Search Results (2,124)

Distance protection is widely applied in AC transmission systems. It may operate incorrectly under power swings, so a power swing blocking unit (PSBU) is needed to work with the distance protection relay. Such a unit should not only block the protection relay in time when a power swing occurs, but also deblock the protection relay after detecting a fault during the power swing. In this paper, a method that satisfies these requirements is proposed. To discriminate between power swings and faults, the characteristics of three-phase voltage under a power swing and fault situation are used. Principal Component Analysis (PCA) is applied to extract and quantify the characteristics. To detect faults during power swings, an index is proposed, and the change rate of the index is used to form the criterion. Simulations for different kinds of power swing and fault situations are conducted based on a two-end system and a nine-bus system in PSCAD/EMTDC. The simulation test results indicate that the proposed method can block the protection relay reliably under a power swing and deblock the relay quickly after detecting a fault during the power swing. Moreover, the proposed method is compared with other methods. The comparison results show that the proposed method has an advantage in terms of response speed and is less affected by measurement noise. Full article

When a 35 kV distribution network has the problem of insufficient reactive power, the input of a shunt reactor is a common compensation method. Vacuum circuit breakers are widely used in 35 kV distribution networks because of their superior arc extinguishing performance and convenient maintenance. However, in recent years, accidents involving vacuum circuit breakers breaking shunt reactors have occurred more frequently in China, such as high-frequency phase-to-phase short circuits, inter-turn burning losses, bus outlet short circuits, etc., which can cause serious damage and pose a greater threat to the safety of the power system. This paper focuses on the switching overvoltage generated by the vacuum circuit breaker cutting off the shunt reactor. Firstly, the mechanism of overvoltage generation is analyzed theoretically. It is concluded that the equivalent chopping current of the other two phases caused by the continuous reignition of the first open phase is the root cause of the high-amplitude interphase overvoltage. Based on the MODELS custom programming module in EMTP/ATP, according to the process of breaking and reigniting the circuit breaker, this paper uses Fortran language to compile the program and establishes a model of a vacuum circuit breaker, including power frequency current interception, high-frequency current, zero-crossing, breaking, and arc reignition modules. The vacuum circuit breaker is simulated for hundreds of continuous reignitions in milliseconds. Finally, a simulation study on the overvoltage suppression measures of a 35 kV shunt reactor is carried out. The comprehensive comparison of various suppression measures provides a reference for the reasonable selection of actual engineering conditions. Full article

We investigate integrated silicon ring resonators with regard to the influence of design parameters and intra-wafer variations. First, we show the effect of different ring radii and gaps between ring and bus waveguide on optical properties (peak width, finesse, Q factor, and extinction ratio), from which we calculate the resonators’ coupling and loss coefficients. The dependence on the gap of these properties is discussed at the wafer scale. Second, by incorporating the spectra of 2242 resonators from 59 nominally identical dies on a 200 mm wafer, we show how these properties depend on the resonators’ position on the wafer. Third, we demonstrate how curve fitting of loss and coupling coefficients as a function of the gaps can be used to estimate the optimal gap that realizes critical coupling with a significantly reduced number of manufactured test structures needed to find optimal design parameters. Full article

This contribution is aimed at analyzing a series of life-prolonging and rejuvenating treatments (bcud len), recipes of ambrosia for immortality (bdud rtsi sman), and yogic and meditative techniques incorporated in the Man ngag bye ba ring bsrel (Ten Million of Quintessential Instructions, The Relics; henceforth Ring bsrel), a medical corpus mainly authored by Zur mkhar ba mNyam nyid rdo rje (1439–1475). The many treads of mNyam nyid rdo rje’s literary production reflect his rNying ma and bKa’ brgyud spiritual legacies: the author systematically elaborated materials drawn from the rNying ma gter ma tradition and complex medico–alchemical practices ascribed to the third Karmapa Rang byung rdo rje (1284–1339) and O rgyan pa rin chen dpal (1230–1309). The key ingredients of the recipes include saxifrage [bdud rtsi ’od ldan; Micranthes melanocentra; Saxifraga melanocentra], purple sage [lug mur; Phlomoides bracteosa], potent substances such as black aconite [bstan dug; Aconitum spicatum;], nightshade [thang phrom; Anisodus spp.; Mandragora caulescens], mercury–sulfide ashes (zla bcud; bcud rgyal), aphrodisiacs containing salamander meat [da byid, gangs sbal; Batrachuporus pinchonii], caterpillar fungus [dByar rtswa dgun ’bu; Cordyceps sinensis], and other substances endowed with hot potencies that can enhance gtum mo practices such as the dwarf rhododendron [da lis; Rhododendron spp.] and compounds containing long peer [pi pi ling; Piper longum], black pepper, [pho bar is; Piper nigrum], ginger, and so forth. The consecrated medicines and the rituals can bestow protection from any sort of diseases, diseases-carrier forces (gdon), and poisoning and lead to spiritual achievements. The analysis of these scriptural materials brings into focus the historical interrelation of diverse traditions that are represented by the heterogeneity of ideas and practices handed down through the Zur medical lineage. Full article

In the context of the rapid development of modern science and technology, time synchronization technology has become a critical support in the fields of communication and scientific research. Especially in large-scale research projects such as the China Spallation Neutron Source, the accuracy of time synchronization directly affects the precision of experimental data and the reliability of experimental results. White Rabbit (WR) technology surpasses the sub-microsecond precision limitations of traditional PTPs by precisely controlling and calibrating the delays between master and slave clocks, achieving sub-nanosecond time synchronization that meets the stringent timing accuracy requirements of 5G networks and quantum communications. To meet the demands for high precision, high flexibility, and broad applicability, a switch with WR functionality has been designed based on the Zynq platform. This design not only reduces the number of required components and the complexity of the soldering process but also allows for simple AXI bus communication between the PS and PL ends, thereby decreasing the development time and cost of both software and hardware. The hardware design includes power circuits, clock circuits, and SFP interface circuits. The time synchronization module encompasses the design of the RTU, NIC, SoftPLL, and PPS modules, as well as the design of the AXI to Wishbone bridge. Testing has shown that this switch can achieve sub-nanosecond level time synchronization accuracy. Full article

Bus networks are a crucial support for urban commuting. By studying the evolutionary characteristics of bus networks, we can uncover their development patterns, coverage efficiency, and changes in regional balance, providing a scientific basis for sustainable urban development and the optimization of transportation resources. This study systematically analyzes the spatiotemporal evolution characteristics of the bus network in Beijing from 2006 to 2024 using specific spatial analysis tools to analyze spatiotemporal evolution characteristics. By analyzing spatial coverage rates of transit stations using road network and administrative division data, the study reveals the convenience of bus networks in different regions. By combining the research methodology of the Sustainable Development Goals (SDGs) report, a 500-m service radius for bus stops was assessed. A complex network model was used to extract the nodes and edges of the bus network, and the betweenness centrality (BC) characteristics were analyzed. The findings indicate that Beijing’s bus network has gradually expanded from the central urban areas to peripheral regions, with notable expansion in Tongzhou and Yanqing, resulting in an improved balance in the distribution of stations and routes and the emergence of Tongzhou as a new bus hub. The diffusion characteristics of the bus network are significantly influenced by administrative boundaries and the layout of the ring roads. Bus routes and stops are highly concentrated in the central urban areas and within the Second Ring Road, while as the number of ring roads increases, various network indices gradually decrease. The distribution of bus stops shows notable clustering and an uneven directional development. Beijing’s bus stop distribution exhibits significant clustering characteristics, and the areas with a high Population Conveniently Served by Buses (PCSB) are predominantly concentrated in the central urban areas, with a large gap compared to the outer suburban districts. These conclusions expand on the exploration of isolated and static characteristics of the bus network structure, revealing the dynamic mechanisms and evolution patterns of Beijing’s bus network. They provide guidance and recommendations for improving the bus network and offer more comprehensive support for urban planning and resource allocation. Full article

In recent years, power outages due to typhoon-induced rainstorms, waterlogging, and other extreme weather events have become increasingly common, and accurately assessing the risk of damage to the distribution system during a disaster is critical to enhancing the resilience of the power system. Therefore, a risk assessment method for power distribution systems considering the spatiotemporal characteristics of the typhoon disaster chain is proposed. The mechanism of forming the typhoon disaster chain is first analyzed and its spatiotemporal characteristics are modeled. Secondly, the failure probability of the distribution system equipment during the evolution process of the disaster chain is modeled. Then, the non-sequential Monte Carlo state sampling method combined with the distribution system risk assessment index is proposed to establish the disaster risk assessment system of the distribution system. Finally, based on the IEEE 33-bus power system, the proposed distribution system disaster risk assessment method is verified. Simulation solutions show that the proposed assessment method can effectively assess the disaster risk of the distribution system under the influence of the typhoon disaster chain. The simulation results show that at the time step of typhoon landfall, the load shedding reaches 1315.3 kW with a load shedding rate of 35.4%. The total economic loss at the time step is 2,289,200 CNY. These results demonstrate the effectiveness of the proposed method in assessing disaster risks and improving the resilience of power systems during typhoon events. Full article

Power transmission lines transfer energy between power plants and substations by means of a linear chain of towers. These towers are often situated over extensive distances, sometimes in regions that are difficult to access. Wireless sensor networks present a viable solution for monitoring these long chains of towers due to their wide coverage, ease of installation and cost-effectiveness. The proposed LoRaBUS approach implements and analyses the benefits of a linear topology using a mixture of LoRa and LoRaWAN protocols. This approach is designed to enable automatic detection of nearby nodes, optimise energy consumption and provide a prioritised transmission mode in emergency situations. On remote, hard-to-reach towers, a prototype fire protection system was implemented and tested. The results demonstrate that LoRaBUS creates a self-configurable linear topology which proves advantageous for installation processes, node maintenance and troubleshooting node failures. The discovery process collects data from a neighbourhood to construct the network and to save energy. The network’s autonomous configuration can be completed within approximately 2 min. In addition, energy consumption is effectively reduced 25% by dynamically adjusting the transmission power based on the detected channel quality and the distance to the nearest neighbour nodes. Full article

The development of smart grids has led to an increased focus by transmission and distribution network operators on the Optimal Power Flow (OPF) problem. The solutions identified for an OPF problem are vital to ensure the real-time optimal control and operation of electric networks and can help enhance their efficiency. In this context, this paper proposed an original solution to the OPF problem, represented by optimal voltage control in electric networks integrating wind farms. Based on a fuzzy inference system (FIS) built in the Fuzzy Logic Designer of the Matlab environment, where the fuzzification process was improved through fuzzy K-means clustering, two approaches were developed, representing novel tools for OPF analysis. The decision-maker can use these two approaches only successively. The FIS-based first approach considers the load requested at the PQ-type buses and the powers injected by the wind farms as the fuzzy input variables. Based on the fuzzy inference rules, the FIS determines the suitable tap positions for power transformers to minimise active power losses. The second approach (I-FIS), representing an improved variant of FIS, calculates the steady-state regime to determine power losses based on the suitable tap positions for power transformers, as determined with FIS. A real 10-bus network integrating two wind farms was used to test the two proposed approaches, considering comprehensive characteristic three-day tests to thoroughly highlight the performance under different injection active power profiles of the wind farms. The results obtained were compared with those of the best methods in constrained nonlinear mathematical programming used in OPF analysis, specifically sequential quadratic programming (SQP). The errors calculated throughout the analysis interval between the SQP-based approach, considered as the reference, and the FIS and I-FIS-based approaches were 5.72% and 2.41% for the first day, 1.07% and 1.19% for the second day, and 1.61% and 1.33% for the third day. The impact of the OPF, assessed by calculating the efficiency of the electric network, revealed average percentage errors between 0.04% and 0.06% for the FIS-based approach and 0.01% for the I-FIS-based approach. Full article

Considering the influence of high-speed obstacle avoidance trajectory in the optimization design stage of intelligent bus aerodynamic shape. A collaborative optimization method aiming at aerodynamic structure and trajectory control system for intelligent bus rollover stability is proposed to reduce the interference of lateral aerodynamic load caused by large bus side area on driving stability and improve the rollover safety of intelligent bus in high-speed obstacle avoidance process. At the conceptual design stage, a multidisciplinary co-design optimization frame of aerodynamics/dynamics/control is built, and an adaptive Gaussian Process Regression approximate modeling method is proposed to establish an approximate model of high-precision and high-efficiency rollover evaluation index with rollover stability as the optimization objective and obstacle avoidance safety and resistance to crosswind interference as constraints. Taking rollover stability and obstacle avoidance safety as the optimization objectives, the integrated design of static structural parameters and dynamic control parameters of intelligent buses is carried out. The results show that the proposed MDO method can obtain the aerodynamic shape of the vehicle body with low crosswind sensitivity and a safe and stable obstacle avoidance trajectory. Compared with the initial trajectory, the peak lateral load transfer rate during the obstacle avoidance process decreases by 33.91%, which significantly reduces the risk of rollover. Compared with the traditional serial optimization method, the proposed co-design optimization method has obvious advantages and can further improve the driving safety performance of intelligent buses. Full article

Spoofing events are increasingly affecting the performance of devices and operations relying on Global Navigation Satellite Systems (GNSSs). Developing powerful and robust GNSS spoofing detection and mitigation algorithms is an important endeavor in the GNSS community nowadays; some of the challenges in this field are limited access to spoofing measurement data, as spoofing over wireless channels is not legally allowed and in-lab spoofing emulators are not necessarily able to precisely capture the effects of radio channels, and the fact that classical Receiver Autonomous Integrity Monitoring approaches are typically quite complex, especially when dealing with complex or targeted spoofers. Our paper addresses these two challenges, first, by proposing a targeted spoofing model with a variable number of spoofed satellites, starting from Android raw pseudorange measurements, and second, by introducing a consistency-check-based iterative approach for spoofing detection and mitigation. We test our solution in various dynamic scenarios (bus, walk, ferry, car, flight, and bike), and we show that the positioning error correction rates depend on the number of spoofing pseudorandom (PRN) codes, as well as on the spoofing error introduced by our model. We also show that a large part of the spoofing errors can be mitigated with the proposed algorithms if the number of spoofed satellites (or pseudoranges) is sufficiently low with respect to the total number of visible satellites. Full article

Most research on bicycling and public transportation integration centers around the developed world and inter-modal bicycle–train travel. Similarly, existing research into the factors influencing bicycling to public transport focuses solely on one aspect of the issue, such as physical infrastructure, social environment, user or individual characteristics, etc. On the other hand, interventions to promote bicycling are less likely to be successful when carried out together since there can be multiple levels of barriers and enablers to bicycling. Hence, this study addresses this gap and utilizes a socio-ecological model as a theoretical foundation to understand the potential of using bicycles as a feeder for bus services by analyzing the barriers and enablers. Data were collected through a face-to-face questionnaire survey conducted in public spaces, including bus stops in Riyadh, Saudi Arabia. Two binary logistics models were developed using Statistical Package for the Social Sciences (SPSS) to analyze the key factors influencing bicycle use as a feeder mode to public buses. The findings reveal that individual socio-demographic factors, reported barriers, and enablers are essential in explaining the users’ likelihood of bicycle use in accessing public buses. The barriers model indicates that existing bicycle parking facilities, bicycle theft and safety issues, bus reliability, and distance to bus stops play an essential role. Effective shading, dedicated bicycle tracks, appropriate lighting, and vital public services are explanatory for the enablers model. The findings offer valuable insights and policy recommendations to improve bicycling infrastructure and promote comprehensive accessibility to public transportation. Full article

Battery energy storage systems (BESSs) can play a significant role in overcoming the challenges in Distribution Systems (DSs) with a high level of penetration from renewable energy sources (RESs). In this paper, the goal is to determine the optimal location, size, and charging/discharging dispatches of BESSs in DSs with a high level of photovoltaic (PV) installations. The problem of the location and size of BESSs is solved with multi-criteria optimization using Non-dominated Sorting Genetic Algorithm-II (NSGA-II). The criteria of the multi-criteria optimization are minimal investment costs for BESS and improvement of the network performance index. The network performance index includes the reduction in annual losses of active energy in DSs and the minimization of voltage deviations. The dispatch of a BESS is determined using auxiliary optimization. Linear Programming (LP) is used for auxiliary optimization, with the aim of dispatching the BESS to smooth the load profile in DS. The proposed optimization method differs from previous studies because it takes in its calculations all days of the year. This was performed using the K-means clustering technique. The days of one year are classified by the level of consumption and PV production. The optimization was performed for five different levels of PV penetration (60%, 70%, 80%, 90%, and 100%) and for two scenarios: the first with one BESS and the second with two BESSs. The proposed methodology is applied to the IEEE 33 bus balanced radial distribution system. The results demonstrate that with an optimal choice of location and parameters of the BESS, significant improvement in network performance is achieved. This refers to a reduction in losses of active power, improvement of voltage profile, smoothing the load diagram, and reducing the peak load. For the scenario with one BESS and PV penetration of 100%, the reduction in daily energy losses reaches a value of up to 10% compared to the base case (case without a BESS). The reduction in peak load goes to 20%. Further, the highest voltage during the day is significantly lower in all buses compared to the base case. Similarly, the lowest voltage during the day is considerably higher. The methodology from this paper can be applied to any radial distribution network with a variable number of BESSs. The testing results confirm the effectiveness of the proposed method. Full article

Reconfigurable new energy storage can effectively address the security and limitation issues associated with traditional battery energy storage. To enhance the reliability of the microgrid system and ensure power balance among generation units, this paper proposes a power coordination control strategy based on reconfigurable energy storage. First, a new microgrid system incorporating reconfigurable energy storage, photovoltaic power generation, and a supercapacitor is introduced. By leveraging the structural advantages of reconfigurable energy storage, the potential safety hazards of traditional battery energy storage can be mitigated and the reliability of the microgrid system can be improved. Second, a novel control strategy for reconfigurable energy storage, photovoltaic units, and supercapacitors is proposed. The reconfigurable energy storage achieves constant current charge/discharge control through a DC-DC converter, while the supercapacitor maintains DC bus voltage stability via another DC–DC converter. Next, the power flow relationship within the microgrid system is analyzed. The dynamic reconfiguration characteristics of the reconfigurable energy storage, combined with the high power density of the supercapacitor, enable dynamic compensation of the photovoltaic power generation unit to meet the load’s power demand. Finally, a simulation model is developed in the MATLAB/Simulink environment to compare and analyze the power compensation effects of traditional energy storage and reconfigurable energy storage. The results demonstrate that the proposed control strategy achieves constant current charge/discharge control for reconfigurable energy storage, addressing the issue of battery life degradation caused by the continuous variation in charge/discharge current when traditional energy storage compensates for photovoltaic fluctuations. Additionally, the proposed control strategy can effectively and rapidly adjust the system’s power output, mitigating power fluctuations caused by variations in photovoltaic generation and load changes in the microgrid system, thereby improving the system’s reliability and stability. Full article

The polar energy router is a key device in the polar clean energy system which converges the output of wind power, photovoltaic units, energy storage units and hydrogen fuel cells through the power electronic power converter to the DC bus, which requires the use of a variety of specifications of DC/DC converters; as a result, the efficiency of the DC/DC converter is directly connected to the efficiency of the polar energy router. This paper presents an enhanced isolated DC/DC converter with a phase-shifted full-bridge topology designed to meet the high-efficiency conversion requirements of polar energy routers. Although soft switching can be realized naturally in phase-shifted full-bridge topology, it also faces challenges, such as the difficulty of realizing soft switching under light load conditions, large circulation losses, a loss of duty cycle and oscillation in the secondary-side voltage. To solve these problems, an improved scheme of the phase-shifted full-bridge converter with an active clamp circuit is proposed in this paper. The scheme realized zero-voltage switch (ZVS) under light load by utilizing clamp capacitor energy. The on-state loss was reduced by zeroing the primary-side current during the circulating phase. This paper provides a detailed description of the topology, working principle and performance characteristics of the improved scheme, and its feasibility has been verified through experiments. Full article