Analysis and Control of Excitation, Field Weakening and Stability in Direct Torque Controlled Electrically Excited Synchronous Motor Drives

Direct torque control (DTC) is a new control method for rotating field electrical machines. DTC controls directly the motor stator flux linkage with the stator voltage, and no stator current controllers are used. With the DTC method very good torque dynamics can be achieved. Until now, DTC has been applied to asynchronous motor drives. The purpose of this work is to analyse the applicability of DTC to electrically excited synchronous motor drives. Compared with asynchronous motor drives, electrically excited synchronous motor drives require an additional control for the rotor field current. The field current control is called excitation control in this study. The dependence of the static and dynamic performance of DTC synchronous motor drives on the excitation control has been analysed and a straightforward excitation control method has been developed and tested. In the field weakening range the stator flux linkage modulus must be reduced in order to keep the electro motive force of the synchronous motor smaller than the stator voltage and in order to maintain a sufficient voltage reserve. The dynamic performance of the DTC synchronous motor drive depends on the stator flux linkage modulus. Another important factor for the dynamic performance in the field weakening range is the excitation control. The field weakening analysis considers both dependencies. A modified excitation control method, which maximises the dynamic performance in the field weakening range, has been developed. In synchronous motor drives the load angle must be kept in a stabile working area in order to avoid loss of synchronism. The traditional vector control methods allow to adjust the load angle of the synchronous motor directly by the stator current control. In the DTC synchronous motor drive the load angle is not a directly controllable variable, but it is formed freely according to the motor’s electromagnetic state and load. The load angle can be limited indirectly by limiting the torque reference. This method is however parameter sensitive and requires a safety margin between the theoretical torque maximum and the actual torque limit. The DTC modulation principle allows however a direct load angle adjustment without any current control. In this work a direct load angle control method has been developed. The method keeps the drive stabile and allows the maximal utilisation of the drive without a safety margin in the torque limitation.

Working Capital Management: a Bibliometric Study

This thesis is a study of articles published in scientific journals about working capital management using bibliometric methods. The study was restricted to articles published in 1990–2010 that deal with the whole working capital management topic not a single sub-area of it. Working capital is defined as current assets minus current liabilities; sometimes also a definition of inventory plus accounts receivable minus accounts payable is used. The data was retrieved from the databases ISI Web of Science and Sciverse Scopus. Articles about working capital management were found 23. Content analysis, statistical analysis and citation analysis was performed to the articles. The most cited articles found in citation analysis were also analyzed by nearly same methods. This study found that scientific research of working capital management seems not to be concentrated to specific persons, organizations or journals. The originality and novelty in many articles is low. Many articles studied relation between working capital management and profitability in firms or working capital management practices of firms using statistical analyses. Data in articles was firms of all sizes, except in developing economies only big firms were used. Interesting areas for future research could be surveys made about working capital management practices in firms, finding of best practices, tools for working capital management, inventing or improving alternative views to working capital management like process-oriented view and firm or industry specific studies.

Working capital management in the value chain of automotive industry

The objective of this Master’s thesis is to examine working capital management in the automotive industry in years 2006-2008. The study is conducted by the analysis of financial statements. The sample consists of 65 companies that represent different stages in the value chain of automotive industry beginning from raw material suppliers and ending to car dealers. Working capital management is studied by the cash conversion cycle (CCC). The results show that the average CCC of the value chain is 67 days. Car manufacturers had the longest CCC, 106 days, whereas the CCC of oil companies was the shortest, 22 days. The findings suggest that the cycle time of working capital usually follows the cycle time of inventories, since the changes in cycle times of accounts receivable and payable compensate each other. Improvements in working capital management could be achieved by sharing more accurate information in the chain for example about inventory levels and order points of customer. It could also be discussed within the automotive industry, if the long credit periods, which tie up working capital, are really needed. New technologies enable faster payments, which would reduce the cash conversion cycles, improve the profitability of companies, and increase the competitiveness of the value chain. Working capital should not be reduced at the expense of value chain partners, because nowadays the competition is rather between the value chains than between the companies. Similar research design is applied earlier to study working capital management in the value chain of pulp and paper industry. Even if the industries and the structures of the chains differ from each other, results were surprisingly similar. In future research, working capital management in other industries’ value chains could still be studied and compared to previous studies. ICT industry, for example, could be an interesting object.

Pyörivien sähkökoneiden kotelointia koskevat standardit ja aksiaalivuokoneen jäähdytyksen kehittäminen

Tämä diplomityö on osa Lappeenrannan teknillisen yliopiston ja Visedo Oy:n yhteistyöprojektia. Työssä selvitetään pyörivien sähkökoneiden kotelointeja koskevia standardeja ja niiden vaikutukset koneiden suunnittelulle ja valmistukselle. Lisäksi työssä käsitellään aksiaalivuokoneen jäähdytykseen liittyviä ongelmia, kehitetään koneen nykyisiä jäähdytysratkaisuja ja ideoidaan käytettävissä olevia uusia jäähdytysmenetelmiä. Kehitysideoiden rajoitteena toimii koneelta vaadittu kotelointiluokka IP 64 – IP 68 sekä koneelle määritetty kestomagnetoitu aksiaalivuorakenne. Sähkökoneiden kotelointeja koskevien standardien asettamien vaatimusten määrittäminen tapahtui suurilta osin kirjallisuusselvityksenä. Standardien vaikutukset koneiden suunnittelulle ja valmistettavuudelle on selvitetty standardien kotelointien rakenteelle asettamien vaatimusten perusteella. Aksiaalivuokoneen jäähdytysongelmien selvittäminen, käytössä olevien jääh-dytysratkaisujen kehittäminen ja uusien menetelmien ideointi suoritettiin projektiluontoisesti yhdessä eri alojen asiantuntijoista koostuvan jäähdytystyöryhmän kanssa. Työn tuloksena laadittiin Visedo Oy:lle standardikäsikirja, jonka avulla Visedon sähkökoneiden tuoteperheeseen kuuluvien koneiden suunnitteluvaiheessa voidaan varmistaa koneiden standardienmukaisuus. Käsikirjassa on myös esitetty huomioita eri kotelointiluokkien asettamista vaatimuksista koneiden valmistukselle. Aksiaalivuokoneiden jäähdytykseen liittyen tavoitteena oli ratkaista aksiaalivuokoneisiin liittyviä jäähdytysongelmia. Työn tuloksena saa-tiin selville aksiaalivuokoneissa jäähdytyksen kehittämistä vaativat kohteet, laadittiin nykyisten jäähdytysratkaisujen parannusehdotuksia ja kehitettiin täysin uusia jäähdytysmenetelmiä.

Usability of laser–arc hybrid welding processes in industrial applications

Metal industries producing thick sections have shown increasing interest in the laser–arc hybrid welding process because of its clear advantages compared with the individual processes of autogenous laser welding and arc welding. One major benefit of laser–arc hybrid welding is that joints with larger gaps can be welded with acceptable quality compared to autogenous laser welding. The laser-arc hybrid welding process has good potential to extend the field of applications of laser technology, and provide significant improvements in weld quality and process efficiency in manufacturing applications. The objective of this research is to present a parameter set-up for laser–arc hybrid welding processes, introduce a methodical comparison of the chosen parameters, and discuss how this technology may be adopted in industrial applications. The research describes the principles, means and applications of different types of laser–arc hybrid welding processes. Conducted experiment processing variables are presented and compared using an analytical model which can also be used for predictive simulations. The main argument in this thesis is that profound understanding of the advanced technology of laser-arc hybrid welding will help improve the productivity of welding in industrial applications. Based on a review of the current knowledge base, important areas for further research are also identified. This thesis consists of two parts. The first part introduces the research topic and discusses laser–arc hybrid welding by characterizing its mechanism and most important variables. The second part comprises four research papers elaborating on the performance of laser– arc hybrid welding in the joining of metals. The study uses quantitative and qualitative research methods which include in-depth, interpretive analyses of results from a number of research groups. In the interpretive analysis, the emphasis is placed on the relevance and usefulness of the investigative results drawn from other research publications. The results of this study contribute to research on laser–arc hybrid welding by increasing understanding of how old and new perspectives on laser–arc hybrid welding are evidenced in industry. The research methodology applied permits continued exploration of how laser–arc hybrid welding and various process factors influence the overall quality of the weld. Thestudy provides a good foundation for future research, creates improved awareness of the laser–arc hybrid welding process, and assists the metal industry to maximize welding productivity.

Tilaus-toimitusprosessin kehittäminen eräässä painotalossa

Tämä diplomityö on tehty painotaloon. Yrityksen tilaus-toimitusketjua on kehitetty ennen diplomityötä. Muutoksen kohteena on ollut toimintamallit, laatu, läpäisy ja tuotanto- ja varastotilojen layout, lisäksi koneitakin on uusittu ja korjattu runsaasti. Muutosten yhteydessä henkilöstöä sopeutettiin vastaamaan uutta toimintamallia ja samalla myös johtamisen vastuu jaettiin uudelleen. Diplomityö koostuu kolmesta merkittävästä osasta ja sen tarkoituksena on kuvata sisäiset prosessit ja kehittää valittuja ongelmia. Ensimmäinen osa käsittelee leania ja sen teoriaa. Lisäksi määritellään lean-työkalut, joita työssä hyödynnetään. Toinen osa keskittyy kuvaamaan työn käytännön osuutta, jossa selvitetään prosessin nykytilaa. Suuri osa tätä diplomityötä on työn tutkimista ja sen kuvaamista yksinkertaisilla prosessikuvauksilla. Nykytilan kuvauksessa etsittiin myös ongelmakohtia, joita käytetään osittain tämän työn kehitysprojekteissa. Ongelmakohtien listan avulla voidaan toteuttaa jatkossa jatkuvan parantamisen projekteja. Kolmas osa työstä liittyy valittujen kehitysprojektien toteutukseen. Ensin työssä kuvataan jatkuvan parantamisen projektien työskentelytavat ja perustellaan syyt projektien valintaan. Valinnan jälkeen kuvataan valittujen projektien toteuttaminen ja lopuksi käydään läpi tulokset. Lisäksi yhteenvedossa esitellään työstä syntyvät jatkotoimenpide-ehdotukset. Kehitysprojektien tuloksien perusteella pystyttiin arvioimaan tulevia kehityskohteita ja niihin käytettäviä työkaluja. Koska kyseessä oli pilottiprojekti, oppimista tapahtui paljon ja tulokset saattavat näyttää positiivisimmilta kun kehitystoimintaa jatketaan. Tuloksina syntyivät prosessikuvaukset melkein jokaiseen työvaiheeseen. Tämän lisäksi prosessikuvausten yhteydessä syntyneitä kehitysehdotuksia voidaan pitää tuloksina. Ensimmäinen kehitysprojekteista oli työmääräimen kehittäminen. Työmääräintä muutettiin informatiivisemmaksi, mutta muu parantaminen jäi diplomityön ulkopuolelle. Toinen kehitysprojekti oli varastotuotteiden hallinnan kehittäminen, jossa aloitettiin ennakoida asiakkaan tilauksia ja varastojen arvot saatiin paremmin hallintaan. Tuloksia saavutetaan enemmän, mikäli toimintaa laajennetaan. Viimeisenä kehitysprojektina oli työpisteen toiminnan kehittäminen. Kehittämisessä keskityttiin pohjapiirroksen järkevöittämiseen, työtapojen vakiointiin ja lean-työkalu 5S toteutukseen. Työpisteen tehokkuutta saatiin nostettua jonkun verran, tosin painopiste oli uuden toimintatavan oppimisessa.

Luistonestojärjestelmän ja elektronisen tasauspyörästön suunnittelu ja implementointi hybridityökoneympäristöön

Ympäristörasituksen vähentäminen, tiukkenevat päästörajat ja ehtyvät öljyvarat ovat ajaneet kulkuvälineteollisuuden hakemaan uusia vaihtoehtoja ajoneuvojen energiatehokkuuden kehittämiseksi. Hybriditeknologia tarjoaa ratkaisuja kustannustehokkuuden ja ympäristöystävällisyyden parantamiseksi. Hybriditeknologian yleistyessä myös työkoneympäristössä saadaan paitsi kehitettyä energiatehokkaampia ja pienemmillä käyttökustannuksilla olevia työkoneita, niin myös tuotua siviiliajoneuvoista tuttuja turvallisuusominaisuuksia työkoneympäristöön. Perinteisten diesel-moottorien korvaaminen nopeavasteisilla ja tarkasti säädettävillä sähkömoottoreilla tarjoaa mahdollisuuksia toteuttaa tarkempia ja monipuolisempia säätöjärjestelmiä kuin perinteisessä ympäristössä. Tässä diplomityössä suunnitellaan luistonestojärjestelmä ja elektroninen tasauspyörästö hybridityökoneympäristöön. Järjestelmä voi käyttökohteesta riippuen pienentää huomattavasti käyttökustannuksia ja mahdollistaa uusien sovellusten tuomista markkinoille, kuten esimerkiksi kääntymisen avustaminen differentiaalisella ohjauksella.

Sähkömoottoriprototyypin mekaniikkasuunnittelu järjestelmällisen tuotesuunnittelun avulla

Työn tavoitteena oli suunnitella sähkömoottoriprototyyppi, joka soveltuu hybridiajoneuvon ajomoottoriksi. Mekaniikkasuunnittelu toteutettiin samanaikaisesti sähkösuunnittelun kanssa ja siinä käytettiin yleisesti käytössä olevaa järjestelmällistä tuotesuunnittelua. Järjestelmällinen tuotesuunnittelu soveltuu laajoihin suunnitteluprojekteihin, sillä sen avulla suunnitteluprosessi on jaoteltu useampiin pieniin askeliin. Työssä esitetään sähkömoottorin yleistä toimintaperiaatetta sekä niitä sähköteknisiä erityispiirteitä, joita mekaniikkasuunnittelussa tulee ottaa huomioon. Työn tuloksissa käytiin yksityiskohtaisesti läpi roottorin suunnittelu. Muille komponenteille käytettiin samaa järjestelmällistä tuotesuunnittelua mutta niitä ei esitetä yksityiskohtaisesti tässä työssä. Kokonaisuudessaan sähkömoottorista saatiin suunniteltua ratkaisuehdotus, joka täyttää halutut vaatimukset. Lisäksi työssä kerättiin kattava lista standardeista, jotka tukevat sähkömoottorin suunnittelua. Järjestelmällisen tuotesuunnittelun todettiin soveltuvan sähkömoottorin suunnitteluun hyvin ja saatua ratkaisuehdotusta voidaan pitää toimivana. Moottori suunnitelmasta valmistetaan ensimmäinen prototyyppi keväällä 2012. Prototyyppiä voidaan kehittää suunnittelemalla siitä paremmin sarjatuotantoon soveltuva malli esimerkiksi vähentämällä koneistettavien osien määrää ja korvaamalla ne valukappaleilla.

Hybrid warfare – just a twist of compound warfare? : views on warfare from the United States Armed Forces perspective

The wars the Western armies are involved with today are different from those that were fought in the end of 20th century. To explain this change, the Western military thinkers have come up with various different types of definitions of warfare over the last 30 years, each describing the tendencies involved in the conflicts of the time. The changing nature of conflicts surfaced a new term – hybrid warfare. The term was to describe and explain the multi-modality and complexity of modern day conflict. This thesis seeks the answer for the question: what is the development of thought behind hybrid warfare? In this thesis the Vietnam War (1965-1975) is used as an example of compound warfare focusing on the American involvement in the war. The Second Lebanon War (2006) serves as an example of hybrid warfare. Both case studies include an irregular opposing force, namely National Liberation Front in Vietnam War and Hezbollah in the Second Lebanon War. These two case studies are compared with the term full spectrum operations introduced in the current U.S. Department of Army Field Manual No. 3-0 Operations to see the differences and similarities of each term. The perspective of this thesis is the American point of view. This thesis concludes that hybrid warfare, compound warfare and full spectrum operations are very similar. The first two terms are included in the last one. Although hybrid warfare is not officially defined, it will most likely remain to be used in the discussion in the future, since hybrid wars and hybrid threats are officially accepted terms.

Feasibility study of metal to polymer hybrid joining

The increasing demand for lightweight components has led to a huge exploitation of non-metallic materials such as polymers, fibers and elastomers in industrial and manufacturing processes. Recent trends towards cost effectiveness, weight reduction and production flexibility in industrial production and manufacturing processes has led to a growing interest in hybrid components where two or more dissimilar materials coexist to achieving specifically optimized characteristics. The importance of this research is to serve as a bridge to understanding the theories behind various joining techniques and the adaptation of the process for metal to polymer hybrid joints. Moreso, it helps companies to select the most productive and yet economical joining process for realization of lightweight metal to polymer hybrid components. This thesis is a literature review analyzing various materials that has been published on various joining methods for metal to polymer hybrid joints on the feasibility and eventual realization of the joint between these dissimilar materials. This study is aimed at theoretically evaluating the feasibility of joining processes between metal and plastic components by exploiting exhaustively joining and welding sources.

Working capital management in the small and medium-sized enterprises Case: Project-based business environment in Flowrox Oy

This Master´s thesis illustrates how growing a business ties up the company´s working capital and what the cost of committed capital. In order to manage a company´s working capital in rapid business growth phase, the thesis suggests that by monitoring and managing the operating and cash conversion cycles of customers´ projects, a company can find ways to secure the required amount of capital. The research method of this thesis was based on literature reviews and case study research. The theoretical review presents the concepts of working capital and provides the background for understanding how to improve working capital management. The company in subject is a global small and medium-sized enterprise that manufactures pumps and valves for demanding process conditions. The company is expanding, which creates lots of challenges. This thesis concentrates to the company´s working capital management and its efficiency through the supply chain and value chain perspective. The main elements of working capital management are inventory management, accounts receivable management and accounts payable management. Prepayments also play a significant role, particularly in project-based businesses. Developing companies´ working capital management requires knowledge from different kind of key operations´ in the company, like purchasing, production, sales, logistics and financing. The perspective to develop and describe working capital management is an operational. After literature reviews the thesis present pilot projects that formed the basis of a model to monitor working capital in the case company. Based on analysis and pilot projects, the thesis introduces a rough model for monitoring capital commitments in short time period. With the model the company can more efficiently monitor and manage their customer projects.

The role of advance payments in working capital management and profitability

The objective of this thesis is to study the role of received advance payments in working capital management by creating a new measurement and to study the relationship between advance payments and profitability. The study has been conducted using narrative literature review and quantitative research methods. The research was made analyzing 108 companies listed in Helsinki Stock Exchange. The results indicate that 68 % of the studied companies are receiving advance payments and the average cycle time for received advance payments is 13 days. A new key figure is created to include received advance payments into the calculation of working capital. Received advance payments shorten the working capital cycle, by 13 days, when they are used in the calculation. The role of advance payments is not as significant as the role of receivables and inventories but advance payments may have a larger role than payables if the company is receiving noticeable amounts of advance payments. There are three branches where companies are receiving more advance payments than average companies. The branches are project business and ICT and publishing sectors. There is a negative correlation between profitability and advance payments based on the results of this study.

Design of salient pole PM synchronous machines for a vehicle traction application – Analysis and

This doctoral thesis presents a study on the development of a liquid-cooled frame salient pole permanent-magnet-exited traction machine for a four-wheel-driven electric car. The emphasis of the thesis is put on a radial flux machine design in order to achieve a light-weight machine structure for traction applications. The design features combine electromagnetic and thermal design methods, because traction machine operation does not have a strict operating point. Arbitrary load cycles and the flexible supply require special attention in the design process. It is shown that accurate modelling of the machine magnetic state is essential for high-performance operation. The saturation effect related to the cross-saturation has to be taken carefully into account in order to achieve the desired operation. Two prototype machines have been designed and built for testing: one totally enclosed machine with a special magnet module pole arrangement and another through-ventilated machine with a more traditional embedded magnet structure. Both structures are built with magnetically salient structures in order to increase the torque production capability with the reluctance torque component. Both machine structures show potential for traction usage. However, the traditional embedded magnet design turns out to be mechanically the more secure one of these two machine options.

Novel Methods for Error Modeling and Parameter Identification of a Redundant Serial-Parallel Hybrid Robot

To obtain the desirable accuracy of a robot, there are two techniques available. The first option would be to make the robot match the nominal mathematic model. In other words, the manufacturing and assembling tolerances of every part would be extremely tight so that all of the various parameters would match the “design” or “nominal” values as closely as possible. This method can satisfy most of the accuracy requirements， but the cost would increase dramatically as the accuracy requirement increases. Alternatively, a more cost-effective solution is to build a manipulator with relaxed manufacturing and assembling tolerances. By modifying the mathematical model in the controller, the actual errors of the robot can be compensated. This is the essence of robot calibration. Simply put, robot calibration is the process of defining an appropriate error model and then identifying the various parameter errors that make the error model match the robot as closely as possible. This work focuses on kinematic calibration of a 10 degree-of-freedom (DOF) redundant serial-parallel hybrid robot. The robot consists of a 4-DOF serial mechanism and a 6-DOF hexapod parallel manipulator. The redundant 4-DOF serial structure is used to enlarge workspace and the 6-DOF hexapod manipulator is used to provide high load capabilities and stiffness for the whole structure. The main objective of the study is to develop a suitable calibration method to improve the accuracy of the redundant serial-parallel hybrid robot. To this end, a Denavit–Hartenberg (DH) hybrid error model and a Product-of-Exponential (POE) error model are developed for error modeling of the proposed robot. Furthermore, two kinds of global optimization methods, i.e. the differential-evolution (DE) algorithm and the Markov Chain Monte Carlo (MCMC) algorithm, are employed to identify the parameter errors of the derived error model. A measurement method based on a 3-2-1 wire-based pose estimation system is proposed and implemented in a Solidworks environment to simulate the real experimental validations. Numerical simulations and Solidworks prototype-model validations are carried out on the hybrid robot to verify the effectiveness, accuracy and robustness of the calibration algorithms.