Stability analysis and parameter configuration of parallel virtual synchronous generators in microgrid

The current small-signal stability analysis and parameter selection of converters that mimic synchronous generators usually ignore some dynamic characteristics and the changes of steady-state operating points for simplicity. It could only judge the trend of small-signal stability and the analysis result was not accurate enough. Firstly, this paper established a small-signal model that mimics synchronous generators by connecting two isolated converters in parallel, the eigenvalues of the system were calculated and some of their physical meanings were obtained. Following that, in order to demonstrate the relationship of eigenvalues and state variables, the participation factor was calculated. Considering that, there will be some variability of the operating points with the parameters variation. As a function of the system settings, numerous root locus plots were created. For individual eigenvalue close to the real axis, in order to reveal the contribution of different parameters to the oscillation patterns, a separate eigenvalue sensitivity analysis was performed. The rules of the influence are essential to guide the design of parameters and their optimization of isolated converters connected in parallel that mimic synchronous generators

Surface plasmon induced direct detection of long wavelength photons

Millimeter and terahertz wave photodetectors have long been of great interest due to a wide range of applications, but they still face challenges in detection performance. Here, we propose a new strategy for the direct detection of millimeter and terahertz wave photons based on localized surface-plasmon-polariton (SPP)-induced non-equilibrium electrons in antenna-assisted subwavelength ohmic metal–semiconductor–metal (OMSM) structures. The subwavelength OMSM structure is used to convert the absorbed photons into localized SPPs, which then induce non-equilibrium electrons in the structure, while the antenna increases the number of photons coupled into the OMSM structure. When the structure is biased and illuminated, the unidirectional flow of the SPP-induced non-equilibrium electrons forms a photocurrent. The energy of the detected photons is determined by the structure rather than the band gap of the semiconductor. The detection scheme is confirmed by simulation and experimental results from the devices, made of gold and InSb, and a room temperature noise equivalent power (NEP) of 1.5 × 10−13 W Hz−1/2 is achieved.MOE (Min. of Education, S’pore)EDB (Economic Devt. Board, S’pore)Published versio

Self-assembled chitosan nanotemplates for biomineralization of controlled calcite nano-architectures

Three-dimensional chitosan self-assembled nanostructures are reported whose morphology can be adjusted by tuning of the processing parameters, including the rate of solvent removal, the surface roughness of the substrate, and the polarity of the solvent used. Upon this, chitosan nanostructures of more interesting morphology and even higher complexity can be prepared, which can serve as nanotemplates for subsequent biomineralization of calcium carbonate, leading to controllable three-dimensional biominerals having the same complex morphology as that exhibited by the self-assembled chitosan nanotemplates

Research on internal external collaborative optimization strategy for multi microgrids interconnection system

Microgrid is one of the most effective solutions to integrate renewable generation into power system. However, microgrids also have some limitations, such as increasing renewable energy accommodation, promoting multi-energy complementarity, and improving energy efficiency. Through autonomous management and energy interaction among microgrids. The establishment of multi microgrids provides ideas for solving the above problems. Multi microgrids has obvious advantages in promoting renewable energy accommodation, improving the economy and energy utilization of power grid operation, and reducing the impact on the distribution network. Therefore, from the perspective of energy scheduling, this paper proposes a internal external collaborative optimization strategy for multi microgrids. Firstly, a cogeneration microgrid model based on graph theory is established, which can not only represent the energy transmission process inside the microgrid, but also the energy interaction process between microgrids. Secondly, a microgrid interconnection pipeline transmission model based on the loss function is established. This model can not only reflect the energy transmission state in the pipeline, but also facilitate the linear solution of the optimization model. Finally, by setting new decision variables and constraints, the linear solution of the internal external collaborative optimization of the multi microgrids is realized, and its rationality and feasibility are verified by a case

Highly Sensitive Dual‐Band Switchable between Ultraviolet and Visible Region Photomultiplication Type Polymer Photodetectors

Abstract Dual‐band photomultiplication type polymer photodetectors (PM‐PPDs) are achieved with the structure of ITO/PDIN/poly[N,N′‐bis(4‐butylphenyl)‐N,N′‐bis(phenyl)benzidine] (poly‐TPD):2,2′‐((2Z,2′Z‐(12,13‐bis(2‐ethylhexyl)‐3,9‐diundecyl‐12,13‐dihydro‐[1,2,5]thiadiazolo[3,4‐e]thieno[2′′,3′′:4′,5′]thieno‐[2′,3′:4,5] pyrrolo‐[3,2‐g]thieno[2′,3′:4,5]thieno[3,2‐b]indole‐2,10‐diyl)bis‐(methanylylidene)) bis‐(5,6‐difluoro‐3‐oxo‐2,3‐dihydro‐1H‐indene‐2,1‐diylidene))‐dimalononitrile (Y6) (100:2, wt/wt)/MoO3/poly(3‐hexylthiophene) (P3HT):[6,6]‐phenyl‐C71‐butyric acid methyl ester (PC71BM) (100:2, wt/wt)/Al. Electron traps can be formed with Y6 surrounded by poly‐TPD or with PC71BM surrounded by P3HT. Trapped electrons near ITO/PDIN or Al electrode can assist hole tunneling injectionunder forward or reverse bias, respectively. The dual‐band PM‐PPDs exhibit ultraviolet spectral response under forward bias dependent on trapped electron distribution near ITO/PDIN electrode, while presenting visible spectral response under reverse bias determined by trapped electron distribution near Al electrode. The performance of dual‐band PM‐PPDs can be optimized by decreasing P3HT:PC71BM layer thickness. The optimal dual‐band PM‐PPDs exhibit external quantum efficiency (EQE) of 2800% at 350 nm under +10 V bias with full‐width at half‐maximum of 80 nm, while achieving EQE of 7500% at 430 nm under −10 V bias. The EQE values of optimal dual‐band PM‐PPDs are markedly improved by raising bias, reaching 13 000% at 350 nm under +16 V bias and 27 000% at 430 nm under −16 V bias. This work provides an effective method to prepare dual‐band PM‐PPDs by manipulating the interfacial trapped electron distribution

Elemental Precursor Solution Processed (Cu_1–<i>x</i>Ag_<i>x</i>)₂ZnSn(S,Se)₄ Photovoltaic Devices with over 10% Efficiency

The partial substitution of Cu⁺ with Ag⁺ into the host lattice of Cu₂ZnSn­(S,Se)₄ thin films can reduce the open-circuit voltage deficit (<i>V</i>_oc,deficit) of Cu₂ZnSn­(S,Se)₄ (CZTSSe) solar cells. In this paper, elemental Cu, Ag, Zn, Sn, S, and Se powders were dissolved in solvent mixture of 1,2-ethanedithiol (edtH₂) and 1,2-ethylenediamine (en) and used for the formation of (Cu_1–<i>x</i>Ag_<i>x</i>)₂ZnSn­(S,Se)₄ (CAZTSSe) thin films with different Ag/(Ag + Cu) ratios. The key feature of this approach is that the impurity atoms can be absolutely excluded. Further results indicate that the variations of grain size, band gap, and depletion width of the CAZTSSe layer are generally determined by Ag substitution content. Benefiting from the <i>V</i>_oc enhancement (∼50 mV), the power conversion efficiency is successfully increased from 7.39% (<i>x</i> = 0) to 10.36% (<i>x</i> = 3%), which is the highest efficiency of Ag substituted devices so far

Manipulating mode degeneracy for tunable spectral characteristics in multi-microcavity photonic molecules

10.1364/oe.420462Optics Express27911181-1119

Polarization-robust mid-infrared carpet cloak with minimized lateral shift

With the advent and rapid development of the transformation optics and metamaterials, invisibility cloaks have captivated much attention in recent years. While most cloaking schemes suffer from limited bandwidth, the carpet cloak, which can hide an object on a reflecting plane, can operate over a broadband frequency range. However, the carpet cloaks experimentally realized thus far still have several limitations. For example, the quasi-conformal mapping carpet cloak leads to a lateral shift of the reflected light ray, while the birefringent carpet cloak only works for a specific polarization. In this work, we propose a conformal transformation scheme to tackle these two problems simultaneously. As an example, we design a mid-infrared carpet cloak in a silicon platform and demonstrate its polarization-insensitive property as well as the minimized lateral shift over a broad frequency band from 24 to 28.3 THz.Ministry of Education (MOE)National Research Foundation (NRF)Ministry of Education - Singapore (MOE 2018- T2-2-189 (S), MOE2018-T2-1-176); National Research Foundation Singapore (NRF-CRP18-2017-02, NRFCRP22-2019-0006); Agency for Science, Technology and Research (A18A7b0058, A20E5c0095); National Natural Science Foundation of China (61871127)

Defocus incorporated multiple segments (DIMS) spectacle lenses increase the choroidal thickness: a two-year randomized clinical trial

Abstract Background Myopia control interventions, such as defocus incorporated multiple segments (DIMS) spectacle lenses, have been adopted in school-aged children to reduce the prevalence of myopia and its complications. This study aimed to investigate the effect of DIMS spectacle lenses on subfoveal choroidal thickness (SfChT) over a period of two years, as the choroidal response to myopic control is a crucial factor in exploring its potential effect on predicting myopia progression. Methods This study involved a secondary analysis of our previous randomized clinical trial. Myopic school-aged children aged 8–13 years were recruited in a two-year study investigating the effect of DIMS spectacle lenses on myopia progression. The treated group received DIMS spectacle lenses (n = 78), while the control group was treated with a pair of single vision (SV) spectacle lenses (n = 80). SfChT was monitored at 1 week, 1, 3, 6, 12, 18 and 24 months post lens wear using spectral-domain optical coherence tomography and a custom made auto-segmentation algorithm utilizing convolutional neural networks. Results SfChT increased significantly after one week of DIMS spectacle lens wear compared to those wearing SV spectacle lenses (adjusted mean change relative to baseline ± SEM at one week; DIMS vs. SV, 6.75 ± 1.52 µm vs. − 3.17 ± 1.48 µm; P < 0.0001, general linear model). The thickness of choroid increased to 13.64 ± 2.62 µm after 12 months of DIMS lens wear while the choroid thinned in SV group (− 9.46 ± 2.55 µm). Choroidal changes demonstrated a significant negative association with axial elongation over two years in both the DIMS and SV groups. Choroidal change at three months significantly predicted the changes in AL at 12 months after controlling the effect of age and gender. Conclusions Our study demonstrated a significant choroidal thickening in response to myopic defocus incorporated in a spectacle lens after one week of lens wear, sustained over the two-year study period. The results suggested that choroidal changes at three months may help predict changes in axial length after one year. Trial registration ClinicalTrials.gov. Myopia control with the multi-segment lens. NCT02206217. Registered 29 July 2014, https://clinicaltrials.gov/ct2/show/study/NCT0220621