Energy Margin Research Articles

Response-driven adaptive under frequency load shedding scheme based on energy model

Developing reasonable and effective adaptive under frequency load shedding (AUFLS) schemes is crucial for preventing system frequency drops. In order to overcome the mismatching of event-driven load shedding scheme in the traditional second line of defense, this paper proposes a response-driven AUFLS scheme based on energy model. In this scheme, the energy model is established by the kinetic energy theorem, which represents the equivalent conversion relationship between rotor kinetic energy deviation (KED) and the unbalanced power does work (UPDW) of each component. Furthermore, a kinetic energy margin indicator (KEMI) reflecting the system frequency is introduced, and the minimum load shedding amount (MLSA) corresponding to the critical KEMI is calculated. The comprehensive load shedding allocation weight is established by combining the UPDW of load and shedding costs. The combination of MLSA and comprehensive load allocation weights enables precise control with minimal cost. Modified IEEE 10-generator 39-bus test system and CSEE-SSFS 197-bus real system are used to verify the performance of the proposed AUFLS scheme.

Characterizing Manipulation Robustness Through Energy Margin and Caging Analysis

Characterizing Manipulation Robustness Through Energy Margin and Caging Analysis

Evaluating the Effects of Reducing Voltage Margins for Energy-Efficient Operation of MPSoCs

Voltage margins, or guardbands, are imposed on DVFS systems to account for process, voltage, and temperature variability effects. While necessary to assure correctness, guardbands reduce energy efficiency, a crucial requirement for embedded systems. The literature shows that error detection techniques can be used to maintain the system’s reliability while reducing or eliminating the guardbands. This letter assesses the practically available margins of a commercial RISC-V MPSoC while violating its guardband limits. The primary motivation of this work is to support the development of an efficient system leveraging the redundancy of multicore architectures for an error detection and correction scheme capable of mitigating the errors caused by aggressive voltage margin reduction. For an equivalent performance, we achieved up to 27% energy reduction while violating the manufacturer’s defined guardband, leaving reasonable energy margins for further development.

Coordinated pricing mechanism for parking clusters considering interval-guided uncertainty-aware strategies

With the increasing penetration of electric vehicles into the existing power networks, the development of proper energy management tools become essential to mitigate the damaging effects of emerging high-power charging modes. To facilitate the management of vehicles, they can be gathered into clusters in order to aggregate their charging profiles. This paradigm is called cluster of vehicles and can be forward developed by gathering a group of parking, thus forming a parking cluster where the characteristics of different parking lots are aggregated. In this paper, a coordinated charging price mechanism for clusters of parking lots is proposed. The new proposal is casted as a game-based framework which seeks for the equilibrium between the cluster coordinator and parking lots, instead of conventional tools where the pricing strategy is decided by a central entity disregarding the interests of users. The developed model is established as a bi-level optimization problem, which is further linearized to be tractable and solvable by off-the-shelf solvers. The implications of vehicle-to-grid are also studied by fully modelling bi-directional power flows in chargers. In addition, two uncertainty-aware strategies are proposed to cope with uncertain energy margins in parking lots. A case study is conducted and various results are analysed and discussed. It is shown that enabling vehicle-to-grid characteristics discloses significant economic benefits for users and the cluster coordinator. In addition, vehicle-to-grid impacts notably on the risk-averse character of the uncertainty-aware strategies proposed. The developed pricing mechanism is also compared with the conventional pricing policies based on key of repartitions, showing that the new proposal is able to reduce the cost for users, avoiding to directly translate the energy cost to charging points.

Service stacking on residential BESS: RES integration by flexibility provision on ancillary services markets

Opening the Balancing Markets (BMs) to Renewable Energy Sources (RES) and Battery Energy Storage Systems (BESS) could support the integration of RES in decarbonizing power systems; nevertheless, the limited energy content of BESS can reduce their reliability on the BMs. A novel control strategy for revenue stacking of behind-the-meter and front-of-the-meter services on a domestic prosumer equipped with photovoltaic production and BESS is presented in this study. The aim is to maximize self-consumption and the economics while guaranteeing BESS state-of-charge management. A new control (and bidding) strategy is developed to offer the available energy (and power) margins on the Italian BMs, without saturating or depleting the energy content. The results show synergies between self-consumption maximization and flexibility provision, i.e., the proposed approach demonstrates how a multiservice-oriented operation of BESS improves the economic sustainability of the solution, with a payback time between 5 to 9 years, decreases the energy exchange with the public grid and the RES imbalance (imbalance reduced by 90%), and provides flexibility with high reliability (ranging 89%–97%). Due to this, the strategy of reducing the imbalance of variable RES and then providing flexibility with the left margins candidates itself as a standard routine for massively integrating RES via BESS.

Low Carbon Operation Optimization Study of Integrated Energy Systems Considering Interruptible Loads

Aiming at the consumption of renewable energy, researched controllable load mechanisms and energy storage regulation strategies in an electric-thermal coupled network, and a comprehensive flexible resource model was constructed to optimize the low-carbon operation of the system. Firstly, analyzed the industrial load regulation mechanism of differentiated layout in the regional power grid. Based on the electric-thermal coupled system in the urban energy grid, the regulation model of controllable load and electric/thermal energy storage was established. Then a comprehensive benefit model was constructed with an economic cost, wind and solar usage, and carbon emissions as indicators. Proposed a carbon emission flow topology to describe the carbon emission flow information attached to the energy flow. Finally, combined with the IEEE 33-node distribution network and 45-node heat network coupling system, the improvement effect of the multiple flexible resource response on the comprehensive benefits of the system was analyzed. And the carbon emission flow process of the electricity-thermal network in the typical scenario was visually displayed through topology. The results show that exploring flexible resources can improve the consumption margin of wind and solar energy in the integrated energy system, which verifies the rationality and effectiveness of the proposed method.

Avoiding module capacitance over-dimensioning of Modular Multilevel Converters with constrained and unconstrained modulator-based Model Predictive Control

The power density of Modular Multilevel Converters (MMCs) is often limited by the over-dimensioning of the module capacitance value. This is common because with conventional control schemes, large voltage and energy margins must be included in the MMC design to avoid overvoltages in the module capacitors and saturation effects due to undervoltages in the module capacitors. This paper presents two Model Predictive Control methods that can reduce the necessary voltage and energy margins to a minimum and therefore increase the power density of the MMC system compared to conventionally controlled MMCs. A trade-off between computational effort and module capacitance over-dimensioning is discovered for the proposed constrained MPC. The unconstrained MPC is compared to the constrained MPC and conventional PI control using simulations. Finally, the performance of the unconstrained MPC is experimentally verified with an MMC system prototype and compared to a traditional PI control system.

A hybrid-extreme learning machine based ensemble method for online dynamic security assessment of power systems

• A hybrid model is developed, blending ELM and Levenberg-Marquardt. • Particle swarm optimization-based weighted averaging ensemble is developed. • Energy margin and time margin are calculated for better application of techniques. • Hybrid ELM is found most suited technique for online DSA application. This manuscript develops a new hybrid-extreme learning machine (ELM) based ensemble model for real-time dynamic security assessment (DSA) of power systems. In order to boost the forecasting accuracy of ELM algorithm, a Levenberg-Marquardt (LM) backpropagation algorithm is used. The Ensemble strategy takes advantage of complementary information to improve the generalization capability of model. To realize an accurate ensemble model, particle swarm optimization (PSO) based weighted averaging is used to combine the individual forecasts. Transient energy function (TEF) terms, generator real and reactive power outputs and fault location are taken as input features for classification as well as prediction of transient energy margin (TEM) and time margin (TM) for a given operating condition and fault location. The potential of the proposed technique is validated on New England 39-bus and 68-bus test power systems. The results demonstrate that the developed model outperforms other state-of-the-art methods.

Do global environmental drivers' ocean acidification and warming exacerbate the effects of oil pollution on the physiological energetics of Scylla serrata?

Global climate change-induced ocean warming and acidification have complex reverberations on the physiological functioning of marine ectotherms. The Sundarbans estuarine system has been under threat for the past few decades due to natural and anthropogenic disturbances. In recent years, petroleum products' transportation and their usage have increased manifold, which causes accidental oil spills. The mud crab (Scylla serrata) is one of the most commercially exploited species in the Sundarbans. The key objective of this study was to delineate whether rearing under global environmental drivers (ocean acidification and warming) exacerbates the effect of a local driver (oil pollution) on the physiological energetics of mud crab (Scylla serrata) from the Sundarbans estuarine system. Animals were reared separately for 30days under (a) the current climatic scenario (pH 8.1, 28°C) and (b) the predicted climate change scenario (pH 7.7, 34°C). After rearing for 30days, 50% of the animals from each treatment were exposed to 5mg L-1 of marine diesel oil for the next 24h. Physiological energetics (ingestion rate, absorption rate, respiration rate, excretion rate, and scope for growth), thermal performance, thermal critical maxima (CTmax), acclimation response ratio (ARR), Arrhenius activation energy (AAE), temperature coefficient (Q10), warming tolerance (WT), and thermal safety margin (TSM) were evaluated. Ingestion and absorption rates were significantly reduced, whereas respiration and ammonia excretion rates significantly increased in stressful treatments, resulting in a significantly lower scope for growth. A profound impact on thermal performance was also noticed, leading to a downward shift in CTmax value for stress-acclimated treatment. The present results clearly highlighted the detrimental combined effect of global climatic stressors and pollution on the physiological energetics of crabs that might potentially reduce their population and affect coastal aquaculture in forthcoming years.

Relation between constituent material fraction in multifilamentary MgB2 wires and requirements for MRI magnets

Magnetic resonance imaging (MRI) occupies the largest segment of the commercial applications of superconductivity. The NbTi wire is typically applied to MRI magnets and fulfils their strict requirements. On the other hand, the dramatically large energy margin in the MgB2 wire is attractive for liquid helium-saving MRI magnets. However, there are many types of cross-sections in the MgB2 wires. This makes it difficult to analyse the applicability of the MgB2 wires to the MRI magnets systematically. This paper focuses on the in situ MgB2 wires with an iron matrix and a Monel reinforced member. Multiple evaluations are conducted for several types of MgB2 wires, and their applicability to the MRI magnets is discussed. Because the critical current density of the superconducting filaments does not largely depend on the cross-section of the wires, the engineering critical current density (J e) is roughly proportional to the superconducting fraction (λ sc). The acceptable bending strain of the heat-treated wires increases with the Monel fraction and is in the range of 0.3%–0.65%, which is larger than the value required for coil winding of the MRI magnets. Two types of protection approaches of the magnet are considered. One is an active protection. This approach requires a large fraction of the copper stabilizer in the cross-section of the wire and relatively reduces λ sc and J e. The other is the avoidance of quenches over the product lifetime using quick ramp-down of the magnet for unfortunate events, such as cooling system failure and emergency rundown. This approach requires no copper stabilizer and increases λ sc and J e thus widens the acceptable operational temperature range. The cross-section of the MgB2 wire can be designed with a certain level of freedom depending on its functional requirements.

Energy Flow Analysis of Excavator System Based on Typical Working Condition Load

Accurate energy flow results are the premise of excavator energy-saving control research. Only through an accurate energy flow analysis based on operating data can a practical excavator energy-saving control scheme be proposed. In order to obtain the excavator’s accurate energy flow, the excavator components’ performance and operating data requirements are obtained, and the experimental schemes are designed to collect it under typical working conditions. The typical working condition load is reconstructed based on wavelet decomposition, harmonic function, and theoretical weighting methods. This paper analyzes the excavator system’s energy flow under the typical working condition load. In operation conditions, the output energy of the engine only accounts for 50.21% of the engine’s fuel energy, and the actuation and the swing system account for 9.33% and 4%, respectively. In transportation conditions, the output energy of the engine only accounts for 49.80% of the engine’s fuel energy, and the torque converter efficiency loss and excavator driving energy account for 15.09% and 17.98%, respectively. The research results show that the energy flow analysis method based on typical working condition load can accurately obtain each excavator component’s energy margin, which provides a basis for designing energy-saving schemes and control strategies.

New evidence for avian and small non-avian theropod ichnotaxa from the Lower Cretaceous of Canada: Implications for theropod ichnodiversity

A diverse continental ichnofauna from the Lower Cretaceous (Aptian) Gething Formation occurs at the Ninesting Creek site in northeastern British Columbia. Vertebrate tracks including Wupus and Saurexallopus are inferred to represent medium-sized (footprint length ∼10 cm) tridactyl avian and larger (footprint length ∼15–17 cm), gracile, tetradactyl non-avian theropod trackmakers respectively. Shape, length-to-width and divarication ratios, suggest two morphotypes that are distinct from the poorly known, and infrequently-cited, Gething Formation ichnogenera Columbosauripus and Irenichnites (footprint lengths ∼12.5 and ∼15.0 cm respectively). This suggests a diverse theropod ichnofauna representing size classes which are quite distinct from the better-known large theropod ichnogenus Irenesauripus with footprint lengths in the range of ∼38.0–53.5 cm. Thus, current evidence suggests that the ichnodiversity of smaller avian and non-avian theropod tracks (footprint length ∼<15.0 cm) outnumbers large ‘megatheropod’ morphotypes by about 7:1. The implications of this distribution are consistent with recently proposed palaeoecological models. The assemblage also includes probable pterosaur tracks and distinctive arcuate compound Archaeonassa-Lockeia traces, attributed to freshwater unionid bivalves. The trace fossils comprise a composite Mermia-Scoyenia Ichnofacies assemblage. Palaeoenvironmentally the site represents the low energy margin of an open lake basin or floodplain pond, or a fluvial point bar.

Adaptive Optimal Management of EV Battery Distributed Energy for Concurrent Services to Transportation and Power Grid in a Fleet System Under Dynamic Service Pricing

Deployment of electric vehicles (EVs) in a fleet system to deal with environmental issues has been at the center of attention over the past several years. While the battery of each EV offers small storage, hundreds of EVs collectively can offer large energy storage to serve a power grid. This article develops a model for a central controller in a fleet system that allows adaptive utilization of EV batteries distributed energy for concurrent services to the transportation and power grid. The optimization model integrates various slack variables and control parameters for managing real-time fare prices, adaptive energy, and reserve margin allocation, interaction with the grid operator, and meeting the fleet target revenue. The proposed model incorporates EV driver's input into the scheduling process to allow the driver to flexibly manage their battery capacities based on their availability and assessment of the transportation services demand. A dynamic pricing mechanism is developed for real-time calculation of fare rates to allow the EV fleet optimization problem to achieve a daily revenue target while limiting fare prices in a competitive market. Numerical results indicate that the model can manage several EVs for various services while enhancing the fleet financial metrics.

The Decisive Role of Spin States and Spin Coupling in Dictating Selective O2 Adsorption in Chromium(II) Metal-Organic Frameworks.

The coordinatively unsaturated chromium(II)-based Cr3 [(Cr4 Cl)3 (BTT)8 ]2 (Cr-BTT; BTT3- =1,3,5-benzenetristetrazolate) metal-organic framework (MOF) has been shown to exhibit exceptional selectivity towards adsorption of O2 over N2 /H2 . Using periodic density functional theory (DFT) calculations, we attempted to decipher the origin of this puzzling selectivity. By computing and analyzing the magnetic exchange coupling, binding energies, the partial density of states (pDOS), and adsorption isotherms for the pristine and gas-bound MOFs [(Cr4 (X)4 Cl)3 (BTT)8 ]3- (X=O2 , N2 , and H2 ), we unequivocally established the role of spin states and spin coupling in controlling the gas selectivity. The computed geometries and gas adsorption isotherms are consistent with the earlier experiments. The binding of O2 to the MOF follows an electron-transfer mechanism resulting in a CrIII superoxo species (O2 .- ) with a very strong antiferromagnetic coupling between the two centers, whereas N2 /H2 are found to weakly interact with the metal center and hence only slightly perturb the associated coupling constants. Although the gas-bound and unbound MOFs have an S=0 ground state (GS), the nature of spin the configurations and the associated magnetic exchanges are dramatically different. The binding energy and the number of oxygen molecules that can favorably bind to the Cr center were found to vary with respect to the spin state, with a significant energy margin (47.6 kJ mol-1 ). This study offers a hitherto unknown strategy of using spin state/spin couplings to control gas adsorption selectivity in MOFs.

Multivariable Coordinated Nonlinear Gain Droop Control for PV-Battery Hybrid DC Microgrid Access System via a T-S Fuzzy Decision Approach

The PV-Battery hybrid DC microgrid is an important structural form for distributed renewable energy microgrid applications. This paper focuses on improving the access utilization rate of PV-Battery energy and enhancing the access stability of the DC bus voltage. Firstly, based on the voltage droop control method for multi-source access system, the relationship between the power margin of PV-Battery energy and the regulation of DC bus voltage deviation is analyzed. Then, a multivariable T-S fuzzy decision approach is used to design a nonlinear virtual resistance-based voltage droop gain coefficient function, which achieves a highly adaptive coordinated distribution of PV-Battery power as well as supports DC bus voltage stabilization. The T-S fuzzy input variables include the DC bus voltage deviation of the access point, the state of charge of the battery, and the PV sunlight intensity. Finally, the simulation system is built employing MATLAB/Simulink, and the feasibility and effectiveness of the proposed strategy are verified through multi-scheme simulations.

Calculation of the transient stability boundary of AC/DC inter‐connected system based on the stability margin of dynamic energy

Concerning the transient power angle stability problem in AC/DC inter-connected system caused by DC line grounding fault, a transient stability analysis method based on the stability margin of dynamic energy is proposed. First, the analytical expressions of the dynamic energy function before alpha retard, during alpha retard and after alpha retard are derived. According to the topologies of system and the integration intervals of energy function in different stages, the expressions of the acceleration energy, position energy and margin energy are obtained, which, respectively, reflect the rotating speed of system, the swing range of power angle and the system's ability of resisting in stability. Then, the surplus energy in the system is calculated by subtracting the sum of the acceleration energy and position energy from the margin energy, and the stability margin of the system is obtained. And then, the stability boundary of the system is derived. It is revealed that, if the stability margin is exactly right 0 at the end moment of alpha retard, the system is critical stable. Finally, hardware-in-the-loop tests are conducted in RT-LAB platform. The simulation results verify that, the stability margin reaches the minimal value at the end moment of alpha retard, and this value can clearly reflect the stability of system. Besides, the earlier the alpha retard starts or the longer the distance between the fault point and the rectifier outlet is, the better it is for the stability of system.

TRIGGERING PULSE GENERATORS DEVELOPED FOR THE HIGH-VOLTAGE DISCHARGERS OF MAGNETIC SYSTEMS AND FOR THE GENERATOR OF PULSE VOLTAGES USED BY THE RELATIVISTIC ELECTRON BEAM ACCELERATOR “TEMP-B”

The pulse generators were developed to trigger the high-voltage dischargers of magnetic systems and the dischargers of the generators of pulsed voltages used by the relativistic electron beam (REB) accelerator “TEMP-B”. The description of the triggering pulse generators designed by the NSC KIPT to actuate the dischargers of the pulsed voltage generators (PVG) and the dischargers of magnetic systems has been given. These are used by the commutation systems of capacitor banks with the stored energy margin in the range of 60 to 150 kJ. The generators provide the generation of voltage pulses with the amplitude of up to 20 kV.

Energy-aware trajectory planning for planetary rovers

Planetary rovers are becoming indispensable for exploration activities and science missions. The rover used in such mission is often limited in its operation time owing to power and computational resources of the rover. In this paper, a trajectory planning method for a planetary rover is proposed that considers vehicle dynamics, and energy management of the rover. The vehicle dynamics is approximated from a dynamic simulation of the rover, which can estimate the power consumption in accordance with terrain traversability of the rover. The power generation of the solar array panel mounted on the rover is also taken into account. The simulation study confirmed the usefulness of the proposed method, especially in scenarios where slopes could be observed, and one result indicated that the energy margin could be improved by 4.1 kJ, 13.9 at maximum.

Research on Flexibility Evaluation of Microgrid System with Energy Storage

Background: Microgrid is an effective integration mode of distributed generation (DG). It can eliminate the negative effect caused by the intermittent DG and consume the energy locally. Methods: For a public distribution network, a microgrid performs as a controllable and flexible unit. However, when the public distribution network has the demand of flexible regulation, there is no reasonable quantitative indexes to evaluate the flexibility of microgrid for dispatching decision. For this problem, the operational flexibility indexes of a microgrid are defined in this paper. Results: The indexes are quantified according to the maximum energy and active power regulation margin of each flexible equipment in the microgrid. The operational flexibility of microgrid is closely related to the scheduling strategy. Therefore the corresponding dispatching model of a microgrid is also provided in this paper. Conclusion: A case study shows how to calculate and use these flexibility indexes in an operation cycle of a microgrid system with energy storage (ES) facility and demonstrates the availability and practicability of the evaluation indexes and the method.

High temperature superconductors for fusion applications and new developments for the HTS CroCo conductor design

Recent improvements in the superconducting performance and technical maturity of high-temperature-superconductors (HTS) lead to considerations of using HTS in future fusion magnets in addition to the presently used low-temperature superconductors (LTS). Compact high field magnet systems entirely made of HTS for compact tokamaks, hybrid HTS-LTS magnets for enhanced operational capabilities (e.g. larger flux swing) in conventional tokamaks and future stellarator devices with HTS magnet systems are presently investigated. An overview of recent concepts, developments and designs of HTS-based future fusion magnet systems is given and a number of physical and technical challenges will be addressed, too: In particular, the so-called second generation HTS Rare-Earth-Barium-Copper-Oxide (REBCO) shows an excellent superconducting performance over a wide range of magnetic fields and temperatures. The layered architecture of these technical REBCO conductors and the ceramic nature of REBCO lead to mechanical challenges at high Lorentz forces, which is relevant for cable-in-conduit-conductors (CICC) of future fusion magnets due to the high currents and high field strengths. Different high-current cable concepts for future fusion magnets are discussed. High loads are not only a challenge for potential future HTS conductors but also for the conductor jackets and the coil casing of the magnet systems. An increase of the numbers of load cycles on the path towards a future fusion power plant requires superior mechanical strength. The high critical temperature of HTS materials allows to design HTS CICC with a noticeably higher minimum quench energy and temperature margin compared to LTS conductors – but leads inevitably to substantially slower quench propagation velocity and challenges related to quench detection. Recent results from numerical modeling and experimental investigation of quench in high-current HTS CrossConductor (HTS CroCo) based CICC are addressed.