### Browsing by Author "Repo, Anna-Kaisa"

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Item The combined solution of electromagnetic field and circuit equations in modelling the excitation control of the synchronous generator(2003) Repo, Anna-Kaisa; Kanerva, Sami; Sähkö- ja tietoliikennetekniikan osasto; Teknillinen korkeakoulu; Helsinki University of Technology; Arkkio, AnteroTämän työn tavoitteena on yhdistää tahtikoneen numeerinen malli tilayhtälöillä mallinnettuun säätöpiiriin. FEM-ohjelman ja piirisimulaattorin välillä on heikko kytkentä, jolloin kumpikin ohjelma toimii itsenäisesti, mutta piirin muuttujat siirtyvät ohjelmien välillä jokaisella aika-askeleella. Simuloinnissa tahtikoneen magneettikenttä ratkaistaan FCSMEK-ohjelmalla ja mallia käsitellään yhtenä piirin osana. Muut komponentit mallinnetaan SIMULINK-mallinnusohjelmalla. Menetelmää on aiemmin kokeiltu epätahtikoneiden toiminnan mallintamisessa. Mallinnettu tahtikone on turbogeneraattori, jonka magnetointijärjestelmä sisältää magnetointimuuntajan, tyristorisillan ja diodisillan mallit. Säätöpiirissa on jännitteensäätäjän lisäksi tehostabilisaattori ja ylimagnetointirajoitin. Myös alimagnetointirajoittimen ja vuorajoittimen mallit on toteutettu, mutta niitä ei ole vielä liitetty säätöpiiriin. Säätöpiirin toiminta on ennen FEM-mallin yhdistämistä testattu analyyttisella tahtikonemallilla. FEM-malli on ensin liitetty yksinkertaiseen piiriin ja kokeiltu sen toimintaa sysäysoikosulkukokeen avulla. Seuraavaksi analyyttisen tahtikonemallin avulla on viritetty jännitteensäätäjän parametrit, ja molempien mallien toimintaa on arvioitu askelvastekokeiden avulla. Kokeiden tuloksia on verrattu mitattuihin arvoihin. Työn perusteella voidaan todeta, että numeerisen kenttälaskennan käyttäminen SIMULINK-ohjelmasta toimii hyvin, kun muut komponentit on mallinnettu SIMULINK-lohkoilla. Säätöpiirin suhteellisen helpon mallintamisen lisäksi SIMULINK-ohjelman käytöstä on hyötyä myös siksi, että MATLAB sisältää paljon mahdollisuuksia tulosten jatkokäsittelyyn ja esittämiseen. Tulosten parantamiseksi FEM-mallin parametreja pitäisi hioa, ja FEM-mallin ja piirin alkutilan yhteensovittaminen täytyisi tehdä tarkemmin, jotta piiri asettuisi nopeammin vakaaseen tilaan.Item Inclusion of hysteresis and eddy current losses in dynamic induction machine models(Institute of Electrical & Electronics Engineers (IEEE), 2009) Ranta, Mikaela; Hinkkanen, Marko; Dlala, Emad; Repo, Anna-Kaisa; Luomi, Jorma; Sähkötekniikan ja automaation laitos; Department of Electrical Engineering and Automation; Electric Drives; Sähkötekniikan korkeakoulu; School of Electrical EngineeringThis paper proposes a method for including both hysteresis losses and eddy current losses in the dynamic space vector model of induction machines. The losses caused by the rotation and magnitude changes of the flux vector are taken into account. The model can be applied, for example, to time-domain simulations and real-time applications such as drive control. Finite element analysis, simulations, and laboratory experiments of a 45-kW motor are used for the investigation. It is shown that the model can predict the iron losses in a wide frequency range. The accuracy is significantly improved as compared to earlier models.Item Influence of magnetic saturation on induction motor model selection(International Conference on Electrical Machines (ICEM), 2006) Hinkkanen, Marko; Repo, Anna-Kaisa; Luomi, Jorma; Sähkötekniikan ja automaation laitos; Department of Electrical Engineering and Automation; Electric Drives; Sähkötekniikan korkeakoulu; School of Electrical EngineeringEffects of magnetic saturation on various equivalent circuit models of an induction motor are studied. The parameters of 2.2-kW and 37-kW motors with closed rotor slots are analyzed using finite element computations. Both skewed and unskewed rotor slots are studied. The magnetizing inductance not only depends on the main flux, but is also dependent on the rotor current, especially if the rotor slots are skewed or closed. The stator leakage inductance is essentially constant, while the rotor leakage inductance depends significantly on the rotor current. The performance of vector-controlled drives can be improved by using a T or Γ-equivalent circuit model whose inductances also depend on the rotor current.Item Influence of magnetic saturation on induction motor model selection(2006-09-02) Hinkkanen, Marko; Repo, Anna-Kaisa; Luomi, JormaEffects of magnetic saturation on various equivalent circuit models of an induction motor are studied. The parameters of 2.2-kW and 37-kW motors with closed rotor slots are analyzed using finite element computations. Both skewed and unskewed rotor slots are studied. The magnetizing inductance not only depends on the main flux, but is also dependent on the rotor current, especially if the rotor slots are skewed or closed. The stator leakage inductance is essentially constant, while the rotor leakage inductance depends significantly on the rotor current. The performance of vector-controlled drives can be improved by using a T or Γ-equivalent circuit model whose inductances also depend on the rotor current.Item Numerical impulse response tests to identify dynamic induction-machine models(Helsinki University of Technology, 2008-04-04) Repo, Anna-Kaisa; Department of Electrical Engineering; Sähkötekniikan laitos; Faculty of Electronics, Communications and Automation; Elektroniikan, tietoliikenteen ja automaation tiedekuntaThe aim of the study is to identify dynamic models for induction machines using two-dimensional finite-element analyses. Attention is given mainly to cage-induction machines with closed rotor slots and deep rotor bars. However, cage-induction machines with semi-closed rotor slots and slip-ring machines are considered as well. Two new applications of numerical impulse response tests are presented. The tests are performed within a time-stepping finite-element analysis. First, an impulse excitation is applied to the stator voltage and the response of the stator current is studied. Next, an impulse excitation is applied to the rotor position angle and the response of electromagnetic torque is studied. The results of the impulse tests are used to estimate parameters for small-signal models in the frequency domain. The estimation is performed by fitting the results of an impulse response test to the corresponding analytical small-signal model. The analytical models are based on the theory of electrical machines and their parameters have a physical meaning. Based on the study, it is concluded that the skin effect in rotor bars has a significant influence on the results of the impulse response tests. In order to obtain a good fit, the skin effect has to be taken into account in the structure of the analytical model. In addition, the saturation of iron has a prominent effect. The effects of saturation can be detected as harmonics in the frequency response and in the values of parameter estimates. A model for saturation can be included in the small-signal models. In the case of this more advanced model, the parameter estimates obtain a clear physical interpretation. The applicability of impulse response tests is based on the assumption of linear time-invariant behaviour of the system. The assumption is studied by several means. Within the tests, the amplitude, length, and initial time of the impulse excitation is varied and the results are compared. It is concluded that, in the case of normal operation points, the assumption can be made. The reasonability of the parameter estimates is evaluated by comparing the values with steady-state circuit parameters. The steady-state parameters are estimated using a time-harmonic finite-element analysis. When the impulse is applied to the rotor position angle and the torque response is computed, the results predict negative electromagnetic damping within some frequency ranges. This phenomenon is also studied by measurements. It is observed that, within the range of predicted negative damping, self-excited torsional oscillations occur.Item Parameter estimation for synchronous machine models(2010) Mäkelä, Olli; Repo, Anna-Kaisa; Sähkötekniikan laitos; Sähkötekniikan korkeakoulu; School of Electrical Engineering; Arkkio, AnteroItem Small-signal analysis of a saturated induction motor(Helsinki University of Technology, 2008) Ranta, Mikaela; Hinkkanen, Marko; Repo, Anna-Kaisa; Luomi, Jorma; Department of Electrical Engineering; Sähkötekniikan laitos; Faculty of Electronics, Communications and Automation; Elektroniikan, tietoliikenteen ja automaation tiedekuntaDue to magnetic saturation, the small-signal admittance of an induction motor is dependent on the direction of the excitation signal. The angle-dependence of the admittance can be used in the estimation of the flux angle, and it should be taken into account when identifying motor parameters. In this paper, the small-signal admittance of a 2.2-kW induction motor is measured at different excitation frequencies and operating points. The measured admittances are compared to data obtained by means of finite element analysis (FEA). A small-signal model of the induction motor is fitted to the admittances to analyze the results. The admittances obtained from FEA and laboratory experiments correspond well to each other, particularly at low excitation frequencies.Item Small-signal analysis of a saturated induction motor(2008-06-09) Ranta, Mikaela; Hinkkanen, Marko; Repo, Anna-Kaisa; Luomi, JormaDue to magnetic saturation, the small-signal admittance of an induction motor is dependent on the direction of the excitation signal. The angle-dependence of the admittance can be used in the estimation of the flux angle, and it should be taken into account when identifying motor parameters. In this paper, the small-signal admittance of a 2.2-kW induction motor is measured at different excitation frequencies and operating points. The measured admittances are compared to data obtained by means of finite element analysis (FEA). A small-signal model of the induction motor is fitted to the admittances to analyze the results. The admittances obtained from FEA and laboratory experiments correspond well to each other, particularly at low excitation frequencies.Item Small-signal model for saturated deep-bar induction machines(Institute of Electrical & Electronics Engineers (IEEE), 2007) Hinkkanen, Marko; Repo, Anna-Kaisa; Cederholm, Mikaela; Luomi, Jorma; Sähkötekniikan ja automaation laitos; Department of Electrical Engineering and Automation; Electric Drives; Sähkötekniikan korkeakoulu; School of Electrical EngineeringA small-signal model is presented for saturated deep-bar induction machines. Inductances are allowed to saturate as a function of their own current (or flux), and the mutual saturation effect originating mainly from closed or skewed rotor slots is also included in the model. The model fulfills the reciprocity conditions, and it can applied to parameter estimation and to the analysis and development of flux angle estimation methods. The model is applied to estimating the parameters of a 37-kW deep-bar cage-induction machine, using the data from time-stepping finite-element analysis (FEA). The proposed model fits very well to the FEA data in a wide frequency range.Item Small-signal modeling of mutual saturation in induction machines(2010-05-18) Hinkkanen, Marko; Repo, Anna-Kaisa; Ranta, Mikaela; Luomi, Jorma; Electric DrivesA small-signal model is derived for saturated induction machines. Inductances are allowed to saturate as a function of their own current (or flux), and the mutual saturation effect originating mainly from skewed or closed rotor slots is also included in the model. The model fulfills the reciprocity conditions, and it can be applied to parameter identification and to the analysis and development of flux-angle estimation methods. As application examples, the parameters of a 2.2-kW induction machine were identified using the data obtained from time-stepping finite-element analysis and locked-rotor measurements. The proposed model fits well to the data, and the fitted parameters are physically reasonable.Item Small-Signal Modeling of Mutual Saturation in Induction Machines(Institute of Electrical & Electronics Engineers (IEEE), 2010) Hinkkanen, Marko; Repo, Anna-Kaisa; Ranta, Mikaela; Luomi, Jorma; Sähkötekniikan ja automaation laitos; Department of Electrical Engineering and Automation; Electric Drives; Sähkötekniikan korkeakoulu; School of Electrical EngineeringA small-signal model is derived for saturated induction machines. Inductances are allowed to saturate as a function of their own current (or flux), and the mutual saturation effect originating mainly from skewed or closed rotor slots is also included in the model. The model fulfills the reciprocity conditions, and it can be applied to parameter identification and to the analysis and development of flux angle estimation methods. As application examples, the parameters of a 2.2-kW induction machine were identiﬁed using the data obtained from time-stepping finite-element analysis and locked-rotor measurements. The proposed model fits well to the data, and the fitted parameters are physically reasonable.