Control of sensorless electrical drives operating in a hybrid flying platform

In the paper, the results of an investigation on the electrical drive of a hybrid flying platform (BAL) are presented. Due to restrictions on flying platforms it is necessary to use solutions with a limited number of sensors. For that purpose an investigation of two versions of electrical drives with a BLDC motor without a speed feedback has been conducted. The obtained results have been compared and conclusions regarding the practical use of the motor drive have been made. The investigations discussed in the paper concern only the proposed methods of speed estimation based on current measurement

Unveiling the Potential of Probabilistic Embeddings in Self-Supervised Learning

In recent years, self-supervised learning has played a pivotal role in advancing machine learning by allowing models to acquire meaningful representations from unlabeled data. An intriguing research avenue involves developing self-supervised models within an information-theoretic framework, but many studies often deviate from the stochasticity assumptions made when deriving their objectives. To gain deeper insights into this issue, we propose to explicitly model the representation with stochastic embeddings and assess their effects on performance, information compression and potential for out-of-distribution detection. From an information-theoretic perspective, we seek to investigate the impact of probabilistic modeling on the information bottleneck, shedding light on a trade-off between compression and preservation of information in both representation and loss space. Emphasizing the importance of distinguishing between these two spaces, we demonstrate how constraining one can affect the other, potentially leading to performance degradation. Moreover, our findings suggest that introducing an additional bottleneck in the loss space can significantly enhance the ability to detect out-of-distribution examples, only leveraging either representation features or the variance of their underlying distribution.Comment: Under review by AISTATS 202

RAFEN -- Regularized Alignment Framework for Embeddings of Nodes

Learning representations of nodes has been a crucial area of the graph machine learning research area. A well-defined node embedding model should reflect both node features and the graph structure in the final embedding. In the case of dynamic graphs, this problem becomes even more complex as both features and structure may change over time. The embeddings of particular nodes should remain comparable during the evolution of the graph, what can be achieved by applying an alignment procedure. This step was often applied in existing works after the node embedding was already computed. In this paper, we introduce a framework -- RAFEN -- that allows to enrich any existing node embedding method using the aforementioned alignment term and learning aligned node embedding during training time. We propose several variants of our framework and demonstrate its performance on six real-world datasets. RAFEN achieves on-par or better performance than existing approaches without requiring additional processing steps.Comment: ICCS 202

Prediction of Young's modulus of trabeculae in microscale using macro-scale's relationships between bone density and mechanical properties

According to the literature, there are many mathematical relationships between density of the trabecular bone and mechanical properties obtained in macro-scale testing. In micro-scale, the measurements provide only the ranges of Young's modulus of trabeculae, but there are no experimentally tested relationships allowing the calculation of the distribution of Young's modulus of trabeculae within these experimental ranges. This study examined the applicability of relationships between bone density and mechanical properties obtained in macro-scale testing for the calculation of Young's modulus distribution in micro-scale. Twelve cubic specimens from eleven femoral heads were cut out and micro-computed tomography (micro-CT) scanned. A mechanical compression test and Digital Image Correlation (DIC) measurements were performed to obtain the experimental displacement and strain full-field evaluation for each specimen. Five relationships between bone density and Young's modulus were selected for the test; those were given by Carter and Hayes (1977), Ciarelli et al. (2000), Kaneko et al. (2004), Keller (1994) for the human femur, and Li and Aspden, 1997. Using these relationships, five separate finite element (FE) models were prepared, with different distribution of Young's modulus of trabeculae for each specimen. In total, 60 FE analyses were carried out. The obtained displacement and strain full-field measurements from numerical calculations and experiment were compared. The results indicate that the highest accuracy of the numerical calculation was obtained for the Ciarelli et al. (2000) relationship, where the relative error was 17.87% for displacements and 50.94 % for strains. Therefore, the application of the Ciarelli et al. (2000) relationship in the microscale linear FE analysis is possible, but mainly to determine bone displacement

Catalytic residues in hydrolases: analysis of methods designed for ligand-binding site prediction

The comparison of eight tools applicable to ligand-binding site prediction is presented. The methods examined cover three types of approaches: the geometrical (CASTp, PASS, Pocket-Finder), the physicochemical (Q-SiteFinder, FOD) and the knowledge-based (ConSurf, SuMo, WebFEATURE). The accuracy of predictions was measured in reference to the catalytic residues documented in the Catalytic Site Atlas. The test was performed on a set comprising selected chains of hydrolases. The results were analysed with regard to size, polarity, secondary structure, accessible solvent area of predicted sites as well as parameters commonly used in machine learning (F-measure, MCC). The relative accuracies of predictions are presented in the ROC space, allowing determination of the optimal methods by means of the ROC convex hull. Additionally the minimum expected cost analysis was performed. Both advantages and disadvantages of the eight methods are presented. Characterization of protein chains in respect to the level of difficulty in the active site prediction is introduced. The main reasons for failures are discussed. Overall, the best performance offers SuMo followed by FOD, while Pocket-Finder is the best method among the geometrical approaches

A Conductance-Based MPPT Method with Reduced Impact of the Voltage Ripple for One-Phase Solar Powered Vehicle or Aircraft Systems

This paper presents a novel maximum power point tracking method for photovoltaic inverters with a single phase connection to the onboard 400Hz vehicle or aircraft grid, supplying drives operating in a critical mode. By taking into account that the power fluctuations cause voltage ripples at the termini of photovoltaic panels connected to the DC-link capacitor, this paper proposes a conductance base maximum power point tracking method. The impact of varying voltage has been reduced to ensure the constant reference current for the grid current calculation problem, which has been reported in previous studies. Accordingly, a conductance base tracking method, grid current control, is proposed and implemented to ensure the expected output current with respect to varying power. As described in this paper, the exemplified solar converter prototype can implement constant reference photovoltaic current control with a maximum power point achievement under continuous voltage rippling. Experimental results are given to verify the feasibility of the proposed MPPT method, which significantly improves the power efficiency for solar powered vehicles or aircraft

Fuzzy Logic Based Synchronization Method for Solar Powered High Frequency On-Board Grid

This paper proposes a method for synchronizing a grid inverter with the voltage of an on-board high-frequency power grid. The described synchronization method belongs to the adaptive methods, which use fuzzy logic in the process of estimating the fundamental component of the voltage. The synchronization system has been tuned to achieve the primary goal of achieving synchronization in the shortest possible time. This is to allow for the efficient energy fed from photovoltaic sources into the on-board grid at 400 Hz. The proposed method was implemented in the field programmable gate array (FPGA) based power converter controller and static and dynamic tests for harmonic, interharmonic and subharmonic voltage disturbances were performed. Dynamic tests for phase jump, frequency jump and sag of the on-board voltage were also performed. To evaluate the effectiveness of synchronization with high-frequency voltage, the grid current control system in the grid tied inverter was elaborated. Proper current waveforms at the perturbed voltage were recorded while identifying the effectiveness of power ripple suppression. The results obtained were compared with the enhanced phase locked loop (EPLL) synchronization method. Satisfactory test results confirmed the suitability of the proposed method in systems coupling the photovoltaic source to the on-board high-frequency power grid

Closed-loop Control with the Active Component of the Three-Phase Current

Stosowane w elektrotechnice układy regulacji potrzebują do właściwej i bezpiecznej pracy informacji o wartościach prądów płynących w sterowanych obiektach. W przypadku prądów zmiennych trójfazowych ich wartości chwilowe zmieniają się w czasie, często pozostając w przesunięciu fazowym względem napięcia. W artykule przedstawiono metodę pozyskiwania informacji o wartości składowej aktywnej prądu, która to w głównej mierze odpowiada za wykonywaną pracę. Zmierzona wartość składowej aktywnej prądu wykorzystywana jest jako sygnał sprzężenia zwrotnego w procesie regulacji prądu silnika indukcyjnego. Przedstawiony w artykule sposób pomiaru prądu został zamodelowany i przebadany w środowisku Power Sim.The control systems used in electrical engineering need an information about values of currents flowing in the controlled objects for the correct and safe operation . In the case of three-phase currents their momentary values change over time, often remaining in the moving phase relative to the voltage. This article presents a method of obtaining information about the active component, which is largely responsible for the load operation. The measured value of active component is used as a feedback signal in the process of adjusting current induction motor. The current measurement method described in the article has been modeled and examined in a Power Sim environement

Simultaneous Real-Time Models of Power Electronics Converters

Badanie układów energoelektronicznych zarówno do celów dydaktycznych, jak i naukowych wymaga przeprowadzania testów układów sterowania i regulacji. Testy te nie zawsze kończą się sukcesem, zwłaszcza w sytuacji nieprzewidzianych zdarzeń lub niewłaściwie dobranych parame-trów sterowania. W przypadku stanowiska laboratoryjnego ewentualne zwarcia lub błędy mogą skutkować zniszczeniem wrażliwych, kosztownych elementów. W artykule przedstawiono koncepcję stanowiska laboratoryjnego przeznaczonego do fazy prototypowania, które w czasie rzeczywistym wykonywało współbieżnie obliczenia modeli przekształtników energoelektronicznych i realizowało zadania sterowania.The power electronics converters study, both for the purposes of teaching and scientific research, requires the testing of control systems and regulations. These tests do not always end with success, especially in a situation not provided for events or inappropriately selected control parameters. In the case of a laboratory station possible short circuits or errors can result in the destruction of sensitive, costly items. The article shows the concept of a laboratory station intended for prototyping phase, which in real time performed calculation in parallel of the power electronic converter models and provided the control tasks

The Impact of FPGA Clocking Time on the Accuracy of DC Motor Speed Estimation

W artykule przedstawiono dwa problemy badawcze. Pierwszy z nich odnosi się do zastosowania napędu bezczujnikowego sterowanego układem FPGA, który wykorzystuje do estymacji filtrację Kalmana. Drugi problem badawczy koncentruje sie na wpływie częstotliwości taktowania procesu uruchamianego na FPGA na dokładność estymacji. Artykuł przedstawia wyniki badań różnych stanów pracy napędu bezczujnikowego. Przedstawione analizy dotyczą dynamiki zmian napięcia i momentu obciążenia silnika. Wartość prędkości wyznaczona bezpośrednio z modelu odniesienia silnika prądu stałego stanowiła wartość, do której odnoszono wyniki estymacji.Two problems are considered in the paper. One of them applies to sensorless drive with a DC motor, which uses Kalman filtering. The second problem concerns the description of performed investigations of sampling frequency effect for precision of speed estimation. The investigations concern the simulation of different cases of sensorless drive operation. The analysis regarding the speed estimation precision at voltage and load torque jumps for a different value of sample time has been performed. The speed determined directly from a mathematical model of motor is the base value for comparison