Thermal modelling of semiconductor switches in three-level Neutral Point Clamped Medium Voltage DTC-inverter

The aim of this thesis is to investigate the thermal loading of medium voltage three-level NPC inverter���s semiconductor IGCT switches in different operation points. The objective is to reach both a fairly accurate off-line simulation program and also so simple a simulation model that its implementation into an embedded system could be reasonable in practice and a real time use should become feasible. Active loading limitation of the inverter can be realized with a thermal model which is practical in a real time use. Determining of the component heating has been divided into two parts; defining of component losses and establishing the structure of a thermal network. Basics of both parts are clarified. The simulation environment is Matlab-Simulink. Two different models are constructed ��� a more accurate one and a simplified one. Potential simplifications are clarified with the help of the first one. Simplifications are included in the latter model and the functionalities of both models are compared. When increasing the calculation time step a decreased number of considered components and time constants of the thermal network can be used in the simplified model. Heating of a switching component is dependent on its topological position and inverter���s operation point. The output frequency of the converter defines mainly which one of the switching components is ��� because of its losses and heating ��� the performance limiting component of the converter. Comparison of results given by different thermal models demonstrates that with larger time steps, describing of fast occurring switching losses becomes difficult. Generally articles and papers dealing with this subject are written for two-level inverters. Also inverters which apply direct torque control (DTC) are investigated rarely from the heating point of view. Hence, this thesis completes the former material.

Pinnan karheuden mittaus kolmiaaltolaserilla

Ty��ss�� suunniteltiin ja rakennettiin kolmiaaltolaser pinnankarheuden mittaamiseen. Keskeisen�� kysymyksen�� oli mittausalueen laajentaminen verrattuna perinteisiin yksiaaltomittauksiin. Laitteen toimivuus todennettiin mittaamalla suhteellisia pinnankarheuksia useista eri tunnetuista paperin��ytteist��.

Kaasun dispergoituminen tehdasmittakaavaisessa keskisakean massan sekoittimessa

Ty��n tarkoituksena oli selvitt���� Proto 10 kemikaalisekoittimen kyky dispergoida kaasua keskisakean valkaistun m��ntysellun joukkoon. Ty��ss�� k��ytettiin kuvantamistekniikkaa, jonka avulla pystyttiin n��kem����n sekoittimen ja putkiston sis��lle sekoitustapahtuman aikana. Muodostunutta dispersiota tarkasteltiin kolmesta kuvauspisteest��, joista yksi sijaitsi sekoittimen pes��ss�� ja kaksi putkistossa sekoittimen j��lkeen. Ty��ss�� verrattiin my��s laboratoriosekoittimella saatuja tuloksia teollisen mittakaavan sekoittimella saatuihin tuloksiin, sek�� m����ritettiin tarvittava pinta-aktiivisen aineen konsentraatio, jolla saavutettiin ruskeaa massaa vastaava vaahtoaminen. Ty��n kokeellinen osuus koostui kolmesta osasta. Ensimm��isess�� vaiheessa tutkittiin ruskeasta m��nty- ja koivumassasta lingotun suodoksen vaahtoamista ja verrattiin sit�� vedell�� ja pesuaineella saatavaan vaahtoon. Toisessa vaiheessa suoritettiin referenssiajot laboratoriosekoittimen ja teollisen mittakaavan sekoittimen vertailua varten Quantum Mark IV laboratoriosekoittimella. Kolmannessa vaiheessa tutkittiin Proto 10 sekoittimen kyky�� dispergoida kaasua m��ntysellun joukkoon eri py��rimisnopeuksilla ja virtaamilla. Ty��n tuloksien perusteella energiank��yt��n kannalta paras py��rimisnopeus Proto 10 sekoittimelle on 1500 min-1. Nostamalla kierrosnopeutta yli t��m��n ei saavutettu merkitt��v���� parannusta dispersion laadussa varsinkaan suuremmilla virtaamilla. Virtaamalla todettiin olevan suuri merkitys sekoitustulokseen. Laboratoriosekoittimella tehtyjen kokeiden todettiin vastaavan parhaiten teollisen mittakaavan tuloksia py��rimisnopeudella 1200 min-1.

Development of railway logistics��� information flows

Objective of this thesis was to develop the exchange of information and reduce the manual work done in the supply chain. In addition, the possibility to introduce electronic information exchange was studied between suppliers and Borealis. The aim was to create an accurate picture of Borealis��� current information flows and create from the basis of it short- and long-term improvement and development proposals. In this study the company's received and send information flows were mapped by interviewing persons who were responsible for the railroad imports and by examining documents that are used in the exchange of information. The data content of the information flows were prioritized and only the most important information contents were used for further development. Literature data was acquired concerning knowledge of electronic data interchange and information management to support the decisions and proposals. Long-term development proposals were compared with each other and the best one of them was recommended for further study. The final target of the proposal is to be able to receive electronic data and create an own database where to the information is stored and where from it is possible to follow up the rail tank cars and where from the needed reports can be retrieved.

Middle school mediocrity : quality and inequality in secondary education

Centrala teman i min avhandling ��r parallellskolesystem, linjedelning och segregering i h��gstadier och gymnasier. Det finns stora skillnader mellan l��nder g��llande den ��rskurs d�� eleverna sorteras in i olika niv��er genom skilda klasser eller skolor. I Tyskland och Nederl��nderna till exempel delas eleverna upp f��re h��gstadiet medan Sverige och Finland har enhetsskolor p�� h��gstadieniv��. Jag argumenterar att parallellskolesystem har en positiv effekt p�� elevernas testresultat i ��rskurserna f��re linjedelningen. Eleverna har incitament att jobba h��rdare f��r att komma p�� i den akademiska linjen. Jag unders��ker incitamentseffekter empiriskt, och hittar m��nster konsistenta med incitamentseffekter b��de i brittisk och i internationell data. Det andra bidraget i avhandlingen ��r metodologiskt. Nationalekonomer brukar behandla testresultat fr��n t.ex. IQ-tester eller internationella PISA-unders��kningar som om absoluta niv��n p�� po��ngantalen har betydelse i sig. I verkligheten antyder de endast en rangordning. Jag visar att normalf��rdelade testresultat i m��nga fall ligger tillr��ckligt n��ra dess pengav��rde p�� arbetsmarknaden f��r att ��nd�� kunna tolkas som absoluta.

Cognitive Development of Very Low Birth Weight Children from Infancy to Pre-school Age

The survival of preterm born infants has increased but the prevalence of long-term morbidities has still remained high. Preterm born children are at an increased risk for various developmental impairments including both severe neurological deficits as well as deficits in cognitive development. According to the literature the developmental outcome perspective differs between countries, centers, and eras. Definitions of preterm infant vary between studies, and the follow-up has been carried out with diverse methods making the comparison less reliable. It is essential to offer parents upto-date information about the outcome of preterm infants born in the same area. A centralized follow-up of children at risk makes it possible to monitor the consequences of changes in the treatment practices of hospitals on developmental outcome. This thesis is part of a larger regional, prospective multidisciplinary follow-up project entitled ���Development and Functioning of Very Low Birth Weight Infants from Infancy to School Age��� (PIeniPAinoisten RIskilasten k��ytt��ytyminen ja toimintakyky imev��isi��st�� kouluik����n, PIPARI). The thesis consists of four original studies that present data of very low birth weight (VLBW) infants born between 2001 and 2006, who are followed up from the neonatal period until the age of five years. The main outcome measure was cognitive development and secondary outcomes were significant neurological deficits (cerebral palsy, CP, deafness, and blindness). In Study I, the early crying and fussing behavior of preterm infants was studied using parental diaries, and the relation of crying behavior and cognitive and motor development at the age of two years was assessed. In Study II, the developmental outcome (cognitive, CP, deafness, and blindness) at the age of two years was studied in relation to demographic, antenatal, neonatal, and brain imaging data. Development was studied in relationship to a full-term born control group born in the same hospital. In Study III, the stability of cognitive development was studied in VLBW and full-term groups by comparing the outcomes at the ages of two and five years. Finally, in Study IV the precursors of reading skills (phonological processing, rapid automatized naming, and letter knowledge) were assessed for VLBW and full-term children at the age of five years. Pre-reading skills were studied in relation to demographic, antenatal, neonatal, and brain imaging data. The main findings of the thesis were that VLBW infants who fussed or cried more in the infancy were not at greater risk for problems in their cognitive development. However, crying was associated with poorer motor development. The developmental outcome of the present population was better that has been reported earlier and this improvement covered also cognitive development. However, the difference to fullterm born peers was still significant. Major brain pathology and intestinal perforation were independent significant risk factors for adverse outcome, also when several individual risk factors were controlled for. Cognitive development at the age of two years was strongly related with development at the age of five years, stressing the importance of the early assessment, and the possibility for early interventions. Finally, VLBW children had poorer pre-reading skills compared with their full-term born peers, but the IQ was an important mediator even when children with mental retardation were excluded from the analysis. The findings suggest that counseling parents about the developmental perspectives of their preterm infant should be based on data covering the same birth hospital. Neonatal brain imaging data and neonatal morbidity are important predictors for developmental outcome. The findings of the present study stress the importance of both short-term (two years) and long-term (five years) follow-ups for the individual, and for improving the quality of care.