Abstract: Solar power tower plants use large arrays of mirrors, known as heliostats, to concentrate solar radiation on their receiver and heat the working fluid inside them. However, receivers must not be under thermal stress. Otherwise, their life expectancy is reduced, which affects the cost and viability of production plant. Controlling the flux distributions on receivers requires selecting the active heliostats and their target points. It is a challenging task that should not be under the responsibility and expertise of human operators only. This work defines a closed-loop controller to keep the setpoint or desired flux map under certain conditions. It combines real measurements and an ad-hoc analytical model of the target field with a set of heuristic rules that covers how to activate, deactivate, and re-aim heliostats. The proposed system has been applied to a model of the CESA-I field at the Solar Platform of Almería. The open-source ray-tracer Tonatiuh represents the reality. The initial operation point has been determined with a theoretical flux distribution optimizer. According to the experimentation, the controller improves the initial and model-based flux distribution by raising its power from 708.4 to 736.4 kW (with a setpoint of 739.6 kW).

Keywords: solar power tower plant; heliostat field; flux distribution; automatic control; closed-loop control; heuristics

Abstract: Many Reinforcement Learning methods start the learning phase from an empty, or randomly filled knowledge-base. Having some a priori knowledge about the way as the studied system could be controlled, e.g. in the form of some state-action control rules, the convergence speed of the learning process can be significantly improved. In this case, the learning stage could start from a sketch, from a knowledge-base formed based upon the already existing knowledge. In this paper. the a priori (expert) knowledge is considered to be given in the form state-action fuzzy control rules of a Fuzzy Rule Interpolation (FRI) reasoning model and the studied reinforcement learning method is restricted to be a Fuzzy Rule Interpolation-based Q-Learning (FRIQ-Learning) method. The main goal of this paper is the introduction of a methodology, which is suitable for merging the a priori state-action fuzzy control rule-base to the initial state-action-value function (Q-function) representation. For demonstrating the benefits of the suggested methodology, the a priori knowledge-base accelerated FRIQ-Learning solution of the “mountain car” benchmark is also discussed briefly in the paper.

Keywords: Reinforcement Learning; Heuristically Accelerated Reinforcement Learning; Fuzzy Rule Interpolation; Q-Learning; FRIQ-Learning

Abstract: Discrete-Event Systems (DES) are systems that are discrete in nature. A next state of DES depends on the actual state and on the occurrence of a discrete event. DES are often modeled and controlled by Petri Nets (PN) of different kinds (place/transition PN, timed PN, etc.). However, not always real DES, are purely deterministic. In such cases, the PN-based model contains some uncontrollable and/or unobservable transitions or unmeasurable/unobservable places. In order to control DES with the partial non-determinism, special kinds of PN and control methods/procedures have to be used. That's just it - applications of Interpreted PN (IPN) and Labeled PN (LbPN) for modeling analyzing and control of DES are investigated here.

Keywords: control; discrete-event systems; modeling; non-determinism; Petri nets

Abstract: In this paper, the number of shortest paths between any point pairs of the square grid, based on weighted distances, is computed. We use two types of steps on the gridlines and diagonal steps. Consequently, we use an 8-adjacency square grid, that is, one where a first weight is associated with the horizontal and vertical movements, while a second weight (not necessarily different from the first) is assigned to the diagonal steps. The chamfer distance of two points depends on the numbers and weights of the steps in a ‘shortest path’. In special cases, the cityblock and the chessboard distances, the two most basic and widely used digital distances (they are also referred as L1 and L distances, respectively) of the two-dimensional digital space occur. Although our combinatorial result is theoretical, it is closely connected to applications, such as communication networks, path counting in digital images, traces and trajectories in 2D digital grids. We consider all seven cases with non-negative weights and also the case when negative weights are allowed.

Keywords: traces; trajectories; weighted distances; shortest paths; digital distances; combinatorics

Abstract: Cloud infrastructure provides computing services where computing resources can be adjusted on-demand. However, the adoption of cloud infrastructures brings concerns like reliance on the service provider network, reliability, compliance for service level agreements (SLAs), etc. Software-defined networking (SDN) is a networking concept that suggests the segregation of a network’s data plane from the control plane. This concept improves networking behavior. In this paper, we present an SDN-enabled resource-aware topology framework. The proposed framework employs SLA compliance, Path Computation Element (PCE) and shares fair loading to achieve better topology features. We also present an evaluation, showcasing the potential of our framework.

Keywords: cloud computing; big data; fog computing; software-defined; networking; network management; resource management; topology

Abstract: In the last decade student teams at the Faculty of Engineering of the University of Debrecen have designed and constructed several race cars with alternative (electric or pneumatic) drives and took part and achieved successes in domestic and international competitions. For more successful racing a simulation program has been developed in Matlab for the calculation of the vehicle dynamic functions of the cars from their technical data. Currently, it has become a prerequisite of successful racing because of the large number of the possible values of technical data we can select the optimal ones by applying the above program combined with an optimizing procedure. The detailed description of the developed dynamic model and simulation program, together with the vehicle dynamics functions generated by the program are presented here. The description of the optimizing procedure will be presented elsewhere.

Keywords: dynamics modelling; simulation; race car; series DC motor; Matlab

Abstract: This paper provides edge detection analysis on images, which consist of different numbers of details (small, medium and high number of details) and which are compressed by different compression algorithms - JPEG, JPEG2000 and SPIHT. Images from the BSD (Berkeley Segmentation Database) database were used and compressed with different number of bits per pixel. The analysis was performed for five edge detectors: Canny, LoG, Sobel, Prewitt, and Roberts. The fidelity of the detected edges was determined using the objective measures Figure of Merit (FOM), F measure and Performance Ratio (PR), where the reference value was taken from the GroundTruth image. Based on the results presented in the tables, it can be concluded that edge detection behaves differently depending on the number of bits per pixel and applied compression algorithm, as well as, the number of details in the image. Roberts operator has been proven to be the best solution, when it is necessary to perform better edge detection over compressed images with small a number of details, but Canny shows better results for images with a high number of details.

Keywords: edge detection; compression; image processing; Figure of Merit (FOM); F measure; Performance Ratio (PR); image complexity; bit per pixel (BPP)

Abstract: The vector control theory of alternating current machines could provide high performance control during transient events, since these methods do not depend on the static equations of the selected machine, but on the space vector-based differential system of equations. These control methods have a very important common property; all of them require an angle, with which the system’s input can be transformed into the common reference frame in which the space vector notation is construed. The sensorless control methods attempt to estimate the common coordinate system’s angle, without using any information from the encoder, one of which is the high-frequency voltage injection method. This paper presents the mathematical model of the high-frequency synchronous voltage injection method on permanent magnet synchronous machines. The common coordinate system is estimated using a Phase-Locked-Loop (PLL). Based on the detailed mathematical model a new equivalent dynamic model for the PLL structure is proposed, with which the PLL’s controller could be tuned, with the knowledge of the machine’s parameters and injected voltage properties. Simulation results are provided for an off-the-shelf interior magnet synchronous machine.

Keywords: Vector Control; Permanent Magnet Synchronous Machine; Sensorless; High-Frequency Signal Injection

Abstract: This paper deals with the design of a digital sliding mode based minimum variance control on the basis of a discrete-time representation of the ABS model derived from a new type of generalized quasi-orthogonal filter. In the proposed control, the minimum variance enables the design of digital sliding mode control only on the basis of ABS outputs measurements, while sliding mode increases the ABS robustness under certain conditions. On the other hand, it is shown that orthogonal functions can be successfully used to obtain a model of a dynamical system with high accuracy. The proposed control scheme has been applied in the laboratory experimental setup and obtained experimental results show significant improvement in ABS performances.

Keywords: sliding mode control; minimum variance control; orthogonal polynomials; anti-lock braking system

Abstract: One of the possible reasons for student dropout, is the attraction of the labor market. Nowadays, the date of employment does not coincide with the date of graduation, sometimes the income of those without a degree are higher than those with a degree. In addition, it may also lead to the interruption of university studies that the students judge negatively the marketability of their studies, in which case, the appeal of the labor market is even more prevalent. During our research, we tried to identify the process of dropout using quantitative and qualitative methods. As a first step, we interviewed dropped out and ’at risk’ students, but in our current analysis, we only processed those interviews where student work played a significant role in the life of the interviewee and this affected their dropouts. In addition, during our quantitative research, we were looking for individuals who had left their higher education studies without graduation in the last 10 years, and finally we worked with a database of 605 people. Both our qualitative and quantitative results show that financial reasons dominate during student employment that make them fall into a vicious circle. The results draw attention to the fact that working during, or instead of the university is an inevitable point of analysis for dropping out.

Keywords: dropout; student employment; financial burdens; student work

Abstract: Nowadays the increase of photovoltaic penetration and simultaneously, the decentralization of electricity system, poses a number of challenges for distribution system developers and operators. The spread of high output power photovoltaic power plant connections demands the development of a network infrastructure. The analysis of development directions can be done with software simulation, for which network models are needed, which can characterize real networks well. To create such reference networks, knowing existing topologies, hierarchical agglomerative clustering can be a solution. When the parameters of the clusters are specified well, their software implementation can be done. In this study, a possible clustering process of selected Hungarian medium voltage overhead networks (including the determination of the optimal cluster number too), and the formulated network clusters are presented. The clustering of twenty selected 22 kV medium voltage networks was done using hierarchical agglomerative clustering. Then the optimal cluster number was determined. Based on Davis-Bouldin and Silhouette criterions, this cluster number was four. Two of the four generated clusters are single clusters, containing only one feeder. The size and looping of the characterized sample networks are well observable. In this paper a method has been created to generate medium voltage distribution network models, which can be used to simulate the effects of the growing photovoltaic penetration in the Hungarian distribution network.

Keywords: distribution network; network clustering; hierarchical agglomerative clustering

Abstract: In the fields of forestry and horticulture, it is necessary to have forecasts about the growth of trees. This process is affected by a lot of external factors like weather, light conditions, other objects, etc. There are several already existing methods for this purpose, but these can give only rough estimations. This paper presents a novel solution, based on the simulation of the growth of the tree. During this process, the application takes into account the environment of the tree and the properties of the species, which parameters are all easily configurable. The presented application can simulate not just one, but a group of trees parallel, estimating their effects to each other (shadows, etc.). The result of the simulation is a three dimensional model of the tree(s) at any time of the growth process. The distortion effects of these external factors are well visible on this model, giving a realistic estimation about the integration of the tree(s) into the given environment. The simulation has high computational demand; therefore, the most computationally intensive steps of the simulation are implemented on graphics accelerators using the CUDA framework.

Keywords: Computer Simulation; Computer Graphics; Ray-tracing; GPU programming