Aaltodoc Repository :: Browsing by Department "Department of Electrical Engineering"

Browsing by Department "Department of Electrical Engineering"

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Analysis of a multi-axis machinery drive system with a common DC bus and regenerative capabilities
(2013-05-20) Sapone, Marco; Turunen, Harri; Department of Electrical Engineering; Sähkötekniikan korkeakoulu; Hinkkanen, Marko
This research deals with the study of a multi-axis machinery focusing on the analysis of the drive system. Nowadays in industrial applications the energy management of converters and motors is a major point of concern, therefore it is particularly desirable to evaluate an upgrade of an existing machine with an old fashion drive system. Along this study the focus point is mainly directed on the energy management of the machine motors and frequency converters in order to reduce the energy consumption of an existing multi-axis machine used for mechanical testing of optical fiber. A more efficient electrical structure and motor axis control is presented. Since the multi-axis machinery under study uses axes in motoring and braking mode, it is particularly suitable for a future upgrade using a centralized multi-drive system. The main aim of this research is to understand how different drives interact while connected to a common DC bus, how the DC voltage can be controlled and how the surplus energy can be either used by other motoring loads or fed back to the network. The study will be considered from different points of view: from the economical aspect to reduce energy consumption with a new drive system. From the technical point of view, dealing with the dimensioning of the drive system, with the aim to reduce the required space and simplify the system structure. From the control point of view, the control technology involved with the energy regenerative features and drives control is presented. Simulation of the mechanical and electrical system will be conducted and measurements performed on the running machine in order to verify the simulated results. Finally the results will be used to predict the energy consumption and cost variations using different drive configurations.
Calorimetric Power Loss Measurement of a Small Power Converter
(2013-06-10) Nair, Devi; Rasilo, Paavo; Department of Electrical Engineering; Sähkötekniikan korkeakoulu; Arkkio, Antero
Miniaturisation - is the key word in technology today and the general trend in all industries is to seek for smaller and compact electrical and magnetic components. With the increase in energy density, the loss density does too, and so does the need to achieve greater measurement accuracy of device losses. Calorimeters are the way to accomplish this effectively, as proven by the prevailing calorimetric watt-meters for electrical systems. The undertaking of this thesis work was to build a simple yet accurate calorimetric system to measure power losses in highly efficient power converters and similar small devices belonging to a power class of <1 kW. An improved closed, water cooled calorimeter with flow control and input water temperature control has been implemented, as an alternative to the accepted, yet complicated double jacketed calorimeter. The balance tests with the calorimeter yielded the calibration curve, which was followed by the actual test with a 0.75 kW frequency converter. From the power losses measured by the calorimeter, the tested device was confirmed to have a high efficiency of 97%. The calorimeter that was built is characterised by low flow rates and can measure loss powers in range of 25 W - 520 W with an accuracy better than 1.5% for power losses <50 W.
Design of master control unit for laboratory prototype of traction converter for locomotives
(Helsinki University of Technology, 2008) Žák, Jan; Peroutka, Zdeněk; Ovaska, Seppo J.; Department of Electrical Engineering; Sähkötekniikan laitos; Faculty of Electronics, Communications and Automation; Elektroniikan, tietoliikenteen ja automaation tiedekunta
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.
Dovetail rotor poles in synchronous permanent magnet and reluctance machines
(Aalto University, 2011) Kolehmainen, Jere; Sähkötekniikan laitos; Department of Electrical Engineering; Sähkötekniikan korkeakoulu; Arkkio, Antero, Prof.
Robust synchronous permanent magnet and reluctance machine designs are developed. In the designs, the rotor structure is simple and strong and the leakage flux is relatively small. For the new design solution, a dovetail form-blocked rotor structure, specific analyzing principles are also developed. The dovetail designs are shown to be good solutions with their lower leakage flux and at least the same strength against centrifugal forces as the conventional rotor solutions. The compared conventional solutions considered have inseparable rotor sheets in which the parts of the rotor are kept still by using bridges between them. In the dovetail rotor, the forms of the rotor parts keep them together and no bridges between them are needed for support. The simplicity of the dovetail solution has also been kept the same or better. In addition, the manufacturing method is the same for both solutions. The dovetail design can also be used for saving the magnetic material of permanent magnet synchronous machines because it has a smaller leakage flux than the conventional V-shaped designs with supporting bridges. The problem of how to compare the dovetail designs to the conventional ones is considered in depth. The strength of the dovetail structure has to be defined in a different way than in the conventional design with supporting bridges. In bridge-fixed design, the strength of the bridges is critical for rotor durability but in the dovetail design wider areas of the rotor affect the strength of the rotor. However, the basic electrical properties could be defined with the same method. Additional methods for defining the electrical properties of dovetail designs are also considered. One method is that the load angle can be defined only from the forms of phase currents in delta-connected synchronous machines and phase voltage and current in star-connected synchronous machines. The load angles defined are successfully used to find a good model for the test results. The other method is to view the normalized local torque density in the air gap as a function of time. In this work, several dovetail synchronous reluctance and permanent magnet machines are designed, manufactured, tested, and analyzed. The design, manufacturing, testing, and analysis methods are defined and developed especially for dovetail designs.
Dynamic induction machine models including magnetic saturation and iron losses
(Aalto University, 2013) Ranta, Mikaela; Hinkkanen, Marko, Prof., Aalto University, Department of Electrical Engineering, Finland; Sähkötekniikan laitos; Department of Electrical Engineering; Electric drives; Sähkötekniikan korkeakoulu; School of Electrical Engineering; Luomi, Jorma, Prof., Aalto University, Department of Electrical Engineering, Finland; Hinkkanen, Marko, Prof., Aalto University, Department of Electrical Engineering, Finland
Dynamic induction machine models are used as the basis for the design and implementation of control algorithms. Costs can be reduced by applying speed-sensorless control, and advanced control strategies open up for the possibility of using an induction machine in demanding applications. However, a reliable and good control performance requires more detailed induction machine models. This thesis deals with models including the magnetic saturation and iron losses. A small-signal model, which includes the saturation due to variations in the main flux magnitude and the load torque, is used to analyze the transient behavior of the machine. Due to the magnetic saturation, the inductances vary as a function of the operating point, and the machine appears to be salient in transients. Based on the model, an identification method for the leakage inductance is proposed. The identification is based on signal injection and can be performed as the machine is running under different load conditions. A model for the skin effect of the rotor bars can be used in combination with the leakage inductance identification in the case of an induction machine equipped with deep rotor bars. The magnetizing curve can be modeled using a simple power function. An adaptive identification method is developed for the identification of magnetizing curve parameters. Identification of the leakage inductance prior to the magnetizing curve identification improves the results in case a no-load condition cannot be reached. The stator hysteresis and eddy current losses are modeled using a nonlinear resistance. The resistance is not dependent on any frequency, and is thus defined also during transients. The resistance model is experimentally investigated both for the case of an induction machine and a nonlinear inductor. The iron loss model is used in a loss-minimizing control algorithm for the induction machine.
Dynamic Scenario Modelling in Electricity Distribution System Asset Management
(Aalto University, 2014) Palola, Jussi; Hyvärinen, Markku, Dr., Helen Electricity Network Ltd., Network Development, Finland; Sähkötekniikan laitos; Department of Electrical Engineering; Power Systems and High Voltage Engineering; Sähkötekniikan korkeakoulu; School of Electrical Engineering; Lehtonen, Matti, Prof., Aalto University, Department of Electrical Engineering, Finland
The life of individuals, societal welfare and global economics are deeply interconnected with power systems in a multidimensional manner. A change in one entity affects the whole system. This thesis is a research journey from electrical distribution systems to global economics, and finally to power transformer unit asset management. The objective is to investigate dynamic scenario modelling in power system asset management and apply it to a distribution system operator’s power transformer fleet assets. The asset management of a distribution system is directly coupled to the economy, both globally and locally. Economic attributes affect electrical network asset management from many directions simultaneously: electricity demand, network expansion requirements, and component, construction and operational expenditures. A comprehensive cost function is formed and applied with different economic scenarios for asset management. Revealing the dynamics of power transformer asset management with scenarios is relevant in an increasingly turbulent global environment. This thesis offers an approach to assess the techno-economic dependencies in electricity distribution system asset management for more pertinent decision making. Understanding the dynamic balance between asset management and overall expenses is increasingly important while seeking economic efficiency and return on investments.
Effects of slotting and unipolar flux on magnetic pull in a two-pole induction motor with an extra four-pole stator winding
(Aalto University, 2013) Sinervo, Anssi; Sähkötekniikan laitos; Department of Electrical Engineering; Electromechanics; Sähkötekniikan korkeakoulu; School of Electrical Engineering; Arkkio, Antero, Prof., Aalto University, Finland
This thesis is about the radial magnetic forces between the rotor and stator in twopole induction machines. The magnetic forces arise from rotor eccentricity. The asymmetric air-gap makes the flux density on one side of the rotor stronger than on the opposite side. This produces magnetic pull. The magnetic flux density distribution in the air-gap can be expressed with spatial harmonics, i.e. flux densities with different pole-pair numbers. In two-pole machines, the main part of the magnetic force is produced by the interaction of two- and fourpole flux unless the four-pole flux is damped by parallel paths in the stator winding or an extra four-pole stator winding. The rest of the force comes from the interaction of two-pole and unipolar flux and from the higher harmonics of the air-gap flux of which the slot harmonics are a major part. The force caused by the higher harmonics and the unipolar flux is studied in the case where a four-pole stator winding is used to reduce the four-pole flux. The higher harmonics are found to produce, in addition to the traditional unbalanced magnetic pull, a force similar to the effect of the unipolar flux and the two can be distinguished only by measuring the unipolar flux. In measurements at various operation points, the higher harmonics are found to produce much more force than the unipolar flux and two-pole flux but the unipolar flux is still significant. The four-pole winding also is used to actively control the four-pole flux and the magnetic forces. Designing the controller requires a low order model of the system. Such a model is derived and the effect of the slot harmonics and the unipolar flux are included in the model. Different measurements techniques and methods are presented to identify and validate the control model. The operation point dependence of the system dynamics is studied via measurements. All results are obtained from a 30 kW test motor. The rotor of the test machine has a long flexible shaft on external bearings. The shaft is bowed causing mechanical forces. The vibration caused by these forces is suppressed with the four-pole extra winding. The machine also has search coils to measure the unipolar, two-pole, and four-pole fluxes and a unipolar actuator that can be used to control the unipolar flux.
Electromagnetic and mechanical finite element analysis of end region of large-sized three-phase squirrel-cage induction machines
(Aalto-yliopiston teknillinen korkeakoulu, 2010) Lin, Ranran; Sähkötekniikan laitos; Department of Electrical Engineering; Aalto-yliopiston teknillinen korkeakoulu; Arkkio, Antero, Prof.
This piece of research is related to the design of large-sized radial flux electric machines. It aims at studying the end-region magnetic field under the steady-state operation in order for an analysis of some important electromagnetic and mechanical phenomena that require careful thought during the design of the end region. The research work is focused on the end region of two large-sized three-phase squirrel-cage induction machines. In addition to the end-region magnetic field, the stator end-winding leakage inductance, the eddy currents inside the end shield and the end frame, and the end-winding forces and vibrations are covered. The 3-D time-harmonic finite element analysis of the above aspects, carried out with a commercial software package, forms the main part of the research work. The corresponding measurement, as a complement to the finite element analysis, is mainly for validating the models and the numerical calculations. A 3-D time-harmonic finite element analysis of the end-region magnetic field with suitable boundary conditions can give an accurate distribution of the magnetic field. The stator end-winding leakage only affects the core ends; hence, the end-winding leakage inductance can be calculated from the corresponding magnetic energy separated from the total magnetic energy. The eddy currents inside the end shield and the end frame do not affect the end-region magnetic field seriously, and it is feasible to consider them as surface currents and to model them with the standard impedance boundary condition. The end-winding forces cause vibrations and deformation, but the amplitude of vibration and the degree of deformation are small because of the end-winding bracing system. With the bracing system, the natural frequency of the most excitable mode of the end winding and its bracing system is also greatly raised, so resonances may be avoided. Under the steady-state operation of large-sized induction machines, the end-region magnetic field does not bring about severely disadvantageous electromagnetic and mechanical phenomena in the end region. However, from the viewpoint of optimisation, the end frame can be shifted farther from the end winding for eliminating potential hot spots. In addition, fewer bracing parts can be fixed to the knuckle portion and the lower part of the involute portion of the end connections for improving the cooling of the end region.
Energy-based magneto-mechanical model for electrical steel sheets
(Aalto-yliopiston teknillinen korkeakoulu, 2010) Fonteyn, Katarzyna Anna; Belachen, Anouar, Dr.; Sähkötekniikan laitos; Department of Electrical Engineering; Aalto-yliopiston teknillinen korkeakoulu; Arkkio, Antero, Prof.
Within this dissertation an energy-based model for magneto-mechanical coupling in electrical steels has been developed, studied and implemented in finite element software. The method introduces a novel way of explicitly solving magnetic and mechanical fields. Starting from the knowledge of the dependence of magnetostriction on stress and magnetic field, and of the dependence of the magnetic field on the stress, a Helmholtz free energy is presented. The material constitutive equations are explicitly written. The parameters of the model are identified experimentally from a modified Epstein frame. This setup allows stressing a pack of electrical steel sheets and measuring the magnetostriction and B-H curves under pre-stresses. The resulting strains are acquired with a piezo-electric force transducer. The measurements are compared with data obtained from a vertical yoke system at no pre-stress with strain gauges and discussed. The method is then applied to study magneto-mechanical coupling in radial-flux rotating electrical machines. A test device is studied; it consists of a stack of round electrical steel sheets assembled with windings wound to obtain a magnetic flux density as in real electrical machines. This one enables the coupled method to be verified when there is no air gap. The last device is a sample machine wound in the same way as an asynchronous machine used for studying losses. Its advantage is that there is no outer frame that would prevent the placement of accelerometers for measuring the acceleration of the iron yoke when excited. The validity of the model for real electrical machines is verified by the good agreement between those measurements show good agreement with the computed results. The method appeared to be suitable and robust for the computation of displacements in rotating electrical machines. The tangential and radial displacements on the teeth of stators are obtained from the method. The influences of magnetic forces on the structures are studied and quantified.
Enhancing the performance of flexible AC transmission systems (FACTS) by computational intelligence
(Aalto University, 2011) Othman, Ahmed Mohamed; Sähkötekniikan laitos; Department of Electrical Engineering; Sähkötekniikan korkeakoulu; Lehtonen, Matti, Prof.; El-Arini, Mahdi, Prof., Zagazig University
The thesis studies and analyzes UPFC technology concerns the management of active and reactive power in the power networks to improve the performance aiming to reach the best operation criteria. The contributions of the thesis start with formatting, deriving, coding and programming the network equations required to link UPFC steady-state and dynamic models to the power systems. The thesis derives GA applications on UPFC to achieve real criteria on a real world sub-transmission network. An enhanced GA technique is proposed by enhancing and updating the working phases of the GA including the objective function formulation and computing the fitness using the diversity in the population and selection probability. The simulations and results show the advantages of using the proposed technique. Integrating the results by linking the case studies of the steady-state and the dynamic analysis is achieved. In the dynamic analysis section, a new idea for integrating the GA with ANFIS to be applied on the control action procedure is presented. The main subject of the thesis deals with enhancing the steady-state and dynamics performance of the power grids by Flexible AC Transmission System (FACTS) based on computational intelligence. Control of the electric power system can be achieved by designing the FACTS controller, where the new trends as Artificial Intelligence can be applied to this subject to enhance the characteristics of controller performance. The proposed technique will be applied to solve real problems in a Finnish power grid. The thesis seeks to deal, solve, and enhance performances until the year 2020, where the data used is until the conditions of year 2020. The FACTS device, which will be used in the thesis, is the most promising one, which known as the Unified Power Flow Controller (UPFC). The thesis achieves the optimization of the type, the location and the size of the power and control elements for UPFC to optimize the system performance. The thesis derives the criteria to install the UPFC in an optimal location with optimal parameters and then designs an AI based damping controller for enhancing power system dynamic performance. In this thesis, for every operating point GA is used to search for controllers' parameters, parameters found at certain operating point are different from those found at others. ANFISs are required in this case to recognize the appropriate parameters for each operating point.
Eri markkinatoimijoiden väliset eturistiriidat älykkään sähköverkon toimintaympäristössä
(2013-03-18) Aaltomaa, Olli; Gulich, Oleg; Department of Electrical Engineering; Sähkötekniikan laitos; Sähkötekniikan korkeakoulu; Lehtonen, Matti
Energia-ala on keskellä muutosta. Ympäristötavoitteiden saavuttamiseksi on rakennettu uusiutuvaa energiantuotantoa, joka on luonteeltaan epäsäännöllistä niin tuotantomäärältään kuin ajallisesti. Koska sähköverkot ja markkinamekanismit on rakennettu vastaamaan perinteistä systeemiä jossa energia tuotetaan suurissa voimalaitoksissa, aiheuttavat uusiutuvan energian voimakas lisäys uusia vaatimuksia koko infrastruktuurille. Muutos luo tarpeen kehittää uusia ratkaisuja, kuten älyverkot jotka lisäävät automaatiota ja tietotekniikkaa sähköverkkoon. Markkinaympäristön muutosten myötä myös eri toimijoiden roolit kohtaavat muutoksia. Tämä voi aiheuttaa eturistiriitoja toimijoiden välille: useammalla toimijalla olisi valmiudet ja intressejä murtautua samalle sektorille. Esimerkiksi useammalla toimijalla on tarvetta kuormienohjaukseen. Diplomityössä on kartoitettu mahdolliset eturistiriidat joita voi syntyä eri toimijoiden välille. Mahdollisten eturistiriitojen kartoittamiseksi tehtiin 25 eri sähköalan osapuolen asiantuntijahaastattelua, jotta työhön saataisiin mahdollisimman kattava kuvaus mahdollisista riskeistä. Haastatteluiden ja kirjallisuuden perusteella tunnistettiin 33 erilaista eturistiriitaa. Työssä havaitaan että erityisesti reguloidun jakeluverkkoyhtiön roolista on eroavia näkemyksiä ja asiaan odotetaan selvennystä. Älyverkkojen mahdollistamat lisäpalvelut pitäisi saattaa kilpailtuun ympäristöön, eikä näin ollen niitä voisi jakeluverkkoyhtiö tarjota. Työssä käsitellään jakeluverkkoyhtiön ja sähkönmyyjän välistä mahdollista eturistiriitaa kuormien ohjauksen suhteen. Havaitaan, että Suomessa sähkölämmityksen yhdenmukainen ohjaus aggregaattori-myyjän toimesta tapahtuu lähinnä yöaikaan, jolloin muu sähkönkulutus kotitalouksissa on vähäistä. Näin ollen ohjaus voi jopa parantaa nykyistä tilannetta.
Finite element analysis of eddy current losses in steel laminations of inverter-fed electrical machines
(Aalto-yliopiston teknillinen korkeakoulu, 2010) Pippuri, Jenni; Belahcen, Anouar, Doc.; Sähkötekniikan laitos; Department of Electrical Engineering; Aalto-yliopiston teknillinen korkeakoulu; Arkkio, Antero, Prof.
This thesis investigates the eddy currents and regarding losses in electrical steel sheets. For the purpose, two methods of numerical analysis of electromagnetic fields are developed. Both of those are based on the two-dimensional (2-D) finite element computation of the fields. Since the eddy currents of the sheets are, by definition, excluded from the 2-D formulation they need to be included separately. Within this work, the goal is achieved by modeling the eddy currents via a one-dimensional (1-D) penetration equation in association with the 2-D analysis. Formulations for both, general time variation and sinusoidal time variation are shown. The coupling of the 2-D and 1-D models is investigated from several perspectives. For representing the 1-D eddy current solution within the time-discretized analysis two approaches are considered. Numerous simulations carried out reveal that inappropriate coupling might not affect the losses to be obtained but other electromagnetic quantities such as input power or power factor. A proper coupling method that accords with the computation results is proposed. The combining of those two field formulations is discussed in the case of the time-harmonic approach as well, for which the concept of complex reluctivity is employed. The second objective of the work is to study in detail the losses in rotating electrical machines fed by a frequency converter. The higher harmonics associated with the frequency-converter supply are known to increase to losses in comparison with a sinusoidal voltage supply. According to the simulations, (i) the eddy current losses in the rotor sheets are the most sensitive to the distorted input voltage waveforms and (ii) coincidently can be the most reduced by choosing the switching frequency of the frequency converter suitably. The measurements carried out on the test machine and comparative studies of those and the simulation results verify the methods proposed.
Finite Element Modeling of Eddy Currents in Uninsulated Laminated-Steel Stacks
(2013-05-20) Velasco, Jonathan; Belahcen, Anouar; Rasilo, Paavo; Department of Electrical Engineering; Sähkötekniikan korkeakoulu; Arkkio, Antero
This thesis deals with the modeling of eddy currents in uninsulated laminations. A numerical model for the calculation of eddy current losses was implemented using finite element analysis. This model calculates the solution from the electric vector potential also known as the T-𝛺 formulation for the study of eddy current problems. The numerical model was verified by comparing the harmonic solution to different analytical models. Moreover, the results were obtained for non-linear material, i.e. electrical steel. During the manufacturing process the laminations are stacked and the uneven contact between laminations makes it impossible to assume uniformity in conductivity between adjacent laminations. Electrical conductivity degradation and surface roughness in laminated-steel increases the average iron losses. Whenever the values of inter-laminar conductivity tend to zero, the eddy current component in the direction perpendicular to the lamination vanishes. For this reason, the eddy currents will loop only within the thickness of the lamination and the losses will decrease dramatically for a certain frequency range. Assuming a linear permeability (low and high) in the inter-laminar region, and widths between 6𝜇m and 10𝜇m, causes negligible changes in the calculation of the losses for which is recommended to use wider inter-laminar areas and high permeability, as it enhances the convergence of the model. A model dealing with insulated laminated-stacks was implemented for comparison purposes. Uninsulated laminations could be used as an economical alternative for certain applications where laminated cores are used, as in the case of rotational electrical machines and transformers.
Finite-element analysis of eddy currents in the form-wound multi-conductor windings of electrical machines
(Teknillinen korkeakoulu, 2010) Islam, Mohammad Jahirul; Sähkötekniikan laitos; Department of Electrical Engineering; Arkkio, Antero, Prof.
The aim of this research was to develop comprehensive numerical models for considering eddy currents and circulating currents in the form-wound multi-conductor windings of electrical machines and to study the effects of eddy currents and circulating currents. Time-harmonic and time-discretised finite-element methods were developed. The methods were applied to the stator winding of a 1250-kW cage induction motor and in both the stator and rotor windings of a 1.7-MW doubly-fed induction generator (DFIG). The series and parallel connections of the winding were taken into account. The Newton-Raphson iteration method was used to solve the system of non-linear equations. In time-harmonic FEM, the system of equations was solved iteratively just once for the steady-state solution. In time-discretised FEM, the system of equations was solved iteratively at every time step. The backward Euler method was used for the time discretisation. The radial distance of the stator bars from the air gap has a remarkable effect on losses and was found to be an important design parameter. A significant amount of stator-winding eddy-current loss can be reduced by considering this design parameter. A transposition of the conductors was implemented to reduce the circulating currents between the parallel stator conductors. The eddy-current effects in the form-wound multi-conductor windings of electrical machines were studied for both a sinusoidal and non-sinusoidal supply. A pulse-width-modulated (PWM) voltage supply was achieved by sinus triangle comparison and used as a non-sinusoidal supply for the machine. A PWM supply produced a significant amount of additional eddy-current losses in the form-wound stator winding of the cage induction motor when compared to the sinusoidal supply. The fundamental harmonic voltages of the sinusoidal and PWM supplies were equal for comparing the results. Similar sinusoidal and PWM voltages were used to supply the rotor winding of the DFIG as well. The additional eddy-current losses in the form-wound rotor winding as a result of the PWM supply were small.
Finite-Element Modeling and Calorimetric Measurement of Core Losses in Frequency-Converter-Supplied Synchronous Machines
(Aalto University, 2012) Rasilo, Paavo; Belahcen, Anouar, D.Sc., Aalto University, Finland; Sähkötekniikan laitos; Department of Electrical Engineering; Research Group of Electromechanics; Sähkötekniikan korkeakoulu; School of Electrical Engineering; Arkkio, Antero, Prof., Aalto University, Finland
This thesis deals with the modeling and measurement of core losses in salient-pole wound-field synchronous machines. A numerical iron-loss model for ferromagnetic core laminations has been implemented to be used within the 2-D finite-element (FE) analysis of electrical machines. The developed model combines existing models for eddy currents, magnetic hysteresis, and excess eddy-current losses in the laminations. These losses are globally coupled to the FE solution of the magnetic field in the 2-D cross-section of an electrical machine. Numerical results obtained with the iron-loss model show that the hysteresis losses can be neglected from the FE field solution without a significant loss of accuracy in order to improve the convergence properties of the model and to speed up the computation. Coupling of the eddy-current losses and the related skin-effect phenomenon to the FE solution is more essential to predict the losses correctly, especially on the rotor side. The numerical model is applied to minimize the total electromagnetic losses by modifying the shape of the rotor pole shoe. A calorimetric measurement system has been designed and built for experimental determination of the core losses. A 150-kVA synchronous generator is used as the test machine in the measurements, and its core losses are determined both with grid and inverter supply as a function of the load. Three prototype rotors identical in geometry but stacked of 0.5-mm insulated silicon-iron (Fe-Si) sheets and 1-mm and 2-mm uninsulated steel plates are used in the tests. According to the measurement results, the losses in the rotors stacked of the thicker sheets increase much more severely as a result of loading and inverter supply than those in the Fe-Si rotor. When compared to the measurement results, the numerical model proves to estimate the core losses sufficiently, especially in the case of the 0.5-mm Fe-Si rotor. The modeling of the uninsulated laminations is found to be more challenging, since these may conduct currents also in the axial direction. The losses in the steel frame around the stator core are found to be extremely significant with voltages above the rated value. It is concluded that the 2-D model is also a suitable method to estimate the frame losses.
Functional simulations of power electronics components in series-hybrid machinery for the needs of OEM
(Helsinki University of Technology, 2008) Liukkonen, Matti; Hentunen, Ari; Suomela, Jussi; Kyyrä, Jorma; Department of Electrical Engineering; Sähkötekniikan laitos; Faculty of Electronics, Communications and Automation; Elektroniikan, tietoliikenteen ja automaation tiedekunta
This paper proposes method for rapid control prototyping of the series-hybrid transmission system. The rapid control prototyping needs simulation submodels from all system components in order to develop supervisory control software. The same simulation models can also be used to optimize the drive train. The target framework for the rapid control prototyping method is the original equipment manufacturer (OEM), where the objective is to build devices from subcontractor's components. The machinery industry, as a target group, uses high power ratings for the creation of motion, which leads to high voltage and current values used in the system. Therefore, prototyping is started with careful simulations. This paper also seeks to create a general idea about the structure of the series-hybrid power transmission and assists the start of the process for designing the supervisory control.
Geographical Perspectives on the Development of Power Distribution Systems in Sparsely Populated Areas
(Aalto University, 2013) Saarijärvi, Eero; Lehtonen, Matti, Prof., Aalto University, Department of Electrical Engineering, Finland; Sähkötekniikan laitos; Department of Electrical Engineering; Sähkötekniikan korkeakoulu; School of Electrical Engineering; Lehtonen, Matti, Prof., Aalto University, Department of Electrical Engineering, Finland
It has been proposed that the present power distribution overhead lines should be replaced by underground cables, to address the concerns related to major disturbances caused by snow loads and storms. However, in an objective comparison of different network development strategies, the special characteristics of each of the line types and the terrain must be considered when determining optimal network topologies. In sparsely populated areas the need for cost-effective solutions tailored to best fit the specific terrain and operational environment is emphasized. In this thesis, a method capable of providing a network topology planning algorithm with line type specific characteristics of the operational environment, including an accurate dynamic topographic model involving variable costs, was developed. The work included case studies, the initial data of which was provided by Finnish network utilities from a variety of environments. Applying the developed methodology using a terrain model, also a contribution of this thesis, to the case studies provided general perspectives on the factors affecting the network topologies and the relative merits of different development strategies. The results were compared with the literature, which enabled further assessment of the validity of the methodology and parameterization used in this thesis. The results of the case studies showed that the optimal penetration of sectionalization is greatly affected by the load density. However, the quantity, quality and valuation of the interruptions affect the basic level of the penetration. Then again, optimally placing reserve connections was found to be a much more complex task, being partly affected by not only the geographical distribution of the loads but also by the characteristics of the terrain. While comparing fully backed-up against cost-optimally backed-up network topologies, the potential for utilizing lightweight structures was observed to have a considerable impact. Further, the characteristics of the terrain were found to affect not only cabled networks, but also the topologies of cost-optimal overhead line networks. The developed method for finding the cost-optimal network topology by using an accurate geographic model of the operational environment in terms of life cycle cost surfaces was found to be an efficient means for comparing different circumstances and network topologies and their mutual interactions. A close connection between the network data available in network information systems and the various geographic information sources was also recognized. Further, the means to effectively utilize this connection in the different processes of network planning and operation is presented.
High Voltage Direct Current transmission
(Helsinki University of Technology, 2009) Li, Jingqiang; Lehtonen, Matti; Prof.; Department of Electrical Engineering; Sähkötekniikan laitos; Faculty of Electronics, Communications and Automation; Elektroniikan, tietoliikenteen ja automaation tiedekunta; Lehtonen, Matti; Prof.
This thesis is focused on the application and development of HVDC transmission technology based on thyristor without turn-off capability. Compared with other macroelectronics in the power field, thyristor without turn-off capability has successful operation experience to ensure reliability and high power ratings to transfer bulk energy. This thesis covers converter station design and equipments, reactive power compensation and voltage stability, AC/DC filters design, control strategy and function, fault analysis, overvoltage and insulation co-ordination, overhead line and cable transmission, transmission line environmental effects, earth electrode design and development. With the development of new concepts and techniques, the cost of HVDC transmission will be reduced substantially, thereby extending the area of application.
Hybridityökoneen tehoelektroniikkakomponenttien toiminnallinen simulointi
(Helsinki University of Technology, 2008) Liukkonen, Matti; Suomela, Jussi; TkT; Department of Electrical Engineering; Sähkötekniikan laitos; Faculty of Electronics, Communications and Automation; Elektroniikan, tietoliikenteen ja automaation tiedekunta; Kyyrä, Jorma; Prof.
Tämä työ käsittelee hybridityökoneen tehonsiirtoa sarjahybridijärjestelmässä. Kirjallisuustutkimuksena käydään lävitse erilaisia hybridijärjestelmiä, polttokennojärjestelmää ja täyssähköistä järjestelmää ajoneuvokäytöissä. Kirjallisuustutkimuksessa pohditaan eri ajoneuvokäyttöjen tehonsiirrontoimintaa ja eri järjestelmien etuja sekä heikkouksia. Työssä esitellään hybridijärjestelmän tehonsiirrossa ja energian varastoinnissa käytettävät komponentit, komponenttien tarkoitus ja toiminta. Työssä kehitetään hybridityökoneen sarjahybriditehonsiirtojärjestelmälle yleistä simulointimallia, joka mahdollistaa sarjahybridijärjestelmän ohjauksen kehittämisen ja eri valmistajien toimittamien osakomponenttien toimivuuden testauksen. Simulointimalli toteutetaan Matlab Simulink -ohjelmistolla ja siinä tavoitellaan 20 Hz:n aikatason tarkkuutta.
Identification of loss models from measurements of the magnetic properties of electrical steel sheets
(Helsinki University of Technology, 2008) Belkasim, Monear Ali; Belahcen, Anouar; TkT; Department of Electrical Engineering; Sähkötekniikan laitos; Faculty of Electronics, Communications and Automation; Elektroniikan, tietoliikenteen ja automaation tiedekunta; Arkkio, Antero; Prof.
Numerical simulations of electrical machines require good knowledge of the magnetic properties of the materials they are made of. The magnetic cores of these machines are made of electrical steel sheets, the magnetic properties of which are nonlinear and hysteretic. Moreover, the behavior of the magnetic flux density and the magnetic field strength of such materials depends on the form of the supply. In the Laboratory of Electromechanics, there are several projects which aim to model correctly the behavior of the electrical steel sheet (hysteresis, stress-dependency, losses, etc.) when used in electrical machines. For this purpose, numerical models are developed and built in an in-house finite element program package. However, knowledge of the material properties and the parameters of loss models are necessary and needs to be measured. This work is proposed to measure the magnetization curves and specific losses of an electrical steel sheet. The measurements were carried out using a device specially designed for this purpose and adequate programs for field control. The measurements were conducted under rotating and alternating magnetic fields at different fundamental frequencies and amplitudes. The results of the measurements consisted of a large amount of data that has been analyzed, processed and presented in an appropriate manner. Moreover, the parameters of the loss models were estimated from the measurements through identification procedures that have been written and constructed in MATLAB software. The conclusions of this work provide the basis for a better understanding of the parameters needed to improve loss models.

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