Graphene, a wonder material, has made far-reaching developments in many different fields such as materials science, electronics, condensed physics, quantum physics, energy systems, etc. Since its ...discovery in 2004, extensive studies have been done for understanding its physical and chemical properties. Owing to its unique characteristics, it has rapidly became a potential candidate for nano-bio researchers to explore its usage in biomedical applications. In the last decade, remarkable efforts have been devoted to investigating the biomedical utilization of graphene and graphene-based materials, especially in smart drug and gene delivery as well as cancer therapy. Inspired by a great number of successful graphene-based materials integrations into the biomedical area, here we summarize the most recent developments made about graphene applications in biomedicine. In this paper, we review the up-to-date advances of graphene-based materials in drug delivery applications, specifically targeted drug/ gene delivery, delivery of antitumor drugs, controlled and stimuli-responsive drug release, photodynamic therapy applications and optical imaging and theranostics, as well as investigating the future trends and succeeding challenges in this topic to provide an outlook for future researches.
We introduce a new technique for designing wideband polarization converters based on miniaturized-element frequency selective surfaces (MEFSSs). The proposed structure is a two-dimensionally ...anisotropic periodic structure composed of arrays of subwavelength capacitive patches and inductive wire grids separated by thin dielectric substrates. The structure is designed to behave differently for field components of the two orthogonal polarizations and transmits a circularly polarized wave once illuminated by a linearly polarized plane wave. Using equivalent circuit models for MEFSSs, a synthesis procedure is developed that can be used to design the polarization converter from its required bandwidth and center frequency of operation. Using this procedure, a prototype of the proposed polarization converter operating within the X-band is designed, fabricated, and experimentally characterized using a free-space measurement system. The measurement results confirm the theoretical predictions and the design procedure of the structure and demonstrate that the proposed MEFSS-based polarization converter operates in a wide field of view of <inline-formula><tex-math notation="LaTeX">\pm45^{\circ}</tex-math></inline-formula> with a fractional bandwidth of 40%.
Microgrids are increasingly affected by volatile wind energy due to the high penetration of this kind of renewable energy sources. This study investigates the impact of wind energy uncertainty on ...voltage stability and energy management system (EMS) of isolated microgrids in the presence of plug-in electric vehicles (PEVs). A stochastic voltage stability constrained microgrid energy management system (SVSC-MEMS) architecture based on a coordinated unit commitment-optimal power flow (UC-OPF) methodology, which simultaneously considers the UC and OPF constraints, is proposed. The proposed model guarantees the system security from the voltage stability standpoint, considering a specific loading margin. Besides, the role of PEVs in the microgrid EMS is examined. In order to validate the performance of the introduced SVSC-MEMS, a CIGRE benchmark test system is used. The numerical results, obtained from the implementation of the proposed model in the general algebraic modeling system (GAMS) environment, demonstrate the importance of voltage stability and wind power uncertainty on the microgrid EMS, and furthermore, the key role of PEVs in the emerging microgrids.
As an integral component of power systems dominated by inverter-based resources (IBRs), grid-forming (GFM) inverters must ride through low voltages. During an asymmetrical low-voltage ride-through ...(LVRT) condition, the recently approved IEEE Standard 2800-2022 requires that all IBRs absorb negative-sequence reactive current as a function of the voltage at the IBR's terminal. However, existing GFM control methods either suppress the negative-sequence component of the fault current or leave it uncontrolled. To address this issue, this article develops a control scheme that makes GFM-IBRs absorb reactive current in the negative-sequence circuit while they regulate the voltage in the positive-sequence circuit. The developed control system includes a new adaptive virtual impedance-based current-limiting scheme to limit the inverter's current during both initial transients and steady-state fault conditions. To meet the maximum phase current utilization requirement of the IEEE Std. 2800-2022, the paper also develops an adaptive sequence current division scheme. PSCAD/EMTDC simulations of a CIGRE transmission network benchmark supplied primarily by IBRs verify the compliance of the proposed control system with the IEEE Std. 2800-2022.
Severe disruptions caused by natural disasters have highlighted the significance of enhancing the distribution system resilience in recent years. However, due to severe uncertain characteristics of ...natural disasters, there exists an insufficient level of information to evaluate their behavior and consequences. Lack of information such as proper distribution functions for probabilistic methods or known intervals for robust optimization techniques may provide Distribution System Planners (DSPs) with inaccurate designs. This paper presents a new strategy based on Information Gap Decision Theory (IGDT) to facilitate decision making for DSPs in the face of extreme events. Moreover, a detailed analysis is performed to find a trade-off between the DG allocation and the hardening schemes, and to determine the best conservativeness degree in the IGDT approach. The presented resilience model is implemented on 33-bus and 94-bus distribution systems, and numerical case studies are analyzed to demonstrate the merits of the proposed approach. The results indicate that with a limited planning budget, the proposed trade-off analysis can optimally find the best DG allocation and hardening schemes to keep the load shedding level below a desired threshold following a severely uncertain extreme event.
While power swing is a well-understood phenomenon in conventional power systems, the power swing characteristics of systems with inverter-based resources (IBRs) remain significantly under-theorized. ...This paper demonstrates that this knowledge gap carries practical ramifications, including the potential to undermine the stability and reliable protection of future grids, where swing dynamics can be heavily influenced by IBRs. The paper investigates power swing in systems with IBRs in two parts. Part I of the paper develops the necessary relations to devise a novel state-space model for systems with IBRs. This analytical model is necessary to (i) quantitatively identify the distinct characteristics of power swings in IBR-rich grids, and (ii) theoretically prove that these characteristics can be generalized. The paper highlights fundamental differences between this new model and the well-established model for power swings in systems that consist solely of synchronous machines (SMs). To reveal the features of power swing in systems with mixed generation types, the paper also systematically incorporates the dynamic equations of SMs into the developed model. The accuracy of the proposed model is evaluated against PSCAD/EMTDC simulation results for a benchmark test system that includes multiple IBR plants and their detailed control systems. Part II of the paper will build upon the findings from Part I to investigate the implications of the specific features of IBRs' power swing from the perspective of power system protection.
After introducing and analytically proving the distinctive dynamics associated with power swing of inverter-based resources (IBRs) in Part I, Part II of this article investigates the implications of ...such dynamics for power system protection. The paper sheds light on some of the major consequences of IBRs' unique power swing patterns. The study employs theoretical analysis and detailed PSCAD/EMTDC simulation models to unveil the shortcomings of the conventional wisdom regarding the power swing characteristics of IBRs. The article offers new insights into the operation of transmission line relays during power swing conditions. This part of the study is supported by extensive testing of commercial relays. The findings of this paper will provide guidance for future IBR interconnection standards, the design of inverter control schemes, the power swing detection methods used by relays, and the appropriate relay settings.
We present a new approach for designing dual-band miniaturized-element frequency selective surfaces (MEFSSs) with independent control of the frequencies of operation of each band. The proposed device ...is composed of 2-D periodic arrays of subwavelength inductive wire grids and capacitive patches separated by dielectric substrates. The structure is built on an inductively coupled MEFSS that uses capacitively loaded dielectric spacers as its main resonators. The two operating bands of this MEFSS correspond to the first and second resonant frequencies of its constituting resonators. By judiciously choosing the locations where the resonators are loaded and the load values, the frequencies of the first and second resonances can be controlled individually. In this way, a dual-band MEFSS with independent frequency bands of operation can be obtained. Using the equivalent circuit model of this MEFSS, a synthesis procedure is developed that can be used to synthesize the dual-band MEFSS from its system-level performance indicators. A prototype of the proposed dual-band MEFSS with second-order bandpass response at each band is designed, fabricated, and experimentally characterized. The measurement results of this device show a stable frequency response with respect to the angle of incidence up to ±45° for both the TE and TM polarizations of incidence.
Partially shaded (PS) photovoltaic (PV) arrays have multiple peaks at their P-V characteristic. Although conventional maximum power point tracking (MPPT) algorithms are successful when PV arrays are ...under uniform irradiance conditions (UICs), their tracking speeds are low and may fail to track global maximum power point (GMPP) for PS arrays. Several MPPT algorithms have been proposed for PS arrays. Most of them require numerous samplings which decreases MPPT speed and increases energy loss. The proposed method in this paper gets the GMPP deterministically and very fast. It intelligently takes some samples from the array's P-V curve and divides the search voltage range into small subregions. Then, it approximates the I-V curve of each subregion with a simple curve, and accordingly estimates an upper limit for the array power in that subregion. Next, by comparing the measured real power values with the estimated upper limits, the search region of GMPP is limited, and based on some defined criteria, the vicinity of GMPP is determined. Simulation and experimental results and comparisons are presented to highlight the performance and superiority of the proposed approach.
We introduce a new method for designing low-profile reflectarray antennas with broadband, true-time-delay (TTD) responses. Such structures are composed of numerous reflective spatial time-delay units ...distributed over a planar surface. Each spatial time-delay unit is a unit cell of a ground-plane-backed miniaturized-element frequency selective surface (MEFSS) composed of nonresonant elements. Each element is a lowpass type MEFSS composed of a stack of nonresonant patches separated from one another by thin dielectric substrates, and the whole structure is backed with a ground plane. A prototype of the proposed MEFSS-based TTD reflectarray with the focal length to aperture diameter ratio (f/D) of 0.87 operating at the center frequency of 10 GHz is designed, fabricated, and experimentally characterized both in time and frequency domains. It is demonstrated that the fabricated TTD reflectarray operates over a bandwidth of 40% without any significant chromatic aberrations. The proposed antenna provides a realized gain of 23 dB when fed with an X-band horn antenna and shows a gain variation of about 4 dB in the 8-12 GHz range. The antenna also shows consistent radiation characteristics and relatively low side-lobe levels across its entire band of operation.
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