Conventional AC Research Articles

Investigation into the Operating Performance of a Novel Direct Expansion-Based Air Conditioning System

This study introduces a novel direct expansion air conditioning (DX AC) system with three evaporators (DX-TE) to enhance indoor temperature and humidity control. Operating in two modes, the DX-TE system provides variable cooling output, adapting to fluctuating indoor cooling loads while maintaining uniform air supply. Experimental and simulation studies were conducted to investigate the system’s operational characteristics. An experimental setup was established to obtain preliminary steady-state data, followed by the development and validation of a steady-state mathematical model. Simulation studies were then performed to optimize the evaporator sizes. The results indicate that the DX-TE system delivers variable cooling capacities at a constant compressor speed and airflow rate, outperforming conventional variable frequency DX AC systems in cooling and dehumidification. The evaporator area ratio significantly impacts the system’s performance, with smaller ratios yielding a larger output range. As the area ratio increases from 1:1 to 1:3, the cooling capacity range in Modes 1 and 2 increases by 33.6% and 14.3%, respectively, while the dehumidification range expands by 58.6% and 51.69%.

Significant performance enhancement of Zn-ion hybrid supercapacitors based on microwave-assisted pyrolyzed active carbon via synergistic effect of NaHCO3 activation and CNT networks

Zinc-ion hybrid supercapacitors (ZIHSCs) represents a promising technological approach for large-scale energy storage with the combined advantages of supercapacitors and zinc-ion batteries. Unfortunately, it is still challengeable to quickly fabricate low-cost, high-performance carbonaceous cathode materials at relatively low temperature. To address such issues, herein, taking waste Eucommia ulmoides Oliver (EUO) wood as an example, we present a novel microwave-assisted carbonization (MWC) approach at relatively low temperature to quickly prepare active carbon, and we present a synergistic strategy to significantly enhance the electrochemical performance by introducing sodium bicarbonate activation (SA) and constructing conductive carbon nanotubes (CNT) networks. The MWC-SA@CNT hybrid exhibits outstanding specific capacitance of 344.2 F/g at 0.2 A/g within three-electrode system, much better than conventional high-temperature pyrolyzed AC, MWC carbon, and MWC-SA carbon. The superior performance of MWC-SA@CNT can be attributed to the synergistic effect of its large specific surface area of 1102.7 m2/g, high mesoporous percentage of 53.5%, and rich –OH and CO groups due to microwave-assisted carbonization and sodium bicarbonate activation, and rich electron transport paths due to the presence of CNT networks. Furthermore, ZIHSCs assembled by MWC-SA@CNT cathode could delivers impressive performance with excellent capacity (194.37 mA h/g at current density of 1 A/g), energy density (142.30 Wh/kg), and durability (capacitance retention rate of 97.65% after 5000 cycles). This work offers a rapid and low-temperature method for preparing wood-based active carbon with rich nanopores and strong conductivity to improve performance of Zinc ion storage.

Unconditionally maximum principle-preserving linear method for a mass-conserved Allen–Cahn model with local Lagrange multiplier

In this work, we present a conservative Allen–Cahn (CAC) equation and investigate its unconditionally maximum principle-preserving linear numerical scheme. The operator splitting strategy is adopted to split the CAC model into a conventional AC equation and a mass correction equation. The standard finite difference method is used to discretize the equations in space. In the first step, the temporal discretization of the AC equation is performed by using the energy factorization technique. The discrete version of the maximum principle-preserving property for the AC equation is unconditionally satisfied. In the second step, we apply mass correction by using an explicit Euler-type approach. Without the constraint of time step, we estimate that the absolute value of the updated solution is bounded by 1. The unique solvability is analytically proved. In each time step, the proposed method is easy to implement because we only need to solve a linear elliptic type equation and then correct the solution in an explicit manner. Various computational experiments in two-dimensional and three-dimensional spaces are performed to confirm the performance of the proposed method. Moreover, the experiments also indicate that the proposed model can be used to simulate two-phase incompressible fluid flows.

A SSA-based CFFOPID drop deloaded tidal turbine controller using HVDC-link

In contemporary scenario, electric power companies have observed upsurge in penetration level of tidal power plants (TPPs) in the traditional electric power system framework. However, the tidal turbines offer less frequency assistance due to their lesser rotor mass. Hence, TPPs may be collaborated with conventional units like diesel engine generator (DEG) to confirm system frequency stability in multi-area micro-grid system. The DEG comprises of primary and proportional integral derivative (PID) secondary frequency controls. However, in TPPs, to advance the system frequency regulation, deloading control approach is suggested and a cascade fuzzy fractional order PID-ID with derivative filter (CFFOPID-IDF) droop controller is suggested in place of the conventional non-cascade controller droop in the deloaded region. The suggested controller gains are fetched exploiting Salps swarm algorithm. For further enhancement of the dynamic responses, a precise high voltage direct current (AHVDC) link with the inertia emulation-based control (INEC) scheme is adopted, which allows the utilization of the gathered energy from the capacitance of the HVDC interface for frequency regulation. It provides better results compared to conventional AC tie line interface having less undershoot (34 %/20.63 %/43.75 %) and settling time (20.45 %/59.09 %/16.83 %) for variation in area-1 frequency/area-2 frequency/tie line power, respectively. The recommended control scheme is evidenced superior over numerous existing control techniques and provides least cost function in contrast to other control techniques. Additionally, it offers a highly stable performance under variable load conditions.

L2A Cdus Performance and Considerations for Server Rooms Upgrade with Conventional Air Conditioning

Abstract As web-based AI applications are growing rapidly, server rooms face escalating computational demands, prompting enterprises to either upgrade their facilities or outsource to co-located sites. This growth strains conventional HVAC systems, which struggle to handle the substantial thermal load, often resulting in hotspots. Liquid-to-Air (L2A) Coolant Distribution Units (CDUs) emerge as a solution, efficiently cooling servers by circulating liquid coolant through cooling loops mounted on each server board. In this study, the performance of a 24-kW L2A CDU is evaluated across various scenarios, emphasizing cooling effect, stability, and reliability. Experimental tests involve a rack with three thermal test vehicles (TTVs), monitoring both liquid coolant and air sides for analysis. Tests are conducted in a limited air-conditioned environment, resembling upgraded server rooms with conventional AC systems. The study also assesses the impact of high-power density cooling units on the server room environment, measuring noise, air velocity, and ambient temperature against ASHRAE standards for human comfort. Recommendations for optimal practices and potential system improvements are included in the research, addressing the growing need for efficient cooling solutions amidst escalating computational demands.

Review of Switched Reluctance Motor Converters and Torque Ripple Minimisation Techniques for Electric Vehicle Applications

This paper presents a review of the most common power converters and torque ripple minimisation approaches for switched reluctance motors (SRMs). Unlike conventional three-phase AC motors, namely squirrel cage induction motors and permanent magnet synchronous motors, which require a typical three-phase inverter for operation, the switched reluctance motor requires a different topology power converter for reliable and efficient operation. In addition, due to the non-linear, discrete nature of SRM torque production, torque ripple is severely pronounced, which is undesirable in servo applications like electric vehicles. Hence, deploying a proper torque control function for smooth and quiet motor operation is crucial. This paper sheds light over the most popular SRM power converters as well as torque ripple minimisation methods, and it suggests an optimal SRM drive topology for EV applications.

The tumor immune microenvironment features and their prognostic value in rectal and sigmoid colon signet-ring cell carcinoma.

3544 Background: Signet-ring cell carcinoma (SRCC) of the rectum and sigmoid colon is a rare and highly malignant challenge in clinical practice. Although high PD-1+CD8+ tumor-infiltrating lymphocyte (TIL) infiltration has been reported as a positive prognostic factor in gastric cancer, pancreatic cancer, etc., its role in colorectal SRCC remains unclear. This study aims to explore the immune landscape of colorectal SRCC and its prognostic implications. Methods: The study included 34 patients with stage II-IV SRCC of the rectum and sigmoid colon. The immune contextures of tumor tissues were characterized using multiplex immunofluorescence assays and compared with a cohort of 57 cases of stage II-IV AC. The ratio density and spatial distribution of CD3+, CD8+, PD-1+, PD-L1+ cells, M1/M2 macrophages, and NK cells were quantitively analyzed in both parenchymal (p) and interstitial (i) regions. Characteristics of immune cell infiltration and their prognostic value for long-term survival were investigated in SRCC cases. Results: Compared to AC, SRCC exhibited significantly higher infiltration of CD8+ and CD3+ iTILs in the interstitial region (P=0.00024; P=0.00321, respectively) and elevated CD8+ pTILs infiltration in tumor parenchyma (P=0.041). Conversely, parenchymal infiltration of TILs co-expressing PD-1 was significantly lower in SRCC than AC (PD-1+CD8+ pTILs: P=0.00035; PD-1+CD3+ pTILs: P=5.0e-05). SRCC showed significantly lower infiltration of M1 macrophages in both parenchyma and interstitium (P=0.0035; P=5.4e-09, respectively), lower interstitial infiltration of M2 macrophages (P=1.5e-05), and a borderline lower parenchymal infiltration of M2 macrophages (P=0.0522), compared to AC. Additionally, patients with high parenchymal or interstitial infiltration of PD-1+CD8+ TILs exhibited significantly longer DFS (P=0.00024; P=0.0041, respectively) and OS (P=0.011; P=0.0044, respectively) than those with low infiltration. Multivariate analysis indicated that the level of PD-1+CD8+ pTILs infiltration is an independent prognostic factor for DFS, being independent of CEA levels and TNM stage (P = 0.018; P = 0.02, respectively). Among patients with normal CEA level or of stage II-III, high level of PD-1+CD8+ pTILs infiltration was still associated with significantly improved DFS (P<0.0001; P=0.00018, respectively) and OS (P=0.00021; P<0.0001, respectively). Conclusions: SRCC of rectum and sigmoid colon exhibits distinct immune profiles compared to conventional AC, characterized by higher infiltration of CD8+ and CD3+ TILs, but lower infiltration of PD-1+CD8+ TILs. The unique immune landscape in SRCC, particularly the level of PD-1+CD8+ TILs infiltration and its positive predictive value for DFS and OS, provides new perspectives for immune-based stratification and therapeutic strategies for this clinically significant cancer subtype.

Short-circuit current analysis of DC distribution system in a ship with non-electric propulsion

Converting conventional AC radial shipboard distribution system to DC system has been recognized as a potential high impact solution to reduce ship’s fuel consumption. As big ships in Indonesia commonly use low voltage AC (LVAC) distribution system an effort to apply low voltage direct current (LVDC) distribution system without replace the propulsion system is a plausible choice. However, technical and economical investigations are required before recommendation to convert the shipboard distribution system to LVDC is officially launched. In this study, technical aspect in the term of short-circuit current is discussed. The goal of this study is to analyze how much the impact on the short-circuit current when LVDC system replaces LVAC system. The impact may affect the feasibility of LVDC system as the short-circuit current in a system dictate the scheme and capacity of the protection devices. Numerical simulations on a sample vessel are performed to obtain the profile of maximum short-circuit currents on all panels. The results show that the utilization of LVDC system decreases the short-circuit current by 10 times. Further investigations on the economic aspect needs to be performed to give clearer view of the feasibility of the LVDC system.

Optimised projection welding of steel Bars

The article presents tests aimed at optimising the welding of bars, made of steel AISI1005 (ø 4.2 mm), in a cruciform configuration (i.e. using the cross-wire welding process). The authors identified research gaps and carried out a detailed numerical analysis of these cases. The research-related calculations involved the use of SORPAS software. The new areas of research included (i) bars with protective zinc coatings having various thicknesses of 0 µm, 5 µm, 10 µm and 30 µm, (ii) various welding current rise times (up-slope) and (iii) single and multi-pulse welding cycles. The tests were carried out using a DC 1 kHz inverter welding machine; the results concerning welding up-slope times were compared with those obtainable using a conventional AC 50 Hz welding machine. The results of the study, in the form of a welding technology with various values of up-slope time, have been implemented in industry. The inventive idea is protected by patent no. P.229445 at the Polish Patent Office.

Selection of an Optimal Frequency for Offshore Wind Farms

Offshore wind power has attracted significant attention due to its high potential, capability for large-scale farms, and high capacity factor. However, it faces high investment costs and issues with subsea power transmission. Conventional high-voltage AC (HVAC) methods are limited by charging current, while high-voltage DC (HVDC) methods suffer from the high cost of power conversion stations. The low-frequency AC (LFAC) method mitigates the charging current through low-frequency operation and can reduce power conversion station costs. This paper aims to identify the economically optimal frequency by comparing the investment costs of LFAC systems at various frequencies. The components of LFAC, including transformers, offshore platforms, and cables, exhibit frequency-dependent characteristics. Lower frequencies result in an increased size and volume of transformers, leading to higher investment costs for offshore platforms. In contrast, cable charging currents and losses are proportional to frequency, causing the total cost to reach a minimum at a specific frequency. To determine the optimal frequency, simulations of investment costs for varying capacities and distances were conducted.

Abstract PO3-03-06: Real-world efficacy and safety of neoadjuvant pembrolizumab plus chemotherapy in Brazilian patients with early-stage triple-negative breast cancer

Abstract Background: Early-stage triple-negative breast cancer (TNBC) is associated with high risk of early recurrence and disease-specific mortality. Studies suggest a sustained clinical benefit in patients with TNBC who have a pathological complete response (PCR) after neoadjuvant chemotherapy (NACT). In TNBC, the combination of immunotherapy based on immune checkpoint inhibitors (anti-PD-1/PD-L1) combined with chemotherapy has been shown to be effective both in the advanced and early. In the early-stage setting, the addition of pembrolizumab to platinum-containing NACT significantly increased pathological complete response (pCR). Methods: We performed a retrospective observational cohort study of patients diagnosed with TNBC, stage II-III, who received NACT with chemotherapy based on paclitaxel and carboplatin (TC) followed by doxorubicin plus cyclophosphamide (AC) associated with pembrolizumab, treated from June 2022 to July 2023, at AC Camargo Cancer Center, São Paulo, Brazil. Objectives: To investigate the real-world pCR rate and safety profile of early-stage TNBC treated with neoadjuvant chemotherapy (weekly TC, ddAC/AC) associated with pembrolizumab and to describe the clinical-pathological characteristics of this population. Results: Eighty patients received neoadjuvant pembrolizumab plus chemotherapy. Around 50.6% of patients were premenopausal, with a median age of 47 years old at diagnosis. About 18% carried a germline mutation in the BRCA1 (50%) .Regarding the pathological characteristics of the tumor, 90.9% were invasive ductal carcinoma (IDC), 80% had histological grade (HG) III, and average Tumor Infiltrating Lymphocytes (TILs) was 18%. In 94.8% of cases, Ki67 was expressed in more 20% of tumor cells. The expression of HER2 was low in 14%, and 5% were ER-low. Regarding the clinical stage of the primary tumor, (64.9%)cT2, (18%) cT3, (10%) cT1c, and (2.5%) cT4. Regarding regional lymph node staging, 48%, 33.7%, 10.3%, and 6.4% were classified as cN0, cN1, cN2a, and cN, respectively. Clinical stage was IIA (42.8%), IIB (24.6%), IIIA (14.2%), IIIB ( 9%), and IIIC (5%). Regarding chemotherapy, 57.1% received dose dense AC, 54% percent had chemotherapy-related toxicity, 35.7% had neutropenic fever, 32.4% required hospitalization, and 31% used antibiotics. 31% received eight cycles of neoadjuvant pembrolizumab and 53.2% of patients completed all NACT, among these patients, 61% had complete .A cutoff date, about 61% of patients have undergone surgery, and 66.6% achieved a complete pathological response (ypT0ypN0). Patients that received eight cycles of neoadjuvant pembrolizumab had a higher chance of pathological complete response rate (61% vs. 45.2%) p=0.073. Immune-related toxicities (IRT) were observed in 16.8% patients, being the most common endocrinologic and cutaneous, being G3 or higher in 46%. About 15.5% used corticosteroids. Fifty percent had already started or completed adjuvant therapy, from which 66.6% received only adjuvant pembrolizumab, 28% had adjuvant pembrolizumab plus capecitabine, 1.2% received adjuvant capecitabine, and 1.2% had adjuvant olaparib. Eight percent of our patients have already completed nine cycles of adjuvant pembrolizumab, 12.7% did not receive adjuvant pembrolizumab due to prior toxicity. In our cohort, we observed greater intercurrences related to ddAC versus conventional AC 61.4% versus 52.4%, p=0.492, therefore, it did not impact whether or not the chemotherapy was completed. Conclusion: Our cohort is composed mostly of pre-menopausal with stage IIA tumors. Most patients received ddAC, Fifty-four percent had chemotherapy-related toxicity. We observed a high rate of pCR (61%) on our patients have already undergone surgery, 66.6% achieved a complete pathological response.Of those who received 8 cycles of neoadjuvant pembrolizumab had a higher chance of pathological complete response rate (61% vs. 45.2%) p=0.073 Citation Format: isadora sousa, Ana Carolina M. Comini, Italo BORGES, Flavia C. Balint, Livia alexandre Martins, Debora G. Sousa, Solange M. Sanches, Marcelle G. Cesca, Vladmir Cordeiro de Lima, Monique Tavares. Real-world efficacy and safety of neoadjuvant pembrolizumab plus chemotherapy in Brazilian patients with early-stage triple-negative breast cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-03-06.

Airplane motors employing superconducting DC field windings and conventional conductor AC windings

Many organizations are developing compact lightweight highly efficient rotating machines for airplane applications. These machines include permanent magnets for excitation and an iron-core with and without superconducting windings. Air-core (no magnetic iron) machines have the potential to be the most lightweight and efficient. Such machines can use superconductors for both DC excitation field coils and AC armature coils, which need conductors under development, like MgB2 and Bi2212. If liquid-hydrogen (LH2) is available on a plane and can be used as a coolant, it becomes feasible to develop machines with AC armature coils made from conventional conductors like copper, aluminium, and high-conductivity aluminium.This paper describes conceptual designs for a 3 MW, 4,500 RPM motor employing REBCO CORC conductor for the DC field coils and conventional conductor Litz cable for the AC armature coils cooled by LH2 available on the plane. Both rotor and stator coils are contained in separate cryostats. The DC excitation coils on the rotor are operated at 40 K to work successfully with a brushless flux pump exciter. Likewise, stator AC coils are cooled with available LH2 to take advantage of the lower resistivity of conventional conductors at cryogenic temperatures. Motor size, mass and losses are compared for stator windings employing copper, aluminium, and high-conductivity aluminium (Hyper-Al). Compared with copper and aluminium machines, the machine employing Hyper-Al has smaller size, mass and total losses.

Multifunctional Ac@ZIF-8/AgNPs nanoplatform with pH-responsive and ROS scavenging antibacterial properties promotes infected wound healing

The development of non-antibiotic strategies for combating bacterial infections, particularly through reactive oxygen species (ROS) accumulation accompanying inflammation, has attracted much attention. Despite Allicin (Ac) emerges as a promising antimicrobial agent with wide and remarkable bioactivity, it still displays quite limited ROS scavenging and anti-inflammation capacity due to uncontrolled and poor bioavailability. Herein, a multifunctional nanoplatform with pH-dependent and ROS-scavenging antibacterial, anti-inflammatory and proangiogenic properties is introduced to promote infected wound healing by integrating Ac into silver nanoparticles (AgNPs)-loaded zeolite imidazole framework (ZIF-8), namely Ac@ZIF-8/AgNPs. Primarily, the nanoplatform is activated and controlled release in the infection microenvironment, with disrupting biofilms, scavenging ROS and antibacterial capacitys, outperforming conventional Ac. Moreover, in the mouse models induced by bacterial infection, Ac@ZIF-8/AgNPs can alleviate the inflammatory condition, scavenge ROS, facilitate the regeneration of collagen fiber and enhance vascular formation, collectively accelerating wound healing. Overall, this biocompatible nanoplatform is provided as a reliable approach to solve the long-standing problem of infected wound healing.

Analysis and Preliminary Design of Variable Flux Reluctance Machines: A Perspective from Working Field Harmonics

Variable flux reluctance machines (VFRMs) are increasingly attracting research interest due to their magnetless and robust brushless structure. Under the modulation effect of the airgap permeance, the VFRM operates with a series of field harmonics, distinguishing it from conventional AC synchronous machines. This paper deals with the analysis and preliminary design of the VFRM from the perspective of multiple working airgap field harmonics. Firstly, the spatial and temporal order of the working field harmonics are defined. The systematic winding theory, including the unified star of slots and winding factor calculation method, is established to consider all these working harmonics. Then, an average torque model is built and simplified. The key role of 1st-order rotor permeance, 1st- and 3rd-order polarized stator permeance is deduced. The relationship between key parameters and average torque is computed, providing a guideline for the preliminary design of the VFRM.

An economical and simple strategy for overcoming the Hall sensor faults in three phase brushless DC motor drive

SummaryBrushless DC motors (BLDCs) are highly efficient and have the least maintenance requirement due to which they have replaced many conventional AC motors in various applications like electric vehicles, fans, water pumps, and home appliances. However, like all conventional motors, performance degradation of the BLDC motors can occur due to faults like Hall sensors failure, commutation switch failure, and stator‐winding failure. Among all these failures, this paper focuses on Hall sensor failures and the execution of fault tolerant control. Hall sensors produce an output after every 60° of rotation of the rotor, generating six sequences in one electrical cycle. In this study, each sequence is defined as a sector, which corresponds to the rotor position. Based only on this sector information in each electrical cycle, this paper proposes an uncomplicated detection strategy for Hall sensor fault, which is independent of motor loading and high‐performance processing unit. Along with the diagnosis, an improved faulty signal reconstruction is implemented, which bypasses the fault and continues a smooth performance of the motor. The proposed detection and reconstruction strategies have been simulated in MATLAB Simulink 2020, and the experimental analysis has been conducted to validate the proposed strategies.

Multi-scale modified PVDF/Ag@C layer based on dielectric doping and plasma treatment for high-performance triboelectric nanogenerators and self-powered water sterilization

The limitations of dielectric properties and surface electron affinity and the harsh environment including high humidity, high salt content, and biological fouling restricted the efficient ocean energy harvesting of triboelectric nanogenerators (TENGs). Here, Ag@C dielectric doping and two-step O2+CF4 plasma treatment are applied to achieve multi-scale modification of triboelectric materials. The coating of C shell avoided the agglomeration of Ag NPs. Besides, the amorphous C shell inhibited the formation of electron transport pathways, and the mechanism of suppressing dielectric loss of triboelectric layers were clarified via DFT calculations at the particle (Ag@C)-polymer (polyvinylidene difluoride, PVDF) interface. The surface charge density of plasma treated polyvinyl alcohol (PVA)-PVDF/Ag@C-based TENG (PT-TENG) increased from 64.26 µC/m2 to 216.60 µC/m2, representing a significant breakthrough in energy harvesting efficiency. The mechanism of enhanced triboelectric properties was investigated based on modified Overlapped Electron Cloud model. Besides, DFT was applied to analyze the reaction mechanism in depth and predict the products of chemically-surface modification process. The oxygen-containing functional groups introduced by O2 plasma treatment likely serve as a "bridge" for the second-step grafting, which helps to build a more convincing reaction mechanism. The superhydrophobic PVDF/Ag@C exhibited excellent moisture-resistance, salt-resistance, and anti-bioadhensive properties, with outstanding charge density (321.45 µC/m2) at 95% RH, making it very suitable for energy harvesting in harsh marine environments. Moreover, the water sterilization system based on PT-TENG demonstrated a high sterilization rate of 98.74%, which was significantly higher than conventional AC power (89.96%).

Smart AC-DC Coupled Hybrid Railway Microgrids Integrated with Renewable Energy Sources: Current and Next Generation Architectures

In recent years, there has been increasing interest in integrating the smart grid concept into railway networks, which has been driven by the need to enhance energy efficiency and reduce air pollution in such energy-intensive systems. Consequently, experts have actively sought innovative solutions with which to tackle these challenges. One promising strategy involves integrating renewable energy sources (RESs), energy storage systems (ESSs), and electric vehicle charging stations (EVCSs) into current electric railway systems (ERSs). This study begins by examining the concept of implementing smart grids in railway systems through bibliometric analysis. It then delves into the realization of a hybrid railway microgrid (H-RMG) designed to enhance power flow capacities, improve energy efficiency, and address power quality issues in traditional AC railway networks. This paper introduces various future AC–DC-coupled hybrid railway microgrid (ADH-RMG) architectures centered around a shared DC bus acting as a DC hub for upgrading conventional AC railway systems utilizing interfacing static converters. Through an exploration of different possible ADH-RMG configurations, this research aims to offer valuable insights and a roadmap for the modernization and reconstruction of existing railway networks using smart grid technologies. The integration of RESs and EV charging infrastructures within the ADH-RMG concept presents a promising pathway toward establishing more sustainable and environmentally friendly railway systems.

Analysis of Small-Disturbance Stability of Onshore Wind Power All-DC Power Generation System and Identification of Leading Factors

The application of conventional AC collection for the integration of large-scale renewable energy sources may lead to issues concerning harmonic resonance and reactive power transmission. Conversely, the utilization of an all-DC power generation system for wind power (WDCG) can effectively circumvent such issues. In contrast to the conventional power system, the interdependence among subsystems in the WDCG renders it susceptible to oscillation instability in the presence of minor disturbances. To address this concern, this paper first establishes a small-signal model for the WDCG, and validates the accuracy of this model by comparing it with an electromagnetic transient model based on PSCAD/EMTDC. Secondly, employing the eigenvalue analysis method, the principal oscillation modes of the WDCG are identified, and the state variables strongly correlated with these modes are analyzed using the participation factor method. Moreover, a quantitative assessment of the impact of operational and control parameters closely associated with the strongly correlated state variables on the negative damper oscillation model is conducted. The findings of the analysis reveal that the small-disturbance stability of the WDCG is significantly influenced by the operational parameters of the outlet capacitance of the ma-chine-side converter (MSC), the outlet capacitance of the direct current wind turbine (DCWT), the sub-module capacitance of the modular multilevel converter (MMC), and the inductance of the bridge arm. Additionally, the stability is al-so affected by the control parameters of the constant DC voltage control on the DCWT side, the voltage outer-loop–current inner-loop control, and the circulation suppression on the MMC side. The simulation results based on PSCAD validate the efficacy of the proposed method in identifying the dominant factors.

Controlled light energy and perfect absorption in twisted bilayer graphene.

We theoretically study the components of the dynamical optical conductivity tensor and associated finite-frequency dielectric response of bilayer graphene (BLG), where one graphene layer can slide in-plane or commensurably twist on top of the other. Our results reveal that even slight deviations from the conventional AA, AB, or AC stacking orders yield a finite transverse conductivity. Upon calculating the optical conductivity of the BLG at any arbitrary interlayer displacement, Δ, and chemical potential, µ, it is utilized for a layered device with an epsilon-near-zero (ENZ) insert and metallic back plate. We find that both Δ and µ can effectively control the polarization, energy flow direction, and absorptivity of linearly polarized incident light. By appropriately tailoring Δ and µ, near-perfect absorption and tunable dissipation can be accessible through particular angles of incidence and a broad range of ENZ layer thicknesses. Our findings can be applied to the design of programmable optoelectronics devices.

Direct current power system stabilizers for HVDC grids: Current status

AbstractA power system stabilizer (PSS) is a control system integrated into the control structure of specific generation units within AC grids. It monitors current, voltage, and machine shaft speed. Analysing these variables, the PSS generates appropriate control signals to the voltage regulator unit, aiming to damp system oscillations. With the advancement of high‐voltage direct current (HVDC) overlaid high‐voltage alternative current (HVAC) grids, it is anticipated that direct current power system stabilizers (DC‐PSS) will be developed to perform a similar role as their AC counterparts. DC‐PSS will be responsible for monitoring and controlling DC voltage levels, ensuring stable operations. This paper focuses on DC‐PSS in HVDC grids, designed to ensure stable operation and mitigate voltage fluctuations. Unlike conventional AC power systems, HVDC includes only DC voltage and power. The input signal for DC‐PSS is the variations in DC voltage, and the output signal is proportional to the power changes at the specific bus where the DC‐PSS is installed, aiming to minimize DC voltage oscillations. These characteristics pose significant challenges in DC‐PSS. The paper addresses the challenges and highlights issues such as inertia and low‐frequency oscillations associated with DC‐PSS. Various control methods are presented and a comparison is made among these methods.