Активний тяговий перетворювач для електровозів змінного струму з колекторними тяговими двигунами

Abstract

Thesis for candidate degree of technical sciences of speсialty 05.22.09 — Electric transport. Joint-Stock Company “Ukrainian zaliznytsia”, Branch “Design and survey institute of railway transport”, Ministry of Infrastructure of Ukraine, National Technical University “Kharkiv Polytechnic Institute”, MES of Ukraine. Kharkiv, 2020. The dissertation is devoted to the actual scientific and technical problem of increasing the energy efficiency of the AC electric locomotives with DC traction motors due to the improvement of traction converters. The basis of the park of freight and passenger AC electric locomotives of “Ukrzaliznytsya” are electric locomotives with DC traction motors. Such electric locomotives have a relatively low power factor. For electric locomotives with diode rectifiers (VL80K, VL80T) its value is 0.65...0.85, and for electric locomotives with thyristor converters (2ES5K, 2EL5) — 0.3...0.84. The aggregate of the energy defects of the electromotive force and traction power causes a relatively low power factor of the AC electrified railways — about 0.7, while according to modern world standards the power factor is not lower than 0.95. Therefore, increasing the energy efficiency of the traction load is an urgent task. Today, Ukrainian, Russian and foreign specialists have developed a number of technical solutions that provide an increase in the power characteristics of electric locomotives. These solutions can be conventionally grouped into three groups: 1) improved schemes of traction converters and control algorithms; 2) passive and active reactive power compensators installed on the electric locomotives; 3) converters on fully controlled semiconductor devices (active converters). Despite the high energy characteristics of the active converters, investigations of the operation modes of such converters with DC traction motors, today is not enough. Consequently, further development of this research direction can be considered relevant. The base element of the converter for DC motor is a single-phase active current source rectifier. In the paper a mathematical description of the active current source rectifier in the rectifier and inverter modes is obtained. On the basis of the mathematical apparatus of logic algebra, a unified description of pulse-width modulation algorithms with sinusoidal, trapezoidal, and rectangular-step modulation signals is obtained. Investigation of electromagnetic processes and the comparison of the energy characteristics of the active current source rectifier with selected PWM algorithms and modulation frequencies of 900 Hz, 1,200 Hz and 1,800 Hz is carried out by simulation in MATLAB. Studies have shown that for all three algorithms, at a modulation index of 0.2...1.0, the input power factor of the active current source rectifier is 0.6...0.99 regardless of the modulation frequency. The power circuit with two-zone regulation of DC voltage and the control algorithm of the active traction converter of the electric locomotive are proposed. The use of rectangular-stepped PWM with a modulation frequency of 1,200 Hz has been substantiated. The regulation of the DC voltage with a modulation index of less than 0.5 is used only in short-term operating modes. A mathematical model of the AC electric traction system (25 kV, 50 Hz) was developed, taking into account two variants of the traction converter — a thyristor and active converter with pulse-width modulation. From the point of view of modeling of converters control systems, the developed model is universal because on the basis of logic functions of pulse formation and distribution a unified mathematical description of algorithms of thyristor control and active traction converter is developed. This model is implemented in MATLAB. Computer simulation of electromagnetic processes in the “traction network — electric locomotive” system has allowed to investigate the energy efficiency of an electric locomotive with an active traction converter. So, the power factor is 0.839...0.991, and its value is more than 0.9 provided with a modulation index of more than 0.5. In nominal mode, the power factor of an electric locomotive with an active traction converter is 19.4 % higher than that of an electric locomotive with a thyristor converter. The THD of the contact wire voltage of the electric locomotive with the active traction converter in the whole range of regulation varies within the range of 3...11 %, and the THD of the contact wire current is within the range of 9...17 %. When changing the distance from the electric locomotive to the traction substation in the range 0...10 km, the THD of contact wire voltage in nominal mode is 5...9 %. The virtual experiments showed that the active traction converter is the source of a wide spectrum of voltage and current harmonics. The least advantageous is the mode with a modulation index of 0.5...0.6. The results of harmonic analysis allowed to establish characteristic groups of harmonics, which basically determine the nonsinusoidal form of the of voltage and current waveforms. Therefore, in further research works of the active traction converter we must focus on correction of the voltage and current waveforms. In general, the results of the research showed that the active traction converter have higher energy characteristics than traditional rectifiers based on diode and thyristor schemes.