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Research into energy characteristics of single-phase active four-quadrant rectifiers with the improved hysteresis modulation
(Технологический центр, 2019) Plakhtii, Oleksandr; Nerubatskyi, Volodymyr; Karpenko, Nadiia; Hordiienko, Denys; Butova, Olha; Khoruzhevskyi, Hryhorii
The traction electric drives for electric rolling stock of alternating current employ the diode and thyristor rectifiers that predetermine a series of shortcomings. These include the significant emission of reactive power and higher harmonics of currents to the contact network, as well as the impossibility of implementing electricity recuperation to the contact network. In this regard, it is promising to use single-phase four-quadrant active rectifiers with a correction of power coefficient. The advantage of these converters is ensuring a power coefficient close to unity, the implementation of the sinusoidal input current, as well as the possibility of implementing electricity recuperation to the power network. In the systems of control over active rectifiers quite common are the control systems with hysteresis modulation. However, hysteresis modulation predetermines the need to implement high and variable frequency for switching power keys, which negatively affects power losses in a transducer. Therefore, a control system with improved hysteresis modulation has been proposed. Due to the improved algorithm for switching power keys the proposed improved hysteresis control system makes it possible to reduce the number of switching power switches. That decreases the dynamic losses of power in an active rectifier, which makes it possible to improve the efficiency of electric rolling stock in general. The simulation modeling conducted in the MATLAB 2017b software has confirmed effectiveness of the proposed modulation algorithm. In addition, during implementation of the proposed commutation algorithm there is an improvement in the harmonic composition of input current. The reduction in the amplitudes of higher harmonics of input current has been confirmed, as well as the improvement in the resultant coefficient of harmonic distortions.
Use of triangular models of non-stationary processes in modeling variability of heart rhythm
(Харківський національний університет радіоелектроніки, 2019) Akhiiezer, O. B.; Dunaievska, О. I.; Shyshkin, Mykhailo; Butova, Olha; Rohovyi, Anton
The subject matter is a mathematical model describing the process of heart rhythm variability, which is based on the use of triangular models of non-stationary random processes in the Hilbert space. The goal of the research is to develop a mathematical model of nonstationary processes of cardiac activity based on a triangular model. This research was the basis for the development of a Matlab model that implements the proposed method for analyzing heart rate variability. Tasks are: to give a description of the variability heart rate as a non-stationary process in Hilbert space in terms of correlation functions; to research the possibility of constructing a correlation and spectral theory of a non-stationary process using triangular models; to synthesize the mathematical model of nonstationary process on the basis of correlation theory for solving mathematical processing and forecasting tasks on the basis of ECG data. Using the proposed mathematical method, we implemented the Matlab model of a heart signal generator, which allowed us to synthesize an ECG with different variability parameters in noisy conditions. Methods of mathematical statistics, simulation modeling, theory of random processes and control theory are used in this work. Results of this research are as follows: 1) It has been shown that the new approach to the description of the HRV as a random process in the application of the triangular model in the Hilbert space made it possible to obtain expressions for the correlation function. 2) The imitation simulation showed the sensitivity of the method within the 5% error rate under the conditions of different types of influence on HRV. The qualitative assessment of the possibilities of the proposed models to generate artificial ECG provided the possibility of visual analysis by the cardiologist of the identity of the interpretation of real ECG records. The identities of modeling results were checked on time samples of electrocardiographs of 7 patients from open PhysioNet cardiographic libraries on samples with the duration T = 10 s. 3) The standard low-frequency oscillations and "white noise" barrier are clearly differentiated on the applied correlation function by the distribution of spectral density power within the frequency range of 0,15-0,3 Hz. Conclusion. The simulation results confirmed the correctness of the theoretical conclusions about the possibility of using models based on the representation of non-stationary processes in a triangular Hilbert space.
18-Pulse rectifier with electronic phase shifting and pulse width modulation
(2018) Sokol, Yevgen I.; Zamaruiev, Volodymyr V.; Ivakhno, Volodymyr V.; Voitovych, Yurii S.; Butova, Olha; Makarov, Vadim
At present, 12-pulse rectifiers with electronic phase shift are known. Unlike classic rectifiers, they do not use phase-shifting transformers and have a unit power factor. Increasing of the rectifier’s pulse makes it possible to improve the harmonic composition of the input current. This article is devoted to the study of the operation of an 18-pulse rectifier with an electronic phase shift. The use of the principle of electronic phase shift leads to different levels of constant voltage at the output of the rectifiers. The introduction of pulse-width modulation contributes to equalizing the output voltages of the 6-pulse rectifiers which are the parts of the converter. In addition, the use of the pulse-width modulation allows eliminating matching magnetic elements which are used to equalize rectifiers output voltages. This improves the mass and dimension parameters of the converter. The results of modeling are presented.

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