New fast arctangent approximation algorithm for generic real-time embedded applications

Fast and accurate arctangent approximations are used in several contemporary applications, including embedded systems, signal processing, radar, and power systems. Three main approximation techniques are well-established in the literature, varying in their accuracy and resource utilization levels. Those are the iterative coordinate rotational digital computer (CORDIC), the lookup tables (LUTs)-based, and the rational formulae techniques. This paper presents a novel technique that combines the advantages of both rational formulae and LUT approximation methods. The new algorithm exploits the pseudo-linear region around the tangent function zero point to estimate a reduced input arctangent through a modified rational approximation before referring this estimate to its original value using miniature LUTs. A new 2nd order rational approximation formula is introduced for the first time in this work and benchmarked against existing alternatives as it improves the new algorithm performance. The eZDSP-F28335 platform has been used for practical implementation and results validation of the proposed technique. The contributions of this work are summarized as follows: (1) introducing a new approximation algorithm with high precision and application-based flexibility; (2) introducing a new rational approximation formula that outperforms literature alternatives with the algorithm at higher accuracy requirement; and (3) presenting a practical evaluation index for rational approximations in the literature. - 2019 by the authors. Licensee MDPI, Basel, Switzerland.Funding: The publication of this article was funded by the Qatar National Library.Scopu

Reservoir stress path and induced seismic anisotropy: Results from linking coupled fluid-flow/geomechanical simulation with seismic modelling

We present a workflow linking coupled fluid-flow and geomechanical simulation with seismic modelling to predict seismic anisotropy induced by nonhydrostatic stress changes. We generate seismic models from coupled simulations to examine the relationship between reservoir geometry, stress path and seismic anisotropy. The results indicate that geometry influences the evolution of stress, which leads to stress-induced seismic anisotropy. Although stress anisotropy is high for the small reservoir, the effect of stress arching and the ability of the side-burden to support the excess load limit the overall change in effective stress and hence seismic anisotropy. For the extensive reservoir, stress anisotropy and induced seismic anisotropy are high. The extensive and elongate reservoirs experience significant compaction, where the inefficiency of the developed stress arching in the side-burden cannot support the excess load. The elongate reservoir displays significant stress asymmetry, with seismic anisotropy developing predominantly along the long-edge of the reservoir. We show that the link between stress path parameters and seismic anisotropy is complex, where the anisotropic symmetry is controlled not only by model geometry but also the nonlinear rock physics model used. Nevertheless, a workflow has been developed to model seismic anisotropy induced by non-hydrostatic stress changes, allowing field observations of anisotropy to be linked with geomechanical models

High-gain DC-DC converters for high-power PV applications: Performance assessment

Conventional non-isolated DC-DC converters provide limited practical gains at high duty cycles due to their parasitic losses. Such trend is not suitable for renewables grid integration due to the high required gain, while isolated DC-DC converters utilize costly and lossy high-frequency transformers with limited power capability. Alternatively, connecting conventional DC-DC converters in different combinations can provide higher gains, up to MVDC levels in PV applications, while maintaining adequate efficiency margin through design optimizations. This paper addresses cascaded and/or series connection of DC-DC converter modules as a solution to the high gain requirement, and provides a performance assessment based on Cuk and Single-Ended Primary Inductor Converter (SEPIC) topologies. Theoretical analyses are performed, and their trends are experimentally-verified by lab-scale prototypes. � 2018 IEEE.Scopu

Robust Sliding Mode Controller Design for DC-DC Converters with Adaptive Gains

Conventional DC-DC converters are an industry standard in several fields such as in solar PV applications for maximum energy extraction. However, the inherent non-linearity in these conventional types (e.g., boost, buck and buck-boost) makes it necessary to develop robust control techniques that can maintain the desired system operation in the presence of system disturbances. Variable Space Structure (VSS) controllers are convenient for such systems as their switching nature matches the DC-DC converters operational principle, and the Sliding Mode Control (SMC) mechanism may be employed in this context. This paper proposes an adaptive SMC method for the fourth order SEPIC converter, based on altering the sliding surface dynamics to continuously adjust the gains and drive the system to slide along an adaptive sliding surface to achieve stable converter operation. The mathematical model of the fourth order SEPIC is derived and the proposed adaptive SMC approach is simulated in MATLAB/Simulink. It is shown that one can achieve enhanced performance compared to the conventional SMC methods in the presence of system disturbances. The same methodology employed to SEPIC can also be expanded to other converters.Scopu

Assessment of isolated and non-isolated DC-DC converters for medium-voltage PV applications

The potential of Photovoltaic (PV) panels as a main tool of harnessing solar energy is increasing with the advancements in their power conditioning and conversion stages that vary based on applications. This paper focuses on the conversion of a 22kW PV array output from low-voltage to medium-voltage level (400V to 7kV). This high voltage conversion ratio is difficult to achieve using conventional single-stage DC-DC converters. Thus, different alternatives are proposed and compared here, namely, the Parallel-Input Series-Output (PISO) connection of two different stages using both isolated (full-bridge) and non-isolated DC-DC converters. The converters are compared on the basis of efficiency, footprint, components rating and reliability. Thus, the isolated DC-DC converter system efficiency was estimated at 797%, compared to 93 % for the non-isolated system, keeping into account the variations in terms of the filtering capacitor requirements to maintain a constant minimal voltage ripple at the output which is in favor of the non-isolated systems. ? 2017 IEEE.ACKNOWLEDGMENT This publication was made possible by the National Priority Research Program (NPRP) award [NPRP6-244-2-103] from the Qatar National Research Fund (QNRF); a member of the Qatar Foundation. Its contents are solely the responsibility of the authors and do not necessarily represent the official views of QNRF

Development of innovative indoor/outdoor air quality monitoring for environmental impact assessment in the State of Qatar

Air pollution is one of the most crucial factors affecting the quality of life and health of increasingly urban populations; a country with a fast-growing economy based on hydrocarbons such as Qatar is no exception. In addition to the adverse impact of air pollution on humans, animals and plants, the presence of dust and air-borne particulate matter affect negatively the efficiency of solar panels used for power generation. In this project, a comprehensive wireless solution is proposed for monitoring and measuring the levels of some known harmful gases such as CO2, NO2 and CH4 as well as other environmental parameters such as dust, temperature, humidity, solar irradiance, pressure, wind-direction and wind speed. Data is collected by appropriate sensor nodes (NI-WSN) that communicate wirelessly (using IEEE 802.15.4 protocol) with a host computer (Gateway) that receives, processes, stores and displays the collected information via LabVIEW environment, which represents the software part of the project (Programming and GUI Design). The data processing part includes analysing the environmental parameter levels, which is later used to study the efficiency of using solar panels in Qatar. The complete system has been implemented and successfully tested in a chosen site within Qatar University Campus. In the long term, we hope that the data collected from our air quality monitoring system will help in areas of research related to environmental monitoring and developing systems that correlate indoor and outdoor readings to the operation of an indoor HVAC system.Scopu

Combining the modified discrete element method with the virtual element method for fracturing of porous media

Simulation of fracturing processes in porous rocks can be divided into two main branches: (i) modeling the rock as a continuum enhanced with special features to account for fractures or (ii) modeling the rock by a discrete (or discontinuous) approach that describes the material directly as a collection of separate blocks or particles, e.g., as in the discrete element method (DEM). In the modified discrete element (MDEM) method, the effective forces between virtual particles are modified so that they reproduce the discretization of a first-order finite element method (FEM) for linear elasticity. This provides an expression of the virtual forces in terms of general Hook’s macro-parameters. Previously, MDEM has been formulated through an analogy with linear elements for FEM. We show the connection between MDEM and the virtual element method (VEM), which is a generalization of FEM to polyhedral grids. Unlike standard FEM, which computes strain-states in a reference space, MDEM and VEM compute stress-states directly in real space. This connection leads us to a new derivation of the MDEM method. Moreover, it enables a direct coupling between (M)DEM and domains modeled by a grid made of polyhedral cells. Thus, this approach makes it possible to combine fine-scale (M)DEM behavior near the fracturing region with linear elasticity on complex reservoir grids in the far-field region without regridding. To demonstrate the simulation of hydraulic fracturing, the coupled (M)DEM-VEM method is implemented using the Matlab Reservoir Simulation Toolbox (MRST) and linked to an industry-standard reservoir simulator. Similar approaches have been presented previously using standard FEM, but due to the similarities in the approaches of VEM and MDEM, our work provides a more uniform approach and extends these previous works to general polyhedral grids for the non-fracturing domain.acceptedVersio

Distance-Independent Contactless Interrogation of Quartz Resonator Sensor with Printed-on-Crystal Coil

A novel quartz crystal resonator sensor, which embeds a conductive printed planar coil that enables electromagnetic contactless interrogation techniques is presented. An aerosol-jet process is used to precisely and accurately deposit electronic inks onto a 330 µm-thick bare piezoelectric quartz crystal to print the planar coil and the electrodes. The proposed interrogation technique enables distance-independent operation, and is based on the measurement of the reflected impedance of the quartz resonator sensor through the planar primary coil of the coupled inductors. The resonant frequency, measured without contact using the primary coil connected to an impedance analyzer, results 4.790260 MHz. Contactless operation distances up to 12.2 mm have been obtained. The experimental results have a maximum deviation of about 50 Hz, i.e. 10.5 ppm, with respect to reference measurements taken via contact probes