Modeling MMC Energy Dynamics in Offshore HVDC Systems Using OpenModelica

Mengden installert havvind har steget kraftig de siste 10 årene. Med fortsatt vekst vil havvind gi betydelig bidrag til at vi kan nå internasjonale klimamål om ren, fornybar energi. Som følge av maritim plassplanlegging og høyere vindhastigheter bygges havvind lengre og lengre fra kysten. Store avstander stiller krav til systemene for krafttransport til land. For å oppnå effektiv krafttransport benyttes derfor høyspent likestrøm (HVDC) systemer i kombinasjon med modulære flernivå omformere, såkalte MMC-topologier. For å forstå hvordan disse komplekse systemene påvirkes av ulike variabler, er nøyaktige simuleringer uhyre viktig. Slike analyser krever bruk av spesialiserte dataprogrammer, som gir mulighet for detaljert modellering av systemets dynamiske egenskaper. I denne avhandlingen er OpenModelica, som er en åpen-kildekode programvare blitt benyttet for å simulere effektdynamikk knyttet til MMC’ene i et HVDC system. Det blir demonstrert at OpenModelica er et velgenet verktøy for slike studier, gjennom tester av to avgjørende egenskaper ved programvaren. Det første omhandler programvarens evne til å presist simulere system preget av relativt høyfrekvent dynamikk. For å oppnå dette ble en to-nivå omformer med en bryterfrekvens på 10 kHz simulert i OpenModelica. Den produserte dynamikken ble sammenlignet med data fra tilsvarende analyser med den veletablerte programvaren MATLAB Simulink. Det viste seg at dynamikken produsert i OpenModelica var meget lik den observert i MATLAB Simulink. OpenModelicas pålitelighet og robusthet i slike analyser ble også undersøkt. Den andre vesentlige egenskapen ved OpenModelica som ble undersøkt, var i hvilken grad modeller utviklet i programvaren lot seg integrere i systemer simulert av sanntidsstimulatorer. For å demonstrere dette ble to modeller utviklet i OpenModelica integrert i system simulert ved simuleringsystemet OP5700 ved bruk av sanntidsimulatoren ePHASORsim. I avhandlingen gis en nøyaktig beskrivelse av hvordan slik integrering kan oppnås. Ved å bruke OpenModelica er der undersøkt hvordan MMCens energilagringsevne kan forbedre effektdynamikken i et HVDC system. Denne undersøkelsen ble gjort ved å studere to scenario som var særlig forskjellig i varighet og energikrav. Ved å velge scenario på en slik måte ble det forsøk å demonstrere hvilke egenskaper som preger MMCen for å legge et beslutningsgrunnlag for hva denne energien bør brukes til. Det første scenariet undersøker MMCens evne til å utjevne effektvariasjoner som følge av turbinakselerasjon når vindhastigheten overstiger nominell verdi. Her vises det at påvirkningen av MMCen kan ignoreres for de fleste dynamikker, men at den relative påvirkningen øker jo kortere effektutslagene er, og at varigheten helst begrenses til to sekunder. I det andre scenariet ble det forsøkt å redusere responstiden til et HVDC system ved et steg i effektreferansen ved bruk av energien lagret i en MMC. Det ble vist at responstiden kunne reduseres med en faktor 32 ned til et par millisekund. Disse karakteristikkene demonstrerer at MMCens energilagringskapasitet best benyttes til å jevne ut effektvariasjoner hvis varighet spenner fra millisekund til 2 sekund. Videre ble det undersøkt om koblingen mellom DC-spenningen og energien lagret i omformeren kan reduseres ved bruk av et feed-forward signal. Det ble vist at utvidelsen av regulatoren til å inkludere et slikt singal reduserte stegresponstiden med en faktor 3 og at oscillasjoner nærmest forsvant helt for både DC-spenningen og MMC-energien. Med håp om felles akademisk fremgang uten sosioøkonomiske grenser har alle modeller utviklet i denne avhandlingen blitt gjort tilgjengelig for alle [1].Our need for clean, renewable energy causes offshore wind to constitute an increasing fraction of our energy mix. Due to considerations of maritime spatial planning and higher wind speeds, the distance to shore increases. This makes modular multilevel converter (MMC) based HVDC systems the superior transmission choice. Because these transmission systems are often large and complex, analyses of the dynamics characterizing them are necessary. Such analyses must be conducted by the use of specialized software that can reproduce the system behavior with sufficient precision. This thesis uses the open source OpenModelica tool to investigate the power dynamics related to the MMC in offshore HVDC systems. The thesis also demonstrates the suitability of the software for such purposes in two regards. Firstly, it is shown that the software can accurately model systems that are characterized by relatively high-frequency dynamics. This is done by modeling a 10kHz two-level voltage source converter (2L-VSC) in OpenModelica and a benchmark software, MATLAB Simulink. The comparison showed that OpenModelica accurately captured all dynamics of interest as well as provide insight into its trustworthiness and computational resilience. Secondly, it is demonstrated that models developed in OpenModelica can be integrated into systems which are modeled using real-time simulation software (ePHASORsim) and real-time simulation hardware (OP5700). How this integration must be executed is described in this thesis. Using OpenModelica, the thesis aims to investigate how the energy storage capability of the MMC can improve the power dynamics of an HVDC system. This is investigated in two scenarios that differ in duration and energy requirement. In doing so, it is attempted to demonstrate the characteristics of the MMC’s storage capability, which might provide guidelines for determining how this energy should be appropriately used. The first scenario studies the MMC’s impact on turbine dynamics caused by wind speed fluctuations around the turbines rated wind speed. It is attempted to smoothen out power fluctuations that arise from the acceleration and deceleration of the turbine rotor upon crossing the rated wind speed. It is demonstrated that the improving impact of the MMC in this regard is almost always negligible, but that the relative impact improves with fluctuation brevity, ideally lasting no longer than two seconds. In the second scenario, it is attempted to reduce the response time of the HVDC system to a step in power reference by utilizing the stored MMC energy. Here, it is shown that the response time is reduced (by a factor of 32) down to a couple of milliseconds. These characteristics demonstrate that the MMC’s energy storage capability is best used to counteract power fluctuations in the range of milliseconds to two seconds when the magnitude of the variations are in percent of the rated MMC power. Moreover, because of the coupling between the stored energy in the converter and the DC voltage, a controller is developed to reduce this coupling by using a feed-forward term in the voltage controller. It is showed that when this control is implemented, the step response time of both the DC voltage and the zero-sequence energy sum is reduced by a factor 3 and that oscillations are almost perfectly removed. In the spirit of joint academic and industrial progress without socioeconomic borders, all models developed in this thesis have been made publicly available [1]

The Zoonotic Potential of Chronic Wasting Disease—A Review

Prion diseases are transmissible neurodegenerative disorders that affect humans and ruminant species consumed by humans. Ruminant prion diseases include bovine spongiform encephalopathy (BSE) in cattle, scrapie in sheep and goats and chronic wasting disease (CWD) in cervids. In 1996, prions causing BSE were identified as the cause of a new prion disease in humans; variant Creutzfeldt-Jakob disease (vCJD). This sparked a food safety crisis and unprecedented protective measures to reduce human exposure to livestock prions. CWD continues to spread in North America, and now affects free-ranging and/or farmed cervids in 30 US states and four Canadian provinces. The recent discovery in Europe of previously unrecognized CWD strains has further heightened concerns about CWD as a food pathogen. The escalating CWD prevalence in enzootic areas and its appearance in a new species (reindeer) and new geographical locations, increase human exposure and the risk of CWD strain adaptation to humans. No cases of human prion disease caused by CWD have been recorded, and most experimental data suggest that the zoonotic risk of CWD is very low. However, the understanding of these diseases is still incomplete (e.g., origin, transmission properties and ecology), suggesting that precautionary measures should be implemented to minimize human exposure.publishedVersio

Narrative insight in psychosis: the relationship with spiritual and religious explanatory frameworks

Objective: When considering psychosis, the concept of narrative insight has been offered as an alternative to clinical insight in determining individuals’ responses to their difficulties, as it allows for a more holistic and person-centred framework to be embraced within professional practice. This study aims to explore the validity of the narrative insight construct within a group of people who have experienced psychosis. Design: Inductive qualitative methods were used to explore how eight participants utilized spiritual or religious explanatory frameworks for their experiences of psychosis and to consider these in relation to the construct of narrative insight. Methods: Semi-structured interviews were undertaken with individuals who identified themselves as interested in spiritual or religious ideas and whose self-reported experiences which were identified as akin to psychosis by experienced academic clinicians. Transcriptions from these interviews were subject to interpretative phenomenological analysis within a broader research question; a selection of themes and data from the resultant phenomenological structure are explored here for their relevance to narrative insight. Results: Participants discussed spiritual and biological explanations for their experiences and were able to hold alternative potential explanations alongside each other. They were reflective regarding the origins of their explanations and would describe a process of testing and proof in relation to them. Conclusions: These findings suggest that the narrative insight construct has the potential to be a valid approach to understanding experiences of psychosis, and challenge the dominance of the clinical insight construct within clinical practice

The Treatment of Hallucinations in Schizophrenia Spectrum Disorders

This article reviews the treatment of hallucinations in schizophrenia. The first treatment option for hallucinations in schizophrenia is antipsychotic medication, which can induce a rapid decrease in severity. Only 8% of first-episode patients still experience mild to moderate hallucinations after continuing medication for 1 year. Olanzapine, amisulpride, ziprasidone, and quetiapine are equally effective against hallucinations, but haloperidol may be slightly inferior. If the drug of first choice provides inadequate improvement, it is probably best to switch medication after 2-4 weeks of treatment. Clozapine is the drug of choice for patients who are resistant to 2 antipsychotic agents. Blood levels should be above 350-450 mu g/ml for maximal effect. For relapse prevention, medication should be continued in the same dose. Depot medication should be considered for all patients because nonadherence is high. Cognitive-behavioral therapy (CBT) can be applied as an augmentation to antipsychotic medication. The success of CBT depends on the reduction of catastrophic appraisals, thereby reducing the concurrent anxiety and distress. CBT aims at reducing the emotional distress associated with auditory hallucinations and develops new coping strategies. Transcranial magnetic stimulation (TMS) is capable of reducing the frequency and severity of auditory hallucinations. Several meta-analyses found significantly better symptom reduction for low-frequency repetitive TMS as compared with placebo. Consequently, TMS currently has the status of a potentially useful treatment method for auditory hallucinations, but only in combination with state of the art antipsychotic treatment. Electroconvulsive therapy (ECT) is considered a last resort for treatment-resistant psychosis. Although several studies showed clinical improvement, a specific reduction in hallucination severity has never been demonstrated

Lessons learned and lingering uncertainties after seven years of chronic wasting disease management in Norway

Chronic wasting disease (CWD) is well known among cervids in North America. Nevertheless, management faced different types and degrees of uncertainty when CWD was first detected in reindeer Rangifer tarandus in Nordfjella, Norway in 2016. We present a timeline of the efforts to control CWD, and identify how the process, measurement, environmental, and implementation uncertainties developed from the onset (2016) to the current situation (2023) after seven years of CWD management. In the ‘acute’ phase (2016–2019), political ambitions were high and depopulation of the Nordfjella reindeer area involving marksmen aimed at eradicating CWD. Subsequently, increased surveillance and increased male harvest was used to enable early detection or to achieve ‘freedom-from-CWD’ status of the adjacent populations. The second phase (2020-now) came when cases were detected in the large reindeer population in Hardangervidda. Management authorities postponed culling using marksmen, signifying an important change, with more emphasis on socio-political acceptance and consideration of the negative long-term consequences of conflicts with local stakeholders. The subsequent dialogue processes between scientists and local management ended in joint advice. However, the Ministry set aside all advice in 2022, halting further actions, after pressure and negative media attention. During this period, there was no clear research plan to increase knowledge of CWD to reduce process uncertainty; however, large surveillance investments were made to reduce measurement uncertainty. Despite this, detecting and estimating CWD among reindeer at low prevalence remains a key challenge. Governance challenges have emerged as significant implementation uncertainties, partly due to the uncertain occurrence of CWD. management uncertainty, prion diseases, prion protein gene (PRNP), prion strains, reindeerpublishedVersio

Systematic assessment of training-induced changes in corticospinal output to hand using frameless stereotaxic transcranial magnetic stimulation.

Measuring changes in the characteristics of corticospinal output has become a critical part of assessing the impact of motor experience on cortical organization in both the intact and injured human brain. In this protocol we describe a method for systematically assessing training-induced changes in corticospinal output that integrates volumetric anatomical MRI with transcranial magnetic stimulation (TMS). A TMS coil is sited to a target grid superimposed onto a 3D MRI of cortex using a stereotaxic neuronavigation system. Subjects are then required to exercise the first dorsal interosseus (FDI) muscle on two different tasks for a total of 30 min. The protocol allows for reliably and repeatedly detecting changes in corticospinal output to FDI muscle in response to brief periods of motor training

Genetic Predictions of Prion Disease Susceptibility in Carnivore Species Based on Variability of the Prion Gene Coding Region

Mammalian species vary widely in their apparent susceptibility to prion diseases. For example, several felid species developed prion disease (feline spongiform encephalopathy or FSE) during the bovine spongiform encephalopathy (BSE) epidemic in the United Kingdom, whereas no canine BSE cases were detected. Whether either of these or other groups of carnivore species can contract other prion diseases (e.g. chronic wasting disease or CWD) remains an open question. Variation in the host-encoded prion protein (PrP(C)) largely explains observed disease susceptibility patterns within ruminant species, and may explain interspecies differences in susceptibility as well. We sequenced and compared the open reading frame of the PRNP gene encoding PrP(C) protein from 609 animal samples comprising 29 species from 22 genera of the Order Carnivora; amongst these samples were 15 FSE cases. Our analysis revealed that FSE cases did not encode an identifiable disease-associated PrP polymorphism. However, all canid PrPs contained aspartic acid or glutamic acid at codon 163 which we propose provides a genetic basis for observed susceptibility differences between canids and felids. Among other carnivores studied, wolverine (Gulo gulo) and pine marten (Martes martes) were the only non-canid species to also express PrP-Asp163, which may impact on their prion diseases susceptibility. Populations of black bear (Ursus americanus) and mountain lion (Puma concolor) from Colorado showed little genetic variation in the PrP protein and no variants likely to be highly resistant to prions in general, suggesting that strain differences between BSE and CWD prions also may contribute to the limited apparent host range of the latter

Assessment of risk of introduction of Echinococcus multilocularis to mainland Norway

Source at https://vkm.no/In the light of the recent findings of the tapeworm Echinococcus multilocularis (EM) in four red foxes from three different locations in Sweden, the Norwegian Scientific Committee for Food Safety (Vitenskapskomiteen; VKM), Panel of Biological Hazards (Faggruppe hygiene og smittestoffer) took the initiative to undertake a risk assessment regarding the probability of this parasite being introduced to mainland Norway and thus becoming a threat to public health in the country.Med bakgrunn i funnet av bendelorm Echinococcus multilocularis (EM) i fire rødrev fra tre forskjellige steder i Sverige, har VKM ved Faggruppe hygiene og smittestoffer tatt initiativ til å foreta en vurdering av sannsynligheten for at EM kan bli introdusert til fastlands Norge og sannsynligheten for at mennesker i så fall også kan bli smittet

CWD – update statement. Opinion of the Panel on Biological Hazards of the Norwegian Scientific Committee for Food Safety

publishedVersio