Exploring the Limits of Early Predictive Maintenance in Wind Turbines Applying an Anomaly Detection Technique

The aim of the presented investigation is to explore the time gap between an anomaly appearance in continuously measured parameters of the device and a failure, related to the end of the remaining resource of the device-critical component. In this investigation, we propose a recurrent neural network to model the time series of the parameters of the healthy device to detect anomalies by comparing the predicted values with the ones actually measured. An experimental investigation was performed on SCADA estimates received from different wind turbines with failures. A recurrent neural network was used to predict the temperature of the gearbox. The comparison of the predicted temperature values and the actual measured ones showed that anomalies in the gearbox temperature could be detected up to 37 days before the failure of the device-critical component. The performed investigation compared different models that can be used for temperature time-series modeling and the influence of selected input features on the performance of temperature anomaly detection.publishedVersio

Cascaded Multilevel Inverter-Based Asymmetric Static Synchronous Compensator of Reactive Power

The topology of the static synchronous compensator of reactive power for a low-voltage three-phase utility grid capable of asymmetric reactive power compensation in grid phases has been proposed and analysed. It is implemented using separate, independent cascaded H-bridge multilevel inverters for each phase. Every inverter includes two H-bridge cascades. The first cascade operating at grid frequency is implemented using thyristors, and the second one—operating at high frequency is based on the high-speed MOSFET transistors. The investigation shows that the proposed compensator is able to compensate the reactive power in a low-voltage three-phase grid when phases are loaded by highly asymmetrical reactive loads and provides up to three times lower power losses in the compensator as compared with the situation when the compensator is based on the conventional three-level inverters implemented using IGBT transistors.publishedVersio

Tolydžiųjų asimetrinių reaktyviosios galios kompensatorių kūrimas

The aim of the performed research is development of reactive power compensators for the smooth and asymmetric reactive power compensation in the low voltage utility grid. The cascaded inverter has been modified and adapted for the smooth compensation of reactive power. The topologies of the conventional and cascaded inverter-based reactive power compensators with the individual inverters for the every phase for the asymmetric compensation of reactive power have been proposed. The shunt-connected compensator for the smooth and asymmetric compensation of reactive power in the low voltage utility grid has been developed. The investigation of developed reactive power compensators was performed using simulation and experimentally. The dissertation consists of an introduction, three chapters, general conclusions, references and the list of author's publications on the topic of the dissertation. The research problem, the relevance of the work, the object of research are presented in the introductory chapter. The aim and objectives of the work, the research methodology, scientific novelty of the work, the practical significance of the work results, defended statements are presented as well. At the end of the introduction, the author's publications and conference papers on the topic of the dissertation and the structure of the dissertation are given. The first chapter analyzes the reactive power compensation techniques and compensator types. The inverter-based reactive power compensators and shunt-connected reactive power compensators are analyzed. The conclusions are drawn out and the tasks of the dissertation are formulated. The conventional and cascaded inverter based reactive power compensators are analyzed in the second chapter. The topologies of reactive power compensators with the individual ordinary inverters and cascaded inverters for the every phase for the asymmetric compensation of reactive power are proposed. The Matlab/Simulink models of compensators were created and investigation of compensators using simulation was performed. In the third chapter the developed shunt-connected compensator for smooth asymmetric compensation of reactive power in low voltage utility grid is presented. The investigation of compensator was performed experimentally using developed experimental test bench. The main results of the dissertation have been published in 4 scientific publications – 3 of them have been published in peer-reviewed scientific journals, 1 in conference proceedings. The results were presented at 5 scientific conferences.Doctoral dissertatio

Control of the hexapod walking robot

The analysis focuses on control features of the hexapod walking robot with three degree-of-freedom legs. This paper describes different servo control methods and presents the developed algorithm for formation of servos control signals. The geometric inverse kinematics method was used to calculate the angles of each joint of a leg. The authors present the results of the experimental investigation on the hexapod robot leg movement trajectory. Article in Lithuanian. Šešiakojo žingsniuojančio roboto valdymas Santrauka. Nagrinėjami šešiakojo žingsniuojančio roboto kojų, turinčių tris judrumo laipsnius, valdymo ypatumai. Aprašomi skirtingi valdomųjų mechanizmų valdymo būdai, pateikiamas sudarytas programos algoritmas valdomųjų mechanizmų valdymo signalams formuoti. Aprašyta, kaip randami atskirų roboto kojos dalių tarpusavio kampai taikant geometrinį atvirkštinės kinematikos metodą. Pateikiami šešiakojo žingsniuojančio roboto maketo tyrimo vienos kojos judėjimo erdvėje rezultatai. Reikšminiai žodžiai: šešiakojis robotas, atvirkštinė kinematika, valdomasis mechanizmas

Constant slip control system of an asynchronous motor

Asynchronous motors are efficiently controlled using the scalar method. Main problems appear when the motor is fully loaded and desired rotation speed is slow. In such cases, the motor slip exceeds the magnitude of the nominal slip, causing the increase in stator current. The constant slip method was designed to control hardly loaded asynchronous motor. In this particular situation, the constant slip method provides a better efficiency than the scalar method. The magnitude of the motor current refers to the slip: the less is the slip, the less is the magnitude. It is impossible to find the optimal slip for minimization of current with the help of a model. Therefore, the nominal slip value was used as optimal. Article in Lithuanian. Pastovaus slydimo asinchroninio elektros variklio rotoriaus greičio valdymo metodas Santrauka. Pasiūlytas pastovaus slydimo asinchroninio elektros variklio rotoriaus greičio valdymo metodas ištirtas modeliuojant, gauti rezultatai palyginti su skaliarinio valdymo metodo tyrimo rezultatais. Tyrimo rezultatai parodė, kad pastovaus slydimo asinchroninio variklio greičio valdymo metodas yra pranašesnis už skaliarinio valdymo metodą, kai valdomo variklio greitis yra nedidelis ir jo apkrova yra artima nominaliajai. Reikšminiai žodžiai: asinchroninis variklis, rotoriaus slydimas, dažnio keitiklis, inverteris, valdymo sistema

Investigation of flyback transformer flux leakage reduction ways

Results of experimental investigation and design optimization of flyback transformer are presented. Aim of the work is to investigate experimentally the impact of the flyback transformer design on the flux leakage and maximal output power. It is difficult to evaluate the effect of the leakage flux mathematically because it depends on various factors: the position of the windings relative to each other; the position of the windings in the transformer; the distance between the winding. A multi-winding flyback transformer was used for experiments. Using the results of the experiments optimal design of the investigated flyback transformer was defined. Article in Lithuanian. Flyback tipo transformatoriaus sklaidos srauto mažinimo tyrimas Santrauka Darbe pateikti flyback tipo impulsinio transformatoriaus eksperimentiniai tyrimai. Tyrimų tikslas – ištirti, nuo ko priklauso flyback tipo transformatoriaus magnetolaidžio sklaidos srauto (angl. leakage inductance) reiškiniai, kurie mažina tokio tipo transformatoriaus efektyvumą ir didžiausiąją darbinę galią. Matematiškai sunku įvertinti sklaidos magnetinio srauto reiškinį transformatoriaus magnetinėje sistemoje, nes jis priklauso nuo transformatoriaus apvijų tarpusavio išsidėstymo. Todėl eksperimentui atlikti panaudotas daugelio apvijų flyback tipo transformatorius, kuris ištirtas eksperimentiškai. Palyginus gautus eksperimentų rezultatus, nustatytas optimalus tirto flyback transformatoriaus darbo režimas ir optimalūs konstrukciniai parametrai. Reikšminiai žodžiai: flyback transformatorius, magnetinis sklaidos srautas, viršįtampiai, slopinimo grandinė

Investigation of electrical power grid microinverter efficiency / Elektros tinklo mikroinverterio naudingumo faktoriaus tyrimas

In this paper the investigation results of a boost Flyback convert-er, which is used in a micro-inverter, are presented. The efficien-cy characteristics of the converter at various carrier frequencies and output loads were investigated. An alternative circuit diagram solution, which is less complex in structure and has fever com-ponents but has the same properties as the classic circuit scheme, for the converter is proposed. The proposed Flyback converter is less expensive. Its efficiency is 2–3 % higher than the classic Flyback converter when the converter output power is less than 95 W. Santrauka  Darbe tirtas fotovoltinės energijos moduliams skirto mikroinverterio įtampą aukštinantis Flyback topologijos keitiklis. Ištirtos šio keitiklio naudingumo faktoriaus charakteristikos esant įvairioms nešlio dažnių ir keitiklio tiekiamos energijos galioms. Ištyrus klasikinį keitiklį, pasiūlytas patobulintas keitiklis, kuriame naudojama mažiau elektronikos komponentų. Pasiūlytas Flyback keitiklis yra pigesnis. Jo naudingumo faktorius yra 2–3 % aukštesnis už klasikinio, kai tiekiama keitiklio galia nesiekia 95 W. Reikšminiai žodžiai: Flyback keitiklis, tinklo mikroinverteris, impulso pločio moduliacija, naudingumo faktorius

Stepless compensator of reactive power

The developed stepless compensation system of reactive power based on the thyristor controlled reactors is presented. The investigation results of the system obtained using simulation and experimental investigation are given. Article in Lithuanian. Bepakopis reaktyviosios galios kompensatorius Santrauka Darbe pristatomas žemosios įtampos elektros tinklui skirtas 12 kVAr bepakopis reaktyviosios galios kompensatorius. Jis įgyvendintas naudojant tiristoriais valdomus induktyvumus, sujungtus žvaigžde, kurios vidurinis taškas prijungtas prie tinklo neutralės. Pateikti sukurto kompensatoriaus tyrimų rezultatai gauti modeliuojant ir eksperimentiškai. Reikšminiai žodžiai: reaktyvioji galia, tiristoriais valdomas reaktorius (TCR), elektros tinklo kokybė. &nbsp

Development of high power microsecond pulse generator

The developed high power microsecond pulse generator (U = 50– 3500 V, I < 250 A, t = 3 μs–1 ms) based on the push-pull inverter has been presented. The generator is developed for the electroporation of biological cells. The high power microsecond pulse generator was tested using simulation and experimental investigation. Article in Lithuanian. Didelės galios mikrosekundinių impulsų generatorius Santrauka Darbe pateikti didelės galios mikrosekundinių impulsų generatoriaus kūrimo ir tyrimo rezultatai. Generatorius skirtas elektroporacijai, t. y. ląstelių poveikiui trumpu stipriu elektrinio lauko impulsu. Jo generuojamų impulsų amplitudė yra 50–3500 V, tiekiama į apkrovą srovė – iki 250 A, impulsų trukmė – 3 μs–1 ms. Pateikti generatoriaus sprendimai ir jo tyrimų rezultatai gauti modeliuojant bei eksperimentiškai. Reikšminiai žodžiai: dvitaktis keitiklis, generatorius, elektroporacija, didelės galios impulsas

Flyback mikroinverterio, sudaryto iš dviejų raktų, modelio Matlab Simulink aplinkoje sudarymas ir tyrimas / Development and research of two switch based Flyback microconverter’s Matlab Simulink model

Paper describes simulation results of proposed micro inverter model based on flyback converter with two transistor switches using Matlab Simulink. The aim of this research to investigate behavior of proposed model of the micro inverter based on flyback converter, when micro inverter operates autonomously (islanding) and running parallel in the local electricity network. The simulation of micro inverter’s operation on autonomous mode using nonlinear load was performed, as well as it runs in parallel with the local power network polluted with harmonics. The main goal of these simulations is to observe the response of output current of micro inverter to the harmonical distortions of local grid. Examination of the proposed micro inverter model based on flyback converter in Matlab Simulink environment helps to determinate the resistance of micro inverter output signal to distortion in local electrical grid using two working modes: 1. the autonomous mode using nonlinear load, 2. the parallel mode with local electric grid polluted by higher order harmonics. Santrauka Darbe pateikti siūlomo flyback tipo mikroinverterio, sudaryto iš dviejų raktų, modeliavimo rezultatai Matlab Simulink aplinkoje. Tyrimo tikslas – įvertinti siūlomo flyback mikroinverterio modelio veikimą virtualioje Matlab Simulink aplinkoje, kai mikroinverteris veikia autonomiškai (energetinėje saloje) ir lygiagrečiai su vietiniu elektros tinklu. Darbe imituojamas autonomiškas mikroinverterio darbas su netiesiniais elektros tinklo apkrovos elementais ir harmonikomis užterštame elektros tinkle. Taip siekiama įvertinti mikroinverterio tiekiamos į tinklą sinusinės formos srovės reakciją į tinklo įtampos harmoninius iškraipymus. Ištyrus pasiūlyto flyback mikroinverterio eksperimentinį modelį Matlab Simulink aplinkoje, nustatytas mikroinverterio išėjimo signalo atsparumas iškraipymams jam veikiant autonomiškai ir imituojant elektros tinklą, paveiktą aukštesniosiomis eilės harmonikomis. Reikšminiai žodžiai: flyback keitiklis, mikroinverteris, viršįtampiai, elektros tinklas, PID reguliatorius, harmonikos