| 1. |
- Ehnberg, Jimmy, 1976, et al.
(författare)
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CONTINUOUS ASSESSMENT IN ELECTRICAL POWER ENGINEERING FOR MARINE ENGINEERS
- 2023
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Ingår i: SEFI 2023 - 51st Annual Conference of the European Society for Engineering Education: Engineering Education for Sustainability, Proceedings. ; , s. 1992-2000
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Konferensbidrag (refereegranskat)abstract
- To tackle the climate challenge, all sectors need to contribute, including electrified shipping. Electrified shipping is not only propulsion but also loading and unloading equipment. This transformation requires increased skills and understanding of electric power engineering for the personal onboard, not least for the marine engineers. Therefore, a changed in the curriculum was needed. However, when more theoretical course content was added to two consecutive courses, the student view and passing rate dropped. Although the student view improved quickly, the passing rate recovered slower. To address this issue, continuous assessment was introduced to counteract the drops. The aim of this study was to evaluate the theoretical parts and determine if continuous assessment could contribute to improve student learning and increase passing rate. The students expressed satisfaction with the changes, and the passing rate has increased. Most students also claimed that they learned more compared to standard assessment methods.
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| 2. |
- Ehnberg, Jimmy, 1976, et al.
(författare)
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Introducing Ethics by IEEE Code of Ethics in International Electrical Power Engineering Education
- 2022
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Ingår i: Proceedings of the 2022 31st Annual Conference of the European Association for Education in Electrical and Information Engineering, EAEEIE 2022.
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Konferensbidrag (refereegranskat)abstract
- Ethical awareness has generally increased in the society and specifically for engineers. The examples of where it went wrong, or where ethical dilemmas occur, have been more frequent in the later years. To be able to prepare future engineers in their future carriers, the subject needs to be integrated in university studies. This is hard to do because not all students see the importance for them, seeming instead to rely on technology itself to present solutions. The aim of our study was to introduce the use of the IEEE code of ethics as a relevant tool for students at an international master's program, for their future career as electric power engineers, but also to let students focus on discussion rather than listening to us teachers. The method was tested at the master program mandatory project course, with 45, 50 and 25 students in the academic year 19/20 (on-campus), 20/21 (online) and 21/22 (pre-recorded). Results showed that most of the students found the IEEE code of ethics relevant for their project and for their future career. A difference could be seen between students with a bachelor's degree from Chalmers University of Technology and those from another university, but there was improvement for both groups. The main contribution of the paper is a method to introduce ethics in electric power engineering education that can be found relevant to students and teachers with a background in electric power engineering. All the three approaches of the method showed a similar outcome which makes it possible to use the method as an effective mean to teach ethics for future electric power engineers.
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| 3. |
- Ehnberg, Jimmy, 1976, et al.
(författare)
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Master Program Curriculum in Electric Power Systems, University in Gobal South vs University in Global North
- 2024
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Ingår i: IEEE Global Engineering Education Conference, EDUCON. - 2165-9567 .- 2165-9559.
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Konferensbidrag (refereegranskat)abstract
- Renewable energy integration, electric vehicles, grid modernization, and energy security are becoming increasingly important for societies worldwide. Well-educated electric power system engineers are essential to make this happen. This comparison involves two master's programs in two different regions: the Global South and Global North. Both programs are two-year master's programs based on a series of courses in electric power systems and supporting subjects. Individual and contextual strengths and weaknesses for each program are highlighted, compared, and discussed, including the importance of adapting the programs to local contexts while addressing global challenges in power systems. However, considering the global labor market and the uncertain future, and recognizing that engineers should be professionals for several decades, the programs should not be overly tied to the local context. In conclusion, recommendations for improvement are provided for both programs based on the strengths of the other program and their shared weaknesses. For example, the Global South program should enhance specialization and collaborate more with the industry, while the Global North program should promote interaction with other programs, include more aspects related to societal impact, and provide better guidance for course selection.
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| 4. |
- Harnefors, Lennart, 1968, et al.
(författare)
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Input-admittance calculation and shaping for controlled voltage-source converters
- 2007
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Ingår i: IEEE Transactions on Industrial Electronics. - : Institute of Electrical and Electronics Engineers (IEEE). - 0278-0046 .- 1557-9948. ; 54:6, s. 3323-3334
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Tidskriftsartikel (refereegranskat)abstract
- A controlled power electronic converter can cause local instabilities when interacting with other dynamic subsystems in a power system. Oscillations at a certain frequency cannot, however, build up if the converter differential input admittance has a positive conductance (real part) at that frequency, since power is then dissipated. In this paper, input-admittance expressions for a voltage-source converter are derived. It is seen how the admittance can be shaped in order to get a positive real part in the desired frequency regions by adjusting the controller parameters.
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| 5. |
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| 6. |
- Härsjö, Joachim, 1987, et al.
(författare)
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PERMANENT MAGNET SYNCHRONOUS GENERATOR INTER TURN FAULT IDENTIFICATION USING STATOR CURRENT ANALYSIS
- 2013
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Ingår i: 9th PhD Seminar on Wind Energy in Europe, EAWE.
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Konferensbidrag (refereegranskat)abstract
- A three phase permanent magnet synchronous generator is modeled both as a FEM model and an analytically model with an additional fourth winding that represents the faulty part of the machine. The faulty part is described as a fraction of the healthy machine. The proposed method can be used for multi pole machines as a general method for calculating the inductances is shown. Simulations show that the largest contributing parameter is the fault resistance, i.e. the contact resistance of the inter turn fault. FEM and analytical simulations show similar results but with amplitude an amplitude difference.
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| 7. |
- Lundmark, Sonja, 1966, et al.
(författare)
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Experiences from a distance course in electric drives including on-line labs and tutorials
- 2012
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Ingår i: 2012 20th International Conference on Electrical Machines, ICEM 2012, Marseille, 2 September - 5 September 2012. - 9781467301428 ; , s. 3050-3055
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Konferensbidrag (refereegranskat)abstract
- This paper explains the steps taken to convert the electric drives course activities at Chalmers University of Technology to a distance course directed towards the automotive industry, including interactive remote web-labs, and on-line tutorials and computer lab sessions. A first pilot course is conducted during autumn 2011. From the course evaluation, from student results and from experience of the involved teachers during the work, it could be concluded that the first pilot course worked as planned, yielding good results in students' performance compared to the on-campus course, except for the practical lab part where students from both courses performed equally well. The web course got an average of 4.2 (out of 5.0) from the course evaluations. In order to improve the web-course, the interactivity during the practical labs should be improved.
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| 8. |
- Wallmark, Oskar, et al.
(författare)
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Input Admittance Expressions for Field-Oriented Controlled Salient PMSM Drives
- 2012
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Ingår i: IEEE transactions on power electronics. - 0885-8993 .- 1941-0107. ; 27:3, s. 1514-1520
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents analytical expressions for the converter input admittance in field-oriented controlled permanentmagnet synchronous motor (PMSM) drives. The effect of rotorsaliency is taken into consideration and the derived admittance expressions are valid for maximum-torque-per-ampere as well ashigh-speed (field weakening) operation. Experimental results illustrate the validity of the derived admittance expressions. The presented work can be used to predict dc-link voltage instabilities inPMSM drives in, e.g., railway traction, aerospace and automotive applications.
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| 9. |
- Amin, Mohammad, 1985, et al.
(författare)
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An efficient appliance for low voltage DC house
- 2011
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Ingår i: 2011 IEEE Electrical Power and Energy Conference, EPEC 2011; Winnipeg, MB; 3 October 2011 through 5 October 2011. - 9781457704048 ; , s. 334-339
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Konferensbidrag (refereegranskat)abstract
- Kitchen appliances consume large amount of energy in residential houses. By using efficient appliances energy losses can be reduced. Most of the household appliances use DC internally except some appliances such as stove, refrigerator, dishwasher and microwave oven. The refrigerator and stove is one of the high power consuming kitchen appliances and it consumes large amount of energy. This work investigated on energy efficient home appliance design to run on low DC voltage and the purpose is to reduce energy consumption and losses. A combined refrigerator stove unit is designed to run on low voltage DC. The system is simulated with Matlab / Simulink and finally a prototype is built to analyze the performance. © 2011 IEEE.
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| 10. |
- Amin, Mohammad, 1985, et al.
(författare)
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Low voltage DC distribution system compared with 230 V AC
- 2011
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Ingår i: 2011 IEEE Electrical Power and Energy Conference, EPEC 2011; Winnipeg, MB; 3 October 2011 through 5 October 2011. - 9781457704048 ; , s. 340-345
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Konferensbidrag (refereegranskat)abstract
- In this work low voltage DC distribution systems for a home are investigated by evaluating the advantages and disadvantages to 230V systems. The aim of the work is to connect the systems with local generation such as solar cell, micro turbine and energy storages at the end user level. Data obtained from measurements of power consumption for different household appliances such as refrigerator, microwave oven, rice cooker, dish washer etc. have been used to evaluate the systems. The performance of the 230V AC system and the proposed low voltage DC system is analyzed by considering factors such as losses in the wire, internal loss of the device itself, investment cost for new wiring, energy consumption cost © 2011 IEEE.
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| 11. |
- Berggrund, Malin, et al.
(författare)
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Identification of candidate plasma protein biomarkers for cervical cancer using the multiplex proximity extension assay
- 2019
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Ingår i: Molecular & Cellular Proteomics. - 1535-9476 .- 1535-9484. ; 18:4, s. 735-743
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Tidskriftsartikel (refereegranskat)abstract
- Human papillomavirus (HPV) is recommended as the primary test in cervical cancer screening, with co-testing by cytology for HPV-positive women to identify cervical lesions. Cytology has low sensitivity and there is a need to identify biomarkers that could identify dysplasia that are likely to progress to cancer. We searched for plasma proteins that could identify women with cervical cancer using the multiplex proximity extension assay (PEA). The abundance of 100 proteins were measured in plasma collected at the time of diagnosis of patients with invasive cervical cancer and in population controls using the Olink Multiplex panels CVD II, INF I, and ONC II. Eighty proteins showed increased levels in cases compared to controls. We identified a signature of 11 proteins (PTX3, ITGB1BP2, AXIN1, STAMPB, SRC, SIRT2, 4E-BP1, PAPPA, HB-EGF, NEMO and IL27) that distinguished cases and controls with a sensitivity of 0.96 at a specificity of 1.0. This signature was evaluated in a prospective replication cohort with samples collected before, at or after diagnosis and achieved a sensitivity of 0.78 and a specificity 0.56 separating samples collected at the time of diagnosis of invasive cancer from samples collected prior to diagnosis. No difference in abundance was seen between samples collected prior to diagnosis or after treatment as compared to population controls, indicating that this protein signature is mainly informative close to time of diagnosis. Further studies are needed to determine the optimal window in time prior to diagnosis for these biomarker candidates.
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| 12. |
- Carlson, Ola, 1955, et al.
(författare)
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Integration of Wind Power by DC-Power Systems
- 2005
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The world climate changing is driving the electric power production towards renewable energy sources. The development of wind turbines has reached the power level of 5 MW and wind farms up to 1000 MW are planned. Investigations have shown that the cost for production of wind energy is in the same level as coal and gas. The large amount of hydro power in the Nordic countries can be used tocompensate for the irregularity of producing wind power in Europe. High voltage direct current connections between Sweden and Germany, with a wind farm between can be a solution in the future.
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| 13. |
- Enroth, Stefan, 1976-, et al.
(författare)
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A two-step strategy for identification of plasma protein biomarkers for endometrial and ovarian cancer
- 2018
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Ingår i: Clinical Proteomics. - : Springer Science and Business Media LLC. - 1542-6416 .- 1559-0275. ; 15
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Tidskriftsartikel (refereegranskat)abstract
- BackgroundOver 500,000 women worldwide are diagnosed with ovarian or endometrial cancer each year. We have used a two-step strategy to identify plasma proteins that could be used to improve the diagnosis of women with an indication of gynecologic tumor and in population screening.MethodsIn the discovery step we screened 441 proteins in plasma using the proximity extension assay (PEA) and five Olink Multiplex assays (CVD II, CVD III, INF I, ONC II, NEU I) in women with ovarian cancer (n=106), endometrial cancer (n=74), benign ovarian tumors (n=150) and healthy population controls (n=399). Based on the discovery analyses a set of 27 proteins were selected and two focused multiplex PEA assays were developed. In a replication step the focused assays were used to study an independent set of cases with ovarian cancer (n=280), endometrial cancer (n=228), women with benign ovarian tumors (n=76) and healthy controls (n=57).ResultsIn the discovery step, 27 proteins that showed an association to cancer status were identified. In the replication analyses, the focused assays distinguished benign tumors from ovarian cancer stage III-IV with a sensitivity of 0.88 and specificity of 0.92 (AUC=0.92). The assays had a significantly higher AUC for distinguishing benign tumors from late stage ovarian cancer than using CA125 and HE4 (p=9.56e-22). Also, population controls could be distinguished from ovarian cancer stage III-IV with a sensitivity of 0.85 and a specificity of 0.92 (AUC=0.89).ConclusionThe PEA assays represent useful tools for identification of new biomarkers for gynecologic cancers. The selected protein assays could be used to distinguish benign tumors from ovarian and endometrial cancer in women diagnosed with an unknown suspicious pelvic mass. The panels could also be used in population screening, for identification of women in need of specialized gynecologic transvaginal ultrasound examination.FundingThe Swedish Cancer Foundation, Vinnova (SWELIFE), The Foundation for Strategic Research (SSF), Assar Gabrielsson Foundation.
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| 14. |
- Enroth, Stefan, 1976-, et al.
(författare)
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High throughput proteomics identifies a high-accuracy 11 plasma protein biomarker signature for ovarian cancer
- 2019
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Ingår i: Communications Biology. - : Springer Science and Business Media LLC. - 2399-3642. ; 2
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Tidskriftsartikel (refereegranskat)abstract
- Ovarian cancer is usually detected at a late stage and the overall 5-year survival is only 30-40%. Additional means for early detection and improved diagnosis are acutely needed. To search for novel biomarkers, we compared circulating plasma levels of 593 proteins in three cohorts of patients with ovarian cancer and benign tumors, using the proximity extension assay (PEA). A combinatorial strategy was developed for identification of different multivariate biomarker signatures. A final model consisting of 11 biomarkers plus age was developed into a multiplex PEA test reporting in absolute concentrations. The final model was evaluated in a fourth independent cohort and has an AUC = 0.94, PPV = 0.92, sensitivity = 0.85 and specificity = 0.93 for detection of ovarian cancer stages I-IV. The novel plasma protein signature could be used to improve the diagnosis of women with adnexal ovarian mass or in screening to identify women that should be referred to specialized examination.
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| 15. |
- Fors, Stefan, 1976-
(författare)
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Blood on the tracks : Life-course perspectives on health inequalities in later life
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The overall aim of the thesis was to explore social inequalities in: a) mortality during mid-life, b) health in later life, and c) old-age mortality, from a life-course perspective. The studies are based on longitudinal Swedish survey and registry data. The results from Study I showed substantial inequalities in health, based on social class and gender, among older adults (aged 55+). Moreover, the magnitude of these inequalities did not change during the period 1991-2002. The results from Study II revealed social inequalities in cognitive functioning among the oldest old (aged 77+). Social turbulence and social class during childhood, education and social class in adulthood were all independently associated with level of cognitive functioning in later life. In Study III, social inequalities in mortality during mid-life (i.e., between ages 25 and 69) were explored. The results showed that childhood living conditions were associated with marital status and social class in adulthood and that, in turn, these conditions were associated with mid-life mortality. Thus, the results suggested that childhood disadvantage may serve as a stepping stone to a hazardous life-course trajectory. Study IV explored the association between income in mid-life, income during retirement and old-age mortality (i.e., mortality during retirement). The results showed that both income during mid-life and income during retirement were associated with old-age mortality. Mutually adjusted models showed that income in mid-life was more important for women’s mortality and that income during retirement was more important for men’s. Thus, the results of the present thesis suggest that there are substantial social inequalities in the likelihood of reaching old age, as well as in health and mortality among older adults. These inequalities are shaped by differential exposures throughout the life-course that affect health in later life both through direct effects and through processes of accumulation.
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| 16. |
- Lundberg, Stefan, 1976
(författare)
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Configuration study of large wind parks
- 2003
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis, layouts of various large-scale wind parks, using both AC as well as DC, are investigated. Loss modelling of the wind park components as well as calculations of the energy capture of the turbines using various electrical systems are performed, and the energy production cost of the various park configurations is determined. The most interesting candidate for a DC transmission based wind park was investigated more in detail, the series DC wind park. Finally, the power quality impact in the PCC (point of common coupling) was studied.It was found that from an energy capture point of view, the difference in energy production between various wind turbine systems is very small.Of all the investigated wind park configurations, the wind park with the series connected DC wind turbines seems to have the best potential to give the lowest energy production cost, if the transmission distance is longer then 10-20km. Regarding the series DC wind park it was found that it is the most difficult one to control. However, a control algorithm for the series park and its turbines was derived and successfully tested. Still, several more details regarding the control of the series wind park has to be dealt with.
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| 17. |
- Lundberg, Stefan, 1976, et al.
(författare)
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Design considerations for a power electronic converter for series connection of wind turbines
- 2009
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Ingår i: 2nd EPE Wind Energy Seminar 2009; Stockholm; Sweden; 23 April 2009 through 24 April 2009.
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Konferensbidrag (refereegranskat)abstract
- When connecting the wind turbines in series the output voltage will not be constant as in a shunt connection. The common quantity for the turbines will be the current and the output voltage will vary depending on the power production. For the DC/DC converter transformer a toroid shape is proposed and an approximate expression for the electric field inside the transformer were derived and compared with FEM calculations.
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| 18. |
- Lundberg, Stefan, 1976, et al.
(författare)
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Electrical limiting Factors for Wind Energy Installations in Weak Grids
- 2001
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Ingår i: International Journal of Renewable Energy Engineering. - 1442-133X. ; 3:2, s. 305-310
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Tidskriftsartikel (refereegranskat)abstract
- In this paper the electrical limiting factors for installation of wind turbines have been used to determine which types of power quality problems that will dominate when wind turbines are installed in weak grids. The main limiting factors are static voltage level influence, the flicker emission, and of course, the capacity of the line. The investigation is based on field measurements on a fixed-speed wind turbine and on a semi-variable-speed wind park. It is found that the limiting factor from the power quality point of view is the flicker emissions if one fixed-speed wind turbine is installed. If three or more turbines are installed it is the static voltage variations or the line capacity that sets the limit. It is found that the X/R-ratio of the grid plays a significant influence on the installation possibility, and a ratio of 1.3-2.8 is the most favourable, depending on the short circuit ratio. For variable-speed wind turbines it is the static voltage change and the line capacity that are the limiting factors.
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| 19. |
- Lundberg, Stefan, 1976
(författare)
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Evaluation of wind farm layouts
- 2004
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Ingår i: Nordic Workshop on Power and Industrial Electronics.
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Konferensbidrag (refereegranskat)abstract
- In this paper, layouts of various large-scale wind farms, using both AC as well as DC, are investigated. The criteria in this investigation is the energy production cost. The energy production cost is defined as the total investment cost divided with the total energy production of the wind farm. To determine the energy production and the total investment cost, loss and cost models for the components in the wind farm are used (the most important models are presented in this paper).Of the investigated wind farm configurations, a wind farm with series connected DC wind turbines seems to have the best potential to give the lowest energy production cost, if the transmission distance is longer then 10-20km.
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| 20. |
- Lundberg, Stefan, 1976
(författare)
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Performance comparison of wind park configurations
- 2003
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- In this report, layouts of various large-scale wind parks, both AC as well as DC, are investigated. Loss modelling of the wind park components as well as calculations of the energy capture of the turbines using various electrical systems are performed, and the energy production cost of the various park configurations is determined.It was found that from an energy capture point of view, the difference in energy production between various wind turbine systems is very small. In addition, a study of the suitability of various DC/DC-converters is made. Three DC/DC-converters, Boost, Full Bridge and Full Bridge Isolated Boost, are found to be interesting candidates as the "transformer" component in potential DC-based wind parks.Of all the investigated wind park configurations, the wind park with the series connected DC wind turbines seems to have the best potential to give the lowest energy production cost, if the transmission distance is longer then 10-20km.
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| 21. |
- Lundberg, Stefan, 1976
(författare)
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Wind Farm Configuration and Energy Efficiency Studies - Series DC versus AC Layouts
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis, the design and control of a wind farm utilizing series-connected wind turbines with a DC output has been evaluated. The advantage is that a suitable DC voltage level, appropriate for transmission of the generated power directly, without using a large centralized DC/DC converter, can be obtained. This is achieved by series-connecting a number of wind turbines. In addition, the energy production using various wind turbines and wind park layouts have been investigated. Furthermore, the energy production costs have been determined. Finally, the limiting factors for the installation of smaller wind parks have been evaluated. For instance, when dynamic power pulsations have to be considered, from a power quality point of view, when a wind energy installation is to be connected to the grid.The results found are that the uneven power production from the individual wind turbines creates design as well as control difficulties for the wind farm with series-connected wind turbines. A control scheme for the wind turbines is proposed and investigated in this thesis. It is found that the proposed control scheme manages to safely operate the wind farm, even when large deviations in the individual power production of the turbines exist. A down-scaled prototype has been built, representing one wind turbine unit, and the base current control ability was verified experimentally.Moreover, it is found that it is necessary to design the individual wind turbine converters for a voltage level of about 35 % higher than the nominal voltage. Otherwise there will be a substantial energy loss due to the uneven power production from the individual wind turbines that occurs in actual installation.In addition, it is found that the series dc wind park has a good economical potential, since it eliminates the need for an offshore platform in the wind park.Finally, the electrical limiting factors for the installation of wind farms are determined using field experimental data. For instance, it is shown that for a wind park of about 10 wind turbines, the power pulsations are "smoothened" sufficiently so that the flicker emission never will be the limiting factor, even for fixed-speed turbines, when a wind energy installation is connected to a network. Worth mentioning is that it was found that the summation formula for flicker given in IEC 61400-21 can give a flicker prediction that is too low.
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| 22. |
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| 23. |
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| 24. |
- Nasr, Patrik, 1987-
(författare)
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Non-Alcoholic Fatty Liver Disease : Aspects on Diagnosis and Long-term Prognosis
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Non-alcoholic fatty liver disease (NAFLD) is the most common cause of chronic liver disease affecting approximately 25% of the global population and is commonly recognized as the hepatic manifestation of the metabolic syndrome. The histological spectrum of NAFLD ranges from isolated steatosis to non-alcoholic steatohepatitis (NASH), with risk of developing fibrosis and subsequent cirrhosis and hepatocellular carcinoma. The gold standard for diagnosing NAFLD is liver biopsy. However, because of its invasive nature, several non-invasive methods have been developed and validated in evaluating fat and fibrosis in patients with NAFLD.Liver fat content can be assessed using various methods. The conventional histopathological method consists of a visual semiquantitative approach in which the pathologist uses a four-point scale: grade 0 corresponds to fat deposition in <5% of hepatocytes and grade 1−3 (which is needed for the diagnosis of NAFLD) corresponds to ≥5%. An alternate approach is to quantitatively assess steatosis using stereological point counting (SPC) – which rely on liver biopsy. However, in vivo proton magnetic resonance spectroscopy (1H-MRS) is a reliable noninvasive method that can be used to quantitatively assess total hepatic lipid content, or proton density fat fraction (PDFF).In Paper I we compared the conventional semiquantitative histological method (grade 0-3) with SPC and 1H-MRS. We found a strong positive correlation between 1H-MRS and SPC, whereas the correlations between 1H-MRS or SPC and histopathological grading were substantially weaker. Using the widely used cut-off value of PDFF ≥5%, all participants were found to have steatosis (specificity 100%, sensitivity 53%). Reducing the cut-off value to 3% maintained 100% specificity while increasing sensitivity to 79%.In Paper IV we evaluated quantitative steatosis, by SPC, in 106 biopsy-proven NAFLD patients during a 20-year follow-up. SPC was independently associated with an increased risk of all-cause mortality and development of T2DM. Moreover, in the 59 patients with sequential biopsies (approximately 10 years apart), a reduction of quantitative hepatic steatosis decreased the all-time risk of developing T2DM.NASH is commonly seen as a histological feature portending a worse prognosis in NAFLD. Interestingly, no dual biopsy study has ever shown that NASH predicts fibrosis progression. Yet, NASH is seen as a surrogate marker in pharmaceutical trials – were resolution in NASH is equivalent to future resolution of fibrosis.In Paper II we conducted a long-term follow-up study (20 years) in a large cohort of biopsy-proven NAFLD patients (n=646), in a collaboration with Karolinska Institute. We could not ascertain that NASH had any effect on all-cause, or disease-specific mortality. However, higher stages of fibrosis predicted all-cause and disease specific mortality. In Paper III, we present 129 biopsy-proven NAFLD patients, in which we had prospective, longitudinal data. They were included between 1988 and 1993. All patients alive, were re-invited 2003-2005 and 2013-2015. Dual biopsies were present in 68 patients, and three consecutive biopsies were available in 33 patients. Results showed that NAFLD is a highly heterogeneous disease, with 9.3% developing end-stage liver disease and 16% progressing to advanced stages of fibrosis without any clinically significant baseline data predicting disease progression. In summary, when using 1H-MRS as a diagnostic method for NAFLD, the diagnostic cut-off should be reduced from 5% to 3%. Furthermore, quantitative amount of hepatic steatosis could be used to stratify patients with NAFLD related to future risk of developing T2DM. Moreover, we have shown that NASH does not predict future all-cause or disease-specific mortality nor end-stage liver disease, therefore a different surrogate marker should be used in clinical trials when assessing NAFLD improvement, so to not imbue false reliance in new therapies. Lastly, we have shown that NAFLD has a more dismal prognosis than previously reported, and that it is unexpectedly difficult to predict fibrosis progression in individual NAFLD patients, emphasizing the need for robust non-invasive biomarkers suitable to monitor large number of patients.
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| 25. |
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| 26. |
- Petersson, Andreas, 1974, et al.
(författare)
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A DFIG Wind-Turbine Ride-Through System Influence on the Energy Production
- 2004
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Ingår i: Nordic Wind Energy Conference.
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Konferensbidrag (refereegranskat)abstract
- The influence on the energy production of a voltage sagride-through systems, for a doubly-fed induction generator (DFIG) wind turbine, is investigated. Based on simulations a candidate ride-through system, based on IGBT modules with high current rating and anti-parallel thyristors that can disconnect the stator of the DFIG from the grid, is developed. It has been found that by increasing the current rating, of the converters IGBTs, the losses of the converter can be reduced. However, if anti-parallel thyristors has to be connected between the stator and the grid, in order to achieve a fast disconnection, the over all losses of the total system increase instead.
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| 27. |
- Petersson, Andreas, 1974, et al.
(författare)
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Energy Efficiency Comparison of Electrical Systems for Wind Turbines
- 2002
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Ingår i: Nordic Workshop on Power and Industrial Electronics. - 1650-674X.
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Konferensbidrag (refereegranskat)abstract
- The efficiency of the electrical system of doubly-fed induction generators, for variable speed wind turbines, in comparison to other electrical systems has been investigated. It has been found that there is a possibility to gain a few percent in energy efficiency using a doubly-fed induction generator compared to an ordinary induction generator equipped with an full-power inverter.
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| 28. |
- Tang, Junfei, 1990, et al.
(författare)
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Comprehensive Dynamic Current Control of Electrically Excited Synchronous Machines With Magnetic Mutual Couplings
- 2024
-
Ingår i: IEEE Transactions on Industrial Electronics. - 0278-0046 .- 1557-9948. ; In press
-
Tidskriftsartikel (refereegranskat)abstract
- Electrically excited synchronous machines have become an attractive solution to electric vehicles. The excitation of the machine is controllable by adjusting the field current. However, due to the magnetic mutual couplings between stator and rotor windings, a voltage will be induced in the stator winding in case of a current rise in the field winding and vice-versa. In this article, a dynamic current control algorithm is proposed in which magnetic mutual couplings are comprehensively taken into consideration. To achieve this, first, the expected current derivatives are determined according to the error. Then, the voltages across all self- and mutual inductances are calculated correspondingly. In the end, the resistive voltages, inductive voltages, and the cross-coupling terms are summed up to construct the total controller output. To make sure that the control still works when the voltage output limit is reached, an antiwindup algorithm with adaptive bandwidth is proposed to cooperate with the dynamic current control algorithm. The results from simulations and experiments show that smoother responses can be achieved with the proposed control method.
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| 29. |
- Tang, Junfei, 1990, et al.
(författare)
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Dynamic Current Reference Determination of Electrically Excited Synchronous Machines Based on Torque Gradients of Copper Losses
- 2024
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Ingår i: IEEE Transactions on Power Electronics. - 0885-8993 .- 1941-0107. ; 39:6, s. 7423-7433
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Tidskriftsartikel (refereegranskat)abstract
- Electrically excited synchronous machines (EESMs) have become an attractive solution to electric vehicles. The excitation of the machine can be regulated by adjusting field current. This introduces one additional degree of control freedom. The control of armature current in stator and field current in rotor is expected to not only reduce the total losses, but also dynamically redistribute the load on both windings so that neither of them overheats. To realize this function, an algorithm is proposed in this study to dynamically determine the current references in EESM torque control. A cost function is introduced by placing weights on stator and rotor copper losses separately. The weights can be adjusted dynamically. The cost function is minimized by moving the current reference vector. The moving of the vector is orthogonally decomposed into a torque-related component and a cost-related component. When current or voltage limits are reached, a cancellation technique is activated to constrain the reference vector. It is shown in experimental results that expected performance is achieved in all operating conditions.
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| 30. |
- Tang, Junfei, 1990, et al.
(författare)
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Estimation Algorithm for Current and Temperature of Field Winding in Electrically Excited Synchronous Machines with High-Frequency Brushless Exciters
- 2021
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Ingår i: IEEE Transactions on Power Electronics. - 0885-8993 .- 1941-0107. ; 36:3, s. 3512-3523
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Tidskriftsartikel (refereegranskat)abstract
- Electrically excited synchronous machines (EESMs) have become one of the potential alternatives to permanent magnet synchronous machines (PMSMs) in electric vehicles (EVs) to avoid rare-earth materials. Utilizing high-frequency brushless exciters for rotor excitation is a promising choice to reduce friction losses and maintenance effort and cost. However, with the usage of brushless exciters, the field current and temperature cannot be measured directly. In this paper, an algorithm is proposed to dynamically estimate the field current as well as the field winding temperature. The dc-link current is utilized as a feedback to correct the estimation. The performance of the estimation algorithm is initially evaluated in simulations and then verified by experimental measurements in a prototype. Based on the estimation algorithm, closed-loop control of the field current is developed and verified experimentally.
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| 31. |
- Tang, Junfei, 1990, et al.
(författare)
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Sensorless control of a PMSM with a transmission system including shunt branches
- 2016
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Ingår i: Proceedings - 2016 22nd International Conference on Electrical Machines, ICEM 2016. Lausanne; Switzerland; 4-7 September 2016. - 9781509025381 ; , s. 1160-1166
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Konferensbidrag (refereegranskat)abstract
- In oil and gas applications, permanent magnet synchronous motors (PMSM) are becoming a preferred choice to drive subsea and submersible pumps to achieve higher efficiency than induction motors. In the drive system, a submersible PMSM is fed through a transmission system by a top-side variable speed drive. Previous studies have included the series impedance of the transmission system but excluded the transformer magnetizing branch and the cable capacitive branches. In this work, both the series impedance and the shunt admittance of the transmission system are considered. The PMSM current controller is restructured to be an inverter current controller. A static estimator is implemented to estimate the PMSM stator voltage and current. Sensorless control is realized by combining the statically compensated voltage model method and the high frequency injection method. The developed controller can successfully start and accelerate the PMSM from standing still up to 6000 rev/min within 5 s.
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| 32. |
- Thiringer, Torbjörn, 1966, et al.
(författare)
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Flicker contribution from wind turbine installations
- 2004
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Ingår i: IEEE Transactions on Energy Conversion. - 1558-0059 .- 0885-8969. ; 19:1, s. 157-163
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, the flicker emission from a wind park connected to a grid with a high energy penetration is evaluated. The influence of wind speed, turbulence intensity, grid voltage quality, grid types and number of turbines operating in the same group is measured and analyzed. It is found that the voltage quality of the grid to which the turbines are connected strongly influences the flicker emission of the turbines. Moreover, it is found that the formula used in IEC-61400-21 for determining the flicker contribution from a whole wind park gives too low total flicker value.
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| 33. |
- Xun, Qian, 1990, et al.
(författare)
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Design and experimental verification of a fuel cell/supercapacitor passive configuration for a light vehicle
- 2021
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Ingår i: Journal of Energy Storage. - : Elsevier BV. - 2352-152X. ; 33
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Tidskriftsartikel (refereegranskat)abstract
- The fuel cell/supercapacitor passive configuration without using any DC/DC converters is promising in auto-motive applications as it can downsize the fuel cell stack, maintain the peak power capability, improve the system efficiency, and remove the need of additional control. This paper presents the design and characterization of a fuel cell/supercapacitor passive hybrid system for a 60 V light vehicle. A detailed design procedure for the passive hybrid test platform is presented with each component modelled and experimentally verified. The voltage error of the fuel cell and the supercapacitor model in the steady state is within 2% and 3%, respectively. Experimental results also validate the function of the passive configuration under conditions of a step load and a drive cycle. The simulation model of the passive hybrid system matches the measurements when a step load current is applied. The supercapacitor provides the transient current due to its smaller resistance while the fuel cell handles the steady state current, which makes it possible to downsize the fuel cell stack. For the drive cycle examined in this paper, the fuel cell stack can be downsized to one third of the load peak power.
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| 34. |
- Xun, Qian, 1990, et al.
(författare)
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Experimental Characterization of Fuel Cells, Supercapacitors, and Their Passive Connection
- 2022
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Ingår i: 2022 IEEE 13th International Symposium on Power Electronics for Distributed Generation Systems, PEDG 2022.
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Konferensbidrag (refereegranskat)abstract
- This paper investigates a passive hybrid configuration consisting of a fuel cell stack and a supercapacitor bank. In this configuration, the fuel cell and the supercapacitor are directly connected in parallel without the use of any DC/DC converters. Extensive experiments are performed on the fuel cell stack, the supercapacitor bank, and their passive hybrid connection. The internal impedance of the supercapacitor bank is 10 times lower than that of the fuel cell stack. The hybrid system shows a capacitive behavior in the selected frequency range, as given by the electrochemical impedance spectroscopy results. For the fuel cell stack, its voltage response to the step load current shows an inductive behavior, which can be represented by an RL circuit. On the other hand, the dynamics of the supercapacitor bank can be represented by two RC branches. When a step load current is applied, the supercapacitor provides the transient current while the fuel cell provides the steady current.
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