Taajuusmuuttajaohjatun pumppukäytön simulointimallin kehittäminen ja testaus

Pumppukäytöt vastaavat noin neljänneksestä Euroopan sähkömoottoreissa kulutettavasta sähkötehosta. Energian kallistumisen vuoksi energian säästämisestä ja energiatehokkuudesta on tullut yhä tärkeämpää. Taajuusmuuttajat ovat tuoneet yksinkertaisen säätötavan, jolla suurimmassa osassa pumppukäyttöjä voidaan saada huomattavia energiasäästöjä. Koko energiansäästöpotentiaalin hyödyntämiseksi täytyy kuitenkin pumppujen toimintaa tarkkailla. Tarkkailu voidaan toteuttaa käyttämällä taajuusmuuttajan sisäisiä mittauksia pumpun toimintapisteen määrittämiseen. Tässä työssä muodostetaan kaksi simulointimallia, joilla voidaan tutkia pumppukäytön toimintapistettä ja energiatehokkuutta. Pumpattavan nesteen ominaisuuksien vaikutusta malleihin tutkitaan ja tapoja korjata virhettä selvitetään. Mallien tuottamia estimaatteja verrataan laboratorio ja pilot-kohteiden mittauksiin. Pilot-kohteiden avulla tutkitaan voidaanko simulointimalleja käyttää teollisuuden energiansäästöpotentiaalia omaavien pumppukäyttöjen havaitsemiseen.

Elinkaaripohjaiseen ABC-analyysiin perustuva päätöksenteontukijärjestelmä

Yritysten vaihto-omaisuudenhallinnasta löytyy usein selviä puutteita. Yksi selkeä syy tähän on perinteisen ABC-analyysin riittämättömyys, joka pohjautuu puhtaasti historiatietoihin. ABC-analyysia oikein tulkitsemalla, voi siitä kuitenkin saada erinomaisen työkalun varastonhallintaan. Tämä edellyttää tuotteen elinkaarenvaiheen huomioimista. Tätä elinkaarenvaiheet huomioivaa ABC-analyysia kutsutaan elinkaaripohjaiseksi ABC-analyysiksi. Koska nykyisissä toiminnanohjausjärjestelmissä ei kuitenkaan ole mahdollista luokitella tuotteita tämän uuden menetelmän mukaisesti, syntyy tarve tukijärjestelmälle. Tukijärjestelmän tarkoituksena on sekä luokitella tuotteet elinkaaripohjaisen ABC-analyysin avulla että antaa tuotteille varastonohjaussuositukset Salmivuori Consulting Oy:n käyttämän ohjausmenetelmän mukaisesti. Varastotasojen määrittämistä helpottamaan luotiin järjestelmän yhteyteen vielä erillinen ohjaustyökalu. Lisäksi työssä on havainnollistettu keskimääräistä varaston arvoa sekä puutekustannuksia minimoivien varastotasojen valintaa case-esimerkin avulla. Järjestelmän luomien tuoteluokkien sekä varastonohjaussuositusten avulla, päätöksentekijällä on mahdollisuudet tehostaa yrityksen vaihto-omaisuudenhallintaa.

Salient Pole Synchronous Machine Modelling in an Industrial Direct Torque Controlled Drive Application

Synchronous motors are used mainly in large drives, for example in ship propulsion systems and in steel factories' rolling mills because of their high efficiency, high overload capacity and good performance in the field weakening range. This, however, requires an extremely good torque control system. A fast torque response and a torque accuracy are basic requirements for such a drive. For large power, high dynamic performance drives the commonly known principle of field oriented vector control has been used solely hitherto, but nowadays it is not the only way to implement such a drive. A new control method Direct Torque Control (DTC) has also emerged. The performance of such a high quality torque control as DTC in dynamically demanding industrial applications is mainly based on the accurate estimate of the various flux linkages' space vectors. Nowadays industrial motor control systems are real time applications with restricted calculation capacity. At the same time the control system requires a simple, fast calculable and reasonably accurate motor model. In this work a method to handle these problems in a Direct Torque Controlled (DTC) salient pole synchronous motor drive is proposed. A motor model which combines the induction law based "voltage model" and motor inductance parameters based "current model" is presented. The voltage model operates as a main model and is calculated at a very fast sampling rate (for example 40 kHz). The stator flux linkage calculated via integration from the stator voltages is corrected using the stator flux linkage computed from the current model. The current model acts as a supervisor that prevents only the motor stator flux linkage from drifting erroneous during longer time intervals. At very low speeds the role of the current model is emphasised but, nevertheless, the voltage model always stays the main model. At higher speeds the function of the current model correction is to act as a stabiliser of the control system. The current model contains a set of inductance parameters which must be known. The validation of the current model in steady state is not self evident. It depends on the accuracy of the saturated value of the inductances. Parameter measurement of the motor model where the supply inverter is used as a measurement signal generator is presented. This so called identification run can be performed prior to delivery or during drive commissioning. A derivation method for the inductance models used for the representation of the saturation effects is proposed. The performance of the electrically excited synchronous motor supplied with the DTC inverter is proven with experimental results. It is shown that it is possible to obtain a good static accuracy of the DTC's torque controller for an electrically excited synchronous motor. The dynamic response is fast and a new operation point is achieved without oscillation. The operation is stable throughout the speed range. The modelling of the magnetising inductance saturation is essential and cross saturation has to be considered as well. The effect of cross saturation is very significant. A DTC inverter can be used as a measuring equipment and the parameters needed for the motor model can be defined by the inverter itself. The main advantage is that the parameters defined are measured in similar magnetic operation conditions and no disagreement between the parameters will exist. The inductance models generated are adequate to meet the requirements of dynamically demanding drives.

On Fault Tolerance Methods for Networks-on-Chip

Technology scaling has proceeded into dimensions in which the reliability of manufactured devices is becoming endangered. The reliability decrease is a consequence of physical limitations, relative increase of variations, and decreasing noise margins, among others. A promising solution for bringing the reliability of circuits back to a desired level is the use of design methods which introduce tolerance against possible faults in an integrated circuit. This thesis studies and presents fault tolerance methods for network-onchip (NoC) which is a design paradigm targeted for very large systems-onchip. In a NoC resources, such as processors and memories, are connected to a communication network; comparable to the Internet. Fault tolerance in such a system can be achieved at many abstraction levels. The thesis studies the origin of faults in modern technologies and explains the classification to transient, intermittent and permanent faults. A survey of fault tolerance methods is presented to demonstrate the diversity of available methods. Networks-on-chip are approached by exploring their main design choices: the selection of a topology, routing protocol, and flow control method. Fault tolerance methods for NoCs are studied at different layers of the OSI reference model. The data link layer provides a reliable communication link over a physical channel. Error control coding is an efficient fault tolerance method especially against transient faults at this abstraction level. Error control coding methods suitable for on-chip communication are studied and their implementations presented. Error control coding loses its effectiveness in the presence of intermittent and permanent faults. Therefore, other solutions against them are presented. The introduction of spare wires and split transmissions are shown to provide good tolerance against intermittent and permanent errors and their combination to error control coding is illustrated. At the network layer positioned above the data link layer, fault tolerance can be achieved with the design of fault tolerant network topologies and routing algorithms. Both of these approaches are presented in the thesis together with realizations in the both categories. The thesis concludes that an optimal fault tolerance solution contains carefully co-designed elements from different abstraction levels

Mobile system for pump working point estimation

In the current economy situation companies try to reduce their expenses. One of the solutions is to improve the energy efficiency of the processes. It is known that the energy consumption of pumping applications range from 20 up to 50% of the energy usage in the certain industrial plants operations. Some studies have shown that 30% to 50% of energy consumed by pump systems could be saved by changing the pump or the flow control method. The aim of this thesis is to create a mobile measurement system that can calculate a working point position of a pump drive. This information can be used to determine the efficiency of the pump drive operation and to develop a solution to bring pump’s efficiency to a maximum possible value. This can allow a great reduction in the pump drive’s life cycle cost. In the first part of the thesis, a brief introduction in the details of pump drive operation is given. Methods that can be used in the project are presented. Later, the review of available platforms for the project implementation is given. In the second part of the thesis, components of the project are presented. Detailed description for each created component is given. Finally, results of laboratory tests are presented. Acquired results are compared and analyzed. In addition, the operation of created system is analyzed and suggestions for the future development are given.

Utilization of a Time Domain Simulator in the Technical and Economic Analysis of a Wind Turbine Electric Drive Train

The amount of installed wind power has been growing exponentially during the past ten years. As wind turbines have become a significant source of electrical energy, the interactions between the turbines and the electric power network need to be studied more thoroughly than before. Especially, the behavior of the turbines in fault situations is of prime importance; simply disconnecting all wind turbines from the network during a voltage drop is no longer acceptable, since this would contribute to a total network collapse. These requirements have been a contributor to the increased role of simulations in the study and design of the electric drive train of a wind turbine. When planning a wind power investment, the selection of the site and the turbine are crucial for the economic feasibility of the installation. Economic feasibility, on the other hand, is the factor that determines whether or not investment in wind power will continue, contributing to green electricity production and reduction of emissions. In the selection of the installation site and the turbine (siting and site matching), the properties of the electric drive train of the planned turbine have so far been generally not been taken into account. Additionally, although the loss minimization of some of the individual components of the drive train has been studied, the drive train as a whole has received less attention. Furthermore, as a wind turbine will typically operate at a power level lower than the nominal most of the time, efficiency analysis in the nominal operating point is not sufficient. This doctoral dissertation attempts to combine the two aforementioned areas of interest by studying the applicability of time domain simulations in the analysis of the economicfeasibility of a wind turbine. The utilization of a general-purpose time domain simulator, otherwise applied to the study of network interactions and control systems, in the economic analysis of the wind energy conversion system is studied. The main benefits of the simulation-based method over traditional methods based on analytic calculation of losses include the ability to reuse and recombine existing models, the ability to analyze interactions between the components and subsystems in the electric drive train (something which is impossible when considering different subsystems as independent blocks, as is commonly done in theanalytical calculation of efficiencies), the ability to analyze in a rather straightforward manner the effect of selections other than physical components, for example control algorithms, and the ability to verify assumptions of the effects of a particular design change on the efficiency of the whole system. Based on the work, it can be concluded that differences between two configurations can be seen in the economic performance with only minor modifications to the simulation models used in the network interaction and control method study. This eliminates the need ofdeveloping analytic expressions for losses and enables the study of the system as a whole instead of modeling it as series connection of independent blocks with no lossinterdependencies. Three example cases (site matching, component selection, control principle selection) are provided to illustrate the usage of the approach and analyze its performance.

Teollisuuden ja yhdyskuntien energiatehokkuusselvitykset, auditoinnit 2008–2010

Nykypäivänä energiansäästötavoitteet ovat haasteena yhä useammalle energiankuluttajalle. Tavoitteisiin päästäkseen yritykset ja kunnalliset energiankuluttajat kaipaavat usein apua kannattavien energiansäätökeinojen löytämiseksi. Erilaiset energiakatselmukset vastaavat tähän tarpeeseen ja ovat esimerkki tuloksellisesta energiansäästöstä. Lappeenrannan teknillinen yliopisto on tutkinut energiatehokkuutta pitkään erilaisissa projekteissa teollisuuden kanssa yhteistyössä. Osa LUT:n energiatehokkuustutkimusta ovat energia-auditoinnit yrityksille ja kunnille, joita LUT Energian projektin puitteissa alettiin kehittää vuoden 2008 syksyllä. Energia-auditointien fokuksena on pyritty pitämään pumppausprosessien energiatehokkuuden optimointia, sillä aihetta on tutkittu yliopistolla laajasti. Pumppausprosesseissa on todettu olevan merkittävä energiansäästöpotentiaali: pumppauksen kuluttamasta energiasta voi olla mahdollista säästää jopa 50 % erilaisilla laite- ja säästötaparatkaisuilla. Pumppausprosessien energia-auditointeja on tehty teollisuuden pumppauskohteisiin kuin myös kunnallisiin vesi-huoltolaitoksiin. Lisäksi energia-auditointien puitteissa on tutkittu energiansäästömahdollisuuksia rakennuksissa. Energiansäästökohteita etsitään sekä lämpö- että sähköenergian osalta. Energia-auditoinneissa pumppausten osalta energiansäästöpotentiaalia on todettu olevan etenkin suuren kokoluokan pumpuissa, joilla on pitkä vuosittainen käyttöaika. Myös pumppujen säätötavalla on suuri merkitys energiankulutukseen. Rakennusten osalta on pyritty selvittämään, kuinka energiankulutus jakautuu eri kulutusryhmien kesken. Säästökohteita on löydetty muun muassa rakennusten tiiviydestä, ilmanvaihdosta kuin valaistuksestakin. Monia auditointien asiakkaita on kiinnostanut etenkin led-teknologian hyödyntäminen yleisvalaistuksessa sekä muut keinot säästää valaistuksen energiankulutuksessa. Pyrkimyksenä on kehittää energia-auditointeja projektin aikana saavutettujen kokemusten avulla sekä myös liiketaloudellisessa mielessä opinnäytetutkielmien avulla. Menestyksekäs palveluliiketoiminta edellyttää määriteltyjä toimintatapoja, riittävän tarkkaa palvelujen rajausta ja koko energia-auditointiprosessin kehittämistä aina asiakassuhteen luomisesta sen jatko-hoitoon saakka.

Diskreettiaikainen liukuvan moodin säätö kiinteäoksidipolttokennon DC-tasonnostossa

Huoli ympäristön tilasta ja fossiilisten polttoaineiden hinnan nousu ovat vauhdittaneet tutkimusta uusien energialähteiden löytämiseksi. Polttokennot ovat yksi lupaavimmista tekniikoista etenkin hajautetun energiantuotannon, varavoimalaitosten sekä liikennevälineiden alueella. Polttokenno on tehonlähteenä kuitenkin hyvin epäideaalinen, ja se asettaa tehoelektroniikalle lukuisia erityisvaatimuksia. Polttokennon kytkeminen sähköverkkoon on tavallisesti toteutettu käyttämällä galvaanisesti erottavaa DC/DC hakkuria sekä vaihtosuuntaajaa sarjassa. Polttokennon kulumisen estämiseksi tehoelektroniikalta vaaditaan tarkkaa polttokennon lähtövirran hallintaa. Perinteisesti virran hallinta on toteutettu säätämällä hakkurin tulovirtaa PI (Proportional and Integral) tai PID (Proportional, Integral and Derivative) -säätimellä. Hakkurin epälineaarisuudesta johtuen tällainen ratkaisu ei välttämättä toimi kaukana linearisointipisteestä. Lisäksi perinteiset säätimet ovat herkkiä mallinnusvirheille. Tässä diplomityössä on esitetty polttokennon jännitettä nostavan hakkurin tilayhtälökeskiarvoistusmenetelmään perustuva malli, sekä malliin perustuva diskreettiaikainen integroiva liukuvan moodin säätö. Esitetty säätö on luonteeltaan epälineaarinen ja se soveltuu epälineaaristen ja heikosti tunnettujen järjestelmien säätämiseen.

Monitoring of centrifugal pump operation by a frequency converter

Centrifugal pumps are widely used in industrial and municipal applications, and they are an important end-use application of electric energy. However, in many cases centrifugal pumps operate with a significantly lower energy efficiency than they actually could, which typically has an increasing effect on the pump energy consumption and the resulting energy costs. Typical reasons for this are the incorrect dimensioning of the pumping system components and inefficiency of the applied pump control method. Besides the increase in energy costs, an inefficient operation may increase the risk of a pump failure and thereby the maintenance costs. In the worst case, a pump failure may lead to a process shutdown accruing additional costs. Nowadays, centrifugal pumps are often controlled by adjusting their rotational speed, which affects the resulting flow rate and output pressure of the pumped fluid. Typically, the speed control is realised with a frequency converter that allows the control of the rotational speed of an induction motor. Since a frequency converter can estimate the motor rotational speed and shaft torque without external measurement sensors on the motor shaft, it also allows the development and use of sensorless methods for the estimation of the pump operation. Still today, the monitoring of pump operation is based on additional measurements and visual check-ups, which may not be applicable to determine the energy efficiency of the pump operation. This doctoral thesis concentrates on the methods that allow the use of a frequency converter as a monitoring and analysis device for a centrifugal pump. Firstly, the determination of energy-efficiency- and reliability-based limits for the recommendable operating region of a variable-speed-driven centrifugal pump is discussed with a case study for the laboratory pumping system. Then, three model-based estimation methods for the pump operating location are studied, and their accuracy is determined by laboratory tests. In addition, a novel method to detect the occurrence of cavitation or flow recirculation in a centrifugal pump by a frequency converter is introduced. Its sensitivity compared with known cavitation detection methods is evaluated, and its applicability is verified by laboratory measurements for three different pumps and by using two different frequency converters. The main focus of this thesis is on the radial flow end-suction centrifugal pumps, but the studied methods can also be feasible with mixed and axial flow centrifugal pumps, if allowed by their characteristics.

Evaluation of energy efficiency and best available techniques in pumping processes

The potential for enhancing the energy efficiency of industrial pumping processes is estimated to be in some cases up to 50 %. One way to define further this potential is to implement techniques in accordance to definition of best available techniques in pumping applications. These techniques are divided into three main categories: Design, control method & maintenance and distribution system. In the theory part of this thesis first the definition of best available techniques (BAT) and its applicability on pumping processes is issued. Next, the theory around pumping with different pump types is handled, the main stress being in centrifugal pumps. Other components needed in a pumping process are dealt by presenting different control methods, use of an electric motor, variable speed drive and the distribution system. Last part of the theory is about industrial pumping processes from water distribution, sewage water and power plant applications, some of which are used further on in the empirical part as example cases. For the empirical part of this study four case studies on typical pumping processes from older Master’s these were selected. Firstly the original results were analyzed by studying the distribution of energy consumption between different system components and using the definition of BAT in pumping, possible ways to improve energy efficiency were evaluated. The goal in this study was that by the achieved results it would be possible to identify the characteristic energy consumption of these and similar pumping processes. Through this data it would then be easier to focus energy efficiency actions where they might be the most applicable, both technically and economically.

Hitsausvirtalähteen ohjaus lämmöntuonnin ja jatkuvan jäähtymisen S-käyrän perusteella

Lämmöntuonnilla on oleellinen vaikutus hitsausliitoksen ominaisuuksiin, koska se vaikuttaa liitoksen jäähtymisnopeuteen, jolla on puolestaan suuri vaikutus jäähtymisessä syntyviin mikrorakenteisiin. Jatkuvan jäähtymisen S-käyrältä voidaan ennustaa hitsausliitokseen syntyvät mikrorakenteet. S-käyrät voidaan laatia hitsausolosuhteiden mukaisesti, jolloin faasimuutoskäyttäytyminen sularajalla saadaan selvitettyä. Tämän diplomityön tavoitteena oli kehittää hitsausvirtalähteen ohjaustapaa lämmöntuontiin ja jatkuvan jäähtymisen S-käyriin perustuen. Jatkuvan jäähtymisen S-käyrillä ja lämmöntuontiin perustuvalla hitsausparametrien säädöllä on yhteys. Työssä tutkittiin, miten haluttuun jäähtymisnopeuteen johtava lämmöntuonti voidaan määrittää S-käyrälle luotettavasti. Työssä perehdyttiin jatkuvan jäähtymisen S-käyriin ja eri jäähtymisnopeuksilla hitsausliitokseen syntyviin mikrorakenteisiin sekä hitsaus-inverttereiden ohjaus- ja säätötekniikkaan. Teoriaosuuden jälkeen tarkasteltiin eri vaihtoehtoja, miten hitsattavan materiaalin koostumusvaihtelut sekä lämmöntuontiin vaikuttavat tekijät voidaan ottaa huomioon virtalähteen ohjauksessa lämmöntuonnin perusteella. S-käyrältä määritettyjen lämmöntuonnin arvojen perusteella tehtiin kahdet koehitsaukset, joissa käytettiin kolmea eri aineenpaksuutta. Tulosten perusteella arvioitiin lämmöntuonnin arvojen toimivuutta käytännössä ja tutkittiin liitokseen syntyviä mikrorakenteita. Tutkimuksen pohjalta esitettiin jatkokehitystoimenpiteitä, joiden mukaan voidaan edetä lämmöntuontiin perustuvan säätöjärjestelmän kehitysprojektissa.

Asiakastyytyväisyyteen vaikuttavien tekijöiden tunnistaminen sosiaalisen median seurantapalvelun ja kriittisten tapausten tekniikan avulla

Tutkimuksen tavoitteena on muodostaa liikkeenjohdon päätöksentekoa tukeva toimintatapa, jonka avulla pystytään keräämään ja suodattamaan sosiaalisesta mediasta olennainen asiakastyytyväisyyden muodostumiseen vaikuttava informaatio. Tavoitteena on myös täsmentää sosiaalisen median viestien tarkastelutapaa ja tarjota liikkeenjohdolle käytännönläheinen ja vaihtoehtoinen tiedonkeruumenetelmä perinteisten asiakastyytyväisyyskyselyiden rinnalle. Tutkimuksen case-yrityksenä käytetään Fox International Channels Oy:tä, joka alkuvuodesta 2012 hankki SuomiTV:n ja lanseerasi tämän tilalle uuden FOX-kanavan. Sosiaalisen median viestit kerätään sosiaalisen median seurannan avulla ja kerättyä aineistoa tarkastellaan kriittisten tapausten tekniikan avulla.Tämän tutkimuksen perusteella voidaan todeta, että on olemassa valtava määrä käsittelemätöntä tietoa, jota keräämällä, suodattamalla ja analysoimalla voidaan kerätä tavoitteita tukevaa relevanttia informaatiota. Tutkimuksessa tulee ilmi, että viestit sisältävät paljon ironiaa, slangia, sarkasmia ja metaforia, minkä takia automaattinen hakusanoihin perustuva seuranta- ja analysointipalvelu ei riitä syvällisen ymmärryksen luomiseen. Yrityksen ulkopuolinen tieto ja sosiaalisen median viestit ovat puhtaimmillaan hyvin tärkeää ulkoista informaatiota yrityksille, mitä hyväksikäyttämällä voidaan luoda kilpailuetua pidemmällä aikavälillä.

Pk-yrityksen materiaalivarastotasojen seurannan kehittäminen

Tässä diplomityössä selvitettiin kuinka pk-yrityksen materiaalivarastotasojen seurantaa pystyttäisiin kehittämään. Tarkoituksena oli tutkia yrityksen nykyisiä materiaalivarastotasojen seurantamenetelmiä haastattelujen ja erilaisten raporttien avulla, sekä löytää näiden avulla tarvittavat kehityskohteet ylivarastoinnin ja puutetilanteiden estämiseksi. Työn keskeiseksi sisällöksi nousivat ABC-analyysin ja eri varastonohjausmenetelmien teoriat, joiden pohjalta kehityskohteita alettiin työstämään. Diplomityön keskeisimpinä tuloksina saatiin pk-yrityksen nimikkeiden ABC-analyysit ja niiden mukaan määritetyt palveluasteet. Kaikille nimikkeille saatiin ABC-analyysien perusteella määriteltyä varastonohjausmenetelmät sekä varastotasojen seurantaa ja hankintaa varten tarvittavat parametrit, kuten tilauspisteet ja täydennyseräkoot. Näiden tulosten avulla yrityksen materiaalivarastotasojen seurantaa pystyttiin helpottamaan ja yksinkertaistamaan.

Assessment of Young Learners’ English Proficiency in Bilingual Content Instruction CLIL

This applied linguistic study in the field of second language acquisition investigated the assessment practices of class teachers as well as the challenges and visions of language assessment in bilingual content instruction (CLIL) at primary level in Finnish basic education. Furthermore, pupils’ and their parents’ perceptions of language assessment and LangPerform computer simulations as an alternative, modern assessment method in CLIL contexts were examined. The study was conducted for descriptive and developmental purposes in three phases: 1) a CLIL assessment survey; 2) simulation 1; and 3) simulation 2. All phases had a varying number of participants. The population of this mixed methods study were CLIL class teachers, their pupils and the pupils’ parents. The sampling was multi-staged and based on probability and random sampling. The data were triangulated. Altogether 42 CLIL class teachers nationwide, 109 pupils from the 3rd, 4th and 5th grade as well as 99 parents from two research schools in South-Western Finland participated in the CLIL assessment survey followed by an audio-recorded theme interview of volunteers (10 teachers, 20 pupils and 7 parents). The simulation experimentations 1 and 2 produced 146 pupil and 39 parental questionnaires as well as video interviews of volunteered pupils. The data were analysed both quantitatively using percentages and numerical frequencies and qualitatively employing thematic content analysis. Based on the data, language assessment in primary CLIL is not an established practice. It largely appears to be infrequent, incidental, implicit and based on impressions rather than evidence or the curriculum. The most used assessment methods were teacher observation, bilingual tests and dialogic interaction, and the least used were portfolios, simulations and peer assessment. Although language assessment was generally perceived as important by teachers, a fifth of them did not gather assessment information systematically, and 38% scarcely gave linguistic feedback to pupils. Both pupils and parents wished to receive more information on CLIL language issues; 91% of pupils claimed to receive feedback rarely or occasionally, and 63% of them wished to get more information on their linguistic coping in CLIL subjects. Of the parents, 76% wished to receive more information on the English proficiency of their children and their linguistic development. This may be a response to indirect feedback practices identified in this study. There are several challenges related to assessment; the most notable is the lack of a CLIL curriculum, language objectives and common ground principles of assessment. Three diverse approaches to language in CLIL that appear to affect teachers’ views on language assessment were identified: instrumental (language as a tool), dual (language as a tool and object of learning) and eclectic (miscellaneous views, e.g. affective factors prioritised). LangPerform computer simulations seem to be perceived as an appropriate alternative assessment method in CLIL. It is strongly recommended that the fundamentals for assessment (curricula and language objectives) and a mutual assessment scheme should be determined and stakeholders’ knowledge base of CLIL strengthened. The principles of adequate assessment in primary CLIL are identified as well as several appropriate assessment methods suggested.

Power semiconductor nonlinearities in active du/dt output filtering

This doctoral thesis introduces an improved control principle for active du/dt output filtering in variable-speed AC drives, together with performance comparisons with previous filtering methods. The effects of power semiconductor nonlinearities on the output filtering performance are investigated. The nonlinearities include the timing deviation and the voltage pulse waveform distortion in the variable-speed AC drive output bridge. Active du/dt output filtering (ADUDT) is a method to mitigate motor overvoltages in variable-speed AC drives with long motor cables. It is a quite recent addition to the du/dt reduction methods available. This thesis improves on the existing control method for the filter, and concentrates on the lowvoltage (below 1 kV AC) two-level voltage-source inverter implementation of the method. The ADUDT uses narrow voltage pulses having a duration in the order of a microsecond from an IGBT (insulated gate bipolar transistor) inverter to control the output voltage of a tuned LC filter circuit. The filter output voltage has thus increased slope transition times at the rising and falling edges, with an opportunity of no overshoot. The effect of the longer slope transition times is a reduction in the du/dt of the voltage fed to the motor cable. Lower du/dt values result in a reduction in the overvoltage effects on the motor terminals. Compared with traditional output filtering methods to accomplish this task, the active du/dt filtering provides lower inductance values and a smaller physical size of the filter itself. The filter circuit weight can also be reduced. However, the power semiconductor nonlinearities skew the filter control pulse pattern, resulting in control deviation. This deviation introduces unwanted overshoot and resonance in the filter. The controlmethod proposed in this thesis is able to directly compensate for the dead time-induced zero-current clamping (ZCC) effect in the pulse pattern. It gives more flexibility to the pattern structure, which could help in the timing deviation compensation design. Previous studies have shown that when a motor load current flows in the filter circuit and the inverter, the phase leg blanking times distort the voltage pulse sequence fed to the filter input. These blanking times are caused by excessively large dead time values between the IGBT control pulses. Moreover, the various switching timing distortions, present in realworld electronics when operating with a microsecond timescale, bring additional skew to the control. Left uncompensated, this results in distortion of the filter input voltage and a filter self-induced overvoltage in the form of an overshoot. This overshoot adds to the voltage appearing at the motor terminals, thus increasing the transient voltage amplitude at the motor. This doctoral thesis investigates the magnitude of such timing deviation effects. If the motor load current is left uncompensated in the control, the filter output voltage can overshoot up to double the input voltage amplitude. IGBT nonlinearities were observed to cause a smaller overshoot, in the order of 30%. This thesis introduces an improved ADUDT control method that is able to compensate for phase leg blanking times, giving flexibility to the pulse pattern structure and dead times. The control method is still sensitive to timing deviations, and their effect is investigated. A simple approach of using a fixed delay compensation value was tried in the test setup measurements. The ADUDT method with the new control algorithm was found to work in an actual motor drive application. Judging by the simulation results, with the delay compensation, the method should ultimately enable an output voltage performance and a du/dt reduction that are free from residual overshoot effects. The proposed control algorithm is not strictly required for successful ADUDT operation: It is possible to precalculate the pulse patterns by iteration and then for instance store them into a look-up table inside the control electronics. Rather, the newly developed control method is a mathematical tool for solving the ADUDT control pulses. It does not contain the timing deviation compensation (from the logic-level command to the phase leg output voltage), and as such is not able to remove the timing deviation effects that cause error and overshoot in the filter. When the timing deviation compensation has to be tuned-in in the control pattern, the precalculated iteration method could prove simpler and equally good (or even better) compared with the mathematical solution with a separate timing compensation module. One of the key findings in this thesis is the conclusion that the correctness of the pulse pattern structure, in the sense of ZCC and predicted pulse timings, cannot be separated from the timing deviations. The usefulness of the correctly calculated pattern is reduced by the voltage edge timing errors. The doctoral thesis provides an introductory background chapter on variable-speed AC drives and the problem of motor overvoltages and takes a look at traditional solutions for overvoltage mitigation. Previous results related to the active du/dt filtering are discussed. The basic operation principle and design of the filter have been studied previously. The effect of load current in the filter and the basic idea of compensation have been presented in the past. However, there was no direct way of including the dead time in the control (except for solving the pulse pattern manually by iteration), and the magnitude of nonlinearity effects had not been investigated. The enhanced control principle with the dead time handling capability and a case study of the test setup timing deviations are the main contributions of this doctoral thesis. The simulation and experimental setup results show that the proposed control method can be used in an actual drive. Loss measurements and a comparison of active du/dt output filtering with traditional output filtering methods are also presented in the work. Two different ADUDT filter designs are included, with ferrite core and air core inductors. Other filters included in the tests were a passive du/dtfilter and a passive sine filter. The loss measurements incorporated a silicon carbide diode-equipped IGBT module, and the results show lower losses with these new device technologies. The new control principle was measured in a 43 A load current motor drive system and was able to bring the filter output peak voltage from 980 V (the previous control principle) down to 680 V in a 540 V average DC link voltage variable-speed drive. A 200 m motor cable was used, and the filter losses for the active du/dt methods were 111W–126 W versus 184 W for the passive du/dt. In terms of inverter and filter losses, the active du/dt filtering method had a 1.82-fold increase in losses compared with an all-passive traditional du/dt output filter. The filter mass with the active du/dt method was 17% (2.4 kg, air-core inductors) compared with 14 kg of the passive du/dt method filter. Silicon carbide freewheeling diodes were found to reduce the inverter losses in the active du/dt filtering by 18% compared with the same IGBT module with silicon diodes. For a 200 m cable length, the average peak voltage at the motor terminals was 1050 V with no filter, 960 V for the all-passive du/dt filter, and 700 V for the active du/dt filtering applying the new control principle.