induction motor (SP-IM) for ceiling fan, is a nonlinear problem involving several design variables. In this work, time-stepping 2D FEA (Two Dimension-Finite Element Analysis) is used to design an energy-efficient ceiling fan SP-IM consuming below 35 W in accordance with BEE (Bureau of Energy Efficiency) star ratings and IS374 standard. A new design is presented and compared for better performance and air delivery with commercial blades. Various performance indices of the new design are presented, including the overall losses and their distribution, airgap flux density plot, and its harmonic spectrum.

International audience; Almost all induction motor applications suffer from unbalanced supply voltage. Under such conditions the motor operation can be seriously affected. Performance, control and monitoring are directly connected to the knowledge of the supply harmonics effects on the motor, therefore there is a real need to derive a general mathematical formula predicting the harmonics growth and to describe through an analytical analysis in steady state operation, the impact of unbalanced voltage supply on induction machine performance. In this paper an original analytical formula of harmonics components is developed to propose an accurate indicator of unbalanced supply voltage fault. The validity of this analytical study is confirmed by a comparison with simulation and experimental results. NOMENCLATURE  fundamental pulsation f frequency of the supply voltage (50HZ) sd V effective values of the supply voltages of the direct systems si V effective values of the supply voltages of inverse systems s s s R L   stator time constant r r r R L   rotor time constant r s L L M 2 1   leakage factor sa i Stator current   e  Real part of the quantity ed  Direct electromagnetic torque ei  Inverse electromagnetic torque e  pulsating electromagnetic torques.

Modern wind power plants typically comprise of type IV wind turbines and therefore switched power converters form an integral part of these plants. These converters produce harmonics in output voltage and currents, which can trigger electrical resonances formed by cable capacitances and transformer inductances. Lower frequencies above the fundamental (referred to as baseband) have a high quality factor, Q, thus these frequencies are poorly damped. It is therefore essential to know the harmonic spectrum of the converter. This paper investigates harmonics generated due to widely used non-symmetrical regular sampling, taking into consideration the effect of dead time (when switching the semiconductors) and the phase of the output current relative to the fundamental voltage reference. The investigation has been performed in theory, through simulations and laboratory measurements. A detailed discussion of the results obtained through the three methods has been provided. New contributions in this paper are the investigation of harmonic amplitude and phase due to the phase of the load current together with coupling of both baseband and sideband harmonics.

International audience; The present study aims to propose an analytical model with the purpose of spectral analysis of the terminal voltage (to the neutral point which is phase voltage) in a brushless synchronous generator for fault detection. In this type of generator which comprises one exciter as exciter and the main machine, rotating parts such as rectifier bridge, exciter armature, and their connections are more likely to defect. Therefore, considering the relevant literature, the exciter armature open-circuit fault is taken into account for the investigation. Consequently, the brushless generator model is developed for two states, including healthy and exciter armature open-phase fault under no-load condition. Then, an analytical approach is proposed for the terminal voltage harmonic analysis which is utilized for the two states. Thus, the harmonic spectrum can be achieved for these states. These harmonic components are compared for healthy and faulty states, and the major distinctive components are determined. Hence, the occurred exciter fault can be detected using these components. In order to evaluate the model and its efficiency, finite element analysis, and experimental results are utilized.

The paper presents design considerations and circuit simulation of digitally controlled high current, six pulse thyristor rectifier system. The rectifier system is utilized for powering Fuel Rod Cluster Simulator of thermal hydraulic experimental R&D facilities for simulating temperature and power transients expected in nuclear reactor. To maintain the desired amount of nuclear fission heat flux across Fuel Rod Cluster Simulator, suitably scaled rectifier system is necessary. A 5300 Amp thyristor controlled rectifier system is designed to cater the requirement of 600 kW power for experimental R&D facilities. The digital control philosophy has been designed for generating pulses for triggering thyristors. Design calculations for the configuration of six pulse hexa-phase thyristor rectifier system with inter phase transformer has been presented. The simulation of power circuit configuration including closed loop feedback control mechanism has been performed utilizing circuit simulation software. The simulation results including harmonic spectrum have been highlighted in the paper.

In 2010, South Africa introduced the Renewable Energy Independent Power Producer Procurement Programme to invigorate low-carbon energy generation using renewable energy resources. Amongst the development of wind and hydro plants; solar photovoltaic plants then took off rapidly. The volume of solar PV plants connected to the grid in 2015 and 2016 was unparalleled. However, the solar PV electric power distribution network is challenged with the presence of unacceptable harmonics and distortion content at the point of common coupling due to the switching action of inverters and operation of non-linear loads. It therefore essential to precisely estimate the resultant increased load losses in order to estimate the hot spot temperature and total losses during service.In order to demonstrate the significance of these challenges, this paper provides a comprehensive harmonic analysis of an oil-filled transformer for the supplied geometrical data and harmonic spectrum of an oil-filled transformer. The load losses are evaluated under fundamental and harmonic conditions. The load losses are classified into I2R and stray losses. The I2R losses can be easily obtained by analytical calculations and also through practical measurement. On one hand, analytical calculation of the stray losses cannot give an optimized estimation and practically their immeasurable. In this paper, a 2D FEM model that is dynamic to any transformer geometrical data is developed to produce a pragmatic loss estimation by using knowledge of the magnetic flux density. Generally, analytical formulations neglect the radial magnetic flux density component. During operation, this component becomes predominant towards the winding ends and cannot be disregarded.

A control scheme based on finite control set ---model predictive (FCS-MPC) improved with a Feedback Quantizer is presented. The FCS-MPC is a control scheme popularly used in power converters because, among others, (i) the nonlinearities and constraints of the converter’s operation, are quickly considering, (ii) it uses the natural discrete operation of power converters, and (iii) the rapid response to changes in both references or disturbances. However, the variable switching frequency operation in model-based predictive control results in a spread harmonic spectrum, generating resonances or saturation in input transformers when used in active front-end (AFE) rectifiers. This paper proposes an improved FCS-MPC, using a feedback Quantizer applied in a multi-cell AFE rectifier. This above consists of a feedback modulation technique, which allows minimizing the low-frequency harmonics in the converter PWM voltage. Simulation results verify the performance of the proposal obtaining improved harmonic spectrum of both input current and PWM voltage waveforms of the converter.

HHG of up to 70th order utilizing graphene subjected to bicircular electromagnetic fields of terahertz frequencies was investigated. A momentum-resolved harmonic spectrum and induced electron current densities were obtained and analyzed.

Distribution transformers are commonly designed and manufactured to operate at fundamental frequency and to facilitate sinusoidal loads. The operation of loads that draw distorted currents culminate in higher losses, hotspot temperatures, degradation of insulation materials and declined service life. To avert these technical challenges, the continuous power rating of the transformer under current harmonics has to be reduced. This paper presents some analysis into the effect of current harmonics on the maximum loading capability of oil-filled transformers that are intended to operate within solar power plants. The harmonic spectrum derived by the presence of non-linear loads and seen by the transformer during service is presented. A recommended practice for derating the transformer described in the IEEE std. C57. 10–2018 is adopted in the study.

Band structure and transition dipole moment play important roles in high-order harmonic generation from solid materials. In this work we provide a new all-optical technique to reconstruct the momentum-dependent transition dipole moment using the harmonic spectrum from MgO crystal driven by an ultrashort mid-infrared laser pulse. Under the influence of the ultrashort laser pulse, the emitted photon energy and the crystal momentum form a one-to-one match, in the same way between the intensity of the harmonic above the minimum bandgap and the square of the amplitude of the transition dipole moment, resulting in a realization of directly probing the transition dipole moment. Our all-optical method paves a way to image the two-dimensional transition dipole moment of crystals with the inversion symmetry.

DSM (Demand Side Management) is a short term and comparatively low cost solution for energy starved countries. Replacement of IB (Incandescent Bulbs) with CFL (Compact Fluorescent Lamps) has proved its success throughout the world. The same solution, at larger scale, was proposed to Pakistan to mitigate power shortage on short term basis. Accordingly in year 2008, ADB (Asian Development Bank) conducted a study and it was found that replacement of conventional IB with 30 million CFL will result into series of benefits for the stake holders and above all the Environment. The study, unfortunately didn't take enough consideration of effect of CFLs on the power system being non-linear device and so the power quality issues remained a secondary consideration. The focus of this paper remains on the effect of such non-linear load on consumers, it also envisages the erratic behaviour of such large penetration of CFLs on direct single phase, three phase, digital as well as electromechanical energy meters, under different loading conditions e.g. resistive load, SMPS (Switch Mode Power Supply), half and full-wave rectifiers. It also reflects harmonic pollution caused by CFLs, their effect on power system quality and the registration ability of electromechanical as well as digital energy meters. To this end Harmonic spectrum was recorded up to the 31st harmonic.

We theoretically investigate the spectral caustics of high-order harmonics in solids. We analyze the 1-dimension model of solids HHG and find that, apart from the caustics originated from the van Hove singularities in the energy-band structure, another kind of catastrophe singularities also emerge when the different branches of electron-hole trajectories generating high-order harmonics coalesce into a single branch. We solve time-dependent Schr\"odinger equation in periodic potential and demonstrate the control of this kind of singularities in HHG with the aids of two-color laser fields. The diffraction patterns of the harmonic spectrum near the caustics agree well with the inter-band electron-hole recombination trajectories predicted by the semiconductor semi-classical equation. This work is expected to help to understand the HHG dynamics in solids and manipulate the harmonic spectrum by adjusting driving field parameters., Comment: 4 pages, 3 Postscript figures

Purpose The purpose of this paper is the development of a new numerical method for the calculation of the air-gap magnetic flux harmonics in synchronous machines with permanent magnet (PM) excitation. The harmonic analysis results are used as input data for the eddy-current loss calculation and for the rotor heating evaluation. Design/methodology/approach The method is based on the finite element analysis (FEA). The model takes into account toothed stator design, rotor asymmetrical magnetic reluctance and saturation. At first, a series of static DC magnetic (magnetostatic) simulations is run. Each problem corresponds to specific rotor position and the momentary stator winding currents. The Fourier analysis performed for each problem yields the harmonic spectrum variation in time. Then, a series of AC magnetic (time-harmonic) simulations is run. Each problem corresponds to a specific harmonic. The result is the eddy-current losses distribution. After total loss is calculated, the heat transfer analysis is conducted. Findings The analysis reveals that 90 per cent of losses are located in the sleeve that holds PMs together. Rotor eccentricity brings even harmonics of low magnitude that have little impact on heating. Originality/value In general, the study requires transient electromagnetic analysis with motion. The purposed method allows to simplify the problem. The method is based on static and quasi-static (time-harmonic) problems simulation. It is fast and highly automated. The method allows simultaneous taking into account of tooth-order harmonics, stator winding harmonics and eccentricity for heating calculation.

The paper investigates sensorless field-oriented control of a two-pole surface mounted permanent magnet synchronous machine (PMSM) with a symmetrical nine-phase winding configuration. Reduced magnet span on rotor causes production of highly non-sinusoidal back-electromotive force (EMF) in the stator windings. FFT analysis of the EMF reveals a high-magnitude low-order harmonic spectrum, with third-harmonic magnitude almost equal to the fundamental. Harmonics with such magnitudes have been used in the past to increase electromagnetic torque of the multiphase machines. An alternative use of such harmonics is for speed/position estimation, as discussed here. It is believed that an I-f starting method for smooth and fast transition from open-loop frequency to sensorless field-oriented control (SFOC) based on phase-locked-loop (PLL) can also be implemented for studied PMSM, employing the same low-order harmonic spectrum. The objective of this work is therefore to investigate sensorless control possibilities, i.e. to implement closed loop control without use of either the encoder/resolver or standard three-phase observers/schemes (e.g. Luenberger, extended Kalman filter etc.). As it will be shown, the main advantage of the developed method is related to the significantly reduced computation time and algorithm complexity. Derived hybrid control schematic and corresponding simulation results are also shown. Some simulation results are validated using real machine in an experimental setup.

In this paper, a constant switching frequency predictive control method for a three-level flying capacitor active front end converter is presented for the first time. This predictive control scheme results in reduced switching frequency operation of the converter with reduced computation burden compared to conventional predictive control methods. For the predictive controller, the cost function is defined in terms of grid current error vector in synchronously rotating $d-q$ frame and the condition for optimal converter voltage vector is derived. The optimal converter voltage vector is then synthesized using level shifted carrier based space vector modulation. Thus the proposed method overcomes the disadvantage of variable switching frequency in predictive based control methods. The controller ensures very low harmonic distortion of line currents with minimum computational requirement of the predictive controller. The performance of the proposed predictive controller is analysed using MATLAB/SIMULINK and the results are compared with that of a conventional PI based control. It can be observed that the proposed controller results in similar performance in terms of harmonic spectrum, better performance in response time and decoupled control compared to a classical PI based controller and can be readily used for grid connected power conversion applications and distributed generation systems.

Condition monitoring of electrical machines is essential in industrial operations for improving workplace safety and ensuring reliable and economical exploitation of the machines. Motor current signature analysis (MCSA) monitoring technique is gaining heightened popularity due to the simplicity of its algorithms and the least number of sensors required. In this paper, the harmonic spectrum of industrial inverter fed induction motor is investigated for the detection of broken rotor bars. To improve the legibility of the spectrum, the fundamental component is attenuated using infinite impulse response (IIR) filter because of its good transition band, less passband ripples and low order. The results are first taken from finite element method (FEM) based simulation, where the motor is fed with pure sinusoidal current and only faulty and spatial frequencies are investigated and used as a benchmark. The practical results are based on the measurements taken from the laboratory setup, where the motor under investigation is fed through an industrial inverter working under scalar control mode. The data acquisition is done with a good sampling rate of 100 kHz for better resolution.

The harmonic spectrum of the magnetic flux density is essential for torque interaction and efficiency of magnetic gears. In this paper a design of coaxial magnetic gear has been modeled in order to estimate the magnetic flux density harmonic spectrum of in the air-gaps, magnets, rotors and in the modulating steel segments. A time dependent Finite Element Method model of the coaxial magnetic gear has been implemented. The model simulations are carried out by Ansys-Maxwell package. The flux density harmonic spectrum depending on rotor’s relative positions and rotational angle has been calculated and analysed. The harmonic spectrum is implemented by Matlab software.

Ultrafast laser pulses are one of the main tools to control quantum systems (e.g., atoms, molecules). High-order harmonic process has a critical impact on generating ultrafast laser pulses. The high-order harmonic process of muonic atoms driven by few-cycle spatially inhomogeneous laser fields is theoretically investigated. It is found that the cutoff of the high-order harmonic spectrum extends dramatically, and a very broad continuum spectrum appears due to the large mass of the muon and the inhomogeneity of the driver field. With proper inhomogeneity parameters, an isolated-zeptosecond pulse can be obtained from the continuum spectrum without any phase compensation.

In this paper, the frequency spectrum of a three-phase induction motor's stator current on a linear scale is investigated. The broken rotor bar, spatial and grid fed harmonics are taken into consideration. Since the fundamental component of the power supply is always the most powerful component, it makes the spectrum less legible, increases the spectral leakage and makes the logarithmic scale inevitable. In this paper, a Chebyshev filter is used for attenuation of the fundamental component, because of its good transition band and no passband ripples. The current signals are taken from both simulation and laboratory environment and harmonics due to above-mentioned causes are segregated.

The high harmonic generation of heteronuclear hydrogen molecular ions in few-cycle infrared strong laser fields is studied by numerically simulating the time-dependent Schr\"odinger equation. By reversing the carrier envelope phase of the few-cycle laser pulse, the electron dynamics is reversed as well. However, due to the different nuclear masses, two nuclei move with different repulsive speeds, which makes the rescattering processes not identical when the carrier envelope phase shifts by $\ensuremath{\pi}$. The different rescattering processes lead to distinct harmonic spectra in the cutoff region. The mass-dependent harmonic spectrum offers a view angle to diagnose the isotope dynamics in molecules with unprecedent high time and spatial resolutions.

High-order harmonic generation from the asymmetric helium hydrogen molecular ion exposed to a few-cycle chirped laser field is theoretically investigated by numerically solving the reduced one-dimension non-Born–Oppenheimer time dependent Schrodinger equation. The numerical results show that the plateau of the high-order harmonic spectrum is dramatically broadened and smoother with the introduction of the chirp. Further study presents that only the short quantum path contributes to harmonic emission and the long quantum path disappears in the chirped laser. In addition, an 80-as isolated attosecond pulse is obtained by superposing the harmonics from the 100th to the 130th order in the chirped field. The time-frequency distributions and the electronic probability distributions are presented to explain the underlying physical mechanism.

High-order harmonic generation (HHG) is a remarkable frequency up-conversion process in which an ultrafast femtosecond laser pulse at high intensity (>10 14 W/cm 2 ) interacts with a gaseous target to generate coherent extreme ultraviolet radiation. High-order harmonics, due to their high repetition rate operation, tunable wavelength and high coherence degree, have been widely used in many fields. HHG is currently a cornerstone of attosecond pulse, and promises to be a valuable tabletop light source. Their main drawback, however, is the low conversion efficiency, which limits many applications. In this work we present a promising way to increase harmonic yield by using the synthesized two-color field, whose validity is demonstrated both on single-atom and macroscopic levels. The single-atom harmonic spectrum is calculated by the strong field approximation method. The macroscopic propagation of the fundamental and harmonic fields in an ionizing medium is obtained by solving Maxwell equations, which involves the dispersion, absorption, Kerr and plasma effects. The waveform of two-color laser field is determined by using a genetic algorithm to optimize the maximum single-atom Ne harmonic yield, for the lasers with fundamental wavelengths of 800 nm to 3000 nm. Optimizations are performed on condition that the cutoff and total laser power for the single-color field and the optimized wave are the same. The optimizations show that the optimal wavelengths and intensities meet the conditions of λ 1 / λ 2 ≈ 3 , I 1 / I 2 ≈ 5 for two component fields, and carrier-envelop phases are f 1 =0, f 2 =1.6 p . Our analysis show that the spreading of the electron wavepacket is almost the same in the optimized and single-color field. But the ionization level and yields of harmonics emitted from short-trajectory returning electrons are enhanced in the optimized field. Thus, the harmonic conversion efficiency generated by the optimized laser field can be increased by at least one order without increasing total laser power even after considering macroscopic propagation effects. We also compare the wavelength scaling laws of harmonic yield generated by the single- and optimized two-color fields. For the single atom, the present wavelength scaling in the single-color field agrees with the previous results, which scales as l - 5 ~ l - 8 . In the two-color field, the scaling law is slightly worse than that in the homochromous field mainly due to different contributions of short and long trajectories. While for the macroscopic high harmonic generation, its efficiency falls more dramatically with increasing wavelength because of the unfavourable phase-matching and dominant contribution of harmonics from short-trajectory electrons, with a very unfavorable scaling law of l - 8 ~ l - 13 . Although we can not obtain a much better wavelength scaling of harmonic yield in the two-color fields, the conversion efficiency can be enhanced more than one order. Further analysis shows that the stability of optimized waveform is maintained in consideration of relative intensity, wavelength and phase fluctuations of ±10%, ±40 nm and ±0.05 p , respectively. Due to the great advent of the ultrafast lasers technology, such as waveform synthesizing, optical parametric amplification and optical parametric chirped-pulse amplification, this work gives helpful guidance for intense harmonic generation.

The non-dipole (ND) effects on high-order harmonic generation (HHG) with the laser wavelength increasing towards the long wavelength region are investigated. Two major phenomena due to the ND effects, the decrease of the HHG intensity and the shift of the harmonic spectrum, are discussed. It is shown that, for the commonly used laser intensity I∼1014 W/cm2 and target with ionization potential I p ∼ 0.5 a . u . , the ND effects become nonnegligible when the laser wavelength is increased to the mid-infrared region of several thousand nanometers. It is also found that the variation of the ND effects presents different rules compared with those towards the high intensity region. Two fitting formulas are proposed to describe the variation rules. The physical meanings of the fitting results are discussed with classical calculation.

We investigate high-order harmonic generation from atoms irradiated by bichromatic counter-rotating circularly polarized laser pulses by numerically solving the time-dependent Schrödinger equation. It is found that the minimum energy position of the harmonic spectrum and the non-integer order optical radiation are greatly discrepant for different atomic potentials. By analyzing the quantum trajectory of the harmonic emission, discrepancies among the harmonic spectra from different potentials can be attributed to the action of the potential on the ionized electrons. In addition, based on the influence of the driving light intensity on the overall intensity and ellipticity of higher order harmonics, the physical conditions for generating a high-intensity circularly polarized harmonic can be obtained.

Coherent-wake plasma emission induced by ultrashort mid-infrared laser pulses on a solid target is shown to give rise to high-brightness, high-order harmonic radiation, offering a promising source of attosecond pulses and a probe for ultrafast subrelativistic plasma dynamics. With 80-fs, 0.2-TW pulses of 3.9-μm radiation used as a driver, optical harmonics up to the 34th order are detected, with their spectra stretching from the mid-infrared region to the extreme ultraviolet region. The harmonic spectrum is found to be highly sensitive to the chirp of the driver. Particle-in-cell analysis of this effect suggests, in agreement with the generic scenario of coherent-wake emission, that optical harmonics are radiated as trains of extremely short, attosecond ultraviolet pulses with a pulse-to-pulse interval varying over the pulse train. A positive chirp of the driver pulse can partially compensate for this variation in the interpulse separation, allowing harmonics of the highest orders to be generated in the plasma emission spectrum.

An efficient approach to obtain the high-intensity isolated attosecond X-ray pulse has been proposed and studied by using the low-intensity ultraviolet–mid-infrared (UV–MIR) laser beam. It is found that with the superposition of the UV–MIR beam, not only the harmonic efficiency can be enhanced, but also the harmonic cutoff can be extended to the X-ray region. In detail, the results can be separated into two parts. Firstly, when the fundamental field is chosen to be the linearly polarization MIR field, the enhancement of the harmonic efficiency is sensitive to the pulse duration and the delay time of the UV pulse. Moreover, the enhancement of the harmonic spectrum is coming from the multiple harmonic emission peaks (HEPs). Secondly, when the fundamental field is chosen to be the polarization gating two circularly polarization MIR fields, the enhancement of the harmonic efficiency is independent on the pulse duration and the delay time of the UV pulse, which is much better for experimental realization. Moreover, the enhancement of the harmonic spectrum is nearly coming from the single HEP. Further, with the introduction of the unipolar pulse, the harmonic cutoff can be further extended and some sub-40 as single X-ray pulses with the intensity enhancement of 450 dB can be obtained.

In this paper the harmonic components in the stator's current and the developed torque of a faulty induction machine (IM) driven by Direct Torque Control (DTC) is investigated. The fault under consideration is the inter-turn short-circuit (ITSC) in stator's winding. Deep study of the harmonic and inter-harmonic content is conducted for fault detection (FD) purposes. The harmonics in the spectrum appear as a result of diverse causes including stator fault, DTC reaction to the fault, switching activities of the inverter, core saturation effect, and noise signal for IM operating in harsh industrial environment. Simulation reinforced by experimental results demonstrated the correctness of the frequency domain analysis.

In this study, the impact of electric vehicle (EV) battery charging on distribution transformer (DT) is assessed in addition to the conventional loads connected to the grid. Current harmonic spectrums of different charging levels are used to analyze the effects of commercially available EV chargers on the losses, temperature rise and lifetime of a sample 1500 kVA transformer. The harmonic spectrum data take into account the state-of-charge (SOC) for more accuracy. The results for Level I/II chargers and Level III chargers are both discussed.