Power cycling lifetime estimation of IGBT power modules based on chip temperature modeling

In this doctoral thesis, methods to estimate the expected power cycling life of power semiconductor modules based on chip temperature modeling are developed. Frequency converters operate under dynamic loads in most electric drives. The varying loads cause thermal expansion and contraction, which stresses the internal boundaries between the material layers in the power module. Eventually, the stress wears out the semiconductor modules. The wear-out cannot be detected by traditional temperature or current measurements inside the frequency converter. Therefore, it is important to develop a method to predict the end of the converter lifetime. The thesis concentrates on power-cycling-related failures of insulated gate bipolar transistors. Two types of power modules are discussed: a direct bonded copper (DBC) sandwich structure with and without a baseplate. Most common failure mechanisms are reviewed, and methods to improve the power cycling lifetime of the power modules are presented. Power cycling curves are determined for a module with a lead-free solder by accelerated power cycling tests. A lifetime model is selected and the parameters are updated based on the power cycling test results. According to the measurements, the factor of improvement in the power cycling lifetime of modern IGBT power modules is greater than 10 during the last decade. Also, it is noticed that a 10 C increase in the chip temperature cycle amplitude decreases the lifetime by 40%. A thermal model for the chip temperature estimation is developed. The model is based on power loss estimation of the chip from the output current of the frequency converter. The model is verified with a purpose-built test equipment, which allows simultaneous measurement and simulation of the chip temperature with an arbitrary load waveform. The measurement system is shown to be convenient for studying the thermal behavior of the chip. It is found that the thermal model has a 5 C accuracy in the temperature estimation. The temperature cycles that the power semiconductor chip has experienced are counted by the rainflow algorithm. The counted cycles are compared with the experimentally verified power cycling curves to estimate the life consumption based on the mission profile of the drive. The methods are validated by the lifetime estimation of a power module in a direct-driven wind turbine. The estimated lifetime of the IGBT power module in a direct-driven wind turbine is 15 000 years, if the turbine is located in south-eastern Finland.

Internal quality control indicators of cervical cytopathology exams performed in laboratories monitored by the External Quality Control Laboratory

PURPOSE: To evaluate the impact of continued education provided by an external quality control laboratory on the indicators of internal quality control of cytopathology exams.METHODS: The internal quality assurance indicators for cytopathology exams from 12 laboratories monitored by the External Quality Control Laboratory were evaluated. Overall, 185,194 exams were included, 98,133 of which referred to the period preceding implementation of a continued education program, while 87,061 referred to the period following this intervention. Data were obtained from the Cervical Cancer Database of the Brazilian National Health Service.RESULTS: Following implementation of the continued education program, the positivity index (PI) remained within recommended limits in four laboratories. In another four laboratories, the PI progressed from below the limits to within the recommended standards. In one laboratory, the PI remained low, in two laboratories, it remained very low, and in one, it increased from very low to low. The percentage of exams compatible with a high-grade squamous intraepithelial lesion (HSIL) remained within the recommended limits in five laboratories, while in three laboratories it progressed from below the recommended levels to >0.4% of the total number of satisfactory exams, and in four laboratories it remained below the standard limit. Both the percentage of atypical squamous cells of undetermined significance (ASC-US) in relation to abnormal exams, and the ratio between ASC-US and intraepithelial lesions remained within recommended levels in all the laboratories investigated.CONCLUSION: An improvement was found in the indicators represented by the positivity index and the percentage of exams compatible with a high-grade squamous intraepithelial lesion, showing that the role played by the external quality control laboratory in providing continued education contributed towards improving laboratory staff skills in detecting cervical cancer precursor lesions.

Spatial multicriteria decision analysis for the siting of on-shore wind power in Kemiönsaari

Wind power is a low-carbon energy production form that reduces the dependence of society on fossil fuels. Finland has adopted wind energy production into its climate change mitigation policy, and that has lead to changes in legislation, guidelines, regional wind power areas allocation and establishing a feed-in tariff. Wind power production has indeed boosted in Finland after two decades of relatively slow growth, for instance from 2010 to 2011 wind energy production increased with 64 %, but there is still a long way to the national goal of 6 TWh by 2020. This thesis introduces a GIS-based decision-support methodology for the preliminary identification of suitable areas for wind energy production including estimation of their level of risk. The goal of this study was to define the least risky places for wind energy development within Kemiönsaari municipality in Southwest Finland. Spatial multicriteria decision analysis (SMCDA) has been used for searching suitable wind power areas along with many other location-allocation problems. SMCDA scrutinizes complex ill-structured decision problems in GIS environment using constraints and evaluation criteria, which are aggregated using weighted linear combination (WLC). Weights for the evaluation criteria were acquired using analytic hierarchy process (AHP) with nine expert interviews. Subsequently, feasible alternatives were ranked in order to provide a recommendation and finally, a sensitivity analysis was conducted for the determination of recommendation robustness. The first study aim was to scrutinize the suitability and necessity of existing data for this SMCDA study. Most of the available data sets were of sufficient resolution and quality. Input data necessity was evaluated qualitatively for each data set based on e.g. constraint coverage and attribute weights. Attribute quality was estimated mainly qualitatively by attribute comprehensiveness, operationality, measurability, completeness, decomposability, minimality and redundancy. The most significant quality issue was redundancy as interdependencies are not tolerated by WLC and AHP does not include measures to detect them. The third aim was to define the least risky areas for wind power development within the study area. The two highest ranking areas were Nordanå-Lövböle and Påvalsby followed by Helgeboda, Degerdal, Pungböle, Björkboda, and Östanå-Labböle. The fourth aim was to assess the recommendation reliability, and the top-ranking two areas proved robust whereas the other ones were more sensitive.

Indoor air quality at a waste incineration plant in Finland

Waste has been incinerated for energy utilization for more than a hundred years, but the harmful emissions emitted from the incineration plants did not begin to cause concern until the 1980s. Many plants were shutdown and the waste incineration plant in Kyläsaari Helsinki was one of them. In later years, new landfill regulations have increased the interest in waste incineration. During the last year, four new plants were taken into operation in Finland, Westenergy in Vaasa among them. The presence of dust has been observed indoors at Westenergy waste incineration plant. Dust is defined as particles with a diameter above 10 μm, while fine particles have a diameter smaller than 2.5 μm, ultrafine under 0.1 μm and nanoparticles under 0.05 μm. In recent years, the focus of particle health research has been changed to investigate smaller particles. Ultrafine particles have been found to be more detrimental to health than larger particles. Limit values regulating the concentrations of ultrafine particles have not been determined yet. The objective of this thesis was to investigate dust and particles present inside the Westenergy waste incineration facility. The task was to investigate the potential pollutant sources and to give recommendations of how to minimize the presence of dust and particles in the power plant. The total particle number concentrations and size distributions where measured at 15 points inside the plant with an Engine Exhaust Particle Sizer (EEPS) Spectrometer. The measured particles were mainly in the ultrafine size range. Dust was only visually investigated, since the main purpose was to follow the dust accumulation. The measurement points inside the incineration plant were chosen according to investigate exposure to visitors and workers. At some points probable leakage of emissions were investigated. The measurements were carried out during approximately one month in March–April 2013. The results of the measurements showed that elevated levels of dust and particles are present in the indoor air at the waste incineration plant. The cleanest air was found in the control room, warehouse and office. The most polluted air was near the sources that were investigated due to possible leakage and in the bottom ash hall. However, the concentrations were near measured background concentrations in European cities and no leakage could be detected. The high concentrations were assumed to be a result of a lot of dust and particles present on surfaces that had not been cleaned in a while. The main source of the dust and particles present inside the waste incineration plant was thought to be particles and dust from the outside air. Other activities in the area around the waste incineration facility are ground work activities, stone crushing and traffic, which probably are sources of particle formation. Filtration of the outside air prior entering the facility would probably save personnel and visitors from nuisance and save in cleaning and maintenance costs.

Mitigation possibilities to Greenhouse gas emissions from power production in India

Global warming is assertively the greatest environmental challenge for humans of 21st century. It is primarily caused by the anthropogenic greenhouse gas (GHG) that trap heat in the atmosphere. Because of which, the GHG emission mitigation, globally, is a critical issue in the political agenda of all high-profile nations. India, like other developing countries, is facing this threat of climate change while dealing with the challenge of sustaining its rapid economic growth. India’s economy is closely connected to its natural resource base and climate sensitive sectors like water, agriculture and forestry. Due to Climate change the quality and distribution of India’s natural resources may transform and lead to adverse effects on livelihood of its people. Therefore, India is expected to face a major threat due to the projected climate change. This study proposes possible solutions for GHG emission mitigation that are specific to the power sector of India. The methods discussed here will take Indian power sector from present coal dominant ideology to a system, centered with renewable energy sources. The study further proposes a future scenario for 2050, based on the present Indian government policies and global energy technologies advancements.

Characterization Of Process Efficiency Improvement In Laser Additive Manufacturing

Laser additive manufacturing (LAM), known also as 3D printing, has gained a lot of interest in past recent years within various industries, such as medical and aerospace industries. LAM enables fabrication of complex 3D geometries by melting metal powder layer by layer with laser beam. Research in laser additive manufacturing has been focused in development of new materials and new applications in past 10 years. Since this technology is on cutting edge, efficiency of manufacturing process is in center role of research of this industry. Aim of this thesis is to characterize methods for process efficiency improvements in laser additive manufacturing. The aim is also to clarify the effect of process parameters to the stability of the process and in microstructure of manufactured pieces. Experimental tests of this thesis were made with various process parameters and their effect on build pieces has been studied, when additive manufacturing was performed with a modified research machine representing EOSINT M-series and with EOS EOSINT M280. Material used was stainless steel 17-4 PH. Also, some of the methods for process efficiency improvements were tested. Literature review of this thesis presents basics of laser additive manufacturing, methods for improve the process efficiency and laser beam – material- interaction. It was observed that there are only few public studies about process efficiency of laser additive manufacturing of stainless steel. According to literature, it is possible to improve process efficiency with higher power lasers and thicker layer thicknesses. The process efficiency improvement is possible if the effect of process parameter changes in manufactured pieces is known. According to experiments carried out in this thesis, it was concluded that process parameters have major role in single track formation in laser additive manufacturing. Rough estimation equations were created to describe the effect of input parameters to output parameters. The experimental results showed that the WDA (width-depth-area of cross-sections of single track) is correlating exponentially with energy density input. The energy density input is combination of the input parameters of laser power, laser beam spot diameter and scan speed. The use of skin-core technique enables improvement of process efficiency as the core of the part is manufactured with higher laser power and thicker layer thickness and the skin with lower laser power and thinner layer thickness in order to maintain high resolution. In this technique the interface between skin and core must have overlapping in order to achieve full dense parts. It was also noticed in this thesis that keyhole can be formed in LAM process. It was noticed that the threshold intensity value of 106 W/cm2 was exceeded during the tests. This means that in these tests the keyhole formation was possible.

School Bullies’ Quest for Power: Implications for Group Dynamics and Intervention

Bullying is characterized by an inequality of power between perpetrator and target. Findings that bullies can be highly popular have helped redefine the old conception of the maladjusted school bully into a powerful individual exerting influence on his peers from the top of the peer status hierarchy. Study I is a conceptual paper that explores the conditions under which a skillful, socially powerful bully can use the peer group as a means of aggression and suggests that low cohesion and low quality of friendships make groups easier to manipulate. School bullies’ high popularity should be a major obstacle for antibullying efforts, as bullies are unlikely to cease negative actions that are rewarding, and their powerful position could discourage bystanders from interfering. Using data from the Finnish program KiVa, Study II supported the hypothesis that antibullying interventions are less effective with popular bullies in comparison to their unpopular counterparts. In order to design interventions that can address the positive link between popularity and aggression, it is necessary to determine in which contexts bullies achieve higher status. Using an American sample, Study III examined the effects of five classroom features on the social status that peers accord to aggressive children, including classroom status hierarchy, academic level and grade level, controlling for classroom mean levels of aggression and ethnic distribution. Aggressive children were more popular and better liked in fifth grade relative to fourth grade and in classrooms of higher status hierarchy. Surprisingly, the natural emergence of status hierarchies in children’s peer groups has long been assumed to minimize aggression. Whether status hierarchies hinder or promote bullying is a controversial question in the peer relations’ literature. Study IV aimed at clarifying this debate by testing the effects of the degree of classroom status hierarchy on bullying. Higher hierarchy was concrrently associated with bullying and predictive of higher bullying six months later. As bullies’ quest for power is increasingly acknowledged, some researchers suggest teaching bullies to attain the elevated status they yearn for through prosocial acts. Study V cautions against such solutions by reviewing evidence that prosocial behaviors enacted with the intention of controlling others can be as harmful as aggression.

Software product line for power converters

Työn tilaajana toimi Visedo Oy. Työn tavoitteina oli tutkia Visedo Oy:n ohjelmistokehityksen nykytila, tunnistaa seuraavat parannuskohteet ja antaa ohjeita havaittujen parannuskohteiden korjaamiseksi. Visedo Oy:n tehonmuokkain ohjelmistokehityksen nykytilaa käsiteltiin neljän valitun osa-alueen näkökulmasta: ohjelmistoarkkitehtuurityyli, komponenttipohjainen ohjelmistokehitys, ohjelmistotuotelinjojen kehitysmenetelmät ja ohjelmistovariaatioiden hallinta. Valituilla osa-alueilla havaittujen parannuskohteiden perusteella annettiin korjausehdotuksia: ohjelmistoarkkitehtuurin rakenteeseen, komponenttien jakautumiselle, komponenttien koostamiselle ja komponenttien versioinnille. Lisäksi ehdotettiin uudenlaista ohjelmistotuotelinja rakennetta, joka yhdistää kerros- ja komponenttipohjaiset arkkitehtuurityylit mahdollistaen ominaisuuksiltaan eroavien tehonmuokkain ohjelmistojen hallinnan.

Correlation between high molecular weight gluten subunits composition and bread-making quality in Brazilian wheat

Bread-making quality is one of the most important targets in the genetic improvement of wheat. Although extensive analyses of quality traits such as farinography, sodium dodecyl sulfate (SDS) sedimentation, alveography, and baking are made in breeding programs, these analyses require high amounts of seeds which are obtained only in late generations. In this experiment the statistical correlations between the high molecular weight subunit of glutenin and bread-making quality measured by alveograph, farinograph and SDS sedimentation were evaluated. Seventeen wheat genotypes were grown under the same conditions, each producing about 1 kg of seeds for the evaluations. The high molecular weight (HMW) glutenin subunits were analyzed by SDS-PAGE. Statistical correlations were highly significant between HMW glutenin subunits and alveograph and SDS sedimentation. These results indicate the possibility of manipulating major genes for wheat seed quality by coupling traditional breeding with non-destructive single seed analysis. Only half seed is necessary to perform the SDS-PAGE analysis. Therefore, the other half seed can be planted to generate the progeny. Seed yield and SDS sedimentation were statistically correlated, indicating the possibility of simultaneous selection for both traits

Efficacy, safety, quality control, marketing and regulatory guidelines for herbal medicines (phytotherapeutic agents)

This review highlights the current advances in knowledge about the safety, efficacy, quality control, marketing and regulatory aspects of botanical medicines. Phytotherapeutic agents are standardized herbal preparations consisting of complex mixtures of one or more plants which contain as active ingredients plant parts or plant material in the crude or processed state. A marked growth in the worldwide phytotherapeutic market has occurred over the last 15 years. For the European and USA markets alone, this will reach about $7 billion and $5 billion per annum, respectively, in 1999, and has thus attracted the interest of most large pharmaceutical companies. Insufficient data exist for most plants to guarantee their quality, efficacy and safety. The idea that herbal drugs are safe and free from side effects is false. Plants contain hundreds of constituents and some of them are very toxic, such as the most cytotoxic anti-cancer plant-derived drugs, digitalis and the pyrrolizidine alkaloids, etc. However, the adverse effects of phytotherapeutic agents are less frequent compared with synthetic drugs, but well-controlled clinical trials have now confirmed that such effects really exist. Several regulatory models for herbal medicines are currently available including prescription drugs, over-the-counter substances, traditional medicines and dietary supplements. Harmonization and improvement in the processes of regulation is needed, and the general tendency is to perpetuate the German Commission E experience, which combines scientific studies and traditional knowledge (monographs). Finally, the trend in the domestication, production and biotechnological studies and genetic improvement of medicinal plants, instead of the use of plants harvested in the wild, will offer great advantages, since it will be possible to obtain uniform and high quality raw materials which are fundamental to the efficacy and safety of herbal drugs.

Kunnossapidon työlupakäytäntöjen parantaminen mobiilijärjestelmän avulla

Viranomaisvaatimuksen mukaan ydinvoimalaitoksen toiminnan perustana tulee olla johtamisjärjestelmä, joka kattaa organisaation rakenteen ja prosessit, henkilöstön vastuut ja valtuudet sekä päätöksentekomenettelyt. Sen tulee myös tukea hyvää turvallisuuskulttuuria ja varmistaa että ydin- ja säteilyturvallisuuteen liittyvät vaatimukset täyttyvät kaikessa toiminnassa. Loviisan voimalaitoksen johtamisjärjestelmä ohjaa voimalaitoksen käyttötoimintaa ja se on kuvattuna voimalaitosohjeistossa joka käsittää voimalaitoksen politiikat, laadunvarmistuskäsikirjat sekä erilaiset ohjeet. Loviisan voimalaitoksen toimintaa seurataan ja arvioidaan säännöllisesti mm. auditoinneilla. Seurannan ja arvioinnin tarkoituksena on tunnistaa johtamisjärjestelmän mahdolliset kehittämisalueet ja varmistaa täyttääkö toiminta sille asetetut vaatimukset. Tämä opinnäyte pohjautuu sisäisessä auditoinnissa havaittuun puutteeseen voimalaitoksen työlupakäytännöissä. Työssä toteutettiin mobiilijärjestelmä, jonka tarkoituksena on parantaa kunnossapitotöihin liittyvien työlupien jälkiseurantaa. Tällaisia työlupaa vaativia töitä ovat mm. tuli- ja säteilytyöt, joiden suorittamiseen liittyy riskejä kuten palo- ja räjähdysvaara tai tarpeeton altistuminen säteilylle. Mobiilijärjestelmä toteutettiin monikansallisena projektina osana laajempaa Loviisan voimalaitoksen laitostietojärjestelmän uusintaprojektia.

Defining the keyhole modes – the effects on the weld geometry and the molten pool behaviour in high power laser welding of stainless steels

Keyhole welding, meaning that the laser beam forms a vapour cavity inside the steel, is one of the two types of laser welding processes and currently it is used in few industrial applications. Modern high power solid state lasers are becoming more used generally, but not all process fundamentals and phenomena of the process are well known and understanding of these helps to improve quality of final products. This study concentrates on the process fundamentals and the behaviour of the keyhole welding process by the means of real time high speed x-ray videography. One of the problem areas in laser welding has been mixing of the filler wire into the weld; the phenomena are explained and also one possible solution for this problem is presented in this study. The argument of this thesis is that the keyhole laser welding process has three keyhole modes that behave differently. These modes are trap, cylinder and kaleidoscope. Two of these have sub-modes, in which the keyhole behaves similarly but the molten pool changes behaviour and geometry of the resulting weld is different. X-ray videography was used to visualize the actual keyhole side view profile during the welding process. Several methods were applied to analyse and compile high speed x-ray video data to achieve a clearer image of the keyhole side view. Averaging was used to measure the keyhole side view outline, which was used to reconstruct a 3D-model of the actual keyhole. This 3D-model was taken as basis for calculation of the vapour volume inside of the keyhole for each laser parameter combination and joint geometry. Four different joint geometries were tested, partial penetration bead on plate and I-butt joint and full penetration bead on plate and I-butt joint. The comparison was performed with selected pairs and also compared all combinations together.

Linking supplier delivery risk to outbound delivery service performance improvement

Customer satisfaction should be the main focus for all of the parts of the business. Usually supply chain behind the business is in a key role when this focus is pursued especially in repair service business. When focusing on the materials that are needed to make repairs to equipment under service contracts, the time aspect of quality is critical. Do late deliveries from supplier have an effect on the service performance of repairs when distribution center of a centralized purchasing unit is acting as a buffer between suppliers and repair service business? And if so, how should the improvement efforts be prioritized? These are the two main questions that this thesis focuses on. Correlation and linear regression was tested between service levels of supplier and distribution center. Percentage of on-time deliveries were compared to outbound delivery service level. It was found that there is statistically significant correlation between inbound and outbound operations success. The other main question of the thesis, improvement prioritization, was answered by creating material availability based supplier classification and additional to that, by developing the decision process for the analysis of most critical suppliers. This was built on a basis of previous supplier and material classification methods.

Power efficiency estimation and simulation of different control methods for the rotary screw compressor

Nowadays the energy efficiency has become one of the most concerned topics. Compressors are the equipment, which is very common in industry. Moreover, they tend to operate during long cycles and therefore even small decrease in power consumption can significantly reduce electricity costs during the year. And therefore it is important to investigate ways of increasing the energy efficiency of the compressors. In the thesis rotary screw compressor alongside with different control approaches is described. Simulation models for various control types of rotary screw compressor are developed. Analysis of laboratory equipment is conducted and results are compared with simulation. Suggestions of the real laboratory equipment improvement are given.

Green welding in practice

Efficient production and consumption of energy has become the top priority of national and international policies around the world. Manufacturing industries have to address the requirements of the government in relation to energy saving and ecologically sustainable products. These industries are also concerned with energy and material usage due to their rising costs. Therefore industries have to find solutions that can support environmental preservation yet maintain competitiveness in the market. Welding, a major manufacturing process, consumes a great deal of material and energy. It is a crucial process in improving a product’s life-cycle cost, strength, quality and reliability. Factors which lead to weld related inefficiencies have to be effectively managed, if industries are to meet their quality requirements and fulfil a high-volume production demand. Therefore it is important to consider some practical strategies in welding process for optimization of energy and material consumption. The main objective of this thesis is to explore the methods of minimizing the ecological footprint of the welding process and methods to effectively manage its material and energy usage in the welding process. The author has performed a critical review of the factors including improved weld power source efficiency, efficient weld techniques, newly developed weld materials, intelligent welding systems, weld safety measures and personnel training. The study lends strong support to the fact that the use of eco-friendly welding units and the quality weld joints obtained with minimum possible consumption of energy and materials should be the main directions of improvement in welding systems. The study concludes that, gradually implementing the practical strategies mentioned in this thesis would help the manufacturing industries to achieve on the following - reduced power consumption, enhanced power control and manipulation, increased deposition rate, reduced cycle time, reduced joint preparation time, reduced heat affected zones, reduced repair rates, improved joint properties, reduced post-weld operations, improved automation, improved sensing and control, avoiding hazardous conditions and reduced exposure of welder to potential hazards. These improvement can help in promotion of welding as a green manufacturing process.