Browsing by Author "Ovaska, Seppo J."
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- Adopting a Multi-stage Modeling Approach to Series-Hybrid Powertrain Design
Sähkötekniikan korkeakoulu | Licentiate thesis(2012) Liukkonen, MattiThis research concentrates on the modeling, design, and control of series-hybrid powertrains in Non-Road Mobile Machineries (NRMMs). Hybridization of mobile machinery powertrains is a topical subject due to needs to decrease CO2 emissions and energy consumption, and the possibility of using alternative power sources. This research proposes a combination of backward, functional, static, quasi-static, and dynamic modeling methods as an approach for the systematic series-hybrid powertrain design. As a result, this research introduces an efficient and systematic modeling approach for the design of series-hybrid powertrains in NRMMs, and investigates the accuracies of the approach. In addition, the research proposes an energy management algorithm for an ultra-capacitor buffered diesel series-hybrid powertrain. The results significantly benefit NRMM powertrain designers and scholars by providing an efficient approach with computationally light and easy to adapt modeling tools for similar studies. The study was conducted due to a need for system-design guidelines for different powertrain options, which are somewhat lacking in the literature. Thus, research into hybridizing or introducing fuel cell powertrain to NRMMs still needs persistent attention by many researchers and engineers for several years until the feasibilities and design principles of different powertrain options will be thoroughly explored and concluded. - Angular velocity measurement by correlating rough surface images
Helsinki University of Technology | Master's thesis(2001) Pokki, KalleTässä diplomityössä on tutkittu korrelaatiomenetelmien mahdollisuuksia kulmanopeuden mittaamisessa. Pyörivän kappaleen pinta on valmistusprosessin vuoksi karhea. Työssä esitellään edullinen anturipää, joka koostuu ainoastaan valodiodeista ja muovisesta valokuidusta. Anturi käyttää myös laskentayksikköä nopeustiedon selvittämiseksi kuidun näkemästä karheasta kuvasta. Mittausongelmaa lähestytään kahdesta näkökulmasta. Ensimmäinen hyödyntää kahta peräkkäin asetettua valokuitua. Siinä kulmanopeus lasketaan selvittämällä kahden tosiaikaisesti näytteistetyn signaalin välinen viive. Tällä menetelmällä osoitetaan kuitenkin olevan merkittäviä haittapuolia. Toisessa lähestymistavassa toinen valokuiduista korvataan laskennallisella algoritmilla. Nyt mitattua pintakuvaa verrataan etukäteen tallennettuun kuvaan kulmanopeuden laskemiseksi. Tämä menetelmä laskee myös kiertymäkulman sivutuotteena. Menetelmässä ori kuitenkin vielä ratkaisemattomia ongelmia pienillä nopeuksilla. Noin 20 millisekunnin mittausviive on myös liian suuri käytännön sovelluksiin. Projektissa rakennettiin digitaaliseen signaaliprosessoriin pohjautuva mittauskortti. - Artificial Immune Optimization and Its Application in Industrial Electronics
Helsinki University of Technology | Master's thesis(2005) Wang, XiaoleiAs we know that natural immune systems are complex and enormous self-defence systems with the distinguished capabilities of learning, memory, and adaptation. Artificial Immune System (AIS), based on the natural immune systems, can be considered as an emerging kind of biologically inspired computational intelligence methods, which have attracted considerable research interest from different communities over the past decade. Artificial Immune Optimization (AIO) methods are an important partner of the AIS. They have been successfully applied to handle numerous challenging optimization problems with superior performances over classical approaches. In this Master's thesis, the essential natural immune principles of circulatory, regulatory, and memory mechanisms are first introduced. Next, we present a few typical AIS models and algorithms. In addition, the recent advances of the AIO methods with their applications are discussed. We also demonstrate the application of the clonal selection algorithm in nonlinear function optimization and LC passive power filter optimal design. Computer simulations are made to verify its optimization effectiveness. - Automatic Test System for Type Tests of the Uninterruptible Power Supply
Master's thesis(2012) Nummijoki, EsaTuotekehityksen oleellinen osa on laitteiden testaaminen. UPS-tuotekehityksessä erilaisia testejä tehdään joka päivä. Testaaminen vaatii monenlaisia mittausvälineitä sekä muita laitteita, kuten laajan kuormajärjestelmän sekä erilaisia testikokoonpanoja. Merkittävä määrä testeistä perustuu UPS:n tyyppitesteihin, jotka ovat määritelty IEC-62040 standardissa. Testaaminen kuluttaa paljon aikaa ja resursseja. Ongelman ratkaisuksi on tyyppitestien suorittamiseen mietitty automaattista testausjärjestelmää. Tämän diplomityön tavoitteena oli selventää tarvetta tälle automaattiselle testausjärjestelmälle sekä selventää vaatimuksia sen toteuttamiseen. Työssä syvennyttiin tyyppitesteihin ja automaattisen testausjärjestelmän eri osa-alueisiin. Näiden lisäksi tehtiin kokeiluja, joiden tuloksena syntyi prototyyppi, jolla voidaan suorittaa automaattisesti suuntaa-antava hyötysuhdetesti UPS:lle. Hyötysuhdetestin lisäksi tutkittiin mahdollisuuksia automatisoida dynaamisen suorituskyvyn testi, joka on tyyppitesteistä vaativin. Tuloksena syntyi testiprosessin kuvaus sekä LabVIEW-ohjelmia helpottamaan testin suorittamista. Lopulta päädyttiin kuitenkin siihen, ettei testin automatisointi ole järkevää, koska sitä ei toisteta kovinkaan usein ja automatisointi vaatii paljon aikaa. Tutkimus ja kokeilut osoittivat, että automaattisen testausjärjestelmän toteuttaminen kaikille tyyppitesteille vaatii paljon aikaa ja resursseja. Tästä johtuen automaattinen testausjärjestelmä tyyppitestien suorittamiseen ei ole paras ratkaisu vähentää testaamiseen kuluvaa aikaa ja resursseja. - Comparison of Direction of Arrival and Beamforming Methods
Helsinki University of Technology | Master's thesis(1997) Karttunen, PetriRajoitetun taajuuskaistan tehokkaammalle käytölle asetetaan yhä tiukempia vaatimuksia. Nykyisten matkapuhelinjärjestelmien kapasiteettia on kasvatettu solujen sektoroinnin avulla, pienentämällä solukokoa ja käyttämällä tiheämpää taajuuksien uudelleenkäyttöä. Ensisijaisesti adaptiiviset antennit tarjoavat matkapuhelinkäyttäjien spatiaalisen erottelun. Ne tuottavat kapeita antennikeiloja halutun käyttäjän suuntaan. Tämä vaatii antennialgoritmien tutkimustarvetta, joiden avulla voidaan paikallistaa ja seurata matkapuhelinkäyttäjiä. Perusongelma näiden menetelmien kanssa on, että ne eivät välttämättä tarjoa riittävää toiminnallista tehokkuutta. Joissakin tapauksissa ne voivat täysin epäonnistua saavuttamaan mitään tehokkuutta todellisessa antenniympäristössä epätäydellisen antennimallin tai riittämättömän prosessorikapasiteetin takia. Tässä työssä tarkastellaan eri suunnanestimointi- ja keilanmuodostusmenetelmien ominaisuuksia. Suuntavektoriin pohjautuvat keilanmuodostusmenetelmät tarvitsevat etukäteistietoa käyttäjien sijainnista. Niinpä eri suunnanestimointimenetelmiä on vertailtu simulointituloksin. Menetelmät on jaettu kolmeen perusryhmään: parametrisiin menetelmiin, ei-parametrisiin Fourier-pohjaisiin menetelmiin ja resoluutiomenetelmiin. Simulointitulokset osoittavat, että resoluutiomenetelmillä on nimensä mukaisesti parempi erottelukyky verrattuna muihin menetelmiin. Niiden estimointitehokkuus ei ole riippuvainen lähteiden sijainnista. Ne saattavat kuitenkin epäonnistua estimoinnissa jos näytteiden määrä on vähäinen tai jos tulosignaalit korreloivat keskenään. Lisäksi perinteiset Fourier-pohjaiset menetelmät eivät ole laskennallisesti vaativia, mutta niillä on haittana alhainen erottelukyky. Keilanmuodostusmenetelmät jaettiin myös kolmeen perusryhmään: suuntavektoripohjaisiin menetelmiin, referenssisignaalipohjaisiin menetelmiin ja sokeisiin menetelmiin. Simulointitulokset osoittavat, että suuntavektoripohjaiset menetelmät ovat herkkiä virheisiin suuntavektorissa ja satunnaisiin virheisiin suuntavektorin elementeissä. Referenssisignaalipohjaiset menetelmät tarvitsevat useita kymmeniä iterointiaskeleita ennen kuin ne pystyvät saavuttamaan optimin. Lisäksi suppeneminen on riippuvainen askelkoon valinnasta ja lähteiden sijainnista. Sokeat menetelmät eivät tarvitse referenssisignaalia, mutta ne eivät välttämättä konvergoidu. - Design of master control unit for laboratory prototype of traction converter for locomotives
Faculty of Electronics, Communications and Automation | A4 Artikkeli konferenssijulkaisussa(2008) Žák, Jan; Peroutka, Zdeněk; Ovaska, Seppo J.This paper deals with the prototype of a main traction converter with medium-frequency transformer for AC trolley wire-fed locomotives. The attention is paid to the new master control and diagnostic unit. The designed master control unit has been implemented in the LabVIEW environment. Our master control unit ensures an effective human interface between a user and the control hardware. In this case, the master unit makes possible both extensive control and diagnostic operations of the laboratory prototype of the traction converter. The master unit was tested extensively by experiments performed on a designed traction converter prototype of 12-kW rated power. - Developing Evolutionary Algorithms for Time-Constrained Optimization
Helsinki University of Technology | Licentiate thesis(2005) Martikainen, Jarno - Digital Control of Power Supplies - Opportunities and Constraints
Helsinki University of Technology | Master's thesis(1997) Vallittu, Petri - Direct-to-chip liquid cooling for reducing power consumption in a subarctic supercomputer centre
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2016) Ovaska, Seppo J.; Dragseth, Roy E.; Hanssen, Svenn A.Reduction of data centre power consumption is a timely challenge. Waste heat reuse is another focus area when developing energy efficient and sustainable data centres. And these two issues are interconnected through liquid cooling of server racks and/or direct-to-chip liquid cooling. Both of these solutions make it possible to transfer a significant proportion of the waste heat energy back to profitable use. Nevertheless, the heat reusing opportunity is not the only benefit direct-to-chip liquid cooling may offer. Another benefit is the notable reduction of power consumption related to cooling fans associated with server blades and rack-level cooling systems. To evaluate this benefit, we performed power consumption and performance measurements in a subarctic supercomputer centre hosting a cluster of 632 blade nodes. Our study concentrated on a 47-node subset that we analysed when the servers were executing the LINPACK benchmark. Our conclusion is that direct-to-chip liquid cooling can reduce the total power consumption, in this case, up to 14.4% depending on the inlet air temperature. - Modeling and Optimization of Unit Load Behavior for Cloud Radio Network Controller
Sähkötekniikan korkeakoulu | Master's thesis(2019-08-19) Ali, SyedWith the telecommunications industry having transitioned to cloud computing and virtualization since the advent of 3G, we are now seeing the benefits of these technologies with regards to dynamic scalability for the effective and timely management and allocation of network resources for managing evolving demands in customer needs. Nokia's AirScale Radio Network Controller uses cloud computing and network function virtualization to yield a scalable solution for managing customer traffic. In order to completely avail the scalability of the AirScale Radio Network Controller from the very start, a revamped dimensioning solution is needed that can provide a reasonable approximation of the virtual network function configuration needed in order to meet the traffic and load threshold demands defined by the customer. This study explores the possiblity of a data driven Machine Learning approach to learn models that can approximate the relationship between virtual network function configuration, telecommunications traffic, and virtual network function load thresholds. Several features representing traffic are included in the dataset and tested for redundancy, and each type of virtual network function component is assigned its own regression target. Insights about the dataset are gained through exploratory data analysis, which reveals strong collinearity between many features, and the need for a more extensive data generation / collection process with respect to regression target values. Linear as well as non-linear machine learning models are evaluated, and the best performing model selected using a two-pronged selection process. The study concludes that non-linear methods yield the best generalization performance, in particular, Artificial Neural Networks and Kernel Ridge Regression. The study also shows that linear models, which are explainable, cannot keep up with non-linear models in terms of generalization performance, so further study involving more sophisticated explainable models e.g. decision trees, needs to be carried out in the future. - Modeling of multiport DC busses in power-electronic systems
A4 Artikkeli konferenssijulkaisussa(2013-02-25) Liukkonen, Matti; Hinkkanen, Marko; Kyyrä, Jorma; Ovaska, Seppo J.This paper deals with dynamic modeling of multi-port DC busses, which are increasingly applied in various DC-power distribution systems, such as hybrid powertrains and DC microgrids. Parasitic impedances of long DC cabling together with distributed DC capacitors introduce a potential risk of small-signal instabilities in the DC bus, if resonance frequencies of the bus appear below (or around) switching frequencies of power-electronic converters. In order to predict the resonance behavior of the bus, a systematic approach for dynamic modeling of the DC bus in power-electronic systems is presented. The DC-bus model is validated by means of experiments. Furthermore, application of the model in small-signal analysis and time-domain simulations is illustrated. - A prototype device for rotary angle and angular velocity determination based on surface identities
Helsinki University of Technology | Master's thesis(2001) Ruusunen, Matti - Reference signal generator for active power filters using MGP-FIR filter designed by evolutionary programming
Faculty of Electronics, Communications and Automation | A4 Artikkeli konferenssijulkaisussa(2008) Komrska, Tomáš; Ovaska, Seppo J.This paper describes a high-performance reference signal generator for active power filters extracting the fundamental signal component from distorted current signals. In order to achieve high-quality output as well as computationally effective algorithm, the generator employs an adaptive and predictive MGP-FIR (Multiplicative General Parameter) bandpass filter designed by evolutionary programming. Detailed procedures of MGP-FIR filtering and evolutionary optimization are first discussed; theoretical conclusions are verified by illustrative simulation results. - Solar energy and free cooling potential in European data centers
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2012) Malkamäki, Tuomo; Ovaska, Seppo J.Energy efficiency has become one of the key issues for data center operators in recent years. Significant power and consequent cost savings are perceived to be attainable and are also considered to be mandatory due to environmental aspects and for sustainable development. Use of economizers and free cooling is currently one the most prominent ways to make data centers more efficient. Besides efficiency, solutions for green energy production are becoming more and more of a reality and while providing clean energy, intermittency is a considerable challenge, not least due to high reliability requirements in data centers. Solar energy, while currently being somewhat uneconomical solution, is ex–pected to increase in the future with improved and cost-effective photovoltaic systems and due to its significant potential surpassing all the other renewable sources combined. Solar energy also has to a certain extent, when compared with e.g. wind energy, a more predictable pattern. It also correlates with temperature, making it an attractive source for systems in which power consumption is temperature related, such as with data center cooling. Unfortunately, locations with high solar energy production potential are somewhat less optimal for economizers and free cooling. This paper investi–gates basic relationships between solar energy and air temperature and subsequent data center cooling requirements. Of particular interest is the optimal data center location in terms of free cooling and solar energy potential. - Towards sustainable and energy-efficient data centers; A Finnish viewpoint
Sähkötekniikan korkeakoulu | Licentiate thesis(2013) Malkamäki, TuomoIn recent years, the rapid rates of growth in energy use have steered industry towards energy-efficient solutions. Thus, the energy efficiency of data centers and ICT in general have also recently received considerable attention. Furthermore, both economic and environmental benefits are seen to be attainable if proper actions are taken in these data centers. This thesis examines data center energy efficiency and sustainability focusing specifically on currently portrayed 'state-of-the-art' solutions to improve efficiency and sustainability. Trends and future prospects within the industry are also studied to better understand the evolving direction of the field. Another more specific focal point is the evaluation of these energy efficiency and sustainability related improvements against local conditions in Finland. The most important results include a comparison of various power distribution and cooling solutions with estimates of attainable improvement and figures of merit. Regarding sustainability, the viability of powering data centers with renewable energy sources is estimated and complemented with examples of achievable economic and environmental benefits.