Authors:Wojciech Kołodziejski, Jacek Jasielski, Stanisław W. Kuta, Grzegorz Szerszeń, Witold Machowski Pages: 1 - 19 Abstract: Transformerless inverters are widely used in different photovoltaic nonisolated ac module applications, mainly in grid-tied photovoltaic (PV) generation systems, due to the benefits of achieving high efficiency over a wide load range, and low cost. Various transformerless inverter topologies have been proposed to meet the safety requirement of low ground leakage currents, such as specified in the VDE-4105 standard and low-output ac-current distortion. Topology modifications of transformerless full bridge inverters are designed to balance and maintain a constant common mode output voltage, thereby eliminating or reducing leakage currents. This article reviews and compares the different methods for limiting leakage currents in known topologies of the full-bridge transformerless inverters, such as: H4, H5, H6, HERIC, and their improvements. The main topologies and strategies used to reduce the leakage current in transformerless schemes are summarized, highlighting advantages and disadvantages and establishing points of comparison with similar topologies. To compare the properties of different medium to high power inverters, PV inverter topologies were implemented using IGBTs and tested with the same components, same simulation parameters in PSPICE to evaluate their performance in terms of energy efficiency and leakage current characteristics. The detailed power stage operating principles, extended PWM modulator, and integrated universal gate driver with galvanic isolation in the transmission path of control signal for all IGBTs of the inverter, as well isolated and floating bias power supply for gate drivers are described. PubDate: 2023-03-31 DOI: 10.55225/sti.477 Issue No:Vol. 16, No. 3-4 (2023)
Authors:Tomasz Bardel Pages: 20 - 27 Abstract: Field and laboratory tests of soils provide a large amount of data, but most of them are measured parameters, which are converted by various formulas and correlations into parameters used for design. General correlations does not always lead to obtaining compatible values, therefore it is desirable to search for local correlations. This article presents the correlation between the undrained shear strength from the field vane tests (FVT) and the pocket penetrometer for tills in the Tarnów region. On the basis of this correlation, a dependence curve of the unconfined compressive strength measured by pocket penetrometer and the liquidity index was developed. This correlation was then used of river’s clay muds in the Dunajec valley. The high values of the correlation coefficient were obtained. The results confirm the usefulness of the pocket penetrometer as a method of quick determination of the undrained shear strength and liquidity index. PubDate: 2023-03-31 DOI: 10.55225/sti.443 Issue No:Vol. 16, No. 3-4 (2023)
Authors:Jerzy Szczepański Pages: 28 - 41 Abstract: We consider Bernstein-Walsh-Siciak-type theorems on the polynomial approximation in the case of regular functions of one quaternionic variable and their applications to the uniform approximation and approximation in Lp norms with respect to measures satisfying the Bernstein-Markov condition. PubDate: 2023-03-31 DOI: 10.55225/sti.441 Issue No:Vol. 16, No. 3-4 (2023)
Authors:Tomasz Beberok Pages: 42 - 49 Abstract: In this note we give sharp Schur type inequalities for univariate polynomials with convex weights. Our approach will rely on application of two-dimensional Markov type inequalities, and also certain properties of Jacobi polynomials in order to prove sharpness. PubDate: 2023-03-31 DOI: 10.55225/sti.463 Issue No:Vol. 16, No. 3-4 (2023)
Authors:Jiajia Xu Pages: 50 - 56 Abstract: In this paper, we characterize the boundedness of composition operator Cφ from Morrey space H²K₁ to H²K₂ on the unit complex disk. PubDate: 2023-04-21 DOI: 10.55225/sti.478 Issue No:Vol. 16, No. 3-4 (2023)
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