Variable Grid Research Articles

Correlation between extreme/ unusual ozone events and corona effect from electric power transmission & distribution grids. Assessing the health and environmental impact of high-voltage direct current (HVDC) grid on ozone ground levels in Sao Paulo metropolitan area, Brazil.

• BACKGROUND AND AIM 1- Ozone ground levels pose a risk for public health 2- The increasing ozone levels measured in parts of the metropolitan area of Sao Paulo have brought the attention of researchers. Proposed mechanisms do not provide a clear outcome for establishing root causes, and for clarifying sources of ozone. Spatial distribution of ozone also depends on wind patterns. 3- As an alternate hypothesis for explaining unusual high levels of ozone, the corona discharge from electric transmission grid, known as corona effect, can play a significative role in the absence of, or in coincidence with other concomitant factors, to explain ozone (O3) and nitric oxide (NO) unusual levels. Negative coronas emits more ozone than Positive coronas. 4- The Environmental Protection Agency- EPA, found in a report of 1973 (EPA-650/4-73-003), following a research carried out in areas of high concentration of transmission lines that "under minimal wind conditions, such transmission line concentrations can produce sizeable local ozone levels.” 5- Research applies geospatial and statistical analysis with the aim of better understanding correlations between exposures and ozone levels. • METHODS Geographic Information System (GIS)-based systems with average grid cell edge length of 10 km minimum. Global InMAP (Intervention Model for Air Pollution) with a variable resolution grid (4 km horizontal grid cell widths) in combination with GEOS- Chem simulations. Data analysis by machine-learning model. • RESULTS Applying Predictive Machine Learning algorithm as regression models, research found that coronas could generate significant ozone levels downwind of the power line. • CONCLUSIONS Evidence of correlation between unusual ozone measurements and location of key power electric grid transmission lines and distribution centers with potential for corona effect are found in Sao Paulo state and Sao Paulo city metropolitan area. • KEYWORDS Corona effect, ozone, electric grids, spatial simulation, wind patterns, air pollution

A co-design framework for wind energy integrated with storage

<h2>Summary</h2> The global growth of wind energy markets offers opportunities to reduce greenhouse gas emissions. However, wind variability and intermittency (across multiple timescales) indicate that these energy resources must be carefully integrated into the power system to avoid mismatches with grid demand and associated grid reliability issues. At the same time, community concerns regarding the local installation of renewable energy and energy storage systems have already delayed or even halted the proposed projects. We propose a broadly defined, co-design approach that considers wind energy from a full social, technical, economic, and political viewpoint. Such a co-design can address the coupled inter-related challenges of cost, technology readiness, system integration, and societal considerations of acceptance, adoption, and equity. Such a successful design depends on the understanding of the needs of relevant communities, the regional grid infrastructure and its demand variability, local and global grid decarbonization targets, available land and resources for system siting, policy and political constraints for energy development, and the projected regional and global impact of these systems on the environment, jobs, and communities.

Deep neural networks for the quantile estimation of regional renewable energy production

Wind and solar energy forecasting have become crucial for the inclusion of renewable energy in electrical power systems. Although most works have focused on point prediction, it is currently becoming important to also estimate the forecast uncertainty. With regard to forecasting methods, deep neural networks have shown good performance in many fields. However, the use of these networks for comparative studies of probabilistic forecasts of renewable energies, especially for regional forecasts, has not yet received much attention. The aim of this article is to study the performance of deep networks for estimating multiple conditional quantiles on regional renewable electricity production and compare them with widely used quantile regression methods such as the linear, support vector quantile regression, gradient boosting quantile regression, natural gradient boosting and quantile regression forest methods. A grid of numerical weather prediction variables covers the region of interest. These variables act as the predictors of the regional model. In addition to quantiles, prediction intervals are also constructed, and the models are evaluated using different metrics. These prediction intervals are further improved through an adapted conformalized quantile regression methodology. Overall, the results show that deep networks are the best performing method for both solar and wind energy regions, producing narrow prediction intervals with good coverage.

Seismic Tomographic Modeling of the Crust and Upper Mantle beneath Israel and the Middle East: Improved Resolution through Optimized Model Parameterization

ABSTRACT Accurate regional seismic travel-time (RSTT) predictions rely on regional phases (e.g., Pg, Lg, Pn, Sn) to account for 3D effects in the crust and upper mantle that are not captured by 1D models traditionally used for real-time location. The RSTT prediction model accounts for regional-scale crust and upper mantle structure globally by incorporating regional seismic phases into its travel-time calculations. Previous versions of the RSTT model have used a constant grid cell size of 1°. To improve the tomographic accuracy of recovering velocity structure at regional scales, we perform data-driven grid refinement on the RSTT model down to a 0.125° grid (∼14 km) in pursuit of two main goals: (1) to test the limits of RSTT capability and accuracy of determined velocity structure through variable grid refinement and (2) to image smaller structures in Israel and the Middle East and illuminate upper mantle dynamics operating in this complex tectonic area. We investigate the effects of model parameterization as grid cell size decreases and the trade-offs between recovered velocity structures. Our final dataset includes 4751 events and 499 stations that recorded 79,344 Pn and 7489 Pg. The variable grid refinement method allows recovery of finer-scale velocity structures and reduces travel-time residuals in areas with the highest data coverage. At smaller grid cell sizes, longer paths need to be upweighted to stabilize the inversion. Results illuminate tectonic features undefined in coarser grid-size models; in particular, we observe mantle perturbations related to the subduction zone around the Cyprian arc and crustal anomalies near the Dead Sea fault and throughout the Anatolian plate.

박용고속엔진의 프로판 개조를 위한 점화시기 분석

Regulations on exhaust emissions of marine engines are being strengthened, and many related technologies are being developed. In this study, the combustion characteristics of the engine were analyzed for the propane conversion of a 225 kW high-speed engine. The movement of the piston was simulated using a variable grid from 120 degrees before TDC to 120 degrees after TDC, and the ignition timing was analyzed by changing the ignition timing from 20 degrees before TDC to five degrees after TDC at intervals of five degrees. Residual fuel mass fraction was rapidly reduced to 80% during ten degrees of crank angle after ignition, and then decreased slowly thereafter. After combustion, the amount of residual fuel increased significantly when the ignition timing was later than five degrees before TDC. Nitrogen oxide was greatly reduced as the ignition timing was delayed. The engine output was highest at five degree before TDC and decreased when the ignition timing was earlier or later. Considering performance and exhaust emissions, the optimal ignition timing is five degrees before TDC under this engine operating condition.

Analysis and Experiment of Heat Transfer Performance of Straight-Channel Grid Regenerator

The design of heat transfer performance of regenerator is the key technology of Stirling machine and is of great significance to ensure the operation efficiency of equipment. In this study the temperature difference between the two ends of regenerator at room temperature is less than 50K. This paper attempts to study the heat transfer performance of the straight channel grid regenerator at room temperature and verify its accuracy. At first, a straight-channel grid regenerator was designed in this study by analyzing the influence of structural parameters on the regenerator in order to reduce the flow resistance loss. The Pore Scale method and Representative Elementary Volume methods were combined to analyze the heat transfer characteristics of the grid regenerator. Compared with the wire mesh regenerator under the same condition, the straight-channel grid regenerator’s flow resistance could reduce by 96.2%. When the length-diameter ratio is 2:1 and the porosity is between 0.4 and 0.5, the heat transfer performance of the grid regenerator is satisfactory when it is applied in Stirling heat pump at room temperature. Then, A segmented variable porosity grid regenerator was designed based on the grid regenerator, and its performance was proved to be better than that of the grid regenerator. Finally, the two regenerators were developed based on additive manufacturing technology, and a single blow experiment platform was built. The experimental results fit well with the simulation results, with the maximum error being less than 1.5%. The experimental results prove the correctness of the model, which lays a foundation for the subsequent analysis of the periodic heat transfer characteristics of the straight-channel grid regenerator.

Numerical study on variable aperture extraction grids of a titanium hydride cathodic vacuum arc ion source

Titanium hydride cathodic vacuum arc ion sources are widely used in particle accelerators, neutron sources, etc. For the application in neutron sources, higher H+/D+ fraction and higher beam uniformity are preferred. In this work, to improve the beam uniformity of a miniature titanium hydride cathodic vacuum arc ion source, a new scheme of variable aperture extraction grids is proposed. A 2D numerical model is developed for the investigation of the variable aperture extraction grids. Numerical results indicate that the extraction grid plays important roles in the titanium hydride cathodic vacuum arc ion source that can improve the stability of ion source. Moreover, simulated results show that the designed variable aperture extraction grids can reduce the beam nonuniformity to less than ±10%, while the beam nonuniformity of the fixed aperture extraction grids are between ±22% and ±37%. Thus, the presented work can provide a potential reference for the improvement of beam uniformity of the vacuum arc ion sources.

Global, high-resolution, reduced-complexity air quality modeling for PM2.5 using InMAP (Intervention Model for Air Pollution).

Each year, millions of premature deaths worldwide are caused by exposure to outdoor air pollution, especially fine particulate matter (PM2.5). Designing policies to reduce these deaths relies on air quality modeling for estimating changes in PM2.5 concentrations from many scenarios at high spatial resolution. However, air quality modeling typically has substantial requirements for computation and expertise, which limits policy design, especially in countries where most PM2.5-related deaths occur. Lower requirement reduced-complexity models exist but are generally unavailable worldwide. Here, we adapt InMAP, a reduced-complexity model originally developed for the United States, to simulate annual-average primary and secondary PM2.5 concentrations across a global-through-urban spatial domain: “Global InMAP”. Global InMAP uses a variable resolution grid, with horizontal grid cell widths ranging from 500 km in remote locations to 4km in urban locations. We evaluate Global InMAP performance against both measurements and a state-of-the-science chemical transport model, GEOS-Chem. Against measurements, InMAP predicts total PM2.5 concentrations with a normalized mean error of 62%, compared to 41% for GEOS-Chem. For the emission scenarios considered, Global InMAP reproduced GEOS-Chem pollutant concentrations with a normalized mean bias of 59%–121%, which is sufficient for initial policy assessment and scoping. Global InMAP can be run on a desktop computer; simulations here took 2.6–8.4 hours. This work presents a global, open-source, reduced-complexity air quality model to facilitate policy assessment worldwide, providing a screening tool for reducing air pollution-related deaths where they occur most.

Thermal analysis for solidification of PCM including nanoparticles within a container

To expedite the freezing of PCM, inclusion of nano-powders and apply of fins were scrutinized in this work. The base PCM is water and nano-sized material (CuO) was added. Simulations with assumptions of neglecting gravity force and neglecting the slip velocity of nanomaterial were presented via Galerkin approach. In this modeling, variable grid with adaption with place of solid front was applied and quantity of time step has been designated automatically to reach lower computational price. Verification procedure showed a good agreement of present numerical simulation and selecting such assumptions were verified, too. With increasing shape factor, the time of converting whole water to ice, declines about 5.49%. Also, raising the concentration of CuO leads to reduction of time of process around 11.1%.

Weak Grid-Induced Stability Problems and Solutions of Distributed Static Compensators with Voltage Droop Support

Distributed static compensators (DSTATCOMs) are grid-connected power electronic equipment dedicated to compensating reactive power as well as improving voltage regulation in distribution networks. They eclipse conventional compensation approaches, such as capacitor banks, in terms of flexibility and effectiveness. Despite their identified advantages, STATCOMs with voltage droop are subject to weak grid-induced stability problems, as first revealed by this paper. Specifically, the voltage droop controller that couples the amplitude of point of common coupling (PCC) voltages to the reactive current reference creates a local control loop. Such a loop greatly deteriorates system stability in weak grids, which feature large and variable grid impedances. To address such stability problems, we propose a novel virtual resistance control scheme, which improves system stability through mitigation of local control loop gains in the low-frequency band. Experimental results obtained from a DSTATCOM prototype clearly demonstrate the correctness of stability analysis and the effectiveness of stability improvement.

Enhanced dynamic performance of grid feeding distributed generation under variable grid inductance

&lt;p&gt;Controlling weak grid-connected systems is very challenging. In transient, frequency and voltage oscillations may lead to voltage and/or frequency stability problems and finally lead to system collapse. During steady-state operation and at the point of common coupling (PCC), voltage degradation and grid voltage background harmonics restrict the inverter's functionality, reduce the power flow capability and cause poor power quality. With weak grid connection, grid impedance variance will contaminate the voltage waveform by harmonics and augment the resonance, destabilizing the inverter operation. In this paper, complete mathematical modeling is carried out and state feedback-plus-integral control is implemented to support the stabilization of the system. The proposed controller is adopted to provide a smooth transient under sudden load change by controlling the injected grid current under different grid inductance values. Furthermore, the proposed control is used to reduce the order and size of the inverter output filter while maintaining system stability. The proposed control has been compared with the conventional proportional integral (PI) controller under different scenarios to validate its effectiveness and to strengthen its implementation as a simple controller for distributed generator applications.&lt;/p&gt;

The Experimental Evaluation of Energy Efficiency and Carbonic Emission Rates for All Stable Loads of Larger-Scale (+600 MW) Coal-Fired Power Generation Units in Vietnam

Performance guarantees and tests of thermal power plants are usually carried out at 100% rate output capacity. However, fossil-fired power plants have decreased full load hours, affecting energy efficiency, and are subjected to frequent load changes caused by variable renewable electricity and potential grid stability. Therefore, this study is conducted to calculate and draw the characteristic curves for all stable loads of coal-fired power units including the 60%, 75%, and 100% rate output. The study focuses on the corrected plant net heat rates—gross unit outputs, net standard coal consumption rates—throttle steam pressures, and corrected plant net efficiencies—carbonic emission rates. In addition, the experimental investigation for energy efficiency and carbonic emission of the latest larger-scale (+600 MW) coal-fired power generation units in Vietnam are also implemented using a performance guarantee calculation software called “PG_Cal” version 0.0, which is based on a mass and energy balance method by MATLAB programing language. From the results of this study, it is suggested that the performance guarantees and tests of new coal-fired units should be carried out at different stable loads, including minimum load. Vietnam should apply the ultra-supercritical technology for new units in order to increase their efficiency and decrease carbon dioxide emissions.

Acoustic field simulations of logging while drilling by cylindrical finite difference with variable grids

Acoustic field simulations of logging while drilling by cylindrical finite difference with variable grids

Reduced DC sensor based grid-interactive operation of single-stage solar photovoltaic water pumping system

ABSTRACT The grid-interactive operation of a single-stage solar photovoltaic water pumping system (SPVWPS) requires additional power electronic interface and a number of sensors. This paper realizes the grid-interactive operation of the single-stage SPVWPS with reduced sensor and without adding to the cost of the grid-interface converter. The single-phase grid is connected directly with the SPVWPS and the three-phase inverter is controlled as a single-phase grid-interactive inverter. The motor winding inductance is utilized as a current filter. This arrangement functions as a photovoltaic-static synchronous compensator (PV-STATCOM) with voltage-oriented current control by feeding the peak solar photovoltaic (SPV) power to the grid and supporting the reactive power to alleviate steady-state grid voltage variations. The modified adaptive second-order generalized integrator (SOGI) is utilized for effective grid-angle estimation under the presence of DC-bias in the input signal. The modified perturb and observed maximum power point tracking (MPPT) technique is implemented using grid-side quantities, which curtails the requirement of the SPV current sensor. Extensive experiments are performed on the developed prototype under the variable atmospheric and the variable grid voltage conditions. The presented grid-interactive SPVWPS is realized with single power electronics device and three sensors. The cost of power electronics interface is reduced in presented single-stage grid-interactive SPVWPS by 22% compared to two-stage grid-interactive SPVWPS. Abbreviations: FLL: Frequency Looked Loop; PFC: Power Factor Correction; FFT: Fast Fourier Transform; PV: Photovoltaic; SPVWPS: Solar Photovoltaic Water Pumping System; MPPT: Maximum Power Point Tracking; P & O: Perturb and Observe; SPV: Solar Photovoltaic; OSG: Orthogonal Signal Generator; PWM: Pulse Width Modulation; SOGI: Second-order Generalized Integrator; PEC: Power Electronic Converter; RMS: Root Mean Square; VSI: Voltage Source Inverter; PF: Power Factor; RMF: Rotating Magnetic Field; VSC: Voltage Source Converter; PI: Proportional Integral; SySPWM: Synchronous Sine Pulse Width Modulation

Target Detection of Shipborne Lidar Based on Variable Size Grid Map

Target Detection of Shipborne Lidar Based on Variable Size Grid Map

A Robust Controller Design Methodology Addressing Challenges Under System Uncertainty

This paper proposes a generalized design methodology of a robust controller to mitigate the impact of system uncertainty on controller stability and performance which includes steady-state error, disturbance rejection, high-frequency noise attenuation and speed of dynamic response. The first step is to select the weighting functions that bound the transfer functions for the entire range of uncertainty. The second step is to form mathematical representation for both robust stability and robust performance. The third step is to conduct the robust H-infinity controller synthesis to generate the full-order controller, and then carry out order reduction and recheck of the design objectives. The last step is to select an optimized controller based on the multi-dimensional Pareto Front algorithm. The proposed method has been firstly applied to the current controller design of a grid-connected inverter with variable grid impedance, and secondly to the voltage controller design of an LLC resonant DC&#x002F;DC converter with variable resonant capacitance. The results indicate that the selected optimal H-infinity controller has an overall more satisfactory performance in terms of stability, steady-state error, disturbance&#x002F;noise rejection capability and dynamic performance, compared with conventional PI and PR controllers when there is a large variation of system parameters.

A Numerical Method for Computing Double Integrals with Variable Upper Limits

We propose and justify a numerical method for computing the double integral with variable upper limits that leads to the variableness of the region of integration. Imposition of simple variables as functions for upper limits provides the form of triangles of integration region and variable in the external limit of integral leads to a continuous set of similar triangles. A variable grid is overlaid on the integration region. We consider three cases of changes of the grid for the division of the integration region into elementary volumes. The first is only the size of the imposed grid changes with the change of variable of the external upper limit. The second case is the number of division elements changes with the change of the external upper limit variable. In the third case, the grid size and the number of division elements change after fixing their multiplication. In these cases, the formulas for computing double integrals are obtained based on the application of cubatures in the internal region of integration and performing triangulation division along the variable boundary. The error of the method is determined by expanding the double integral into the Taylor series using Barrow’s theorem. Test of efficiency and reliability of the obtained formulas of the numerical method for three cases of ways of the division of integration region is carried out on examples of the double integration of sufficiently simple functions. Analysis of the obtained results shows that the smallest absolute and relative errors are obtained in the case of an increase of the number of division elements changes when the increase of variable of the external upper limit and the grid size is fixed.

A Less-Intrusive Approach to Stabilize VSC Transmission Against Highly Variable Grid Strength

A less-intrusive solution to stabilize a voltage source converter (VSC) over an unknown grid strength is presented in this article. The existence of equilibrium point is investigated as a prerequisite to stabilization. By partially imposing grid forming control, a simple auxiliary outer loop is proposed to exhaust the physical limit of power delivery in steady state and provide support to fault-ride-through (FRT) operations over a wide range of grid strength. The proposed control can be used to upgrade a commissioned VSC with inner current loop intact and overcome the impact of negative voltage sensitivity; it also offers a robust nonintrusive solution to stabilize VSCs externally. The effectiveness of the proposed schemes is verified by analysis in frequency domain and simulations in electromagnetic transient (EMT) time domain considering change of grid strength and FRT.

Marginal Value of Vehicle-to-Grid Ancillary Service in a Power System with Variable Renewable Energy Penetration and Grid Side Flexibility

Regulating the frequencies of power grids by controlling electric vehicle charging and discharging, known as vehicle-to-grid (V2G) ancillary services, is a promising and profitable means of providing flexibility that integrates variable renewable energy (VRE) into traditional power systems. However, the ancillary services market is a niche, and the scale, saturation, and time-dependency are unclear when assuming future changes in the power system structure. We studied the marginal value of V2G ancillary services as a balancing capacity of the power system operation on the load-frequency control (LFC) timescale and evaluated the reasonable maximum capacity of the LFC provided by V2G. As a case study, we assumed that the Japanese power system would be used under various VRE penetration scenarios and considered the limited availability time of V2G, based on the daily commuter cycle. The power system operation was modeled by considering pumped storage, interconnection lines, and thermal power–partial load operations. The results show that the marginal value of V2G was greater during the daytime than overnight, and the maximum cost saving (USD 705.6/EV/year) occurred during the daytime under the high-VRE scenario. Improving the value and size of V2G ancillary services required coordination with energy storage and excess VRE generation.

Error analysis of the Crank–Nicolson SAV method for the Allen–Cahn equation on variable grids

The variable time-stepping technique is powerful in capturing the multi-scale behaviors (e.g., the solution changes rapidly in certain regions of time) for the Allen–Cahn equation. Based on the scalar auxiliary variable (SAV) approach and the Crank–Nicolson schemes, we establish the unconditional energy stability and error estimates rigorously for the Allen–Cahn equation on variable grids. A numerical experiment is performed to verify the theoretical results. To the best of our knowledge, this is the first topic on the convergence analysis for the SAV schemes on variable grids.