Search results for "Grid"

Theoretical and Experimental Comparison of Total Harmonic Distortion Factors for the Evaluation of Harmonic and Interharmonic Pollution of Grid-Conne…

2006

Grid connected photovoltaic systems are increasingly used in electrical distribution systems. However, they inject distorted currents. Therefore special attention must be paid to harmonic and interharmonic measurements. The new edition of IEC 61000-4-7 introduces the concept of harmonic and interharmonic groups, which implies new expressions for Total Harmonic Distortion factors. In the paper a theoretical and experimental comparison is made between the different total harmonic distortion factors in order to show which of the currently defined distortion factors is best-suited to detect harmonic and interharmonic pollution. Experimental tests were carried out first by means of a calibrator …

Comparison of two different approaches for harmonic distortion sources assessment

2021

The paper focuses the attention on the comparison of two approaches for power quality assessment in the electric grid. Both approaches are suitable for investigating the harmonic pollution source and discovering if the harmonic source comes from the customer or the utility grid. The two approaches have the same purpose but they are deeply different. The first approach is based on the knowledge of the customer and utility equivalent impedance while the second is based on single point measurement at point of common coupling PCC. In this paper, the advantages and drawbacks of the two approaches are investigated also supported by a case study.

Mixed Harmonic Elimination Control for a Single-Phase 9 Level Grid-Connected Inverter

2018

The power quality requirements are increasingly stringent, due to the continuous growth of devices connected to the grid that introduce harmonics. These devices include DC to AC energy conversion systems, i.e. grid connected inverters. The design, control and operation of these systems must take into account the rules of interconnection to the electricity grid. To improve the quality of the output waveform of the grid-connected inverter, Multilevel Converters (MC) with selective harmonic elimination modulation technique can be used. This paper presents a single-phase nine level grid-connected inverter with DC/DC input stages. The obtained switching angles for THD minimization are independen…

Load Demand Analysis of Nordic Rural Area with Holiday Resorts for Network Capacity Planning

2019

Most of the Nordic holiday resorts are in rural area with low capacity distributed network. The rural area network is weak and needs capacity expansion planning as the load demand of this area are going to increase due to penetration of electric vehicles and heat pumps. Such type of rural network can also be operated as a micro-grid, and therefore load analysis is required for appropriate operation. The load analysis will also be useful for finding proper sizing of distributed energy resources including energy storage. In this work, load demand analysis of a typical Nordic holiday resorts, connected in rural grid, is presented to find out the load variation during the usage periods. The loa…

Vertical grid refinement for stratocumulus clouds in the radiation scheme of a global climate model

2021

Abstract. In this study, we implement a vertical grid refinement scheme in the radiation routine of the global aerosol-climate model ECHAM-HAM, aiming to improve the representation of stratocumulus clouds and address the underestimation of their cloud cover. The scheme is based on a reconstruction of the temperature inversion as a physical constraint for the cloud top. On the refined grid, the boundary layer and the free troposphere are separated and the cloud's layer is made thinner. The cloud cover is re-calculated either by conserving the cloud volume (SC-VOLUME) or by using the Sundqvist cloud cover routine on the new grid representation (SC-SUND). In global climate simulations, we find…

2021

Abstract. In this study, we implement a vertical grid refinement scheme in the radiation routine of the global aerosol–climate model ECHAM-HAM, aiming to improve the representation of stratocumulus clouds and address the underestimation of their cloud cover. The scheme is based on a reconstruction of the temperature inversion as a physical constraint for the cloud top. On the refined grid, the boundary layer and the free troposphere are separated and the cloud's layer is made thinner. The cloud cover is recalculated either by conserving the cloud volume (SC-VOLUME) or by using the Sundqvist cloud cover routine on the new grid representation (SC-SUND). In global climate simulations, we find …

Effects of model configuration for superparametrised long-term simulations – Implementation of a cloud resolving model in EMAC (v2.50)

2019

Abstract. A new module has been implemented in the ECHAM5/MESSy Atmospheric Chemistry (EMAC) Model that simulates cloud related processes on a much smaller grid. This so called superparametrisation acts as a replacement for the convection parametrisation and large-scale cloud scheme. The concept of embedding an ensemble of cloud resolving models (CRMs) inside of each grid box of a general circulation model leads to an explicit representation of cloud dynamics. The new model component is evaluated against observations and the conventional usage of EMAC using a convection parametrisation. In particular, effects of applying different configurations of the superparametrisation are analyzed in a…

Pervasive access to MRI bias artifact suppression service on a grid.

2009

Bias artifact corrupts magnetic resonance images in such a way that the image is afflicted by illumination variations. Some of the authors proposed the Exponential Entropy Driven - Homomorphic Unsharp Masking (E2D-HUM) algorithm that corrects this artifact without any a priori hypothesis about the tissues or the Magnetic Resonance image modality. Moreover, E2D-HUM does not care about the body part under examination and does not require any particular training task. People who want to use this algorithm, which is Matlab-based, have to set their own computers in order to execute it. Furthermore, they have to be Matlab-skilled to exploit all the features of the algorithm. In our work we propos…

Global Understanding Environment: Towards Self-managed Web of Everything

2012

Current Web grows rapidly to several directions (from the Web of Documents to the Webs of Humans, Things, Services, Knowledge, Intelligence, etc.). Consequently the recent and future Web-based applications, systems and frameworks (like, e.g., Social and Ubiquitous Computing, SOA and Cloud Computing, etc.) should take into account challenges related to extremely high heterogeneity of components and exponentially increased complexity of a business logic connecting and making them interoperable. Enabling self-management enhanced with semantic technology seems to be an only option to handle that. We suggest adding a "virtual representative" to every resource in the Web to solve the global inter…

Splines Computation by Subdivision

2015

In this chapter, fast stable algorithms are presented, which compute splines’ values at dyadic and triadic rational points starting from their samples at integer grid points. The algorithms are implemented by the causal-anticausal recursive filtering of initial data samples, which is followed by iterated application of FIR filters. Extension of the algorithms to the multidimensional case is straightforward. A natural application of the presented subdivision algorithms is for upsampling of signals and images. A few upsampling examples are provided.