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Peak-current-mode (PCM) control was published first time in open literature in 1976. The observed peculiar behavior caused by the application of PCM-control in a power electronic converter have fascinated the researchers to attempting to capture the dynamics associated to it. It is commonly assumed that the peculiar phenomena originate from the sampling process in the PCM control. A resistor is usually connected as a load, when modeling the converter dynamics and during the frequencyresponse measurements. The load resistor will actually dominate the frequency responses and hide the real dynamics associated to PCM control. Other measurement problems will arise from the non-modeled circuit elements dominating, especially, the highfrequency dynamic behavior of the converters. Because of these problems, the PCM models are not usually properly validated. The investigations, in this paper, show that: i) the PCM models have to be accurate also at the low frequencies for ensuring, for example, stable design of output-current-feedback-controlled converters, ii) the high low-frequency accuracy can be obtained only by means of duty-ratio gain becoming infinite at the mode limit, iii) the highfrequency accuracy of the PCM models can be obtained by means of different high-frequency extensions, iv) the key for the PCM modeling lies in the proper duty-ratio constraints, and v) the highfrequency magnitude and phase behaviors are caused by the second-harmonic-mode operation of the converter due to the frequency-response-measurement injection signal. The main objective of this paper is to show that such a modeling technique, which fully matches the above criteria, has been developed already in early 1990's and later elaborated for more general form. Validation of the dynamic models is performed by simulation, where the converter and its operational environment are perfectly known. The load-resistor effect is removed computationally for performing the complete validation. A PCM-controlled buck converter is used as an example.
The application of a resistor as a load of the pulse-width-modulated DC-DC converters has dominated the dynamic modelling since the development of the modelling methods in early 1970s. In 1990s, the research in the source and load interactions was very active providing valuable information to justify the necessity to develop unterminated dynamic models for characterising the dynamics of the converters. The small-signal modelling can be performed always by using the ideal load, which is determined by the output-terminal variable to be kept constant, regardless of whether the actual open-loop converter can operate or not with the ideal load. This paper will review the feasibility of using the load-resistor-affected models in control design of switched mode converters. The best strategy is always to use unterminated models, which can be used to obtain different load-impedance-affected models if needed. A buck converter is used as the source of information.
Peak-current-mode (PCM) control has been very popular control method in power electronic converters. The small-signal modeling of the dynamics associated to the PCM control has turned out to be extremely challenging. Most of the modeling attempts have been dedicated to the converters operating in continuous conduction mode (CCM) and just a few to the converters operating in discontinuous operation mode (DCM). The DCM modeling method published in 2001 was proved recently to be very accurate when applied to a buck converter. This paper provides the small-signal models for a boost converter, and analyses first time its real dynamic behavior in DCM. The objectives of this paper are: i) To provide the full-order dynamic models for DCM-operated PCM-controlled boost converter, ii) to analyze the accuracy of the full and reduced-order dynamic models, and iii) to verify the validity of the high-frequency extension applied in the DCM-operated PCM-controlled buck converter in case of the boost converter. It is also shown that the DCM-operated boost converter can operate only in even harmonic modes similarly as all the CCM-operated PCM-controlled converters. In case of the DCM-operated PCM-controlled buck converter, the operation in the odd harmonic modes is the consequence of unstable pole in its open-loop power-stage dynamics.
Peak-current-mode (PCM) control was proposed in 1978. The observed peculiar behavior caused by the application of PCM-control in the behavior of a switched-mode converter, which operates in continuous conduction mode (CCM), has led to a multitude of attempts to capture the dynamics associated to it. Only a few similar models have been published for a PCM-controlled converter, which operates in discontinuous conduction mode (DCM). PCM modeling is actually an extension of the modeling of direct-duty-ratio (DDR) or voltage-mode (VM) control, where the perturbed duty ratio is replaced by proper duty-ratio constraints. The modeling technique, which produces accurate PCM models in DCM, is developed in early 2000s. The given small-signal models are, however, load-resistor affected, which hides the real dynamic behavior of the associated converter. The objectives of this paper are as follows: (i) proving the accuracy of the modeling method published in 2001, (ii) performing a comprehensive dynamic analysis in order to reveal the real dynamics of the buck converter under PCM control in DCM, (iii) providing a method to improve the high-frequency accuracy of the small-signal models, and (iv) developing control-engineering-type block diagrams to facilitate the development of generalized transfer functions, which are applicable for PCM-controlled DCM-operated buck, boost, and buck-boost converters.
The heuristic perturb-and-observe-based maximum-power-point tracking (MPPT) algorithm of photovoltaic (PV) generator is still the most popular technique in use, despite the broad spectrum of developed other MPPT algorithms. The correct direction of the next perturbation step requires that the previous perturbation is settled down properly and the applied perturbation step size is large enough to overcome the PV-power changes induced by the varying irradiation level and/or the power-grid-originated PV-voltage ripple. The requirements for the minimum perturbation step size are well defined in the available literature. The design equations to predict the PV-power settling time are derived by assuming that the PV-interfacing converter operates in continuous conduction mode (CCM). A large perturbation step size may drive the interfacing converter to enter into discontinuous conduction mode (DCM), which will delay the PV-power settling process and destroy the validity of the predicted settling times. In order to avoid confusing the MPPT process, the maximum perturbation step size has to be limited as well. This paper provides theoretical foundations for the proper design of the maximum step size based on the DC-DC interfacing-converter dynamic behavior. The theoretical findings are validated with experiments as well as by simulations by means of a boost-type DC-DC converter and real PV panel.
Effective teaching of electric drives is highly important for the electrical engineers, because almost half of the global produced electrical energy is consumed by electric motor drives. Electric drives are a key technology for reducing energy consumption of industrial processes, for wind power generation and for electric transportation. The pedagogical premise is to improve the educational methods of an Electrical Drives course by activating students to work on their own. The paper describes the educational strategy and course objectives. Student feedback was collected at the end of the course and the results of the evaluation are summarized.
This paper provides a simple analytical model for the closed-loop output impedance of a direct-duty-ratio-controlled buck converter, which can be used to predict the behavior of the output voltage during a load-current transient. The modeling method utilizes standard control theory to obtain the model for the sensitivity function based on the crossover frequency and phase margin of the output-voltage feedback loop as well as on a clever estimate for the corresponding open-loop output impedance. The modeling method is validated by means of simulations and experimental tests.
Application of constant-power control and inclusion of energy storage in grid-connected photovoltaic (PV) energy systems may increase the use of two-stage system structures composing of DC-DC-converter-interfaced PV generator and grid-connected inverter connected in cascade. Typical PV-generator-interfacing DC-DC converter is a boost-power-stage converter. The renewable energy system may operate in three different operation modes – grid forming, grid feeding, and grid supporting modes. In the last two operation modes, the outmost feedback loops are taken from the input terminal of the associated power electronic converters, which usually does not pose stability problems in terms of their input sources. In the grid-forming operation mode, the outmost feedback loops have to be connected to the output terminal of the associated power electronic converters, and hence the input terminal will behave as a negative incremental resistor at low frequencies. This property will limit the operation of the PV interfacing converter either in the constant-voltage or constant-current region of the PV generator for ensuring stable operation. The boost-power-stage converter can be applied as a voltage or current-fed converter limiting the stable operation region accordingly. The investigations of this paper shows explicitly that only the voltage-fed mode would provide feasible dynamic and stability properties as a viable interfacing converter.
An open-loop and closed-loop operating boost-power-stage converter with relatively low damping factor exhibit resonant behavior in transient conditions. Such an undamped transient characteristic introduces overshoot to the control-to-output-variable transfer function, which is also visible in the inductor current transient behavior. Therefore, due to the either too large duty ratio or voltage-reference step change, the inductor current can move from continuous conduction mode to discontinuous conduction mode. That transforms the second-order system into an equivalent first-order dynamic system extending the PV-power settling time significantly and reducing power tracking performance of the system. This paper introduces design guidelines to determine maximum perturbation step size for duty ratio and input-voltage reference under open-loop and closed-loop operation, respectively. Two different closed-loop design examples are considered in this paper, based on the application of pure integral controller with phase margin (PM) close to 90 degrees and proportional-integral-derivative controller with PM close to 40 degrees, respectively. The closed-loop system dynamics is known to be characterized by the dominating poles and zeros, which locate closest to the origin. This means that the closed-loop system can be usually characterized by the well-known second-order transfer function. Therefore, the minimum and maximum overshoot of the inductor current can be well approximated as demonstrated by deterministic analysis and experimental results.
Owing to the good trade-off between implementation and performance, fixed-step direct maximum power point tracking techniques (e.g., perturb and observe and incremental conductance algorithms) have gained popularity over the years. In order to optimize their performance, perturbation frequency and perturbation step size are usually determined a priori. While the first mentioned design parameter is typically dictated by the worst-case settling time of the combined energy conversion system, the latter must be high enough to both differentiate the system response from that caused by irradiation variation and match the finite resolution of the analog-to-digital converter in case of digital implementation. Well-established design guidelines, however, aim to optimize steady-state algorithm performance while leaving transients nearly untreated. To improve transient behavior while keeping the steady-state operation unaltered, variable step direct maximum power point tracking algorithms based on adaptive perturbation step size were proposed. This paper proposes a concept of utilizing adaptive perturbation frequency rather than variable step size, based on recently revised guidelines for designing fixed-step direct maximum power point tracking techniques. Preliminary results demonstrate the superiority of the proposed method over adaptive perturbation step size operation during transients, without compromising the steady state performance.
The grid-forming mode of the voltage source inverters (VSI) is applied in uninterruptible power supplies and micro-grids to improve the reliability of electricity distribution. During the intentional islanding of an inverter-based micro-grid, the grid-forming inverters (GFI) are responsible for voltage control, similarly as in the case of uninterruptible power supplies (UPS). The unterminated model of GFI can be developed by considering the load as an ideal current sink. Thus, the load impedance always affects the dynamic behavior of the GFI. This paper proposes a method, to analyze how the dynamics of GFI and the controller design are affected by the load. Particularly, how the frequency response of the voltage loop gain changes according to the load and, how it can be used to the predict time-domain step response. The frequency responses that are measured from a hardware-in-the-loop simulator are used to verify and illustrate explicitly the load effect.
Solar and magnetic energy harvesting may benefit from the use of current-sourced converters for interfacing those sources into the practical usage due to their current-source nature. The paper investigates the implementation and dynamics of such converters by means of a current-sourced buck converter. Duality concepts are applied to obtain the converter from the corresponding voltage-sourced buck converter. The dynamic analysis is carried out in continuous capacitor-voltage-mode under direct-duty-ratio control. The theoretical findings are verified by extracting the transfer functions from the Matlab™-Simulink-based switching models.
LCL-filter is commonly used to attenuate the switching harmonics of grid-connected converters. LCL-filter creates resonances in the converter dynamics which shall be damped for ensuring robust performance of the converter. Active damping methods can be used to attenuate the resonant behavior effectively. Accordingly, the output impedance is affected and the grid-interaction sensitivity of the converter varies with the active damping design. In order to carry out impedance-based stability analysis or assessment of the harmonic rejection capability, an accurate analytical model to predict the output impedance is necessary. This paper investigates the output impedance properties of capacitor-current-feedback active damping, which are so far not considered thoroughly in the literature. The output impedance modification with the active damping design is explained, thus, the stability and harmonic rejection capability of the converter can be improved. Furthermore, in order to validate the model, experimental measurements of the output impedance with active damping are presented for the first time in literature.
A maximum-power-point tracking (MPPT) algorithm is essential in all controllers of solar power electronic converters due to the nonlinear current-voltage characteristics of a photovoltaic generator. One of the most widely utilized algorithms are perturbative MPPT techniques such as perturb and observe and incremental conductance methods due to their simple implementation with relatively good tracking performance. However, in order to optimize the performance of such algorithms, the design parameters - sampling frequency and perturbation step size - need to be designed in respect to interfaced power electronic converter. Recent studies have provided state-of-art MPP-tracking design rules for single and two-stage grid-connected PV systems. Unfortunately, the analysis of those studies does not provide analytical results for PV power transient response under feedback-controlled converters. This paper provides reduced-order transfer functions for the converters equipped with either I-type or PID-type controllers in order to approximate the maximum sampling or perturbation frequency for MPP-tracking algorithms. The analysis reveals the factors affecting the transient behavior similarly as in open-loop converter providing valuable tools for optimizing MPP-tracking perturbation frequency design.
In order to optimize the performance of direct (or perturbative) fixed-step maximum power point tracking algorithms (e.g., perturb and observe and incremental conductance), two design parameters-perturbation frequency and step size-must be selected. The main requirement for perturbation frequency design is ensuring the period between two successive perturbations is longer than settling time of photovoltaic generator power transient. According to existing design guidelines, perturbation frequency should be selected at maximum power point, corresponding to standard test conditions. However, due to finite resolution of digital controllers, maximum power region rather than single maximum power point exists in practice. Therefore, operating point can arbitrarily reside within this region, belonging either to constant-current or constant-voltage I-V curve parts. It is shown that the photovoltaic generator power transient settling process is significantly slower in constant current than maximum power region due to increased value of dynamic resistance. Consequently, perturbation frequency design should be carried out in constant-current region rather than at maximum power point. Short-circuit condition should be selected as worst-case design operation point, where photovoltaic generator dynamic resistance obtains highest value. Then, perturbation frequency design becomes photovoltaic generator independent, influenced only by interfacing converter component values. Experimental results validate presented findings successfully.
Voltage-type sources have dominated as an input source for power electronics converters for a long type. The existence of duality implies that there are also current-type sources as well. The growing application of renewable energy sources such as wind and solar energy has evidently shown that the current-type input sources exist in reality such as photovoltaic (PV) generator or the feedback technique used in controlling the power electronics converters in the renewable energy systems changes the power electronic converters to behaving as such. The recent research on the renewable energy systems has indicated that the current-type input sources are very challenging input sources affecting the dynamics of the interfacing converters profoundly. This paper provides a comprehensive survey of the effects of the PV generator on the dynamic behavior of the corresponding interfacing power electronic converters.
Due to relatively good performance and simple implementation, fixed-step direct maximum power point tracking techniques such as perturb & observe and incremental conductance are the most popular algorithms aimed to maximize the energy yield of photovoltaic energy conversion systems. In order to optimize maximum power point tracking process performance, two design parameters – perturbation frequency and perturbation step size – need to be set a priori, taking into account the properties of both interfacing power converter and photovoltaic generator. While perturbation frequency is limited by the combined energy conversion system settling time, perturbation step size must be high enough to differentiate system response from that caused by irradiation variation. Recent studies have provided explicit design guidelines for single-loop maximum power point tracking structures only, where the algorithm directly sets the interfacing converter duty cycle. It was shown that dynamic resistance of the photovoltaic generator, which is both operation point and environmental conditions dependent, significantly affects the combined energy conversion system settling time. On the other hand, no design guidelines were explicitly given for multi-loop maximum power point tracking structures, where the algorithm sets the reference signal for photovoltaic generator voltage and inner voltage controller performs the regulation task. This paper introduces perturbation frequency and perturbation step size design guidelines for such systems. It is shown that while perturbation step size design is similar to that of single-loop structures, perturbation frequency design is quite different. It is revealed that once the inner voltage loop is properly closed, the influence of photovoltaic generator dynamic resistance on settling time (and thus on perturbation frequency design) is negligible. Experimental results are provided to verify the proposed guidelines validity.
In order to enhance maximum power point tracking (MPPT) speed of photovoltaic generators (PVGs) upon fast irradiation changes, maximum power line (MPL)-based control is often used. MPL is a curve, linking all possible MPP coordinates for a given temperature. In the literature so far, PVG MPL was either assumed linear, which is inaccurate for all irradiation levels, or possessed photocurrent dependence, requiring real-time estimation of the latter. In this letter, an irradiation-independent explicit expression for PVG MPL is derived, valid for all practical irradiation levels, thus allowing real-time implementation without the need of photocurrent estimation.
Impedance-ratio-based interaction analyses in terms of stability and performance of DC-DC converters is well established. Similar methods are applied to grid-connected three-phase converters as well, but the multivariable nature of the converters and the grid makes these analyses very complex. This paper surveys the state of the interaction analyses in the grid-connected three-phase converters, which are used in renewable-energy applications. The surveys show clearly that the impedance-ratio-based stability assessment are usually performed neglecting the cross-couplings between the impedance elements for reducing the complexity of the analyses. In addition, the interactions, which affect the transient performance, are not treated usually at all due to the missing of the corresponding analytic formulations. This paper introduces the missing formulations as well as explicitly showing that the cross-couplings of the impedance elements have to be taken into account for the stability assessment to be valid. In addition, this paper shows that the most accurate stability information can be obtained by means of the determinant related to the associated multivariable impedance ratio. The theoretical findings are also validated by extensive experimental measurements.
Kaivosympäristö asettaa taajuusmuuttajakäytölle erityisvaatimuksia henkilö- ja laiteturvallisuuden takaamiseksi. Tässä työssä tarkastellaan taajuusmuuttajan tuottaman yhteismuotoisen virran vaikutusta maasulkusuojauksen toimintaan. Työssä käsitellään ensin taajuusmuuttajakäytön teoriaa ja yhteismuotoisen virran syntymistä taajuusmuuttajakäytössä. Tämän jälkeen käydään läpi kaivoksiin sijoitettavien taajuusmuuttajakäyttöjen ominaisuuksia. Yhteismuotoisen virran virran vaikutusta taajuusmuuttajakäytön rakenteeseen tarkastellaan simuloimalla. Ensin taajuusmuuttajakäytölle rakennetaan simulointimalli. Tämän jälkeen simuloinneilla selvitetään mallin toimivuutta ja sitä kuinka mallin eri osat vaikuttavat tuloksiin. Lopuksi käydään läpi laboratoriomittauksen tuloksia, joita verrataan simulointituloksiin. Simulointimallista rakennettiin kolmivaiheinen malli, johon sisältyy kaikki tärkeimmät taajuusmuuttajakäytön osat. Malli käyttäytyi suurelta osin, kuten ennalta arvioitiin. Simulointimallilla tutkittiin yhteismuotoisen virran suuruutta muun muassa erilaisilla kaapelimalleilla ja eripituisilla kaapeleilla sekä maasulkuvirran suuruutta eri paikkoihin kytkeytyvien maasulkujen aikana. Simulointimallia tarkastelevien laboratoriomittausten perusteella etenkin kuormapuolen simuloidut yhteismuotoiset virrat olivat halutunlaisia. Työstä saatujen tulosten perusteella simulointimalli soveltuu työhön liittyvien ilmiöden tutkimiseen. Malli ei ole kuitenkaan vielä riittävän tarkka, jotta sitä voitaisiin käyttää taajuusmuuttajakäytön mitoituksen suunnittelussa.
Aurinkosähkön merkitys energiantuotannossa on kasvanut viime vuosina merkittävästi. Pyrkimys vähentää fossiilisten polttoaineiden käyttöä tulevaisuudessa kasvattanee sen suosiota entisestään. Tämä puolestaan tarkoittaa jakeluverkkoon kytkettävien aurinkosähköjärjestelmien määrän lisääntymistä, sekä järjestelmien tehon kasvamista. Järjestelmien muuttuessa teholtaan suuremmiksi tulee niiden käyttäjien ja asentajien turvallisuuteen, sekä laitteiston suojaamiseen kiinnittää entistä enemmän huomiota. Tämän työn tavoitteena oli tutkia vaihtoehtoista menetelmää nykyiselle PV-sulakkeilla ja sarjadiodeilla toteutettavalle vikavirtasuojaukselle. Aluksi tutkittiin aurinkosähköjärjestelmässä esiintyviä vikatilanteita, joissa vikavirtasuojausta tarvitaan. Aurinkogeneraattorin simulointimallin avulla tarkasteltiin osittaisen varjostumisen ja paneelien oikosulun vaikutusta takavirran muodostumiseen aurinkogeneraattorissa. Todettiin, että käytännössä vain paneeliketjun osittainen tai täydellinen oikosulku mahdollistaa takavirran kulkemisen generaattorissa. Lisäksi tarkasteltiin maavikavirran ja takavirran muodostumista sekä galvaanisesti erotetun että erottamattoman järjestelmän tapauksessa. Työssä keskityttiin PV-sulakkeet ja sarjadiodit korvaavan järjestelmäkohtaisen elektronisen sulakkeen suunnitteluun pienjänniteverkkoon kytkettävään aurinkosähköjärjestelmään. Todettiin, että elektroninen sulake on toteutettavissa rinnakkais- ja sarjakytkimillä, joilla takavirran kulkeminen generaattorissa voidaan estää ja katkaista virtapiiri maavikavirran noustessa turvallisuuden kannalta liian korkeaksi. Elektronisen sulakepiirin toimintaa mallinnettiin lopuksi simulointimallin avulla.
The observed changes in weather conditions have accelerated the installation of renewable energy-based electricity systems around the world. Large-scale utilization of renewable energy sources in electricity production requires the use of power electronic converters to integrate the renewable energy systems into the power grids. This integration brings about certain challenges in terms of stability and robust performance of the power grids, which have to be solved before the wellbeing of the power grids can be guaranteed. This Special Issue of Energies aims to reveal the state-of-art in addressing interfacing problematics. According to the published papers, clear advancements have taken place, but the most critical issues remain unsolved. Direct power control with self-synchronizing synchronverters may be the most promising technique for solving the main stability problem, although many unsolved problems still persist. Another challenge in renewable energy production is the fluctuating nature of the available energy in renewable energy sources, which require utilization of stored energy to smooth the fluctuations. Different storage battery technologies are available, but their production may pose problems in the long term.
Tämä diplomityö on tehty Etteplan Design Center Oy:lle Hyvinkäällä. Työssä tutkittiin jännitevälipiirillisen taajuusmuuttajan elektrolyyttikondensaattoreiden virkistyslaitteen tuotteistamista. Tutkimuksen aineistona käytettiin yrityksen työntekijöiden kokemuksia eri projekteista sekä yhdisteltiin usean eri toimipisteen käytäntöjä uudella tavalla. Tiedon keräämisessä käytettiin työntekijöiden haastatteluja ja aikaisempien projektien yhteydessä syntynyttä aineistoa. Tuotteistaminen käsittää kaikki toimenpiteet, joita tarvitaan tuotteen valmistamiseen ja markkinoille tuomiseen. Siihen kuuluu esimerkiksi laadunhallinta, dokumentointisuunnitelma, työmenetelmät ja tuotekuvaukset. Suurin osa tuotteen elinkaaren kustannuksista syntyy suunnitteluvaiheessa, minkä vuoksi sen mahdollisimman tehokkaalla toiminnalla voidaan pienentää tuotekehityksen kustannuksia. Tuotteen tuotekehitysprosessi käsittää suuren määrän erilaisia työvaiheita, katselmointeja, dokumenttien laadintaa, iteraatiokierroksia ja testaamisia. Selkeästi määritelty ja kuvattu tuotekehitysprosessi toimii tuotekehityksen yleiskaavana. Se auttaa tuotekehitysprosessin koordinoinnissa ja määrittää jokaisen työntekijän roolin tuotekehityksessä. Työssä luotiin Etteplanin tuotekehitysprosessin mallintava prosessimalli, jonka tarkoituksena on toimia esitutkimuksena myöhemmin alkavalle virkistinlaitteen tuotekehitysprojektille. Virkistinlaitteen lisäksi prosessimallia on tarkoitus hyödyntää myös yrityksen prosessien parantamiseen. Luotu prosessikuvaus esittää tuotekehitysprosessin tärkeimmät vaiheet, virstanpylväät ja tuotekehitysprosessin aikana syntyvät dokumentit. Prosessikuvaus tehtiin mahdollisimman kattavaksi ilman, että se olisi kuitenkaan liian monimutkainen.
Akkutekniikan kehitys on mahdollistanut akkujen kayttämisen suuritehoisissa kannettavissa laitteissa. Akkujen uudesta käyttökohteesta johtuen, aiempaa kokemusta akkujen luotettavuudesta ei kuitenkaan ole. Lisäksi hintapaineet pakottavat käyttämään ennen tuntemattomia toimittajia, joiden laadusta ja luotettavuudesta ei ole aiempaa kokemusta. Tässä työssä tutkittiin 6:n kiinalaisen litumakkuvalmistajan akkujen luotettavuutta hitsauskonekäyttöä simuloivassa kuormitustestissä. Testin tavoitteena oli selvittään akkujen odotettavissa oleva elinikä lopullisessa sovelluksessa ja selvittää tekijöitä, jotka vaikuttavat akkujen elinikään, tai ennustavat vanhenemista. Työ koostuu kolmesta pääosasta. Ensiksi potentiaaliset akkuvalmistajat etsittiin internetistä, ja sähköpostikirjeenvaihdon jälkeen valittiin yhtiöt, joiden ratkaisut näyttivät paperilla parhaimmilta. Seuraavaksi akkujen testaamisen tarvittava automaattinen järjestelmä suunniteltiin ja rakennettiin. Testejä ajettiin syyskuusta maaliskuuhun. Testeissä akkuvalmistajien välillä ilmeni selkeitä eroja. Parhaat akut kestivät yli 1000 latauspurkaus sykliä, kun taas osa akuista oli testin alussa hieman kyseenalaisessa kunnossa. Tietyissä mittajärjestelmän osissa olleet lämpötila-anturit eivät toimineet. Tämän vuoksi lämpötilan vaikutuksen arviointi akkujen vanhenemiseen ei ole kovin luotettavaa. Lisäksi akkuja testattiin ulkona eri vuodenaikoina, joten akut myös altistuivat eri lämpötiloille. Akkujen eliniät ovat silti vertailukelpoisia, sillä suurin osa akuista testattiin samaan aikaan keskenään. Mitään selkeää akkujen elinikää ennustavaa tekijää ei testin aikana ilmennyt. Monessa tapauksessa akkujen kuntoa kuvaava parametri, näyttää mittausten perusteella olevan akun sisäinen resistanssi.
Parallel-connected photovoltaic inverters are required in large solar plants where it is not economically or technically reasonable to use a single inverter. Currently, parallel inverters require individual isolating transformers to cut the path for the circulating current. In this doctoral dissertation, the problem is approached by attempting to minimize the generated circulating current. The circulating current is a function of the generated common-mode voltages of the parallel inverters and can be minimized by synchronizing the inverters. The synchronization has previously been achieved by a communication link. However, in photovoltaic systems the inverters may be located far apart from each other. Thus, a control free of communication is desired. It is shown in this doctoral dissertation that the circulating current can also be obtained by a common-mode voltage measurement. A control method based on a short-time switching frequency transition is developed and tested with an actual photovoltaic environment of two parallel inverters connected to two 5 kW solar arrays. Controls based on the measurement of the circulating current and the common-mode voltage are generated and tested. A communication-free method of controlling the circulating current between parallelconnected inverters is developed and verified.
Tuotteen testaaminen on merkittävä osa nosturin valmistusprosessia. Testauksessa pyritään havaitsemaan kokoonpanovirheiden lisäksi sähkö- ja automaatiosuunnittelun kautta nosturiin päätyviä virheitä. Jokaisen sähkölaitteen testauksen lisäksi nosturin sähköjärjestelmälle tehdään toiminnallinen testaus. Toiminnallisen testauksen aikana sähkölaitteet yhdistetään toimivaksi kokonaisuudeksi, jonka toiminnot todennetaan apulaitteiden avulla. Testattavan sähköjärjestelmän pääosat ovat sijoitettuna nosturin sähköhuoneeseen ja ohjaamoon. Sähkölaitetehtaalla tapahtuneiden uudelleenjärjestelyiden vuoksi nosturin ohjaamoa ei valmisteta tehtaalla eikä valmista ohjaamoa toimiteta sähkölaitetehtaalle. Järjestely vaikuttaa merkittävästi nosturin sähköjärjestelmän toiminnalliseen testaukseen. Tämän diplomityön tavoitteena oli kehittää ratkaisu toiminnallisen testauksen toteuttamiseen ilman ohjaamoa. Työ rajattiin koskemaan kumipyöräkonttinosturin eli RTG -nosturin uutta Smart Cabin -mallia. Tutkimuksessa tarkasteltiin nosturin sähkökäyttöjen prosesseja ja ohjausjärjestelmän toimintaa osana nosturia. Lisäksi ohjausjärjestelmän kenttäväylätekniikkaa ja sitä hyödyntäviä laitteita tarkasteltiin erikseen vaihtoehtoratkaisujen luomiseksi. Teorian pohjalta tutkittiin mahdollisuutta korvata uusi Smart Cabin -mallin ohjaamo sähköjärjestelmän testauksessa ohjaamosimulaattorilla. Ohjaamosimulaattori mahdollistaa toiminnallisen testauksen nopeuttamisen ja helpottamisen. Tutkimuksen pohjalta rakennettiin ohjaustuolia muistuttava simulaattori. Kehitetyn ohjaamosimulaattorin sähköinen rakenne valittiin siten, että se olisi mahdollisimman yhteensopiva eri nosturijärjestelmien kanssa ja mahdollisimman helposti käyttöönotettava. Tätä varten kehitystyössä tarkasteltiin ja hyödynnettiin toteutuneissa nostureissa käytettyjä ratkaisuja, jotta laitteisto toimisi yleisesti RTG -nostureissa. Ohjaamosimulaattoriin kehitettiin informatiivisia ja toiminnallisia funktioita, jotka tehostavat testauksen kulkua. Näiden funktioiden käytölle kehitettiin helppokäyttöinen käyttöliittymä, joka edesauttaa ohjaamosimulaattorin testauksen aikaista käyttöä.
Working with electricity causes injuries and deaths around the world every year. At the same time, the employers are more interested in their employee’s safety at work. The purpose of this thesis is to create a base to electrical safety in work instruction leaning strongly on existing standards. This electrical safety instruction is made to reduce injuries and possible deaths, as well as to improve overall electrical safety in all Motors and Generators business units around the world. In this thesis electrical work is thought to mean electrical work and testing related to manufacturing motors and generators. This thesis discusses the path of electrical work from need to do electrical work to completion of the work. This chain begins with a risk assessment, which is used to identify potential hazards associated with the work. By using this information it is possible to create work instructions and measurement plans. Needed tools and work place can be found with the help of these instructions. Electrical work cannot be carried out without working people, so organization around electrical work is reviewed from employee level to management level not forgetting responsibilities and tasks including to every level. All the levels have their own significances and all these levels should work conveniently together to ensure safety in work.
Diplomityön tavoitteena oli tutkia eri pulssianturitekniikoiden käyttöä nopeasti pyörivässä oikosulkumoottorissa nopeuden mittauksessa. Työssä nopeasti pyörivä moottori on määritelty maksiminopeuden perusteella, joka on 9000 rpm. Työssä selvitettiin nostinkäytössä olevan sähkömoottorikäytön toimintaperiaate sekä takaisinkytketyssä säädössä tarvittavan pulssianturin käyttötarve. Erityistä tarkkuutta vaativissa nostinkäytöissä tarvitaan takaisinkytketty säätömenetelmä moottorin säätöä varten, jolloin takaisinkytkentänä taajuusmuuttajalle tuodaan pulssianturin mittaama moottorin nopeus. Työssä esiteltiin pulssiantureiden toimintaperiaatteet, jotka voidaan jakaa inkrementaali- ja absoluuttipulssiantureihin. Tämän työn kannalta inkrementaalianturi on tärkein näist, sillä se on riittävä nopeuden mittausta varten. Se on myös edullisempi verrattuna absoluuttianturiin. Pulssianturit jaetaan toteutusteknologian perusteella optisiin, magneettisiin, kapasitiivisiin ja mekaanisiin pulssiantureihin. Näistä yleisimmin moottorisäädössä käytössä olevat ovat optinen ja magneettinen pulssianturi. Työssä vertailtiin optista ja magneettista pulssianturia nopeasti pyörivässä moottorissa käytännön mittausten perusteella. Mittaukset suoritettiin testijärjestelyssä, jossa ohjattiin taajuusmuuttajalla oikosulkumoottoria open-loop säädöllä, jotta pulssiantureiden mittaustarkkuus verrattuna moottorin nopeuteen voitiin määrittää. Anturien ulostulosignaalit vietiin taajuusmuuttajalle 50 metrin häiriösuojatulla signaalikaapelilla. Mittauksissa todennettiin antureiden toimintakykyä koko nopeusalueella sekä eri suuruisilla kaapelipituuksilla. Lisäksi testattiin antureiden sähköisten häiriöiden kestoisuutta. Mittausten perusteella magneettiseen mittaukseen perustuva pulssianturi suoriutui kaikista mittauksista hyväksytysti. Optisen pulssianturin mittaustarkkuus oli samaa luokkaa magneettianturin kanssa 50 metrin kaapelilla, mutta 200 metrin kaapelipituudella optisen anturin virransyöttökyky ei ollut riittävä ja ulostulosignaalista alkoi pudota pulsseja pois. Hintatasoltaan vertailuun valittu magneettianturi oli noin 30 % kalliimpi kuin optinen anturi. Käyttökohteessa tarvittavan signaalikaapelipituuden ollessa maksimissaan 50 metriä voi kyseinen optinen pulssianturi olla mahdollinen vaihtoehto. Antureiden elinikää tai mekaanista kestävyyttä ei työssä testattu.