Tehokerrointa korjaava skalaariohjaus puoliohjatussa ja kuusikytkintasasuuntaajassa

Verkon harmonisvirtoja rajoittavien standardien tiukentuessa joudutaan etenkin suuritehoisissa tehoelektronisissa laitteissa siirtymään aktiivisiin transistoriohjattuihin tasasuuntaajiin, jotka korjaavat tehokerrointa ja siten pienentävät verkkoon kytkeytyviä häiriövirtoja. Tässä diplomityössä esitellään yleisimpien kolmivaiheisten tasasuuntaajatopologioiden eroja ja vertaillaan puoliohjatun kolmikytkintopologian ja kuusikytkintopologian suorituskykyä tehokertoimen ja harmonissärön osalta, 16 kilowatin teholuokan taajuusmuuttajassa. Tasasuuntaajille tehtiin skalaariohjaukseen perustuva simulointimalli. Työn tavoitteena esitellään simulointitulokset harmonistason sekä tehokertoimen osalta. Työ liittyy Lappeenrannan teknillisen yliopiston sovelletun elektroniikan laboratorion ja Vacon Oyj:n yhteiseen hankkeeseen.

New Distance Transforms for Gray Level Image Compression

This thesis deals with distance transforms which are a fundamental issue in image processing and computer vision. In this thesis, two new distance transforms for gray level images are presented. As a new application for distance transforms, they are applied to gray level image compression. The new distance transforms are both new extensions of the well known distance transform algorithm developed by Rosenfeld, Pfaltz and Lay. With some modification their algorithm which calculates a distance transform on binary images with a chosen kernel has been made to calculate a chessboard like distance transform with integer numbers (DTOCS) and a real value distance transform (EDTOCS) on gray level images. Both distance transforms, the DTOCS and EDTOCS, require only two passes over the graylevel image and are extremely simple to implement. Only two image buffers are needed: The original gray level image and the binary image which defines the region(s) of calculation. No other image buffers are needed even if more than one iteration round is performed. For large neighborhoods and complicated images the two pass distance algorithm has to be applied to the image more than once, typically 3 10 times. Different types of kernels can be adopted. It is important to notice that no other existing transform calculates the same kind of distance map as the DTOCS. All the other gray weighted distance function, GRAYMAT etc. algorithms find the minimum path joining two points by the smallest sum of gray levels or weighting the distance values directly by the gray levels in some manner. The DTOCS does not weight them that way. The DTOCS gives a weighted version of the chessboard distance map. The weights are not constant, but gray value differences of the original image. The difference between the DTOCS map and other distance transforms for gray level images is shown. The difference between the DTOCS and EDTOCS is that the EDTOCS calculates these gray level differences in a different way. It propagates local Euclidean distances inside a kernel. Analytical derivations of some results concerning the DTOCS and the EDTOCS are presented. Commonly distance transforms are used for feature extraction in pattern recognition and learning. Their use in image compression is very rare. This thesis introduces a new application area for distance transforms. Three new image compression algorithms based on the DTOCS and one based on the EDTOCS are presented. Control points, i.e. points that are considered fundamental for the reconstruction of the image, are selected from the gray level image using the DTOCS and the EDTOCS. The first group of methods select the maximas of the distance image to new control points and the second group of methods compare the DTOCS distance to binary image chessboard distance. The effect of applying threshold masks of different sizes along the threshold boundaries is studied. The time complexity of the compression algorithms is analyzed both analytically and experimentally. It is shown that the time complexity of the algorithms is independent of the number of control points, i.e. the compression ratio. Also a new morphological image decompression scheme is presented, the 8 kernels' method. Several decompressed images are presented. The best results are obtained using the Delaunay triangulation. The obtained image quality equals that of the DCT images with a 4 x 4

Radio Frequency Measurement Method for Detecting Bearing Currents in Induction Motors

Induction motors are widely used in industry, and they are generally considered very reliable. They often have a critical role in industrial processes, and their failure can lead to significant losses as a result of shutdown times. Typical failures of induction motors can be classified into stator, rotor, and bearing failures. One of the reasons for a bearing damage and eventually a bearing failure is bearing currents. Bearing currents in induction motors can be divided into two main categories; classical bearing currents and inverter-induced bearing currents. A bearing damage caused by bearing currents results, for instance, from electrical discharges that take place through the lubricant film between the raceways of the inner and the outer ring and the rolling elements of a bearing. This phenomenon can be considered similar to the one of electrical discharge machining, where material is removed by a series of rapidly recurring electrical arcing discharges between an electrode and a workpiece. This thesis concentrates on bearing currents with a special reference to bearing current detection in induction motors. A bearing current detection method based on radio frequency impulse reception and detection is studied. The thesis describes how a motor can work as a “spark gap” transmitter and discusses a discharge in a bearing as a source of radio frequency impulse. It is shown that a discharge, occurring due to bearing currents, can be detected at a distance of several meters from the motor. The issues of interference, detection, and location techniques are discussed. The applicability of the method is shown with a series of measurements with a specially constructed test motor and an unmodified frequency-converter-driven motor. The radio frequency method studied provides a nonintrusive method to detect harmful bearing currents in the drive system. If bearing current mitigation techniques are applied, their effectiveness can be immediately verified with the proposed method. The method also gives a tool to estimate the harmfulness of the bearing currents by making it possible to detect and locate individual discharges inside the bearings of electric motors.

Managerial Careers in the IT Industry: Women in China and in Finland

This research focuses on the career experiences of women managers in the IT industry in China and Finland, two countries with different cultures, policies, size of population, and social and economic structures regarding work-life support and equal opportunities. The object of this research is to present a cross-cultural comparison of women’s career experiences and how women themselves understand and account for their careers. The study explores how the macro and the micro levels of cultural and social processes become manifested in the lives of individual women. The main argument in this thesis is that culture plays a crucial role in making sense of women’s career experiences, although its role should be understood through its interrelationship with other social processes, e.g., institutional relations, social policies, industrial structures and organizations, as well as globalization. The interrelationship of a series of cultural and social processes affects individuals’ attitudes to, and arrangement and organization of, their work and family lives. This thesis consists of two parts. The first part introduces the research topic and discusses the overall results. The second part comprises five research papers. The main research question of the study is: How do cultural and social processes affect the experiences of women managers? Quantitative and qualitative research methods, which include in-depth interviews, Q-methodology, interpretive analysis, and questionnaires, are used in the study. The main theoretical background is culturally sensitive career theory and the theory of individual differences. The results of this study are viewed through a feminist lens. The research methodology applied allows new explorations on how demographic factors, work experiences, lifestyle issues, and organizational cultures can jointly affect women’s managerial careers. The sample group used in the research is 42 women managers working in IT companies in China (21) and Finland (21). The results of the study illustrate the impact of history, tradition, culture, institutional relations, social politics, industry and organizations, and globalization on the careers of women managers. It is claimed that the role of culture – cultural norms within nations and organizations – is of great importance in the relationship of gender and work. Women’s managerial careers are affected by multiple factors (personal, social and cultural) reflecting national and inter-individual differences. The results of the study contribute to research on careers, adding particularly to the literature on gender, work and culture, and offering a complex and holistic perspective for a richer understanding of pluralism and global diversity. The results of the study indicate how old and new career perspectives are evidenced in women managers in the IT industry. The research further contributes to an understanding of women’s managerial careers from a cross-culture perspective. In addition, the study contributes to the literature on culture and extends understanding of Hofstede’s work. Further, most traditional career theories do not perceive the importance of culture in determining an individual’s career experience and this study richens understanding of women managers’ careers and has considerable implications for international human resource management. The results of this study emphasize the need, when discussing women managers’ careers, to understand the ways by which gendering is produced rather than merely examining gender differences. It is argued that the meaning of self-knowledge is critical. Further, the environment where the careers under study develop differs greatly; China and Finland are very different – culturally, historically and socially. The findings of this study should, therefore, be understood as a holistic, specific, and contextually-bound.

ACM/IEEE Curricula ja tietotekniikan osaston kandidaatin tutkinnon vertailu, arviointi ja soveltaminen

Tietotekniikan käyttö on yleistynyt sekä yritysmaailmassa että kotikäytössä viimeisen kahden vuosikymmenen aikana. Tietotekniikan opetuksen ajanmukaisuus onkin tärkeää, jotta yritykset saisivat palkattua tarpeitaan vastaavia tietotekniikan ammattilaisia. Tässä kandidaatintyössä perehdytään ACM/IEEE:n opetussuunnitelmiin vertailemalla ja arvioimalla niitä Lappeenrannan teknillisen yliopiston tietotekniikan kandidaatin tutkintoon. Työssä tehtävä vertailu ja arviointi pohjautuvat kirjallisuuteen sekä haastatteluihin Lappeenrannan teknillisen yliopiston tietotekniikan osastolla.

Inter organizational learning within and by innovation networks

The thesis deals with the phenomenon of learning between organizations in innovation networks that develop new products, services or processes. Inter organizational learning is studied especially at the level of the network. The role of the network can be seen as twofold: either the network is a context for inter organizational learning, if the learner is something else than the network (organization, group, individual), or the network itself is the learner. Innovations are regarded as a primary source of competitiveness and renewal in organizations. Networking has become increasingly common particularly because of the possibility to extend the resource base of the organization through partnerships and to concentrate on core competencies. Especially in innovation activities, networks provide the possibility to answer the complex needs of the customers faster and to share the costs and risks of the development work. Networked innovation activities are often organized in practice as distributed virtual teams, either within one organization or as cross organizational co operation. The role of technology is considered in the research mainly as an enabling tool for collaboration and learning. Learning has been recognized as one important collaborative process in networks or as a motivation for networking. It is even more important in the innovation context as an enabler of renewal, since the essence of the innovation process is creating new knowledge, processes, products and services. The thesis aims at providing enhanced understanding about the inter organizational learning phenomenon in and by innovation networks, especially concentrating on the network level. The perspectives used in the research are the theoretical viewpoints and concepts, challenges, and solutions for learning. The methods used in the study are literature reviews and empirical research carried out with semi structured interviews analyzed with qualitative content analysis. The empirical research concentrates on two different areas, firstly on the theoretical approaches to learning that are relevant to innovation networks, secondly on learning in virtual innovation teams. As a result, the research identifies insights and implications for learning in innovation networks from several viewpoints on organizational learning. Using multiple perspectives allows drawing a many sided picture of the learning phenomenon that is valuable because of the versatility and complexity of situations and challenges of learning in the context of innovation and networks. The research results also show some of the challenges of learning and possible solutions for supporting especially network level learning.

Haja-asutusalueiden sähkönjakelujärjestelmien kehittäminen – erityisesti 1000 V jakelujännitteen käyttömahdollisuudet

Yhteiskunnan riippuvuus sähköstä on lisääntynyt voimakkaasti viime vuosikymmenien aikana. Sähkönjakelussa esiintyneet lyhyet ja pitkät keskeytykset ovat osoittaneet yhteiskunnan haavoittuvuuden ja yhteiskunta kestää entistä vähemmän sähkönjakelussa tapahtuvia häiriöitä. Keskeytyksistä aiheutuneiden haittojen arvostus on kasvanut ja tämä on luonut taloudelliset perusteet sähkön laatua parantaville investoinneille. Haja-asutusalueiden keskijänniteverkon johdot on rakennettu avojohtoina ja siten ne ovat alttiita sääolosuhteista johtuville myrsky- ja lumikuormavaurioille. Ilmastomuutoksen ennustetaan lisäävän tuulisuutta ja siten ongelmat sähkönjakelussa mahdollisesti lisääntyvät. Taajamissa käytetään enemmän kaapeleita ja johtolähdöt ovat lyhyitä, joten myrskyistä aiheutuvia keskeytyksiä on vähemmän kuin haja-asutusalueella. Olemassa olevat jakeluverkot ovat käytössä vielä vuosikymmeniä, joten uuden tekniikan kehittämisen rinnalla on kehitettävä myös olemassa olevaa jakeluverkkoa ja sen ylläpitoa. Ylläpidon tavoitteena on käyttövarmuuden parantamisen lisäksi huolehtia siitä, että jakeluverkkoihin sitoutunut omaisuus säilyttää arvonsa mahdollisimman hyvin pitoajan loppuun saakka. Jakeluverkkoihin investoitiin paljon 1950–70-luvuilla. Tältä ajalta on yhä käytössä puupylväitä, joiden ikääntymisen takia korvausinvestointien tarve kasvaa. Hyvänä puolena tässä on että käyttövarmuuden parantamiseksi olemassa olevaa jakeluverkkoa ei tarvitse uusia ennenaikaisesti. Tutkimuksessa päähuomio on haja-asutusalueiden 20 kV keskijänniteverkon kehittämisessä, sillä yli 90 % asiakkaiden kokemista keskeytyksistä johtuu keskijänniteverkon vioista. Erityisesti johtorakenteisiin ja johtojen sijoittamiseen on kiinnitettävä huomiota. Käyttövarmuuden lisäksi jakeluverkkojen kehittämistä ohjaavia tekijöitä ovat taloudellisuus, ympäristön huomioiminen, viranomaisvalvonta sekä asiakkaiden ja omistajien odotukset. Haja-asutusalueilla taloudelliset haasteet ovat suuret vakituisen väestön vähenemisen ja mahdollisesti sähköntarpeen pienenemisen takia. Taloudellisuus korostuu ja riskit kasvavat, kun tuottojen määrä supistuu tarvittaviin jakeluverkon investointeihin ja ylläpitokustannuksiin verrattuna. Ristiriitaa aiheuttaa se, että asiakkaat odottavat sähkönjakelulta parempaa luotettavuutta, mutta paremmasta sähkönlaadusta ei olla valmiita maksamaan juurikaan nykyistä enempää. Jakeluverkkojen kehittämistä voi hidastaa myös viranomaisvalvonta, jos tuottoja ei voida lisätä investointien lisätarpeiden suhteessa. Tutkimuksessa on analysoitu yleisellä tasolla kaapeloinnin lisäämistä, korkeiden pylväiden käyttämistä, leveitä johtokatuja, edullisten ja yksinkertaisten sähköasemien rakentamista haja-asutusalueille ja automaatioasemien lisäämistä keskijänniteverkon solmupisteisiin. Erityisesti tutkimuksessa on analysoitu uutena tekniikkana 1000 V jännitteen käyttömahdollisuutta jakeluverkkojen kehittämisessä. Sähköjohtojen siirtäminen teiden varsiin parantaa käyttövarmuutta, vaikka johdot rakennetaan samalla tekniikalla kuin olemassa olevat johdot. Hajaasutusalueille rakennettavilla sähköasemilla pitkät syöttöjohdot voidaan jakaa pienemmiksi syöttöalueiksi, jolloin keskeytyksistä aiheutuvat haitat koskettavat kerrallaan pienempää asiakasmäärää. Samaan tulokseen päästään oikein sijoitetuilla ja toteutetuilla automaatioasemilla. Tutkimuksen mukaan lupaavaksi tekniikaksi jakeluverkkojen kehittämisessä on osoittautumassa 1000 V jänniteportaan ottaminen 400 V pienjännitteen lisäksi. 1000 V verkoilla voidaan korvata häiriöherkkiä 20 kV keskijänniteverkon lyhyitä, alle viiden kilometrin pituisia haarajohtoja ja haarajohtojen jatkeita, missä siirrettävät tehot ovat pieniä. Uudessa jakelujärjestelmässä sähkö tuodaan 1000 V jännitteellä lähelle asiakasta, jossa jännite muunnetaan normaaliksi asiakkaille soveltuvaksi 400/230 V jännitteeksi. Edullisuus perustuu siihen, että rakentamisessa käytetään samoja pienjännitejohtoja kuin asiakkaille menevässä 400 V pienjänniteverkossa. 1000 V jakelutekniikassa sekä investointikustannukset että ylläpitokustannukset ovat pienemmät kuin perinteisessä 20 kV ilmajohtotekniikassa. 1000 V johdot säästävät maisemaa, sillä ne eivät tarvitse leveää johtokatua kuten 20 kV keskijännitejohdot. 1000 V verkkojen käyttö soveltuukin erityisesti vapaa-ajanasuntojen sähköistykseen herkissä ranta- ja järvimaisemissa. 1000 V verkot mahdollistavat kaapeliauraamisen lisäämisen ja näin voidaan vähentää ympäristöä haittaavien kyllästettyjen pylväiden käyttöä. 1000 V jakeluverkkojen osalta tutkimustyön tuloksia on sovellettu suomalaisessa Suur-Savon Sähkö Oy:ssä. Käytännön kokemuksia 1000 V jakelujärjestelmästä on useista kymmenistä kohteista. Tutkimustulokset osoittavat, ettei keskijänniteverkon maakaapelointi hajaasutusalueilla ole taloudellisesti kannattavaa nykyisillä keskeytyksistä aiheutuvilla haitta-arvoilla, mutta jos keskeytyskustannusten arvostus kasvaa, tulee kaapelointi kannattavaksi monissa paikoissa. Myös myrskyisyyden ja myrskyistä aiheutuvien jakelukeskeytysten lisääntyminen tekisi kaapeloinnista kannattavan. Tulevaisuudessa jakeluverkkojen rakentaminen on entistä monimuotoisempi tehtävä, jossa taloudellisuuden ja käyttövarmuuden lisäksi on huomioitava asiakkaat, omistajat, viranomaiset ja ympäristö. Tutkimusta jakelutekniikan kehittämiseksi tarvitaan edelleen. Tulevaisuuden osalta haja-asutusalueiden jakeluverkkojen kehittämiseen liittyy paljon epävarmuuksia. Hajautetun kiinteistökohtaisen sähköntuotannon lisääntyminen voi tehdä jakeluverkoista nykyistä tarpeettomampia, mutta esimerkiksi liikenteen sähköistyminen voi kasvattaa jakeluverkkojen merkitystä. Tästä syystä jakeluverkkojen rakentamisessa tarvitaan joustavuutta, jotta tarvittaessa voidaan helposti sopeutua erilaisiin kehityssuuntiin.

RTOS Framework for Real-Time Control System

This thesis is done as a complementary part for the active magnet bearing (AMB) control software development project in Lappeenranta University of Technology. The main focus of the thesis is to examine an idea of a real-time operating system (RTOS) framework that operates in a dedicated digital signal processor (DSP) environment. General use real-time operating systems do not necessarily provide sufficient platform for periodic control algorithm utilisation. In addition, application program interfaces found in real-time operating systems are commonly non-existent or provided as chip-support libraries, thus hindering platform independent software development. Hence, two divergent real-time operating systems and additional periodic extension software with the framework design are examined to find solutions for the research problems. The research is discharged by; tracing the selected real-time operating system, formulating requirements for the system, and designing the real-time operating system framework (OSFW). The OSFW is formed by programming the framework and conjoining the outcome with the RTOS and the periodic extension. The system is tested and functionality of the software is evaluated in theoretical context of the Rate Monotonic Scheduling (RMS) theory. The performance of the OSFW and substance of the approach are discussed in contrast to the research theme. The findings of the thesis demonstrates that the forged real-time operating system framework is a viable groundwork solution for periodic control applications.

Position sensorless electrically excited synchronous motor drive for industrial use based on direct flux linkage and torque control

Synchronous machines with an AC converter are used mainly in large drives, for example in ship propulsion drives as well as in rolling mill drives in steel industry. These motors are used because of their high efficiency, high overload capacity and good performance in the field weakening area. Present day drives for electrically excited synchronous motors are equipped with position sensors. Most drives for electrically excited synchronous motors will be equipped with position sensors also in future. This kind of drives with good dynamics are mainly used in metal industry. Drives without a position sensor can be used e.g. in ship propulsion and in large pump and blower drives. Nowadays, these drives are equipped with a position sensor, too. The tendency is to avoid a position sensor if possible, since a sensor reduces the reliability of the drive and increases costs (latter is not very significant for large drives). A new control technique for a synchronous motor drive is a combination of the Direct Flux Linkage Control (DFLC) based on a voltage model and a supervising method (e.g. current model). This combination is called Direct Torque Control method (DTC). In the case of the position sensorless drive, the DTC can be implemented by using other supervising methods that keep the stator flux linkage origin centered. In this thesis, a method for the observation of the drift of the real stator flux linkage in the DTC drive is introduced. It is also shown how this method can be used as a supervising method that keeps the stator flux linkage origin centered in the case of the DTC. In the position sensorless case, a synchronous motor can be started up with the DTC control, when a method for the determination of the initial rotor position presented in this thesis is used. The load characteristics of such a drive are not very good at low rotational speeds. Furthermore, continuous operation at a zero speed and at a low rotational speed is not possible, which is partly due to the problems related to the flux linkage estimate. For operation in a low speed area, a stator current control method based on the DFLC modulator (DMCQ is presented. With the DMCC, it is possible to start up and operate a synchronous motor at a zero speed and at low rotational speeds in general. The DMCC is necessary in situations where high torque (e.g. nominal torque) is required at the starting moment, or if the motor runs several seconds at a zero speed or at a low speed range (up to 2 Hz). The behaviour of the described methods is shown with test results. The test results are presented for the direct flux linkage and torque controlled test drive system with a 14.5 kVA, four pole salient pole synchronous motor with a damper winding and electric excitation. The static accuracy of the drive is verified by measuring the torque in a static load operation, and the dynamics of the drive is proven in load transient tests. The performance of the drive concept presented in this work is sufficient e.g. for ship propulsion and for large pump drives. Furthermore, the developed methods are almost independent of the machine parameters.

An analytic approach to distribution logistics strategic management

Logistics management is increasingly being recognised by many companies to be of critical concern. The logistics function includes directly or indirectly many of the new areas for achieving or maintaining competitive advantage that companies have been forced to develop due to increasing competitive pressures. The key to achieving a competitive advantage is to manage the logistics function strategically which involves determining the most cost effective method of providing the necessary customer service levels from the many combinations of operating procedures in the areas of transportation, warehousing, order processing and information systems, production, and inventory management. In this thesis, a comprehensive distribution logistics strategic management process is formed by integrating the periodic strategic planning process with a continuous strategic issues management process. Strategic planning is used for defining the basic objectives for a company and assuring co operation and synergy between the different functions of a company while strategic issues management is used on a continuous basis in order to deal with environmental and internal turbulence. The strategic planning subprocess consists of the following main phases: (1) situational analyses, (2) defining the vision and strategic goals for the logistics function, (3) determining objectives and strategies, (4) drawing up tactical action plans, and (5) evaluating the implementation of the plans and making the needed adjustments. The aim of the strategic issues management subprocess is to continuously scan the environment and the organisation for early identification of the issues having a significant impact on the logistics function using the following steps: (1) the identification of trends, (2) assessing the impact and urgency of the identified trends, (3) assigning priorities to the issues, and (4) planning responses to the, issues. The Analytic Hierarchy Process (AHP) is a systematic procedure for structuring any problem. AHP is based on the following three principles: decomposition, comparative judgements, and synthesis of priorities. AHP starts by decomposing a complex, multicriteria problem into a hierarchy where each level consists of a few manageable elements which are then decomposed into another set of elements. The second step is to use a measurement methodology to establish priorities among the elements within each level of the hierarchy. The third step in using AHP is to synthesise the priorities of the elements to establish the overall priorities for the decision alternatives. In this thesis, decision support systems are developed for different areas of distribution logistics strategic management by applying the Analytic Hierarchy Process. The areas covered are: (1) logistics strategic issues management, (2) planning of logistic structure, (3) warehouse site selection, (4) inventory forecasting, (5) defining logistic action and development plans, (6) choosing a distribution logistics strategy, (7) analysing and selecting transport service providers, (8) defining the logistic vision and strategic goals, (9) benchmarking logistic performance, and (10) logistic service management. The thesis demonstrates the potential of AHP as a systematic and analytic approach to distribution logistics strategic management.

Size Effect and Notch Size Effect in Metal Fatigue

It is a well known phenomenon that the constant amplitude fatigue limit of a large component is lower than the fatigue limit of a small specimen made of the same material. In notched components the opposite occurs: the fatigue limit defined as the maximum stress at the notch is higher than that achieved with smooth specimens. These two effects have been taken into account in most design handbooks with the help of experimental formulas or design curves. The basic idea of this study is that the size effect can mainly be explained by the statistical size effect. A component subjected to an alternating load can be assumed to form a sample of initiated cracks at the end of the crack initiation phase. The size of the sample depends on the size of the specimen in question. The main objective of this study is to develop a statistical model for the estimation of this kind of size effect. It was shown that the size of a sample of initiated cracks shall be based on the stressed surface area of the specimen. In case of varying stress distribution, an effective stress area must be calculated. It is based on the decreasing probability of equally sized initiated cracks at lower stress level. If the distribution function of the parent population of cracks is known, the distribution of the maximum crack size in a sample can be defined. This makes it possible to calculate an estimate of the largest expected crack in any sample size. The estimate of the fatigue limit can now be calculated with the help of the linear elastic fracture mechanics. In notched components another source of size effect has to be taken into account. If we think about two specimens which have similar shape, but the size is different, it can be seen that the stress gradient in the smaller specimen is steeper. If there is an initiated crack in both of them, the stress intensity factor at the crack in the larger specimen is higher. The second goal of this thesis is to create a calculation method for this factor which is called the geometric size effect. The proposed method for the calculation of the geometric size effect is also based on the use of the linear elastic fracture mechanics. It is possible to calculate an accurate value of the stress intensity factor in a non linear stress field using weight functions. The calculated stress intensity factor values at the initiated crack can be compared to the corresponding stress intensity factor due to constant stress. The notch size effect is calculated as the ratio of these stress intensity factors. The presented methods were tested against experimental results taken from three German doctoral works. Two candidates for the parent population of initiated cracks were found: the Weibull distribution and the log normal distribution. Both of them can be used successfully for the prediction of the statistical size effect for smooth specimens. In case of notched components the geometric size effect due to the stress gradient shall be combined with the statistical size effect. The proposed method gives good results as long as the notch in question is blunt enough. For very sharp notches, stress concentration factor about 5 or higher, the method does not give sufficient results. It was shown that the plastic portion of the strain becomes quite high at the root of this kind of notches. The use of the linear elastic fracture mechanics becomes therefore questionable.

Salient Pole Synchronous Machine Modelling in an Industrial Direct Torque Controlled Drive Application

Synchronous motors are used mainly in large drives, for example in ship propulsion systems and in steel factories' rolling mills because of their high efficiency, high overload capacity and good performance in the field weakening range. This, however, requires an extremely good torque control system. A fast torque response and a torque accuracy are basic requirements for such a drive. For large power, high dynamic performance drives the commonly known principle of field oriented vector control has been used solely hitherto, but nowadays it is not the only way to implement such a drive. A new control method Direct Torque Control (DTC) has also emerged. The performance of such a high quality torque control as DTC in dynamically demanding industrial applications is mainly based on the accurate estimate of the various flux linkages' space vectors. Nowadays industrial motor control systems are real time applications with restricted calculation capacity. At the same time the control system requires a simple, fast calculable and reasonably accurate motor model. In this work a method to handle these problems in a Direct Torque Controlled (DTC) salient pole synchronous motor drive is proposed. A motor model which combines the induction law based "voltage model" and motor inductance parameters based "current model" is presented. The voltage model operates as a main model and is calculated at a very fast sampling rate (for example 40 kHz). The stator flux linkage calculated via integration from the stator voltages is corrected using the stator flux linkage computed from the current model. The current model acts as a supervisor that prevents only the motor stator flux linkage from drifting erroneous during longer time intervals. At very low speeds the role of the current model is emphasised but, nevertheless, the voltage model always stays the main model. At higher speeds the function of the current model correction is to act as a stabiliser of the control system. The current model contains a set of inductance parameters which must be known. The validation of the current model in steady state is not self evident. It depends on the accuracy of the saturated value of the inductances. Parameter measurement of the motor model where the supply inverter is used as a measurement signal generator is presented. This so called identification run can be performed prior to delivery or during drive commissioning. A derivation method for the inductance models used for the representation of the saturation effects is proposed. The performance of the electrically excited synchronous motor supplied with the DTC inverter is proven with experimental results. It is shown that it is possible to obtain a good static accuracy of the DTC's torque controller for an electrically excited synchronous motor. The dynamic response is fast and a new operation point is achieved without oscillation. The operation is stable throughout the speed range. The modelling of the magnetising inductance saturation is essential and cross saturation has to be considered as well. The effect of cross saturation is very significant. A DTC inverter can be used as a measuring equipment and the parameters needed for the motor model can be defined by the inverter itself. The main advantage is that the parameters defined are measured in similar magnetic operation conditions and no disagreement between the parameters will exist. The inductance models generated are adequate to meet the requirements of dynamically demanding drives.

Computational Techniques for Spectral Image Analysis

Multispectral images are becoming more common in the field of remote sensing, computer vision, and industrial applications. Due to the high accuracy of the multispectral information, it can be used as an important quality factor in the inspection of industrial products. Recently, the development on multispectral imaging systems and the computational analysis on the multispectral images have been the focus of a growing interest. In this thesis, three areas of multispectral image analysis are considered. First, a method for analyzing multispectral textured images was developed. The method is based on a spectral cooccurrence matrix, which contains information of the joint distribution of spectral classes in a spectral domain. Next, a procedure for estimating the illumination spectrum of the color images was developed. Proposed method can be used, for example, in color constancy, color correction, and in the content based search from color image databases. Finally, color filters for the optical pattern recognition were designed, and a prototype of a spectral vision system was constructed. The spectral vision system can be used to acquire a low dimensional component image set for the two dimensional spectral image reconstruction. The data obtained by the spectral vision system is small and therefore convenient for storing and transmitting a spectral image.