Power quality improving with virtual flux-based voltage source line converter

Line converters have become an attractive AC/DC power conversion solution in industrial applications. Line converters are based on controllable semiconductor switches, typically insulated gate bipolar transistors. Compared to the traditional diode bridge-based power converters line converters have many advantageous characteristics, including bidirectional power flow, controllable de-link voltage and power factor and sinusoidal line current. This thesis considers the control of the lineconverter and its application to power quality improving. The line converter control system studied is based on the virtual flux linkage orientation and the direct torque control (DTC) principle. A new DTC-based current control scheme is introduced and analyzed. The overmodulation characteristics of the DTC converter are considered and an analytical equation for the maximum modulation index is derived. The integration of the active filtering features to the line converter isconsidered. Three different active filtering methods are implemented. A frequency-domain method, which is based on selective harmonic sequence elimination, anda time-domain method, which is effective in a wider frequency band, are used inharmonic current compensation. Also, a voltage feedback active filtering method, which mitigates harmonic sequences of the grid voltage, is implemented. The frequency-domain and the voltage feedback active filtering control systems are analyzed and controllers are designed. The designs are verified with practical measurements. The performance and the characteristics of the implemented active filtering methods are compared and the effect of the L- and the LCL-type line filteris discussed. The importance of the correct grid impedance estimate in the voltage feedback active filter control system is discussed and a new measurement-based method to obtain it is proposed. Also, a power conditioning system (PCS) application of the line converter is considered. A new method for correcting the voltage unbalance of the PCS-fed island network is proposed and experimentally validated.

Global virtual teamwork. Building and communicating trust through technology

Tutkimuksen ensisijaisena tavoitteena oli tarkastella luottamuksen rakentumista virtuaalitiimissä. Keskeistä tarkastelussa olivat luottamuksen lähteiden löytäminen, suhteen rakentuminen sekä teknologiavälitteinen kommunikaatio. Myös käytännön keinoja ja sovelluksia etsittiin. Tässä tutkimuksessa luottamus nähtiin tärkeänä yhteistyön mahdollistajana sekä keskeisenä elementtinä ihmisten välisten suhteiden rakentumisessa. Tämä tutkimus oli empiirinen ja kuvaileva tapaustutkimus. Tutkimuksessa kvalitatiivista aineistoa kerättiin pääasiassa web-pohjaisen kyselyn sekä puhelinhaastattelun avulla. Aineistonkeruu toteutettiin siis pääasiassa virtuaalisesti. Saatu aineisto analysoitiin teemoittelun avulla. Tässä työssä teemoja etsittiin tekstistä pääasiassa teoriasta johdettujen oletusten perusteella. Tutkimuksen tuloksena oli, että luottamusta rakentavia mekanismeja ovat, karkeasti luokiteltuna, yhteiset päämäärät ja vastuut, kommunikaatio, sosiaalinen kanssakäyminen ja informaation jakaminen, toisten huomioiminen ja henkilökohtaiset ominaisuudet. Mekanismit eivät suuresti eronneet luottamuksen rakentumisen mekanismeista perinteisessä kontekstissa. Virtuaalitiimityön alkuvaiheessa luottamus pohjautui käsityksille toisten tiimin jäsenten kyvykkyydestä. Myös institutionaalinen identifioituminen loi pohjaa luottamukselle alkuvaiheessa. Muuten luottamus rakentui vähän kerrassaan tehtävään liittyvän kommunikaation ja sosiaalisen kommunikaation kautta. Tekojen merkitys korostui erityisesti ajan myötä. Työssä esitettiin myös käytännön keinoja luottamuksen rakentamiseksi. Olemassa olevien teknologioiden havaittiin tukevan hyvin suhteen rakentumista tiedon jakamiseen ja sen varastoimiseen liittyvissä tehtävissä. Sen sijaan vuorovaikutuksen näkökulmasta tuen ei nähty olevan yhtä kattavaa. Kaiken kaikkiaan kuitenkin parannuksella sosiaalisissa suhteissa voitaneen saada enemmän aikaan kuin parannuksilla teknologian suhteen.

Communication challenges in virtual teams – a case study of implementing computer-mediated communication technologies in inter-organisational virtual teams

This thesis seeks to answer, if communication challenges in virtual teams can be overcome with the help of computer-mediated communication. Virtual teams are becoming more common work method in many global companies. In order for virtual teams to reach their maximum potential, effective asynchronous and synchronous methods for communication are needed. The thesis covers communication in virtual teams, as well as leadership and trust building in virtual environments with the help of CMC. First, the communication challenges in virtual teams are identified by using a framework of knowledge sharing barriers in virtual teams by Rosen et al. (2007) Secondly, the leadership and trust in virtual teams are defined in the context of CMC. The performance of virtual teams is evaluated in the case study by exploiting these three dimensions. With the help of a case study of two virtual teams, the practical issues related to selecting and implementing communication technologies as well as overcoming knowledge sharing barriers is being discussed. The case studies involve a complex inter-organisational setting, where four companies are working together in order to maintain a new IT system. The communication difficulties are related to inadequate communication technologies, lack of trust and the undefined relationships of the stakeholders and the team members. As a result, it is suggested that communication technologies are needed in order to improve the virtual team performance, but are not however solely capable of solving the communication challenges in virtual teams. In addition, suitable leadership and trust between team members are required in order to improve the knowledge sharing and communication in virtual teams.

Managing virtual project teams

The purpose of the Master’s Thesis is to study the best practices to virtual project management from the project manager’ point of view. The best practices are divided according to a five-phase virtual project life cycle model. Each phase include concrete suggestions for actions. Research’s theoretical background is wide because of the broad subject matter. In the theoretical part topics such as virtual working, virtual project management challenges are examined and some concrete actions to tackle these challenges are introduced. Thesis’ approach is constructive, where a known problem is solved piece by piece after creating a pre-understanding of the topic. Existing research work is utilized when creating a model for virtual project team management. The basis of the model comes from various best practices read from literature and from the interviews conducted on experienced virtual project managers in the case organization. As a result the model combines both previous research and the organizations empirical experience. As an output of the thesis a model for virtual project team management is developed, which can be used as a guideline by the virtual project managers in their work. The model includes actions and practices what can be used to overcome the challenges of virtual project management.