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.

Magni Ducatus Finlandiae Russiae partim, partim Sueciae subjecti Sinus item Bothnici ac Finnici nova et accurata delinaetio - [Yleisnäkymä - Overview]

S.l. : Georg. Aug. Vind ca 1750

Use of scenario analysis in studying emerging technology – Case Grid computing

Tutkimuksen selvitettiin miten skenaarioanalyysia voidaan käyttää uuden teknologian tutkimisessa. Työssä havaittiin, että skenaarioanalyysin soveltuvuuteen vaikuttaa eniten teknologisen muutoksen taso ja saatavilla olevan tiedon luonne. Skenaariomenetelmä soveltuu hyvin uusien teknologioiden tutkimukseen erityisesti radikaalien innovaatioiden kohdalla. Syynä tähän on niihin liittyvä suuri epävarmuus, kompleksisuus ja vallitsevan paradigman muuttuminen, joiden takia useat muut tulevaisuuden tutkimuksen menetelmät eivät ole tilanteessa käyttökelpoisia. Työn empiirisessä osiossa tutkittiin hilaverkkoteknologian tulevaisuutta skenaarioanalyysin avulla. Hilaverkot nähtiin mahdollisena disruptiivisena teknologiana, joka radikaalina innovaationa saattaa muuttaa tietokonelaskennan nykyisestä tuotepohjaisesta laskentakapasiteetin ostamisesta palvelupohjaiseksi. Tällä olisi suuri vaikutus koko nykyiseen ICT-toimialaan erityisesti tarvelaskennan hyödyntämisen ansiosta. Tutkimus tarkasteli kehitystä vuoteen 2010 asti. Teorian ja olemassa olevan tiedon perusteella muodostettiin vahvaan asiantuntijatietouteen nojautuen neljä mahdollista ympäristöskenaariota hilaverkoille. Skenaarioista huomattiin, että teknologian kaupallinen menestys on vielä monen haasteen takana. Erityisesti luottamus ja lisäarvon synnyttäminen nousivat tärkeimmiksi hilaverkkojen tulevaisuutta ohjaaviksi tekijöiksi.

Tasasähköjakelu ja kiinteistöjen tasasähköverkot

Perinteisesti sähkönjakelu on toteutettu vaihtosähköjärjestelmänä, mutta varsinkin tehoelektroniikan kehittymisen ja halpenemisen myötä on paljon keskusteltu tasasähköisistä jakelujärjestelmistä. Tässä työssä on tutkittu ja koetettu tuoda esille tasasähkön hyödyntämismahdollisuuksia sähkönjakelussa, sekä erityisesti kiinteistöjen kuten kotien ja toimistojen sähköverkoissa. DC-verkko parantaa mm. järjestelmän luotettavuutta ja jännitteenlaatua. Myös hajautetun energiantuotannon ja energiavarastojen lisääminen sähkövoimajärjestelmään olisi yksinkertaisempaa tasasähköiseen verkkoon. Monet nykyajan kotien ja toimistojen sähkölaitteista olisi nykyiselläänkin ilman modifikaatioita liitettävissä DC-verkkoon. Monien laitteiden sisäinen käyttöjännite on nykyään tasajännitettä kuten esimerkiksi tietokoneiden ja viihde-elektroniikan. Näiden laitteiden tarvitsemissa lukuisissa tasasuuntaajissa hukataan paljon energiaa. Yhdistämällä laitteet DC-verkkoon voitaisiin suuntauksista luopua, jolloin järjestelmän kokonaishyötysuhde paranisi. Lisäksi kiinteistöissä tasajännitteellä voitaisiin hyödyntää entistä paremmin muun muassa aurinkoenergiaa, polttokennoja ja energiavarastoja eli uusiutuvia ja ympäristöystävällisiä energialähteitä.

Developing of AC magnetometer and investigation of magnetic properties of LSMO

In this work AC magnetometer was developed and primary test measurements were performed for temperature range from 77 K up to 350 K in frequency range from 1 kHz up to 20 kHz. In the course of the present work dependencies of magnetization on temperature for Lao7Sr03Mni _yFeyO3 with y = 0.15, 0.20, 0.25 were obtained in DC magnetic field using SQUID magnetometer and in AC magnetic field using the developed AC magnetometer. Lai.XSrXMnO3 (LSMO) compounds belong to the class of Mn perovskites, which demonstrate very high degree of spin polarization. These materials are of great importance for nowadays applications in spintronics, where spin polarized electron transport is used. Spin glass like behavior was found as a characteristic feature of these solid solutions with the freezing temperature in the range 65 — 210 K.

Modelling of North-West Russian market behavior considering technical restrictions of transmission grid

Nowadays the Finnish-Russian electric energy interaction is carried out through the back-to-back DC Vyborg substation and several power plants working synchronously with Finnish power system. Constant amount of energy flows in one direction — from Russia to Finland. But the process of electricity market development in Russian energy system makes the new possibilities of electrical cooperation available. The goal of master's thesis is to analyze the current state and possible evolution trends of North-West Russian system in relation with future possible change in power flow between Russia and Finland. The research is done by modelling the market of North-West Russia and examination of technical grid restrictions. The operational market models of North-West region of Russia for the years 2008 and 2015 were created during the research process. The description of prepared market models together with modelling results and their analysis are shown in the work. The description of power flow study process and results are also presented.

Development of power flows around Baltic countries with new grid links

In the Thesis main focus is done on power flow development paths around the Baltic States as well as on market-based requirements for creation of the common Baltic electricity market. Current market regulations between the countries are presented; barriers for creating competitive common Baltic power market and for electricity trading with third countries are clarified; solutions are offered and corresponding road map is developed. Future power development paths around the Baltic States are analysed. For this purpose the 330 kV transmission grid of Estonia, Latvia and Lithuania is modelled in a power flow tool. Power flow calculations are carried out for winter and summer peak and off-peak load periods in 2020 with different combinations of interconnections. While carrying out power balance experiments several power flow patterns in the Baltic States are revealed. Conclusions are made about security of supply, grid congestion and transmission capacity availability for different scenarios.

Active du/dt Filtering for Variable-Speed AC Drives

An oscillating overvoltage has become a common phenomenon at the motor terminal in inverter-fed variable-speed drives. The problem has emerged since modern insulated gate bipolar transistors have become the standard choice as the power switch component in lowvoltage frequency converter drives. Theovervoltage phenomenon is a consequence of the pulse shape of inverter output voltage and impedance mismatches between the inverter, motor cable, and motor. The overvoltages are harmful to the electric motor, and may cause, for instance, insulation failure in the motor. Several methods have been developed to mitigate the problem. However, most of them are based on filtering with lossy passive components, the drawbacks of which are typically their cost and size. In this doctoral dissertation, application of a new active du/dt filtering method based on a low-loss LC circuit and active control to eliminate the motor overvoltages is discussed. The main benefits of the method are the controllability of the output voltage du/dt within certain limits, considerably smaller inductances in the filter circuit resulting in a smaller physical component size, and excellent filtering performance when compared with typical traditional du/dt filtering solutions. Moreover, no additional components are required, since the active control of the filter circuit takes place in the process of the upper-level PWM modulation using the same power switches as the inverter output stage. Further, the active du/dt method will benefit from the development of semiconductor power switch modules, as new technologies and materials emerge, because the method requires additional switching in the output stage of the inverter and generation of narrow voltage pulses. Since additional switching is required in the output stage, additional losses are generated in the inverter as a result of the application of the method. Considerations on the application of the active du/dt filtering method in electric drives are presented together with experimental data in order to verify the potential of the method.

De usu symbolorum circa geometrica theoremata ac problemata demonstranda

Invocatio: D.D.