Vuotasapainon hallinta kokosiltasyötetyssä muuntajassa

Keskitaajuudella toimivia muuntajia käytetään laajalti tehoelektroniikkasovelluksissa kuten DC/DC-konverttereissa ja muissa hakkuriteholähteissä. Muuntaja on induktiivinen komponentti, jonka magneettisen tasapainon säilyttäminen hakkuriteholähteissä on laitteen virheettömän toiminnan kannalta tärkeää. Muuntajaa syöttävän virtapiirin on muodostettava symmetrinen syöttöjännite, jotta muuntajan vuo ei ajaudu positiiviseen tai negatiiviseen kyllästykseen. Tässä diplomityössä esitetään muuntajan sähkömagneettinen toimintaperiaate, kyllästymisen syyt hakkuriteholähteissä sekä kehitetään aktiivinen ohjaus vuotasapainon säilyttämiseksi. Hakkuriteholähteissä käytettävissä muuntajissa on monesti useampi kuin kaksi käämiä. Tässä työssä tutkittavassa muuntajassa on useita ensiöitä ja useita toisioita ja muuntajaa syötetään keskitaajuudella. Tämä tuo uusia ongelmia verrattuna perinteiseen yksivaiheiseen DC/DC-konvertteriin. Näihin ongelmiin esitetään ratkaisut diplomityön tutkimuksessa.

Autokaupan automyynnin volyymiasiakkaiden asiakaskannattavuus

Autoalalla automyynnin transaktiokustannukset ovat merkittävä osa myyntikustannuksista. Yritykset pyrkivät alentamaan näitä kustannuksia hakemalla lisää volyymia ja keskittymällä voimakkaammin volyymikauppoihin. Tämän tutkimuksen tarkoituksena on löytää keinoja, joilla autokaupan volyymimyynnin kannattavuutta voidaan parantaa. Tutkimuksen teoreettisessa viitekehyksessä esitettiin teoriamalleja, joita hyödyntämällä autokaupan kovassa kilpailutilanteessa yritykset voisivat menestyä paremmin. Tutkimusmetodina käytettiin ei-kokeellista tutkimusasetelmaa, jossa tieto kerättiin strukturoiduilla kysymyksillä. Tutkimusaineistoksi saatiin kohdeyrityksessä ja joukosta kilpailevien yritysten henkilöiltä haastattelemalla hankittua tietoa. Johtopäätöksenä voidaan todeta, että autokaupassa liikkeenjohdon teoriat ja käytäntö seurailevat toisiaan osin hyvinkin paljon, vaikka tiettyjä ristiriitoja on havaittavissa. Yritysten tietojärjestelmistä saatavan tiedon laadun parantamisella, sovittujen toimintaprosessien noudattamisella ja olemassa olevia toimintatapoja kyseenalaistamalla volyymikaupan tuottavuutta pystytään jo nyt kohentamaan.

Nikkelin, koboltin, lyijyn ja sinkin selektiivinen erottaminen ioninleimaustekniikalla syntetisoiduilla kelatoivilla erotusmateriaaleilla

Kelatoivat erotusmateriaalit ovat osoittautuneet lupaaviksi haitallisten metallien erottamiseksi vedestä. Puhdistettava vesiliuos sisältää vain harvoin pelkästään erotettavaksi tarkoitettuja metallikationeja, sillä useimmiten mukana on erotusmateriaalien tehokkuutta heikentäviä kationeja. Parantamalla erotusmateriaalin selektiivisyyttä voitaisiin häiritsevien ionien vaikutusta vähentää selvästi. Kandidaatintyön tavoitteena oli tutkia ioninleimaustekniikan avulla syntetisoitujen kelatoivien erotusmateriaalien selektiivisyyttä nikkelille, koboltille, lyijylle ja sinkille. Käyttämällä esimerkiksi nikkelitemplaattia materiaalin synteesivaiheessa materiaalin nikkeliselektiivisyys kasvaa verrattuna perinteiseen synteesitekniikkaan. Tässä työssä tutkittiin erotusmateriaaleja, joissa oli käytetty nikkeli- tai lyijytemplaattia, vertaamalla niitä ilman templaattia syntetisoituihin materiaaleihin. Lisäksi erotustehokkuutta verrattiin kaupalliseen erotusmateriaaliin häiritsevien magnesium- ja kalsiumionien tapauksessa. Lyijyn havaittiin sitoutuvan tehokkaimmin kaikkiin syntetisoituihin materiaaleihin riippumatta nikkelitemplaatin käyttämisestä. Kinetiikkakokeet osoittivat lyijyn sitoutumisnopeudenkin olevan vertailtavista metalleista suurin. Kaikki kokeet suoritettiin huoneenlämpötilassa liuoksen pH-arvon ollessa 7,5. Nikkelitemplaatin käyttö lisäsi materiaalin selektiivisyyttä nikkelille verrattuna templaatittomaan muuten identtiseen materiaaliin. Kuitenkin materiaalien lyijyselektiivisyys oli huomattavasti nikkeliselektiivisyyttä suurempi. Lyijytemplaatin käyttö ei lisännyt lyijyselektiivisyyttä, mutta materiaalin nikkeliselektiivisyys parantui. Materiaaliin sitoutuneet nikkeli-, koboltti- ja sinkkipitoisuudet jäivät huomattavasti vähäisemmiksi verrattuna kaupalliseen materiaaliin. Magnesiumin ja kalsiumin tarttumista syntetisoituihin materiaaleihin tutkittiin myös ja tulosten mukaan IIPD2:een ja IIPD2-Methoxiin sitoutui erittäin vähän magnesiumia ja kalsiumia verrattuna kaupalliseen materiaaliin, jonka kalsiumkapasiteetti oli erityisen suuri. Kyseiset materiaalit soveltuvat tulosten perusteella myös häiritseviä ioneja sisältävien liuosten puhdistamiseen. Näin ollen valittujen kahden materiaalin jatkotutkimuksella olisi mahdollista parantaa nikkelikapasiteettia ja -selektiivisyyttä.

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.

Applications and Benefits of Adaptive Pulsed GMAW

In ship and offshore terminal construction, welded cross sections are thick and the number of welds very high. Consequently, there are two aspects of great importance; cost and heat input. Reduction in the welding operation time decreases the costs of the work force and avoids excessive heat, preventing distortion and other weld defects. The need to increase productivity while using a single wire in the GMAW process has led to the use of a high current and voltage to improve the melting rate. Unfortunately, this also increases the heat input. Innovative GMAW processes, mostly implemented for sheet plate sections, have shown significant reduction in heat input (Q), low distortion and increase in welding speed. The aim of this study is to investigate adaptive pulsed GMAW processes and assess relevant applications in the high power range, considering possible benefits when welding thicker sections and high yield strength steel. The study experimentally tests the usability of adaptive welding processes and evaluates their effects on weld properties, penetration and shapes of the weld bead.The study first briefly reviews adaptive GMAW to evaluate different approaches and their applications and to identify benefits in adaptive pulsed. Experiments are then performed using Synergic Pulsed GMAW, WiseFusionTM and Synergic GMAW processes to weld a T-joint in a horizontal position (PB). The air gap between the parts ranges from 0 to 2.5 mm. The base materials are structural steel grade S355MC and filler material G3Si1. The experiment investigates heat input, mechanical properties and microstructure of the welded joint. Analysis of the literature reveals that different approaches have been suggested using advanced digital power sources with accurate waveform, current, voltage, and feedback control. In addition, studies have clearly indicated the efficiency of lower energy welding processes. Interest in the high power range is growing and a number of different approaches have been suggested. The welding experiments in this study reveal a significant reduction of heat input and a weld microstructure with the presence of acicular ferrite (AF) beneficial for resistance to crack propagation. The WiseFusion bead had higher dilution, due to the weld bead shape, and low defects. Adaptive pulse GMAW processes can be a favoured choice when welding structures with many welded joints. The total heat reduction mitigates residual stresses and the bead shape allows a higher amperage limit. The stability of the arc during the process is virtually spatter free and allows an increase in welding speed.

Nikkelille selektiivisen kelatoivan adsorbenttimateriaalin valmistus ja tutkiminen

Metallien laajamittaisen ja runsaan käytön vuoksi nykyään on keskityttävä aikaisempaa tarkemmin metallipäästöjen estämiseen ja puhdistamiseen. Metallien puhdistamiseen jätevesistä voidaan käyttää erilaisia yksikköoperaatiomenetelmiä, mutta selektiivisempään erotukseen päästään ioninvaihto- ja adsorbenttimateriaaleilla. Työn tarkoitusena on valmistaa ja tutkia nikkeliselektiivisiä adsorbenttimateriaaleja. Lisäksi tutkimuskohteena on nikkelin ja 1,10-fenantroliinin välisen kompleksin muodostuminen eri pH-arvoilla. Selektiivisten adsorbenttimateriaalien valmistaminen onnistuu liittämällä kiinteään kantajaan ligandi. Tämän työn tapauksessa nikkelitemplaatin liittäminen kiinteään kantajaan funktionalisointivaiheessa muodostaa adsorbenttiin nikkelille spesifisen kohdan. Käytännössä spesifisyyden syntyminen ei ole itsestäänselvyys, vaan se riippuu paljon funktionalisointitavasta. Tässä työssä funktionalisointitapana olivat fysikaalinen adsorptio ja impregnointi. Nikkelin ja 1,10-fenantroliinin välisen kompleksin muodostumista tutkittiin eri pH-arvojen lisäksi neljällä eri happokonsentraatiolla. Tuloksia verrattiin sellaisen liuoksen spektriin, missä oli pelkkää nikkeliä. Tuloksista havaittiin, että komplekseja muodostuu käytännössä samalla tavalla pH:n ollessa 1–6. Vasta 5 M HNO3 alkoi heikentää kompleksien muodostumista, ja 10 M HNO3 esti kompleksien muodostumisen täysin. Adsorbenttimateriaaleja valmistettiin useita erilaisia, joihin osaan liitettiin nikkelitemplaatti ja osa jätettiin ilman templaattia. Työssä keskityttiin tutkimaan erityisesti kolmea silikasta valmistettua materiaalia, joissa vain kahdessa oli nikkelitemplaatti. Nikkelitemplaattien olemassaololla ei havaittu olevan juurikaan merkitystä nikkelin erottamiseen vesiliuoksista. Materiaaleille tehdyt regenerointikokeet osoittivat, että materiaalien toiminta ja kapasiteetti eivät olleet toivotulla tasolla.

Prediction of 3D structure and ligand-binding properties : ABC transporters and flavodiiron proteins from Synechocystis sp. strain PCC 6803

Cyanobacteria are unicellular, non-nitrogen-fixing prokaryotes, which perform photosynthesis similarly as higher plants. The cyanobacterium Synechocystis sp. strain PCC 6803 is used as a model organism in photosynthesis research. My research described herein aims at understanding the function of the photosynthetic machinery and how it responds to changes in the environment. Detailed knowledge of the regulation of photosynthesis in cyanobacteria can be utilized for biotechnological purposes, for example in the harnessing of solar energy for biofuel production. In photosynthesis, iron participates in electron transfer. Here, we focused on iron transport in Synechocystis sp. strain PCC 6803 and particularly on the environmental regulation of the genes encoding the FutA2BC ferric iron transporter, which belongs to the ABC transporter family. A homology model built for the ATP-binding subunit FutC indicates that it has a functional ATPbinding site as well as conserved interactions with the channel-forming subunit FutB in the transporter complex. Polyamines are important for the cell proliferation, differentiation and apoptosis in prokaryotic and eukaryotic cells. In plants, polyamines have special roles in stress response and in plant survival. The polyamine metabolism in cyanobacteria in response to environmental stress is of interest in research on stress tolerance of higher plants. In this thesis, the potd gene encoding an polyamine transporter subunit from Synechocystis sp. strain PCC 6803 was characterized for the first time. A homology model built for PotD protein indicated that it has capability of binding polyamines, with the preference for spermidine. Furthermore, in order to investigate the structural features of the substrate specificity, polyamines were docked into the binding site. Spermidine was positioned very similarly in Synechocystis PotD as in the template structure and had most favorable interactions of the docked polyamines. Based on the homology model, experimental work was conducted, which confirmed the binding preference. Flavodiiron proteins (Flv) are enzymes, which protect the cell against toxicity of oxygen and/or nitric oxide by reduction. In this thesis, we present a novel type of photoprotection mechanism in cyanobacteria by the heterodimer of Flv2/Flv4. The constructed homology model of Flv2/Flv4 suggests a functional heterodimer capable of rapid electron transfer. The unknown protein sll0218, encoded by the flv2-flv4 operon, is assumed to facilitate the interaction of the Flv2/Flv4 heterodimer and energy transfer between the phycobilisome and PSII. Flv2/Flv4 provides an alternative electron transfer pathway and functions as an electron sink in PSII electron transfer.

Tuotemallin ylläpito- ja pienkehitysprosessin kehittäminen

Työn tavoitteena oli selvittää yrityksen tuotekehitysorganisaation tuoteylläpitotoiminnan nykytila ja kartoittaa sen mahdolliset ongelmakohdat sekä kehityskohteet. Lisäksi tavoitteena oli vertailla yrityksen toimintamalleja toisen yrityksen vastaavaan organisaatioon kartoitettujen ongelmakohtien pohjalta, ja laatia kehitysehdotus ongelmien ratkaisemiseksi. Tutkimusmenetelminä käytettiin nykytilaselvityksessä semistrukturoituja asiantuntijahaastatteluja ja vertailututkimusta (engl. benchmarking). Kehitysehdotuksen laatimisen tueksi työhön sisältyi myös kirjallisuuskatsaus, jossa käsiteltiin esimerkiksi tuotteen elinkaarenhallintaa, konfiguraationhallintaa ja prosessijohtamista. Nykytilaselvityksen tuloksena oli kuvaus yrityksen tuoteylläpidontoiminnasta sekä havaituista ongelmakohdista. Vertailututkimuksen tuloksena saatiin kuvaus kohdeyrityksen kartoitettuihin ongelmakohtiin liittyvistä toimintamalleista, sekä joitain ratkaisuvaihtoehtoja. Nykytilaselvityksen ja vertailututkimuksen tulosten sekä kirjallisuuskatsauksen perusteella laadittu kehitysehdotus perustuu konfiguraationhallintasuunnitelman pohjaan, johon on sisällytetty kaikki ratkaisuehdotukset. Kehitysehdotuksessa esitetyt ratkaisuehdotukset vastaavat lähtökohtaisesti kartoitettuihin ongelmakohtiin, mutta ne vaativat vielä jatkokehittelyä. Työn tulokset toimivat pohjana yksityiskohtaisemmalle suunnittelulle ja jatkokehittelylle.

Regioselective modification of galactose-containing polysaccharides in aqueous media

Biorefining is defined as sustainable conversion of biomass into marketable products and energy. Forests cover almost one third of earth’s land area, and account for approximately 40% of the total annual biomass production. In forest biorefining, the wood components are, in addition to the traditional paper and board products, converted into chemicals and biofuels. The major components in wood are cellulose, hemicelluloses, and lignin. The main hemicellulose in softwoods, which are of interest especially for the Nordic forest industry, is O-acetyl galactoglucomannan (GGM). GGM can be isolated in industrial scale from the waste waters of the mechanical pulping process, but is not yet today industrially utilized. In order to attain desired properties of GGM for specific end-uses, chemical and enzymatic modifications can be performed. Regioselective modifications of GGM, and other galactose-containing polysaccharides were done by oxidations, and by combining oxidations with subsequent derivatizations of the formed carbonyl or carboxyl groups. Two different pathways were investigated: activation of the C-6 positions in different sugar units by TEMPO-mediated oxidation, and activation of C-6 position in only galactose-units by oxidation catalyzed by the enzyme galactose oxidase. The activated sites were further selectively derivatized; TEMPO-oxidized GGM by a carbodiimide-mediated reaction forming amides, and GO-oxidized GGM by indium-mediated allylation introducing double or triple bonds to the molecule. In order to better understand the reaction, and to develop a MALDI-TOF-MS method for characterization of regioselectively allylated GGM, α-D-galactopyranoside and raffinose were used as model compounds. All reactions were done in aqueous media. To investigate the applicability of the modified polysaccharides for, e.g., cellulose surface functionalization, their sorption onto pulp fibres was studied. Carboxylation affects the sorption tendency significantly; a higher degree of oxidation leads to lower sorption. By controlling the degree of oxidation of the polysaccharides and the ionic strength of the sorption media, high degrees of sorption of carboxylated polysaccharides onto cellulose could, however, be obtained. Anionic polysaccharides were used as templates during laccase-catalyzed polymerization of aniline, offering a green, chemo-enzymatic route for synthesis of conducting polyaniline (PANI) composite materials. Different polysaccharide templates, such as, native GGM, TEMPO-oxidized GGM, naturally anionic κ-carrageenan, and nanofibrillated cellulose produced by TEMPO-oxidation, were assessed. The conductivity of the synthesized polysaccharide/PANI biocomposites varies depending on the polysaccharide template; κ-CGN, the anionic polysaccharide with the lowest pKa value, produces the polysaccharide/PANI biocomposites with the highest conductivity. The presented derivatization, sorption, and polymerization procedures open new application windows for polysaccharides, such as spruce GGM. The modified polysaccharides and the conducting biocomposites produced provide potential applications in biosensors, electronic devices, and tissue engineering.

The adjustment from Russia to Finland for corporate repatriates: How the repatriation experience influences readjustment in the workplace

To manage foreign operations, companies must often send their employees on international assignments. Repatriating these expatriates can be difficult because they have been forgotten during their posting, and their new experiences are not utilised. In addition to the possible difficulties in organisational repatriation, the returnee can suffer from readjustment problems after a lengthy stay abroad has changed their habits and even identity. This thesis examines the repatriation experience of Finnish assignees returning from Russia. The purpose of the study is to understand how the repatriation experience influences their readjustment to work in Finland. This experience is influenced by many factors including personal and situational changes, the repatriation process, job and organisational factors, and individual’s motives. The theoretical background of the study is founded on two models of repatriation adjustment. A refined, holistic theoretical framework for the study is created. It describes the formation of the repatriation experience and its importance for readjustment to work and retention. The qualitative research approach is suitable for the thesis which examines the returnees’ personal experiences and feelings: a qualitative case study aims to explain the phenomenon in-depth and comprehensively. The data was collected in summer 2013 through semi-standardised interviews with eight Finnish repatriates. They had returned from Russia within the last two years. The data was analysed by structuring the interview transcripts using template analysis. The results supported earlier literature and suggest that the re-entry remains a challenging phase for both the individual and the company. For some, adjusting to a new job was difficult for various reasons. The repatriates underwent personal change and development and felt it was for the better. Many repatriates criticised the company’s repatriation process upon return. Finding a suitable return job was not clear. Instead, the returnees had to be active in finding a new position. Many assignees had only modest career-related motives regarding the assignment and they had realistic expectations about the return. Therefore they were not extremely surprised or dissatisfied when they were not actively offered positions or support by the company. The significance of motives stood out even more than the theory predicted. As predicted, they are linked to the expectations of employees. Moreover, if the employees are motivated to remain in the company, they can tolerate partly a negative repatriation experience. Despite the complexity of the return and readjustment, the assignment as a whole was seen as a rewarding experience by all participants.

Synthesis, characterization and chemical sensor application of conducting polymers

Polymeric materials that conduct electricity are highly interesting for fundamental studies and beneficial for modern applications in e.g. solar cells, organic field effect transistors (OFETs) as well as in chemical and bio‐sensing. Therefore, it is important to characterize this class of materials with a wide variety of methods. This work summarizes the use of electrochemistry also in combination with spectroscopic methods in synthesis and characterization of electrically conducting polymers and other π‐conjugated systems. The materials studied in this work are intended for organic electronic devices and chemical sensors. Additionally, an important part of the presented work, concerns rational approaches to the development of water‐based inks containing conducting particles. Electrochemical synthesis and electroactivity of conducting polymers can be greatly enhanced in room temperature ionic liquids (RTILs) in comparison to conventional electrolytes. Therefore, poly(para‐phyenylene) (PPP) was electrochemically synthesized in the two representative RTILs: bmimPF6 and bmiTf2N (imidazolium and pyrrolidinium‐based salts, respectively). It was found that the electrochemical synthesis of PPP was significantly enhanced in bmimPF6. Additionally, the results from doping studies of PPP films indicate improved electroactivity in bmimPF6 during oxidation (p‐doping) and in bmiTf2N in the case of reduction (n‐doping). These findings were supported by in situ infrared spectroscopy studies. Conducting poly(benzimidazobenzophenanthroline) (BBL) is a material which can provide relatively high field‐effect mobility of charge carriers in OFET devices. The main disadvantage of this n‐type semiconductor is its limited processability. Therefore in this work BBL was functionalized with poly(ethylene oxide) PEO, varying the length of side chains enabling water dispersions of the studied polymer. It was found that functionalization did not distract the electrochemical activity of the BBL backbone while the processability was improved significantly in comparison to conventional BBL. Another objective was to study highly processable poly(3,4‐ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) water‐based inks for controlled patterning scaled‐down to nearly a nanodomain with the intention to fabricate various chemical sensors. Developed PEDOT:PSS inks greatly improved printing of nanoarrays and with further modification with quaternary ammonium cations enabled fabrication of PEDOT:PSS‐based chemical sensors for lead (II) ions with enhanced adhesion and stability in aqueous environments. This opens new possibilities for development of PEDOT:PSS films that can be used in bio‐related applications. Polycyclic aromatic hydrocarbons (PAHs) are a broad group of π‐conjugated materials consisting of aromatic rings in the range from naphthalene to even hundred rings in one molecule. The research on this type of materials is intriguing, due to their interesting optical properties and resemblance of graphene. The objective was to use electrochemical synthesis to yield relatively large PAHs and fabricate electroactive films that could be used as template material in chemical sensors. Spectroscopic, electrochemical and electrical investigations evidence formation of highly stable films with fast redox response, consisting of molecules with 40 to 60 carbon atoms. Additionally, this approach in synthesis, starting from relatively small PAH molecules was successfully used in chemical sensor for lead (II).

Risk Assessment of a Supplier in the Pharmaceutical Industry

The topic of this Master’s Thesis is risk assessment in the supply chain, and the work was done for a company operating in the pharmaceutical industry. The unique features of the industry bring additional challenges to risk management, due to high regulatory, docu-mentation and traceability requirements. The objective of the thesis was to generate a template for assessing the risks in the supply chain of current and potential suppliers of the case company. Risks pertaining to the case setting were sought mainly from in-house expertise of this specific product and supply chain as well as academic research papers and theory on risk management. A questionnaire was set up to assess the found risks on impact, occurrence and possibility of detection. Through this classification of the severity of the risks, the supplier assessment template was formed. A questionnaire template, comprised of the top 10 risks affecting the flow of information and materials in this setting, was formulated to serve as a generic tool for assessing risks in the supply chain of a pharmaceutical company. The template was tested on another supplier for usability and accuracy of found risks, and it demonstrated functioning in a differing supply chain and product setting.

Power semiconductor nonlinearities in active du/dt output filtering

This doctoral thesis introduces an improved control principle for active du/dt output filtering in variable-speed AC drives, together with performance comparisons with previous filtering methods. The effects of power semiconductor nonlinearities on the output filtering performance are investigated. The nonlinearities include the timing deviation and the voltage pulse waveform distortion in the variable-speed AC drive output bridge. Active du/dt output filtering (ADUDT) is a method to mitigate motor overvoltages in variable-speed AC drives with long motor cables. It is a quite recent addition to the du/dt reduction methods available. This thesis improves on the existing control method for the filter, and concentrates on the lowvoltage (below 1 kV AC) two-level voltage-source inverter implementation of the method. The ADUDT uses narrow voltage pulses having a duration in the order of a microsecond from an IGBT (insulated gate bipolar transistor) inverter to control the output voltage of a tuned LC filter circuit. The filter output voltage has thus increased slope transition times at the rising and falling edges, with an opportunity of no overshoot. The effect of the longer slope transition times is a reduction in the du/dt of the voltage fed to the motor cable. Lower du/dt values result in a reduction in the overvoltage effects on the motor terminals. Compared with traditional output filtering methods to accomplish this task, the active du/dt filtering provides lower inductance values and a smaller physical size of the filter itself. The filter circuit weight can also be reduced. However, the power semiconductor nonlinearities skew the filter control pulse pattern, resulting in control deviation. This deviation introduces unwanted overshoot and resonance in the filter. The controlmethod proposed in this thesis is able to directly compensate for the dead time-induced zero-current clamping (ZCC) effect in the pulse pattern. It gives more flexibility to the pattern structure, which could help in the timing deviation compensation design. Previous studies have shown that when a motor load current flows in the filter circuit and the inverter, the phase leg blanking times distort the voltage pulse sequence fed to the filter input. These blanking times are caused by excessively large dead time values between the IGBT control pulses. Moreover, the various switching timing distortions, present in realworld electronics when operating with a microsecond timescale, bring additional skew to the control. Left uncompensated, this results in distortion of the filter input voltage and a filter self-induced overvoltage in the form of an overshoot. This overshoot adds to the voltage appearing at the motor terminals, thus increasing the transient voltage amplitude at the motor. This doctoral thesis investigates the magnitude of such timing deviation effects. If the motor load current is left uncompensated in the control, the filter output voltage can overshoot up to double the input voltage amplitude. IGBT nonlinearities were observed to cause a smaller overshoot, in the order of 30%. This thesis introduces an improved ADUDT control method that is able to compensate for phase leg blanking times, giving flexibility to the pulse pattern structure and dead times. The control method is still sensitive to timing deviations, and their effect is investigated. A simple approach of using a fixed delay compensation value was tried in the test setup measurements. The ADUDT method with the new control algorithm was found to work in an actual motor drive application. Judging by the simulation results, with the delay compensation, the method should ultimately enable an output voltage performance and a du/dt reduction that are free from residual overshoot effects. The proposed control algorithm is not strictly required for successful ADUDT operation: It is possible to precalculate the pulse patterns by iteration and then for instance store them into a look-up table inside the control electronics. Rather, the newly developed control method is a mathematical tool for solving the ADUDT control pulses. It does not contain the timing deviation compensation (from the logic-level command to the phase leg output voltage), and as such is not able to remove the timing deviation effects that cause error and overshoot in the filter. When the timing deviation compensation has to be tuned-in in the control pattern, the precalculated iteration method could prove simpler and equally good (or even better) compared with the mathematical solution with a separate timing compensation module. One of the key findings in this thesis is the conclusion that the correctness of the pulse pattern structure, in the sense of ZCC and predicted pulse timings, cannot be separated from the timing deviations. The usefulness of the correctly calculated pattern is reduced by the voltage edge timing errors. The doctoral thesis provides an introductory background chapter on variable-speed AC drives and the problem of motor overvoltages and takes a look at traditional solutions for overvoltage mitigation. Previous results related to the active du/dt filtering are discussed. The basic operation principle and design of the filter have been studied previously. The effect of load current in the filter and the basic idea of compensation have been presented in the past. However, there was no direct way of including the dead time in the control (except for solving the pulse pattern manually by iteration), and the magnitude of nonlinearity effects had not been investigated. The enhanced control principle with the dead time handling capability and a case study of the test setup timing deviations are the main contributions of this doctoral thesis. The simulation and experimental setup results show that the proposed control method can be used in an actual drive. Loss measurements and a comparison of active du/dt output filtering with traditional output filtering methods are also presented in the work. Two different ADUDT filter designs are included, with ferrite core and air core inductors. Other filters included in the tests were a passive du/dtfilter and a passive sine filter. The loss measurements incorporated a silicon carbide diode-equipped IGBT module, and the results show lower losses with these new device technologies. The new control principle was measured in a 43 A load current motor drive system and was able to bring the filter output peak voltage from 980 V (the previous control principle) down to 680 V in a 540 V average DC link voltage variable-speed drive. A 200 m motor cable was used, and the filter losses for the active du/dt methods were 111W–126 W versus 184 W for the passive du/dt. In terms of inverter and filter losses, the active du/dt filtering method had a 1.82-fold increase in losses compared with an all-passive traditional du/dt output filter. The filter mass with the active du/dt method was 17% (2.4 kg, air-core inductors) compared with 14 kg of the passive du/dt method filter. Silicon carbide freewheeling diodes were found to reduce the inverter losses in the active du/dt filtering by 18% compared with the same IGBT module with silicon diodes. For a 200 m cable length, the average peak voltage at the motor terminals was 1050 V with no filter, 960 V for the all-passive du/dt filter, and 700 V for the active du/dt filtering applying the new control principle.

Modelling of ultrasound assisted mixing in Newtonian and non-Newtonian liquids

The purpose of this work is to obtain a better understanding of behaviour of possible ultrasound appliance on fluid media mixing. The research is done in the regard to Newtonian and non-Newtonian fluids. The process of ultrasound appliance on liquids is modelled in COMSOL Multiphysics software. The influence of ultrasound using is introduced as waveform equation. Turbulence modelling is fulfilled by the k-ε model in Newtonian fluid. The modeling of ultrasound assisted mixing in non-Newtonian fluids is based on the power law. To verify modelling results two practical methods are used: Particle Image Velocimetry and measurements of mixing time. Particle Image Velocimetry allows capturing of velocity flow field continuously and presents detailed depiction of liquid dynamics. The second way of verification is the comparison of mixing time of homogeneity. Experimentally achievement of mixing time is done by conductivity measurements. In modelling part mixing time is achieved by special module of COMSOL Multiphysics – the transport of diluted species. Both practical and modelling parts show similar radial mechanism of fluid flow under ultrasound appliance – from the horn tip fluid moves to the bottom and along the walls goes back. Velocity profiles are similar in modelling and experimental part in the case of Newtonian fluid. In the case of non-Newtonian fluid velocity profiles do not agree. The development track of ultrasound-assisted mixing modelling is presented in the thesis.

Molecular Mechanisms of Sexual Dimorphism in Threespine Stickleback

Sexual dimorphism is commonly understood as differences in external features, such as morphological features or coloration. However, it can more broadly encompass behavior and physiology and at the core of these differences is the genetic mechanism – mRNA and protein expression. How, and which, molecular mechanisms influence sexually dimorphic features is not well understood thus far. DNA, RNA and proteins are the template required to create the phenotype of an individual, and they are connected to each other via processes of transcription and translation. As the genome of males and females are almost identical with the exception of the few genes on the sex chromosome or the sex-determining alleles (in the case of organisms without sex chromosomes), it is likely that many of the downstream processes resulting in sexual dimorphism are produced by changes in gene regulation and result from a regulatory cascade and not from a vastly different gene composition. Thus, in this thesis a systems biology approach is used to understand sexual dimorphism at all molecular levels and how different genomic features, e.g. sex chromosome evolution, can affect the interplay of these molecules. The threespine stickleback, Gasterosteus aculeatus, is used as the model to investigate molecular mechanisms of sexual dimorphism. It has well-characterized ecology and behavior, especially in the breeding season when sexual dimorphism is high. Moreover, threespine stickleback has a recently evolved Y chromosome in the early stages of sex chromosome evolution, characterized by a lack of recombination leading to degeneration (i.e. gene loss). The aim of my thesis is to investigate how the genotype links to the molecular phenotype and relates to differences in molecular expression between males and females. Based on previous research on sex differences in mRNA expression, I investigated sex-biased protein expression in adult fish outside the breeding season to see if differences persisted after translation. As sex-biased expression also prevailed in the proteome and previous transcription expression seemed to be related to the sex chromosomes, I investigated the genome level with a particular focus on the sex-chromosomes. I characterized the status of Y chromosome degeneration in the threespine stickleback and its effects on gene function. Furthermore, since the degeneration process leaves genes in a single copy in males, I examined whether the resulting dosage difference of messenger RNA for hemizygous genes is compensated as it is in other organisms. In addition, threespine sticklebacks have wellcharacterized behavioral differences related to the male’s social status during the breeding season. To understand the connection between the genotype and behavior, I examined gene expression patterns related to breeding behavior using dominant and subordinate males as well as female