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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Harmonic Concatenation of 1.5-Femtosecond-Pulses in the Deep UV
摘要： Waveforms with durations short enough to probe the electronic timescale can be generated both in the extreme UV and in the IR-VIS region of the electromagnetic spectrum. In the deep UV (DUV), where for example many basic aromatic molecules absorb radiation and undergo photochemical reactions, pulses with such extremely short durations have not yet been demonstrated. A fundamental difficulty is rooted in the large group velocity dispersion of any optical component in the DUV, causing a DUV pulse to be readily broadened and distorted before it reaches the sample. The present record for the shortest DUV pulses is 2.8 fs. Here, a scheme for the coherent synthesis of DUV waveforms is presented. The principle is the concatenation of spatial and temporal harmonics that are created by two noncollinear IR-VIS pulses. Cascaded processes of frequency conversion and self-diffraction in a thin MgF2 plate yield a multifaceted emission pattern of temporal and spatial harmonics. The emission angle Φ of the harmonic orders depends on the frequency. Broadband waveforms arise, of which the lower frequency bands belong to one spatial harmonic, and the higher frequency bands belong to the other spatial harmonic. In order to synthesize ultrashort waveforms from these frequency bands, their phases must be adjusted. This is accomplished by controlling the groove-envelope phase (φGEP) of the fundamental pulses, which is determined by their delay on the subcycle timescale. Using temporal harmonics of third order, the concatenation of two spatial harmonics synthesizes DUV pulses of 1.5 fs. A generic feature is that these waveforms are spatially separated from the fundamental pulses and are therefore available for immediate spectroscopy usage without any subsequent optical elements.
关键词： Harmonic concatenation,femtosecond-pulses,spatial harmonics,deep UV,temporal harmonics,coherent synthesis
更新于2025-09-12 10:27:22
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Circuit Model of LED Light Bulb suitable for typical voltage THD on LV distribution networks
摘要： In lighting system design, the LED light bulb technology is gaining more and more advantages in comparison to other previous solutions. On the other hand, the designers of lighting systems have to face the specific problems created by this technology in terms of deterioration of the power quality on the mains. The knowledge of lamp electrical models is a key point for the optimal design of the lighting systems but such models are not provided by the manufactures. Moreover, the voltage on the mains may vary along the day due to the load fluctuation as well as due to the variation of the power generated by distributed renewable resources. Consequently, suitable electrical models have to be able at emulating the lamp behavior according to the voltage variability. The paper proposes an equivalent electrical circuit of LED light bulb. The components of the model are identified by means of simple electrical measurements. In particular, the circuit enables to emulate the current waveform in the case of network voltage variability. The validation has highlighted that the simulated currents waveforms have a good matching with the experimental data obtained in presence of distorted voltage on the mains (provided that the voltage THD is compliant with IEEE-Std-519). The validation has been performed also at voltage values different from the ones used for the components identification.
关键词： Current harmonics,power conversion,optimal design,modelling,power quality,lighting,equivalent circuits
更新于2025-09-12 10:27:22
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Discrete exited states influence on the harmonics spectrum generated in two-colour laser fields
摘要： The contribution of excited discrete atomic levels to the generation of high- and low-order harmonics in the interaction of a single atom with a two-color laser field has been studied for the first time. The studies were carried out for two types of atoms with different symmetry of the ground state wave functions (Ag, Ne) and for a two-color laser field consisting of the linearly polarized fundamental and second harmonics of Ti:Sa laser (ω + 2ω). The angle between the polarization of the ω + 2ω laser field components is varied. A significant effect of the symmetry of populated excited levels on the polarization characteristics of the generated harmonics is shown. A new method of control over the polarization state of the generated radiation is proposed.
关键词： non-perturbative theory,high harmonics generation,single atom response
更新于2025-09-12 10:27:22
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Simulation Analysis of Harmonic Characteristics of Photovoltaic Power Generation System Based on MATLAB
摘要： Photovoltaic (PV) power generation system, as a kind of clean energy power, is increasingly applied in the power grid. However, due to the uncertainty and fluctuation of PV system, it has negative influence on the power quality, such as power factor deterioration, voltage waveform distortion and electromagnetic interference. In this paper, by doing the equivalent impedance transformation of the high voltage transmission and distribution system with photovoltaic power supply, the influence of photovoltaic power generation on amplification of harmonic voltage and harmonic current of high voltage transmission side is analyzed. The capacity of PV system varies with the range of harmonics. Finally, the optimal operation mode of photovoltaic power generation is put forward innovatively based on harmonic characteristics under different operating conditions and capacity. It aims to guide the harmonic suppression of photovoltaic power generation system.
关键词： transmission and distribution,harmonic suppression,photovoltaic power generation system,harmonics
更新于2025-09-12 10:27:22
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[IEEE 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Paris, France (2019.9.1-2019.9.6)] 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Terahertz Physics of Graphene, Possibly The Most Nonlinear Material We Know
摘要： In this presentation gigantic THz-range optical nonlinearity of graphene will be demonstrated and explained. In particular, nonlinear THz conductivity and saturable absorption, and extremely efficient THz high harmonics generation in graphene will be presented and explained within a framework of a simple thermodynamic model of THz-graphene interaction.
关键词： nonlinearity,high harmonics generation,saturable absorption,THz,graphene
更新于2025-09-12 10:27:22
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Circularly polarised antenna with wide harmonics suppression by two angled C-shaped structures
摘要： In this Letter, a circularly polarised (CP) antenna is proposed. The proposed antenna is realised by combining two angled C-shaped structures. By setting different widths (WL and WR) for the left and right angled C-shaped structures, respectively, an asymmetric structure is obtained. Therefore, the proposed antenna exhibits CP characteristics. From repeated simulation results, the authors find that the optimum ratio WL: WR to make the proposed structure operate as a CP antenna is 5: 8. Moreover, the measured reflection coefficient is lower than ?2.4 dB within a stopband up to 12 GHz. This means that wide harmonics suppression (up to the fifth harmonic) is successfully achieved.
关键词： C-shaped structures,harmonics suppression,circularly polarised antenna
更新于2025-09-12 10:27:22
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Advances in reduction of total harmonic distortion in solar photovoltaic systems: A literature review
摘要： The use of photovoltaic (PV) systems has increased in recent years due to the high demand for clean energy sources. PV systems can utilize abundant and free energy from the sun, which is a substantial advantage. However, compared with other renewable technologies, the PV system still faces major obstacles such as high cost and low efficiency. In addition, fluctuating incident energy from the sun creates harmonics in the generated power that might lead to undesirable system performance. Total harmonic distortion (THD) is the ratio of distorted power to the main power of the signal, and is most commonly used to indicate the amount of signal distortion. THD has become a serious concern as more PV systems are integrated into grid systems. Previous research and reviews have attempted to reduce THD and its effect, but unfortunately focused on reducing THD at individual parts of the PV system. For the first time, this study holistically and systematically reviews the advances in THD reduction techniques for the entire PV system. The causes of harmonics, current solutions, and research gaps for further investigation are described in detail. Moreover, the current THD reduction techniques used in each stage of the PV system are compared, including their main benefits and drawbacks. Finally, this study recommends the use of adaptive filters as a possible solution for THD reduction because these filters have effectively reduced noise and disturbance in other systems.
关键词： THD reduction,DC-DC converter,harmonics,THD,photovoltaic,inverters,PV,adaptive filters,renewable energy,MPPT
更新于2025-09-12 10:27:22
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Frequency‐scaled optimized time‐frequency transform for harmonic estimation in photovoltaic‐based microgrid
摘要： Renewable (especially photovoltaic [PV])‐based distributed generations (DGs) integrated via converter stations pose serious challenge against effective monitoring of fundamental and harmonic phasors because of the presence of time‐varying Nth‐order harmonics, which get escalated in terms of voltage flicker, total harmonics distortion profiles with increased penetration level of such renewable sources. The generalized S‐transform (ST) has been used extensively for these nonstationary power signals analysis because it localizes the signal spectrum in time and yields a phase spectrum also for obtaining both amplitude and phase characteristics. However, the transform suffers from large execution time and arbitrary choice of window parameters. The paper, therefore, presents a new approach to extract time‐frequency response (TFR) from a harmonically scaled Fourier kernel ST optimized by metaheuristic firefly algorithm suitable for monitoring of microgrid phasors in real time, which can be ultimately used for effective power management and coordination. This new formulation uses selective frequency scaling to achieve a significant time reduction (within a half cycle of the initiation of the disturbance) in monitoring and tracking time‐varying harmonic disturbances, especially for DG‐integrated operations. Extensive simulation results for monitoring of time‐varying fundamental and harmonics in PV‐based grid‐connected power networks are presented against efficacy measures. Further, to validate in real time, a TMS320 C6713 digital signal processor (DSP) test bench is included in the paper for fundamental and harmonics estimation.
关键词： monitoring,photovoltaic,filtering,nonstationary power signal,harmonics,scaling methods,real‐time S‐transform
更新于2025-09-11 14:15:04
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[IEEE 2019 IEEE 2nd Ukraine Conference on Electrical and Computer Engineering (UKRCON) - Lviv, Ukraine (2019.7.2-2019.7.6)] 2019 IEEE 2nd Ukraine Conference on Electrical and Computer Engineering (UKRCON) - Surface and Bulk Wave Modes of Two Dimensional Photonic Crystal Waveguide
摘要： Electrodynamical characteristics of the two-dimensional photonic crystal waveguide are considered. Effect of the width of hollow waveguide channel on the dispersion characteristics and spatial distribution of electric field is analyzed. Slow wave localized modes with phase velocity less than speed of light are supported by photonic crystal waveguide and can be used for synchronization with linear electron beams in the terahertz beam-wave systems. Widening of the waveguide hollow channel does not result in significant decrease of the electric field intensity on the axis of waveguide as occur in metallic slow-wave systems.
关键词： spatial harmonics,dispersion characteristics,two-dimensional photonic crystal waveguide,terahertz range,slow wave modes
更新于2025-09-11 14:15:04
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Symmetric-component decoupled control of grid-connected inverters for voltage unbalance correction and harmonic compensation
摘要： In this paper, a strategy is investigated for control of distributed generators to additionally support the local grid on top of conventional electricity generation. The strategy decouples unbalance and harmonic compensation in the phase sequences and the frequency domain for a grid-connected inverter with local unbalanced and distorting loads. Unlike conventional control schemes for grid-connected converters, the proposed strategy is designed to be sequence-asymmetric for the purpose of unbalanced and harmonic local voltage correction. A frequency-domain Norton equivalent model is derived to illustrate the working principle of the strategy. Accordingly, it is shown that following a frequency-domain decoupled method the fundamental positive-sequence, the harmonic symmetrical sequence, the fundamental zero-sequence and the fundamental negative-sequence components can be regulated independently. Consistent to the model analysis, experiments validate the reduction of the local voltage total harmonic distortion and unbalanced factor when the converter is programmed for both harmonic sinking and voltage unbalance correction.
关键词： Harmonics,Control,Voltage unbalance,Grid-interactive power converters,Compensation
更新于2025-09-11 14:15:04