Power Margin Research Articles

Static Voltage Stability Assessment of Ethiopian power System Using Normalized Active Power Margin Index

Voltage stability assessments, made so far on the Ethiopian electric power system (EEP), are limited both in number and in methodology. Here, in this paper the static voltage stability of the Ethiopian power system is investigated using an index called normalized active power margin. The methodology starts from determining Thevenin equivalent of a system as viewed from the load buses. The Thevenin equivalent parameters help to determine the load bus maximum active power transfer limit and to draw the PV relation curves. The approach avoids the time-consuming method of PV curve based maximum active power transfer determination, which requires large number of power flow computations. The resulting maximum active power transfer and current operating active power load are used for the index calculation. The index is tested using IEEE 30 bus system and produced results matching with other previously established indices. The index is capable of ranking vulnerability of load buses to voltage instability. Then, scenarios of heavy load and light load EEP cases, with and without system reactive power compensation, are investigated. Results reveal weakest buses are supplied from 66kV transmission lines, load bus 232 being the weakest of all. On the other hand, the most stable buses are supplied from 132 kV transmission lines, bus 149 being the most stable bus. PV curves drawn, also, reveal the improvement that come with reactive power compensation and with operating in light load condition.

Adaptive integrated control strategy for MMC-MTDC transmission system considering dynamic frequency response and power sharing

Due to the lack of grid inertia caused by the increasing penetration of renewable energy sources, the ability of system to withstand disturbance is reduced. In attempt to address this challenge, an adaptive virtual inertial frequency control (AVIFC) strategy for multi-terminal dc (MMC-MTDC) transmission system considering dynamic frequency response is proposed. Based on the frequency variation characteristics in inertia response and primary response stages, the virtual inertia coefficient can be automatically adjusted. In the inertia response stage, considering the limitation of DC voltage, the virtual inertia coefficient adaptively decreases according to the frequency deviation to reduce the maximum frequency deviation. In the primary response stage, the virtual inertia coefficient decreases to 0 rapidly following the frequency deviation to speed up the frequency recovery. Furthermore, aiming at the problem of coordinated power sharing between converter stations of weak AC systems after disturbance, an adaptive droop control (ADC) strategy based on DC voltage deviation and converter station power margin is studied to realize the optimal distribution of unbalanced power so that DC voltage deviation is reduced, DC voltage regulation time is shortened and the stability of DC voltage is maintained at the same time. Finally, based on PSCAD / EMTDC simulation platform, the control model of a five-terminal MMC-MTDC system is established. Three working conditions, namely the load reduction, the load increment and the converter station out of operation, are selected to verify the effectiveness and feasibility of the proposed adaptive integrated control (AIC) strategy including AVIFC and ADC.

Enhancement of Voltage Stability by Optimal Placement of Shunt Compensation using Bus Voltage Stability Indices and Reactive Power Margin

Voltage stability problem has caused several blackouts in many countries in recent years. Impending voltage instability has been a significant threat to modern power system's security and reliability. Moreover, the operation and planning of large interconnected power systems is becoming increasingly complex as power demand rises, posing a security risk to the grid. Appropriate efforts to improve power system security and increase voltage stability margin should be planned to keep the system secure. This work investigates the voltage stability of a power system with and without a shunt capacitor. The bus voltage stability index, L index, is used to measure the distance of the power system to its stability limit in order to assign the shunt capacitor. The L-index for a particular load state is computed for all load buses, and the greatest L-index indicates the system's approach to voltage collapse. The system's load ability margin is being traced utilizing a static voltage stability evaluation approach, i.e., PV and QV curve analysis. The minimal power loss approach is used to calculate the optimal capacitor size. The effect of shunt compensation was simulated, and the results with and without compensation were compared. The IEEE-9 bus system was employed in this work, and the system was simulated using MATLAB and Power World Simulator. The result demonstrates that the shunt capacitor enhances voltage stability by injecting the appropriate reactive power.

Sonic Space-Making on the Margins of Power: Electronic Music, Agency, and Alternative Belonging in the Republic of Macedonia (2011–2014)

Abstract This article examines the space-making practices of an electronic music scene in Skopje, Macedonia, between 2011 and 2014. It argues that such practices can make spaces for “alternative belonging,” enabling individuals and groups to diverge from the powerful without open resistance. The article builds on ethnomusicological literature on how space is mediated by music and sound in ways that are generative and transformative, suggesting that understanding agency as distributed across numerous positionalities assists in thinking beyond dichotomous dominance-resistance frameworks.

From the Editor

From the Editor

Strength of incumbent political symbolism at the simular elections of Seram Regency, east part of Maluku Province 2020

This paper aimed to identify and describe the power of incumbent political symbolism in the simultaneous regional elections of East Seram Regency, Maluku Province. Three candidate pairs followed this election: Alkatiri-Arobi Kelian, Rohani Vanath-Ramli Mahu, and Mukti Keliobas (Incumbent) Idris Rumalutur. Observation results show that the incumbent's political opponent, Rohani Vanath, who is the wife of Abdullah Vanath (former Regent, SBT), is considered to strengthen the politics of political dynasties, where political battles are dominated by coalitions of predatory interests and encourage the marginalization of people's power, as emphasized in Yuki's conceptualization. Fukuoka.

Entropy weight and grey relational analysis based virtual capacitance collaborative control for multiple energy storage units

Flexible virtual capacitance control (FVCC) for converter can improve the stability and dynamics of DC bus voltage, but among multiple converters, essential inertia distribution is capable of optimizing the performance. To improve the rationality of inertia distribution, a virtual capacitance collaborative control (VCCC) strategy for multiple energy storage units (ESUs) is proposed. Firstly, the system required total inertia is adjusted according to each individual battery's rated capacity and state-of-charge (SOC). Then comes the establishment of an evaluation mechanism, which takes the accounts of battery SOC margin, converter power margin and battery power regulation speed. The entropy weight and grey relational analysis are used to calculate each ESU's distribution coefficient and then adjust their virtual capacitance in real-time. The results show that the adjustment and distribution of the total inertia are beneficial to controlling the SOC of the batteries within the safe range. The ESU with the smallest converter power margin or the slowest battery power regulation speed supports least virtual inertia, which can reduce the problems such as overload protection action or auxiliary power limitation, so as to improve the cooperative control effects. Finally, the effectiveness of the proposed control strategy is verified by hardware-in-the-loop (HIL) simulation experiments.

Outage Probability versus Carrier Frequency in GeoSurf Satellite Constellations with Radio-Links Faded by Rain

For sites located in different climatic regions, we estimated the relationship between the annual average probability distributionof exceeding a fixed rain attenuation, and the carrier frequency in the range 16 to 100 GHz, in the zenith paths of GeoSurf satellite constellations. In these constellations rain attenuation is independent of the altitude and number of satellites. Rain attenuation iss calculated with the Synthetic Storm Technique, a reliable prediction method, by using on-site measured rain-rate time series. A suitably defined outage probability factor shows that the outage probability, for fixed power margin, tends to saturate as frequency increases. In wideband radio-links, such as in spread spectrum design, there is very likely a long-term distortion due to the in-band outage probability. The results are oriented to design systems faded by rain attenuation whose value is also the total power margin available due to a mixture of coding and hardware technology, whose combination is not of concern here.

Power budget- and SRLG-aware cost-efficient partial protection planning models and architectures for long-reach passive optical networks

In a long-reach passive optical network (LR-PON), protection for optical network units (ONUs) against their distribution fiber (DF) failures is highly desirable to ensure uninterrupted Internet access to the associated users. In the distribution section of the LR-PON, shared-risk link groups (SRLGs) are formed by DFs due to sharing fiber cables and conduits. Most of the existing SRLG-aware DF protection schemes require residual bandwidth with ONUs. Therefore, they fail to provide protection to all ONUs under high reliability requirements (RRs) and result to be very cost-inefficient as well. We first propose a SRLG-aware reliability framework to compute the connection reliability of every ONU and joint reliability of every ONU-ONU pair and ONU-node pair. Thereafter, we propose two different SRLG-aware nonresidual bandwidth based partial protection schemes and their compatible architectures to provide partial DF protection to ONUs against SRLG failures to satisfy the given RR. Following the proposed schemes, we formulate two different integer linear programming (ILP) based optimization problems to set up backup connections by using backup DFs and other backup optical resources with the minimum protection cost. The proposed ILP-based protection planning models restrict the backup DF lengths to bound the propagation delay to satisfy the strict delay requirement for real-time applications. Since the proposed ILP-based models turn out to be computationally intractable for large network problems, we also propose two heuristic schemes that provide comparable results to that of the ILP-based models. We evaluate the performance of the proposed partial protection schemes with reference to the protection cost and total length of backup DFs (TLBDF). The exhaustive simulation results show that the proposed partial protection schemes not only satisfy high RRs, but also require a much lower protection cost, TLBDF, and optical power margin in comparison to the existing SRLG-aware protection schemes.

Optimization of avian perching manoeuvres

Perching at speed is among the most demanding flight behaviours that birds perform1,2 and is beyond the capability of most autonomous vehicles. Smaller birds may touch down by hovering3–8, but larger birds typically swoop up to perch1,2—presumably because the adverse scaling of their power margin prohibits hovering9 and because swooping upwards transfers kinetic to potential energy before collision1,2,10. Perching demands precise control of velocity and pose11–14, particularly in larger birds for which scale effects make collisions especially hazardous6,15. However, whereas cruising behaviours such as migration and commuting typically minimize the cost of transport or time of flight16, the optimization of such unsteady flight manoeuvres remains largely unexplored7,17. Here we show that the swooping trajectories of perching Harris’ hawks (Parabuteo unicinctus) minimize neither time nor energy alone, but rather minimize the distance flown after stalling. By combining motion capture data from 1,576 flights with flight dynamics modelling, we find that the birds’ choice of where to transition from powered dive to unpowered climb minimizes the distance over which high lift coefficients are required. Time and energy are therefore invested to provide the control authority needed to glide safely to the perch, rather than being minimized directly as in technical implementations of autonomous perching under nonlinear feedback control12 and deep reinforcement learning18,19. Naive birds learn this behaviour on the fly, so our findings suggest a heuristic principle that could guide reinforcement learning of autonomous perching.

Spatial single mode laser source interaction with measured pulse based parabolic index multimode fiber

Abstract The study clarified spatial single mode laser interaction with measured pulse based parabolic index multimode fiber. Peak power level margin, maximum/minimum signal amplitude margin after parabolic index multimode fiber are measured with core radius of 25 µm, cladding thickness of 10 µm, refractive index peak of 1.4142, length of 300 m, and refractive index step of 1%. Maximum signal power margin against spectral frequency after PIN light detector based parabolic fiber properties is tested under the same operating parameters. The signal power amplitude/power within parabolic index multimode fiber is also measured based on variations of fiber lengths and relative refractive index step. The study implies the multimode graded index fibers with parabolic or near parabolic index profile cores have transmission bandwidths than other multimode fibers.

‘Kufa kwa jongololo nkhusiya mphete’: A critique of gender injustice procreation cultural practices of the Sena of Malawi

The central argument of this article is that kufa kwa jongololo nkhusiya mphete, a concept that is used to encourage procreation amongst the Sena people of Nsanje District in Malawi, is a dehumanising concept for the barren men and women, in the context of HIV and AIDS and gender justice, where men and women need concepts that affirm life in all its fullness. The study uses feminist cultural hermeneutics as a tool to analyse dehumanising cultural practices, through the examination of three Sena cultural practices.Contribution: The study also questions the methodology used to engage indigenous knowledge, a methodology that denies traditional communities the right to maintain secrecy on some treasured indigenous practices. At the same time, the article argues that no protection should be afforded to indigenous practices that dehumanise the lives of people on the margins of power.

Near-Field Circular Array for the Transcutaneous Telemetry of UHF RFID-Based Implantable Medical Devices

Wireless communication with Implantable Medical Devices (IMDs) based on Radiofrequency Identification in the UHF band suffers from the constraints on the maximum power absorbed by the body tissues. Accordingly, an interrogating antenna placed onto the skin is capable to monitor only a limited region just below its footprint. In some applications like the hand prosthesis controlled by Electromyographic signals emitted by muscle contractions, multiple IMDs have to be used to increase the degrees of freedom in driving the actuators. An array of interrogators, working in the near-field can mitigate this bottleneck by greatly extend the read region inside the body. Sequentially- and simultaneously-fed arrays by a same reader are here investigated to optimize the multi-sensor backscattering modulated links. The conditions (feeding scheme and alignment) to guarantee a robust interrogation of a relevant number of implanted sensors with no battery onboard are identified also accounting for the safety constraints related to the SAR. Numerical simulations and experimentation with a cylindrical phantom resembling human limbs, hosting reference antennas, demonstrate that the simultaneous feed permits to interact with eight IMDs by using nearly all the available power from typical readers (30 dBm, 22 dBm as a minimum) without exceeding the SAR limit with a power margin (w.r.t. sensor-oriented ICs with −10 dBm power sensitivity) of more than 5 dB for any angular alignment between the array and the sensors.

Modified algorithm for automatic control of the mining harvester according to the load of the engine of the cutting drive

Purpose. To increase the productivity of the cutter-loader by creating a modified algorithm for automatic control of its speed with correction of stable power of cutting drive motors based on the results of statistical analysis of power during operation of the cutter-loader. Research methodology. As a research tool, a complex simulation model of the cutter-loader’scontrol system is used, which includes well-known mathematical models, describing the mining and geological properties of coal seams, as well as processes occurring in the structural elements of the cutter-loader. With the help of calculational experiments, the regularities of changes of statistical estimates of the power of the cutting drive engine for different mining and geological properties of the coal seam and the dynamics of the cutter-loader are established. The analysis of these regularities allowed to establish the dependence of the stable power of the cutting drive motor on the mining and geological parameters of the formation, and on their basis to propose a method of correction of the stable power during the working of the cutter-loader. A study of the effectiveness of the algorithm for automatic control of the speed of the cutter-loader using the proposed method in comparison with the existing algorithm. Research results. It is established, that the steady power of the cutting drive motor, corrected taking into account the standard deviation of the high-frequency component of the cutting drive motor power on a short section of the array, has a clearly determined deterministic component, which is determined by the change of resistance of coal to cutting along the coal seam. Also, steady power has a random component with the weight 15%, which is associated with the unpredictable oscillating nature of the movement of the cutter-loader, and with the complex and random nature of the process of destruction of the coal seam by the executive body. It is determined, that the double value of the standard deviation of the high-frequency power component of the cutting drive motor, as a power reserve, provides the percentage of exceeding by instantaneous power of allowable value, which is as close as possible to its acceptable level without exceeding it. Scientific novelty. For the first time, the dependence of the percentage of instantaneous power, exceeding its allowable value, on the coefficient of proportionality between the power margin and the standard deviation of the high-frequency power component under the condition of calculating the steady power of the cutting drive motor. This allowed us to determine the coefficient of proportionality, at which the percentage of cases of exceeding the instantaneous power of its permissible value is as close as possible to its acceptable level, but without exceeding it. Practical meaning. The method of correcting the stable power of the cutting drive motor during the operation of the cutter-loader is proposed. At the same time, the parameters of the algorithm for calculating the stable power of the cutting drive motor based on statistical processing of the values of the instantaneous motor power are substantiated.

Design of High Stability and Low Power 7T SRAM Cell in 32-NM CNTFET Technology

A novel 7T carbon nanotube field effect transistor (CNTFET)-based static random-access memory (SRAM) cell is proposed in this paper. Power and noise margin performances of the proposed SRAM cell is observed for write, hold and read operations. The power consumption and noise margin of the proposed SRAM cell is compared with the conventional 6T and 8T CNTFET-based SRAM cells. From the simulation, it is noted that the proposed 7T SRAM cell consumes lesser power and offers high static noise margin (SNM) compared to that of conventional 6T and 8T SRAM cells. The introduction of diode-based transistor structure improves the power and noise performance of the proposed SRAM cell. The effect of variation of parameters such as gate oxide thickness, dielectric constant, pitch, temperature, number of carbon nanotubes (CNT) and supply voltage on power and noise performance of proposed 7T SRAM cell is studied. Simulations were carried out with HSPICE simulation tool using Stanford University 32-nm CNTFET model.

Reactive Power and Voltage Optimization of New-Energy Grid Based on the Improved Flower Pollination Algorithm

In order to solve the reactive power and voltage control problem caused by the high proportion of new energy connected to the power grid, this paper takes the minimum voltage deviation, minimum network loss and maximum dynamic reactive power margin of the whole system as the comprehensive optimization objectives and establishes a reactive power and voltage optimization model by considering the reactive power regulation ability of SVC (Static Var Compensator) and new energy units. In view of the continuous and discrete variables in the model, the traditional continuous FPA (Flower Pollination Algorithm) is discretized to form an improved continuous-discrete hybrid FPA, and the tournament selection mechanism is adopted to speed up the convergence. Through the example analysis of the IEEE-39 bus system, the feasibility of the proposed reactive power and voltage optimal control method in the new energy grid is verified. Compared with GA (Genetic Algorithm), the results show that the improved FPA has high optimization accuracy, which is suitable for solving the reactive power and voltage optimization problem of the new energy grid.

Women on the margins of political power. Drivers of the gendered assessment of political leadership in Romania

ABSTRACT This paper explores the gendered assessment of political leadership in Romania. Using recent survey data obtained from a nationally representative sample, we found that men and women are unevenly impacted by various individual, household, and socio-cultural variables that have an unequal influence on their support for the cultural belief that men make better political leaders than women do. Our findings suggest that women’s stereotypical view of male leadership is eroded mostly by education, the presence of older children in the household, and upholding a feminist agenda. For men, only the category of those with tertiary education has a lower likelihood to believe in this stereotype, compared with the reference category of men with secondary education or below. In addition, men are less inclined to support this cultural belief when they choose reading as first leisure preference as compared to men privileging other leisure activities, while for women this relationship has not been identified. A higher income of respondents as compared to their spouses’/partners’ income reinforces the cultural stereotype of men as natural political leaders among male respondents, while for women a positive association is found in relationship with their partners undertaking masculine activities such as fixing things around the house.

Quantitative Analysis of System Operating Margin With the High Penetration of Distributed Generators in Distribution Networks

With the integration of distributed generators (DGs) and multiple types of loads, it is increasingly difficult to cope with the uncertainties of DGs, which brings challenges to the secure operation of distribution networks (DNs). Source and load cannot obtain the power balance locally, which may cause operational problems such as line power overload and node voltage violation. However, the methods for quantitatively analyzing the operating status of DNs have not yet formed a unified standard. For which reason, the concept of operating margin is proposed in this study, to represent the distance from the operating point to the boundary. In this study, to generally evaluate the operating status of DNs, the concept of node power margin is proposed first. Then the evaluation indexes including line power margin (LPM) and node voltage margin (NVM) are introduced. The quantitative calculation method for system operating margin (SOM) is further elaborated, which is supposed to be the evaluation indexes on system level. After that, the analysis process of evaluation methods for SOM is discussed. Finally, case studies are performed on the modified IEEE 33-node system to evaluate the operating margin of DNs and verify the enhancement brought by the energy storage system (ESS) and soft open point (SOP) through the flexible adjustment of power flow. The simulation results show that the distance between the DN and the security boundary is effectively quantified through the proposed method, the value can be easily calculated, and the change can be clearly reflected.

Effective handling of nonlinear distortions in CO-OFDM using affinity propagation clustering.

We experimentally demonstrate a system-agnostic and training-data-free nonlinearity compensator, using affinity propagation (AP) clustering in single- and multi-channel coherent optical OFDM (CO-OFDM) for up to 3200 km transmission. We show that AP outperforms benchmark deterministic and clustering algorithms by effectively tackling stochastic nonlinear distortions and inter-channel nonlinearities. AP offers up to almost 4 dB power margin extension over linear equalization in single-channel 16-quadrature amplitude-modulated CO-OFDM and a 1.4 dB increase in Q-factor over digital back-propagation in multi-channel quaternary phase-shift keying CO-OFDM. Simulated results indicate transparency to higher modulation format orders and better efficiency when a multi-carrier structure is considered.

Prospects and Challenges of Photonic Switching in Data Centers and Computing Systems

This Tutorial will discuss the motivation, benefits, and challenges of photonic switching in data centers and cover prospects of future data centers involving emerging new technologies and cross-layer solutions. The primary motivation for considering photonic switching in data centers rises from the need for energy-efficient and scalable intra-data center networks to meet rapid increases in data traffic driven by emerging applications, including machine learning. The data traffic inside the data centers (East-West traffic) is typically significantly greater than that of the traffic coming in and out of the data centers (North-South traffic) (Benson <i>et al.</i> 2010). To accommodate such traffic, today&#x0027;s large-scale data centers employ cascaded stages of many power-hungry electronic packet switches interconnected across the data center network in fixed hierarchical communication topologies. These electronic switches add significant latency and energy consumption while limiting the communication bandwidth. On the other hand, photonic switches can, in principle, support interconnections at very high data rates on many parallel wavelengths while keeping their energy consumption nearly independent of the switch port bandwidth. Numerous research papers have predicted significant benefits in scalability, throughput, and power efficiency from deploying photonic switches in data centers. However, photonic switching is not yet widely deployed in commercial warehouse-scale data centers at the time of writing this Tutorial due to significant challenges. They are related to 1) cross-layer issues involving control and management planes together with data integrity during switching, 2) scalability to &gt;5000 racks (&gt;a quarter-million servers), 3) performance monitoring required for reliable operation, 4) currently existing standards allowing limited power margin (3 dB), and 5) other practical (technology-dependent) issues relating to polarization sensitivity, temperature sensitivity, cost, etc. In telecom, commercial deployments of reconfigurable optical add-drop multiplexers (ROADMs) (Lightwave, 2003)&#x2013;(Perrin, 2015) also had faced similar challenges and took place nearly ten years after the first research network testbed demonstrations in 1997 (Garrett, 2015) with fully implemented network control and management planes. In data centers, the challenges are far more significant due to the scale of the network and the dynamicity of the traffic. We will discuss possible solutions for future data centers involving cross-layer methods, new topologies, and innovative photonic switching technologies. In particular, the Tutorial broadly surveys state-of-the-art photonic switching technologies, architectures, and experimental results, and further covers the details of arrayed-waveguide-grating-router-based switch fabrics offering hybrid switching methods with distributed control planes towards scalable data center networking.