Active inverter output filtering methods

Frequency converters are widely used in the industry to enable better controllability and efficiency of variable speed AC motor drives. Despite these advantages, certain challenges concerning the inverter and motor interfacing have been present for decades. As insulated gate bipolar transistors entered the market, the inverter output voltage transition rate significantly increased compared with their predecessors. Inverters operate based on pulse width modulation of the output voltage, and the steep voltage edge fed by the inverter produces a motor terminal overvoltage. The overvoltage causes extra stress to the motor insulation, which may lead to a prematuremotor failure. The overvoltage is not generated by the inverter alone, but also by the sum effect of the motor cable length and the impedance mismatch between the cable and the motor. Many solutions have been shown to limit the overvoltage, and the mainstream products focus on passive filters. This doctoral thesis studies an alternative methodology for motor overvoltage reduction. The focus is on minimization of the passive filter dimensions, physical and electrical, or better yet, on operation without any filter. This is achieved by additional inverter control and modulation. The studied methods are implemented on different inverter topologies, varying in nominal voltage and current.For two-level inverters, the studied method is termed active du/dt. It consists of a small output LC filter, which is controlled by an independent modulator. The overvoltage is limited by a reduced voltage transition rate. For multilevel inverters, an overvoltage mitigation method operating without a passive filter, called edge modulation, is implemented. The method uses the capability of the inverter to produce two switching operations in the same direction to cancel the oscillating voltages of opposite phases. For parallel inverters, two methods are studied. They are both intended for two-level inverters, but the first uses individual motor cables from each inverter while the other topology applies output inductors. The overvoltage is reduced by interleaving the switching operations to produce a similar oscillation accumulation as with the edge modulation. The implementation of these methods is discussed in detail, and the necessary modifications to the control system of the inverter are presented. Each method is experimentally verified by operating industrial frequency converters with the modified control. All the methods are found feasible, and they provide sufficient overvoltage protection. The limitations and challenges brought about by the methods are discussed.

Strategic Innovation Management Based on Three Dimensions

This thesis examines innovation development needs of firms in a remote rural region. The perspective of the study is in strategic innovation management and three dimensions of innovation development: innovation environment, value delivery and innovation capability. The framework is studied with a theoretical and methodological approach in the context of the development of a regional innovation system and the defining of innovation development needs. The thesis is based on existing innovation management literature, expanding it by examining the features of the three dimensions. The empirical data of the study comprise 50 purposefully selected firms within the region of Pielinen Karelia located in Eastern Finland. Most of the firms (70%) included in the study represent manufacturing firms, and over 90% are small and medium-sized enterprises. The research data consist of two questionnaires and an interview, which were done during 2011 in the connection of a regional development project. The point of view of the research is in regional development and harnessing the innovation capability of the firms within the region. The principal research approach applies soft systems methodology. The study explores the means to foster the innovativeness of firms from the viewpoints of innovation environment, innovation capability and value delivery. In closer detail, the study examines relations between the innovation capability factors, differences in innovation development needs within the value delivery system, between sectors and between firm size categories. The thesis offers three major contributions. First, the study extends earlier research on strategic innovation management by connecting the frameworks of innovation capability, innovation environment and value delivery process to the defining of innovation development needs at the regional level. The results deepen knowledge especially concerning practice-based innovation, peripheral regions and smaller firms. Second, the empirical work, based on a case study, confirms the existence of a structural connection integrating five factors of innovation capability. Statistical evidence is provided especially for the positive impacts of the improvement of absorption capability, marketing capability and networking capability, which are the main weaknesses of firms according to the study. Third, the research provides a methodological contribution by applying the innovation matrix in the defining of the innovation development needs of firms. The study demonstrates how the matrix improves possibility to target policy instruments and innovation services more efficiently through indicating significant differences between the innovation support needs regarding various time horizons and phases of innovation process.

Aktiivisen verkkosillan tuottaman yhteismuotoisen jännitteen vaimentaminen kaksitasoisessa, jännitevälipiirillisessä, taajuusmuuttajatopologiassa

Pulssinleveysmoduloidun vaihtosuuntaajan hyötysuhteen parantaminen ja kytkentätaajuuden suurentaminen ovat johtaneet lähtöjännitteen suuritaajuiseen taajuussisältöön kaksitasoisessa, jännitevälipiirillisessä taajuusmuuttajatopologiassa. Kasvava tarve siirtää tehoa myös verkkoon päin on lisännyt aktiivisen verkkosillan käyttöä. Kaksitasoisen aktiivisen verkkosillan vaikutuksesta DC-välipiirin keskipisteen ja kolmivaiheisen kuorman tähtipisteen välinen jännite on nollasta poikkeava aiheuttaen suurentuneen yhteismuotoisen jännitteen taajuusmuuttajan lähtöön ja verkon puolelle. Lisäksi yhteismuotoisten jännitteiden aiheuttamat kytkentätaajuiset häiriövirrat voivat aiheuttaa vikavirtasuojien tahatonta laukeamista, vaikeuttaa EMC-standardien vaatimusten täyttämistä, lisätä moottorin käämieristyksien rasitusta ja mahdollisuutta moottorin laakerivaurioille. Diplomityössä tutkitaan aktiivisen ja passiivisen verkkosillan tuottamaa yhteismuotoista jännitettä simuloinneilla. Esitellään aikaisempaa tutkimustietoa yhteismuotoisen jännitteen ja virran vaimennusratkaisuista aktiivista verkkosiltaa käytettäessä. Tutkimustiedon pohjalta suunnitellaan koelaitteistolle soveltuva suodin. Suotimen toiminta testataan simuloinnein sekä kokeellisin mittauksin. Tehdyt mittaukset osoittavat, että suunniteltu suodin vaimentaa yhteismuotoista jännitettä noin 20 dB verkkosillan kytkentätaajuudella ja tämän jälkeen yli 20 dB/dekadi taajuuteen 100 kHz asti. Lisäksi yhteismuotoisen virran suuruus syöttökaapelin kautta pieneni ehdotetun suotimen vaikutuksesta.

Modeling and Parameter Estimation of Double-Star Permanent Magnet Synchronous Machines

The power rating of wind turbines is constantly increasing; however, keeping the voltage rating at the low-voltage level results in high kilo-ampere currents. An alternative for increasing the power levels without raising the voltage level is provided by multiphase machines. Multiphase machines are used for instance in ship propulsion systems, aerospace applications, electric vehicles, and in other high-power applications including wind energy conversion systems. A machine model in an appropriate reference frame is required in order to design an efficient control for the electric drive. Modeling of multiphase machines poses a challenge because of the mutual couplings between the phases. Mutual couplings degrade the drive performance unless they are properly considered. In certain multiphase machines there is also a problem of high current harmonics, which are easily generated because of the small current path impedance of the harmonic components. However, multiphase machines provide special characteristics compared with the three-phase counterparts: Multiphase machines have a better fault tolerance, and are thus more robust. In addition, the controlled power can be divided among more inverter legs by increasing the number of phases. Moreover, the torque pulsation can be decreased and the harmonic frequency of the torque ripple increased by an appropriate multiphase configuration. By increasing the number of phases it is also possible to obtain more torque per RMS ampere for the same volume, and thus, increase the power density. In this doctoral thesis, a decoupled d–q model of double-star permanent-magnet (PM) synchronous machines is derived based on the inductance matrix diagonalization. The double-star machine is a special type of multiphase machines. Its armature consists of two three-phase winding sets, which are commonly displaced by 30 electrical degrees. In this study, the displacement angle between the sets is considered a parameter. The diagonalization of the inductance matrix results in a simplified model structure, in which the mutual couplings between the reference frames are eliminated. Moreover, the current harmonics are mapped into a reference frame, in which they can be easily controlled. The work also presents methods to determine the machine inductances by a finite-element analysis and by voltage-source inverters on-site. The derived model is validated by experimental results obtained with an example double-star interior PM (IPM) synchronous machine having the sets displaced by 30 electrical degrees. The derived transformation, and consequently, the decoupled d–q machine model, are shown to model the behavior of an actual machine with an acceptable accuracy. Thus, the proposed model is suitable to be used for the model-based control design of electric drives consisting of double-star IPM synchronous machines.

The role of organization-level factors on informal learning process

This study discusses the nature of informal learning process in business organizations, and the importance of different organization-level factors in this process. The purpose of this study is to understand the role of organization-level factors on informal learning process with three subquestions: how informal learning process takes place in business organizations, what organization-level factors affects informal learning process, and how informal learning process is affected by organizational-level factors. The theoretical background of this study includes literatures on the concept of informal learning, its process, and organization-level factors that can affect informal learning process. The empirical research has been conducted in this study by face-to-face interviews. The interviews were conducted between June and August 2015 in Dhaka, Bangladesh. Thirteen interviews were made with the employees from different hierarchical levels from four freight forwarding MNCs in Bangladesh. Constant comparative analysis has been used to process the collected data until reaching a level of saturation. The empirical research found that all the phases in an informal learning process are not linear and sequential, and the role of organization-level factors on each phase varies with the degree and nature of each factor. In addition, the results also revealed that all the organization-level factors do not interact with each other while playing their role on informal learning process. The findings of this study considerably extend our understanding of the important role of HRD, manager, colleague, culture, and work structure on informal learning process in the workplace. However, future research in different organizational contexts is required to generalize the findings of this study.

The role of organization-level factors on informal learning process

This study discusses the nature of informal learning process in business organizations, and the importance of different organization-level factors in this process. The purpose of this study is to understand the role of organization-level factors on informal learning process with three subquestions: how informal learning process takes place in business organizations, what organizationlevel factors affects informal learning process, and how informal learning process is affected by organizational-level factors. The theoretical background of this study includes literatures on the concept of informal learning, its process, and organization-level factors that can affect informal learning process. The empirical research has been conducted in this study by face-to-face interviews. The interviews were conducted between June and August 2015 in Dhaka, Bangladesh. Thirteen interviews were made with the employees from different hierarchical levels from four freight forwarding MNCs in Bangladesh. Constant comparative analysis has been used to process the collected data until reaching a level of saturation. The empirical research found that all the phases in an informal learning process are not linear and sequential, and the role of organization-level factors on each phase varies with the degree and nature of each factor. In addition, the results also revealed that all the organization-level factors do not interact with each other while playing their role on informal learning process. The findings of this study considerably extend our understanding of the important role of HRD, manager, colleague, culture, and work structure on informal learning process in the workplace. However, future research in different organizational contexts is required to generalize the findings of this study.

Study on measuring Systems of Innovation on National level- case Finland

Innovation improves human affluence and comfort and is key driver of nation’s economic progression. This study focuses on National innovation systems in general and Finnish national innovation system in particular. It is known that innovation process does not work in isolation; rather it is an outcome of role played numerous actors. In this study three aspects are explained- firstly, to define the most important actors of National innovation systems and secondly, a framework to analyze National innovation system. Third aspect of this study highlights and analyzes the key aspects of Finnish National Innovation system. Moreover, during the course of this study emphasis was given on the utmost central processes which are required to come off in innovation system as they can successfully lead towards innovation.

Foreign direct investment motives and location decision factors under economic recession: Three cases of Finnish FDI in Portugal

The purpose of this thesis was to study how uncertainty in economic conditions of the FDI host country affects location decision of an investment, and what kinds of motives are behind the investment decision to a country in economic recession, in this case Portugal. The country has attracted foreign direct investment steadily, but it is evident that most multinational firms and investors tend to be more interested in emerging economies in general. The aim was to find out also which host country specific advantages are important in this kind of cross-border investment and which factors are important for an FDI to succeed under economic uncertainty at the host country. The study was done by analyzing three Finnish case companies: a private equity and real estate investment firm Pontos Group, A wave energy technology research and development company AW Energy and NSN, Nokia Solutions and Networks, a global telecommunications company. The research was done empirically, by interviewing experts on the subject, mainly persons representing these companies. In addition relevant articles, journals and content from case companies’ web-pages is used for the desk research regarding the topic. The results of this thesis showed that the FDIs with strategic asset-seeking investments seem most profitable FDI types under uncertain economic conditions. This kind of investments aim to strengthen the company’s long-term strategy, including the time after recession. Firm-specific ownership advantages that bring competitive advantage proved out to be important under these circumstances, as well as first-mover advantages and externally created assets such as government promotional policies regarding FDI incentives. Also the location was considered suitable for resource- or efficiency seeking motives, based on the lowered price level at the host country. Problems were related mainly to financing, but as foreign companies receive financing usually from their home countries, the economic recession of the host country does not have significant effect for FDI decision, according to this study