National Institute of Standards and Technology における超伝導研究及び生活

The significant benefits associated with microgrids have led to vast efforts to expand their penetration in electric power systems. Although their deployment is rapidly growing, there are still many challenges to efficiently design, control, and operate microgrids when connected to the grid, and also when in islanded mode, where extensive research activities are underway to tackle these issues. It is necessary to have an across-the-board view of the microgrid integration in power systems. This paper presents a review of issues concerning microgrids and provides an account of research in areas related to microgrids, including distributed generation, microgrid value propositions, applications of power electronics, economic issues, microgrid operation and control, microgrid clusters, and protection and communications issues.

State of the Art in Research on Microgrids: A Review

Metamaterials are artificial media structured on a size scale smaller than wavelength of external stimuli, and they can exhibit a strong localization and enhancement of fields, which may provide novel tools to significantly enhance the sensitivity and resolution of sensors, and open new degrees of freedom in sensing design aspect. This paper mainly presents the recent progress concerning metamaterials-based sensing, and detailedly reviews the principle, detecting process and sensitivity of three distinct types of sensors based on metamaterials, as well as their challenges and prospects. Moreover, the design guidelines for each sensor and its performance are compared and summarized.

https://www.mdpi.com/1424-8220/12/3/2742/pdf

Metamaterials application in sensing.

The black start capability is vital for microgrids, which can potentially improve the reliability of the power grid. This paper proposes a black start strategy for microgrids based on a parallel restoration strategy. Considering the characteristics of distributed generations (DGs), an evaluation model, which is used to assess the black start capability of DGs, is established by adopting the variation coefficient method. Thus, the DGs with good black start capability, which are selected by a diversity sequence method, are restored first in parallel under the constraints of DGs and network. During the selection process of recovery paths, line weight and node importance degree are proposed under the consideration of the node topological importance and the load importance as well as the backbone network restoration time. Therefore, the whole optimization of the reconstructed network is realized. Finally, the simulation results verify the feasibility and effectiveness of the strategy.

A Parallel Restoration for Black Start of Microgrids Considering Characteristics of Distributed Generations

Split-ring resonators (SRRs) are ideal structures for the realization of compact high-sensitivity and high-resolution sensors due to their high-quality factor resonance, compact size, and high sensitivity to changes in the constituent materials and physical dimensions. This paper presents a displacement sensor based on a diamond-shaped tapered SRR coupled to a coplanar waveguide. Two significant improvements over previous designs are reported. Firstly, the proposed sensor has higher dynamic range and linearity for displacement sensing. Secondly, compared with previous designs, where the displacement changes both the resonant frequency and depth of the transmission notch, the proposed sensor has a fixed resonant frequency. This is an important improvement since the sensor can be operated at a single fixed frequency and bypass the need for a frequency-sweeping microwave source and measurement system such as an expensive network analyzer. It is shown that, while preserving the compact size, the proposed sensor also benefits from a lower operating frequency. The design principle and simulation results are validated through measurement.

/pdf/displacement-sensor-based-on-diamond-shaped-tapered-split-2mtjh4e5lb.pdf

Displacement Sensor Based on Diamond-Shaped Tapered Split Ring Resonator

The electromagnetic concentrators play an important role in the harnessing of light in solar cells or similar devices, where high field intensities are required. The material parameters for two-dimensional (2D) metamaterial-assisted electromagnetic concentrators with arbitrary geometries are derived based on transformation-optical approach. Enhancements in field intensities of the 2D concentrator have been shown by full-wave simulation. All theoretical and numerical results validate the material parameters for the 2D concentrator with irregular cross section we developed.

Metamaterial electromagnetic concentrators with arbitrary geometries

Microgrids have become a hot topic driven by the dual pressures of environmental protection concerns and the energy crisis. In this paper, a challenge for the distributed control of a modern electric grid incorporating clusters of residential microgrids is elaborated and a hierarchical multi-agent system (MAS) is proposed as a solution. The issues of how to realize the hierarchical MAS and how to improve coordination and control strategies are discussed. Based on MATLAB and ZEUS platforms, bilateral switching between grid-connected mode and island mode is performed under control of the proposed MAS to enhance and support its effectiveness.

/pdf/hierarchical-mas-based-control-strategy-for-microgrid-29wutsvyhm.pdf

Hierarchical MAS Based Control Strategy for Microgrid

Electromagnetic cloak is a device which makes an object “invisible” for electromagnetic irradiation in a certain frequency range. Material parameters for the complementary medium-assisted external cylindrical cloak with arbitrary cross section are derived based on combining the concepts of complementary media and transformation optics. It can make the object with arbitrary shape outside the cloaking domain invisible, as long as an “antiobject” is embedded in the complementary media layer. Moreover, we find that the shape, size and the position of the “antiobject” is dependent on the contour of the cloak and the coordinate transformation. The external cloaking effect has been verified by full-wave simulation.

An external cloak with arbitrary cross section based on complementary medium and coordinate transformation.

An external acoustic cloak with N-sided regular polygonal cross section based on complementary medium

Metamaterials are artificial media structured on a size scale smaller than the wavelength of external stimuli, and may provide novel tools to significantly enhance the sensitivity and resolution of the sensors. In this paper, we derive the dispersion relation of cylindrical dielectric waveguide loaded on double negative metamaterial (DNM) layer, and compute the resonant frequencies and electric field distribution of the corresponding Whispering-Gallery-Modes (WGM). Theoretical results of resonant frequency and electric field distribution are in good agreement with the simulation results. We show that the DNM sensor based on microring resonator possesses higher sensitivity than the traditional microring sensor since the amplification of evanescent wave, and with the increase of metamaterial layer thickness, the sensitivity will be increased greatly. It might open an avenue for designing perfect sensors.

Ming Huang

Papers

Metamaterial electromagnetic concentrators with arbitrary geometries

Hierarchical MAS Based Control Strategy for Microgrid

An external cloak with arbitrary cross section based on complementary medium and coordinate transformation.

An external acoustic cloak with N-sided regular polygonal cross section based on complementary medium

Double Negative Metamaterial Sensor Based on Microring Resonator