From grid following to grid forming : modeling, control and applications to inverter-based resources

Electrical power generation is drastically shifting from centralized power generation to decentralized distributed power generation as a result of the rising integration of renewable energy sources into the electrical grid. The primary challenge in this transition is replacing synchronous generators (SGs) with inverter-interfaced renewable generations. When there are one or more synchronous generators in the system, grid-connected inverters follow the voltage and frequency reference generated by the synchronous generator and act as a controlled current source to supply necessary quantity of active and reactive power. In the presence of one or more stiff voltage sources, such inverter operation has recently been labeled as ‘Grid-Following’ (GFL) mode of operation. If all synchronous machines are taken out of service, there will not be any voltage reference, rendering grid-following inverter operation infeasible. Hence, the way that the GFL inverters are controlled today results in the inability of the grid to operate 100% inverter-based resources (IBR). Therefore, in the absence of a synchronous generation as a stiff voltage source, the frequency and voltage of the grid must be controlled by some of the inverters. These inverters, referred to as "Grid-Forming" (GFM) inverters, are tasked with supporting a stable voltage and frequency in a variety of situations, including the connection or disconnection of a load or a generator, or the occurrence of a power system fault. Grid-forming inverters (GFMIs) will have a crucial role with the increase in renewable penetration during the coming years. This thesis aims to study the modeling approach and control technique of a GFM inverter in an islanded grid. The droop-based control of a GFL inverter is also studied and compared to that of a GFM inverter to understand the fundamental difference in their operation. As GFM inverters will gradually replace synchronous generators, GFM inverters are expected to behave very similarly to synchronous generators in a grid without a utility connection. Hence, the voltage balancing and short circuit behavior of GFM inverters are further compared to that of synchronous generators. Additional controller modifications are also proposed for the enhanced performance of the GFM inverter. Finally, GFM inverter-based virtually islanded Hybrid AC-DC microgrid architecture is proposed for the power distribution of future residential buildings.Electrical and Computer Engineerin

Leigh syndrome in an infant: autopsy and histopathology findings

Leigh syndrome is an inherited neurodegenerative disorder of infancy that typically manifests between 3 and 12 months of age. The common neurological manifestations are developmental delay or regression, progressive cognitive decline, dystonia, ataxia, brainstem dysfunction, epileptic seizures, and respiratory dysfunction. Although the disorder is clinically and genetically heterogeneous, the histopathological and radiological features characteristically show focal and bilaterally symmetrical, necrotic lesions in the basal ganglia and brainstem. The syndrome has a characteristic histopathological signature that helps in clinching the diagnosis. We discuss these unique findings on autopsy and radiology in a young infant who succumbed to a subacute, progressive neurological illness suggestive of Leigh syndrome. Our case highlights that Leigh syndrome should be considered in the differential diagnosis of infantile-onset, subacute neuroregression with dystonia and seizures, a high anion gap metabolic acidosis, normal ketones, elevated lactates in blood, brain, and urine, and bilateral basal ganglia involvement

Pharmacological and toxicological investigations of etodolac loaded gum katira microspheres prepared by W1/O/W2 emulsion solvent evaporation technique in rats

<div><p>ABSTRACT Etodolac is a non-steroidal anti-inflammatory drug (NSAID) and approved by USFDA as a COX2 inhibitor. Although etodolac therapy provides clinical benefits, it is associated with upper gastrointestinal (GI) tract complications also. Etodolac loaded gum Katira microsphere (ELGKM) was prepared by W1/O/W2 emulsion solvent evaporation technique. The gastric irritation properties of orally administered pure etodolac, ELGKM and blank microspheres (without etodolac) were evaluated in experimental rats treated for 6 days. The stomach examination and biochemical investigation of stomach tissue of treated rats indicated that ELGKM formulation remarkably reduced ulcerogenecity as compared to pure etodolac. The anti-inflammatory activities of pure etodolac and ELGKMs were ascertained by the implantation of cotton pellets in rats for 6 days. Based on the results, ELGKMs showed significant anti-inflammatory activities (P<0.01) as compared to control group. The cotton pellets test suggested that ELGKM formulation retained more anti-inflammatory properties among the groups. The hematological changes, biochemical analysis and histopathological studies of subacute toxicity in rats revealed that ELGKM were the effective sustained release formulation in the treatment of chronic pain and inflammation. In conclusion, the physicochemical characterization, pharmacological and toxicological studies suggest that ELGKMs may represent as a potential candidate for sustained drug delivery (10-12 hours) in chronic joint pain related diseases with remarkably diminished gastrointestinal side effects.</p></div