[comp] Sähkötekniikan korkeakoulu / ELEC

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  • Active control of radial rotor vibrations in electric machines : identification, modeling and control design
    (2008) Orivuori, Juha; Laiho, Antti; Sinervo, Anssi
     Faculty of Electronics, Communications and Automation | A4 Artikkeli konferenssijulkaisussa
    This paper presents results related to modeling, identification, control design and simulation of an electric motor equipped with a new force actuator. The model consists of several partial models, thus separating certain physical phenomena into independent processes. The inputs and outputs of the models to be identified are strongly correlated. This makes the identification process significantly more complicated. Three different control algorithms are designed for the process. The performance of the control algorithms are tested against finite element models in extensive simulations. The paper concludes in description of preliminary test results with an actual test machine.
  • Analysis and design of a position observer with resistance adaptation for synchronous reluctance motor drives
    (2011) Tuovinen, Toni; Hinkkanen, Marko; Luomi, Jorma
     School of Electrical Engineering | A4 Artikkeli konferenssijulkaisussa
    A back-EMF-based reduced-order position observer with stator-resistance adaptation is analyzed for motion-sensorless synchronous reluctance motor drives. Analytical equations for steady-state estimation errors and stability conditions are derived (with and without resistance adaptation), taking into account errors in the parameter estimates. The effect of the observer gain on the noise reduction is studied by means of eigenvector analysis. A robust gain selection is proposed, which maximizes the allowed uncertainties in the parameter estimates. The proposed observer design is experimentally evaluated using a 6.7-kW synchronous reluctance motor drive; stable operation is demonstrated at low speeds under various parameter errors.
  • Analysis and design of a position observer with stator-resistance adaptation for PMSM drives
    (2010) Hinkkanen, Marko; Tuovinen, Toni; Harnefors, Lennart; Luomi, Jorma
     School of Electrical Engineering | A4 Artikkeli konferenssijulkaisussa
    This paper deals with reduced-order observers with stator-resistance adaptation for motion-sensorless permanent-magnet synchronous motor drives. An analytical solution for the stabilizing observer gain and stability conditions for the stator-resistance adaptation are derived. The proposed observer design is experimentally tested using a 2.2-kW motor drive; stable operation at very low speeds under different loading conditions is demonstrated.
  • Analysis of Different Models of Iron Precipitation in Multicrystalline Silicon
    (2014) Morishige, Ashley; Laine, Hannu; Schön, Jonas; Hofstetter, Jasmin; Haarahiltunen, Antti; Schubert, Martin; Savin, Hele; Buonassisi, Tonio
     School of Electrical Engineering | A4 Artikkeli konferenssijulkaisussa
    Simulation of solar cell processing enables inexpensive and rapid process optimization. Over the last twenty years, several models describing the distribution and behavior of iron point defects and iron-silicide precipitates have been developed and incorporated into process simulations. The goal of this work is to elucidate what physics are needed to accurately describe industry-relevant as-grown impurity and defect distributions and processing conditions by simulating different material-processing combinations with each model. This rigorous comparison helps scientists and engineers choose the appropriate level of model complexity, and consequently simulation run time, based on material characteristics and processing conditions.
  • Augmented Reality in Forest Machine Cabin
    (2017) Palonen, Tuomo; Hyyti, Heikki; Visala, Arto
     School of Electrical Engineering | A4 Artikkeli konferenssijulkaisussa
    Augmented reality human machine interface is demonstrated in the cabin of a forest machine outdoors for the first time in real time. In this work, we propose a system setup and a real-time capable algorithm to augment the operator’s visual field with measurements from the forest machine and its environment. In the demonstration, an instrumented forestry crane and a lidar are used to model the pose of the crane and its surroundings. In our approach, a camera and an inertial measurement unit are used to estimate the pose of the operator’s head in difficult lighting conditions with the help of planar markers placed on the cabin structures. Using the estimate, a point cloud and a crane model are superimposed on the video feed to form an augmented reality view. Our system is tested to work outdoors using a forest machine research platform in real time with encouraging initial results.
  • Automatic Speech Recognition for Northern Sámi with comparison to other Uralic Languages
    (2016) Smit, Peter; Leinonen, Juho; Jokinen, Kristiina; Kurimo, Mikko
     School of Electrical Engineering | A4 Artikkeli konferenssijulkaisussa
    Speech technology applications for major languages are becoming widely available, but for many other languages there is no commercial interest in developing speech technology. As the lack of technology and applications will threaten the existence of these languages, it is important to study how to create speech recognizers with minimal effort and low resources. As a test case, we have developed a Large Vocabulary Continuous Speech Recognizer for Northern Sámi, an Finno-Ugric language that has little resources for speech technology available. Using only limited audio data, 2.5 hours, and the Northern Sámi Wikipedia for the language model we achieved 7.6% Letter Error Rate (LER). With a language model based on a higher quality language corpus we achieved 4.2% LER. To put this in perspective we also trained systems in other, better-resourced, Finno-Ugric languages (Finnish and Estonian) with the same amount of data and compared those to state-of-the-art systems in those languages.
  • Categorizing and measuring social ties
    (2012) Nelimarkka, Matti; Karikoski, Juuso
     School of Science | B3 Vertaisarvioimaton artikkeli konferenssijulkaisussa
    he analysis of social networks has boomed recently, mainly as online social networking systems such as Twitter allow researchers to access these data. However, the research is less and less focused on the fundamental question on the validity of the data and interpretation of the results. For example, Golder et al. (2007) use the word 'friend' in quotes while describing their results. To enhance the discussion around the validity of results, our work contributes a categorization of social network data. We also discuss the differences of the data sources, especially highlighting the fact that different data sources disclose different kinds of networks. Our approach is to examine social networks based on several sources of data, and thus acquire a richer data set. Based on this extended data set, we are more equipped to understand the social relations represented via links between nodes. After reviewing the existing literature, we make two observations of social relationships in online services. Firstly, the friendship data may be shared in public or with the specific group of users of that service - this may affect how people perceive and use these relationships, especially when compared with the private displays of relations (e.g., Donath & boyd, 2004). On the other hand, people interact only with part of their social relations (e.g., Golder et al., 2007) and research has started to focus from statical networks to more dynamical activity based networks (e.g., Huberman et al., 2009). Based on the existing literature, shortly discussed above, a 2x2 matrix can be developed. Relations may be public or private and active or passive. For instance, those relations with which you use Instant Messaging can be considered private and active whereas Facebook friends are passive and public. As they are different in this nature, also the conclusions based on the analysis should differ. After confirming that the data measure the phenomenon desired, one should use several kinds of data sources to really understand the social structures behind the group under study. We claim that multiple data sets should be used when measuring social relations. McPherson et al. (2001) have also concluded that the priority for future social network researchers should be to gather dynamic data on multiple social relations. By studying existing research and our own empirical data (e.g., Karikoski & Nelimarkka, 2011), we discuss the opportunities and challenges of using multiple data sets to cover the same group.
  • Circuit paradigm in the 21
    (2001) Porra, Veikko; Valtonen, Martti; Hartimo, Iiro; Ilmonen, Matti; Simula, Olli; Veijola, Timo
     C2 Toimitettu kirja, kokoomateos, konferenssijulkaisu tai lehden erikoisnumero
  • A comparison of an adaptive full-order observer and a reduced-order observer for synchronous reluctance motor drives
    (2011) Tuovinen, Toni; Hinkkanen, Marko; Luomi, Jorma
     School of Electrical Engineering | A4 Artikkeli konferenssijulkaisussa
    Two back-EMF-based position observers are compared for motion-sensorless synchronous reluctance motor drives. The reduced-order observer is of the second order, and the adaptive full-order observer is of the fourth order. The proposed design rules guarantee the stability of the adaptive full-order observer, if the parameter estimates are accurate. The observers are experimentally evaluated using a 6.7-kW synchronous reluctance motor drive in low-speed operation and under parameter errors. The gain selection of the second-order observer is easier, but the adaptive full-order observer is more robust against parameter variations and spatial harmonics.
  • Control principles for blackstart and island operation of microgrid
    (2008) Laaksonen, Hannu; Kauhaniemi, Kimmo
     A4 Artikkeli konferenssijulkaisussa
    In some unexpected situations a microgrid may become unstable after transition to islanded mode and all DG units must be disconnected from microgrid. In case of these events a restoration strategy for microgrid blackstart is needed. Also if the islanded microgrid is divided into different protection zones in case of a fault, fault management strategy with capability of very fast operation is needed to maintain stability in the healthy section of the islanded microgrid. The control of microgrid voltage and frequency during the microgrid blackstart is not possible without energy storage unit. In this paper sequence of actions for the microgrid blackstart operation as well as control principles of some DG units during blackstart are defined and simulated with two different microgrid configurations. Also one simulation case considering fault management strategy and control principles during fault in islanded microgrid is presented. Based on the simulations dimensioning principles for the needed energy storage and size of simultaneously controlled loads can be drawn.
  • Cooperative Game-theoretic Approach to Load Balancing in Smart Grids with Community Energy Storage
    (2015) Rajasekharan, Jayaprakash; Koivunen, Visa
     School of Electrical Engineering | A4 Artikkeli konferenssijulkaisussa
    In this paper, we propose a model for households to share energy from community energy storage (CES) such that both households and utility company benefit from CES. In addition to providing a range of ancillary grid services, CES can also be used for demand side management, to shave peaks and fill valleys in system load. We introduce a method stemming from consumer theory and cooperative game theory that uses CES to balance the load of an entire locality and manage household energy allocations respectively. Load balancing is derived as a geometric programming problem. Each household’s contribution to overall non-uniformity of the load profile is modeled using a characteristic function and Shapley values are used to allocate the amount and price of surplus energy stored in CES. The proposed method is able to perfectly balance the load while also making sure that each household is guaranteed a reduction in energy costs.
  • Current control for IPMSM drives: Direct discrete-time pole-placement design
    (2015) Hinkkanen, Marko; Qu, Zengcai; Awan, Hafiz Asad Ali; Tuovinen, Toni; Briz, Fernando
     School of Electrical Engineering | A4 Artikkeli konferenssijulkaisussa
    This paper deals with discrete-time models and current control methods for synchronous motors with a magnetically anisotropic rotor structure, such as interior permanent-magnet synchronous motors (IPMSMs) and synchronous reluctance motors (SyRMs). Dynamic performance of current controllers based on continuous-time models is limited, especially if the ratio of the sampling frequency to the fundamental frequency is low. An exact closed-form hold-equivalent discrete motor model is derived. The zero-order hold of the stator-voltage input is modeled in stationary coordinates, where it physically is. An analytical discrete-time pole-placement design method for a two-degree-of-freedom state-space current controller with an integral action is proposed. The proposed method is easy to apply: only the desired closed-loop bandwidth and the three motor parameters (R_s, L_d, L_q) are required. The robustness of the proposed current control design against parameter errors is analyzed. The controller is experimentally verified using a 6.7-kW SyRM drive.
  • Current-sourced buck converter
    (2008) Leppäaho, Jari; Karppanen, Matti; Suntio, Teuvo
     A4 Artikkeli konferenssijulkaisussa
    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.
  • Customer-end inverter in an LVDC distribution network
    (2008) Nuutinen, Pasi; Salonen, Pasi; Peltoniemi, Pasi; Silventoinen, Pertti
     A4 Artikkeli konferenssijulkaisussa
    An AC-based low-voltage distribution network can in some cases be replaced with a low-voltage direct current (LVDC) network. With a higher DC voltage, the transmission capacity increases compared with the AC system with the same cable cross-sectional area. The DC link feeds an inverter that converts the DC voltage to a 230 V single-phase or 400 V three-phase AC voltage. Because the three-phase voltage is not necessarily needed in most residential applications, this paper presents two single-phase inverter topologies. Inverter modulation and its suitability for this kind of an application is discussed. The inverter efficiency and its requirements are also discussed in brief, yet more precise analyses are left for future studies. The conclusion is that a half-bridge topology is not suitable for this application, and therefore, a full-bridge inverter should be used instead.
  • Design of master control unit for laboratory prototype of traction converter for locomotives
    (2008) Žák, Jan; Peroutka, Zdeněk; Ovaska, Seppo J.
     Faculty of Electronics, Communications and Automation | A4 Artikkeli konferenssijulkaisussa
    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.
  • Designing maximum length sequence signal for frequency response measurement of switched mode converters
    (2008) Vilkko, Matti; Roinila, Tomi
     A4 Artikkeli konferenssijulkaisussa
    Switched mode power converters are extensively used in powering consumer products. Requirements of short time-to-market and low bill of materials set new challenges to designers. The designers should efficiently create stable and robust designs using low-cost components with high parameter variations. Methods to test statistically the dynamical properties of final design would enable the designers to evaluate control design before production ramp-up. However, currently available testing methods require intervention into internal circuitry or are time consuming and too laborious. This paper describes how Maximum Length Binary Sequences can be used to obtain a high through-put frequency response measurement method to analyze the dynamics of switched mode converters. Some well known computational methods for the frequency response calculation are listed and the design of an appropriate maximum length excitation signal is presented. The proposed signal design procedure takes time-aliasing effect, noise reduction, and the disturbing harmonics generated by pulse width modulation of the converter controller into consideration. The results are verified by experimental measurements from a high-frequency switched mode converter.
  • Detection and species classification of young trees using machine perception for a semi-autonomous forest machine
    (2015) Vihlman, Mikko; Hyyti, Heikki; Kalmari, Jouko; Visala, Arto
     School of Electrical Engineering | A4 Artikkeli konferenssijulkaisussa
    An approach to automatically detect and classify young spruce and birch trees in forest environment is presented. The method could be used in autonomous or semi-autonomous forest machines during tending operations. Detection is done by segmenting laser range images formed by a rotating laser scanner. Classification is done with a two-class Naive Bayes classifier based on image texture features. Multiple combinations of 99 features were tested and the best classifier included eight features from the co-occurrence matrix, local binary patterns, statistical geometrical features and Gabor filter. 79% of spruces and birches in the testing material were detected and 74% of these were correctly classified. Results suggest that the approach is suitable but there are still some challenges in each of the processing steps. Iteration between segmentation and classification is needed to increase reliability.
  • Digital implementation of full-order flux observers for induction motors
    (2002) Hinkkanen, Marko; Luomi, Jorma
     School of Electrical Engineering | A4 Artikkeli konferenssijulkaisussa
    This paper deals with flux estimation for induction motor drives by using a full-order flux observer. A problem of full-order flux observers is their need for computationally demanding discretization methods in order to work stably and accurately at high speeds. An implementation of the full-order flux observer using the stator and rotor fluxes as state variables in the stator reference frame and in the rotor reference frame, respectively, was recently proposed. This paper describes how an observer gain can be included in this structure. It is shown that discretization errors of the proposed implementation are small and that there is more freedom to choose an observer gain, even if the simple forward Euler discretization is used.
  • Discrete-time observer design for sensorless synchronous motor drives
    (2015) Tuovinen, Toni; Awan, Hafiz Asad Ali; Saarakkala, Seppo E.; Hinkkanen, Marko
     School of Electrical Engineering | A4 Artikkeli konferenssijulkaisussa
    This paper deals with the speed and position estimation of interior permanent-magnet synchronous motor (IPMSM) and synchronous reluctance motor (SyRM) drives. A speed adaptive full-order observer is designed and analyzed in the discrete-time domain. The observer design is based on the exact discrete-time motor model, which inherently takes the delays in the control system into account. The proposed observer is experimentally evaluated using a 6.7-kW SyRM drive. The analysis and experimental results indicate that drastic performance improvements can be obtained with the direct discrete-time design, especially if the sampling frequency is relatively low compared to the fundamental frequency.