| 1. |
|
|
| 2. |
- Ekström, Rickard, 1985-, et al.
(author)
-
Fast solid-state tap-change using two current-controlled voltage-source inverters
- 2014
-
In: IET Power Electronics. - : Institution of Engineering and Technology (IET). - 1755-4535 .- 1755-4543. ; 7:10, s. 2610-2617
-
Journal article (peer-reviewed)abstract
- A new topology for on-load tap change using two current-controlled voltage-source inverters is demonstrated. With this topology, no additional tap change circuitry is required. This configuration can be useful when optimising the power extraction from renewable energy sources, and may replace a DC/DC converter. It is possible to run the inverters in parallel for higher current capacity, or run them in series across the transformer to improve the harmonic output. The topology can be extended to any number of taps, adding one mechanical contactor per tap. The procedure for the tap change, including the control implementations to keep active and reactive grid power flows constant throughout the tap change, is described. Experimental results are presented to show the viability of the proposed topology. Tap changes are conducted on all phases simultaneously, and individually at each phase current zero-crossing. Variations in grid power are investigated for the two strategies. Also, a dead-time in the tap change is introduced to evaluate how control system delays will appear as grid power dips.
|
|
| 3. |
|
|
| 4. |
- Krishna, Remya, 1985-
(author)
-
Grid Connected Three-Level Converters : Studies for Wave Energy Conversion
- 2014
-
Doctoral thesis (other academic/artistic)abstract
- This thesis presents an electrical system analysis of a wave energy converter (WEC) for the objective of grid connection. To transfer the enormous amount of power from waves to the load centers, efficient power electronic systems are essential. This thesis includes the modeling of a buoy–translator dynamics and the modeling of a linear permanent magnet generator along with simulation and experimental validation. Diode bridge rectifiers are considered for rectification to avoid the complex linear generator control at the input side. To reduce the size and the cost of energy storage elements, DC voltage regulation is done using a DC/DC converter.To achieve smooth and high power, many WECs need to be connected to a common DC link. A neutral point clamped inverter is considered for the DC/AC conversion due to its advantages over conventional topologies. Various pulse width modulation schemes are tested for the inverter to choose the optimum PWM method. The harmonics in the inverter output voltage is derived numerically and compared with simulation and experiment to understand the effect of dead-time in the inverter operation.Depending on the load current drawn from the inverter, the voltages in the two input capacitors of a three-level neutral point clamped inverter deviates from equilibrium unless the neutral point is grounded. To avoid this voltage imbalance as well as to regulate the DC link voltage a dual output boost converter with pulse delay control is proposed. The modeling, simulation and experiments show an improvement in the compensation voltage using pulse delay control compared to the previously proposed methods in the literature. The synchronous current control and the grid connection of the three-level converter have been accomplished in the laboratory. Finally, the three-level power converter system has been tested with a linear permanent magnet generator at Lysekil to analyze the controller requirements.
|
|
| 5. |
- Leijon, Karin, 1987-, et al.
(author)
-
Nationella domstolar som politiska aktörer : - främjare av rättslig integration eller försvarare av nationella intressen?
- 2013
-
In: Statsvetenskaplig Tidskrift. - Lund : Fahlbeckska Stiftelsen. - 0039-0747. ; 115:1, s. 5-34
-
Journal article (peer-reviewed)abstract
- It has been widely recognised that national courts play a significant role in the process of European integration. By asking the European Court of Justice for preliminary rulings, national courts have contributed in promoting legal integration. Although previous research has recognised the importance of national courts, we still have only limited empirical knowledge on how they act. This article examines whether national courts act as promoters of legal integration or defenders of the national interest. It does so by providing a systematic investigation of: 1, what type of cases they refer to the ECJ, and 2, what type of opinions they attach with preliminary references. The article utilise data from all 67 cases referred to the ECJ during the period 1995-2009. The results indicate that Swedish courts act strategically to balance the claims of providing the ECJ with preliminary references and the demands for taking national considerations into account.
|
|
| 6. |
- Leijon, Matti E., 1970-, et al.
(author)
-
Factors associated with patients self-reported adherence to prescribed physical activity in routine primary health care
- 2010
-
In: BMC Family Practice. - London, UK : BioMed Central. - 1471-2296. ; 11:38
-
Journal article (peer-reviewed)abstract
- Background: Written prescriptions of physical activity, so‐called physical activity referral (PAR) schemes, have increased in popularity in recent years. Such schemes have mostly been evaluated in terms of efficacy. This study reports on a Swedish PAR scheme implemented in routine primary health care (PHC) measuring patients’ self‐reported adherence to physical activity prescriptions. The aim of this study was to evaluate adherence to physical activity prescriptions issued in everyday PHC at 3 and 12 months and to analyse the different characteristics associated with adherence to these prescriptions.Methods: Prospective prescription data were obtained for 37 of the 42 PHC centres in Östergötland County, Sweden, during 2004. The study population consisted of 3300 patients issued PARs by ordinary PHC staff members. Odds ratios were calculated to identify the factors associated with adherence.Results: The average adherence rate was 56% at 3 months and 50% at 12 months. In the descriptive analyses, higher adherence was associated with increased age, higher activity level at baseline, home‐based activities, prescriptions issued by professional groups other than physicians, and among patients issued PARs due to diabetes, high blood pressure and “other PAR reasons”. In the multiple logistic regression models, higher adherence was associated with higher activity level at baseline, and to prescriptions including home‐based activities, both at 3 and 12 months.Conclusions: Prescriptions from ordinary staff in routine PHC yielded adherence in 50% of the patients in this routine care PAR scheme follow‐up. Patients’ activity level at baseline (being at least somewhat physically inactive) and being issued homebased activities were associated with higher adherence at both 3 and 12 months.
|
|
| 7. |
- Leijon, Matti E., et al.
(author)
-
Who is not adhering to physical activity referrals, and why?
- 2011
-
In: Scandinavian Journal of Primary Health Care. - : Informa Healthcare. - 0281-3432 .- 1502-7724. ; 29:4, s. 234-240
-
Journal article (peer-reviewed)abstract
- Objective. To analyse patients self-reported reasons for not adhering to physical activity referrals (PARs). Design and setting. Data on 1358 patients who did not adhere to PARs were collected at 38 primary health care (PHC) centres in Sweden. Intervention. PHC providers issued formal physical activity prescriptions for home-based activities or referrals for facility-based activities. Subjects. Ordinary PHC patients whom regular staff believed would benefit from increased physical activity. Main outcome measure: Reasons for non-adherence to PARs: "sickness", "pain", "low motivation", "no time", "economic factors", and "other". Results. Sickness and pain were the most common motives for non-adherence among older patients. The youngest patients blamed economic factors and lack of time more frequently than those in the oldest age group. Economic factors was a more common reason for non-adherence among those referred for facility-based activities compared with those prescribed home-based activities. Low motivation was a more frequent cause of non-adherence among those prescribed home-based activities compared with those referred for facility-based activities. Furthermore, lack of time was a more common reason for non-adherence among patients issued with PARs due to high blood pressure than other patients, while low motivation was a more common reason among patients issued with PARs because of a BMI of greater than 25. Conclusion. The reasons for non-adherence differ between patients prescribed home-based activities and referred for facility-based activities, as well as between patients with different specific characteristics. The information obtained may be valuable not only for the professionals working in PHC, but also for those who work to develop PARs for use in different contexts.
|
|
| 8. |
- Leijon, Siv, et al.
(author)
-
Pressure Ulcer Prevalence, Use of Preventive Measures, and Mortality Risk in an Acute Care Population : A Quality Improvement Project
- 2013
-
In: Journal of Wound, Ostomy and Continence Nursing (WOCN). - : Lippincott Williams & Wilkins. - 1071-5754 .- 1528-3976. ; 40:5, s. 469-474
-
Journal article (peer-reviewed)abstract
- The primary aim of this quality improvement project was to determine pressure prevalence, risk of mortality, and use of preventive measures in a group of hospitalized patients. Two hundred fifty-eight patients recruited from Skaraborg Hospital in Sweden were assessed. A 1-day point prevalence study was carried out using a protocol advocated by the European PU Advisory Panel. Patients' age, gender, severity of PU (grades I-IV), anatomical location of PU, and use of preventive measures were recorded. The Swedish language version of the Modified Norton Scale was used for PU risk assessment. Data were collected by nurses trained according to the Web-based training: PU classification, “ePuclas2.” After 21 months, a retrospective audit of the electronic records for patients identified with pressure ulcers was completed. The point prevalence of pressure ulcers was 23%. The total number of ulcers was 85, most were grade 1 (n = 39). The most common locations were the sacrum (n = 15) and the heel (n = 10). Three percent of patients (n = 9) had been assessed during their current hospital stay using a risk assessment tool. There was a statistically significant relationship between pressure ulcer occurrence and a low total score on the Modified Norton Scale. The patients' ages correlated significantly to the presence of a pressure ulcer. Patients with a pressure ulcer had a 3.6-fold increased risk of dying within 21 months, as compared with those without a pressure ulcer. Based on results from this quality improvement project, we recommend routine pressure ulcer risk assessment for all patients managed in a hospital setting such as ours. We further recommend that particular attention should be given to older and frail patients who are at higher risk for pressure ulcer occurrence and mortality.
|
|
| 9. |
- Thomas, Karin, et al.
(author)
-
A Permanent Magnet Generator for Energy Conversion from Marine Currents : No Load and Load Experiments
- 2012
-
In: ISNR Renewable Energy. - : Hindawi Limited. - 2090-7451 .- 2090-746X. ; 2012, s. 489379-
-
Journal article (peer-reviewed)abstract
- This paper presents experiments and measurements on a low speed permanent magnet cable wound generator for marine currentenergy conversion.Measurements were made for no load and nominal load (4.44Ω/phase) conditions at nominal speed (10 rpm).For either load condition, the magnetic fields in the air gap were also measured. The measurements on the generator werecompared with the corresponding finite element method simulations used to design the machine. It is shown in the paper thatmeasurements and corresponding case simulations show good agreement. At nominal speed, the measured and simulated loadvoltages (nominal load) differ less than 1% for the rms values and less than 5% for peak values. At no load, measured and simulatedvoltages had larger differences, that is, <9% for rms values and <5% for peak values. Harmonic analyses of measured and simulatedphase voltages and currents show only the presence of third harmonics. The percentage of harmonics in the measured data wascomparable with the corresponding predictions of the simulations. The discussions and results presented in the paper could bebeneficial for future design of efficient and reliable marine current energy converter systems.
|
|
