Purpose. Development and investigation of a method for estimating the three-phase voltage unbalance index based on linear regression to improve the responsiveness of power quality control. The application of a linear relationship between the maximum radius of the space vector and the unbalance magnitude aims to ensure high computational speed (up to 10 ms) while maintaining acceptable accuracy. Methodology. To achieve the goal, the space vector theory was used to analyze three-phase systems in the time domain. Methods of mathematical statistics and linear regression (least squares method) were applied to establish a correlation between the geometric parameters of the space vector locus (Rmax) and the voltage unbalance factor (VUF). Computer modeling of various types of voltage sags was conducted to verify the proposed model. Findings. It was found that the linear regression model provides a high correlation (R2=0.985) between the Rmax parameter and the VUF index, which allows to describe adequately the state of system asymmetry. The main result is the reduction of the unbalance indicator estimation time to 10 ms (half a cycle of the power frequency), which is twice as fast as traditional methods based on the Fortescue transform. It is proven that for calculation by the proposed method, it is sufficient to know only the magnitudes of the line voltages without involving phase angles. Originality. For the first time, the possibility of using a linear regression model to determine the voltage unbalance index through the parameters of the space vector locus was substantiated. A stable mathematical relationship between the semi-major axis of the space vector ellipse and the unbalance factor was identified, allowing for the simplification of the mathematical monitoring model by avoiding complex symmetrical component decomposition. Practical value. The proposed method enables the implementation of real-time power quality monitoring in systems with limited local computational resources (microprocessor-based protection and automation devices). The achieved response speed (10 ms) is critical for the protection of power electronics and ensuring the stability of microgrids (Smart Grids) under rapid transient conditions. The results can be implemented into the algorithms of digital power quality analyzers.
Purpose. The purpose of the work is to develop a set of mathematical models of wheel-road interaction as a part of a comprehensive electric vehicle model suitable for studying acceleration, braking, cornering, load redistribution between axles and wheels, and for analyzing traction electric drive control algorithms under typical and near-limit driving conditions. Methodology. The research is based on theoretical mechanics, vehicle dynamics, electric drive theory, mathematical modelling, as well as empirical relationships describing tyre adhesion to the supporting surface. The Burckhardt empirical model is used to determine forces in the contact patch, while electric vehicle motion is described within a planar motion model that takes into account longitudinal and lateral load transfer, changes in normal reactions, and wheel slip. Findings. A consistent set of models has been formed that makes it possible to determine reactions in the wheel–road contact and to assess the influence of the adhesion coefficient, slip, vehicle speed, vertical load and control mode on electric vehicle behaviour. The model reproduces motion on dry, wet and slippery surfaces and allows analysis of traction loss, reduced controllability and deterioration in the implementation of traction or braking torque. It also makes it possible to compare the operating modes of the driving wheels, evaluate the system sensitivity to road parameters, and use the results for the synthesis of slip limitation, torque redistribution, and yaw stability algorithms. The results are suitable for defining test parameters, verifying control logic and making a preliminary assessment of system energy efficiency. Originality. The scientific novelty lies in integrating a wheel model, an empirical description of tire-road interaction, and a planar electric vehicle motion model into a unified mathematical framework suitable for studying individual wheel electric drive and limited-adhesion conditions. Practical value. The developed set of models can be used as a basis for a computational testing bench for studying traction control, anti-slip and anti-lock control, regenerative braking, and Smart Drive solutions for electric vehicles under different road operating conditions.
Purpose. Conducting a comprehensive research and analysis of the control characteristics and energy performance variations in electromechanical systems based on high-voltage wound-rotor induction motors with a fan-type load and pulse control in the rectified rotor current circuit, aimed at developing scientifically substantiated methods to improve their overall energy efficiency and minimize power losses in steady-state and transient operating modes. Methodology. The theoretical studies are based on the fundamental principles of electrical circuit theory, the theory of electrical machines and automated electric drives, as well as the equations of mathematical physics to describe electromechanical energy conversion processes in high-voltage wound-rotor induction motors, utilizing computer simulation, numerical methods, interpolation, and function approximation. Findings. The electromagnetic and energy processes of an electromechanical system with a fan-type load have been investigated, taking into account the variable aerodynamic parameters of the mine ventilation network. The proposed electromechanical system, featuring pulse control in the rectified rotor current circuit, exhibits pronounced adaptive properties. It demonstrates high robustness and the ability to precisely mitigate any stochastic disturbances in the aerodynamic load. Concurrently, it maintains the stability and reliability of the induction motor's speed control, thereby sustaining stable ventilation of the mine workings even under conditions of a critically reduced switching frequency of the converter switches. It has been established that during speed regulation within the slip range of s = 0.5÷ snom, the system's power factor increases to 0.80–0.93 and its efficiency reaches 92.5–94.5%, which exceeds the performance of an unregulated electric drive by 0.25 and 40%, respectively. Originality. The principles of designing energy-efficient control systems for fan installations have been further developed. It has been proven that the application of pulse control in electromechanical systems with fan loads and variable network aerodynamics not only stabilizes operational processes but also significantly increases the overall power factor (up to 0.80–0.93) and system efficiency at reduced rotor speeds of the induction motor. Practical value. The practical value of the study lies in demonstrating the economic and technical feasibility of implementing pulse control systems for high-voltage induction motors integrated into electromechanical systems for industrial fan installations. The application of such electromechanical systems at operating industrial facilities allows not only to ensure a precise response of the fan unit to changes in the aerodynamic resistance of the network, but also to improve significantly the energy performance of the enterprise, as well as to extend the maintenance interval of expensive high-voltage motors.
Purpose. A study of a method for non-contact diagnosis of induction motors through the analysis of vibration signals. This will enable the timely detection of defects that arise in their early stages during operation without disassembling the equipment. This will improve methods for diagnosing induction motors, thereby enhancing the reliability and safety of their operation. Methodology. Frequency analysis of vibration signals using fast Fourier transform to extract diagnostic features in the time and frequency domains. Findings. The study established a high sensitivity of the vibration characteristics of asynchronous electric motors to typical defects (rotor eccentricity, rod breakage, bearing damage, mechanical imbalance, shaft misalignment, and stator winding weakening). It was shown that a complex frequency analysis using the fast Fourier transform allows detecting signs of defects much earlier than periodic static monitoring. The vibration spectrum clearly shows side slip bands, bearing defect frequencies, amplification of the first harmonic of rotation, and components at power supply frequencies. The proposed non-contact method has high practical applicability for monitoring the technical condition of motors in industrial conditions. Originality. The scientific novelty of the research lies in improving the approach to diagnosing electric motors through a comprehensive analysis of vibration characteristics in the time and frequency domains, which allows increasing the reliability of detecting defects at the early stages of their development. Practical value. The results obtained can be used for the implementation of vibration monitoring systems for the technical condition of electric motors in industrial conditions. The proposed approaches to the analysis of vibration characteristics make it possible to perform early diagnosis of typical defects, reduce the risk of emergency failures and optimize the planning of maintenance and repair of electric machines. The materials of the work can be used during the development of software for diagnostic systems, as well as in the educational process for the training of specialists in electromechanics and power engineering.
Мета роботи. Розробка та дослідження методу оцінки індексу дисбалансу трифазної напруги на основі лінійної регресії для підвищення оперативності контролю якості електроенергії. Застосування лінійного співвідношення між максимальним радіусом просторового вектору та величиною дисбалансу має на меті забезпечити високу швидкість обчислень (до 10 мс) при збереженні прийнятної точності. Методи дослідження. Для досягнення мети використано теорію просторового вектору для аналізу трифазних систем у часовій області. Застосовано методи математичної статистики та лінійної регресії (метод найменших квадратів) для встановлення кореляційної залежності між геометричними параметрами годографа просторового вектору (Rmax) та індексом дисбалансу напруги (VUF). Проведено комп'ютерне моделювання різних типів провалів напруги для верифікації запропонованої моделі. Отримані результати. Встановлено, що модель лінійної регресії забезпечує високу кореляцію (R2=0,985) між параметром Rmax та індексом VUF, що дозволяє адекватно описувати стан асиметрії системи. Головним результатом є скорочення часу оцінки показників небалансу до 10 мс (пів циклу промислової частоти), що у два рази швидше за традиційні методи на основі перетворення Фортеск'ю. Доведено, що для розрахунку за пропонованим методом достатньо знати лише величини лінійних напруг без залучення фазових кутів. Наукова новизна. Вперше обґрунтовано можливість використання лінійної регресійної моделі для визначення індексу дисбалансу напруги через параметри годографа просторового вектору. Виявлено стабільний характер математичного зв'язку між максимальною напіввіссю еліпса просторового вектору та коефіцієнтом несиметрії, що дозволяє спростити математичну модель моніторингу за рахунок відмови від складного розкладання на симетричні складові. Практична цінність. Запропонований метод дозволяє реалізувати моніторинг якості електропостачання в реальному часі в системах з обмеженими обчислювальними ресурсами (мікропроцесорні пристрої захисту та автоматики). Отримана швидкість реакції (10 мс) є критичною для захисту силової електроніки та забезпечення стійкості мікромереж (Smart Grids) в умовах швидких перехідних процесів. Результати можуть бути впроваджені в алгоритми цифрових аналізаторів якості енергії.
