Phase voltage control and filtering in a converter-fed single-phase customer-end system of the LVDC distribution network

In recent years, the network vulnerability to natural hazards has been noticed. Moreover, operating on the limits of the network transmission capabilities have resulted in major outages during the past decade. One of the reasons for operating on these limits is that the network has become outdated. Therefore, new technical solutions are studied that could provide more reliable and more energy efficient power distributionand also a better profitability for the network owner. It is the development and price of power electronics that have made the DC distribution an attractive alternative again. In this doctoral thesis, one type of a low-voltage DC distribution system is investigated. Morespecifically, it is studied which current technological solutions, used at the customer-end, could provide better power quality for the customer when compared with the current system. To study the effect of a DC network on the customer-end power quality, a bipolar DC network model is derived. The model can also be used to identify the supply parameters when the V/kW ratio is approximately known. Although the model provides knowledge of the average behavior, it is shown that the instantaneous DC voltage ripple should be limited. The guidelines to choose an appropriate capacitance value for the capacitor located at the input DC terminals of the customer-end are given. Also the structure of the customer-end is considered. A comparison between the most common solutions is made based on their cost, energy efficiency, and reliability. In the comparison, special attention is paid to the passive filtering solutions since the filter is considered a crucial element when the lifetime expenses are determined. It is found out that the filter topology most commonly used today, namely the LC filter, does not provide economical advantage over the hybrid filter structure. Finally, some of the typical control system solutions are introduced and their shortcomings are presented. As a solution to the customer-end voltage regulation problem, an observer-based control scheme is proposed. It is shown how different control system structures affect the performance. The performance meeting the requirements is achieved by using only one output measurement, when operating in a rigid network. Similar performance can be achieved in a weak grid by DC voltage measurement. An additional improvement can be achieved when an adaptive gain scheduling-based control is introduced. As a conclusion, the final power quality is determined by a sum of various factors, and the thesis provides the guidelines for designing the system that improves the power quality experienced by the customer.

Sähköautojen pikalatauksen verkkovaikutukset

Euroopan unionin energiapolitiikka on luonut paineen parantaa energiatehokkuutta kaikilla energiankäytön aloilla. Merkittävä osa energiasta kulutetaan liikenteessä, joten sähköautojen käyttöönotolla voidaan parantaa energiatehokkuutta merkittävästi. Tämän vuoksi on tarkasteltava sähköautojen laajamittaisen levinneisyyden aiheuttamia vaikutuksia sähköverkolle. Tässä diplomityössä tarkastellaan sähköautojen pikalatauksen verkkovaikutuksia. Tarkastelu painottuu kotilatauksen tarkasteluun taajamissa ja maaseudulla. Kuormituksen kasvu simuloidaan hyödyntäen sähköauton lataukselle laskettua kuormituskäyrää, jonka laskenta perustuu keskimääräiseen henkilöauton liikkumiseen, joka on saatavilla Suomen henkilöliikennetutkimuksesta. Simuloinnin tulosten perusteella sähköauton pikalatauksen verkkovaikutukset ovat merkittäviä keskijänniteverkossa ja pienjänniteverkossa. Suuremmat vaikutukset kohdistuvat pienjänniteverkkoon.

Aurinkopaneeleihin liitettävien vaihtosuuntaajien testaussuunnitelman laadinta ja toteutus

Aurinkoenergia on yksi monista uusiutuvan energian muodoista, joiden suosio on viimeisten vuosien aikana kasvanut fossiilisten polttoaineiden kallistumisen sekä ilmaston lämpenemisen vuoksi. Auringon säteilyn energiaa voidaan muuttaa sähköenergiaksi mm. aurinkopaneeleiden avulla. Aurinkopaneeleihin liitetään usein vaihtosuuntaaja, jolla tuotettu teho voidaan muokata sähköverkkoon tai kotitalouden sähköjärjestelmään sopivaksi. Tässä työssä on esitelty aurinkopaneelilla tuotettavan sähköenergian perusperiaatteet sekä tehoa tuottavan järjestelmän reunaehdot. Tutkimuksessa on perehdytty keskeisiin, aurinkopaneeleihin liitettäville vaihtosuuntaajille laadittuihin standardeihin, hyötysuhteen mittaamisen sekä sähkön laadun näkökulmista. Selvityksen avulla järjestelmän hyötysuhteen sekä lähtötehon laadun määrittämiseksi voidaan laatia standardien mukainen mittaussuunnitelma vaihtosuuntaajan nimellistehosta riippumatta. Standardien avulla on laadittu mittaussuunnitelma Global Inversonne, 100 kW - verkkovaihtosuuntaajayksikölle. Suunnitelman mukaisissa mittauksissa on tutkittu yksikön muunnoshyötysuhdetta sekä lähtöjännitteen- ja virran laatua. Lisäksi työssä on analysoitu mittaustulosten mittausepävarmuuksia ja niitä aiheuttavia tekijöitä.

Electrical Equivalent Circuit for Dry Bacteriorhodopsin Sensor

Bacteriorhodopsin (BR) is a photosensitive protein which functions as a light-driven proton pump. Due to its photoactivity, BR could be used in photosensing and information processing which has inspired researchers to study the photoelectric response and the appropriate measurement instrumentation for BR. In this thesis, the measurement instrumentation connected to a dry BR sensor was confirmed to affect the photovoltage response measured by using voltage amplifiers. Changing of the input impedance of the measurement instrumentation was shown to alter a part of the measured photovoltage response. The photocurrent measurements using transimpedance amplifier and the presented electrical equivalent circuit were used to show that the photocurrent measurements have no significant effect on the photoelectric response. The photocurrent was shown to be a derivate of the photovoltage response measured from the dry BR sensor when it was compared to the response measured with a voltage amplifier. This confirmed that another part of the photovoltage response was not affected by the measurement instrumentation. The time-variant behavior of the dry BR sensor was confirmed in both the photocurrent and the photovoltage measurements. This was caused by the fact that the capacitance of the dry BR sensor changes with the excitation light intensity.

Energy storage in electric drive system

In recent years the environmental issues and the energy saving have become increasingly import in modern society where industry is the major emission factor and energy consumer. Generally, most of the total energy consumption is caused by electrical drives used in industrial applications and thus improving the performance of electrical drives give an opportunity to improve the energy efficiency. In this Master Thesis improving the energy efficiency in different electrical drives is clarified with different cases: regenerative braking in the electric grid or recovery of the braking energy into an energy storage. In addition, as an example, the energy consumption of an elevator is analyzed by measurements. From these measurement results it can be estimated how much the share of the standby energy consumption is from the total energy consumption and how much regenerative energy is available. The latter part of the thesis concentrates on determination of the properties of lithium iron phosphate battery with measurements.

Spatial variability of apparent electrical conductivity and soil properties in a coffee production field

Precision agriculture based on the physical and chemical properties of soil requires dense sampling to determine the spatial variability of these properties. This dense sampling is often expensive and time-consuming. One technique used to reduce sample numbers involves defining management zones based on information collected in the field. Some researchers have demonstrated the importance of soil electrical variables in defining management zones. The objective of this study was to evaluate the relationship between the spatial variability of the apparent electrical conductivity and the soil properties in the coffee production of mountain regions. Spatial variability maps were generated using a geostatistical method. Based on the spatial variability results, a correlation analysis, using bivariate Moran's index, was done to evaluate the relationship between the apparent electrical conductivity and soil properties. The maps of potassium (K) and remaining phosphorus (P-rem) were the closest to the spatial variability pattern of the apparent electrical conductivity.

Sähköntuotannon pienjänniteverkkoon liittäminen - määräykset ja sähköturvallisuus

Älykkäiden sähköverkkojen (Smart Grid) avulla pyritään vastaamaan sähkönkäytön tehostamisvaatimuksiin. Pientuotanto on yksi tärkeimmistä älykkäiden sähköverkkojen osatekijöistä. Suomessa yksityishenkilöiden innostus omaan sähköntuotantoon ei ole vielä virinnyt, monista eri tekijöistä johtuen. Tulevaisuuden sähköverkoissa pientuotannon rooli on kuitenkin merkittävä. Diplomityössä tarkastellaan pientuotannon yleistymisen edellytyksiä ja tuotannon pienjänniteverkkoon liittämistä. Pientuotannon potentiaalia tarkastellaan eri tuotantomuotojen ja niiden kannattavuuden näkökulmasta. Työn tärkein osuus keskittyy verkkoonliittämismääräyksiin ja sähköturvallisuuteen. Pienjänniteverkkoon liitetty tuotantolaitos on uusi syöttöpiste verkossa ja aiheuttaa esimerkiksi suojaushaasteita. Lisäksi aihepiiri on vielä uusi ja toimintamenetelmät ovat osin vaillinaisia. Työssä esitetään tärkeimmät haasteet, pohditaan niiden merkittävyyttä ja käydään läpi ratkaisuvaihtoehtoja. Selviä teknisiä esteitä pientuotannon yleistymiselle ei Suomessa ole.

Performance and scalability of isolated DC-DC converter topologies in low voltage, high current applications

Fuel cells are a promising alternative for clean and efficient energy production. A fuel cell is probably the most demanding of all distributed generation power sources. It resembles a solar cell in many ways, but sets strict limits to current ripple, common mode voltages and load variations. The typically low output voltage from the fuel cell stack needs to be boosted to a higher voltage level for grid interfacing. Due to the high electrical efficiency of the fuel cell, there is a need for high efficiency power converters, and in the case of low voltage, high current and galvanic isolation, the implementation of such converters is not a trivial task. This thesis presents galvanically isolated DC-DC converter topologies that have favorable characteristics for fuel cell usage and reviews the topologies from the viewpoint of electrical efficiency and cost efficiency. The focus is on evaluating the design issues when considering a single converter module having large current stresses. The dominating loss mechanism in low voltage, high current applications is conduction losses. In the case of MOSFETs, the conduction losses can be efficiently reduced by paralleling, but in the case of diodes, the effectiveness of paralleling depends strongly on the semiconductor material, diode parameters and output configuration. The transformer winding losses can be a major source of losses if the windings are not optimized according to the topology and the operating conditions. Transformer prototyping can be expensive and time consuming, and thus it is preferable to utilize various calculation methods during the design process in order to evaluate the performance of the transformer. This thesis reviews calculation methods for solid wire, litz wire and copper foil winding losses, and in order to evaluate the applicability of the methods, the calculations are compared against measurements and FEM simulations. By selecting a proper calculation method for each winding type, the winding losses can be predicted quite accurately before actually constructing the transformer. The transformer leakage inductance, the amount of which can also be calculated with reasonable accuracy, has a significant impact on the semiconductor switching losses. Therefore, the leakage inductance effects should also be taken into account when considering the overall efficiency of the converter. It is demonstrated in this thesis that although there are some distinctive differences in the loss distributions between the converter topologies, the differences in the overall efficiency can remain within a range of a few percentage points. However, the optimization effort required in order to achieve the high efficiencies is quite different in each topology. In the presence of practical constraints such as manufacturing complexity or cost, the question of topology selection can become crucial.

Modeling and Control of the Power Conversion Unit in a Solid Oxide Fuel Cell Environment

In this doctoral thesis, a power conversion unit for a 10 kWsolid oxide fuel cell is modeled, and a suitable control system is designed. The need for research was identified based on an observation that there was no information available about the characteristics of the solid oxide fuel cell from the perspective of power electronics and the control system, and suitable control methods had not previously been studied in the literature. In addition, because of the digital implementation of the control system, the inherent characteristics of the digital system had to be taken into account in the characteristics of the solid oxide fuel cell (SOFC). The characteristics of the solid oxide fuel cell as well the methods for the modeling and control of the DC/DC converter and the grid converter are studied by a literature survey. Based on the survey, the characteristics of the SOFC as an electrical power source are identified, and a solution to the interfacing of the SOFC in distributed generation is proposed. A mathematical model of the power conversion unit is provided, and the control design for the DC/DC converter and the grid converter is made based on the proposed interfacing solution. The limit cycling phenomenon is identified as a source of low-frequency current ripple, which is found to be insignificant when connected to a grid-tied converter. A method to mitigate a second harmonic originating from the grid interface is proposed, and practical considerations of the operation with the solid oxide fuel cell plant are presented. At the theoretical level, the thesis discusses and summarizes the methods to successfully derive a model for a DC/DC converter, a grid converter, and a power conversion unit. The results of this doctoral thesis can also be used in other applications, and the models and methods can be adopted to similar applications such as photovoltaic systems. When comparing the results with the objectives of the doctoral thesis, we may conclude that the objectives set for the work are met. In this doctoral thesis, theoretical and practical guidelines are presented for the successful control design to connect a SOFC-based distributed generation plant to the utility grid.

Electrical Machine Product Development; Transmission to Lean Approach

The requirements set by the market for electrical machines become increasingly demanding requiring more sophisticated technological solutions. Companies producing electrical ma-chines are challenged to develop machines that provide competitive edge for the customer for example through increased efficiency, reliability or some customer specific special requirement. The objective of this thesis is to derive a proposal for the first steps to transform the electrical machine product development process of a manufacturing company towards lean product development. The current product development process in the company is presented together with the processes of four other companies interviewed for the thesis. On the basis of current processes of the electrical machine industry and the related literature, a generalized electrical machine product development process is derived. The management isms and –tools utilized by the companies are analyzed. Adoption of lean Pull-Event –reviews, Oobeya –management and Knowledge based product development are suggested as the initial steps of implementing lean product development paradigm in the manufacturing company. Proposals for refining the cur-rent product development process and increasing the stakeholder involvement in the development projects are made. Lean product development is finding its way to Finnish electrical machine industry, but the results will be available only after the methods have been implemented and adopted by the companies. There is some enthusiasm about the benefits of lean approach and if executed successfully it will provide competitive edge for the Finnish electrical machine industry.

On the development of an unstructured grid solver for inert and reactive high speed flow simulations

An unstructured grid Euler solver for reactive compressible flow applications is presented. The method is implemented in a cell centered, finite volume context for unstructured triangular grids. Three different schemes for spatial discretization are implemented and analyzed. Time march is implemented in a time-split fashion with independent integrators for the flow and chemistry equations. The capability implemented is tested for inert flows in a hypersonic inlet and for inert and reactive supersonic flows over a 2-D wedge. The results of the different schemes are compared with each other and with independent calculations using a structured grid code. The strengths and the possible weaknesses of the proposed methods are discussed.

Influence of duty factor on the die-sinking Electrical Discharge Machining of high-strength aluminum alloy under rough machining

The use of high-strength aluminium alloys as material for injection molding tools to produce small and medium batches of plastic products as well as prototyping molds is becoming of increasing demand by the tooling industry. These alloys are replacing the traditional use of steel in the cases above because they offer many advantages such as very high thermal conductivity associated with good corrosion and wear resistance presenting good machinability in milling and electrical discharge machining operations. Unfortunately there is little technological knowledge on the Electrical Discharge Machining (EDM) of high-strength aluminium alloys, especially about the AMP 8000 alloy. The duty factor, which means the ratio between pulse duration and pulse cycle time exerts an important role on the performance of EDM. This work has carried out an experimental study on the variation of the duty factor in order to analyze its influence on material removal rate and volumetric relative wear under roughing conditions of EDM process. The results showed that high values of duty factor are possible to be applied without bringing instability into the EDM process and with improvement of material removal rate and volumetric relative wear.